Editas Medicine, Inc. — Director's Dealing 2016

Feb 9, 2016

SEC Form 3 — Initial Statement of Beneficial Ownership

Issuer: Editas Medicine, Inc. (EDIT)
CIK: 0001650664
Period of Report: 2016-02-08

Reporting Person: VIKING GLOBAL PERFORMANCE LLC (10% Owner)
Reporting Person: Viking Global Equities LP (10% Owner)
Reporting Person: Viking Global Equities II LP (10% Owner)
Reporting Person: VGE III Portfolio Ltd. (10% Owner)
Reporting Person: Viking Long Fund Master Ltd. (10% Owner)
Reporting Person: Viking Long Fund GP LLC (10% Owner)

Holdings (Non-Derivative)

Security	Shares	Ownership
Common Stock	1020407	Indirect
Common Stock	256986	Direct
Common Stock	15072	Direct
Common Stock	481567	Direct
Common Stock	266782	Direct

Footnotes

F1: O. Andreas Halvorsen, David C. Ott and Daniel S. Sundheim are Executive Committee members of certain management entities, including Viking Global Investors LP ("VGI"), Viking Global Performance LLC ("VGP") and Viking Long Fund GP LLC ("VLFGP"). VGI provides managerial services to various investment funds, including Viking Global Equities LP ("VGE"), Viking Global Equities II LP ("VGE II") and VGE III Portfolio Ltd. ("VGE III"). VGP is the general partner of VGE and VGE II and the investment manager of VGE III. VLFGP serves as the investment manager of Viking Long Fund Master Ltd. ("VLFM" and, together with VGE, VGE II and VGE III, the "Viking Funds" and the Viking Funds together with VGP and VLFGP, the "Reporting Persons"). Each of the Reporting Persons may be deemed to beneficially own the shares reported on this form. VGI and Messrs. Halvorsen, Ott and Sundheim filed a Form 3 in respect of the Issuer on February 2, 2016.

F2: VGI provides managerial services to (i) VGE, which directly holds 256,986 shares of common stock of the Issuer ("Common Stock"); (ii) VGE II, which directly holds 15,072 shares of Common Stock; (iii) VGE III, which directly holds 481,567 shares of Common Stock; and (iv) VLFM, which directly holds 266,782 shares of Common Stock. Because of the relationship between VGI and VGE, VGE II, VGE III and VLFM, VGI may be deemed to beneficially own the shares of Common Stock directly held by VGE, VGE II, VGE III and VLFM.

F3: VGP is the general partner of VGE and VGE II and the investment manager of VGE III. Because of the relationships between VGP and VGE, VGE II and VGE III, respectively, VGP may be deemed to beneficially own the shares of Common Stock directly held by VGE, VGE II and VGE III.

F4: VLFGP serves as the investment manager of VLFM. Because of the relationship between VLFGP and VLFM, VLFGP may be deemed to beneficially own the shares of Common Stock directly held by VLFM.

F5: The Reporting Persons disclaim beneficial ownership of these securities except to the extent of their pecuniary interest therein, and the inclusion of these securities in this report shall not be deemed an admission of beneficial ownership of the reported securities for purposes of Section 16 or for any other purpose.

F6: On February 8, 2016, the Viking Funds acquired an aggregate of 1,000,000 shares of Common Stock at a price of $16.00 per share in connection with the Issuer's initial public offering ("IPO"). VGE acquired 256,986 shares in the IPO, VGE III acquired 481,567 shares in the IPO and VLFM acquired 261,447 shares in the IPO.

F7: On February 8, 2016, the Viking Funds acquired an aggregate of 20,407 shares of Common Stock at a purchase price of $18.00 per share in open-market transactions following the IPO. VGE II acquired 15,072 of such shares and VLFM acquired 5,335 of such shares.