Sesen Bio

About Sesen Bio

Sesen Bio, Inc., initially founded as Eleven Biotherapeutics in 2008, operated as a late-stage clinical company concentrating on the development of targeted fusion protein therapeutics for cancer patients. The company's formation was backed by co-leads Flagship Ventures and Third Rock Ventures, who provided an initial $35 million in Series A financing. In May 2018, Eleven Biotherapeutics rebranded to Sesen Bio to reflect its strategic shift and commitment to oncology, subsequently changing its Nasdaq ticker symbol from EBIO to SESN. The company was led by President and CEO Dr. Thomas Cannell, a veteran from Merck & Co. and Orexigen Therapeutics.

The company's business model centered on the research, development, and eventual commercialization of its therapeutic products. Its most advanced product candidate was Vicineum™ (also known as VB4-845), a locally administered targeted fusion protein designed for patients with non-muscle invasive bladder cancer (NMIBC). Vicineum works by combining an anti-epithelial cell adhesion molecule (EpCAM) antibody fragment with a truncated form of Pseudomonas Exotoxin A, a cytotoxin, to specifically target and eliminate cancer cells. In February 2021, the U.S. Food and Drug Administration (FDA) accepted Sesen Bio's Biologics License Application (BLA) for Vicineum and granted it Priority Review. However, in August 2021, the FDA issued a Complete Response Letter, declining to approve the BLA in its existing form and requesting additional data.

Following the regulatory setback and a reassessment of the development timeline and costs for an additional trial, Sesen Bio voluntarily paused further U.S. development of Vicineum in July 2022. This decision prompted the company's board to explore strategic alternatives to maximize shareholder value. After a review process that included outreach to over 100 parties and consideration of 42 bids, Sesen Bio entered into a definitive merger agreement with Carisma Therapeutics in September 2022. The all-stock transaction closed in March 2023, with the combined entity operating under the Carisma Therapeutics name and trading under the ticker "CARM". The new company focuses on advancing Carisma's cell therapy platform, which utilizes engineered macrophages and monocytes for cancer treatment.