Editas Medicine, Inc. — Director's Dealing 2016

Feb 3, 2016

SEC Form 3 — Initial Statement of Beneficial Ownership

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

Reporting Person: VIKING GLOBAL INVESTORS LP (10% Owner)
Reporting Person: Viking Global Opportunities Illiquid Investments Sub-Master LP (10% Owner)
Reporting Person: Viking Global Opportunities Portfolio GP LLC (10% Owner)
Reporting Person: Viking Global Opportunities GP LLC (10% Owner)
Reporting Person: HALVORSEN OLE ANDREAS (10% Owner)
Reporting Person: Ott David C. (10% Owner)
Reporting Person: Sundheim Daniel S. (10% Owner)

Holdings (Derivative)

Security	Exercise Price	Expiration	Underlying	Shares	Ownership
Series B Preferred Stock	$		Common Stock (1709401)		Indirect
Series B Preferred Stock	$		Common Stock (1709401)		Direct

Footnotes

F1: Pursuant to the Amended and Restated Certificate of Incorporation of the Issuer, upon the closing of a firm commitment underwritten public offering in which the aggregate proceeds raised in the offering equal or exceed $50 million (the "IPO"), the Issuer's Series B Preferred Stock will be automatically converted into shares of common stock of the Issuer ("Common Stock"). The conversion ratio has been adjusted as a result of a one-for-2.6 reverse stock split of the Common Stock. The 4,444,444 shares of Series B Preferred Stock reported on this form will convert into 1,709,401 shares of Common Stock upon the closing of the IPO.

F2: O. Andreas Halvorsen, David 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"), 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"). Opportunities Portfolio GP is the general partner of Opportunities Fund. VGI, Opportunities GP, Opportunities Portfolio GP, Opportunities Fund, Mr. Halvorsen, Mr. Ott and Mr. Sundheim are collectively the "Reporting Persons." Each of the Reporting Persons may be deemed to beneficially own the shares reported on this form.

F3: VGI provides managerial services to Opportunities Fund, which directly holds 4,444,444 shares of Series B Preferred Stock that will convert into 1,709,401 shares of Common Stock upon the closing of the IPO. Because of the relationship between VGI and Opportunities Fund, VGI may be deemed to beneficially own the shares of Series B Preferred Stock held directly by Opportunities Fund.

F4: 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 Series B Preferred 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 Series B Preferred Stock held directly by Opportunities Fund.

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.