EX-4.3



 Exhibit 4.3 

RESTATED CERTIFICATE OF INCORPORATION 

OF 
 HOMOLOGY MEDICINES, INC. 

The name of the corporation is Homology Medicines, Inc., and the corporation was originally incorporated by the filing of its original
Certificate of Incorporation with the Secretary of State of the State of Delaware on March 12, 2015. This Restated Certificate of Incorporation of the corporation, which restates and integrates and also further amends the provisions of the
corporation’s Certificate of Incorporation, was duly adopted in accordance with the provisions of Sections 242 and 245 of the General Corporation Law of the State of Delaware and by the written consent of its stockholders in accordance with
Section 228 of the General Corporation Law of the State of Delaware. The Certificate of Incorporation of the corporation is hereby amended, integrated and restated to read in its entirety as follows: 

FIRST: The name of the Corporation is Homology Medicines, Inc. 

SECOND: The address of the Corporation’s registered office in the State of Delaware is 1209 Orange Street, in the City of
Wilmington, County of New Castle, Delaware 19801. The name of its registered agent at that address is The Corporation Trust Company. 

THIRD: The nature of the business or purposes to be conducted or promoted by the Corporation is to engage in any lawful act or activity
for which corporations may be organized under the General Corporation Law of the State of Delaware. 
 FOURTH: The total number of
shares of all classes of stock which the Corporation shall have authority to issue is 210,000,000 shares, consisting of (a) 200,000,000 shares of Common Stock, $0.0001 par value per share (“Common Stock”), and (b) 10,000,000
shares of Preferred Stock, $0.0001 par value per share (“Preferred Stock”). 
 The following is a statement of the designations
and the powers, privileges and rights, and the qualifications, limitations or restrictions thereof in respect of each class of capital stock of the Corporation. 

A. COMMON STOCK. 

1. General. The voting, dividend and liquidation rights of the holders of the Common Stock are subject to and qualified by the
rights of the holders of the Preferred Stock of any series as may be designated by the Board of Directors of the Corporation (the “Board of Directors”) upon any issuance of the Preferred Stock of any series. 

2. Voting. The holders of the Common Stock shall have voting rights at all meetings of stockholders, each such holder being
entitled to one vote for each share thereof held by such holder; provided, however, that, except as otherwise required by law, holders of Common Stock shall not be entitled to vote on any amendment to this Restated Certificate of
Incorporation 







 
(which, as used herein, shall mean the certificate of incorporation of the Corporation, as amended from time to time, including the terms of any certificate of designations of any series of
Preferred Stock) that relates solely to the terms of one or more outstanding series of Preferred Stock if the holders of such affected series are entitled, either separately or together as a class with the holders of one or more other such series,
to vote thereon pursuant to this Restated Certificate of Incorporation or the General Corporation Law of the State of Delaware. There shall be no cumulative voting. 

The number of authorized shares of Common Stock may be increased or decreased (but not below the number of shares thereof then outstanding) by
the affirmative vote of the holders of a majority of the stock of the Corporation entitled to vote, irrespective of the provisions of Section 242(b)(2) of the General Corporation Law of the State of Delaware. 

3. Dividends. Dividends may be declared and paid on the Common Stock if, as and when determined by the Board of Directors
subject to any preferential dividend or other rights of any then outstanding Preferred Stock and to the requirements of applicable law. 

4. Liquidation. Upon the dissolution or liquidation of the Corporation, whether voluntary or involuntary, holders of Common
Stock will be entitled to receive all assets of the Corporation available for distribution to its stockholders, subject to any preferential or other rights of any then outstanding Preferred Stock. 

B. PREFERRED STOCK. 

Preferred Stock may be issued from time to time in one or more series, each of such series to have such terms as stated or expressed herein and
in the resolution or resolutions providing for the issue of such series adopted by the Board of Directors as hereinafter provided. 

