EX-10.5



 Exhibit 10.5 

HOMOLOGY MEDICINES, INC. 

INDEMNIFICATION AGREEMENT 

THIS INDEMNIFICATION AGREEMENT (the “Agreement”) is made and entered into as of
                    , 20[18] between Homology Medicines, Inc., a Delaware corporation (the “Company”), and [Name]
(“Indemnitee”). 
 WITNESSETH THAT: 

WHEREAS, highly competent persons have become more reluctant to serve corporations as directors, officers or in other capacities unless they
are provided with adequate protection through insurance or adequate indemnification against inordinate risks of claims and actions against them arising out of their service to and activities on behalf of the corporation; 

WHEREAS, the Board of Directors of the Company (the “Board”) has determined that, in order to attract
and retain qualified individuals, the Company will attempt to maintain on an ongoing basis, at its sole expense, liability insurance to protect persons serving the Company and its subsidiaries from certain liabilities. Although the furnishing of
such insurance has been a customary and widespread practice among United States-based corporations and other business enterprises, the Company believes that, given current market conditions and trends, such insurance may be available to it in the
future only at higher premiums and with more exclusions. At the same time, directors, officers, and other persons in service to corporations or business enterprises are being increasingly subjected to expensive and time-consuming litigation relating
to, among other things, matters that traditionally would have been brought only against the Company or business enterprise itself. The Bylaws of the Company require indemnification of the officers and directors of the Company. Indemnitee may also be
entitled to indemnification pursuant to the General Corporation Law of the State of Delaware (“DGCL”). The Bylaws and the DGCL expressly provide that the indemnification provisions set forth therein are not exclusive, and
thereby contemplate that contracts may be entered into between the Company and members of the Board, officers and other persons with respect to indemnification; 

WHEREAS, the uncertainties relating to such insurance and to indemnification have increased the difficulty of attracting and retaining such
persons; 
 WHEREAS, the Board has determined that the increased difficulty in attracting and retaining such persons is detrimental to the
best interests of the Company’s stockholders and that the Company should act to assure such persons that there will be increased certainty of such protection in the future; 

WHEREAS, it is reasonable, prudent and necessary for the Company contractually to obligate itself to indemnify, and to advance expenses on
behalf of, such persons to the fullest extent permitted by applicable law so that they will serve or continue to serve the Company free from undue concern that they will not be so indemnified; 

WHEREAS, this Agreement is a supplement to and in furtherance of the Bylaws of the Company and any resolutions adopted pursuant thereto, and
shall not be deemed a substitute therefor, nor to diminish or abrogate any rights of Indemnitee thereunder; [and] 

  
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 WHEREAS, Indemnitee does not regard the protection available under the Company’s Bylaws and
insurance as adequate in the present circumstances, and may not be willing to serve as an officer or director without adequate protection, and the Company desires Indemnitee to serve in such capacity. Indemnitee is willing to serve, continue to
serve and to take on additional service for or on behalf of the Company on the condition that he be so indemnified; [and] 
 [WHEREAS,
Indemnitee has certain rights to indemnification and/or insurance provided by [NAME] which Indemnitee and [NAME] intend to be secondary to the primary obligation of the Company to indemnify Indemnitee as provided herein, with the Company’s
acknowledgement and agreement to the foregoing being a material condition to Indemnitee’s willingness to serve on the Board;] 
 NOW,
THEREFORE, in consideration of Indemnitee’s agreement to serve as an officer or director from and after the date hereof, the parties hereto agree as follows: 

1. Indemnity of Indemnitee. The Company hereby agrees to hold harmless and indemnify Indemnitee to the fullest extent permitted by law,
as such may be amended from time to time. In furtherance of the foregoing indemnification, and without limiting the generality thereof: 

