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

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2026 Workiva-->
<!--r:019d1daa-0cd8-7662-832c-75d6823673ce,g:7361a93b-7b51-497d-a042-e0193ca0f4bd-->
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:vtl="http://vitaltherapies.com/20260331" xmlns:xbrli="http://www.xbrl.org/2003/instance" xmlns:dtr-types="http://www.xbrl.org/dtr/type/2024-01-31" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" attributeFormDefault="unqualified" elementFormDefault="qualified" targetNamespace="http://vitaltherapies.com/20260331">
  <xs:import namespace="http://fasb.org/srt/2025" schemaLocation="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd"/>
  <xs:import namespace="http://fasb.org/us-gaap/2025" schemaLocation="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd"/>
  <xs:import namespace="http://www.xbrl.org/2003/instance" schemaLocation="http://www.xbrl.org/2003/xbrl-instance-2003-12-31.xsd"/>
  <xs:import namespace="http://www.xbrl.org/2003/linkbase" schemaLocation="http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd"/>
  <xs:import namespace="http://www.xbrl.org/dtr/type/2024-01-31" schemaLocation="https://www.xbrl.org/dtr/type/2024-01-31/types.xsd"/>
  <xs:import namespace="http://xbrl.org/2005/xbrldt" schemaLocation="http://www.xbrl.org/2005/xbrldt-2005.xsd"/>
  <xs:import namespace="http://xbrl.sec.gov/country/2025" schemaLocation="https://xbrl.sec.gov/country/2025/country-2025.xsd"/>
  <xs:import namespace="http://xbrl.sec.gov/dei/2025" schemaLocation="https://xbrl.sec.gov/dei/2025/dei-2025.xsd"/>
  <xs:import namespace="http://xbrl.sec.gov/ecd/2025" schemaLocation="https://xbrl.sec.gov/ecd/2025/ecd-2025.xsd"/>
  <xs:annotation>
    <xs:appinfo>
      <link:linkbaseRef xmlns:xlink="http://www.w3.org/1999/xlink" xlink:arcrole="http://www.w3.org/1999/xlink/properties/linkbase" xlink:href="vtl-20260331_pre.xml" xlink:role="http://www.xbrl.org/2003/role/presentationLinkbaseRef" xlink:type="simple"/>
      <link:linkbaseRef xmlns:xlink="http://www.w3.org/1999/xlink" xlink:arcrole="http://www.w3.org/1999/xlink/properties/linkbase" xlink:href="vtl-20260331_def.xml" xlink:role="http://www.xbrl.org/2003/role/definitionLinkbaseRef" xlink:type="simple"/>
      <link:linkbaseRef xmlns:xlink="http://www.w3.org/1999/xlink" xlink:arcrole="http://www.w3.org/1999/xlink/properties/linkbase" xlink:href="vtl-20260331_lab.xml" xlink:role="http://www.xbrl.org/2003/role/labelLinkbaseRef" xlink:type="simple"/>
      <link:linkbaseRef xmlns:xlink="http://www.w3.org/1999/xlink" xlink:arcrole="http://www.w3.org/1999/xlink/properties/linkbase" xlink:href="vtl-20260331_cal.xml" xlink:role="http://www.xbrl.org/2003/role/calculationLinkbaseRef" xlink:type="simple"/>
      <link:roleType id="CoverPage" roleURI="http://vitaltherapies.com/role/CoverPage">
        <link:definition>0000001 - Document - Cover Page</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="CondensedConsolidatedBalanceSheets" roleURI="http://vitaltherapies.com/role/CondensedConsolidatedBalanceSheets">
        <link:definition>9952151 - Statement - Condensed Consolidated Balance Sheets</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="CondensedConsolidatedBalanceSheetsParenthetical" roleURI="http://vitaltherapies.com/role/CondensedConsolidatedBalanceSheetsParenthetical">
        <link:definition>9952152 - Statement - Condensed Consolidated Balance Sheets (Parenthetical)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="CondensedConsolidatedStatementsofOperations" roleURI="http://vitaltherapies.com/role/CondensedConsolidatedStatementsofOperations">
        <link:definition>9952153 - Statement - Condensed Consolidated Statements of Operations</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="CondensedConsolidatedStatementsofComprehensiveLoss" roleURI="http://vitaltherapies.com/role/CondensedConsolidatedStatementsofComprehensiveLoss">
        <link:definition>9952154 - Statement - Condensed Consolidated Statements of Comprehensive Loss</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="CondensedConsolidatedStatementsofStockholdersEquityDeficit" roleURI="http://vitaltherapies.com/role/CondensedConsolidatedStatementsofStockholdersEquityDeficit">
        <link:definition>9952155 - Statement - Condensed Consolidated Statements of Stockholders&#8217; Equity (Deficit)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="CondensedConsolidatedStatementsofStockholdersEquityDeficitParenthetical" roleURI="http://vitaltherapies.com/role/CondensedConsolidatedStatementsofStockholdersEquityDeficitParenthetical">