Authority is hereby expressly granted to the Board of Directors from time to time to issue the Preferred Stock in one or more series, and in
connection with the creation of any such series, by adopting a resolution or resolutions providing for the issuance of the shares thereof and by filing a certificate of designations relating thereto in accordance with the General Corporation Law of
the State of Delaware, to determine and fix the number of shares of such series and such voting powers, full or limited, or no voting powers, and such designations, preferences and relative, participating, optional or other special rights, and
qualifications, limitations or restrictions thereof, including without limitation thereof, dividend rights, conversion rights, redemption privileges and liquidation preferences, as shall be stated and expressed in such resolutions, all to the
fullest extent now or hereafter permitted by the General Corporation Law of the State of Delaware. The powers, preferences and relative, participating, optional and other special rights of each such series of Preferred Stock, and the qualifications,
limitations or restrictions thereof, if any, may differ from those of any and all other series at any time outstanding. Without limiting the generality of the foregoing, the resolution or resolutions providing for the issuance of any series of
Preferred Stock may provide that such series shall be superior or rank equally or be junior to any other series of Preferred Stock to the extent permitted by law. 

  
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 Subject to the rights of the holders of any series of Preferred Stock pursuant to the terms of
this Restated Certificate of Incorporation or any resolution or resolutions providing for the issuance of such series of stock adopted by the Board of Directors, the number of authorized shares of Preferred Stock may be increased or decreased (but
not below the number of shares thereof then outstanding) by the affirmative vote of the holders of a majority of the stock of the Corporation entitled to vote, irrespective of the provisions of Section 242(b)(2) of the General Corporation Law
of the State of Delaware. 
 FIFTH: Except as otherwise provided herein, the Corporation reserves the right to amend, alter, change or
repeal any provision contained in this Restated Certificate of Incorporation, in the manner now or hereafter prescribed by statute and this Restated Certificate of Incorporation, and all rights conferred upon stockholders, directors or any other
persons herein are granted subject to this reservation. 
 SIXTH: In furtherance and not in limitation of the powers conferred upon it
by the General Corporation Law of the State of Delaware, and subject to the terms of any series of Preferred Stock, the Board of Directors shall have the power to adopt, amend, alter or repeal the Bylaws of the Corporation. The stockholders may
not adopt, amend, alter or repeal the Bylaws of the Corporation, or adopt any provision inconsistent therewith, unless such action is approved, in addition to any other vote required by this Restated Certificate of Incorporation, by the affirmative
vote of the holders of at least two-thirds in voting power of the outstanding shares of capital stock of the Corporation entitled to vote thereon. Notwithstanding any other provisions of law, this Restated Certificate of Incorporation or the
Bylaws of the Corporation, and notwithstanding the fact that a lesser percentage may be specified by law, the affirmative vote of the holders of at least two-thirds in voting power of the outstanding shares of capital stock of the Corporation
entitled to vote thereon shall be required to amend or repeal, or to adopt any provision inconsistent with, this Article SIXTH. 

SEVENTH: Except to the extent that the General Corporation Law of the State of Delaware prohibits the elimination or limitation of
liability of directors for breaches of fiduciary duty, no director of the Corporation shall be personally liable to the Corporation or its stockholders for monetary damages for any breach of fiduciary duty as a director, notwithstanding any
provision of law imposing such liability. No amendment to or repeal of this provision shall apply to or have any effect on the liability or alleged liability of any director of the Corporation for or with respect to any acts or omissions of
such director occurring prior to such amendment or repeal. If the General Corporation Law of the State of Delaware is amended to permit further elimination or limitation of the personal liability of directors, then the liability of a director
of the Corporation shall be eliminated or limited to the fullest extent permitted by the General Corporation Law of the State of Delaware as so amended.

EIGHTH: This Article EIGHTH is inserted for the management of the business and for the conduct of the affairs of the Corporation. 

