X0306 4 2016-09-06 0 0001650664 Editas Medicine, Inc. EDIT 0001192603 STARR KEVIN P C/O THIRD ROCK VENTURES, LLC 29 NEWBURY STREET, 3RD FLOOR BOSTON MA 02116 0 0 1 0 Common Stock 2016-09-06 4 S 0 5890 15.9025 D 0 D Common Stock 3906176 I See Footnote Such shares were received as a distribution from Third Rock Ventures III, L.P. ("TRV III") on August 16, 2016 in a transaction exempt pursuant to Rule 16a-13 and Rule 16a-9. These shares are directly held by TRV III. The general partner of TRV III is Third Rock Ventures GP III, L.P. ("TRV GP III"). The general partner of TRV GP III is TRV GP III, LLC ("TRV GP III LLC"). The individual managers of TRV GP III LLC are the Reporting Person, Mark Levin ("Levin") and Dr. Robert Tepper ("Tepper"). Each of TRV GP III, TRV GP III LLC, the Reporting Person, Levin and Tepper disclaims beneficial ownership of the shares except to the extent of its or his pecuniary interest therein, if any, and this report shall not be deemed an admission that it or he is the beneficial owner of such shares. /s/ Kevin Gillis by power of attorney for Kevin Starr 2016-09-07