Sec Form 4 Filing - Rock Springs Capital Management LP @ Homology Medicines, Inc. - 2018-04-02

FORM 4 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 Rock Springs Capital Management LP 2. Issuer Name and Ticker or Trading Symbol Homology Medicines, Inc. [ FIXX] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) _____ Director X __ 10% Owner _____ Officer (give title below) _____ Other (specify below) (Last) (First) (Middle) 650 SOUTH EXETER ST. SUITE 1070, 3. Date of Earliest Transaction (MM/DD/YY) 04/02/2018 (Street) BALTIMORE, MD21202 4. If Amendment, Date Original Filed (MM/DD/YY) 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 04/02/2018 C 395,845 A $ 0 395,845 I See footnote ( 1 ) Common Stock 04/02/2018 P 250,000 A $ 16 645,845 I See footnote ( 1 )

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 ( 2 ) 04/02/2018 C 395,845 ( 2 ) ( 2 ) Common Stock 395,845 $ 0 0 I See footnote ( 1 )

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other Rock Springs Capital Management LP 650 SOUTH EXETER ST. SUITE 1070 BALTIMORE, MD21202 X Rock Springs Capital Master Fund LP C/O WALKERS CORPORATE LIMITED CAYMAN CORPORATE CENTRE 27 HOSPITAL ROAD GEORGE TOWN, GRAND CAYMAN, E9KY1-9008 X Rock Springs Capital LLC 650 SOUTH EXETER ST. SUITE 1070 BALTIMORE, MD21202 X Signatures Rock Springs Capital Master Fund LP, By: Rock Springs Capital Management LP, By: /s/ Graham McPhail, Managing Member 04/02/2018 Signature of Reporting Person Date Rock Springs Capital LLC, By: /s/ Graham McPhail, Managing Member 04/02/2018 Signature of Reporting Person Date Rock Springs Capital Management LP, Rock Springs Capital LLC, By: /s/ Graham McPhail, Managing Member 04/02/2018 Signature of Reporting Person Date

Explanation of Responses:

( 1 )The securities reported herein are held of record by Rock Springs Capital Master Fund LP ("Master Fund"). Rock Springs Capital LLC ("RSC") is the general partner of Rock Springs Capital Management LP ("RSCM") which is the investment manager to Master Fund. RSC and RSCM may therefore be deemed to have or share beneficial ownership of the securities held directly by Master Fund. ( 2 )Upon closing of the Issuer's initial public offering, each share of preferred stock was automatically converted into one share of the Issuer's common stock.

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).

** Intentional misstatements or omissions of facts constitute Federal Criminal Violations. See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).

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