--Bradley L. Radoff and Michael Torok to Vote Shares in Support of Transaction

--Michael Torok to Join Carisma Board of Directors as Only Sesen Bio Representative

--Special Meeting of Stockholders to Approve Merger to be Held on March 2, 2023

Sesen Bio, Inc. (Nasdaq: SESN) and Carisma Therapeutics Inc. (Carisma), a privately-held, clinical stage biopharmaceutical company focused on discovering and developing innovative immunotherapies, today announced that the companies have reached a voting and support agreement (the "Support Agreement") with Bradley L. Radoff and Michael Torok (together with their respective affiliates, the "Investor Group"). The Investor Group, which beneficially owns approximately 8.7% of Sesen Bio's outstanding common stock, has committed to vote its shares in support of the pending merger.

In connection with the Support Agreement, Sesen Bio and Carisma have further amended the previously amended merger agreement announced on December 29, 2022, which has been unanimously approved by the Boards of Directors of both companies:

Increased the one-time special cash dividend expected to be paid to Sesen Bio stockholders to $75 million, $0.36 per share(1). This represents an increase from the expected special cash dividend of approximately $70 million, approximately $0.34 per share, under the first amendment to the merger agreement, and an increase from the up to $25 million special cash dividend under the terms of the original merger agreement; Extended the period of time for payments under the Contingent Value Right ("CVR") related to any potential proceeds from the sale of Vicineum and Sesen Bio's other legacy assets to March 31, 2027, from December 31, 2023, under the previous terms. Under the CVR, Sesen Bio stockholders remain entitled to any proceeds from the potential milestone payment under the Roche Asset Purchase Agreement; and Michael Torok will join the Carisma Board of Directors upon closing of the merger as the only Sesen Bio representative.