        <link:definition>9952156 - Statement - Condensed Consolidated Statements of Stockholders&#8217; Equity (Deficit) (Parenthetical)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="CondensedConsolidatedStatementsofCashFlows" roleURI="http://vitaltherapies.com/role/CondensedConsolidatedStatementsofCashFlows">
        <link:definition>9952157 - Statement - Condensed Consolidated Statements of Cash Flows</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="DescriptionofBusinessandBasisofFinancialStatements" roleURI="http://vitaltherapies.com/role/DescriptionofBusinessandBasisofFinancialStatements">
        <link:definition>9952158 - Disclosure - Description of Business and Basis of Financial Statements</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="SummaryofSignificantAccountingPolicies" roleURI="http://vitaltherapies.com/role/SummaryofSignificantAccountingPolicies">
        <link:definition>9952159 - Disclosure - Summary of Significant Accounting Policies</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="BalanceSheetDetails" roleURI="http://vitaltherapies.com/role/BalanceSheetDetails">
        <link:definition>9952160 - Disclosure - Balance Sheet Details</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="Leases" roleURI="http://vitaltherapies.com/role/Leases">
        <link:definition>9952161 - Disclosure - Leases</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="FairValue" roleURI="http://vitaltherapies.com/role/FairValue">
        <link:definition>9952162 - Disclosure - Fair Value</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="CommonStock" roleURI="http://vitaltherapies.com/role/CommonStock">
        <link:definition>9952163 - Disclosure - Common Stock</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="StockBasedCompensationPlans" roleURI="http://vitaltherapies.com/role/StockBasedCompensationPlans">
        <link:definition>9952164 - Disclosure - Stock-Based Compensation Plans</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="RelatedPartyTransactions" roleURI="http://vitaltherapies.com/role/RelatedPartyTransactions">
        <link:definition>9952165 - Disclosure - Related Party Transactions</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="CommitmentsandContingencies" roleURI="http://vitaltherapies.com/role/CommitmentsandContingencies">
        <link:definition>9952166 - Disclosure - Commitments and Contingencies</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="SegmentDisclosures" roleURI="http://vitaltherapies.com/role/SegmentDisclosures">
        <link:definition>9952167 - Disclosure - Segment Disclosures</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="SubsequentEvents" roleURI="http://vitaltherapies.com/role/SubsequentEvents">
        <link:definition>9952168 - Disclosure - Subsequent Events</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="SummaryofSignificantAccountingPoliciesPolicies" roleURI="http://vitaltherapies.com/role/SummaryofSignificantAccountingPoliciesPolicies">
        <link:definition>9955511 - Disclosure - Summary of Significant Accounting Policies (Policies)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="SummaryofSignificantAccountingPoliciesTables" roleURI="http://vitaltherapies.com/role/SummaryofSignificantAccountingPoliciesTables">
        <link:definition>9955512 - Disclosure - Summary of Significant Accounting Policies (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="BalanceSheetDetailsTables" roleURI="http://vitaltherapies.com/role/BalanceSheetDetailsTables">
        <link:definition>9955513 - Disclosure - Balance Sheet Details (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="LeasesTables" roleURI="http://vitaltherapies.com/role/LeasesTables">
        <link:definition>9955514 - Disclosure - Leases (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="FairValueTables" roleURI="http://vitaltherapies.com/role/FairValueTables">
        <link:definition>9955515 - Disclosure - Fair Value (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="CommonStockTables" roleURI="http://vitaltherapies.com/role/CommonStockTables">
        <link:definition>9955516 - Disclosure - Common Stock (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="StockBasedCompensationPlansTables" roleURI="http://vitaltherapies.com/role/StockBasedCompensationPlansTables">