(a) Proceedings Other Than Proceedings by or in the Right of the Company. Indemnitee shall be entitled to the rights of indemnification
provided in this Section l(a) if, by reason of his Corporate Status (as hereinafter defined), the Indemnitee is, or is threatened to be made, a party to or participant in any Proceeding (as hereinafter defined) other than a Proceeding by or
in the right of the Company. Pursuant to this Section 1(a), Indemnitee shall be indemnified against all Expenses (as hereinafter defined), judgments, penalties, fines and amounts paid in settlement actually and reasonably incurred by
him, or on his behalf, in connection with such Proceeding or any claim, issue or matter therein, if the Indemnitee acted in good faith and in a manner the Indemnitee reasonably believed to be in or not opposed to the best interests of the Company,
and with respect to any criminal Proceeding, had no reasonable cause to believe the Indemnitee’s conduct was unlawful. 
 (b)
Proceedings by or in the Right of the Company. Indemnitee shall be entitled to the rights of indemnification provided in this Section 1(b) if, by reason of his Corporate Status, the Indemnitee is, or is threatened to be made, a
party to or participant in any Proceeding brought by or in the right of the Company. Pursuant to this Section 1(b), Indemnitee shall be indemnified against all Expenses actually and reasonably incurred by the Indemnitee, or on the
Indemnitee’s behalf, in connection with such Proceeding if the Indemnitee acted in good faith and in a manner the Indemnitee reasonably believed to be in or not opposed to the best interests of the Company; provided, however, if applicable law
so provides, no indemnification against such Expenses shall be made in respect of any claim, issue or matter in such Proceeding as to which Indemnitee shall have been adjudged to be liable to the Company unless and to the extent that the Court of
Chancery of the State of Delaware shall determine that such indemnification may be made. 
 (c) Indemnification for Expenses of a Party
Who is Wholly or Partly Successful. Notwithstanding any other provision of this Agreement, to the extent that Indemnitee is, by reason of his Corporate Status, a party to and is successful, on the merits or otherwise, in any Proceeding, he shall
be indemnified to the maximum extent permitted by law, 

  
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as such may be amended from time to time, against all Expenses actually and reasonably incurred by him or on his behalf in connection therewith. If Indemnitee is not wholly successful in such
Proceeding but is successful, on the merits or otherwise, as to one or more but less than all claims, issues or matters in such Proceeding, the Company shall indemnify Indemnitee against all Expenses actually and reasonably incurred by him or on his
behalf in connection with each successfully resolved claim, issue or matter. For purposes of this Section and without limitation, the termination of any claim, issue or matter in such a Proceeding by dismissal, with or without prejudice, shall be
deemed to be a successful result as to such claim, issue or matter. 
 (d) Indemnification of Appointing Stockholder. If
(i) Indemnitee is or was affiliated with one or more venture capital funds that has invested in the Company (an “Appointing Stockholder”), and (ii) the Appointing Stockholder is, or is threatened to be made, a party
to or a participant in any Proceeding relating to or arising by reason of Appointing Stockholder’s position as a stockholder of, or lender to, the Company, or Appointing Stockholder’s appointment of or affiliation with Indemnitee or any
other director, including without limitation any alleged misappropriation of a Company asset or corporate opportunity, any claim of misappropriation or infringement of intellectual property relating to the Company, any alleged false or misleading
statement or omission made by the Company (or on its behalf) or its employees or agents, or any allegation of inappropriate control or influence over the Company or its Board members, officers, equity holders or debt holders, then the Appointing
Stockholder will be entitled to indemnification hereunder for Expenses to the same extent as Indemnitee, and the terms of this Agreement as they relate to procedures for indemnification of Indemnitee and advancement of Expenses shall apply to any
such indemnification of Appointing Stockholder. 
 The rights provided to the Appointing Stockholder under this Section 1(d) shall
(i) be suspended during any period during which the Appointing Stockholder does not have a representative on the Company’s Board and (ii) terminate on an initial public offering of the Company’s Common Stock; provided, however,
that in the event of any such suspension or termination, the Appointing Stockholder’s rights to indemnification will not be suspended or terminated with respect to any Proceeding based in whole or in part on facts and circumstances occurring at
any time prior to such suspension or termination regardless of whether the Proceeding arises before or after such suspension or termination. The Company and Indemnitee agree that the Appointing Stockholder is an express third party beneficiary of
the terms of this Section 1(d). 
 2. Additional Indemnity. In addition to, and without regard to any limitations on, the
indemnification provided for in Section 1 of this Agreement, the Company shall and hereby does indemnify and hold harmless Indemnitee against all Expenses, judgments, penalties, fines and amounts paid in settlement actually and
reasonably incurred by him or on his behalf if, by reason of his Corporate Status, he is, or is threatened to be made, a party to or participant in any Proceeding (including a Proceeding by or in the right of the Company), including, without
limitation, all liability arising out of the negligence or active or passive wrongdoing of Indemnitee. The only limitation that shall exist upon the Company’s obligations pursuant to this Agreement shall be that the Company shall not be
obligated to make any payment to Indemnitee that is finally determined (under the procedures, and subject to the presumptions, set forth in Sections 6 and 7 hereof) to be unlawful. 