1. General Powers. The business and affairs of the Corporation shall be managed by or under the direction of the Board of
Directors. 

  
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 2. Number of Directors; Election of Directors. Subject to the rights of holders
of any series of Preferred Stock to elect directors, the number of directors of the Corporation shall be established from time to time by the Board of Directors. Election of directors need not be by written ballot, except as and to the extent
provided in the Bylaws of the Corporation. 
 3. Classes of Directors. Subject to the rights of holders of any series of
Preferred Stock to elect directors, the Board of Directors shall be and is divided into three classes, designated as Class I, Class II and Class III. Each class shall consist, as nearly as may be possible, of one-third of the total number of
directors constituting the entire Board of Directors. The Board of Directors is authorized to assign members of the Board of Directors to Class I, Class II or Class III. 

4. Terms of Office. Subject to the rights of holders of any series of Preferred Stock to elect directors, each director shall
serve for a term ending on the date of the third annual meeting of stockholders following the annual meeting of stockholders at which such director was elected; provided that each director initially assigned to Class I shall serve for a term
expiring at the Corporation’s first annual meeting of stockholders held after the effectiveness of this Restated Certificate of Incorporation; each director initially assigned to Class II shall serve for a term expiring at the
Corporation’s second annual meeting of stockholders held after the effectiveness of this Restated Certificate of Incorporation; and each director initially assigned to Class III shall serve for a term expiring at the Corporation’s third
annual meeting of stockholders held after the effectiveness of this Restated Certificate of Incorporation; provided further, that the term of each director shall continue until the election and qualification of his or her successor and be
subject to his or her earlier death, resignation or removal. 
 5. Quorum. The greater of (a) a majority of the directors at
any time in office and (b) one-third of the number of directors fixed pursuant to Section 2 of this Article EIGHTH shall constitute a quorum of the Board of Directors. If at any meeting of the Board of Directors there shall be less
than such a quorum, a majority of the directors present may adjourn the meeting from time to time without further notice other than announcement at the meeting, until a quorum shall be present. 

6. Action at Meeting. Every act or decision done or made by a majority of the directors present at a meeting duly held at which a
quorum is present shall be regarded as the act of the Board of Directors unless a greater number is required by law or by this Restated Certificate of Incorporation. 

7. Removal. Subject to the rights of holders of any series of Preferred Stock, directors of the Corporation may be removed but only
for cause and only by the affirmative vote of the holders of at least two-thirds in voting power of the outstanding shares of capital stock of the Corporation entitled to vote at an election of directors. 

8. Vacancies. Subject to the rights of holders of any series of Preferred Stock, any vacancy or newly created directorship in the
Board of Directors, however occurring, shall be filled only by vote of a majority of the directors then in office, although less than a quorum, or by a sole remaining director and shall not be filled by the stockholders, unless the Board of
Directors determines by resolution that any such vacancy or newly created directorship shall be 

  
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filled by the stockholders. A director elected to fill a vacancy shall hold office until the next election of the class for which such director shall have been chosen, subject to the
election and qualification of a successor and to such director’s earlier death, resignation or removal. 
 9. Stockholder
Nominations and Introduction of Business, Etc. Advance notice of stockholder nominations for election of directors and other business to be brought by stockholders before a meeting of stockholders shall be given in the manner provided by
the Bylaws of the Corporation. 
 10. Amendments to Article. Notwithstanding any other provisions of law, this Restated
Certificate of Incorporation or the Bylaws of the Corporation, and notwithstanding the fact that a lesser percentage may be specified by law, the affirmative vote of the holders of at least two-thirds in voting power of the outstanding shares of
capital stock of the Corporation entitled to vote thereon shall be required to amend or repeal, or to adopt any provision inconsistent with, this Article EIGHTH. 