        <link:definition>9955517 - Disclosure - Stock-Based Compensation Plans (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="SegmentDisclosuresTables" roleURI="http://vitaltherapies.com/role/SegmentDisclosuresTables">
        <link:definition>9955518 - Disclosure - Segment Disclosures (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="DescriptionofBusinessandBasisofFinancialStatementsDetails" roleURI="http://vitaltherapies.com/role/DescriptionofBusinessandBasisofFinancialStatementsDetails">
        <link:definition>9955519 - Disclosure - Description of Business and Basis of Financial Statements (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="SummaryofSignificantAccountingPoliciesAdditionalInformationDetails" roleURI="http://vitaltherapies.com/role/SummaryofSignificantAccountingPoliciesAdditionalInformationDetails">
        <link:definition>9955520 - Disclosure - Summary of Significant Accounting Policies - Additional Information (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="SummaryofSignificantAccountingPoliciesScheduleofPotentiallyDilutiveSecuritiesNotIncludedinCalculationofDilutedNetLossperShareDetails" roleURI="http://vitaltherapies.com/role/SummaryofSignificantAccountingPoliciesScheduleofPotentiallyDilutiveSecuritiesNotIncludedinCalculationofDilutedNetLossperShareDetails">
        <link:definition>9955521 - Disclosure - Summary of Significant Accounting Policies - Schedule of Potentially Dilutive Securities Not Included in Calculation of Diluted Net Loss per Share (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="BalanceSheetDetailsScheduleofOtherCurrentAssetsandPrepaidExpensesDetail" roleURI="http://vitaltherapies.com/role/BalanceSheetDetailsScheduleofOtherCurrentAssetsandPrepaidExpensesDetail">
        <link:definition>9955522 - Disclosure - Balance Sheet Details - Schedule of Other Current Assets and Prepaid Expenses (Detail)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="BalanceSheetDetailsScheduleofAccountsPayableDetail" roleURI="http://vitaltherapies.com/role/BalanceSheetDetailsScheduleofAccountsPayableDetail">
        <link:definition>9955523 - Disclosure - Balance Sheet Details - Schedule of Accounts Payable (Detail)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="BalanceSheetDetailsScheduleofAccruedExpensesDetail" roleURI="http://vitaltherapies.com/role/BalanceSheetDetailsScheduleofAccruedExpensesDetail">
        <link:definition>9955524 - Disclosure - Balance Sheet Details - Schedule of Accrued Expenses (Detail)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="BalanceSheetDetailsScheduleofOtherCurrentLiabilitiesDetail" roleURI="http://vitaltherapies.com/role/BalanceSheetDetailsScheduleofOtherCurrentLiabilitiesDetail">
        <link:definition>9955525 - Disclosure - Balance Sheet Details - Schedule of Other Current Liabilities (Detail)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="LeasesAdditionalInformationDetails" roleURI="http://vitaltherapies.com/role/LeasesAdditionalInformationDetails">
        <link:definition>9955526 - Disclosure - Leases - Additional Information (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="LeasesScheduleofMaturitiesofOperatingLeaseObligationsDetails" roleURI="http://vitaltherapies.com/role/LeasesScheduleofMaturitiesofOperatingLeaseObligationsDetails">
        <link:definition>9955527 - Disclosure - Leases - Schedule of Maturities of Operating Lease Obligations (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="LeasesScheduleofMaturitiesofOperatingLeaseObligationsDetails_1" roleURI="http://vitaltherapies.com/role/LeasesScheduleofMaturitiesofOperatingLeaseObligationsDetails_1">
        <link:definition>9955527 - Disclosure - Leases - Schedule of Maturities of Operating Lease Obligations (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="FairValueScheduleofFinancialAssetsandLiabilitiesMeasuredatFairValueonRecurringBasisDetails" roleURI="http://vitaltherapies.com/role/FairValueScheduleofFinancialAssetsandLiabilitiesMeasuredatFairValueonRecurringBasisDetails">
        <link:definition>9955528 - Disclosure - Fair Value - Schedule of Financial Assets and Liabilities Measured at Fair Value on Recurring Basis (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="FairValueAdditionalInformationDetails" roleURI="http://vitaltherapies.com/role/FairValueAdditionalInformationDetails">
        <link:definition>9955529 - Disclosure - Fair Value - Additional Information (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="FairValueScheduleofFairValueofTrancheRightsDetails" roleURI="http://vitaltherapies.com/role/FairValueScheduleofFairValueofTrancheRightsDetails">
