<?xml version="1.0" encoding="UTF-8"?>

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2026 Workiva-->
<!--r:019ce811-d3ba-7a24-b224-e3734a79d8c8,g:0cc9972e-0a80-48c2-a6fc-adf373f03d3b-->
<link:linkbase xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd">
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member"/>
  <link:roleRef roleURI="http://allogene.com/role/CondensedStatementsofStockholdersEquity" xlink:type="simple" xlink:href="allo-20260331.xsd#CondensedStatementsofStockholdersEquity"/>
  <link:definitionLink xlink:role="http://allogene.com/role/CondensedStatementsofStockholdersEquity" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019ce811-d478-727c-bed4-bd75b5b8f3ae" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019ce811-d478-7e88-8f9b-c9086dd7aff8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019ce811-d478-727c-bed4-bd75b5b8f3ae" xlink:to="loc_us-gaap_StatementTable_019ce811-d478-7e88-8f9b-c9086dd7aff8" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_019ce811-d478-768e-b4f3-e35ddc99517e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019ce811-d478-7e88-8f9b-c9086dd7aff8" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_019ce811-d478-768e-b4f3-e35ddc99517e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019ce811-d478-768e-b4f3-e35ddc99517e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019ce811-d478-768e-b4f3-e35ddc99517e" xlink:to="loc_us-gaap_EquityComponentDomain_019ce811-d478-768e-b4f3-e35ddc99517e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019ce811-d478-76b7-af1c-e1cfe0a01821" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019ce811-d478-768e-b4f3-e35ddc99517e" xlink:to="loc_us-gaap_EquityComponentDomain_019ce811-d478-76b7-af1c-e1cfe0a01821" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_019ce811-d478-75fd-aded-3b74c9845c1a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019ce811-d478-76b7-af1c-e1cfe0a01821" xlink:to="loc_us-gaap_CommonStockMember_019ce811-d478-75fd-aded-3b74c9845c1a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_019ce811-d478-79bf-b748-06e5c328cb14" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AdditionalPaidInCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019ce811-d478-76b7-af1c-e1cfe0a01821" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_019ce811-d478-79bf-b748-06e5c328cb14" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_019ce811-d478-7387-a896-fa3d6bfcfad5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetainedEarningsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019ce811-d478-76b7-af1c-e1cfe0a01821" xlink:to="loc_us-gaap_RetainedEarningsMember_019ce811-d478-7387-a896-fa3d6bfcfad5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019ce811-d478-74ce-8185-7e85c4b30f9d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019ce811-d478-76b7-af1c-e1cfe0a01821" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019ce811-d478-74ce-8185-7e85c4b30f9d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiarySaleOfStockAxis_019ce811-d478-7a91-847b-a179970a0ea1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsidiarySaleOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019ce811-d478-7e88-8f9b-c9086dd7aff8" xlink:to="loc_us-gaap_SubsidiarySaleOfStockAxis_019ce811-d478-7a91-847b-a179970a0ea1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019ce811-d478-7a91-847b-a179970a0ea1_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_019ce811-d478-7a91-847b-a179970a0ea1" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019ce811-d478-7a91-847b-a179970a0ea1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019ce811-d478-71e4-958e-300e481ade2d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_019ce811-d478-7a91-847b-a179970a0ea1" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019ce811-d478-71e4-958e-300e481ade2d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_ATMOfferingMember_019ce811-d478-7813-bf72-1155f970bcfa" xlink:href="allo-20260331.xsd#allo_ATMOfferingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019ce811-d478-71e4-958e-300e481ade2d" xlink:to="loc_allo_ATMOfferingMember_019ce811-d478-7813-bf72-1155f970bcfa" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019ce811-d478-7354-aaa7-270e63dad15b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019ce811-d478-727c-bed4-bd75b5b8f3ae" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019ce811-d478-7354-aaa7-270e63dad15b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_019ce811-d51b-7b23-a728-10a80b45ae39" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019ce811-d478-7354-aaa7-270e63dad15b" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_019ce811-d51b-7b23-a728-10a80b45ae39" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_019ce811-d51b-7b25-a7b9-8b4e6943d426" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019ce811-d478-7354-aaa7-270e63dad15b" xlink:to="loc_us-gaap_StockholdersEquity_019ce811-d51b-7b25-a7b9-8b4e6943d426" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_019ce811-d51b-7aec-a9b8-cbdf78ddd701" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019ce811-d478-7354-aaa7-270e63dad15b" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_019ce811-d51b-7aec-a9b8-cbdf78ddd701" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised_019ce811-d51b-7aec-949b-30d9ced8e81a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019ce811-d478-7354-aaa7-270e63dad15b" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised_019ce811-d51b-7aec-949b-30d9ced8e81a" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_019ce811-d51b-73a9-9b5b-3b9005f6d4e0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodSharesNewIssues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019ce811-d478-7354-aaa7-270e63dad15b" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_019ce811-d51b-73a9-9b5b-3b9005f6d4e0" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueNewIssues_019ce811-d51b-7c3d-80ea-f1fe0be43d9e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodValueNewIssues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019ce811-d478-7354-aaa7-270e63dad15b" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueNewIssues_019ce811-d51b-7c3d-80ea-f1fe0be43d9e" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_019ce811-d51b-7cb5-a2c0-254fe4cfe04a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019ce811-d478-7354-aaa7-270e63dad15b" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_019ce811-d51b-7cb5-a2c0-254fe4cfe04a" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans_019ce811-d51b-77bc-aeb3-a347aca1c2cc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019ce811-d478-7354-aaa7-270e63dad15b" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans_019ce811-d51b-77bc-aeb3-a347aca1c2cc" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueEmployeeStockPurchasePlan_019ce811-d51b-7a4c-9e9c-3da0d74079d1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodValueEmployeeStockPurchasePlan"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019ce811-d478-7354-aaa7-270e63dad15b" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueEmployeeStockPurchasePlan_019ce811-d51b-7a4c-9e9c-3da0d74079d1" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_019ce811-d51b-7976-8638-b12efd5dd084" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019ce811-d478-7354-aaa7-270e63dad15b" xlink:to="loc_us-gaap_NetIncomeLoss_019ce811-d51b-7976-8638-b12efd5dd084" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentNetOfTax_019ce811-d51b-70d6-b3ad-c75e8bbbc5d7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019ce811-d478-7354-aaa7-270e63dad15b" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentNetOfTax_019ce811-d51b-70d6-b3ad-c75e8bbbc5d7" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_019ce811-d51b-78e6-8118-c3f5f45c37d5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_019ce811-d51b-7571-a3e3-9cd51b33fa76" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockholdersEquity"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://allogene.com/role/CondensedStatementsofStockholdersEquityParenthetical" xlink:type="simple" xlink:href="allo-20260331.xsd#CondensedStatementsofStockholdersEquityParenthetical"/>
  <link:definitionLink xlink:role="http://allogene.com/role/CondensedStatementsofStockholdersEquityParenthetical" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019ce811-d51b-7918-a227-4b632c6191b8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019ce811-d51b-71fc-8b0c-ba236fb1187b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019ce811-d51b-7918-a227-4b632c6191b8" xlink:to="loc_us-gaap_StatementTable_019ce811-d51b-71fc-8b0c-ba236fb1187b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiarySaleOfStockAxis_019ce811-d51b-7df2-8287-d98fc5e5d0df" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsidiarySaleOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019ce811-d51b-71fc-8b0c-ba236fb1187b" xlink:to="loc_us-gaap_SubsidiarySaleOfStockAxis_019ce811-d51b-7df2-8287-d98fc5e5d0df" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019ce811-d51b-7df2-8287-d98fc5e5d0df_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_019ce811-d51b-7df2-8287-d98fc5e5d0df" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019ce811-d51b-7df2-8287-d98fc5e5d0df_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019ce811-d51b-7dbd-96cf-5ec5b01f835a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_019ce811-d51b-7df2-8287-d98fc5e5d0df" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019ce811-d51b-7dbd-96cf-5ec5b01f835a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_ATMOfferingMember_019ce811-d51b-766e-91e8-f485c9622906" xlink:href="allo-20260331.xsd#allo_ATMOfferingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019ce811-d51b-7dbd-96cf-5ec5b01f835a" xlink:to="loc_allo_ATMOfferingMember_019ce811-d51b-766e-91e8-f485c9622906" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsOfStockIssuanceCosts_019ce811-d51b-7675-a1ef-34f2bf88b9bb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PaymentsOfStockIssuanceCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019ce811-d51b-7918-a227-4b632c6191b8" xlink:to="loc_us-gaap_PaymentsOfStockIssuanceCosts_019ce811-d51b-7675-a1ef-34f2bf88b9bb" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://allogene.com/role/CondensedStatementsofCashFlows" xlink:type="simple" xlink:href="allo-20260331.xsd#CondensedStatementsofCashFlows"/>
  <link:definitionLink xlink:role="http://allogene.com/role/CondensedStatementsofCashFlows" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019ce811-d51b-781c-86af-32272a3eb80d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019ce811-d51b-7215-b204-36a911b97b1a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019ce811-d51b-781c-86af-32272a3eb80d" xlink:to="loc_us-gaap_StatementTable_019ce811-d51b-7215-b204-36a911b97b1a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiarySaleOfStockAxis_019ce811-d51b-71cb-b734-db582002ffbf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsidiarySaleOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019ce811-d51b-7215-b204-36a911b97b1a" xlink:to="loc_us-gaap_SubsidiarySaleOfStockAxis_019ce811-d51b-71cb-b734-db582002ffbf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019ce811-d51b-71cb-b734-db582002ffbf_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_019ce811-d51b-71cb-b734-db582002ffbf" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019ce811-d51b-71cb-b734-db582002ffbf_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019ce811-d51b-79fd-bb7e-6746d53e34e9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_019ce811-d51b-71cb-b734-db582002ffbf" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019ce811-d51b-79fd-bb7e-6746d53e34e9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_ATMOfferingMember_019ce811-d51b-7cda-8405-f23d126827c2" xlink:href="allo-20260331.xsd#allo_ATMOfferingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019ce811-d51b-79fd-bb7e-6746d53e34e9" xlink:to="loc_allo_ATMOfferingMember_019ce811-d51b-7cda-8405-f23d126827c2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_019ce811-d51b-72da-84c4-46d620e0a8bd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019ce811-d51b-781c-86af-32272a3eb80d" xlink:to="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_019ce811-d51b-72da-84c4-46d620e0a8bd" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProfitLoss_019ce811-d51b-7acd-b225-eb71ef02ee82" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ProfitLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_019ce811-d51b-72da-84c4-46d620e0a8bd" xlink:to="loc_us-gaap_ProfitLoss_019ce811-d51b-7acd-b225-eb71ef02ee82" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_019ce811-d51b-743d-9d64-2824b878b781" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_019ce811-d51b-72da-84c4-46d620e0a8bd" xlink:to="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_019ce811-d51b-743d-9d64-2824b878b781" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensation_019ce811-d51b-77de-9b4d-0532b58cf1cc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_019ce811-d51b-743d-9d64-2824b878b781" xlink:to="loc_us-gaap_ShareBasedCompensation_019ce811-d51b-77de-9b4d-0532b58cf1cc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DepreciationDepletionAndAmortization_019ce811-d51b-7379-98bc-44c5e63bde6f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DepreciationDepletionAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_019ce811-d51b-743d-9d64-2824b878b781" xlink:to="loc_us-gaap_DepreciationDepletionAndAmortization_019ce811-d51b-7379-98bc-44c5e63bde6f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentIncomeNetAmortizationOfDiscountAndPremium_019ce811-d51b-77ee-8d9d-c90e01466b41" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InvestmentIncomeNetAmortizationOfDiscountAndPremium"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_019ce811-d51b-743d-9d64-2824b878b781" xlink:to="loc_us-gaap_InvestmentIncomeNetAmortizationOfDiscountAndPremium_019ce811-d51b-77ee-8d9d-c90e01466b41" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseExpense_019ce811-d51b-7020-9f87-44a589277eb7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingLeaseExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_019ce811-d51b-743d-9d64-2824b878b781" xlink:to="loc_us-gaap_OperatingLeaseExpense_019ce811-d51b-7020-9f87-44a589277eb7" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_019ce811-d51b-7884-860e-fd0ab3715919" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncreaseDecreaseInOperatingCapitalAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_019ce811-d51b-743d-9d64-2824b878b781" xlink:to="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_019ce811-d51b-7884-860e-fd0ab3715919" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInDepositOtherAssets_019ce811-d51b-7f15-8075-2d589ab3e78e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncreaseDecreaseInDepositOtherAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_019ce811-d51b-7884-860e-fd0ab3715919" xlink:to="loc_us-gaap_IncreaseDecreaseInDepositOtherAssets_019ce811-d51b-7f15-8075-2d589ab3e78e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets_019ce811-d51b-7f10-a534-e2d027dd9587" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_019ce811-d51b-7884-860e-fd0ab3715919" xlink:to="loc_us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets_019ce811-d51b-7f10-a534-e2d027dd9587" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInOtherNoncurrentAssets_019ce811-d51b-7b05-b642-84fd2ce76b6d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncreaseDecreaseInOtherNoncurrentAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_019ce811-d51b-7884-860e-fd0ab3715919" xlink:to="loc_us-gaap_IncreaseDecreaseInOtherNoncurrentAssets_019ce811-d51b-7b05-b642-84fd2ce76b6d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInAccountsPayable_019ce811-d51b-77eb-a2e1-c7cdd281812e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncreaseDecreaseInAccountsPayable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_019ce811-d51b-7884-860e-fd0ab3715919" xlink:to="loc_us-gaap_IncreaseDecreaseInAccountsPayable_019ce811-d51b-77eb-a2e1-c7cdd281812e" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInAccruedLiabilitiesAndOtherOperatingLiabilities_019ce811-d51b-7768-996c-ca6c0e0e418b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncreaseDecreaseInAccruedLiabilitiesAndOtherOperatingLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_019ce811-d51b-7884-860e-fd0ab3715919" xlink:to="loc_us-gaap_IncreaseDecreaseInAccruedLiabilitiesAndOtherOperatingLiabilities_019ce811-d51b-7768-996c-ca6c0e0e418b" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInOperatingLeaseLiability_019ce811-d51b-7ae7-b033-f54292effbd2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncreaseDecreaseInOperatingLeaseLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_019ce811-d51b-7884-860e-fd0ab3715919" xlink:to="loc_us-gaap_IncreaseDecreaseInOperatingLeaseLiability_019ce811-d51b-7ae7-b033-f54292effbd2" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInOtherNoncurrentLiabilities_019ce811-d51b-79b2-8f41-ccf27bb5e607" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncreaseDecreaseInOtherNoncurrentLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_019ce811-d51b-7884-860e-fd0ab3715919" xlink:to="loc_us-gaap_IncreaseDecreaseInOtherNoncurrentLiabilities_019ce811-d51b-79b2-8f41-ccf27bb5e607" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_019ce811-d51b-72de-a898-1d7f37c3c6b6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_019ce811-d51b-72da-84c4-46d620e0a8bd" xlink:to="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_019ce811-d51b-72de-a898-1d7f37c3c6b6" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_019ce811-d51b-7f44-814a-a38b0f0339cd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019ce811-d51b-781c-86af-32272a3eb80d" xlink:to="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_019ce811-d51b-7f44-814a-a38b0f0339cd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_019ce811-d51b-7948-8a51-2c44775ae183" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PaymentsToAcquirePropertyPlantAndEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_019ce811-d51b-7f44-814a-a38b0f0339cd" xlink:to="loc_us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_019ce811-d51b-7948-8a51-2c44775ae183" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromMaturitiesPrepaymentsAndCallsOfAvailableForSaleSecurities_019ce811-d51b-72ed-8cf0-43e5794bab85" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ProceedsFromMaturitiesPrepaymentsAndCallsOfAvailableForSaleSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_019ce811-d51b-7f44-814a-a38b0f0339cd" xlink:to="loc_us-gaap_ProceedsFromMaturitiesPrepaymentsAndCallsOfAvailableForSaleSecurities_019ce811-d51b-72ed-8cf0-43e5794bab85" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireInvestments_019ce811-d51b-7a6a-8b7c-06d8ffae15a6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PaymentsToAcquireInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_019ce811-d51b-7f44-814a-a38b0f0339cd" xlink:to="loc_us-gaap_PaymentsToAcquireInvestments_019ce811-d51b-7a6a-8b7c-06d8ffae15a6" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_019ce811-d51b-75e7-9a3b-1f4edb8086b7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_019ce811-d51b-7f44-814a-a38b0f0339cd" xlink:to="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_019ce811-d51b-75e7-9a3b-1f4edb8086b7" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_019ce811-d51b-7ad6-a26c-f5adb51b26e5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019ce811-d51b-781c-86af-32272a3eb80d" xlink:to="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_019ce811-d51b-7ad6-a26c-f5adb51b26e5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromIssuanceOfCommonStock_019ce811-d51b-70b3-9317-3e698c1c1855" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ProceedsFromIssuanceOfCommonStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_019ce811-d51b-7ad6-a26c-f5adb51b26e5" xlink:to="loc_us-gaap_ProceedsFromIssuanceOfCommonStock_019ce811-d51b-70b3-9317-3e698c1c1855" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_ProceedsFromGrantAwards_019ce811-d51b-7ba3-a29d-374f23106296" xlink:href="allo-20260331.xsd#allo_ProceedsFromGrantAwards"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_019ce811-d51b-7ad6-a26c-f5adb51b26e5" xlink:to="loc_allo_ProceedsFromGrantAwards_019ce811-d51b-7ba3-a29d-374f23106296" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromIssuanceOfSharesUnderIncentiveAndShareBasedCompensationPlansIncludingStockOptions_019ce811-d51b-7e36-b112-a375c926847c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ProceedsFromIssuanceOfSharesUnderIncentiveAndShareBasedCompensationPlansIncludingStockOptions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_019ce811-d51b-7ad6-a26c-f5adb51b26e5" xlink:to="loc_us-gaap_ProceedsFromIssuanceOfSharesUnderIncentiveAndShareBasedCompensationPlansIncludingStockOptions_019ce811-d51b-7e36-b112-a375c926847c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromStockPlans_019ce811-d51b-7894-bfe1-ca179f019f57" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ProceedsFromStockPlans"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_019ce811-d51b-7ad6-a26c-f5adb51b26e5" xlink:to="loc_us-gaap_ProceedsFromStockPlans_019ce811-d51b-7894-bfe1-ca179f019f57" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_019ce811-d51b-7501-a01a-8565e06479ff" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_019ce811-d51b-7ad6-a26c-f5adb51b26e5" xlink:to="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_019ce811-d51b-7501-a01a-8565e06479ff" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect_019ce811-d51b-7835-af0e-2d38135aef8a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019ce811-d51b-781c-86af-32272a3eb80d" xlink:to="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect_019ce811-d51b-7835-af0e-2d38135aef8a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_019ce811-d51b-7ffc-8437-9b0dd52eb828" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019ce811-d51b-781c-86af-32272a3eb80d" xlink:to="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_019ce811-d51b-7ffc-8437-9b0dd52eb828" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_019ce811-d51b-78ff-ba46-72e289ce0ad7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NoncashInvestingAndFinancingItemsAbstract_019ce811-d51b-717c-9fa8-286bcec0672e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NoncashInvestingAndFinancingItemsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019ce811-d51b-781c-86af-32272a3eb80d" xlink:to="loc_us-gaap_NoncashInvestingAndFinancingItemsAbstract_019ce811-d51b-717c-9fa8-286bcec0672e" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalExpendituresIncurredButNotYetPaid_019ce811-d51b-7b02-8225-5eed0f936822" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CapitalExpendituresIncurredButNotYetPaid"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NoncashInvestingAndFinancingItemsAbstract_019ce811-d51b-717c-9fa8-286bcec0672e" xlink:to="loc_us-gaap_CapitalExpendituresIncurredButNotYetPaid_019ce811-d51b-7b02-8225-5eed0f936822" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SupplementalCashFlowInformationAbstract_019ce811-d51b-7620-9400-4a3d007dc8d2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SupplementalCashFlowInformationAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019ce811-d51b-781c-86af-32272a3eb80d" xlink:to="loc_us-gaap_SupplementalCashFlowInformationAbstract_019ce811-d51b-7620-9400-4a3d007dc8d2" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsForLeasingCostsCommissionsAndTenantImprovements_019ce811-d51b-74f5-a779-e7f0e977139a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PaymentsForLeasingCostsCommissionsAndTenantImprovements"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SupplementalCashFlowInformationAbstract_019ce811-d51b-7620-9400-4a3d007dc8d2" xlink:to="loc_us-gaap_PaymentsForLeasingCostsCommissionsAndTenantImprovements_019ce811-d51b-74f5-a779-e7f0e977139a" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://allogene.com/role/DescriptionofBusinessDetails" xlink:type="simple" xlink:href="allo-20260331.xsd#DescriptionofBusinessDetails"/>
