Sec Form 4/A Filing - VIKING GLOBAL PERFORMANCE LLC @ Editas Medicine, Inc. - 2016-02-08

FORM 4/A Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940

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1. Name and Address of Reporting Person VIKING GLOBAL PERFORMANCE LLC 2. Issuer Name and Ticker or Trading Symbol Editas Medicine, Inc. [ EDIT] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) _____ Director _____ 10% Owner _____ Officer (give title below) X __ Other (specify below) Former 10% Owner (Last) (First) (Middle) 55 RAILROAD AVENUE 3. Date of Earliest Transaction (MM/DD/YY) 02/08/2016 (Street) GREENWICH, CT06830 4. If Amendment, Date Original Filed (MM/DD/YY) 02/08/2016 6. Individual or Joint/Group Filing (Check Applicable Line) _____ Form filed by One Reporting Person __ X __ Form filed by More than One Reporting Person (City) (State) (Zip)

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned 1.Title of Security (Instr. 3) 2. Transaction Date (MM/DD/YY) 2A. Deemed Execution Date, if any (MM/DD/YY) 3. Transaction Code (Instr. 8) 4. Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5) 5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4) 6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4) 7. Nature of Indirect Beneficial Ownership (Instr. 4) Code V Amount (A) or (D) Price Common Stock 02/08/2015 C 1,709,401 A 1,709,401 I See explanation of responses ( 1 ) ( 2 ) ( 3 ) ( 6 ) ( 7 ) ( 8 ) Common Stock 02/08/2015 P 1,000,000 A 2,709,401 I See explanation of responses ( 1 ) ( 2 ) ( 3 ) ( 4 ) ( 5 ) ( 7 ) ( 9 ) Common Stock 02/08/2015 P 20,407 A 2,729,808 I See explanation of responses ( 1 ) ( 2 ) ( 3 ) ( 4 ) ( 5 ) ( 7 ) ( 10 ) Common Stock 02/08/2015 C 1,709,401 A 1,709,401 D ( 3 ) ( 7 ) ( 8 ) Common Stock 02/08/2015 P 256,986 A 256,986 D ( 3 ) ( 7 ) ( 9 ) Common Stock 02/08/2015 P 15,072 A 15,072 D ( 3 ) ( 7 ) ( 10 ) Common Stock 02/08/2015 P 481,567 A 481,567 D ( 3 ) ( 7 ) ( 9 ) Common Stock 02/08/2015 P 261,447 A 261,447 D ( 3 ) ( 7 ) ( 9 ) Common Stock 02/08/2015 P 5,335 A 266,782 D ( 3 ) ( 7 ) ( 10 )

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned ( e.g. , puts, calls, warrants, options, convertible securities) 1. Title of Derivative Security (Instr. 3) 2. Conversion or Exercise Price of Derivative Security 3. Transaction Date (MM/DD/YY) 3A. Deemed Execution Date, if any (MM/DD/YY) 4. Transaction Code (Instr. 8) 5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4, and 5) 6. Date Exercisable and Expiration Date (MM/DD/YY) 7. Title and Amount of Underlying Securities (Instr. 3 and 4) 8. Price of Derivative Security (Instr. 5) 9. Number of Derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4) 10. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 4) 11. Nature of Indirect Beneficial Ownership (Instr. 4) Code V (A) (D) Date Exercisable Expiration Date Title Amount or Number of Shares Series B Preferred Stock ( 8 ) 02/08/2016 C 4,444,444 ( 8 ) ( 8 ) Common Stock 1,709,401 ( 8 ) ( 8 ) 0 I See explanation of responses ( 1 ) ( 2 ) ( 3 ) ( 6 ) ( 7 ) ( 8 ) Series B Preferred Stock ( 8 ) 02/08/2016 C 4,444,444 ( 8 ) ( 8 ) Common Stock 1,709,401 ( 8 ) ( 8 ) 0 D ( 3 ) ( 7 ) ( 8 )

