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                             December 23, 2020

       Geoff McDonough, M.D.
       President and Chief Executive Officer
       Generation Bio Co.
       301 Binney Street
       Cambridge, MA 02142

                                                        Re: Generation Bio Co.
                                                            Draft Registration
Statement on Form S-1
                                                            Submitted December
21, 2020
                                                            CIK No. 0001733294

       Dear Dr. McDonough:

                                                        This is to advise you
that we do not intend to review your registration statement.

               We request that you publicly file your registration statement no
later than 48 hours prior
       to the requested effective date and time. 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 Abby
Adams at (202) 551-6902 with any questions.




                             Sincerely,


                             Division of Corporation Finance

                             Office of Life Sciences
       cc:                                              Stuart Falber, Esq.