        <link:definition>9955530 - Disclosure - Fair Value - Schedule of Fair Value of Tranche Rights (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="FairValueScheduleofKeyAssumptionsUsedInEstimatingtheFairValueofSARsDetails" roleURI="http://vitaltherapies.com/role/FairValueScheduleofKeyAssumptionsUsedInEstimatingtheFairValueofSARsDetails">
        <link:definition>9955531 - Disclosure - Fair Value - Schedule of Key Assumptions Used In Estimating the Fair Value of SARs (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="CommonStockShelfRegistrationStatementDetails" roleURI="http://vitaltherapies.com/role/CommonStockShelfRegistrationStatementDetails">
        <link:definition>9955532 - Disclosure - Common Stock - Shelf Registration Statement (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="CommonStockScheduleofSharesReservedforFutureIssuanceDetails" roleURI="http://vitaltherapies.com/role/CommonStockScheduleofSharesReservedforFutureIssuanceDetails">
        <link:definition>9955533 - Disclosure - Common Stock - Schedule of Shares Reserved for Future Issuance (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="CommonStockEquityOfferingDetails" roleURI="http://vitaltherapies.com/role/CommonStockEquityOfferingDetails">
        <link:definition>9955534 - Disclosure - Common Stock - Equity Offering (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="CommonStockCommonStockDetails" roleURI="http://vitaltherapies.com/role/CommonStockCommonStockDetails">
        <link:definition>9955535 - Disclosure - Common Stock - Common Stock (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="CommonStockPrefundedWarrantsDetails" roleURI="http://vitaltherapies.com/role/CommonStockPrefundedWarrantsDetails">
        <link:definition>9955536 - Disclosure - Common Stock - Pre-funded Warrants (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="CommonStockPreferredStockDetails" roleURI="http://vitaltherapies.com/role/CommonStockPreferredStockDetails">
        <link:definition>9955537 - Disclosure - Common Stock - Preferred Stock (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="StockBasedCompensationPlansAdditionalInformationDetails" roleURI="http://vitaltherapies.com/role/StockBasedCompensationPlansAdditionalInformationDetails">
        <link:definition>9955538 - Disclosure - Stock-Based Compensation Plans - Additional Information (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="StockBasedCompensationPlansScheduleofStockOptionActivityDetails" roleURI="http://vitaltherapies.com/role/StockBasedCompensationPlansScheduleofStockOptionActivityDetails">
        <link:definition>9955539 - Disclosure - Stock-Based Compensation Plans - Schedule of Stock Option Activity (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="StockBasedCompensationPlansScheduleofValuationAssumptionsUsedDetail" roleURI="http://vitaltherapies.com/role/StockBasedCompensationPlansScheduleofValuationAssumptionsUsedDetail">
        <link:definition>9955540 - Disclosure - Stock-Based Compensation Plans - Schedule of Valuation Assumptions Used (Detail)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="StockBasedCompensationPlansScheduleofSARsActivityDetails" roleURI="http://vitaltherapies.com/role/StockBasedCompensationPlansScheduleofSARsActivityDetails">
        <link:definition>9955541 - Disclosure - Stock-Based Compensation Plans - Schedule of SARs Activity (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="StockBasedCompensationPlansScheduleofStockBasedCompensationExpenseforStockAwardsRecognizedDetails" roleURI="http://vitaltherapies.com/role/StockBasedCompensationPlansScheduleofStockBasedCompensationExpenseforStockAwardsRecognizedDetails">
        <link:definition>9955542 - Disclosure - Stock-Based Compensation Plans - Schedule of Stock-Based Compensation Expense for Stock Awards Recognized (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="RelatedPartyTransactionsDetails" roleURI="http://vitaltherapies.com/role/RelatedPartyTransactionsDetails">
        <link:definition>9955543 - Disclosure - Related Party Transactions (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="CommitmentsandContingenciesDetails" roleURI="http://vitaltherapies.com/role/CommitmentsandContingenciesDetails">
