United States securities and exchange commission logo May 3, 2022 Nick Leschly President and Chief Executive Officer 2seventy bio, Inc. 60 Binney Street Cambridge, Massachusetts 02142 Re: 2seventy bio, Inc. Registration Statement on Form S-1 Filed April 28, 2022 File No. 333-264544 Dear Mr. Leschly: This is to advise you that we have not reviewed and will not review your registration statement. Please refer to Rules 460 and 461 regarding requests for acceleration. We remind you that the company and its management are responsible for the accuracy and adequacy of their disclosures, notwithstanding any review, comments, action or absence of action by the staff. Please contact Michael Davis at 202-551-4385 with any questions. Sincerely, Division of Corporation Finance Office of Life Sciences cc: Yasin E. Akbari, Esq.