  <link:definitionLink xlink:role="http://allogene.com/role/DescriptionofBusinessDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiarySaleOfStockLineItems_019ce811-d51c-74b9-a6db-9f415df7881a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsidiarySaleOfStockLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable_019ce811-d51c-7626-9cdb-0fa1b39b1c8a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019ce811-d51c-74b9-a6db-9f415df7881a" xlink:to="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable_019ce811-d51c-7626-9cdb-0fa1b39b1c8a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiarySaleOfStockAxis_019ce811-d51c-7729-8a95-be7fedf5787c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsidiarySaleOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable_019ce811-d51c-7626-9cdb-0fa1b39b1c8a" xlink:to="loc_us-gaap_SubsidiarySaleOfStockAxis_019ce811-d51c-7729-8a95-be7fedf5787c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019ce811-d51c-7729-8a95-be7fedf5787c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_019ce811-d51c-7729-8a95-be7fedf5787c" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019ce811-d51c-7729-8a95-be7fedf5787c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019ce811-d51c-715c-9486-4ad6ee635f37" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_019ce811-d51c-7729-8a95-be7fedf5787c" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019ce811-d51c-715c-9486-4ad6ee635f37" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_AtTheMarketOfferingMember_019ce811-d51c-7f15-b9c4-9ba8983f4192" xlink:href="allo-20260331.xsd#allo_AtTheMarketOfferingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019ce811-d51c-715c-9486-4ad6ee635f37" xlink:to="loc_allo_AtTheMarketOfferingMember_019ce811-d51c-7f15-b9c4-9ba8983f4192" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_StockIssuanceMaximumCompensationDueToThirdPartyPercent_019ce811-d51c-7529-a5ad-a1dbfe50b221" xlink:href="allo-20260331.xsd#allo_StockIssuanceMaximumCompensationDueToThirdPartyPercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019ce811-d51c-74b9-a6db-9f415df7881a" xlink:to="loc_allo_StockIssuanceMaximumCompensationDueToThirdPartyPercent_019ce811-d51c-7529-a5ad-a1dbfe50b221" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction_019ce811-d51c-78fb-9cd6-4b387a587b49" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019ce811-d51c-74b9-a6db-9f415df7881a" xlink:to="loc_us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction_019ce811-d51c-78fb-9cd6-4b387a587b49" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockConsiderationReceivedOnTransaction_019ce811-d51c-7379-9944-efebf2384cdf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SaleOfStockConsiderationReceivedOnTransaction"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019ce811-d51c-74b9-a6db-9f415df7881a" xlink:to="loc_us-gaap_SaleOfStockConsiderationReceivedOnTransaction_019ce811-d51c-7379-9944-efebf2384cdf" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashCashEquivalentsAndShortTermInvestments_019ce811-d51c-7504-9c8c-90128b1af362" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CashCashEquivalentsAndShortTermInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019ce811-d51c-74b9-a6db-9f415df7881a" xlink:to="loc_us-gaap_CashCashEquivalentsAndShortTermInvestments_019ce811-d51c-7504-9c8c-90128b1af362" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsAccumulatedDeficit_019ce811-d51c-7020-a23c-efeffbb61066" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetainedEarningsAccumulatedDeficit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019ce811-d51c-74b9-a6db-9f415df7881a" xlink:to="loc_us-gaap_RetainedEarningsAccumulatedDeficit_019ce811-d51c-7020-a23c-efeffbb61066" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://allogene.com/role/FairValueMeasurementsAdditionalInformationDetails" xlink:type="simple" xlink:href="allo-20260331.xsd#FairValueMeasurementsAdditionalInformationDetails"/>
  <link:definitionLink xlink:role="http://allogene.com/role/FairValueMeasurementsAdditionalInformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019ce811-d51c-7003-95f6-add2a52a2266" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019ce811-d51c-7965-b871-89eea0caabcb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019ce811-d51c-7003-95f6-add2a52a2266" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019ce811-d51c-7965-b871-89eea0caabcb" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019ce811-d51c-74cb-9b38-b95c9dc699cf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019ce811-d51c-7965-b871-89eea0caabcb" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019ce811-d51c-74cb-9b38-b95c9dc699cf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019ce811-d51c-74cb-9b38-b95c9dc699cf_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019ce811-d51c-74cb-9b38-b95c9dc699cf" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019ce811-d51c-74cb-9b38-b95c9dc699cf_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019ce811-d51c-75e3-9c07-76d6effad93b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019ce811-d51c-74cb-9b38-b95c9dc699cf" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019ce811-d51c-75e3-9c07-76d6effad93b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_019ce811-d51c-78d4-9341-58129a99a006" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019ce811-d51c-75e3-9c07-76d6effad93b" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_019ce811-d51c-78d4-9341-58129a99a006" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByMeasurementFrequencyAxis_019ce811-d51c-7a43-b4a5-b718ca71e879" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueByMeasurementFrequencyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019ce811-d51c-7965-b871-89eea0caabcb" xlink:to="loc_us-gaap_FairValueByMeasurementFrequencyAxis_019ce811-d51c-7a43-b4a5-b718ca71e879" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_019ce811-d51c-7a43-b4a5-b718ca71e879_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementFrequencyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_019ce811-d51c-7a43-b4a5-b718ca71e879" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_019ce811-d51c-7a43-b4a5-b718ca71e879_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_019ce811-d51c-76bb-9e57-b964071e0292" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementFrequencyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_019ce811-d51c-7a43-b4a5-b718ca71e879" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_019ce811-d51c-76bb-9e57-b964071e0292" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsRecurringMember_019ce811-d51c-7366-b52c-6b41dbcfcb9c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementsRecurringMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementFrequencyDomain_019ce811-d51c-76bb-9e57-b964071e0292" xlink:to="loc_us-gaap_FairValueMeasurementsRecurringMember_019ce811-d51c-7366-b52c-6b41dbcfcb9c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsFairValueDisclosure_019ce811-d51c-7c64-8c1a-df6690a1bc29" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AssetsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019ce811-d51c-7003-95f6-add2a52a2266" xlink:to="loc_us-gaap_AssetsFairValueDisclosure_019ce811-d51c-7c64-8c1a-df6690a1bc29" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesFairValueDisclosure_019ce811-d51c-76c9-9ad1-0ed43b1bdfe0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LiabilitiesFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019ce811-d51c-7003-95f6-add2a52a2266" xlink:to="loc_us-gaap_LiabilitiesFairValueDisclosure_019ce811-d51c-76c9-9ad1-0ed43b1bdfe0" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://allogene.com/role/FairValueMeasurementsScheduleofFinancialAssetsMeasuredatFairValueonRecurringBasisDetails" xlink:type="simple" xlink:href="allo-20260331.xsd#FairValueMeasurementsScheduleofFinancialAssetsMeasuredatFairValueonRecurringBasisDetails"/>
  <link:definitionLink xlink:role="http://allogene.com/role/FairValueMeasurementsScheduleofFinancialAssetsMeasuredatFairValueonRecurringBasisDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019ce811-d51c-74d4-8e43-58f38ddda7b8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019ce811-d51c-7d8f-8494-dcc271e2cc5f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019ce811-d51c-74d4-8e43-58f38ddda7b8" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019ce811-d51c-7d8f-8494-dcc271e2cc5f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019ce811-d51c-7023-a810-e361ddade262" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019ce811-d51c-7d8f-8494-dcc271e2cc5f" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019ce811-d51c-7023-a810-e361ddade262" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019ce811-d51c-7023-a810-e361ddade262_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019ce811-d51c-7023-a810-e361ddade262" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019ce811-d51c-7023-a810-e361ddade262_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019ce811-d51c-77ef-b8d2-db886964a7f0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019ce811-d51c-7023-a810-e361ddade262" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019ce811-d51c-77ef-b8d2-db886964a7f0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_019ce811-d51c-74ee-8117-da96fa445c50" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueInputsLevel1Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019ce811-d51c-77ef-b8d2-db886964a7f0" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_019ce811-d51c-74ee-8117-da96fa445c50" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_019ce811-d51c-71c9-bb7d-9b10991758e2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueInputsLevel2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019ce811-d51c-77ef-b8d2-db886964a7f0" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_019ce811-d51c-71c9-bb7d-9b10991758e2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_019ce811-d51c-7ee2-8756-a9e2ec992155" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019ce811-d51c-77ef-b8d2-db886964a7f0" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_019ce811-d51c-7ee2-8756-a9e2ec992155" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_019ce811-d51c-7116-9337-9fe99c9d7f5d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019ce811-d51c-7d8f-8494-dcc271e2cc5f" xlink:to="loc_us-gaap_FinancialInstrumentAxis_019ce811-d51c-7116-9337-9fe99c9d7f5d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019ce811-d51c-7116-9337-9fe99c9d7f5d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019ce811-d51c-7116-9337-9fe99c9d7f5d" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019ce811-d51c-7116-9337-9fe99c9d7f5d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019ce811-d51c-7bad-a494-bc32e8ed9173" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019ce811-d51c-7116-9337-9fe99c9d7f5d" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019ce811-d51c-7bad-a494-bc32e8ed9173" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MoneyMarketFundsMember_019ce811-d51c-7707-b748-a17754b4497f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MoneyMarketFundsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019ce811-d51c-7bad-a494-bc32e8ed9173" xlink:to="loc_us-gaap_MoneyMarketFundsMember_019ce811-d51c-7707-b748-a17754b4497f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommercialPaperMember_019ce811-d51c-7753-9af2-07bdd3e4c18b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommercialPaperMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019ce811-d51c-7bad-a494-bc32e8ed9173" xlink:to="loc_us-gaap_CommercialPaperMember_019ce811-d51c-7753-9af2-07bdd3e4c18b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateBondSecuritiesMember_019ce811-d51c-7917-8fb0-be392bd80a87" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CorporateBondSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019ce811-d51c-7bad-a494-bc32e8ed9173" xlink:to="loc_us-gaap_CorporateBondSecuritiesMember_019ce811-d51c-7917-8fb0-be392bd80a87" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USTreasurySecuritiesMember_019ce811-d51c-7339-bdd8-dc2c8da00716" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_USTreasurySecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019ce811-d51c-7bad-a494-bc32e8ed9173" xlink:to="loc_us-gaap_USTreasurySecuritiesMember_019ce811-d51c-7339-bdd8-dc2c8da00716" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USGovernmentCorporationsAndAgenciesSecuritiesMember_019ce811-d51c-762b-b87c-89aafa32abee" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_USGovernmentCorporationsAndAgenciesSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019ce811-d51c-7bad-a494-bc32e8ed9173" xlink:to="loc_us-gaap_USGovernmentCorporationsAndAgenciesSecuritiesMember_019ce811-d51c-762b-b87c-89aafa32abee" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_019d3e04-919e-7fa6-bb17-eb88c218d5e9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AvailableForSaleSecuritiesDebtSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019ce811-d51c-74d4-8e43-58f38ddda7b8" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_019d3e04-919e-7fa6-bb17-eb88c218d5e9" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://allogene.com/role/FinancialInstrumentsScheduleofCashEquivalentsRestrictedCashandInvestmentsClassifiedasAvailableforSaleSecuritiesDetails" xlink:type="simple" xlink:href="allo-20260331.xsd#FinancialInstrumentsScheduleofCashEquivalentsRestrictedCashandInvestmentsClassifiedasAvailableforSaleSecuritiesDetails"/>
  <link:definitionLink xlink:role="http://allogene.com/role/FinancialInstrumentsScheduleofCashEquivalentsRestrictedCashandInvestmentsClassifiedasAvailableforSaleSecuritiesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019ce811-d51c-71f2-84b2-b22761a79f14" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleTable_019ce811-d51c-7e9f-ad54-4b4ba2376881" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtSecuritiesAvailableForSaleTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019ce811-d51c-71f2-84b2-b22761a79f14" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleTable_019ce811-d51c-7e9f-ad54-4b4ba2376881" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_019ce811-d51c-7c42-8337-d5caffabf4a6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtSecuritiesAvailableForSaleTable_019ce811-d51c-7e9f-ad54-4b4ba2376881" xlink:to="loc_us-gaap_FinancialInstrumentAxis_019ce811-d51c-7c42-8337-d5caffabf4a6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019ce811-d51c-7c42-8337-d5caffabf4a6_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019ce811-d51c-7c42-8337-d5caffabf4a6" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019ce811-d51c-7c42-8337-d5caffabf4a6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019ce811-d51c-7e03-aa2b-675edb916a6e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019ce811-d51c-7c42-8337-d5caffabf4a6" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019ce811-d51c-7e03-aa2b-675edb916a6e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MoneyMarketFundsMember_019ce811-d51c-7d71-b77e-7cc2d38f6121" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MoneyMarketFundsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019ce811-d51c-7e03-aa2b-675edb916a6e" xlink:to="loc_us-gaap_MoneyMarketFundsMember_019ce811-d51c-7d71-b77e-7cc2d38f6121" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommercialPaperMember_019ce811-d51c-7b11-9f36-d8c1b205aac5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommercialPaperMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019ce811-d51c-7e03-aa2b-675edb916a6e" xlink:to="loc_us-gaap_CommercialPaperMember_019ce811-d51c-7b11-9f36-d8c1b205aac5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateBondSecuritiesMember_019ce811-d51c-74a1-bc36-e7e5e4c412cf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CorporateBondSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019ce811-d51c-7e03-aa2b-675edb916a6e" xlink:to="loc_us-gaap_CorporateBondSecuritiesMember_019ce811-d51c-74a1-bc36-e7e5e4c412cf" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USTreasurySecuritiesMember_019ce811-d51c-7fc8-be8b-b32f64e8ac94" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_USTreasurySecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019ce811-d51c-7e03-aa2b-675edb916a6e" xlink:to="loc_us-gaap_USTreasurySecuritiesMember_019ce811-d51c-7fc8-be8b-b32f64e8ac94" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USGovernmentCorporationsAndAgenciesSecuritiesMember_019ce811-d51c-78d4-aae9-465014d4b8de" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_USGovernmentCorporationsAndAgenciesSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019ce811-d51c-7e03-aa2b-675edb916a6e" xlink:to="loc_us-gaap_USGovernmentCorporationsAndAgenciesSecuritiesMember_019ce811-d51c-78d4-aae9-465014d4b8de" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis_019ce811-d51c-7980-a387-fb779c347629" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019ce811-d51c-71f2-84b2-b22761a79f14" xlink:to="loc_us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis_019ce811-d51c-7980-a387-fb779c347629" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax_019ce811-d51c-7378-a08a-11cbf6dc052b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019ce811-d51c-71f2-84b2-b22761a79f14" xlink:to="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax_019ce811-d51c-7378-a08a-11cbf6dc052b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax_019ce811-d51c-7226-8a4b-4046b67d48a6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019ce811-d51c-71f2-84b2-b22761a79f14" xlink:to="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax_019ce811-d51c-7226-8a4b-4046b67d48a6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_019ce811-d51c-7a8d-8fc4-d4bd7c89d344" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AvailableForSaleSecuritiesDebtSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019ce811-d51c-71f2-84b2-b22761a79f14" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_019ce811-d51c-7a8d-8fc4-d4bd7c89d344" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashEquivalentsAtCarryingValue_019ce811-d51c-793e-9c8f-68361765b618" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CashEquivalentsAtCarryingValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019ce811-d51c-71f2-84b2-b22761a79f14" xlink:to="loc_us-gaap_CashEquivalentsAtCarryingValue_019ce811-d51c-793e-9c8f-68361765b618" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtSecuritiesCurrent_019ce811-d51c-7b56-b5be-e1199ebf2c04" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AvailableForSaleSecuritiesDebtSecuritiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019ce811-d51c-71f2-84b2-b22761a79f14" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtSecuritiesCurrent_019ce811-d51c-7b56-b5be-e1199ebf2c04" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtSecuritiesNoncurrent_019ce811-d51c-773b-b5a0-db01de72c547" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AvailableForSaleSecuritiesDebtSecuritiesNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019ce811-d51c-71f2-84b2-b22761a79f14" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtSecuritiesNoncurrent_019ce811-d51c-773b-b5a0-db01de72c547" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_CashEquivalentsAndShortTermInvestments_019ce811-d51c-76b0-83f4-680232b91b9d" xlink:href="allo-20260331.xsd#allo_CashEquivalentsAndShortTermInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019ce811-d51c-71f2-84b2-b22761a79f14" xlink:to="loc_allo_CashEquivalentsAndShortTermInvestments_019ce811-d51c-76b0-83f4-680232b91b9d" xlink:type="arc" order="7"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://allogene.com/role/BalanceSheetComponentsScheduleofPropertyandEquipmentNetDetails" xlink:type="simple" xlink:href="allo-20260331.xsd#BalanceSheetComponentsScheduleofPropertyandEquipmentNetDetails"/>
  <link:definitionLink xlink:role="http://allogene.com/role/BalanceSheetComponentsScheduleofPropertyandEquipmentNetDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019ce811-d51c-7b07-a230-d51bdeefa221" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_019ce811-d51c-72c6-88fa-5e6eb18b2bb3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019ce811-d51c-7b07-a230-d51bdeefa221" xlink:to="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_019ce811-d51c-72c6-88fa-5e6eb18b2bb3" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019ce811-d51c-7b30-a999-99bbe16b129c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_019ce811-d51c-72c6-88fa-5e6eb18b2bb3" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019ce811-d51c-7b30-a999-99bbe16b129c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019ce811-d51c-7b30-a999-99bbe16b129c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019ce811-d51c-7b30-a999-99bbe16b129c" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019ce811-d51c-7b30-a999-99bbe16b129c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019ce811-d51c-7d8d-98a2-ca0a459e2795" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019ce811-d51c-7b30-a999-99bbe16b129c" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019ce811-d51c-7d8d-98a2-ca0a459e2795" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LeaseholdImprovementsMember_019ce811-d51c-7810-9e62-438dc955daae" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LeaseholdImprovementsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019ce811-d51c-7d8d-98a2-ca0a459e2795" xlink:to="loc_us-gaap_LeaseholdImprovementsMember_019ce811-d51c-7810-9e62-438dc955daae" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_LaboratoryEquipmentMember_019ce811-d51c-7ab3-8ef9-ed3cea7b8c48" xlink:href="allo-20260331.xsd#allo_LaboratoryEquipmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019ce811-d51c-7d8d-98a2-ca0a459e2795" xlink:to="loc_allo_LaboratoryEquipmentMember_019ce811-d51c-7ab3-8ef9-ed3cea7b8c48" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_ComputerEquipmentAndPurchasedSoftwareMember_019ce811-d51c-7f7d-b41f-f170eaab537f" xlink:href="allo-20260331.xsd#allo_ComputerEquipmentAndPurchasedSoftwareMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019ce811-d51c-7d8d-98a2-ca0a459e2795" xlink:to="loc_allo_ComputerEquipmentAndPurchasedSoftwareMember_019ce811-d51c-7f7d-b41f-f170eaab537f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FurnitureAndFixturesMember_019ce811-d51c-7e53-930c-150d3f356b44" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FurnitureAndFixturesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019ce811-d51c-7d8d-98a2-ca0a459e2795" xlink:to="loc_us-gaap_FurnitureAndFixturesMember_019ce811-d51c-7e53-930c-150d3f356b44" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentGross_019ce811-d51c-73c2-8c26-ce00a26f209a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019ce811-d51c-7b07-a230-d51bdeefa221" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentGross_019ce811-d51c-73c2-8c26-ce00a26f209a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_019ce811-d51c-7faa-83af-02f4da88532e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019ce811-d51c-7b07-a230-d51bdeefa221" xlink:to="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_019ce811-d51c-7faa-83af-02f4da88532e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_019ce811-d51c-75ef-bacd-40b412bb5959" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019ce811-d51c-7b07-a230-d51bdeefa221" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet_019ce811-d51c-75ef-bacd-40b412bb5959" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://allogene.com/role/BalanceSheetComponentsAdditionalInformationDetails" xlink:type="simple" xlink:href="allo-20260331.xsd#BalanceSheetComponentsAdditionalInformationDetails"/>