        <link:definition>9955544 - Disclosure - Commitments and Contingencies (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="SegmentDisclosuresAdditionalInformationDetails" roleURI="http://vitaltherapies.com/role/SegmentDisclosuresAdditionalInformationDetails">
        <link:definition>9955545 - Disclosure - Segment Disclosures - Additional Information (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="SegmentDisclosuresScheduleofSignificantExpenseDetails" roleURI="http://vitaltherapies.com/role/SegmentDisclosuresScheduleofSignificantExpenseDetails">
        <link:definition>9955546 - Disclosure - Segment Disclosures - Schedule of Significant Expense (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="SubsequentEventsDetails" roleURI="http://vitaltherapies.com/role/SubsequentEventsDetails">
        <link:definition>9955547 - Disclosure - Subsequent Events (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
    </xs:appinfo>
  </xs:annotation>
  <xs:element id="vtl_February2026PIPETransactionMember" abstract="true" name="February2026PIPETransactionMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="vtl_May2025PIPETransactionMember" abstract="true" name="May2025PIPETransactionMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="vtl_SeriesBWarrantsMember" abstract="true" name="SeriesBWarrantsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="vtl_PreFundedWarrantsMember" abstract="true" name="PreFundedWarrantsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="vtl_ScheduleOfCommonStockReservedForFutureIssuanceTableTextBlock" abstract="false" name="ScheduleOfCommonStockReservedForFutureIssuanceTableTextBlock" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:textBlockItemType"/>
  <xs:element id="vtl_AccountingPoliciesTable" abstract="true" name="AccountingPoliciesTable" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrldt:hypercubeItem" type="xbrli:stringItemType"/>
  <xs:element id="vtl_NumberOfDevelopmentPrograms" abstract="false" name="NumberOfDevelopmentPrograms" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="xbrli:integerItemType"/>
  <xs:element id="vtl_January2024PreFundedWarrantsMember" abstract="true" name="January2024PreFundedWarrantsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="vtl_May2025PreFundedWarrantsMember" abstract="true" name="May2025PreFundedWarrantsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="vtl_February2026PreFundedWarrantsMember" abstract="true" name="February2026PreFundedWarrantsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="vtl_NumberOfFinancialInstitutionsUsedForCashDeposits" abstract="false" name="NumberOfFinancialInstitutionsUsedForCashDeposits" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="xbrli:integerItemType"/>
  <xs:element id="vtl_GovernmentAssistanceQualifiedResearchAndDevelopmentExpendituresPercent" abstract="false" name="GovernmentAssistanceQualifiedResearchAndDevelopmentExpendituresPercent" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="vtl_GovernmentAssistanceQualifiedResearchAndDevelopmentExpendituresMaximumAmount" abstract="false" name="GovernmentAssistanceQualifiedResearchAndDevelopmentExpendituresMaximumAmount" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="vtl_LesseeOperatingLeasesNumberOfExistingLeases" abstract="false" name="LesseeOperatingLeasesNumberOfExistingLeases" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="xbrli:integerItemType"/>
  <xs:element id="vtl_PlacementAgentWarrantsMember" abstract="true" name="PlacementAgentWarrantsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="vtl_PrepaidClinicalAndRelatedCostsCurrent" abstract="false" name="PrepaidClinicalAndRelatedCostsCurrent" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="vtl_ResearchAndDevelopmentGrant" abstract="false" name="ResearchAndDevelopmentGrant" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="vtl_ClinicalCostsPayableCurrent" abstract="false" name="ClinicalCostsPayableCurrent" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="vtl_LegalAndAuditCostsPayableCurrent" abstract="false" name="LegalAndAuditCostsPayableCurrent" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="vtl_AccruedClinicalCostsCurrent" abstract="false" name="AccruedClinicalCostsCurrent" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="vtl_AccruedLegalAndAuditCostsCurrent" abstract="false" name="AccruedLegalAndAuditCostsCurrent" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="vtl_AccruedCompensationCurrent" abstract="false" name="AccruedCompensationCurrent" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="vtl_StockOptionsIssuedSubjectToSharesAvailable" abstract="false" name="StockOptionsIssuedSubjectToSharesAvailable" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="vtl_NewYorkCityMember" abstract="true" name="NewYorkCityMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="vtl_PlaneggGermanyMember" abstract="true" name="PlaneggGermanyMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="vtl_OperatingLeaseIncrementalBorrowingRate" abstract="false" name="OperatingLeaseIncrementalBorrowingRate" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="vtl_OperatingAndVariableLeasesCost" abstract="false" name="OperatingAndVariableLeasesCost" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="vtl_LesseeOperatingLeaseLiabilityPaymentsDueAfterYearFour" abstract="false" name="LesseeOperatingLeaseLiabilityPaymentsDueAfterYearFour" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="vtl_A2019OmnibusEquityIncentivePlanMember" abstract="true" name="A2019OmnibusEquityIncentivePlanMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="vtl_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsProbabilityRateLiquidationEventOccurringEstimated" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsProbabilityRateLiquidationEventOccurringEstimated" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="vtl_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsProbabilityRateLiquidationEventNotOccurringEstimated" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsProbabilityRateLiquidationEventNotOccurringEstimated" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="vtl_December2020ATMMember" abstract="true" name="December2020ATMMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="vtl_May2022ATMMember" abstract="true" name="May2022ATMMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="vtl_May2024ATMMember" abstract="true" name="May2024ATMMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="vtl_April2025AndMay2025FinancingMember" abstract="true" name="April2025AndMay2025FinancingMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="vtl_MaximumAggregateOfferingPriceOfSecuritiesUnderShelfRegistration" abstract="false" name="MaximumAggregateOfferingPriceOfSecuritiesUnderShelfRegistration" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="vtl_UnsoldSecuritiesRolledOverToBeSoldUnderNewShelfRegistration" abstract="false" name="UnsoldSecuritiesRolledOverToBeSoldUnderNewShelfRegistration" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="vtl_SaleOfStockRemainingCapacity" abstract="false" name="SaleOfStockRemainingCapacity" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="vtl_ShelfRegistrationTerminationPriorWrittenNoticeNumberOfDays" abstract="false" name="ShelfRegistrationTerminationPriorWrittenNoticeNumberOfDays" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="xbrli:integerItemType"/>
  <xs:element id="vtl_SalesOfStockCommissionsPercentOfGrossProceeds" abstract="false" name="SalesOfStockCommissionsPercentOfGrossProceeds" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="vtl_May2025SeriesBWarrantsMember" abstract="true" name="May2025SeriesBWarrantsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="vtl_February2026CommonWarrantsMember" abstract="true" name="February2026CommonWarrantsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="vtl_EmployeeStockOptionsforFutureGrantMember" abstract="true" name="EmployeeStockOptionsforFutureGrantMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="vtl_A2021EmployeeStockPurchasePlanMember" abstract="true" name="A2021EmployeeStockPurchasePlanMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="vtl_A2017InducementEquityIncentivePlanMember" abstract="true" name="A2017InducementEquityIncentivePlanMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="vtl_TwoThousandNineteenOmnibusEquityIncentivePlanMember" abstract="true" name="TwoThousandNineteenOmnibusEquityIncentivePlanMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="vtl_PlacementAgencyAgreementMember" abstract="true" name="PlacementAgencyAgreementMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="vtl_RoyaltyPurchaseAgreementMember" abstract="true" name="RoyaltyPurchaseAgreementMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="vtl_SecuritiesPurchaseAgreementMember" abstract="true" name="SecuritiesPurchaseAgreementMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="vtl_OfferingMember" abstract="true" name="OfferingMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="vtl_SeriesAWarrantsMember" abstract="true" name="SeriesAWarrantsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="vtl_SeriesAWarrantAndSeriesBWarrantMember" abstract="true" name="SeriesAWarrantAndSeriesBWarrantMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="vtl_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRightsConsecutiveTradingDayPeriod" abstract="false" name="ClassOfWarrantOrRightExercisePriceOfWarrantsOrRightsConsecutiveTradingDayPeriod" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="vtl_PlacementAgentAgreementBrokerageFeePercent" abstract="false" name="PlacementAgentAgreementBrokerageFeePercent" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="vtl_ClassOfWarrantOrRightAggregateRoyaltyFeePercentage" abstract="false" name="ClassOfWarrantOrRightAggregateRoyaltyFeePercentage" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:pureItemType"/>
  <xs:element id="vtl_ProceedsFromIssuanceOfCommonStockNetOfOfferingExpenses" abstract="false" name="ProceedsFromIssuanceOfCommonStockNetOfOfferingExpenses" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="vtl_ClassOfWarrantOrRightExpirationPeriodFromTheDateOfIssuance" abstract="false" name="ClassOfWarrantOrRightExpirationPeriodFromTheDateOfIssuance" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="vtl_NumberOfVotesPerEachShareOfCommonStock" abstract="false" name="NumberOfVotesPerEachShareOfCommonStock" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="xbrli:integerItemType"/>
  <xs:element id="vtl_May2025PreFundedWarrantsOfferingMember" abstract="true" name="May2025PreFundedWarrantsOfferingMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="vtl_TwoThousandNineteenOmnibusEquityIncentivePlanEvergreenProvisionMember" abstract="true" name="TwoThousandNineteenOmnibusEquityIncentivePlanEvergreenProvisionMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="vtl_StockAppreciationRightsSARsPlanMember" abstract="true" name="StockAppreciationRightsSARsPlanMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="vtl_TwoThousandFourteenEquityIncentivePlanMember" abstract="true" name="TwoThousandFourteenEquityIncentivePlanMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="vtl_A2026InducementEquityCompensationPlanMember" abstract="true" name="A2026InducementEquityCompensationPlanMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="vtl_IncentiveEmployeeStockOptionMember" abstract="true" name="IncentiveEmployeeStockOptionMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="vtl_NonStatutoryEmployeeStockOptionMember" abstract="true" name="NonStatutoryEmployeeStockOptionMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="vtl_NonEmployeeMember" abstract="true" name="NonEmployeeMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="vtl_EmployeeMember" abstract="true" name="EmployeeMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="vtl_ShareBasedCompensationArrangementByShareBasedPaymentAwardAdditionalSharesAuthorizedPercent" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardAdditionalSharesAuthorizedPercent" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="vtl_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfTranches" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfTranches" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="xbrli:integerItemType"/>
  <xs:element id="vtl_DuaneNashMember" abstract="true" name="DuaneNashMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="vtl_ExecutiveChairmanAgreementMember" abstract="true" name="ExecutiveChairmanAgreementMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="vtl_SalaryAndWageOfficerMonthlyBaseSalary" abstract="false" name="SalaryAndWageOfficerMonthlyBaseSalary" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="vtl_ReportableSegmentMember" abstract="true" name="ReportableSegmentMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="vtl_ClinicalProductCandidates" abstract="false" name="ClinicalProductCandidates" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="vtl_PreClinicalProductCandidates" abstract="false" name="PreClinicalProductCandidates" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="vtl_SalaryAndWageRetentionBonusAgreement" abstract="false" name="SalaryAndWageRetentionBonusAgreement" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="vtl_SalaryAndWageRetentionBonusAgreementTerminationPayoutPeriod" abstract="false" name="SalaryAndWageRetentionBonusAgreementTerminationPayoutPeriod" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
</xs:schema>
