SUBLEASE AMENDMENT NO. 1 This Sublease Amendment No. 1 (this “Amendment”) is made as of this 31st day of August, 2016 by and between ALNYLAM PHARMACEUTICALS, INC., a Delaware corporation (“Sublessor&

SUBLEASE AMENDMENT NO. 1

This Sublease Amendment No. 1 (this Amendment ) is made as of this 31st day of August, 2016 by and between ALNYLAM PHARMACEUTICALS, INC., a Delaware corporation ( Sublessor ) and EDITAS MEDICINE, INC., a Delaware corporation ( Sublessee ).

WHEREAS, Sublessor and Sublessee are parties to that certain sublease, dated December 31, 2013 (the Sublease ), relating to certain Subleased Premises (as defined in the Sublease) at 300 Third Street in Cambridge, Massachusetts;

WHEREAS, the Term of the Sublease is set to expire on September 30, 2016 (the Original Expiration Date );

WHEREAS, Prime Lessor consented to the Sublease pursuant to the Consent to Sublease dated as of December 31, 2013 (the Landlord Consent ) and intends to consent to this Amendment pursuant to a letter agreement by and between Sublessor and Prime Lessor; and

WHEREAS, Sublessor and Sublessee desire to amend the Sublease as set forth in this Amendment.

NOW, THEREFORE, for and in consideration of the premises and mutual covenants herein contained, the parties hereto hereby agree as follows:

The term of this Sublease ( Term ) shall commence upon the Substantial Completion of the Sublessee Improvements (the Commencement Date ), and shall expire on the earlier of (i) 30 calendar days following the Sublessee giving written notice to the Sublessor that the Sublessee intends to vacate the Subleased Premises or November 30, 2016, unless sooner terminated or extended as provided herein. Notwithstanding the foregoing, the term of this Sublease shall not expire unless and until Sublessee has completed all of its obligations that the Sublease by its terms require the Sublessee to complete prior to Sublessee's surrender of the Premises to Sublessor (including, without limitation, the obligations set forth in Section 21 of the Sublease).

[Signature page follows]

Witness the execution hereof as of the day and year first above written.