  <link:definitionLink xlink:role="http://allogene.com/role/BalanceSheetComponentsAdditionalInformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCostAndReserveLineItems_019ce811-d51c-7620-b38a-d31c0dd9b779" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringCostAndReserveLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_019ce811-d51c-7824-8409-98d928840c90" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfRestructuringAndRelatedCostsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_019ce811-d51c-7620-b38a-d31c0dd9b779" xlink:to="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_019ce811-d51c-7824-8409-98d928840c90" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringPlanAxis_019e0802-381e-73a8-ba44-bafefe7e54bd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringPlanAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_019ce811-d51c-7824-8409-98d928840c90" xlink:to="loc_us-gaap_RestructuringPlanAxis_019e0802-381e-73a8-ba44-bafefe7e54bd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringPlanDomain_019e0802-381e-73a8-ba44-bafefe7e54bd_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringPlanDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RestructuringPlanAxis_019e0802-381e-73a8-ba44-bafefe7e54bd" xlink:to="loc_us-gaap_RestructuringPlanDomain_019e0802-381e-73a8-ba44-bafefe7e54bd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringPlanDomain_019e0802-381e-76b9-9e2c-4d3ddbc1148d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringPlanDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RestructuringPlanAxis_019e0802-381e-73a8-ba44-bafefe7e54bd" xlink:to="loc_us-gaap_RestructuringPlanDomain_019e0802-381e-76b9-9e2c-4d3ddbc1148d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_WorkforceReductionMember_019e0802-381e-72ca-b3ac-946fce08e80d" xlink:href="allo-20260331.xsd#allo_WorkforceReductionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringPlanDomain_019e0802-381e-76b9-9e2c-4d3ddbc1148d" xlink:to="loc_allo_WorkforceReductionMember_019e0802-381e-72ca-b3ac-946fce08e80d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationAxis_019e0802-381e-7070-9114-64bd4dd3d90d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_019ce811-d51c-7824-8409-98d928840c90" xlink:to="loc_us-gaap_IncomeStatementLocationAxis_019e0802-381e-7070-9114-64bd4dd3d90d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_019e0802-381e-7070-9114-64bd4dd3d90d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_019e0802-381e-7070-9114-64bd4dd3d90d" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_019e0802-381e-7070-9114-64bd4dd3d90d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_019e0802-381e-7afc-bad3-7f03ca6f826b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_019e0802-381e-7070-9114-64bd4dd3d90d" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_019e0802-381e-7afc-bad3-7f03ca6f826b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchAndDevelopmentExpenseMember_019e0802-381e-74cc-84c8-92bce40715c2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ResearchAndDevelopmentExpenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_019e0802-381e-7afc-bad3-7f03ca6f826b" xlink:to="loc_us-gaap_ResearchAndDevelopmentExpenseMember_019e0802-381e-74cc-84c8-92bce40715c2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GeneralAndAdministrativeExpenseMember_019e0802-381e-7007-8544-066220b6c9aa" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GeneralAndAdministrativeExpenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_019e0802-381e-7afc-bad3-7f03ca6f826b" xlink:to="loc_us-gaap_GeneralAndAdministrativeExpenseMember_019e0802-381e-7007-8544-066220b6c9aa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_ImpairmentLongLivedAssetHeldForUseMember_019e0802-381e-7e2d-8089-6995c73041e6" xlink:href="allo-20260331.xsd#allo_ImpairmentLongLivedAssetHeldForUseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_019e0802-381e-7afc-bad3-7f03ca6f826b" xlink:to="loc_allo_ImpairmentLongLivedAssetHeldForUseMember_019e0802-381e-7e2d-8089-6995c73041e6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CounterpartyNameAxis_019ce811-d51c-7eaa-84eb-8da2b7bf6001" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_CounterpartyNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_019ce811-d51c-7824-8409-98d928840c90" xlink:to="loc_srt_CounterpartyNameAxis_019ce811-d51c-7eaa-84eb-8da2b7bf6001" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019ce811-d51c-7eaa-84eb-8da2b7bf6001_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CounterpartyNameAxis_019ce811-d51c-7eaa-84eb-8da2b7bf6001" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019ce811-d51c-7eaa-84eb-8da2b7bf6001_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019ce811-d51c-7662-85dc-ef7cc03da1da" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CounterpartyNameAxis_019ce811-d51c-7eaa-84eb-8da2b7bf6001" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019ce811-d51c-7662-85dc-ef7cc03da1da" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_CaliforniaInstituteForRegenerativeMedicineCIRMMember_019ce811-d51c-739d-a415-dc5740e2f21a" xlink:href="allo-20260331.xsd#allo_CaliforniaInstituteForRegenerativeMedicineCIRMMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019ce811-d51c-7662-85dc-ef7cc03da1da" xlink:to="loc_allo_CaliforniaInstituteForRegenerativeMedicineCIRMMember_019ce811-d51c-739d-a415-dc5740e2f21a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019ce811-d51c-7066-ac45-d6c493414a8b" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_019ce811-d51c-7824-8409-98d928840c90" xlink:to="loc_srt_RangeAxis_019ce811-d51c-7066-ac45-d6c493414a8b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019ce811-d51c-7066-ac45-d6c493414a8b_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_019ce811-d51c-7066-ac45-d6c493414a8b" xlink:to="loc_srt_RangeMember_019ce811-d51c-7066-ac45-d6c493414a8b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019ce811-d51c-75a0-a65e-9a6ea0b7de4a" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_019ce811-d51c-7066-ac45-d6c493414a8b" xlink:to="loc_srt_RangeMember_019ce811-d51c-75a0-a65e-9a6ea0b7de4a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_019ce811-d51c-7edd-9273-f0b7308b4c0f" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019ce811-d51c-75a0-a65e-9a6ea0b7de4a" xlink:to="loc_srt_MinimumMember_019ce811-d51c-7edd-9273-f0b7308b4c0f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_019ce811-d51c-7f13-bd7a-9ecf59748ba6" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019ce811-d51c-75a0-a65e-9a6ea0b7de4a" xlink:to="loc_srt_MaximumMember_019ce811-d51c-7f13-bd7a-9ecf59748ba6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringAndRelatedCostNumberOfPositionsEliminatedPeriodPercent_019e0806-d837-7383-bea0-ef06acf0a630" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringAndRelatedCostNumberOfPositionsEliminatedPeriodPercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_019ce811-d51c-7620-b38a-d31c0dd9b779" xlink:to="loc_us-gaap_RestructuringAndRelatedCostNumberOfPositionsEliminatedPeriodPercent_019e0806-d837-7383-bea0-ef06acf0a630" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCosts_019e0802-381e-76e3-9938-ff88d98e412d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_019ce811-d51c-7620-b38a-d31c0dd9b779" xlink:to="loc_us-gaap_RestructuringCosts_019e0802-381e-76e3-9938-ff88d98e412d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringReserve_019e0913-4bda-7488-96e0-7d05fb0eff2a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringReserve"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_019ce811-d51c-7620-b38a-d31c0dd9b779" xlink:to="loc_us-gaap_RestructuringReserve_019e0913-4bda-7488-96e0-7d05fb0eff2a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_GrantAwardAmount_019ce811-d51c-7349-a962-3b31a665a1be" xlink:href="allo-20260331.xsd#allo_GrantAwardAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_019ce811-d51c-7620-b38a-d31c0dd9b779" xlink:to="loc_allo_GrantAwardAmount_019ce811-d51c-7349-a962-3b31a665a1be" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_GrantAwardNumberOfPatientsTreatedUnderStudyPlan_019ce811-d51c-77e6-922c-f5ea4764c069" xlink:href="allo-20260331.xsd#allo_GrantAwardNumberOfPatientsTreatedUnderStudyPlan"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_019ce811-d51c-7620-b38a-d31c0dd9b779" xlink:to="loc_allo_GrantAwardNumberOfPatientsTreatedUnderStudyPlan_019ce811-d51c-77e6-922c-f5ea4764c069" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_GrantAwardGranteeMaximumExpectedContribution_019ce811-d51c-7804-ad76-8d1ce11435fa" xlink:href="allo-20260331.xsd#allo_GrantAwardGranteeMaximumExpectedContribution"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_019ce811-d51c-7620-b38a-d31c0dd9b779" xlink:to="loc_allo_GrantAwardGranteeMaximumExpectedContribution_019ce811-d51c-7804-ad76-8d1ce11435fa" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_GrantAwardRoyaltyFeeAmountDueToOtherPartyMultiplier_019ce811-d51c-76f1-8a13-c3e4b8200320" xlink:href="allo-20260331.xsd#allo_GrantAwardRoyaltyFeeAmountDueToOtherPartyMultiplier"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_019ce811-d51c-7620-b38a-d31c0dd9b779" xlink:to="loc_allo_GrantAwardRoyaltyFeeAmountDueToOtherPartyMultiplier_019ce811-d51c-76f1-8a13-c3e4b8200320" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_GrantAwardLoanConversionPeriodDeadlineAnniversaryOfAward_019ce811-d51c-7c8f-a5fb-42eea3f045a8" xlink:href="allo-20260331.xsd#allo_GrantAwardLoanConversionPeriodDeadlineAnniversaryOfAward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_019ce811-d51c-7620-b38a-d31c0dd9b779" xlink:to="loc_allo_GrantAwardLoanConversionPeriodDeadlineAnniversaryOfAward_019ce811-d51c-7c8f-a5fb-42eea3f045a8" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_GrantAwardAmountConvertedToLoanRepaymentPercentage_019ce811-d51c-7a55-98f9-4783055d59c2" xlink:href="allo-20260331.xsd#allo_GrantAwardAmountConvertedToLoanRepaymentPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_019ce811-d51c-7620-b38a-d31c0dd9b779" xlink:to="loc_allo_GrantAwardAmountConvertedToLoanRepaymentPercentage_019ce811-d51c-7a55-98f9-4783055d59c2" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_019ce811-d51c-77c6-92f4-9f1236382897" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentBasisSpreadOnVariableRate1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_019ce811-d51c-7620-b38a-d31c0dd9b779" xlink:to="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_019ce811-d51c-77c6-92f4-9f1236382897" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_ProceedsFromGrantAwards_019ce811-d51c-7d80-86c0-5edb7459d571" xlink:href="allo-20260331.xsd#allo_ProceedsFromGrantAwards"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_019ce811-d51c-7620-b38a-d31c0dd9b779" xlink:to="loc_allo_ProceedsFromGrantAwards_019ce811-d51c-7d80-86c0-5edb7459d571" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpenseNonoperating_019ce811-d51c-778f-80e7-da6b43faaa25" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InterestExpenseNonoperating"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_019ce811-d51c-7620-b38a-d31c0dd9b779" xlink:to="loc_us-gaap_InterestExpenseNonoperating_019ce811-d51c-778f-80e7-da6b43faaa25" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestPayableCurrentAndNoncurrent_019ce811-d51c-7412-865f-afc136a9cffa" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InterestPayableCurrentAndNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_019ce811-d51c-7620-b38a-d31c0dd9b779" xlink:to="loc_us-gaap_InterestPayableCurrentAndNoncurrent_019ce811-d51c-7412-865f-afc136a9cffa" xlink:type="arc" order="12"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://allogene.com/role/LicenseandCollaborationAgreementsPfizerDetails" xlink:type="simple" xlink:href="allo-20260331.xsd#LicenseandCollaborationAgreementsPfizerDetails"/>
  <link:definitionLink xlink:role="http://allogene.com/role/LicenseandCollaborationAgreementsPfizerDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersLineItems_019ce811-d51c-781f-b994-6fcc6943eaf3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfResearchAndDevelopmentArrangementContractToPerformForOthersTable_019ce811-d51c-74d4-881b-e06570aba777" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfResearchAndDevelopmentArrangementContractToPerformForOthersTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersLineItems_019ce811-d51c-781f-b994-6fcc6943eaf3" xlink:to="loc_us-gaap_ScheduleOfResearchAndDevelopmentArrangementContractToPerformForOthersTable_019ce811-d51c-74d4-881b-e06570aba777" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionAxis_019ce811-d51c-75f0-a5f8-b4314d98c254" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyTransactionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfResearchAndDevelopmentArrangementContractToPerformForOthersTable_019ce811-d51c-74d4-881b-e06570aba777" xlink:to="loc_us-gaap_RelatedPartyTransactionAxis_019ce811-d51c-75f0-a5f8-b4314d98c254" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionDomain_019ce811-d51c-75f0-a5f8-b4314d98c254_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionAxis_019ce811-d51c-75f0-a5f8-b4314d98c254" xlink:to="loc_us-gaap_RelatedPartyTransactionDomain_019ce811-d51c-75f0-a5f8-b4314d98c254_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionDomain_019ce811-d51c-798a-a797-05f1f31b6cca" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionAxis_019ce811-d51c-75f0-a5f8-b4314d98c254" xlink:to="loc_us-gaap_RelatedPartyTransactionDomain_019ce811-d51c-798a-a797-05f1f31b6cca" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_AssetContributionAgreementMember_019ce811-d51c-75f3-b9fa-b0609ef3279a" xlink:href="allo-20260331.xsd#allo_AssetContributionAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionDomain_019ce811-d51c-798a-a797-05f1f31b6cca" xlink:to="loc_allo_AssetContributionAgreementMember_019ce811-d51c-75f3-b9fa-b0609ef3279a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019ce811-d51c-76cd-94d7-d5b2995f454e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfResearchAndDevelopmentArrangementContractToPerformForOthersTable_019ce811-d51c-74d4-881b-e06570aba777" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019ce811-d51c-76cd-94d7-d5b2995f454e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_019ce811-d51c-76cd-94d7-d5b2995f454e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019ce811-d51c-76cd-94d7-d5b2995f454e" xlink:to="loc_us-gaap_RelatedPartyDomain_019ce811-d51c-76cd-94d7-d5b2995f454e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_019ce811-d51c-7e59-bfaa-21ba408c03ec" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019ce811-d51c-76cd-94d7-d5b2995f454e" xlink:to="loc_us-gaap_RelatedPartyDomain_019ce811-d51c-7e59-bfaa-21ba408c03ec" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_PfizerIncMember_019ce811-d51c-7098-836b-da2fc07cb3eb" xlink:href="allo-20260331.xsd#allo_PfizerIncMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_019ce811-d51c-7e59-bfaa-21ba408c03ec" xlink:to="loc_allo_PfizerIncMember_019ce811-d51c-7098-836b-da2fc07cb3eb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_MilestonePayments_019ce811-d51c-7d25-85f7-91dae2298cd0" xlink:href="allo-20260331.xsd#allo_MilestonePayments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersLineItems_019ce811-d51c-781f-b994-6fcc6943eaf3" xlink:to="loc_allo_MilestonePayments_019ce811-d51c-7d25-85f7-91dae2298cd0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsForRoyalties_019ce811-d51c-7704-a011-80fd46c0fb71" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PaymentsForRoyalties"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersLineItems_019ce811-d51c-781f-b994-6fcc6943eaf3" xlink:to="loc_us-gaap_PaymentsForRoyalties_019ce811-d51c-7704-a011-80fd46c0fb71" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://allogene.com/role/LicenseandCollaborationAgreementsCellectisDetails" xlink:type="simple" xlink:href="allo-20260331.xsd#LicenseandCollaborationAgreementsCellectisDetails"/>
  <link:definitionLink xlink:role="http://allogene.com/role/LicenseandCollaborationAgreementsCellectisDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersLineItems_019ce811-d51c-7683-a2b1-ea095cb72317" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfResearchAndDevelopmentArrangementContractToPerformForOthersTable_019ce811-d51c-73d3-bc11-f12fb0e42c11" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfResearchAndDevelopmentArrangementContractToPerformForOthersTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersLineItems_019ce811-d51c-7683-a2b1-ea095cb72317" xlink:to="loc_us-gaap_ScheduleOfResearchAndDevelopmentArrangementContractToPerformForOthersTable_019ce811-d51c-73d3-bc11-f12fb0e42c11" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019ce811-d51c-76b7-aa3c-c8ea47589ac0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfResearchAndDevelopmentArrangementContractToPerformForOthersTable_019ce811-d51c-73d3-bc11-f12fb0e42c11" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019ce811-d51c-76b7-aa3c-c8ea47589ac0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_019ce811-d51c-76b7-aa3c-c8ea47589ac0_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019ce811-d51c-76b7-aa3c-c8ea47589ac0" xlink:to="loc_us-gaap_RelatedPartyDomain_019ce811-d51c-76b7-aa3c-c8ea47589ac0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_019ce811-d51c-7255-b08b-dd01d12b0178" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019ce811-d51c-76b7-aa3c-c8ea47589ac0" xlink:to="loc_us-gaap_RelatedPartyDomain_019ce811-d51c-7255-b08b-dd01d12b0178" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_CellectisSAMember_019ce811-d51c-7c4a-8bf7-2e2090ce9040" xlink:href="allo-20260331.xsd#allo_CellectisSAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_019ce811-d51c-7255-b08b-dd01d12b0178" xlink:to="loc_allo_CellectisSAMember_019ce811-d51c-7c4a-8bf7-2e2090ce9040" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfArrangementAxis_019ce811-d51c-7ef2-b3ec-f879bf43287b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TypeOfArrangementAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfResearchAndDevelopmentArrangementContractToPerformForOthersTable_019ce811-d51c-73d3-bc11-f12fb0e42c11" xlink:to="loc_us-gaap_TypeOfArrangementAxis_019ce811-d51c-7ef2-b3ec-f879bf43287b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_019ce811-d51c-7ef2-b3ec-f879bf43287b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_TypeOfArrangementAxis_019ce811-d51c-7ef2-b3ec-f879bf43287b" xlink:to="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_019ce811-d51c-7ef2-b3ec-f879bf43287b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_019ce811-d51c-7aeb-ac52-f36322839bd5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_TypeOfArrangementAxis_019ce811-d51c-7ef2-b3ec-f879bf43287b" xlink:to="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_019ce811-d51c-7aeb-ac52-f36322839bd5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_ResearchCollaborationAndLicenseAgreementMember_019ce811-d51c-756e-a8c4-e7250bfd710a" xlink:href="allo-20260331.xsd#allo_ResearchCollaborationAndLicenseAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_019ce811-d51c-7aeb-ac52-f36322839bd5" xlink:to="loc_allo_ResearchCollaborationAndLicenseAgreementMember_019ce811-d51c-756e-a8c4-e7250bfd710a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionAxis_019ce811-d51c-79e2-b5e1-4863fa99da40" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyTransactionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfResearchAndDevelopmentArrangementContractToPerformForOthersTable_019ce811-d51c-73d3-bc11-f12fb0e42c11" xlink:to="loc_us-gaap_RelatedPartyTransactionAxis_019ce811-d51c-79e2-b5e1-4863fa99da40" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionDomain_019ce811-d51c-79e2-b5e1-4863fa99da40_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionAxis_019ce811-d51c-79e2-b5e1-4863fa99da40" xlink:to="loc_us-gaap_RelatedPartyTransactionDomain_019ce811-d51c-79e2-b5e1-4863fa99da40_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionDomain_019ce811-d51c-726d-8e7d-d1d11fd32d2a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionAxis_019ce811-d51c-79e2-b5e1-4863fa99da40" xlink:to="loc_us-gaap_RelatedPartyTransactionDomain_019ce811-d51c-726d-8e7d-d1d11fd32d2a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_PreClinicalDevelopmentMilestoneMember_019ce811-d51c-7f90-b2f2-c2f58df78e5b" xlink:href="allo-20260331.xsd#allo_PreClinicalDevelopmentMilestoneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionDomain_019ce811-d51c-726d-8e7d-d1d11fd32d2a" xlink:to="loc_allo_PreClinicalDevelopmentMilestoneMember_019ce811-d51c-7f90-b2f2-c2f58df78e5b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchAndDevelopmentExpense_019ce811-d51c-773d-98eb-b533ae163d0b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ResearchAndDevelopmentExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersLineItems_019ce811-d51c-7683-a2b1-ea095cb72317" xlink:to="loc_us-gaap_ResearchAndDevelopmentExpense_019ce811-d51c-773d-98eb-b533ae163d0b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsForRoyalties_019e080a-b110-763f-aca3-8f0cafc39ecc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PaymentsForRoyalties"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersLineItems_019ce811-d51c-7683-a2b1-ea095cb72317" xlink:to="loc_us-gaap_PaymentsForRoyalties_019e080a-b110-763f-aca3-8f0cafc39ecc" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://allogene.com/role/LicenseandCollaborationAgreementsServierDetails" xlink:type="simple" xlink:href="allo-20260331.xsd#LicenseandCollaborationAgreementsServierDetails"/>
  <link:definitionLink xlink:role="http://allogene.com/role/LicenseandCollaborationAgreementsServierDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersLineItems_019ce811-d51c-7997-b098-48466220c964" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfResearchAndDevelopmentArrangementContractToPerformForOthersTable_019ce811-d51c-7cd3-8689-e9272c5841e2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfResearchAndDevelopmentArrangementContractToPerformForOthersTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersLineItems_019ce811-d51c-7997-b098-48466220c964" xlink:to="loc_us-gaap_ScheduleOfResearchAndDevelopmentArrangementContractToPerformForOthersTable_019ce811-d51c-7cd3-8689-e9272c5841e2" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CounterpartyNameAxis_019ce811-d51c-7c2e-83d2-18d53299a607" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_CounterpartyNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfResearchAndDevelopmentArrangementContractToPerformForOthersTable_019ce811-d51c-7cd3-8689-e9272c5841e2" xlink:to="loc_srt_CounterpartyNameAxis_019ce811-d51c-7c2e-83d2-18d53299a607" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019ce811-d51c-7c2e-83d2-18d53299a607_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CounterpartyNameAxis_019ce811-d51c-7c2e-83d2-18d53299a607" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019ce811-d51c-7c2e-83d2-18d53299a607_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019ce811-d51c-774c-bc06-e60ab983da5d" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CounterpartyNameAxis_019ce811-d51c-7c2e-83d2-18d53299a607" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019ce811-d51c-774c-bc06-e60ab983da5d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_ServierMember_019ce811-d51c-71fb-9789-639aa86954fb" xlink:href="allo-20260331.xsd#allo_ServierMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019ce811-d51c-774c-bc06-e60ab983da5d" xlink:to="loc_allo_ServierMember_019ce811-d51c-71fb-9789-639aa86954fb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionAxis_019ce811-d51c-700c-a1c3-fdb7e2e84121" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyTransactionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfResearchAndDevelopmentArrangementContractToPerformForOthersTable_019ce811-d51c-7cd3-8689-e9272c5841e2" xlink:to="loc_us-gaap_RelatedPartyTransactionAxis_019ce811-d51c-700c-a1c3-fdb7e2e84121" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionDomain_019ce811-d51c-700c-a1c3-fdb7e2e84121_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionAxis_019ce811-d51c-700c-a1c3-fdb7e2e84121" xlink:to="loc_us-gaap_RelatedPartyTransactionDomain_019ce811-d51c-700c-a1c3-fdb7e2e84121_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionDomain_019ce811-d51c-734c-9d6a-fb1d74c3a555" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionAxis_019ce811-d51c-700c-a1c3-fdb7e2e84121" xlink:to="loc_us-gaap_RelatedPartyTransactionDomain_019ce811-d51c-734c-9d6a-fb1d74c3a555" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_RegulatoryMilestoneMember_019ce811-d51c-7360-ab47-764a865e0705" xlink:href="allo-20260331.xsd#allo_RegulatoryMilestoneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionDomain_019ce811-d51c-734c-9d6a-fb1d74c3a555" xlink:to="loc_allo_RegulatoryMilestoneMember_019ce811-d51c-7360-ab47-764a865e0705" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_SalesMilestoneMember_019ce811-d51c-72fa-8077-10bc425deb65" xlink:href="allo-20260331.xsd#allo_SalesMilestoneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionDomain_019ce811-d51c-734c-9d6a-fb1d74c3a555" xlink:to="loc_allo_SalesMilestoneMember_019ce811-d51c-72fa-8077-10bc425deb65" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