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Merger with Sesen Bio - Schedule of Net Assets Acquired in the Merger (Details) $ in Thousands | 10 Months Ended |  |  |
--- | --- | --- | --- | ---
Dec. 31, 2023 USD ($) shares | Jun. 30, 2025 shares | Dec. 31, 2024 stockholder shares | Mar. 07, 2023 USD ($) shares
Merger with Sesen Bio |  |  |  |
Number of board seats | stockholder |  |  | 7 |
Entity common stock, shares outstanding immediately after merger (in shares) | shares | 40,609,915 | 41,788,096 | 41,750,109 |
Cash and cash equivalents |  |  |  | $ 37,873
Marketable securities |  |  |  | 44,588
Prepaid expenses and other assets |  |  |  | 1,316
Restricted cash |  |  |  | 30
Accounts payable and accrued expenses |  |  |  | (3,499)
Total net assets acquired |  |  |  | 80,308
Less: Transaction costs |  |  |  | (8,264)
Total net assets acquired less transaction costs |  |  |  | $ 72,044
Carisma Therapeutics Inc. |  |  |  |
Merger with Sesen Bio |  |  |  |
Number of board seats | stockholder |  |  | 6 |
Severance and personnel costs paid | $ 4,600 |  |  |
CARISMA Therapeutics Inc, Legacy, Stockholders | Carisma Therapeutics Inc. |  |  |  |
Merger with Sesen Bio |  |  |  |
Business acquisition percentage of voting interests acquired (as a percent) |  |  |  | 74.20%
Entity common stock, shares outstanding immediately after merger (in shares) | shares |  |  |  | 40,254,666

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