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other VIKING GLOBAL PERFORMANCE LLC 55 RAILROAD AVENUE GREENWICH, CT06830 Former 10% Owner Viking Global Equities LP 55 RAILROAD AVENUE GREENWICH, CT06830 Former 10% Owner Viking Global Equities II LP 55 RAILROAD AVENUE GREENWICH, CT06830 Former 10% Owner VGE III Portfolio Ltd. 55 RAILROAD AVENUE GREENWICH, CT06830 Former 10% Owner Viking Long Fund GP LLC 55 RAILROAD AVENUE GREENWICH, CT06830 Former 10% Owner Viking Long Fund Master Ltd. 55 RAILROAD AVENUE GREENWICH, CT06830 Former 10% Owner Signatures /s/ O. Andreas Halvorsen (11)(12) 02/09/2016 Signature of Reporting Person Date /s/ David C. Ott (11)(12) 02/09/2016 Signature of Reporting Person Date /s/ Daniel S. Sundheim (11)(12) 02/09/2016 Signature of Reporting Person Date

Explanation of Responses:

( 1 )O. Andreas Halvorsen, Davi d C. Ott and Daniel S. Sundheim are Executive Committee members of certain management entities, including Viking Global Partners LLC, the general partner of Viking Global Investors LP ("VGI"), Viking Global Performance LLC ("VGP"), Viking Long Fund GP LLC ("VLFGP") and Viking Global Opportunities GP LLC ("Opportunities GP"), the sole owner of Viking Global Opportunities Portfolio GP LLC ("Opportunities Portfolio GP"). VGI provides managerial services to various investment funds, including Viking Global Opportunities Illiquid Investments Sub-Master LP ("Opportunities Fund"), Viking Global Equities LP ("VGE"), Viking Global Equities II LP ("VGE II"), VGE III Portfolio Ltd. ("VGE III") and Viking Long Fund Master Ltd. ("VLFM," and together with VGE, VGE II, VGE III and Opportunities Fund, the "Viking Funds"). ( 2 )VGP is the general partner of VGE and VGE II and the investment manager of VGE III. Opportunities Portfolio GP is the general partner of Opportunities Fund. VLFGP serves as the investment manager of VLFM. Each of the Viking Funds, VGI, VGP, VLFGP, Opportunities GP, Opportunities Portfolio GP, Mr. Halvorsen, Mr. Ott and Mr. Sundheim (collectively, the "Reporting Persons") may be deemed to beneficially own the shares reported on this form. ( 3 )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; (iv) VLFM, which directly holds 266,782 shares of Common Stock; and (v) Opportunities Fund, which directly holds 1,709,401 shares of Common Stock. Because of the relationship between VGI and the Viking Funds, VGI may be deemed to beneficially own the shares of Common Stock directly held by the Viking Funds. ( 4 )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. ( 5 )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. ( 6 )Opportunities Portfolio GP is the general partner of Opportunities Fund. Because of the relationship between Opportunities Portfolio GP and Opportunities Fund, Opportunities Portfolio GP may be deemed to beneficially own the shares of Common Stock held directly by Opportunities Fund. Opportunities GP is the sole owner of Opportunities Portfolio GP. Because of the relationship between Opportunities GP and Opportunities Portfolio GP, Opportunities GP may be deemed to beneficially own the shares of Common Stock held directly by Opportunities Fund. ( 7 )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. ( 8 )On February 8, 2016, the 4,444,444 shares of Series B Preferred Stock held by Opportunities Fund automatically converted into 1,709,401 shares of Common Stock in connection with the Issuer's initial public offering ("IPO"). The conversion reflected an adjustment for a one-for-2.6 reverse stock split of the Common Stock. ( 9 )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 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. ( 10 )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.

Remarks: (11) The Reporting Persons are jointly filing this Form 4/A pursuant to Rule 16a-3(j) under the Exchange Act. (12) Each of O. Andreas Halvorsen, David C. Ott and Daniel S. Sundheim is signing as an Executive Committee Member of VIKING GLOBAL PERFORMANCE LLC, on behalf of itself and VIKING GLOBAL EQUITIES LP, VIKING GLOBAL EQUITIES II LP and VGE III PORTFOLIO LTD., and as an Executive Committee Member of VIKING LONG FUND GP LLC, on behalf of itself and VIKING LONG FUND MASTER LTD. (13) Because no more than 10 reporting persons can file any one Form 4/A through the Securities and Exchange Commission's EDGAR system, VGI, Opportunities Fund, Opportunities GP, Opportunities Portfolio GP, Mr. Halvorsen, Mr. Ott and Mr. Sundheim have jointly filed with the Reporting Persons on a separate Form 4/A filing submitted on the same day hereof. (14) This amendment is being filed to check the box indicating that the Reporting Persons are no longer subject to Section 16.

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.

* If the form is filed by more than one reporting person, see Instruction 4(b)(v).

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