_RegulatoryAndSalesMilestonesMember_019ce811-d51c-7ffe-98be-0be870f67cee" xlink:href="allo-20260331.xsd#allo_RegulatoryAndSalesMilestonesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionDomain_019ce811-d51c-734c-9d6a-fb1d74c3a555" xlink:to="loc_allo_RegulatoryAndSalesMilestonesMember_019ce811-d51c-7ffe-98be-0be870f67cee" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfArrangementAxis_019ce811-d51c-7b47-9ced-44eeed3f70ad" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TypeOfArrangementAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfResearchAndDevelopmentArrangementContractToPerformForOthersTable_019ce811-d51c-7cd3-8689-e9272c5841e2" xlink:to="loc_us-gaap_TypeOfArrangementAxis_019ce811-d51c-7b47-9ced-44eeed3f70ad" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_019ce811-d51c-7b47-9ced-44eeed3f70ad_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_TypeOfArrangementAxis_019ce811-d51c-7b47-9ced-44eeed3f70ad" xlink:to="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_019ce811-d51c-7b47-9ced-44eeed3f70ad_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_019ce811-d51c-77a9-9f43-4bfe84cb8805" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_TypeOfArrangementAxis_019ce811-d51c-7b47-9ced-44eeed3f70ad" xlink:to="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_019ce811-d51c-77a9-9f43-4bfe84cb8805" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_LicenseAndCollaborationAgreementMember_019ce811-d51c-7e81-8bd5-ba953049ef68" xlink:href="allo-20260331.xsd#allo_LicenseAndCollaborationAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_019ce811-d51c-77a9-9f43-4bfe84cb8805" xlink:to="loc_allo_LicenseAndCollaborationAgreementMember_019ce811-d51c-7e81-8bd5-ba953049ef68" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementGeographicalAxis_019ce811-d51c-76df-88a3-138d9a89bebd" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_StatementGeographicalAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfResearchAndDevelopmentArrangementContractToPerformForOthersTable_019ce811-d51c-7cd3-8689-e9272c5841e2" xlink:to="loc_srt_StatementGeographicalAxis_019ce811-d51c-76df-88a3-138d9a89bebd" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_019ce811-d51c-76df-88a3-138d9a89bebd_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementGeographicalAxis_019ce811-d51c-76df-88a3-138d9a89bebd" xlink:to="loc_srt_SegmentGeographicalDomain_019ce811-d51c-76df-88a3-138d9a89bebd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_019ce811-d51c-7779-b54b-b7f428567a20" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementGeographicalAxis_019ce811-d51c-76df-88a3-138d9a89bebd" xlink:to="loc_srt_SegmentGeographicalDomain_019ce811-d51c-7779-b54b-b7f428567a20" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_US_019ce811-d51c-7a48-9072-d985574bac67" xlink:href="https://xbrl.sec.gov/country/2025/country-2025.xsd#country_US"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_019ce811-d51c-7779-b54b-b7f428567a20" xlink:to="loc_country_US_019ce811-d51c-7a48-9072-d985574bac67" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019ce811-d51c-7bde-89d4-38e72657acef" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfResearchAndDevelopmentArrangementContractToPerformForOthersTable_019ce811-d51c-7cd3-8689-e9272c5841e2" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019ce811-d51c-7bde-89d4-38e72657acef" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_019ce811-d51c-7bde-89d4-38e72657acef_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019ce811-d51c-7bde-89d4-38e72657acef" xlink:to="loc_us-gaap_RelatedPartyDomain_019ce811-d51c-7bde-89d4-38e72657acef_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_019ce811-d51c-76c5-ace6-69f50dfd4151" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019ce811-d51c-7bde-89d4-38e72657acef" xlink:to="loc_us-gaap_RelatedPartyDomain_019ce811-d51c-76c5-ace6-69f50dfd4151" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_ServierMember_019ce811-d51c-7829-959f-329d751357a5" xlink:href="allo-20260331.xsd#allo_ServierMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_019ce811-d51c-76c5-ace6-69f50dfd4151" xlink:to="loc_allo_ServierMember_019ce811-d51c-7829-959f-329d751357a5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_CollaborativeArrangementRightsAndObligationsMaximumAggregateMilestonePayments_019ce811-d51c-7824-8e2d-4b7623dbade1" xlink:href="allo-20260331.xsd#allo_CollaborativeArrangementRightsAndObligationsMaximumAggregateMilestonePayments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersLineItems_019ce811-d51c-7997-b098-48466220c964" xlink:to="loc_allo_CollaborativeArrangementRightsAndObligationsMaximumAggregateMilestonePayments_019ce811-d51c-7824-8e2d-4b7623dbade1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_CollaborativeArrangementRightsAndObligationsMaximumAggregateMilestonePaymentsRemaining_019ce811-d51c-7e32-a8fd-dbdc6c3f8507" xlink:href="allo-20260331.xsd#allo_CollaborativeArrangementRightsAndObligationsMaximumAggregateMilestonePaymentsRemaining"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersLineItems_019ce811-d51c-7997-b098-48466220c964" xlink:to="loc_allo_CollaborativeArrangementRightsAndObligationsMaximumAggregateMilestonePaymentsRemaining_019ce811-d51c-7e32-a8fd-dbdc6c3f8507" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_CollaborativeArrangementRightsAndObligationsAggregateMilestonePaymentsPerAdditionalIndication_019ce811-d51c-764e-b49e-26781c9d299a" xlink:href="allo-20260331.xsd#allo_CollaborativeArrangementRightsAndObligationsAggregateMilestonePaymentsPerAdditionalIndication"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersLineItems_019ce811-d51c-7997-b098-48466220c964" xlink:to="loc_allo_CollaborativeArrangementRightsAndObligationsAggregateMilestonePaymentsPerAdditionalIndication_019ce811-d51c-764e-b49e-26781c9d299a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_CollaborativeArrangementRightsAndObligationsAggregateMilestonePaymentsPerAdditionalIndicationRemainingAmount_019ce811-d51c-7254-90ce-bb7b67c24bcf" xlink:href="allo-20260331.xsd#allo_CollaborativeArrangementRightsAndObligationsAggregateMilestonePaymentsPerAdditionalIndicationRemainingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersLineItems_019ce811-d51c-7997-b098-48466220c964" xlink:to="loc_allo_CollaborativeArrangementRightsAndObligationsAggregateMilestonePaymentsPerAdditionalIndicationRemainingAmount_019ce811-d51c-7254-90ce-bb7b67c24bcf" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_CollaborativeArrangementRightsAndObligationsMilestonePayable_019ce811-d51c-7ec9-bffe-c8943e2df0ba" xlink:href="allo-20260331.xsd#allo_CollaborativeArrangementRightsAndObligationsMilestonePayable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersLineItems_019ce811-d51c-7997-b098-48466220c964" xlink:to="loc_allo_CollaborativeArrangementRightsAndObligationsMilestonePayable_019ce811-d51c-7ec9-bffe-c8943e2df0ba" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_CollaborationAgreementNetCashProceedsRemitted_019de15d-9303-72cc-bcd6-8762baabecd0" xlink:href="allo-20260331.xsd#allo_CollaborationAgreementNetCashProceedsRemitted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersLineItems_019ce811-d51c-7997-b098-48466220c964" xlink:to="loc_allo_CollaborationAgreementNetCashProceedsRemitted_019de15d-9303-72cc-bcd6-8762baabecd0" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_CollaborativeArrangementRightsAndObligationsRoyaltiesPayableAnnualRatePercent_019ce811-d51c-7cc7-bcff-666aca5e05e8" xlink:href="allo-20260331.xsd#allo_CollaborativeArrangementRightsAndObligationsRoyaltiesPayableAnnualRatePercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersLineItems_019ce811-d51c-7997-b098-48466220c964" xlink:to="loc_allo_CollaborativeArrangementRightsAndObligationsRoyaltiesPayableAnnualRatePercent_019ce811-d51c-7cc7-bcff-666aca5e05e8" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_CollaborativeArrangementRightsAndObligationsRoyaltiesPayableAnnualRateReductionPercent_019ce811-d51c-7cf4-8a03-d346d34a0f3e" xlink:href="allo-20260331.xsd#allo_CollaborativeArrangementRightsAndObligationsRoyaltiesPayableAnnualRateReductionPercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersLineItems_019ce811-d51c-7997-b098-48466220c964" xlink:to="loc_allo_CollaborativeArrangementRightsAndObligationsRoyaltiesPayableAnnualRateReductionPercent_019ce811-d51c-7cf4-8a03-d346d34a0f3e" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchAndDevelopmentExpense_019ce811-d51c-7f30-8dc4-0b74166328d6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ResearchAndDevelopmentExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersLineItems_019ce811-d51c-7997-b098-48466220c964" xlink:to="loc_us-gaap_ResearchAndDevelopmentExpense_019ce811-d51c-7f30-8dc4-0b74166328d6" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsForRoyalties_019e080c-45ed-7468-bd45-9763b591261a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PaymentsForRoyalties"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersLineItems_019ce811-d51c-7997-b098-48466220c964" xlink:to="loc_us-gaap_PaymentsForRoyalties_019e080c-45ed-7468-bd45-9763b591261a" xlink:type="arc" order="9"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://allogene.com/role/LicenseandCollaborationAgreementsNotchTherapeuticsDetails" xlink:type="simple" xlink:href="allo-20260331.xsd#LicenseandCollaborationAgreementsNotchTherapeuticsDetails"/>
  <link:definitionLink xlink:role="http://allogene.com/role/LicenseandCollaborationAgreementsNotchTherapeuticsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersLineItems_019ce811-d51c-7d1b-865f-14fa0a702d7e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfResearchAndDevelopmentArrangementContractToPerformForOthersTable_019ce811-d51c-7a2c-8413-aca19f0e38b7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfResearchAndDevelopmentArrangementContractToPerformForOthersTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersLineItems_019ce811-d51c-7d1b-865f-14fa0a702d7e" xlink:to="loc_us-gaap_ScheduleOfResearchAndDevelopmentArrangementContractToPerformForOthersTable_019ce811-d51c-7a2c-8413-aca19f0e38b7" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_019ce811-d51c-700e-a281-846bfd4515b1" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfResearchAndDevelopmentArrangementContractToPerformForOthersTable_019ce811-d51c-7a2c-8413-aca19f0e38b7" xlink:to="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_019ce811-d51c-700e-a281-846bfd4515b1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_EquityMethodInvesteeNameDomain_019ce811-d51c-700e-a281-846bfd4515b1_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_EquityMethodInvesteeNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_019ce811-d51c-700e-a281-846bfd4515b1" xlink:to="loc_srt_EquityMethodInvesteeNameDomain_019ce811-d51c-700e-a281-846bfd4515b1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_EquityMethodInvesteeNameDomain_019ce811-d51c-7a41-a961-f555250aeefb" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_EquityMethodInvesteeNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_019ce811-d51c-700e-a281-846bfd4515b1" xlink:to="loc_srt_EquityMethodInvesteeNameDomain_019ce811-d51c-7a41-a961-f555250aeefb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_NotchTherapeuticsIncMember_019ce811-d51c-7e8f-bfc3-6b16f899e2ca" xlink:href="allo-20260331.xsd#allo_NotchTherapeuticsIncMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_EquityMethodInvesteeNameDomain_019ce811-d51c-7a41-a961-f555250aeefb" xlink:to="loc_allo_NotchTherapeuticsIncMember_019ce811-d51c-7e8f-bfc3-6b16f899e2ca" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionAxis_019ce811-d51c-79d0-bca3-bcd597c7140e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyTransactionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfResearchAndDevelopmentArrangementContractToPerformForOthersTable_019ce811-d51c-7a2c-8413-aca19f0e38b7" xlink:to="loc_us-gaap_RelatedPartyTransactionAxis_019ce811-d51c-79d0-bca3-bcd597c7140e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionDomain_019ce811-d51c-79d0-bca3-bcd597c7140e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionAxis_019ce811-d51c-79d0-bca3-bcd597c7140e" xlink:to="loc_us-gaap_RelatedPartyTransactionDomain_019ce811-d51c-79d0-bca3-bcd597c7140e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionDomain_019ce811-d51c-71e4-9ed3-128f61cedf88" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionAxis_019ce811-d51c-79d0-bca3-bcd597c7140e" xlink:to="loc_us-gaap_RelatedPartyTransactionDomain_019ce811-d51c-71e4-9ed3-128f61cedf88" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_PreClinicalDevelopmentMilestoneMember_019ce811-d51c-75c4-bcb1-3047a98e1c01" xlink:href="allo-20260331.xsd#allo_PreClinicalDevelopmentMilestoneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionDomain_019ce811-d51c-71e4-9ed3-128f61cedf88" xlink:to="loc_allo_PreClinicalDevelopmentMilestoneMember_019ce811-d51c-75c4-bcb1-3047a98e1c01" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019ce811-d51c-7b4b-8014-0d8093a25344" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfResearchAndDevelopmentArrangementContractToPerformForOthersTable_019ce811-d51c-7a2c-8413-aca19f0e38b7" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019ce811-d51c-7b4b-8014-0d8093a25344" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_019ce811-d51c-7b4b-8014-0d8093a25344_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019ce811-d51c-7b4b-8014-0d8093a25344" xlink:to="loc_us-gaap_RelatedPartyDomain_019ce811-d51c-7b4b-8014-0d8093a25344_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_019ce811-d51c-71be-84f5-e70373dce812" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019ce811-d51c-7b4b-8014-0d8093a25344" xlink:to="loc_us-gaap_RelatedPartyDomain_019ce811-d51c-71be-84f5-e70373dce812" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_NotchTherapeuticsIncMember_019ce811-d51c-786e-8aeb-208ec7ff2d19" xlink:href="allo-20260331.xsd#allo_NotchTherapeuticsIncMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_019ce811-d51c-71be-84f5-e70373dce812" xlink:to="loc_allo_NotchTherapeuticsIncMember_019ce811-d51c-786e-8aeb-208ec7ff2d19" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfArrangementAxis_019ce811-d51c-7c36-a1ff-18a2bd70dae0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TypeOfArrangementAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfResearchAndDevelopmentArrangementContractToPerformForOthersTable_019ce811-d51c-7a2c-8413-aca19f0e38b7" xlink:to="loc_us-gaap_TypeOfArrangementAxis_019ce811-d51c-7c36-a1ff-18a2bd70dae0" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_019ce811-d51c-7c36-a1ff-18a2bd70dae0_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_TypeOfArrangementAxis_019ce811-d51c-7c36-a1ff-18a2bd70dae0" xlink:to="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_019ce811-d51c-7c36-a1ff-18a2bd70dae0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_019ce811-d51c-776a-8e2d-a93788fb3b18" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_TypeOfArrangementAxis_019ce811-d51c-7c36-a1ff-18a2bd70dae0" xlink:to="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_019ce811-d51c-776a-8e2d-a93788fb3b18" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_ResearchCollaborationAndLicenseAgreementMember_019ce811-d51c-7d12-9250-f41963da9bdb" xlink:href="allo-20260331.xsd#allo_ResearchCollaborationAndLicenseAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_019ce811-d51c-776a-8e2d-a93788fb3b18" xlink:to="loc_allo_ResearchCollaborationAndLicenseAgreementMember_019ce811-d51c-7d12-9250-f41963da9bdb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquitySecuritiesFvNiCurrentAndNoncurrent_019ce811-d51c-7c69-9850-0502476fb048" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquitySecuritiesFvNiCurrentAndNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersLineItems_019ce811-d51c-7d1b-865f-14fa0a702d7e" xlink:to="loc_us-gaap_EquitySecuritiesFvNiCurrentAndNoncurrent_019ce811-d51c-7c69-9850-0502476fb048" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchAndDevelopmentExpense_019ce811-d51c-7e77-af3d-db31e2b18cf4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ResearchAndDevelopmentExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersLineItems_019ce811-d51c-7d1b-865f-14fa0a702d7e" xlink:to="loc_us-gaap_ResearchAndDevelopmentExpense_019ce811-d51c-7e77-af3d-db31e2b18cf4" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://allogene.com/role/LicenseandCollaborationAgreementsMDAndersonCancerCenterDetails" xlink:type="simple" xlink:href="allo-20260331.xsd#LicenseandCollaborationAgreementsMDAndersonCancerCenterDetails"/>
  <link:definitionLink xlink:role="http://allogene.com/role/LicenseandCollaborationAgreementsMDAndersonCancerCenterDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersLineItems_019ce811-d51c-7d21-bec8-fdf6f66b5e4b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfResearchAndDevelopmentArrangementContractToPerformForOthersTable_019ce811-d51c-7a09-9014-809fd5da99e7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfResearchAndDevelopmentArrangementContractToPerformForOthersTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersLineItems_019ce811-d51c-7d21-bec8-fdf6f66b5e4b" xlink:to="loc_us-gaap_ScheduleOfResearchAndDevelopmentArrangementContractToPerformForOthersTable_019ce811-d51c-7a09-9014-809fd5da99e7" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CounterpartyNameAxis_019ce811-d51c-7fe8-8570-8ffab515f035" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_CounterpartyNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfResearchAndDevelopmentArrangementContractToPerformForOthersTable_019ce811-d51c-7a09-9014-809fd5da99e7" xlink:to="loc_srt_CounterpartyNameAxis_019ce811-d51c-7fe8-8570-8ffab515f035" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019ce811-d51c-7fe8-8570-8ffab515f035_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CounterpartyNameAxis_019ce811-d51c-7fe8-8570-8ffab515f035" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019ce811-d51c-7fe8-8570-8ffab515f035_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019ce811-d51c-7044-89d8-cd48acfa73fe" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CounterpartyNameAxis_019ce811-d51c-7fe8-8570-8ffab515f035" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019ce811-d51c-7044-89d8-cd48acfa73fe" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_UniversityOfTexasMDAndersonCancerCenterMember_019ce811-d51c-7ba0-a810-f782aa3e34d6" xlink:href="allo-20260331.xsd#allo_UniversityOfTexasMDAndersonCancerCenterMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019ce811-d51c-7044-89d8-cd48acfa73fe" xlink:to="loc_allo_UniversityOfTexasMDAndersonCancerCenterMember_019ce811-d51c-7ba0-a810-f782aa3e34d6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_CollaborationAgreementTerm_019ce811-d51c-7587-8840-07bc5c87c16f" xlink:href="allo-20260331.xsd#allo_CollaborationAgreementTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersLineItems_019ce811-d51c-7d21-bec8-fdf6f66b5e4b" xlink:to="loc_allo_CollaborationAgreementTerm_019ce811-d51c-7587-8840-07bc5c87c16f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_CollaborationAgreementCommittedFunding_019ce811-d51c-755f-a936-1e41903ab380" xlink:href="allo-20260331.xsd#allo_CollaborationAgreementCommittedFunding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersLineItems_019ce811-d51c-7d21-bec8-fdf6f66b5e4b" xlink:to="loc_allo_CollaborationAgreementCommittedFunding_019ce811-d51c-755f-a936-1e41903ab380" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_CollaborationAgreementCommittedFundingRemainingToBePaid_019ce811-d51c-7c3b-93aa-2376b0ce3f6a" xlink:href="allo-20260331.xsd#allo_CollaborationAgreementCommittedFundingRemainingToBePaid"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersLineItems_019ce811-d51c-7d21-bec8-fdf6f66b5e4b" xlink:to="loc_allo_CollaborationAgreementCommittedFundingRemainingToBePaid_019ce811-d51c-7c3b-93aa-2376b0ce3f6a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_CollaborationArrangementExpense_019ce811-d51c-7533-962e-260f98285f00" xlink:href="allo-20260331.xsd#allo_CollaborationArrangementExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersLineItems_019ce811-d51c-7d21-bec8-fdf6f66b5e4b" xlink:to="loc_allo_CollaborationArrangementExpense_019ce811-d51c-7533-962e-260f98285f00" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://allogene.com/role/LicenseandCollaborationAgreementsOverlandTherapeuticsIncDetails" xlink:type="simple" xlink:href="allo-20260331.xsd#LicenseandCollaborationAgreementsOverlandTherapeuticsIncDetails"/>
  <link:definitionLink xlink:role="http://allogene.com/role/LicenseandCollaborationAgreementsOverlandTherapeuticsIncDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersLineItems_019ce811-d51c-7f9c-860d-8e1d326ee9d5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfResearchAndDevelopmentArrangementContractToPerformForOthersTable_019ce811-d51c-7d1e-b4cd-cc1463b58840" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfResearchAndDevelopmentArrangementContractToPerformForOthersTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersLineItems_019ce811-d51c-7f9c-860d-8e1d326ee9d5" xlink:to="loc_us-gaap_ScheduleOfResearchAndDevelopmentArrangementContractToPerformForOthersTable_019ce811-d51c-7d1e-b4cd-cc1463b58840" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_OwnershipAxis_019ce811-d51c-7de9-90ce-90063d2983a4" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_OwnershipAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfResearchAndDevelopmentArrangementContractToPerformForOthersTable_019ce811-d51c-7d1e-b4cd-cc1463b58840" xlink:to="loc_srt_OwnershipAxis_019ce811-d51c-7de9-90ce-90063d2983a4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_OwnershipDomain_019ce811-d51c-7de9-90ce-90063d2983a4_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_OwnershipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_OwnershipAxis_019ce811-d51c-7de9-90ce-90063d2983a4" xlink:to="loc_srt_OwnershipDomain_019ce811-d51c-7de9-90ce-90063d2983a4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_OwnershipDomain_019ce811-d51c-7a63-926e-d1cb5d7db6d5" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_OwnershipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_OwnershipAxis_019ce811-d51c-7de9-90ce-90063d2983a4" xlink:to="loc_srt_OwnershipDomain_019ce811-d51c-7a63-926e-d1cb5d7db6d5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_OverlandTherapeuticsFormerlyKnownAsAllogeneOverlandMember_019ce811-d51c-7840-8ca8-26e5e3b3f77b" xlink:href="allo-20260331.xsd#allo_OverlandTherapeuticsFormerlyKnownAsAllogeneOverlandMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_OwnershipDomain_019ce811-d51c-7a63-926e-d1cb5d7db6d5" xlink:to="loc_allo_OverlandTherapeuticsFormerlyKnownAsAllogeneOverlandMember_019ce811-d51c-7840-8ca8-26e5e3b3f77b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_OverlandUSMember_019ce811-d51c-7d0b-9ce6-296b0876080b" xlink:href="allo-20260331.xsd#allo_OverlandUSMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_OwnershipDomain_019ce811-d51c-7a63-926e-d1cb5d7db6d5" xlink:to="loc_allo_OverlandUSMember_019ce811-d51c-7d0b-9ce6-296b0876080b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_019ce811-d51c-7b74-ad4e-5e7fd2615d7c" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfResearchAndDevelopmentArrangementContractToPerformForOthersTable_019ce811-d51c-7d1e-b4cd-cc1463b58840" xlink:to="loc_dei_LegalEntityAxis_019ce811-d51c-7b74-ad4e-5e7fd2615d7c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019ce811-d51c-7b74-ad4e-5e7fd2615d7c_default" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_019ce811-d51c-7b74-ad4e-5e7fd2615d7c" xlink:to="loc_dei_EntityDomain_019ce811-d51c-7b74-ad4e-5e7fd2615d7c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019ce811-d51c-7ace-8cf3-3e4adb8a801a" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_019ce811-d51c-7b74-ad4e-5e7fd2615d7c" xlink:to="loc_dei_EntityDomain_019ce811-d51c-7ace-8cf3-3e4adb8a801a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_OverlandPharmaceuticalsIncMember_019ce811-d51c-7465-aa1d-f591822efc2a" xlink:href="allo-20260331.xsd#allo_OverlandPharmaceuticalsIncMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019ce811-d51c-7ace-8cf3-3e4adb8a801a" xlink:to="loc_allo_OverlandPharmaceuticalsIncMember_019ce811-d51c-7465-aa1d-f591822efc2a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