3. Contribution. 

  
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 (a) Whether or not the indemnification provided in Sections 1 and 2 hereof is
available, in respect of any threatened, pending or completed action, suit or proceeding in which the Company is jointly liable with Indemnitee (or would be if joined in such action, suit or proceeding), the Company shall pay, in the first instance,
the entire amount of any judgment or settlement of such action, suit or proceeding without requiring Indemnitee to contribute to such payment and the Company hereby waives and relinquishes any right of contribution it may have against Indemnitee.
The Company shall not enter into any settlement of any action, suit or proceeding in which the Company is jointly liable with Indemnitee (or would be if joined in such action, suit or proceeding) unless such settlement provides for a full and final
release of all claims asserted against Indemnitee. 
 (b) Without diminishing or impairing the obligations of the Company set forth in the
preceding subparagraph, if, for any reason, Indemnitee shall elect or be required to pay all or any portion of any judgment or settlement in any threatened, pending or completed action, suit or proceeding in which the Company is jointly liable with
Indemnitee (or would be if joined in such action, suit or proceeding), the Company shall contribute to the amount of Expenses, judgments, fines and amounts paid in settlement actually and reasonably incurred and paid or payable by Indemnitee in
proportion to the relative benefits received by the Company and all officers, directors or employees of the Company, other than Indemnitee, who are jointly liable with Indemnitee (or would be if joined in such action, suit or proceeding), on the one
hand, and Indemnitee, on the other hand, from the transaction or events from which such action, suit or proceeding arose; provided, however, that the proportion determined on the basis of relative benefit may, to the extent necessary to conform to
law, be further adjusted by reference to the relative fault of the Company and all officers, directors or employees of the Company other than Indemnitee who are jointly liable with Indemnitee (or would be if joined in such action, suit or
proceeding), on the one hand, and Indemnitee, on the other hand, in connection with the transaction or events that resulted in such expenses, judgments, fines or settlement amounts, as well as any other equitable considerations which applicable law
may require to be considered. The relative fault of the Company and all officers, directors or employees of the Company, other than Indemnitee, who are jointly liable with Indemnitee (or would be if joined in such action, suit or proceeding), on the
one hand, and Indemnitee, on the other hand, shall be determined by reference to, among other things, the degree to which their actions were motivated by intent to gain personal profit or advantage, the degree to which their liability is primary or
secondary and the degree to which their conduct is active or passive. 
 (c) The Company hereby agrees to fully indemnify and hold
Indemnitee harmless from any claims of contribution which may be brought by officers, directors or employees of the Company, other than Indemnitee, who may be jointly liable with Indemnitee. 

(d) To the fullest extent permissible under applicable law, if the indemnification provided for in this Agreement is unavailable to
Indemnitee for any reason whatsoever, the Company, in lieu of indemnifying Indemnitee, shall contribute to the amount incurred by Indemnitee, whether for judgments, fines, penalties, excise taxes, amounts paid or to be paid in settlement and/or for
Expenses, in connection with any claim relating to an indemnifiable event under this Agreement, in such proportion as is deemed fair and reasonable in light of all of the circumstances of such Proceeding in order to reflect (i) the relative
benefits received by the Company and Indemnitee as a result of the event(s) and/or transaction(s) giving cause to such Proceeding and/or (ii) the relative fault of the Company (and its directors, officers, employees and agents) and Indemnitee
in connection with such event(s) and/or transaction(s). 

