X0306 4 2022-05-31 1 0001651431 Checkmate Pharmaceuticals, Inc. CMPI 0001202793 POWELL MICHAEL C/O CHECKMATE PHARMACEUTICALS, INC. 245 MAIN STREET, 2ND FLOOR CAMBRIDGE MA 02142 1 0 0 0 Stock Option (Right to Buy) 5.19 2022-05-31 4 D 0 30000 D 2031-08-09 Common Stock 30000 0 D Stock Option (Right to Buy) 6.27 2022-05-31 4 D 0 10030 D 2031-06-16 Common Stock 10030 0 D Stock Option (Right to Buy) 10.95 2022-05-31 5 D 0 E 30000 D 2030-11-09 Common Stock 30000 0 D At the effective time of the merger contemplated by the Agreement and Plan of Merger dated April 18, 2022, among Checkmate Pharmaceuticals, Inc. (the "Issuer"), Regeneron Pharmaceuticals, and Scandinavian Acquisition Sub, Inc. (the "Merger"), each option granted by the Issuer to purchase Issuer Common Stock, whether or not vested, which has a per share exercise price that is less than $10.50 (each, an "In the Money Issuer Option") that was outstanding and unexercised as of immediately prior to the effective time of the Merger was cancelled and automatically converted into the right to receive an amount in cash equal to the product of (1) the total number of Issuer Common Stock subject to such In the Money Issuer Option and (2) the excess of $10.50 over the exercise price of such In the Money Issuer Option, subject to any required withholding of taxes. At the effective time of the Merger, each option granted by the Issuer to purchase Issuer Common Stock which has a per share exercise price greater than or equal to $10.50 that was outstanding and unexercised as of immediately prior to the effective time of the Merger was cancelled with no consideration payable. /s/ Kleem Chaudhary, attorney-in-fact 2022-05-31