Nature of the Business	3 Months Ended
Mar. 31, 2026
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Nature of the Business	1. Nature of the Business Description of the Business Kalaris Therapeutics, Inc. (“Kalaris” or “the Company”) is a clinical stage biopharmaceutical company dedicated to the development and commercialization of treatments for prevalent retinal diseases with major unmet medical needs. The Company is developing TH103, a novel, clinical stage anti-vascular endothelial growth factor (“VEGF”) drug, specifically engineered to achieve extended intraocular retention with enhanced VEGF inhibition in patients with exudative and/or neovascular retinal diseases. On March 18, 2025 (the “Closing Date”), AlloVir, Inc., a Delaware corporation (“AlloVir”), consummated the previously announced merger (the “Merger”) pursuant to the terms of the Agreement and Plan of Merger, dated as of November 7, 2024 (the “Merger Agreement”), by and among AlloVir, Aurora Merger Sub, Inc., a Delaware corporation and wholly-owned subsidiary of AlloVir (“Merger Sub”) and Kalaris Tx, Inc. (formerly Kalaris Therapeutics, Inc.), a Delaware corporation (“Legacy Kalaris”). At the effective time of the Merger (the “Effective Time”), Merger Sub merged with and into Legacy Kalaris, with Legacy Kalaris continuing as a wholly-owned subsidiary of AlloVir and the surviving corporation of the Merger and, after giving effect to the Merger, Legacy Kalaris became a wholly-owned subsidiary of AlloVir. Immediately following the Effective Time, AlloVir changed its name to “Kalaris Therapeutics, Inc.” At the Effective Time, the Company’s business became primarily the business conducted by Legacy Kalaris. The Company's common stock, which was previously listed on The Nasdaq Capital Market and traded under the ticker symbol “ALVR” through the close of business on the Closing Date, commenced trading on The Nasdaq Global Market under the ticker symbol “KLRS” on March 19, 2025. Refer to Note 3, “Merger with AlloVir”, for further details of the Merger. Samsara BioCapital L.P. and its affiliates (collectively, “Samsara”), the Company's majority stockholder and a related party, have provided Legacy Kalaris with significant equity and debt financing since its inception, and management and operational support services to the Company. Refer to Note 15 for further details of the related party transactions with Samsara. Liquidity The Company has incurred significant losses and negative cash flows from operations since its inception. During the three months ended March 31, 2026 and 2025 , the Company incurred net losses of $10.9 million and $10.2 million, respectively. During the three months ended March 31, 2026 and 2025, the Company had negative cash flows from operations of $11.6 million and $7.4 million, respectively. As of March 31, 2026 and December 31, 2025, the Company had an accumulated deficit of $170.9 million and $160.0 million, respectively. The Company expects to continue to incur substantial losses for the foreseeable future, and its ability to achieve and sustain profitability will depend on the successful development, approval, and commercialization of product candidates and on the achievement of sufficient revenues to support the Company’s operations. Since its inception, the Company has funded its operations primarily with proceeds from sales of its redeemable convertible preferred stock, issuances of convertible promissory notes and a simple agreement for future equity (“SAFE”), from cash and cash equivalents of AlloVir received in the Merger, and with proceeds from the 2025 Private Placement (as defined below). Refer to Note 12 for further details of the 2025 Private Placement. As of March 31, 2026, the Company had cash, cash equivalents and marketable securities of $104.9 million. The Company expects that the existing cash, cash equivalents and marketable securities will be sufficient to fund its operating expenses and capital expenditure requirements for at least twelve months from the issuance date of these condensed consolidated financial statements. The Company will need to raise additional financing to continue its product's development for the foreseeable future until it becomes profitable. The Company plans to monitor expenses and raise additional capital through a combination of equity and debt financings, strategic alliances, and licensing arrangements. The Company’s ability to access capital when needed is not assured and, if capital is not available to the Company when, and in the amounts needed, the Company may be required to significantly curtail, delay or discontinue one or more of its research or development programs or the commercialization of any product candidate, or be unable to expand its operations or otherwise capitalize on the Company’s business opportunities, as desired, which could materially harm the Company’s business, financial condition and results of operations.

