X0306 4 2016-11-16 0 0001650664 Editas Medicine, Inc. EDIT 0001665594 Polaris Venture Management Co. VI, L.L.C. ONE MARINA PARK DRIVE, 10TH FLOOR BOSTON MA 02210 0 0 1 0 0001493463 Polaris Venture Partners VI, L.P. ONE MARINA PARK DRIVE, 10TH FLOOR BOSTON MA 02210 0 0 1 0 0001575691 Polaris Venture Partners Founders' Fund VI, L.P. ONE MARINA PARK DRIVE, 10TH FLOOR BOSTON MA 02210 0 0 1 0 Common Stock 2016-11-16 4 S 0 30830 16.30 D 4036443 I See Footnote Represents 29,128 shares disposed of by Polaris Venture Partners VI, L.P. ("PVP VI") and 1,702 shares disposed of by Polaris Venture Partners Founders' Fund VI, L.P ("PVPFF VI"). The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $16.25 to $16.5167, inclusive. The Reporting Person undertakes to provide to the Issuer, any security holder of the Issuer or the staff of the Securities Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote (2) to this Form 4. 3,813,590 of these shares are owned directly by PVP VI and 222,853 of the shares are owned by PVPFF VI (together with PVP VI, the "Polaris Funds"). 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, Attorney-in-Fact for Polaris Venture Partners VI, L.P. 2016-11-17 /s/ Max Eisenberg, Attorney-in-Fact for Polaris Venture Partners Founders' Fund VI, L.P. 2016-11-17 /s/ Max Eisenberg, Attorney-in-Fact for Polaris Venture Management Co. VI, L.L.C. 2016-11-17