  
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 4. Indemnification for Expenses of a Witness. Notwithstanding any other provision of this
Agreement, to the extent that Indemnitee is, by reason of his Corporate Status, a witness, or is made (or asked) to respond to discovery requests, in any Proceeding to which Indemnitee is not a party, he shall be indemnified against all Expenses
actually and reasonably incurred by him or on his behalf in connection therewith. 
 5. Advancement of Expenses. Notwithstanding any
other provision of this Agreement, the Company shall advance all Expenses incurred by or on behalf of Indemnitee in connection with any Proceeding by reason of Indemnitee’s Corporate Status within thirty (30) days after the receipt by the
Company of a statement or statements from Indemnitee requesting such advance or advances from time to time, whether prior to or after final disposition of such Proceeding. Such statement or statements shall reasonably evidence the Expenses incurred
by Indemnitee. The Indemnitee shall qualify for advances upon the execution and delivery to the Corporation of this Agreement, which shall constitute an undertaking by Indemnitee to repay any Expenses advanced if it shall ultimately be determined
that Indemnitee is not entitled to be indemnified against such Expenses. Any advances and undertakings to repay pursuant to this Section 5 shall be unsecured and interest free. 

6. Procedures and Presumptions for Determination of Entitlement to Indemnification. It is the intent of this Agreement to secure for
Indemnitee rights of indemnity that are as favorable as may be permitted under the DGCL and public policy of the State of Delaware. Accordingly, the parties agree that the following procedures and presumptions shall apply in the event of any
question as to whether Indemnitee is entitled to indemnification under this Agreement: 
 (a) To obtain indemnification under this
Agreement, Indemnitee shall submit to the Company a written request, including therein or therewith such documentation and information as is reasonably available to Indemnitee and is reasonably necessary to determine whether and to what extent
Indemnitee is entitled to indemnification. The Secretary of the Company shall, promptly upon receipt of such a request for indemnification, advise the Board in writing that Indemnitee has requested indemnification. Notwithstanding the foregoing, any
failure of Indemnitee to provide such a request to the Company, or to provide such a request in a timely fashion, shall not relieve the Company of any liability that it may have to Indemnitee unless, and to the extent that, such failure actually and
materially prejudices the interests of the Company. 
 (b) Upon written request by Indemnitee for indemnification pursuant to the first
sentence of Section 6(a) hereof, a determination with respect to Indemnitee’s entitlement thereto shall be made in the specific case by one of the following four methods, which shall be at the election of the Board: (1) by a
majority vote of the disinterested directors, even though less than a quorum, (2) by a committee of disinterested directors designated by a majority vote of the disinterested directors, even though less than a quorum, (3) if there are no
disinterested directors or if the disinterested directors so direct, by independent legal counsel in a written opinion to the Board, a copy of which shall be delivered to the Indemnitee, or (4) if so directed by the Board, by the stockholders
of the Company. For purposes hereof, disinterested directors are those members of the Board who are not parties to the action, suit or proceeding in respect of which indemnification is sought by Indemnitee. 

  
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 (c) If the determination of entitlement to indemnification is to be made by Independent Counsel
pursuant to Section 6(b) hereof, the Independent Counsel shall be selected as provided in this Section 6(c). The Independent Counsel shall be selected by the Board. Indemnitee may, within ten (10) days after such written
notice of selection shall have been given, deliver to the Company a written objection to such selection; provided, however, that such objection may be asserted only on the ground that the Independent Counsel so selected does not meet the
requirements of “Independent Counsel” as defined in Section 13 of this Agreement, and the objection shall set forth with particularity the factual basis of such assertion. Absent a proper and timely objection, the person so
selected shall act as Independent Counsel. If a written objection is made and substantiated, the Independent Counsel selected may not serve as Independent Counsel unless and until such objection is withdrawn or a court has determined that such
objection is without merit. If, within twenty (20) days after the conclusion of the Proceeding giving rise to the request for indemnification, no Independent Counsel shall have been selected and not objected to, either the Company or Indemnitee
may petition the Court of Chancery of the State of Delaware for resolution of any objection which shall have been made by the Indemnitee to the Company’s selection of Independent Counsel and/or for the appointment as Independent Counsel of a
person selected by the court or by such other person as the court shall designate, and the person with respect to whom all objections are so resolved or the person so appointed shall act as Independent Counsel under Section 6(b) hereof.
The Company shall pay any and all reasonable fees and expenses of Independent Counsel incurred by such Independent Counsel in connection with acting pursuant to Section 6(b) hereof, and the Company shall pay all reasonable fees and
expenses incident to the procedures of this Section 6(c), regardless of the manner in which such Independent Counsel was selected or appointed. 