Nature of the Business

3 Months Ended

Mar. 31, 2026

Organization, Consolidation and Presentation of Financial Statements [Abstract]

1. Nature of the Business

Description of the Business

Kalaris Therapeutics, Inc. (“Kalaris” or “the Company”) is a clinical stage biopharmaceutical company dedicated to the development and commercialization of treatments for prevalent retinal diseases with major unmet medical needs. The Company is developing TH103, a novel, clinical stage anti-vascular endothelial growth factor (“VEGF”) drug, specifically engineered to achieve extended intraocular retention with enhanced VEGF inhibition in patients with exudative and/or neovascular retinal diseases.

On March 18, 2025 (the “Closing Date”), AlloVir, Inc., a Delaware corporation (“AlloVir”), consummated the previously announced merger (the “Merger”) pursuant to the terms of the Agreement and Plan of Merger, dated as of November 7, 2024 (the “Merger Agreement”), by and among AlloVir, Aurora Merger Sub, Inc., a Delaware corporation and wholly-owned subsidiary of AlloVir (“Merger Sub”) and Kalaris Tx, Inc. (formerly Kalaris Therapeutics, Inc.), a Delaware corporation (“Legacy Kalaris”). At the effective time of the Merger (the “Effective Time”), Merger Sub merged with and into Legacy Kalaris, with Legacy Kalaris continuing as a wholly-owned subsidiary of AlloVir and the surviving corporation of the Merger and, after giving effect to the Merger, Legacy Kalaris became a wholly-owned subsidiary of AlloVir. Immediately following the Effective Time, AlloVir changed its name to “Kalaris Therapeutics, Inc.” At the Effective Time, the Company’s business became primarily the business conducted by Legacy Kalaris. The Company's common stock, which was previously listed on The Nasdaq Capital Market and traded under the ticker symbol “ALVR” through the close of business on the Closing Date, commenced trading on The Nasdaq Global Market under the ticker symbol “KLRS” on March 19, 2025. Refer to Note 3, “Merger with AlloVir”, for further details of the Merger.

Samsara BioCapital L.P. and its affiliates (collectively, “Samsara”), the Company's majority stockholder and a related party, have provided Legacy Kalaris with significant equity and debt financing since its inception, and management and operational support services to the Company. Refer to Note 15 for further details of the related party transactions with Samsara.

Liquidity

The Company has incurred significant losses and negative cash flows from operations since its inception. During the three months ended March 31, 2026 and 2025 , the Company incurred net losses of $10.9 million and $10.2 million, respectively. During the three months ended March 31, 2026 and 2025, the Company had negative cash flows from operations of $11.6 million and $7.4 million, respectively. As of March 31, 2026 and December 31, 2025, the Company had an accumulated deficit of $170.9 million and $160.0 million, respectively. The Company expects to continue to incur substantial losses for the foreseeable future, and its ability to achieve and sustain profitability will depend on the successful development, approval, and commercialization of product candidates and on the achievement of sufficient revenues to support the Company’s operations.

Since its inception, the Company has funded its operations primarily with proceeds from sales of its redeemable convertible preferred stock, issuances of convertible promissory notes and a simple agreement for future equity (“SAFE”), from cash and cash equivalents of AlloVir received in the Merger, and with proceeds from the 2025 Private Placement (as defined below). Refer to Note 12 for further details of the 2025 Private Placement.

As of March 31, 2026, the Company had cash, cash equivalents and marketable securities of $104.9 million. The Company expects that the existing cash, cash equivalents and marketable securities will be sufficient to fund its operating expenses and capital expenditure requirements for at least twelve months from the issuance date of these condensed consolidated financial statements.

The Company will need to raise additional financing to continue its product's development for the foreseeable future until it becomes profitable. The Company plans to monitor expenses and raise additional capital through a combination of equity and debt financings, strategic alliances, and licensing arrangements. The Company’s ability to access capital when needed is not assured and, if capital is not available to the Company when, and in the amounts needed, the Company may be required to significantly curtail, delay or discontinue one or more of its research or development programs or the commercialization of any product candidate, or be unable to expand its operations or otherwise capitalize on the Company’s business opportunities, as desired, which could materially harm the Company’s business, financial condition and results of operations.