Nature of the Business	6 Months Ended
Jun. 30, 2025
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 focused on developing and commercializing innovative therapeutics aimed at becoming the standard of care for prevalent retinal diseases for which there is a major unmet medical need. The Company is developing TH103, a novel, clinical-stage anti-vascular endothelial growth factor (“VEGF”) drug, engineered to potentially provide longer lasting and increased anti-VEGF activity in patients with exudative and 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 14, “Related Parties,” 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 six months ended June 30, 2025 and 2024, the Company incurred net losses of $21.5 million and $9.1 million, respectively. During the six months ended June 30, 2025 and 2024, the Company had negative cash flows from operations of $20.0 million and $8.5 million, respectively. As of June 30, 2025 and December 31, 2024, the Company had an accumulated deficit of $138.1 million and $116.6 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”), and from cash and cash equivalents of AlloVir received in the Merger. As of June 30, 2025, the Company had cash and cash equivalents of $88.4 million. The Company expects that the existing cash and cash equivalents 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

6 Months Ended

Jun. 30, 2025

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 focused on developing and commercializing innovative therapeutics aimed at becoming the standard of care for prevalent retinal diseases for which there is a major unmet medical need. The Company is developing TH103, a novel, clinical-stage anti-vascular endothelial growth factor (“VEGF”) drug, engineered to potentially provide longer lasting and increased anti-VEGF activity in patients with exudative and 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 14, “Related Parties,” 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 six months ended June 30, 2025 and 2024, the Company incurred net losses of $21.5 million and $9.1 million, respectively. During the six months ended June 30, 2025 and 2024, the Company had negative cash flows from operations of $20.0 million and $8.5 million, respectively. As of June 30, 2025 and December 31, 2024, the Company had an accumulated deficit of $138.1 million and $116.6 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”), and from cash and cash equivalents of AlloVir received in the Merger.

As of June 30, 2025, the Company had cash and cash equivalents of $88.4 million. The Company expects that the existing cash and cash equivalents 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.