X0306 4 2017-05-22 0 0001650664 Editas Medicine, Inc. EDIT 0001591747 Bitterman Kevin ONE MARINA PARK DRIVE, 10 FLOOR BOSTON MA 02210 1 0 0 0 Common Stock 2017-05-22 4 S 0 1000000 17.00 D 2797144 I See Footnote Represents 944,789 shares disposed of by Polaris Venture Partners VI, L.P. ("PVP VI") and 55,211 shares disposed of by Polaris Venture Partners Founders' Fund VI, L.P. ("PVPFF VI", together with PVPVI, the "Polaris Funds"). 2,642,714 of these shares are owned directly by PVP VI and 154,430 of the shares are owned by PVPFF VI. Polaris Venture Management Co. VI, L.L.C. ("Polaris Management") is the general partner of each of the Polaris Funds. Kevin Bitterman, a member of the Board of Directors of the Issuer, has an assignee interest in Polaris Management. Each of Polaris Management and Mr. Bitterman disclaim beneficial ownership of all the shares owned by the Polaris Funds and this report shall not be deemed an admission that either is the beneficial owner of such shares for purposes of Section 16 or for any other purpose, except to the extent of their pecuniary interests therein. /s/ Max Eisenberg 2017-05-24