CounterpartyNameAxis_019ce811-d51c-7c46-80f5-3d0c129eebd9" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_CounterpartyNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfResearchAndDevelopmentArrangementContractToPerformForOthersTable_019ce811-d51c-7d1e-b4cd-cc1463b58840" xlink:to="loc_srt_CounterpartyNameAxis_019ce811-d51c-7c46-80f5-3d0c129eebd9" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019ce811-d51c-7c46-80f5-3d0c129eebd9_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CounterpartyNameAxis_019ce811-d51c-7c46-80f5-3d0c129eebd9" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019ce811-d51c-7c46-80f5-3d0c129eebd9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019ce811-d51c-76f9-bb0c-b86d23e687bf" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CounterpartyNameAxis_019ce811-d51c-7c46-80f5-3d0c129eebd9" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019ce811-d51c-76f9-bb0c-b86d23e687bf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_OverlandTherapeuticsFormerlyKnownAsAllogeneOverlandMember_019ce811-d51c-7de9-8989-45f2634a32f5" xlink:href="allo-20260331.xsd#allo_OverlandTherapeuticsFormerlyKnownAsAllogeneOverlandMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019ce811-d51c-76f9-bb0c-b86d23e687bf" xlink:to="loc_allo_OverlandTherapeuticsFormerlyKnownAsAllogeneOverlandMember_019ce811-d51c-7de9-8989-45f2634a32f5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_OverlandPharmaceuticalsIncMember_019ce811-d51c-79bf-bb76-275d8ea08793" xlink:href="allo-20260331.xsd#allo_OverlandPharmaceuticalsIncMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019ce811-d51c-76f9-bb0c-b86d23e687bf" xlink:to="loc_allo_OverlandPharmaceuticalsIncMember_019ce811-d51c-79bf-bb76-275d8ea08793" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_019ce811-d51c-73ce-95a6-3b38c16f1615" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfResearchAndDevelopmentArrangementContractToPerformForOthersTable_019ce811-d51c-7d1e-b4cd-cc1463b58840" xlink:to="loc_srt_ProductOrServiceAxis_019ce811-d51c-73ce-95a6-3b38c16f1615" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019ce811-d51c-73ce-95a6-3b38c16f1615_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_019ce811-d51c-73ce-95a6-3b38c16f1615" xlink:to="loc_srt_ProductsAndServicesDomain_019ce811-d51c-73ce-95a6-3b38c16f1615_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019ce811-d51c-7853-af0d-1b5445f5d487" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_019ce811-d51c-73ce-95a6-3b38c16f1615" xlink:to="loc_srt_ProductsAndServicesDomain_019ce811-d51c-7853-af0d-1b5445f5d487" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LicenseMember_019ce811-d51c-7cbf-956f-c87ef0dea950" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LicenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019ce811-d51c-7853-af0d-1b5445f5d487" xlink:to="loc_us-gaap_LicenseMember_019ce811-d51c-7cbf-956f-c87ef0dea950" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019ce811-d51c-761c-b06d-74a09c066542" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfResearchAndDevelopmentArrangementContractToPerformForOthersTable_019ce811-d51c-7d1e-b4cd-cc1463b58840" xlink:to="loc_srt_RangeAxis_019ce811-d51c-761c-b06d-74a09c066542" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019ce811-d51c-761c-b06d-74a09c066542_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_019ce811-d51c-761c-b06d-74a09c066542" xlink:to="loc_srt_RangeMember_019ce811-d51c-761c-b06d-74a09c066542_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019ce811-d51c-77f0-8bcb-1e3baa4c320d" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_019ce811-d51c-761c-b06d-74a09c066542" xlink:to="loc_srt_RangeMember_019ce811-d51c-77f0-8bcb-1e3baa4c320d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_019ce811-d51c-7efe-9035-a8bf4e65498a" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019ce811-d51c-77f0-8bcb-1e3baa4c320d" xlink:to="loc_srt_MaximumMember_019ce811-d51c-7efe-9035-a8bf4e65498a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_019ce811-d51c-7ebc-aa0b-eb92d893a0da" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfResearchAndDevelopmentArrangementContractToPerformForOthersTable_019ce811-d51c-7d1e-b4cd-cc1463b58840" xlink:to="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_019ce811-d51c-7ebc-aa0b-eb92d893a0da" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_EquityMethodInvesteeNameDomain_019ce811-d51c-7ebc-aa0b-eb92d893a0da_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_EquityMethodInvesteeNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_019ce811-d51c-7ebc-aa0b-eb92d893a0da" xlink:to="loc_srt_EquityMethodInvesteeNameDomain_019ce811-d51c-7ebc-aa0b-eb92d893a0da_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_EquityMethodInvesteeNameDomain_019ce811-d51c-7aaf-932f-2bc7e9152e6b" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_EquityMethodInvesteeNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_019ce811-d51c-7ebc-aa0b-eb92d893a0da" xlink:to="loc_srt_EquityMethodInvesteeNameDomain_019ce811-d51c-7aaf-932f-2bc7e9152e6b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_OverlandTherapeuticsFormerlyKnownAsAllogeneOverlandMember_019ce811-d51c-7e18-a43e-69d5cd69acaf" xlink:href="allo-20260331.xsd#allo_OverlandTherapeuticsFormerlyKnownAsAllogeneOverlandMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_EquityMethodInvesteeNameDomain_019ce811-d51c-7aaf-932f-2bc7e9152e6b" xlink:to="loc_allo_OverlandTherapeuticsFormerlyKnownAsAllogeneOverlandMember_019ce811-d51c-7e18-a43e-69d5cd69acaf" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_EquityInvestmentBasisAxis_019ce811-d51c-7e7d-b412-d6077b9bc0af" xlink:href="allo-20260331.xsd#allo_EquityInvestmentBasisAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfResearchAndDevelopmentArrangementContractToPerformForOthersTable_019ce811-d51c-7d1e-b4cd-cc1463b58840" xlink:to="loc_allo_EquityInvestmentBasisAxis_019ce811-d51c-7e7d-b412-d6077b9bc0af" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_EquityInvestmentBasisDomain_019ce811-d51c-7e7d-b412-d6077b9bc0af_default" xlink:href="allo-20260331.xsd#allo_EquityInvestmentBasisDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_allo_EquityInvestmentBasisAxis_019ce811-d51c-7e7d-b412-d6077b9bc0af" xlink:to="loc_allo_EquityInvestmentBasisDomain_019ce811-d51c-7e7d-b412-d6077b9bc0af_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_EquityInvestmentBasisDomain_019ce811-d51c-7509-92e7-b51a78ebef14" xlink:href="allo-20260331.xsd#allo_EquityInvestmentBasisDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_allo_EquityInvestmentBasisAxis_019ce811-d51c-7e7d-b412-d6077b9bc0af" xlink:to="loc_allo_EquityInvestmentBasisDomain_019ce811-d51c-7509-92e7-b51a78ebef14" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_VotingInterestMember_019ce811-d51c-70cf-8459-a6a1235422f6" xlink:href="allo-20260331.xsd#allo_VotingInterestMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_allo_EquityInvestmentBasisDomain_019ce811-d51c-7509-92e7-b51a78ebef14" xlink:to="loc_allo_VotingInterestMember_019ce811-d51c-70cf-8459-a6a1235422f6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeAxis_019e17bc-a753-7d59-8827-094cdd86b798" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfResearchAndDevelopmentArrangementContractToPerformForOthersTable_019ce811-d51c-7d1e-b4cd-cc1463b58840" xlink:to="loc_us-gaap_SubsequentEventTypeAxis_019e17bc-a753-7d59-8827-094cdd86b798" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_019e17bc-a753-7d59-8827-094cdd86b798_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_019e17bc-a753-7d59-8827-094cdd86b798" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_019e17bc-a753-7d59-8827-094cdd86b798_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_019e17bc-a753-7786-b895-5617650cd55a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_019e17bc-a753-7d59-8827-094cdd86b798" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_019e17bc-a753-7786-b895-5617650cd55a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventMember_019e17bc-be72-796c-853e-93f6348d3c47" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventTypeDomain_019e17bc-a753-7786-b895-5617650cd55a" xlink:to="loc_us-gaap_SubsequentEventMember_019e17bc-be72-796c-853e-93f6348d3c47" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityMethodInvestmentOwnershipPercentage_019ce811-d51c-725f-a1cc-87042e543ba1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityMethodInvestmentOwnershipPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersLineItems_019ce811-d51c-7f9c-860d-8e1d326ee9d5" xlink:to="loc_us-gaap_EquityMethodInvestmentOwnershipPercentage_019ce811-d51c-725f-a1cc-87042e543ba1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MinorityInterestOwnershipPercentageByParent_019ce811-d51c-7952-ada1-c818f5fece3b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MinorityInterestOwnershipPercentageByParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersLineItems_019ce811-d51c-7f9c-860d-8e1d326ee9d5" xlink:to="loc_us-gaap_MinorityInterestOwnershipPercentageByParent_019ce811-d51c-7952-ada1-c818f5fece3b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners_019ce811-d51c-7425-8553-a68f5ab61cae" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersLineItems_019ce811-d51c-7f9c-860d-8e1d326ee9d5" xlink:to="loc_us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners_019ce811-d51c-7425-8553-a68f5ab61cae" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_LicenseAgreementMinimumOwnershipThresholdPercent_019ce811-d51c-726d-9a92-ab020fe2b971" xlink:href="allo-20260331.xsd#allo_LicenseAgreementMinimumOwnershipThresholdPercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersLineItems_019ce811-d51c-7f9c-860d-8e1d326ee9d5" xlink:to="loc_allo_LicenseAgreementMinimumOwnershipThresholdPercent_019ce811-d51c-726d-9a92-ab020fe2b971" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_RevenueRemainingPerformanceObligationVariableConsiderationAmount_019ce811-d51c-7c4f-b329-73ea37b6918d" xlink:href="allo-20260331.xsd#allo_RevenueRemainingPerformanceObligationVariableConsiderationAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersLineItems_019ce811-d51c-7f9c-860d-8e1d326ee9d5" xlink:to="loc_allo_RevenueRemainingPerformanceObligationVariableConsiderationAmount_019ce811-d51c-7c4f-b329-73ea37b6918d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityMethodInvestmentOwnershipPercentage_019ce811-d51c-7342-ac03-62d87b6099dc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityMethodInvestmentOwnershipPercentage"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityMethodInvestments_019ce811-d51c-7091-ab77-e7291e1fccd8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityMethodInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersLineItems_019ce811-d51c-7f9c-860d-8e1d326ee9d5" xlink:to="loc_us-gaap_EquityMethodInvestments_019ce811-d51c-7091-ab77-e7291e1fccd8" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019ce811-d51c-7b98-b423-cd55dfa3d8d3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersLineItems_019ce811-d51c-7f9c-860d-8e1d326ee9d5" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019ce811-d51c-7b98-b423-cd55dfa3d8d3" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligation_019ce811-d51c-71ae-a7e9-c2060ccf3687" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueRemainingPerformanceObligation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersLineItems_019ce811-d51c-7f9c-860d-8e1d326ee9d5" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligation_019ce811-d51c-71ae-a7e9-c2060ccf3687" xlink:type="arc" order="8"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://allogene.com/role/LicenseandCollaborationAgreementsAntionDetails" xlink:type="simple" xlink:href="allo-20260331.xsd#LicenseandCollaborationAgreementsAntionDetails"/>
  <link:definitionLink xlink:role="http://allogene.com/role/LicenseandCollaborationAgreementsAntionDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersLineItems_019ce811-d51c-7476-af70-deb1a032b094" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfResearchAndDevelopmentArrangementContractToPerformForOthersTable_019ce811-d51c-7cb0-a368-77d4dc27a0e5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfResearchAndDevelopmentArrangementContractToPerformForOthersTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersLineItems_019ce811-d51c-7476-af70-deb1a032b094" xlink:to="loc_us-gaap_ScheduleOfResearchAndDevelopmentArrangementContractToPerformForOthersTable_019ce811-d51c-7cb0-a368-77d4dc27a0e5" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfArrangementAxis_019ce811-d51c-7c0c-ad76-71d14a8d70c9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TypeOfArrangementAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfResearchAndDevelopmentArrangementContractToPerformForOthersTable_019ce811-d51c-7cb0-a368-77d4dc27a0e5" xlink:to="loc_us-gaap_TypeOfArrangementAxis_019ce811-d51c-7c0c-ad76-71d14a8d70c9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_019ce811-d51c-7c0c-ad76-71d14a8d70c9_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_TypeOfArrangementAxis_019ce811-d51c-7c0c-ad76-71d14a8d70c9" xlink:to="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_019ce811-d51c-7c0c-ad76-71d14a8d70c9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_019ce811-d51c-7d12-8a8b-87482fb2bcfd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_TypeOfArrangementAxis_019ce811-d51c-7c0c-ad76-71d14a8d70c9" xlink:to="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_019ce811-d51c-7d12-8a8b-87482fb2bcfd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_AntionCollaborationAgreementMember_019ce811-d51c-73ca-a489-46913ed98f77" xlink:href="allo-20260331.xsd#allo_AntionCollaborationAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_019ce811-d51c-7d12-8a8b-87482fb2bcfd" xlink:to="loc_allo_AntionCollaborationAgreementMember_019ce811-d51c-73ca-a489-46913ed98f77" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_019ce811-d51c-7ea0-bc59-31a5c7a4a6e7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfResearchAndDevelopmentArrangementContractToPerformForOthersTable_019ce811-d51c-7cb0-a368-77d4dc27a0e5" xlink:to="loc_us-gaap_StatementClassOfStockAxis_019ce811-d51c-7ea0-bc59-31a5c7a4a6e7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019ce811-d51c-7ea0-bc59-31a5c7a4a6e7_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019ce811-d51c-7ea0-bc59-31a5c7a4a6e7" xlink:to="loc_us-gaap_ClassOfStockDomain_019ce811-d51c-7ea0-bc59-31a5c7a4a6e7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019ce811-d51c-7864-98ce-61fb8a9ebdf5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019ce811-d51c-7ea0-bc59-31a5c7a4a6e7" xlink:to="loc_us-gaap_ClassOfStockDomain_019ce811-d51c-7864-98ce-61fb8a9ebdf5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockMember_019ce811-d51c-7d47-9b08-b057c1542169" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019ce811-d51c-7864-98ce-61fb8a9ebdf5" xlink:to="loc_us-gaap_PreferredStockMember_019ce811-d51c-7d47-9b08-b057c1542169" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CounterpartyNameAxis_019ce811-d51c-74c0-96f1-d19131865ef1" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_CounterpartyNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfResearchAndDevelopmentArrangementContractToPerformForOthersTable_019ce811-d51c-7cb0-a368-77d4dc27a0e5" xlink:to="loc_srt_CounterpartyNameAxis_019ce811-d51c-74c0-96f1-d19131865ef1" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019ce811-d51c-74c0-96f1-d19131865ef1_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CounterpartyNameAxis_019ce811-d51c-74c0-96f1-d19131865ef1" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019ce811-d51c-74c0-96f1-d19131865ef1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019ce811-d51c-76ef-8198-265d563ccf8e" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CounterpartyNameAxis_019ce811-d51c-74c0-96f1-d19131865ef1" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019ce811-d51c-76ef-8198-265d563ccf8e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_AntionMember_019ce811-d51c-7ecb-a65e-6d752d23ddaa" xlink:href="allo-20260331.xsd#allo_AntionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019ce811-d51c-76ef-8198-265d563ccf8e" xlink:to="loc_allo_AntionMember_019ce811-d51c-7ecb-a65e-6d752d23ddaa" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationAxis_019ce811-d51c-74e5-8119-4ea31ded6620" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BalanceSheetLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfResearchAndDevelopmentArrangementContractToPerformForOthersTable_019ce811-d51c-7cb0-a368-77d4dc27a0e5" xlink:to="loc_us-gaap_BalanceSheetLocationAxis_019ce811-d51c-74e5-8119-4ea31ded6620" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationDomain_019ce811-d51c-74e5-8119-4ea31ded6620_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BalanceSheetLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BalanceSheetLocationAxis_019ce811-d51c-74e5-8119-4ea31ded6620" xlink:to="loc_us-gaap_BalanceSheetLocationDomain_019ce811-d51c-74e5-8119-4ea31ded6620_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationDomain_019ce811-d51c-70ad-929f-e31feb1cbdba" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BalanceSheetLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BalanceSheetLocationAxis_019ce811-d51c-74e5-8119-4ea31ded6620" xlink:to="loc_us-gaap_BalanceSheetLocationDomain_019ce811-d51c-70ad-929f-e31feb1cbdba" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherNoncurrentAssetsMember_019ce811-d51c-70e3-9c61-0175eb1e1dfc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherNoncurrentAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetLocationDomain_019ce811-d51c-70ad-929f-e31feb1cbdba" xlink:to="loc_us-gaap_OtherNoncurrentAssetsMember_019ce811-d51c-70e3-9c61-0175eb1e1dfc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_CollaborativeArrangementRightsAndObligationsPriorInvestmentObligationAmount_019ce811-d51c-7826-af9a-e76db07c7c2c" xlink:href="allo-20260331.xsd#allo_CollaborativeArrangementRightsAndObligationsPriorInvestmentObligationAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersLineItems_019ce811-d51c-7476-af70-deb1a032b094" xlink:to="loc_allo_CollaborativeArrangementRightsAndObligationsPriorInvestmentObligationAmount_019ce811-d51c-7826-af9a-e76db07c7c2c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_CollaborativeArrangementRightsAndObligationsPreferredStockInvestmentPayable_019ce811-d51c-7092-8132-8352eb387ca9" xlink:href="allo-20260331.xsd#allo_CollaborativeArrangementRightsAndObligationsPreferredStockInvestmentPayable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersLineItems_019ce811-d51c-7476-af70-deb1a032b094" xlink:to="loc_allo_CollaborativeArrangementRightsAndObligationsPreferredStockInvestmentPayable_019ce811-d51c-7092-8132-8352eb387ca9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WarrantsAndRightsOutstanding_019ce811-d51c-732b-927a-ed018ee2191d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_WarrantsAndRightsOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersLineItems_019ce811-d51c-7476-af70-deb1a032b094" xlink:to="loc_us-gaap_WarrantsAndRightsOutstanding_019ce811-d51c-732b-927a-ed018ee2191d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquitySecuritiesFvNiCurrentAndNoncurrent_019ce811-d51c-7cb8-9171-3dc8ec6aef80" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquitySecuritiesFvNiCurrentAndNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersLineItems_019ce811-d51c-7476-af70-deb1a032b094" xlink:to="loc_us-gaap_EquitySecuritiesFvNiCurrentAndNoncurrent_019ce811-d51c-7cb8-9171-3dc8ec6aef80" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://allogene.com/role/LicenseandCollaborationAgreementsForesightDiagnosticsDetails" xlink:type="simple" xlink:href="allo-20260331.xsd#LicenseandCollaborationAgreementsForesightDiagnosticsDetails"/>
  <link:definitionLink xlink:role="http://allogene.com/role/LicenseandCollaborationAgreementsForesightDiagnosticsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersLineItems_019ce811-d51c-7f10-a0a8-c5ba4b30b3d5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfResearchAndDevelopmentArrangementContractToPerformForOthersTable_019ce811-d51c-71f7-80b0-749f502e16c0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfResearchAndDevelopmentArrangementContractToPerformForOthersTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersLineItems_019ce811-d51c-7f10-a0a8-c5ba4b30b3d5" xlink:to="loc_us-gaap_ScheduleOfResearchAndDevelopmentArrangementContractToPerformForOthersTable_019ce811-d51c-71f7-80b0-749f502e16c0" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfArrangementAxis_019ce811-d51c-7ce6-ab7e-432cd43c76df" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TypeOfArrangementAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfResearchAndDevelopmentArrangementContractToPerformForOthersTable_019ce811-d51c-71f7-80b0-749f502e16c0" xlink:to="loc_us-gaap_TypeOfArrangementAxis_019ce811-d51c-7ce6-ab7e-432cd43c76df" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_019ce811-d51c-7ce6-ab7e-432cd43c76df_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_TypeOfArrangementAxis_019ce811-d51c-7ce6-ab7e-432cd43c76df" xlink:to="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_019ce811-d51c-7ce6-ab7e-432cd43c76df_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_019ce811-d51c-72d2-b295-49eab5df081d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_TypeOfArrangementAxis_019ce811-d51c-7ce6-ab7e-432cd43c76df" xlink:to="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_019ce811-d51c-72d2-b295-49eab5df081d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_ForesightDiagnosticsCollaborationAgreementMember_019ce811-d51c-72e5-9738-d2e92d7de2c7" xlink:href="allo-20260331.xsd#allo_ForesightDiagnosticsCollaborationAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_019ce811-d51c-72d2-b295-49eab5df081d" xlink:to="loc_allo_ForesightDiagnosticsCollaborationAgreementMember_019ce811-d51c-72e5-9738-d2e92d7de2c7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationAxis_019ce811-d51c-7c9c-8b56-1b13bd481a88" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BalanceSheetLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfResearchAndDevelopmentArrangementContractToPerformForOthersTable_019ce811-d51c-71f7-80b0-749f502e16c0" xlink:to="loc_us-gaap_BalanceSheetLocationAxis_019ce811-d51c-7c9c-8b56-1b13bd481a88" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationDomain_019ce811-d51c-7c9c-8b56-1b13bd481a88_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BalanceSheetLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BalanceSheetLocationAxis_019ce811-d51c-7c9c-8b56-1b13bd481a88" xlink:to="loc_us-gaap_BalanceSheetLocationDomain_019ce811-d51c-7c9c-8b56-1b13bd481a88_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationDomain_019ce811-d51c-78ec-ace8-50355dca09ee" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BalanceSheetLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BalanceSheetLocationAxis_019ce811-d51c-7c9c-8b56-1b13bd481a88" xlink:to="loc_us-gaap_BalanceSheetLocationDomain_019ce811-d51c-78ec-ace8-50355dca09ee" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_CurrentAccruedAndOtherLiabilitiesMember_019ce811-d51c-7d46-bf25-656d1745305b" xlink:href="allo-20260331.xsd#allo_CurrentAccruedAndOtherLiabilitiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetLocationDomain_019ce811-d51c-78ec-ace8-50355dca09ee" xlink:to="loc_allo_CurrentAccruedAndOtherLiabilitiesMember_019ce811-d51c-7d46-bf25-656d1745305b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_CollaborationAgreementCommittedFunding_019ce811-d51c-705c-9845-8b46a69639d2" xlink:href="allo-20260331.xsd#allo_CollaborationAgreementCommittedFunding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersLineItems_019ce811-d51c-7f10-a0a8-c5ba4b30b3d5" xlink:to="loc_allo_CollaborationAgreementCommittedFunding_019ce811-d51c-705c-9845-8b46a69639d2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchAndDevelopmentExpense_019ce811-d51c-7cde-b987-ba773eb91c8b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ResearchAndDevelopmentExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersLineItems_019ce811-d51c-7f10-a0a8-c5ba4b30b3d5" xlink:to="loc_us-gaap_ResearchAndDevelopmentExpense_019ce811-d51c-7cde-b987-ba773eb91c8b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_AccruedAndOtherLiabilitiesCurrent_019ce811-d51c-733e-8a45-56c33bf9fa01" xlink:href="allo-20260331.xsd#allo_AccruedAndOtherLiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersLineItems_019ce811-d51c-7f10-a0a8-c5ba4b30b3d5" xlink:to="loc_allo_AccruedAndOtherLiabilitiesCurrent_019ce811-d51c-733e-8a45-56c33bf9fa01" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://allogene.com/role/CommitmentsandContingenciesAdditionalInformationDetails" xlink:type="simple" xlink:href="allo-20260331.xsd#CommitmentsandContingenciesAdditionalInformationDetails"/>
