On June 2, 2022, William Sellers, M.D. informed 2seventy bio, Inc. of his intention to resign as a member of the Company's Board of Directors, effective June 3, 2022. Dr. Sellers's decision to resign from the Board did not result from any disagreement with the Company on any matter relating to its operations, policies, or practices. Following his resignation from the Board, Dr. Sellers will begin serving as a scientific and technical consultant to the Company.