NINTH: No action that is required or permitted to be taken by the stockholders of the Corporation at any annual or special meeting of
stockholders may be effected by written consent of stockholders in lieu of a meeting. Notwithstanding any other provisions of law, this Restated Certificate of Incorporation or the Bylaws of the Corporation, and notwithstanding the fact that a
lesser percentage may be specified by law, the affirmative vote of the holders of at least two-thirds in voting power of the outstanding shares of capital stock of the Corporation entitled to vote thereon shall be required to amend or repeal, or to
adopt any provision inconsistent with, this Article NINTH. 
 TENTH: Special meetings of stockholders for any purpose or purposes may
be called at any time only by the Board of Directors, the chairperson of the Board of Directors, the chief executive officer or the president (in the absence of a chief executive officer) of the Corporation, and may not be called by any other person
or persons. Business transacted at any special meeting of stockholders shall be limited to the purpose or purposes stated in the notice of meeting. Notwithstanding any other provisions of law, this Restated Certificate of Incorporation or
the Bylaws of the Corporation, and notwithstanding the fact that a lesser percentage may be specified by law, the affirmative vote of the holders of at least two-thirds in voting power of the outstanding shares of capital stock of the Corporation
entitled to vote thereon shall be required to amend or repeal, or to adopt any provision inconsistent with, this Article TENTH. 

ELEVENTH: Unless the Corporation consents in writing to the selection of an alternative forum, the Court of Chancery of the State of Delaware
shall, to the fullest extent permitted by law, be the sole and exclusive forum for (a) any derivative action or proceeding brought on behalf of the Corporation, (b) any action asserting a claim of breach of fiduciary duty owed by any
director, officer, employee or stockholder of the Corporation to the Corporation or the Corporation’s stockholders, (c) any action asserting a claim arising pursuant to any provision of the General Corporation Law of the State of Delaware
or as to which the General Corporation Law of the State of Delaware confers jurisdiction on the Court of Chancery of the State of Delaware or (d) any action asserting a claim governed by the internal affairs doctrine, in each case subject to
said Court of Chancery having personal jurisdiction over the indispensable parties named as defendants therein; provided that, if and only if the Court of Chancery of the State of 

  
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Delaware dismisses any such action for lack of subject matter jurisdiction, such action may be brought in another state or federal court sitting in the State of Delaware. To the fullest extent
permitted by applicable law, any person or entity purchasing or otherwise acquiring or holding any interest in shares of capital stock of the Corporation shall be deemed to have notice of and consented to the provisions of this Article ELEVENTH.
Notwithstanding any other provisions of law, this Restated Certificate of Incorporation or the Bylaws of the Corporation, and notwithstanding the fact that a lesser percentage may be specified by law, the affirmative vote of the holders of at least
two-thirds in voting power of the outstanding shares of capital stock of the Corporation entitled to vote thereon shall be required to amend or repeal, or to adopt any provision inconsistent with, this Article ELEVENTH. If any provision or
provisions of this Article ELEVENTH shall be held to be invalid, illegal or unenforceable as applied to any person or entity or circumstance for any reason whatsoever, then, to the fullest extent permitted by law, the validity, legality and
enforceability of such provisions in any other circumstance and of the remaining provisions of this Article ELEVENTH (including, without limitation, each portion of any sentence of this Article ELEVENTH containing any such provision held to be
invalid, illegal or unenforceable that is not itself held to be invalid, illegal or unenforceable) and the application of such provision to other persons or entities and circumstances shall not in any way be affected or impaired thereby. 

  
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 IN WITNESS WHEREOF, this Restated Certificate of Incorporation, which restates, integrates and
amends the certificate of incorporation of the Corporation, and which has been duly adopted in accordance with Sections 228, 242 and 245 of the General Corporation Law of the State of Delaware, has been executed by its duly authorized officer this
     day of                     , 2018. 

 

					
	HOMOLOGY MEDICINES, INC.
		
	By:	 	 
		 	Name:	 	Arthur O. Tzianabos, Ph.D.
		 	Title:	 	President and Chief Executive Officer