  <link:definitionLink xlink:role="http://allogene.com/role/CommitmentsandContingenciesAdditionalInformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeasedAssetsLineItems_019ce811-d51c-73c3-a074-db5ba9e4056c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingLeasedAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfOperatingLeasedAssetsTable_019ce811-d51c-7973-a9a4-e13de96f7b9b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfOperatingLeasedAssetsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_OperatingLeasedAssetsLineItems_019ce811-d51c-73c3-a074-db5ba9e4056c" xlink:to="loc_us-gaap_ScheduleOfOperatingLeasedAssetsTable_019ce811-d51c-7973-a9a4-e13de96f7b9b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LeaseContractualTermAxis_019ce811-d51c-78b8-a2a3-772e1e93f1e5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LeaseContractualTermAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfOperatingLeasedAssetsTable_019ce811-d51c-7973-a9a4-e13de96f7b9b" xlink:to="loc_us-gaap_LeaseContractualTermAxis_019ce811-d51c-78b8-a2a3-772e1e93f1e5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LeaseContractualTermDomain_019ce811-d51c-78b8-a2a3-772e1e93f1e5_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LeaseContractualTermDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LeaseContractualTermAxis_019ce811-d51c-78b8-a2a3-772e1e93f1e5" xlink:to="loc_us-gaap_LeaseContractualTermDomain_019ce811-d51c-78b8-a2a3-772e1e93f1e5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LeaseContractualTermDomain_019ce811-d51c-729b-bb23-11b721f1b2a2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LeaseContractualTermDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LeaseContractualTermAxis_019ce811-d51c-78b8-a2a3-772e1e93f1e5" xlink:to="loc_us-gaap_LeaseContractualTermDomain_019ce811-d51c-729b-bb23-11b721f1b2a2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_HQLeaseMember_019ce811-d51c-7514-87fb-3394d879404b" xlink:href="allo-20260331.xsd#allo_HQLeaseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LeaseContractualTermDomain_019ce811-d51c-729b-bb23-11b721f1b2a2" xlink:to="loc_allo_HQLeaseMember_019ce811-d51c-7514-87fb-3394d879404b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_SouthSanFranciscoBuildingTwoMember_019ce811-d51c-7ccb-a4ac-7209388c9618" xlink:href="allo-20260331.xsd#allo_SouthSanFranciscoBuildingTwoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LeaseContractualTermDomain_019ce811-d51c-729b-bb23-11b721f1b2a2" xlink:to="loc_allo_SouthSanFranciscoBuildingTwoMember_019ce811-d51c-7ccb-a4ac-7209388c9618" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementGeographicalAxis_019ce811-d51c-79e0-ab96-9e9d4a9d899e" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_StatementGeographicalAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfOperatingLeasedAssetsTable_019ce811-d51c-7973-a9a4-e13de96f7b9b" xlink:to="loc_srt_StatementGeographicalAxis_019ce811-d51c-79e0-ab96-9e9d4a9d899e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_019ce811-d51c-79e0-ab96-9e9d4a9d899e_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementGeographicalAxis_019ce811-d51c-79e0-ab96-9e9d4a9d899e" xlink:to="loc_srt_SegmentGeographicalDomain_019ce811-d51c-79e0-ab96-9e9d4a9d899e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_019ce811-d51c-7e65-b7c1-f2da0119ac09" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementGeographicalAxis_019ce811-d51c-79e0-ab96-9e9d4a9d899e" xlink:to="loc_srt_SegmentGeographicalDomain_019ce811-d51c-7e65-b7c1-f2da0119ac09" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_NewarkCaliforniaMember_019ce811-d51c-76de-9846-ea8fcd34d76a" xlink:href="allo-20260331.xsd#allo_NewarkCaliforniaMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_019ce811-d51c-7e65-b7c1-f2da0119ac09" xlink:to="loc_allo_NewarkCaliforniaMember_019ce811-d51c-76de-9846-ea8fcd34d76a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_SouthSanFranciscoCaliforniaMember_019d54db-ed99-7206-85c9-490021712046" xlink:href="allo-20260331.xsd#allo_SouthSanFranciscoCaliforniaMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_019ce811-d51c-7e65-b7c1-f2da0119ac09" xlink:to="loc_allo_SouthSanFranciscoCaliforniaMember_019d54db-ed99-7206-85c9-490021712046" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CounterpartyNameAxis_019ce811-d51c-7b28-b884-8d393d5d310f" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_CounterpartyNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfOperatingLeasedAssetsTable_019ce811-d51c-7973-a9a4-e13de96f7b9b" xlink:to="loc_srt_CounterpartyNameAxis_019ce811-d51c-7b28-b884-8d393d5d310f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019ce811-d51c-7b28-b884-8d393d5d310f_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CounterpartyNameAxis_019ce811-d51c-7b28-b884-8d393d5d310f" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019ce811-d51c-7b28-b884-8d393d5d310f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019ce811-d51c-7278-9c3b-bba6bbae7a18" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CounterpartyNameAxis_019ce811-d51c-7b28-b884-8d393d5d310f" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019ce811-d51c-7278-9c3b-bba6bbae7a18" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_BellcoCapitalLLCMember_019ce811-d51c-7762-9b61-9865b7cb9eb8" xlink:href="allo-20260331.xsd#allo_BellcoCapitalLLCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019ce811-d51c-7278-9c3b-bba6bbae7a18" xlink:to="loc_allo_BellcoCapitalLLCMember_019ce811-d51c-7762-9b61-9865b7cb9eb8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_019ce811-d51c-73b6-a6db-d820305c3fa6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfOperatingLeasedAssetsTable_019ce811-d51c-7973-a9a4-e13de96f7b9b" xlink:to="loc_us-gaap_CreditFacilityAxis_019ce811-d51c-73b6-a6db-d820305c3fa6" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_019ce811-d51c-73b6-a6db-d820305c3fa6_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_019ce811-d51c-73b6-a6db-d820305c3fa6" xlink:to="loc_us-gaap_CreditFacilityDomain_019ce811-d51c-73b6-a6db-d820305c3fa6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_019ce811-d51c-7750-8505-043e874d2002" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_019ce811-d51c-73b6-a6db-d820305c3fa6" xlink:to="loc_us-gaap_CreditFacilityDomain_019ce811-d51c-7750-8505-043e874d2002" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LetterOfCreditMember_019ce811-d51c-7d2c-a609-585f53e53607" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LetterOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_019ce811-d51c-7750-8505-043e874d2002" xlink:to="loc_us-gaap_LetterOfCreditMember_019ce811-d51c-7d2c-a609-585f53e53607" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionAxis_019ce811-d51c-718d-856f-2d4702b6293f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyTransactionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfOperatingLeasedAssetsTable_019ce811-d51c-7973-a9a4-e13de96f7b9b" xlink:to="loc_us-gaap_RelatedPartyTransactionAxis_019ce811-d51c-718d-856f-2d4702b6293f" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionDomain_019ce811-d51c-718d-856f-2d4702b6293f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionAxis_019ce811-d51c-718d-856f-2d4702b6293f" xlink:to="loc_us-gaap_RelatedPartyTransactionDomain_019ce811-d51c-718d-856f-2d4702b6293f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionDomain_019ce811-d51c-72c2-a59a-7819b21ec895" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionAxis_019ce811-d51c-718d-856f-2d4702b6293f" xlink:to="loc_us-gaap_RelatedPartyTransactionDomain_019ce811-d51c-72c2-a59a-7819b21ec895" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_SubleaseAgreementMember_019ce811-d51c-74e5-880a-b68888d5c083" xlink:href="allo-20260331.xsd#allo_SubleaseAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionDomain_019ce811-d51c-72c2-a59a-7819b21ec895" xlink:to="loc_allo_SubleaseAgreementMember_019ce811-d51c-74e5-880a-b68888d5c083" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019ce811-d51c-7ab1-aab0-2bfcf0f78fca" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfOperatingLeasedAssetsTable_019ce811-d51c-7973-a9a4-e13de96f7b9b" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019ce811-d51c-7ab1-aab0-2bfcf0f78fca" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_019ce811-d51c-7ab1-aab0-2bfcf0f78fca_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019ce811-d51c-7ab1-aab0-2bfcf0f78fca" xlink:to="loc_us-gaap_RelatedPartyDomain_019ce811-d51c-7ab1-aab0-2bfcf0f78fca_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_019ce811-d51c-7ff9-8a71-60ed6d62d9d8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019ce811-d51c-7ab1-aab0-2bfcf0f78fca" xlink:to="loc_us-gaap_RelatedPartyDomain_019ce811-d51c-7ff9-8a71-60ed6d62d9d8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyMember_019ce811-d51c-71d2-adbc-fe016585d826" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_019ce811-d51c-7ff9-8a71-60ed6d62d9d8" xlink:to="loc_us-gaap_RelatedPartyMember_019ce811-d51c-71d2-adbc-fe016585d826" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_AreaOfNewOfficeBuilding_019ce811-d51c-78f3-80ec-13bfba3685b0" xlink:href="allo-20260331.xsd#allo_AreaOfNewOfficeBuilding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingLeasedAssetsLineItems_019ce811-d51c-73c3-a074-db5ba9e4056c" xlink:to="loc_allo_AreaOfNewOfficeBuilding_019ce811-d51c-78f3-80ec-13bfba3685b0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_AdditionalAreaOfNewOfficeBuilding_019ce811-d51c-7fcb-b2a9-4eb70bf81528" xlink:href="allo-20260331.xsd#allo_AdditionalAreaOfNewOfficeBuilding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingLeasedAssetsLineItems_019ce811-d51c-73c3-a074-db5ba9e4056c" xlink:to="loc_allo_AdditionalAreaOfNewOfficeBuilding_019ce811-d51c-7fcb-b2a9-4eb70bf81528" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeOperatingLeaseRenewalTerm_019ce811-d51c-79de-9434-126d31fa0215" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LesseeOperatingLeaseRenewalTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingLeasedAssetsLineItems_019ce811-d51c-73c3-a074-db5ba9e4056c" xlink:to="loc_us-gaap_LesseeOperatingLeaseRenewalTerm_019ce811-d51c-79de-9434-126d31fa0215" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_AreaOfOperatingLease_019ce811-d51c-71f1-839d-f749c84f5993" xlink:href="allo-20260331.xsd#allo_AreaOfOperatingLease"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingLeasedAssetsLineItems_019ce811-d51c-73c3-a074-db5ba9e4056c" xlink:to="loc_allo_AreaOfOperatingLease_019ce811-d51c-71f1-839d-f749c84f5993" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_NumberOfOptionsToExtendLease_019ce811-d51c-77ac-b35b-86c601524a9b" xlink:href="allo-20260331.xsd#allo_NumberOfOptionsToExtendLease"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingLeasedAssetsLineItems_019ce811-d51c-73c3-a074-db5ba9e4056c" xlink:to="loc_allo_NumberOfOptionsToExtendLease_019ce811-d51c-77ac-b35b-86c601524a9b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_AreaOfOfficeSpace_019ce811-d51c-7d4a-a48d-c71ff4913e5a" xlink:href="allo-20260331.xsd#allo_AreaOfOfficeSpace"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingLeasedAssetsLineItems_019ce811-d51c-73c3-a074-db5ba9e4056c" xlink:to="loc_allo_AreaOfOfficeSpace_019ce811-d51c-7d4a-a48d-c71ff4913e5a" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LessorOperatingLeaseTermOfContract_019ce811-d51c-7f81-878c-b6dc0095543b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LessorOperatingLeaseTermOfContract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingLeasedAssetsLineItems_019ce811-d51c-73c3-a074-db5ba9e4056c" xlink:to="loc_us-gaap_LessorOperatingLeaseTermOfContract_019ce811-d51c-7f81-878c-b6dc0095543b" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LettersOfCreditOutstandingAmount_019ce811-d51c-70f4-95cd-98f38109fc5c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LettersOfCreditOutstandingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingLeasedAssetsLineItems_019ce811-d51c-73c3-a074-db5ba9e4056c" xlink:to="loc_us-gaap_LettersOfCreditOutstandingAmount_019ce811-d51c-70f4-95cd-98f38109fc5c" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseWeightedAverageDiscountRatePercent_019ce811-d51c-71e0-b92e-0bb695844d78" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingLeaseWeightedAverageDiscountRatePercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingLeasedAssetsLineItems_019ce811-d51c-73c3-a074-db5ba9e4056c" xlink:to="loc_us-gaap_OperatingLeaseWeightedAverageDiscountRatePercent_019ce811-d51c-71e0-b92e-0bb695844d78" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseWeightedAverageRemainingLeaseTerm1_019ce811-d51c-7e3b-bc64-29e38543734c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingLeaseWeightedAverageRemainingLeaseTerm1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingLeasedAssetsLineItems_019ce811-d51c-73c3-a074-db5ba9e4056c" xlink:to="loc_us-gaap_OperatingLeaseWeightedAverageRemainingLeaseTerm1_019ce811-d51c-7e3b-bc64-29e38543734c" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_NumberOfLesseesUnaffiliatedCompany_019ce811-d51c-7348-869e-1dc9435dfe62" xlink:href="allo-20260331.xsd#allo_NumberOfLesseesUnaffiliatedCompany"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingLeasedAssetsLineItems_019ce811-d51c-73c3-a074-db5ba9e4056c" xlink:to="loc_allo_NumberOfLesseesUnaffiliatedCompany_019ce811-d51c-7348-869e-1dc9435dfe62" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_NumberOfPropertiesToBeSubleased_019ce811-d51c-79f1-a951-d96b0842538c" xlink:href="allo-20260331.xsd#allo_NumberOfPropertiesToBeSubleased"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingLeasedAssetsLineItems_019ce811-d51c-73c3-a074-db5ba9e4056c" xlink:to="loc_allo_NumberOfPropertiesToBeSubleased_019ce811-d51c-79f1-a951-d96b0842538c" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseLeaseIncome_019ce811-d51c-7585-b675-39de278be5a7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingLeaseLeaseIncome"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingLeasedAssetsLineItems_019ce811-d51c-73c3-a074-db5ba9e4056c" xlink:to="loc_us-gaap_OperatingLeaseLeaseIncome_019ce811-d51c-7585-b675-39de278be5a7" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeFinanceLeaseTermOfContract1_019ce811-d51c-789f-be4a-999c821176f7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LesseeFinanceLeaseTermOfContract1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingLeasedAssetsLineItems_019ce811-d51c-73c3-a074-db5ba9e4056c" xlink:to="loc_us-gaap_LesseeFinanceLeaseTermOfContract1_019ce811-d51c-789f-be4a-999c821176f7" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_LesseeFinanceLeasePaymentUponContractTermination_019ce811-d51c-7fb7-a520-9cc5a85358ca" xlink:href="allo-20260331.xsd#allo_LesseeFinanceLeasePaymentUponContractTermination"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingLeasedAssetsLineItems_019ce811-d51c-73c3-a074-db5ba9e4056c" xlink:to="loc_allo_LesseeFinanceLeasePaymentUponContractTermination_019ce811-d51c-7fb7-a520-9cc5a85358ca" xlink:type="arc" order="14"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://allogene.com/role/StockBasedCompensationAdditionalInformationDetails" xlink:type="simple" xlink:href="allo-20260331.xsd#StockBasedCompensationAdditionalInformationDetails"/>
  <link:definitionLink xlink:role="http://allogene.com/role/StockBasedCompensationAdditionalInformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ce811-d51c-7476-abc6-8fe38c8613f3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019ce811-d51c-7cee-a641-02154a133b9e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ce811-d51c-7476-abc6-8fe38c8613f3" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019ce811-d51c-7cee-a641-02154a133b9e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_TitleOfIndividualAxis_019ce811-d51c-7058-8db0-b24e6fa10c8a" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_TitleOfIndividualAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019ce811-d51c-7cee-a641-02154a133b9e" xlink:to="loc_srt_TitleOfIndividualAxis_019ce811-d51c-7058-8db0-b24e6fa10c8a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_019ce811-d51c-7058-8db0-b24e6fa10c8a_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_TitleOfIndividualWithRelationshipToEntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_TitleOfIndividualAxis_019ce811-d51c-7058-8db0-b24e6fa10c8a" xlink:to="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_019ce811-d51c-7058-8db0-b24e6fa10c8a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_019ce811-d51c-7f91-a463-9c747b020270" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_TitleOfIndividualWithRelationshipToEntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_TitleOfIndividualAxis_019ce811-d51c-7058-8db0-b24e6fa10c8a" xlink:to="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_019ce811-d51c-7f91-a463-9c747b020270" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_CertainExecutiveOfficersAndOtherEmployeesMember_019ce811-d51c-767a-aca6-c240c928b3e1" xlink:href="allo-20260331.xsd#allo_CertainExecutiveOfficersAndOtherEmployeesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_019ce811-d51c-7f91-a463-9c747b020270" xlink:to="loc_allo_CertainExecutiveOfficersAndOtherEmployeesMember_019ce811-d51c-767a-aca6-c240c928b3e1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_019ce811-d51c-7985-8ce2-400556198a14" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019ce811-d51c-7cee-a641-02154a133b9e" xlink:to="loc_us-gaap_AwardTypeAxis_019ce811-d51c-7985-8ce2-400556198a14" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ce811-d51c-7985-8ce2-400556198a14_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_019ce811-d51c-7985-8ce2-400556198a14" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ce811-d51c-7985-8ce2-400556198a14_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ce811-d51c-7d63-ac00-968702f959bc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_019ce811-d51c-7985-8ce2-400556198a14" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ce811-d51c-7d63-ac00-968702f959bc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_PerformanceBasedRestrictedStockUnitsMember_019ce811-d51c-7e68-886c-8baf817fa58f" xlink:href="allo-20260331.xsd#allo_PerformanceBasedRestrictedStockUnitsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ce811-d51c-7d63-ac00-968702f959bc" xlink:to="loc_allo_PerformanceBasedRestrictedStockUnitsMember_019ce811-d51c-7e68-886c-8baf817fa58f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_RestrictedStockUnitsRSUsWithMarketConditionMember_019ce811-d51c-7421-bba8-0c97adcbeb2e" xlink:href="allo-20260331.xsd#allo_RestrictedStockUnitsRSUsWithMarketConditionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ce811-d51c-7d63-ac00-968702f959bc" xlink:to="loc_allo_RestrictedStockUnitsRSUsWithMarketConditionMember_019ce811-d51c-7421-bba8-0c97adcbeb2e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockCapitalSharesReservedForFutureIssuance_019ce811-d51c-7f33-ab61-e55e1ace1b22" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockCapitalSharesReservedForFutureIssuance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ce811-d51c-7476-abc6-8fe38c8613f3" xlink:to="loc_us-gaap_CommonStockCapitalSharesReservedForFutureIssuance_019ce811-d51c-7f33-ab61-e55e1ace1b22" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_019ce811-d51c-7023-a857-d856f98acda5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ce811-d51c-7476-abc6-8fe38c8613f3" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_019ce811-d51c-7023-a857-d856f98acda5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_019ce811-d51c-79ce-bd4a-fcedad0a3228" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ce811-d51c-7476-abc6-8fe38c8613f3" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_019ce811-d51c-79ce-bd4a-fcedad0a3228" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_019ce811-d51c-738d-8f55-d3f2934c4772" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AllocatedShareBasedCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ce811-d51c-7476-abc6-8fe38c8613f3" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_019ce811-d51c-738d-8f55-d3f2934c4772" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://allogene.com/role/StockBasedCompensationScheduleofStockOptionActivityDetails" xlink:type="simple" xlink:href="allo-20260331.xsd#StockBasedCompensationScheduleofStockOptionActivityDetails"/>
  <link:definitionLink xlink:role="http://allogene.com/role/StockBasedCompensationScheduleofStockOptionActivityDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ce811-d51c-7f99-9de8-93cf1cca3c05" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019ce811-d51c-7b4b-a475-24eab5f85daa" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ce811-d51c-7f99-9de8-93cf1cca3c05" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019ce811-d51c-7b4b-a475-24eab5f85daa" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_019ce811-d51c-7a37-be98-24815ff8fdfa" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019ce811-d51c-7b4b-a475-24eab5f85daa" xlink:to="loc_us-gaap_AwardTypeAxis_019ce811-d51c-7a37-be98-24815ff8fdfa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ce811-d51c-7a37-be98-24815ff8fdfa_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_019ce811-d51c-7a37-be98-24815ff8fdfa" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ce811-d51c-7a37-be98-24815ff8fdfa_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ce811-d51c-7d5f-a0da-f24c5d5a9a14" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_019ce811-d51c-7a37-be98-24815ff8fdfa" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ce811-d51c-7d5f-a0da-f24c5d5a9a14" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_TwoThousandEighteenPlanMember_019ce811-d51c-7db0-bcb8-5edd20677a56" xlink:href="allo-20260331.xsd#allo_TwoThousandEighteenPlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ce811-d51c-7d5f-a0da-f24c5d5a9a14" xlink:to="loc_allo_TwoThousandEighteenPlanMember_019ce811-d51c-7db0-bcb8-5edd20677a56" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_019ce811-d51c-72e5-8f7a-50d5cc07811e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ce811-d51c-7f99-9de8-93cf1cca3c05" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_019ce811-d51c-72e5-8f7a-50d5cc07811e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_019ce811-d51c-7c31-8285-31d2273eec32" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_019ce811-d51c-72e5-8f7a-50d5cc07811e" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_019ce811-d51c-7c31-8285-31d2273eec32" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_019ce811-d51c-7d92-9414-208b15197451" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_019ce811-d51c-72e5-8f7a-50d5cc07811e" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_019ce811-d51c-7d92-9414-208b15197451" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_019dcdd4-ccde-7369-aa83-5e4d77e2fa30" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_019ce811-d51c-72e5-8f7a-50d5cc07811e" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_019dcdd4-ccde-7369-aa83-5e4d77e2fa30" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod_019ce811-d51c-752d-8d92-1722d38a0f4f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_019ce811-d51c-72e5-8f7a-50d5cc07811e" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod_019ce811-d51c-752d-8d92-1722d38a0f4f" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_019ce811-d51c-7005-9e27-a6d557a7e91a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber_019ce811-d51c-76eb-af83-fd1f9703be3b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ce811-d51c-7f99-9de8-93cf1cca3c05" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber_019ce811-d51c-76eb-af83-fd1f9703be3b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingNumber_019ce811-d51c-7c14-8311-334872420d69" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ce811-d51c-7f99-9de8-93cf1cca3c05" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingNumber_019ce811-d51c-7c14-8311-334872420d69" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_019ce811-d51c-7b0a-9bca-bd32ad13da08" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ce811-d51c-7f99-9de8-93cf1cca3c05" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_019ce811-d51c-7b0a-9bca-bd32ad13da08" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice_019ce811-d51c-71a0-a7b7-5de23f49a7bd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_019ce811-d51c-7b0a-9bca-bd32ad13da08" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice_019ce811-d51c-71a0-a7b7-5de23f49a7bd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice_019ce811-d51c-7e89-99a6-3a9841bf1816" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_019ce811-d51c-7b0a-9bca-bd32ad13da08" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice_019ce811-d51c-7e89-99a6-3a9841bf1816" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice_019dcdd5-70c3-79c7-97f8-40204e0bec8b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_019ce811-d51c-7b0a-9bca-bd32ad13da08" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice_019dcdd5-70c3-79c7-97f8-40204e0bec8b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice_019ce811-d51c-737a-a4a3-35f7d1f33d5b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_019ce811-d51c-7b0a-9bca-bd32ad13da08" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice_019ce811-d51c-737a-a4a3-35f7d1f33d5b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice_019ce811-d51c-78f1-8a6e-5fd6853d6788" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice_019ce811-d51c-7368-87b7-8036e227c65b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ce811-d51c-7f99-9de8-93cf1cca3c05" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice_019ce811-d51c-7368-87b7-8036e227c65b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageExercisePrice_019ce811-d51c-7f0d-b62e-cd8cfb3126bb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageExercisePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ce811-d51c-7f99-9de8-93cf1cca3c05" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageExercisePrice_019ce811-d51c-7f0d-b62e-cd8cfb3126bb" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2_019ce811-d51c-748e-9eff-54b1922e60f2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ce811-d51c-7f99-9de8-93cf1cca3c05" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2_019ce811-d51c-748e-9eff-54b1922e60f2" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableWeightedAverageRemainingContractualTerm1_019ce811-d51c-7702-9367-6561be34c88a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableWeightedAverageRemainingContractualTerm1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ce811-d51c-7f99-9de8-93cf1cca3c05" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableWeightedAverageRemainingContractualTerm1_019ce811-d51c-7702-9367-6561be34c88a" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageRemainingContractualTerm1_019ce811-d51c-7320-8e7c-150fcd6c3fa5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageRemainingContractualTerm1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ce811-d51c-7f99-9de8-93cf1cca3c05" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageRemainingContractualTerm1_019ce811-d51c-7320-8e7c-150fcd6c3fa5" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue_019ce811-d51c-783c-98f9-3074c789f739" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ce811-d51c-7f99-9de8-93cf1cca3c05" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue_019ce811-d51c-783c-98f9-3074c789f739" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue_019d3e48-cbae-70fe-a671-64e9a39e7b92" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1_019ce811-d51c-741e-94ee-3b3259527f73" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ce811-d51c-7f99-9de8-93cf1cca3c05" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1_019ce811-d51c-741e-94ee-3b3259527f73" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestExercisableAggregateIntrinsicValue_019ce811-d51c-7e76-aab5-4971c5d17ff8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestExercisableAggregateIntrinsicValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ce811-d51c-7f99-9de8-93cf1cca3c05" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestExercisableAggregateIntrinsicValue_019ce811-d51c-7e76-aab5-4971c5d17ff8" xlink:type="arc" order="12"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://allogene.com/role/StockBasedCompensationScheduleofRestrictedStockUnitsActivityDetails" xlink:type="simple" xlink:href="allo-20260331.xsd#StockBasedCompensationScheduleofRestrictedStockUnitsActivityDetails"/>
  <link:definitionLink xlink:role="http://allogene.com/role/StockBasedCompensationScheduleofRestrictedStockUnitsActivityDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ce811-d51c-7ad5-9b1b-aad78889e4dd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019ce811-d51c-720a-9a9b-958a751ee76a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ce811-d51c-7ad5-9b1b-aad78889e4dd" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019ce811-d51c-720a-9a9b-958a751ee76a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_019ce811-d51c-791a-b1f3-4b52d65ca57c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019ce811-d51c-720a-9a9b-958a751ee76a" xlink:to="loc_us-gaap_AwardTypeAxis_019ce811-d51c-791a-b1f3-4b52d65ca57c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ce811-d51c-791a-b1f3-4b52d65ca57c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_019ce811-d51c-791a-b1f3-4b52d65ca57c" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ce811-d51c-791a-b1f3-4b52d65ca57c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ce811-d51c-76a6-8ca1-42c762541d76" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_019ce811-d51c-791a-b1f3-4b52d65ca57c" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ce811-d51c-76a6-8ca1-42c762541d76" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_019ce811-d51c-7a5b-9a57-2cc8b9ccc87f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ce811-d51c-76a6-8ca1-42c762541d76" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_019ce811-d51c-7a5b-9a57-2cc8b9ccc87f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_PerformanceBasedRestrictedStockUnitsMember_019ce811-d51c-7ddc-8f3f-e0cb759a8323" xlink:href="allo-20260331.xsd#allo_PerformanceBasedRestrictedStockUnitsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ce811-d51c-76a6-8ca1-42c762541d76" xlink:to="loc_allo_PerformanceBasedRestrictedStockUnitsMember_019ce811-d51c-7ddc-8f3f-e0cb759a8323" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019ce811-d51c-7787-a427-ed5e01e02f06" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ce811-d51c-7ad5-9b1b-aad78889e4dd" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019ce811-d51c-7787-a427-ed5e01e02f06" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_019ce811-d51c-705b-aefe-ac264f2f98b6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019ce811-d51c-7787-a427-ed5e01e02f06" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_019ce811-d51c-705b-aefe-ac264f2f98b6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_019ce811-d51c-7368-8aaa-529fd74ce2dd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019ce811-d51c-7787-a427-ed5e01e02f06" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_019ce811-d51c-7368-8aaa-529fd74ce2dd" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsReleasedInPeriod_019ce811-d51c-7455-9b44-b64be4c42413" xlink:href="allo-20260331.xsd#allo_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsReleasedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019ce811-d51c-7787-a427-ed5e01e02f06" xlink:to="loc_allo_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsReleasedInPeriod_019ce811-d51c-7455-9b44-b64be4c42413" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_019ce811-d51c-764f-a614-ae5e9bd447ab" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019ce811-d51c-7787-a427-ed5e01e02f06" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_019ce811-d51c-764f-a614-ae5e9bd447ab" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_019ce811-d51c-7ae9-9655-bb487a4bd5a9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedAndExpectedToVestOutstandingNumber_019ce811-d51c-742f-8747-576399fe2099" xlink:href="allo-20260331.xsd#allo_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedAndExpectedToVestOutstandingNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019ce811-d51c-7787-a427-ed5e01e02f06" xlink:to="loc_allo_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedAndExpectedToVestOutstandingNumber_019ce811-d51c-742f-8747-576399fe2099" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedUndUnreleased_019d861a-c342-7121-86a9-949009b485b4" xlink:href="allo-20260331.xsd#allo_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedUndUnreleased"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019ce811-d51c-7787-a427-ed5e01e02f06" xlink:to="loc_allo_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedUndUnreleased_019d861a-c342-7121-86a9-949009b485b4" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019ce811-d51c-7eb9-ac30-9056a5f8ba31" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ce811-d51c-7ad5-9b1b-aad78889e4dd" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019ce811-d51c-7eb9-ac30-9056a5f8ba31" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_019ce811-d51c-7f8c-aad0-f7d47f2d8250" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019ce811-d51c-7eb9-ac30-9056a5f8ba31" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_019ce811-d51c-7f8c-aad0-f7d47f2d8250" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_019ce811-d51c-7d1b-a5e8-a8368cd5efa0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019ce811-d51c-7eb9-ac30-9056a5f8ba31" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_019ce811-d51c-7d1b-a5e8-a8368cd5efa0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsReleasedInPeriodWeightedAverageGrantDateFairValue_019ce811-d51c-76ed-9911-f296fe643993" xlink:href="allo-20260331.xsd#allo_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsReleasedInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019ce811-d51c-7eb9-ac30-9056a5f8ba31" xlink:to="loc_allo_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsReleasedInPeriodWeightedAverageGrantDateFairValue_019ce811-d51c-76ed-9911-f296fe643993" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsNonvestedOptionsForfeitedWeightedAverageGrantDateFairValue_019ce811-d51c-7f8e-8c20-9be9d269adf6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsNonvestedOptionsForfeitedWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019ce811-d51c-7eb9-ac30-9056a5f8ba31" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsNonvestedOptionsForfeitedWeightedAverageGrantDateFairValue_019ce811-d51c-7f8e-8c20-9be9d269adf6" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_019ce811-d51c-7214-b23c-4388b559ce43" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedAndExpectedToVestOutstandingWeightedAverageExercisePrice_019ce811-d51c-7c66-b068-fb9b38940e3d" xlink:href="allo-20260331.xsd#allo_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedAndExpectedToVestOutstandingWeightedAverageExercisePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019ce811-d51c-7eb9-ac30-9056a5f8ba31" xlink:to="loc_allo_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedAndExpectedToVestOutstandingWeightedAverageExercisePrice_019ce811-d51c-7c66-b068-fb9b38940e3d" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedAndUnreleasedWeightedAverageGrantDateFairValue_019d861b-45f1-7ceb-8509-fb85146406f9" xlink:href="allo-20260331.xsd#allo_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedAndUnreleasedWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019ce811-d51c-7eb9-ac30-9056a5f8ba31" xlink:to="loc_allo_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedAndUnreleasedWeightedAverageGrantDateFairValue_019d861b-45f1-7ceb-8509-fb85146406f9" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsOutstandingWeightedAverageRemainingContractualTerms_019ce811-d51c-77e1-b334-0bb94e5bac9f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsOutstandingWeightedAverageRemainingContractualTerms"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ce811-d51c-7ad5-9b1b-aad78889e4dd" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsOutstandingWeightedAverageRemainingContractualTerms_019ce811-d51c-77e1-b334-0bb94e5bac9f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_ShareBasedCompensationArrangementByShareBasedPaymentAwardsOtherThanOptionsVestedAndExpectedToVestOutstandingWeightedAverageRemainingContractualTerm_019ce811-d51c-7962-bb44-1adbb9f82d50" xlink:href="allo-20260331.xsd#allo_ShareBasedCompensationArrangementByShareBasedPaymentAwardsOtherThanOptionsVestedAndExpectedToVestOutstandingWeightedAverageRemainingContractualTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ce811-d51c-7ad5-9b1b-aad78889e4dd" xlink:to="loc_allo_ShareBasedCompensationArrangementByShareBasedPaymentAwardsOtherThanOptionsVestedAndExpectedToVestOutstandingWeightedAverageRemainingContractualTerm_019ce811-d51c-7962-bb44-1adbb9f82d50" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardEquityInstrumentsOtherThanOptionsAggregateIntrinsicValueNonvested_019ce811-d51c-7eca-a37d-2cd9ee6e6b69" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardEquityInstrumentsOtherThanOptionsAggregateIntrinsicValueNonvested"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ce811-d51c-7ad5-9b1b-aad78889e4dd" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardEquityInstrumentsOtherThanOptionsAggregateIntrinsicValueNonvested_019ce811-d51c-7eca-a37d-2cd9ee6e6b69" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedAndExpectedToVestAggregateIntrinsicValue_019ce811-d51c-7b1f-9d0f-b010561005fd" xlink:href="allo-20260331.xsd#allo_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedAndExpectedToVestAggregateIntrinsicValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ce811-d51c-7ad5-9b1b-aad78889e4dd" xlink:to="loc_allo_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedAndExpectedToVestAggregateIntrinsicValue_019ce811-d51c-7b1f-9d0f-b010561005fd" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedAndUnreleasedAggregateIntrinsicValue_019d8623-1e3f-74f1-98db-119849e794b1" xlink:href="allo-20260331.xsd#allo_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedAndUnreleasedAggregateIntrinsicValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ce811-d51c-7ad5-9b1b-aad78889e4dd" xlink:to="loc_allo_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedAndUnreleasedAggregateIntrinsicValue_019d8623-1e3f-74f1-98db-119849e794b1" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://allogene.com/role/StockBasedCompensationScheduleofStockBasedCompensationExpenseDetails" xlink:type="simple" xlink:href="allo-20260331.xsd#StockBasedCompensationScheduleofStockBasedCompensationExpenseDetails"/>
  <link:definitionLink xlink:role="http://allogene.com/role/StockBasedCompensationScheduleofStockBasedCompensationExpenseDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_019ce811-d51c-7fb1-98ce-be21cd2f4a67" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_019ce811-d51c-732c-a81b-641dcb0614c8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_019ce811-d51c-7fb1-98ce-be21cd2f4a67" xlink:to="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_019ce811-d51c-732c-a81b-641dcb0614c8" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationAxis_019ce811-d51c-73c6-b536-c35cec95accc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_019ce811-d51c-732c-a81b-641dcb0614c8" xlink:to="loc_us-gaap_IncomeStatementLocationAxis_019ce811-d51c-73c6-b536-c35cec95accc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_019ce811-d51c-73c6-b536-c35cec95accc_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_019ce811-d51c-73c6-b536-c35cec95accc" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_019ce811-d51c-73c6-b536-c35cec95accc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_019ce811-d51c-713c-bee4-bcd4f2e41939" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_019ce811-d51c-73c6-b536-c35cec95accc" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_019ce811-d51c-713c-bee4-bcd4f2e41939" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchAndDevelopmentExpenseMember_019ce811-d51c-7124-91a8-9055514641b6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ResearchAndDevelopmentExpenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_019ce811-d51c-713c-bee4-bcd4f2e41939" xlink:to="loc_us-gaap_ResearchAndDevelopmentExpenseMember_019ce811-d51c-7124-91a8-9055514641b6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GeneralAndAdministrativeExpenseMember_019ce811-d51c-740a-a215-e890b887e72f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GeneralAndAdministrativeExpenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_019ce811-d51c-713c-bee4-bcd4f2e41939" xlink:to="loc_us-gaap_GeneralAndAdministrativeExpenseMember_019ce811-d51c-740a-a215-e890b887e72f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_019ce811-d51c-7fb6-9712-1f272e6691d4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AllocatedShareBasedCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_019ce811-d51c-7fb1-98ce-be21cd2f4a67" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_019ce811-d51c-7fb6-9712-1f272e6691d4" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://allogene.com/role/RelatedPartyTransactionsDetails" xlink:type="simple" xlink:href="allo-20260331.xsd#RelatedPartyTransactionsDetails"/>
  <link:definitionLink xlink:role="http://allogene.com/role/RelatedPartyTransactionsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionLineItems_019ce811-d51c-7691-8c4d-8bc105c95514" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyTransactionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_019ce811-d51c-7c39-9824-a80de597d9e7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019ce811-d51c-7691-8c4d-8bc105c95514" xlink:to="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_019ce811-d51c-7c39-9824-a80de597d9e7" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementGeographicalAxis_019ce811-d51c-79b3-8271-c850201fdd17" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_StatementGeographicalAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_019ce811-d51c-7c39-9824-a80de597d9e7" xlink:to="loc_srt_StatementGeographicalAxis_019ce811-d51c-79b3-8271-c850201fdd17" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_019ce811-d51c-79b3-8271-c850201fdd17_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementGeographicalAxis_019ce811-d51c-79b3-8271-c850201fdd17" xlink:to="loc_srt_SegmentGeographicalDomain_019ce811-d51c-79b3-8271-c850201fdd17_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_019ce811-d51c-7974-82a5-7352a0d11d26" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementGeographicalAxis_019ce811-d51c-79b3-8271-c850201fdd17" xlink:to="loc_srt_SegmentGeographicalDomain_019ce811-d51c-7974-82a5-7352a0d11d26" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_stpr_CA_019ce811-d51c-7d37-ad0a-f64c1b513fad" xlink:href="https://xbrl.sec.gov/stpr/2025/stpr-2025.xsd#stpr_CA"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_019ce811-d51c-7974-82a5-7352a0d11d26" xlink:to="loc_stpr_CA_019ce811-d51c-7d37-ad0a-f64c1b513fad" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019ce811-d51c-70dd-a244-637bfe80f911" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_019ce811-d51c-7c39-9824-a80de597d9e7" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019ce811-d51c-70dd-a244-637bfe80f911" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_019ce811-d51c-70dd-a244-637bfe80f911_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019ce811-d51c-70dd-a244-637bfe80f911" xlink:to="loc_us-gaap_RelatedPartyDomain_019ce811-d51c-70dd-a244-637bfe80f911_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_019ce811-d51c-76db-835f-9589e7971837" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019ce811-d51c-70dd-a244-637bfe80f911" xlink:to="loc_us-gaap_RelatedPartyDomain_019ce811-d51c-76db-835f-9589e7971837" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyMember_019ce811-d51c-7e40-8134-19aa6c56b111" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_019ce811-d51c-76db-835f-9589e7971837" xlink:to="loc_us-gaap_RelatedPartyMember_019ce811-d51c-7e40-8134-19aa6c56b111" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionAxis_019ce811-d51c-73e0-9855-82f92b5feb29" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyTransactionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_019ce811-d51c-7c39-9824-a80de597d9e7" xlink:to="loc_us-gaap_RelatedPartyTransactionAxis_019ce811-d51c-73e0-9855-82f92b5feb29" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionDomain_019ce811-d51c-73e0-9855-82f92b5feb29_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionAxis_019ce811-d51c-73e0-9855-82f92b5feb29" xlink:to="loc_us-gaap_RelatedPartyTransactionDomain_019ce811-d51c-73e0-9855-82f92b5feb29_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionDomain_019ce811-d51c-7d5d-9963-f252a4f15200" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionAxis_019ce811-d51c-73e0-9855-82f92b5feb29" xlink:to="loc_us-gaap_RelatedPartyTransactionDomain_019ce811-d51c-7d5d-9963-f252a4f15200" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_SubleaseAgreementMember_019ce811-d51c-79a3-ae31-b080bdeb57c7" xlink:href="allo-20260331.xsd#allo_SubleaseAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionDomain_019ce811-d51c-7d5d-9963-f252a4f15200" xlink:to="loc_allo_SubleaseAgreementMember_019ce811-d51c-79a3-ae31-b080bdeb57c7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_ConsultingAgreementsMember_019ce811-d51c-7e48-9fac-af4e7cb111d1" xlink:href="allo-20260331.xsd#allo_ConsultingAgreementsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionDomain_019ce811-d51c-7d5d-9963-f252a4f15200" xlink:to="loc_allo_ConsultingAgreementsMember_019ce811-d51c-7e48-9fac-af4e7cb111d1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_CoManagerAgreementMember_019df0f9-fe63-7ceb-bf36-7c0fab8718a8" xlink:href="allo-20260331.xsd#allo_CoManagerAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionDomain_019ce811-d51c-7d5d-9963-f252a4f15200" xlink:to="loc_allo_CoManagerAgreementMember_019df0f9-fe63-7ceb-bf36-7c0fab8718a8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_PaymentTermsAxis_019ce811-d51c-72b3-9cca-ad14661241fb" xlink:href="allo-20260331.xsd#allo_PaymentTermsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_019ce811-d51c-7c39-9824-a80de597d9e7" xlink:to="loc_allo_PaymentTermsAxis_019ce811-d51c-72b3-9cca-ad14661241fb" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_PaymentTermsDomain_019ce811-d51c-72b3-9cca-ad14661241fb_default" xlink:href="allo-20260331.xsd#allo_PaymentTermsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_allo_PaymentTermsAxis_019ce811-d51c-72b3-9cca-ad14661241fb" xlink:to="loc_allo_PaymentTermsDomain_019ce811-d51c-72b3-9cca-ad14661241fb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_PaymentTermsDomain_019ce811-d51c-7064-ab75-246a8b0a1e35" xlink:href="allo-20260331.xsd#allo_PaymentTermsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_allo_PaymentTermsAxis_019ce811-d51c-72b3-9cca-ad14661241fb" xlink:to="loc_allo_PaymentTermsDomain_019ce811-d51c-7064-ab75-246a8b0a1e35" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_PaymentsCommencingJanuary2021Member_019ce811-d51c-75b6-aea3-de7ff6f03a54" xlink:href="allo-20260331.xsd#allo_PaymentsCommencingJanuary2021Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_allo_PaymentTermsDomain_019ce811-d51c-7064-ab75-246a8b0a1e35" xlink:to="loc_allo_PaymentsCommencingJanuary2021Member_019ce811-d51c-75b6-aea3-de7ff6f03a54" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019ce811-d51c-78e0-8b60-dde4ca0771f6" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_019ce811-d51c-7c39-9824-a80de597d9e7" xlink:to="loc_srt_RangeAxis_019ce811-d51c-78e0-8b60-dde4ca0771f6" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019ce811-d51c-78e0-8b60-dde4ca0771f6_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_019ce811-d51c-78e0-8b60-dde4ca0771f6" xlink:to="loc_srt_RangeMember_019ce811-d51c-78e0-8b60-dde4ca0771f6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019ce811-d51c-7eee-b1d5-3f0527ce7521" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_019ce811-d51c-78e0-8b60-dde4ca0771f6" xlink:to="loc_srt_RangeMember_019ce811-d51c-7eee-b1d5-3f0527ce7521" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_019ce811-d51c-7534-9b04-d34655ea3be6" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019ce811-d51c-7eee-b1d5-3f0527ce7521" xlink:to="loc_srt_MaximumMember_019ce811-d51c-7534-9b04-d34655ea3be6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CounterpartyNameAxis_019ce811-d51c-7301-8bc2-443aa66da4b0" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_CounterpartyNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_019ce811-d51c-7c39-9824-a80de597d9e7" xlink:to="loc_srt_CounterpartyNameAxis_019ce811-d51c-7301-8bc2-443aa66da4b0" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019ce811-d51c-7301-8bc2-443aa66da4b0_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CounterpartyNameAxis_019ce811-d51c-7301-8bc2-443aa66da4b0" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019ce811-d51c-7301-8bc2-443aa66da4b0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019ce811-d51c-7f8d-8a14-4ceb35246826" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CounterpartyNameAxis_019ce811-d51c-7301-8bc2-443aa66da4b0" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019ce811-d51c-7f8d-8a14-4ceb35246826" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_BellcoCapitalLLCMember_019ce811-d51c-7d4e-8c09-21523c3c64a0" xlink:href="allo-20260331.xsd#allo_BellcoCapitalLLCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019ce811-d51c-7f8d-8a14-4ceb35246826" xlink:to="loc_allo_BellcoCapitalLLCMember_019ce811-d51c-7d4e-8c09-21523c3c64a0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_TPGCapitalBDLLCMember_019e1775-9c86-7115-9149-8d9d799d5b7e" xlink:href="allo-20260331.xsd#allo_TPGCapitalBDLLCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019ce811-d51c-7f8d-8a14-4ceb35246826" xlink:to="loc_allo_TPGCapitalBDLLCMember_019e1775-9c86-7115-9149-8d9d799d5b7e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiarySaleOfStockAxis_019df0f9-fe63-7781-85a4-7bf79c448407" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsidiarySaleOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_019ce811-d51c-7c39-9824-a80de597d9e7" xlink:to="loc_us-gaap_SubsidiarySaleOfStockAxis_019df0f9-fe63-7781-85a4-7bf79c448407" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019df0f9-fe63-7781-85a4-7bf79c448407_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_019df0f9-fe63-7781-85a4-7bf79c448407" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019df0f9-fe63-7781-85a4-7bf79c448407_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019df0f9-fe63-7e0b-90a8-b41fdbc38725" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_019df0f9-fe63-7781-85a4-7bf79c448407" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019df0f9-fe63-7e0b-90a8-b41fdbc38725" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_April2026PublicOfferingMember_019e17cc-3d91-7f26-8374-c2cc97b9f147" xlink:href="allo-20260331.xsd#allo_April2026PublicOfferingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019df0f9-fe63-7e0b-90a8-b41fdbc38725" xlink:to="loc_allo_April2026PublicOfferingMember_019e17cc-3d91-7f26-8374-c2cc97b9f147" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeAxis_019df0f9-fe63-78c0-af6c-48fb46a58efd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_019ce811-d51c-7c39-9824-a80de597d9e7" xlink:to="loc_us-gaap_SubsequentEventTypeAxis_019df0f9-fe63-78c0-af6c-48fb46a58efd" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_019df0f9-fe63-78c0-af6c-48fb46a58efd_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_019df0f9-fe63-78c0-af6c-48fb46a58efd" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_019df0f9-fe63-78c0-af6c-48fb46a58efd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_019df0f9-fe63-737a-80b0-20643c47642e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_019df0f9-fe63-78c0-af6c-48fb46a58efd" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_019df0f9-fe63-737a-80b0-20643c47642e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventMember_019df0f9-fe63-76ee-a68d-2664bb287d95" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventTypeDomain_019df0f9-fe63-737a-80b0-20643c47642e" xlink:to="loc_us-gaap_SubsequentEventMember_019df0f9-fe63-76ee-a68d-2664bb287d95" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_AreaOfOfficeSpace_019ce811-d51c-74e4-ac99-4ce6585e7957" xlink:href="allo-20260331.xsd#allo_AreaOfOfficeSpace"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019ce811-d51c-7691-8c4d-8bc105c95514" xlink:to="loc_allo_AreaOfOfficeSpace_019ce811-d51c-74e4-ac99-4ce6585e7957" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeOperatingLeaseTermOfContract_019ce811-d51c-7d39-8357-28fc6ac5b15e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LesseeOperatingLeaseTermOfContract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019ce811-d51c-7691-8c4d-8bc105c95514" xlink:to="loc_us-gaap_LesseeOperatingLeaseTermOfContract_019ce811-d51c-7d39-8357-28fc6ac5b15e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_AreaOfOffice_019ce811-d51c-7684-897b-3a257af518a1" xlink:href="allo-20260331.xsd#allo_AreaOfOffice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019ce811-d51c-7691-8c4d-8bc105c95514" xlink:to="loc_allo_AreaOfOffice_019ce811-d51c-7684-897b-3a257af518a1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LessorOperatingLeaseTermOfContract_019ce811-d51c-78e4-9805-75b1a8d14c49" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LessorOperatingLeaseTermOfContract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019ce811-d51c-7691-8c4d-8bc105c95514" xlink:to="loc_us-gaap_LessorOperatingLeaseTermOfContract_019ce811-d51c-78e4-9805-75b1a8d14c49" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseRightOfUseAsset_019ce811-d51c-700a-a5c2-5dff70f74123" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingLeaseRightOfUseAsset"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019ce811-d51c-7691-8c4d-8bc105c95514" xlink:to="loc_us-gaap_OperatingLeaseRightOfUseAsset_019ce811-d51c-700a-a5c2-5dff70f74123" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseLiability_019ce811-d51c-7fec-8932-79ef3be032ac" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingLeaseLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019ce811-d51c-7691-8c4d-8bc105c95514" xlink:to="loc_us-gaap_OperatingLeaseLiability_019ce811-d51c-7fec-8932-79ef3be032ac" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_OperatingLeaseBaseRentAndSecurityDepositPayment_019ce811-d51c-74f8-ae39-12ce9628c300" xlink:href="allo-20260331.xsd#allo_OperatingLeaseBaseRentAndSecurityDepositPayment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019ce811-d51c-7691-8c4d-8bc105c95514" xlink:to="loc_allo_OperatingLeaseBaseRentAndSecurityDepositPayment_019ce811-d51c-74f8-ae39-12ce9628c300" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseExpense_019ce811-d51c-7c34-bee1-7eec6f144d73" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingLeaseExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019ce811-d51c-7691-8c4d-8bc105c95514" xlink:to="loc_us-gaap_OperatingLeaseExpense_019ce811-d51c-7c34-bee1-7eec6f144d73" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_RelatedPartyTransactionMonthlyPaymentsInArrears_019ce811-d51c-752d-b21a-beeb1e6fe16d" xlink:href="allo-20260331.xsd#allo_RelatedPartyTransactionMonthlyPaymentsInArrears"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019ce811-d51c-7691-8c4d-8bc105c95514" xlink:to="loc_allo_RelatedPartyTransactionMonthlyPaymentsInArrears_019ce811-d51c-752d-b21a-beeb1e6fe16d" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_RelatedPartyTransactionConsultingFeePercentageIncrease_019dce07-5e81-71a5-bcf5-17572531ba5c" xlink:href="allo-20260331.xsd#allo_RelatedPartyTransactionConsultingFeePercentageIncrease"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019ce811-d51c-7691-8c4d-8bc105c95514" xlink:to="loc_allo_RelatedPartyTransactionConsultingFeePercentageIncrease_019dce07-5e81-71a5-bcf5-17572531ba5c" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_RelatedPartyTransactionMonthlyConsultingFee_019dce07-5e81-7619-9f7b-7500028f5048" xlink:href="allo-20260331.xsd#allo_RelatedPartyTransactionMonthlyConsultingFee"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019ce811-d51c-7691-8c4d-8bc105c95514" xlink:to="loc_allo_RelatedPartyTransactionMonthlyConsultingFee_019dce07-5e81-7619-9f7b-7500028f5048" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_RelatedPartyTransactionCompensationPercentage_019ce811-d51c-70f9-9e43-055d3ff63e99" xlink:href="allo-20260331.xsd#allo_RelatedPartyTransactionCompensationPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019ce811-d51c-7691-8c4d-8bc105c95514" xlink:to="loc_allo_RelatedPartyTransactionCompensationPercentage_019ce811-d51c-70f9-9e43-055d3ff63e99" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfRevenue_019ce811-d51c-7fde-9859-b206f4e2d3b1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CostOfRevenue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019ce811-d51c-7691-8c4d-8bc105c95514" xlink:to="loc_us-gaap_CostOfRevenue_019ce811-d51c-7fde-9859-b206f4e2d3b1" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction_019df0f9-fe63-7786-8edf-f111e7d72e94" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019ce811-d51c-7691-8c4d-8bc105c95514" xlink:to="loc_us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction_019df0f9-fe63-7786-8edf-f111e7d72e94" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockPricePerShare_019df0f9-fe63-7fe6-88a7-3a5ebee634a4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SaleOfStockPricePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019ce811-d51c-7691-8c4d-8bc105c95514" xlink:to="loc_us-gaap_SaleOfStockPricePerShare_019df0f9-fe63-7fe6-88a7-3a5ebee634a4" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_SaleOfStockUnderwritingDiscountPerShare_019e17d3-982a-7b8b-ad6c-f9319998af20" xlink:href="allo-20260331.xsd#allo_SaleOfStockUnderwritingDiscountPerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019ce811-d51c-7691-8c4d-8bc105c95514" xlink:to="loc_allo_SaleOfStockUnderwritingDiscountPerShare_019e17d3-982a-7b8b-ad6c-f9319998af20" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_SaleOfStockUnderwritingDiscount_019df0f9-fe63-7e71-9462-93a91176fcb1" xlink:href="allo-20260331.xsd#allo_SaleOfStockUnderwritingDiscount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019ce811-d51c-7691-8c4d-8bc105c95514" xlink:to="loc_allo_SaleOfStockUnderwritingDiscount_019df0f9-fe63-7e71-9462-93a91176fcb1" xlink:type="arc" order="16"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://allogene.com/role/NetLossPerShareDetails" xlink:type="simple" xlink:href="allo-20260331.xsd#NetLossPerShareDetails"/>
  <link:definitionLink xlink:role="http://allogene.com/role/NetLossPerShareDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_019ce811-d51c-7f00-a256-c1379ca8ea11" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_019ce811-d51c-7ef5-979d-0248c2b58b4d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_019ce811-d51c-7f00-a256-c1379ca8ea11" xlink:to="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_019ce811-d51c-7ef5-979d-0248c2b58b4d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_019ce811-d51c-7bb2-b707-cd59262eae60" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_019ce811-d51c-7ef5-979d-0248c2b58b4d" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_019ce811-d51c-7bb2-b707-cd59262eae60" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019ce811-d51c-7bb2-b707-cd59262eae60_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_019ce811-d51c-7bb2-b707-cd59262eae60" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019ce811-d51c-7bb2-b707-cd59262eae60_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019ce811-d51c-7abf-b8e2-1e29e67199b2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_019ce811-d51c-7bb2-b707-cd59262eae60" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019ce811-d51c-7abf-b8e2-1e29e67199b2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_019ce811-d51c-75d9-a749-16fa79678061" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019ce811-d51c-7abf-b8e2-1e29e67199b2" xlink:to="loc_us-gaap_EmployeeStockOptionMember_019ce811-d51c-75d9-a749-16fa79678061" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_019ce811-d51c-7025-b95f-373ae7c2d497" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019ce811-d51c-7abf-b8e2-1e29e67199b2" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_019ce811-d51c-7025-b95f-373ae7c2d497" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockMember_019ce811-d51c-7096-a6a1-ab466b9e0825" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019ce811-d51c-7abf-b8e2-1e29e67199b2" xlink:to="loc_us-gaap_EmployeeStockMember_019ce811-d51c-7096-a6a1-ab466b9e0825" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_019ce811-d51c-791e-8604-55517310cb84" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_019ce811-d51c-7f00-a256-c1379ca8ea11" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_019ce811-d51c-791e-8604-55517310cb84" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://allogene.com/role/SegmentReportingSegmentProfitorLossandSegmentExpensesDetails" xlink:type="simple" xlink:href="allo-20260331.xsd#SegmentReportingSegmentProfitorLossandSegmentExpensesDetails"/>
  <link:definitionLink xlink:role="http://allogene.com/role/SegmentReportingSegmentProfitorLossandSegmentExpensesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_019ce811-d51c-7771-a4b6-3771721ad1b9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019ce811-d51c-7c41-8967-993bcc8c0e96" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019ce811-d51c-7771-a4b6-3771721ad1b9" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019ce811-d51c-7c41-8967-993bcc8c0e96" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_019ce811-d51c-7663-90df-1778c1bd26f4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019ce811-d51c-7c41-8967-993bcc8c0e96" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_019ce811-d51c-7663-90df-1778c1bd26f4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019ce811-d51c-7663-90df-1778c1bd26f4_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019ce811-d51c-7663-90df-1778c1bd26f4" xlink:to="loc_us-gaap_SegmentDomain_019ce811-d51c-7663-90df-1778c1bd26f4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019ce811-d51c-7107-8540-9e8b04d39b8f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019ce811-d51c-7663-90df-1778c1bd26f4" xlink:to="loc_us-gaap_SegmentDomain_019ce811-d51c-7107-8540-9e8b04d39b8f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_ReportableSegmentMember_019ce811-d51c-7b9b-a893-6efc7998f77e" xlink:href="allo-20260331.xsd#allo_ReportableSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019ce811-d51c-7107-8540-9e8b04d39b8f" xlink:to="loc_allo_ReportableSegmentMember_019ce811-d51c-7b9b-a893-6efc7998f77e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingExpensesAbstract_019ce811-d51c-7fea-ab27-1b0da530f025" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingExpensesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019ce811-d51c-7771-a4b6-3771721ad1b9" xlink:to="loc_us-gaap_OperatingExpensesAbstract_019ce811-d51c-7fea-ab27-1b0da530f025" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_ResearchAndDevelopmentExpenseCemaCel_019ce811-d51c-7fb7-b2af-fe5cfd8ddeee" xlink:href="allo-20260331.xsd#allo_ResearchAndDevelopmentExpenseCemaCel"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_019ce811-d51c-7fea-ab27-1b0da530f025" xlink:to="loc_allo_ResearchAndDevelopmentExpenseCemaCel_019ce811-d51c-7fb7-b2af-fe5cfd8ddeee" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_ResearchAndDevelopmentExpenseOtherDevelopmentCosts_019ce811-d51c-7e8d-90bd-60d5acf917a7" xlink:href="allo-20260331.xsd#allo_ResearchAndDevelopmentExpenseOtherDevelopmentCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_019ce811-d51c-7fea-ab27-1b0da530f025" xlink:to="loc_allo_ResearchAndDevelopmentExpenseOtherDevelopmentCosts_019ce811-d51c-7e8d-90bd-60d5acf917a7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LaborAndRelatedExpense_019ce811-d51c-7a07-9c91-eb29210080d6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LaborAndRelatedExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_019ce811-d51c-7fea-ab27-1b0da530f025" xlink:to="loc_us-gaap_LaborAndRelatedExpense_019ce811-d51c-7a07-9c91-eb29210080d6" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_FacilitiesAndITRelatedExpense_019ce811-d51c-7d47-9620-7d1941d54712" xlink:href="allo-20260331.xsd#allo_FacilitiesAndITRelatedExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_019ce811-d51c-7fea-ab27-1b0da530f025" xlink:to="loc_allo_FacilitiesAndITRelatedExpense_019ce811-d51c-7d47-9620-7d1941d54712" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_SupportingExternalSpendExpense_019ce811-d51c-7145-8eb0-8ab9027854e8" xlink:href="allo-20260331.xsd#allo_SupportingExternalSpendExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_019ce811-d51c-7fea-ab27-1b0da530f025" xlink:to="loc_allo_SupportingExternalSpendExpense_019ce811-d51c-7145-8eb0-8ab9027854e8" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherCostAndExpenseOperating_019ce811-d51c-7ed4-95f4-4e21bb51f39e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherCostAndExpenseOperating"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_019ce811-d51c-7fea-ab27-1b0da530f025" xlink:to="loc_us-gaap_OtherCostAndExpenseOperating_019ce811-d51c-7ed4-95f4-4e21bb51f39e" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingExpenses_019ce811-d51c-7eef-b147-4edc00ad0d24" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_019ce811-d51c-7fea-ab27-1b0da530f025" xlink:to="loc_us-gaap_OperatingExpenses_019ce811-d51c-7eef-b147-4edc00ad0d24" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonoperatingIncomeExpense_019ce811-d51c-72e2-b07f-ae866f9f4b93" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NonoperatingIncomeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019ce811-d51c-7771-a4b6-3771721ad1b9" xlink:to="loc_us-gaap_NonoperatingIncomeExpense_019ce811-d51c-72e2-b07f-ae866f9f4b93" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_019ce811-d51c-76e3-916c-3cf266813029" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019ce811-d51c-7771-a4b6-3771721ad1b9" xlink:to="loc_us-gaap_NetIncomeLoss_019ce811-d51c-76e3-916c-3cf266813029" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://allogene.com/role/SubsequentEventsDetails" xlink:type="simple" xlink:href="allo-20260331.xsd#SubsequentEventsDetails"/>
  <link:definitionLink xlink:role="http://allogene.com/role/SubsequentEventsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventLineItems_019df108-9bea-7254-9f2b-38973f83b7c0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTable_019ce811-d51c-790f-910c-3c708f98274a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SubsequentEventLineItems_019df108-9bea-7254-9f2b-38973f83b7c0" xlink:to="loc_us-gaap_SubsequentEventTable_019ce811-d51c-790f-910c-3c708f98274a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeAxis_019e17d7-d76e-7235-bb71-6b8ef580f796" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_019ce811-d51c-790f-910c-3c708f98274a" xlink:to="loc_us-gaap_SubsequentEventTypeAxis_019e17d7-d76e-7235-bb71-6b8ef580f796" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_019e17d7-d76e-7235-bb71-6b8ef580f796_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_019e17d7-d76e-7235-bb71-6b8ef580f796" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_019e17d7-d76e-7235-bb71-6b8ef580f796_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_019e17d7-d76e-74fb-b634-1922ca5f9f28" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_019e17d7-d76e-7235-bb71-6b8ef580f796" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_019e17d7-d76e-74fb-b634-1922ca5f9f28" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventMember_019e17d7-d76e-752b-a72b-81a27482fbe5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventTypeDomain_019e17d7-d76e-74fb-b634-1922ca5f9f28" xlink:to="loc_us-gaap_SubsequentEventMember_019e17d7-d76e-752b-a72b-81a27482fbe5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiarySaleOfStockAxis_019e17d7-d76e-7c73-9a64-413396548c40" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsidiarySaleOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_019ce811-d51c-790f-910c-3c708f98274a" xlink:to="loc_us-gaap_SubsidiarySaleOfStockAxis_019e17d7-d76e-7c73-9a64-413396548c40" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019e17d7-d76e-7c73-9a64-413396548c40_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_019e17d7-d76e-7c73-9a64-413396548c40" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019e17d7-d76e-7c73-9a64-413396548c40_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019e17d7-d76e-7632-ac93-60e7d6939249" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_019e17d7-d76e-7c73-9a64-413396548c40" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019e17d7-d76e-7632-ac93-60e7d6939249" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_April2026PublicOfferingMember_019e17d7-d76e-7cf1-b28a-5a200ffde435" xlink:href="allo-20260331.xsd#allo_April2026PublicOfferingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019e17d7-d76e-7632-ac93-60e7d6939249" xlink:to="loc_allo_April2026PublicOfferingMember_019e17d7-d76e-7cf1-b28a-5a200ffde435" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OverAllotmentOptionMember_019e17d7-d76e-746a-9752-c635e3f949bb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OverAllotmentOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019e17d7-d76e-7632-ac93-60e7d6939249" xlink:to="loc_us-gaap_OverAllotmentOptionMember_019e17d7-d76e-746a-9752-c635e3f949bb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction_019e17d7-d76e-7377-98a4-d9f7850c4a72" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_019df108-9bea-7254-9f2b-38973f83b7c0" xlink:to="loc_us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction_019e17d7-d76e-7377-98a4-d9f7850c4a72" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockPricePerShare_019e17d7-d76e-7526-bfcb-e9c3b059224a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SaleOfStockPricePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_019df108-9bea-7254-9f2b-38973f83b7c0" xlink:to="loc_us-gaap_SaleOfStockPricePerShare_019e17d7-d76e-7526-bfcb-e9c3b059224a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromIssuanceOfCommonStock_019e17d7-d76e-759a-a7a4-13f04be45445" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ProceedsFromIssuanceOfCommonStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_019df108-9bea-7254-9f2b-38973f83b7c0" xlink:to="loc_us-gaap_ProceedsFromIssuanceOfCommonStock_019e17d7-d76e-759a-a7a4-13f04be45445" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockConsiderationReceivedOnTransaction_019e17d7-d76e-7e70-87b9-99f8cd12f065" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SaleOfStockConsiderationReceivedOnTransaction"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_019df108-9bea-7254-9f2b-38973f83b7c0" xlink:to="loc_us-gaap_SaleOfStockConsiderationReceivedOnTransaction_019e17d7-d76e-7e70-87b9-99f8cd12f065" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://fasb.org/us-gaap/role/eedm/ExtensibleEnumerationLists" xlink:type="simple" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-roles-2025.xsd#eedm"/>
  <link:definitionLink xlink:role="http://fasb.org/us-gaap/role/eedm/ExtensibleEnumerationLists" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsAbstract" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AssetsAbstract"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PrepaidExpenseAndOtherAssetsCurrent" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PrepaidExpenseAndOtherAssetsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract" xlink:to="loc_us-gaap_PrepaidExpenseAndOtherAssetsCurrent" xlink:type="arc" order="101"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesCurrentAbstract" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LiabilitiesCurrentAbstract"/>
    <link:loc xlink:type="locator" xlink:label="loc_allo_AccruedAndOtherLiabilitiesCurrent_019ce811-d3ba-73ad-8473-63e966d4cd83" xlink:href="allo-20260331.xsd#allo_AccruedAndOtherLiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract" xlink:to="loc_allo_AccruedAndOtherLiabilitiesCurrent_019ce811-d3ba-73ad-8473-63e966d4cd83" xlink:type="arc" order="41"/>
  </link:definitionLink>
</link:linkbase>
