X0306 4 2016-02-08 0 0001650664 Editas Medicine, Inc. EDIT 0001665594 Polaris Venture Management Co. VI, L.L.C. 1000 WINTER STREET, SUITE 3350 WALTHAM MA 02451 0 0 1 0 0001493463 Polaris Venture Partners VI, L.P. 1000 WINTER STREET, SUITE 3350 WALTHAM MA 02451 0 0 1 0 0001575691 Polaris Venture Partners Founders' Fund VI, L.P. 1000 WINTER STREET, SUITE 3350 WALTHAM MA 02451 0 0 1 0 Common Stock 2016-02-08 4 C 0 2549435 A 2549435 I See Footnote Common Stock 2016-02-08 4 C 0 2021269 A 4570704 I See Footnote Common Stock 2016-02-08 4 C 0 85469 A 4656173 I See Footnote Series A-1 Preferred Stock 2016-02-08 4 C 0 6628542 0.00 D Common Stock 2549435 0 I See Footnote Series A-2 Preferred Stock 2016-02-08 4 C 0 5255300 0.00 D Common Stock 2021269 0 I See Footnote Series B Preferred Stock 2016-02-08 4 C 0 222222 0.00 D Common Stock 85469 0 I See Footnote The Series A-1, Series A-2 and Series B Preferred Stock converted into Common Stock on a 2.6-for-one basis upon the closing of the Issuer's initial public offering without payment of consideration. The Series A-1, Series A-2 and Series B Preferred Stock were convertible at any time at the holder's election and automatically upon the closing of the Issuer's initial public offering. The shares had no expiration date. These shares are owned directly by Polaris Venture Partners VI, L.P. and Polaris Venture Partners Founders' Fund VI, L.P. (together with Polaris Venture Partners VI, L.P., the "Polaris Funds"). Polaris Venture Management Co. VI, L.L.C. ("Polaris Management") is the general partner of the Polaris Funds. Kevin Bitterman has an assignee interest in Polaris Management. Kevin Bitterman disclaims beneficial ownership of all the shares held by the Polaris Funds except to the extent of his pecuniary interest therein. /s/ Mary Blair, Attorney-in-Fact for Polaris Venture Management Co. VI, L.L.C. 2016-02-09 /s/ Mary Blair, Attorney-in-Fact for Polaris Venture Management Co. VI, L.L.C., the General Partner of Polaris Venture Partners VI, L.P. 2016-02-09 /s/ Mary Blair, Attorney-in-Fact for Polaris Venture Management Co. VI, L.L.C., the General Partner of Polaris Venture Partners Founders' Fund VI, L.P. 2016-02-09