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                          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.