(d) In making a determination with respect to entitlement to indemnification hereunder, the person or persons or entity making such
determination shall presume that Indemnitee is entitled to indemnification under this Agreement. Anyone seeking to overcome this presumption shall have the burden of proof and the burden of persuasion by clear and convincing evidence. Neither the
failure of the Company (including by its directors or independent legal counsel) to have made a determination prior to the commencement of any action pursuant to this Agreement that indemnification is proper in the circumstances because Indemnitee
has met the applicable standard of conduct, nor an actual determination by the Company (including by its directors or independent legal counsel) that Indemnitee has not met such applicable standard of conduct, shall be a defense to the action or
create a presumption that Indemnitee has not met the applicable standard of conduct. 
 (e) Indemnitee shall be deemed to have acted in good
faith if Indemnitee’s action is based on the records or books of account of the Enterprise (as hereinafter defined), including financial statements, or on information supplied to Indemnitee by the officers of the Enterprise in the course of
their duties, or on the advice of legal counsel for the Enterprise or on information or records given or reports made to the Enterprise by an independent certified public accountant or by an appraiser or other expert selected with reasonable care by
the Enterprise. In addition, the knowledge and/or actions, or failure to act, of any director, officer, agent or employee of the Enterprise shall not be imputed to Indemnitee for purposes of determining the right to indemnification under this
Agreement. Whether or not the foregoing provisions of this Section 6(e) are satisfied, it shall in any event be presumed that Indemnitee has 

  
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at all times acted in good faith and in a manner he reasonably believed to be in or not opposed to the best interests of the Company. Anyone seeking to overcome this presumption shall have the
burden of proof and the burden of persuasion by clear and convincing evidence. 
 (f) If the person, persons or entity empowered or selected
under Section 6 to determine whether Indemnitee is entitled to indemnification shall not have made a determination within sixty (60) days after the conclusion of the Proceeding giving rise to the request for indemnification, the
requisite determination of entitlement to indemnification shall be deemed to have been made and Indemnitee shall be entitled to such indemnification absent (i) a misstatement by Indemnitee of a material fact, or an omission of a material fact
necessary to make Indemnitee’s statement not materially misleading, in connection with the request for indemnification, or (ii) a prohibition of such indemnification under applicable law; provided, however, that such sixty (60)-day period
may be extended for a reasonable time, not to exceed an additional thirty (30) days, if the person, persons or entity making such determination with respect to entitlement to indemnification in good faith requires such additional time to obtain
or evaluate documentation and/or information relating thereto; and provided, further, that the foregoing provisions of this Section 6(f) shall not apply if the determination of entitlement to indemnification is to be made by the
stockholders pursuant to Section 6(b) of this Agreement and if (A) within fifteen (15) days after the conclusion of the Proceeding giving rise to the request for indemnification, the Board or the Disinterested Directors, if
appropriate, resolve to submit such determination to the stockholders for their consideration at an annual meeting thereof to be held within seventy-five (75) days after such resolution and such determination is made thereat, or (B) a
special meeting of stockholders is called within fifteen (15) days after such resolution and such meeting is held for such purpose within sixty (60) days after having been so called and such determination is made thereat. 

(g) Indemnitee shall cooperate with the person, persons or entity making such determination with respect to Indemnitee’s entitlement to
indemnification, including providing to such person, persons or entity upon reasonable advance request any documentation or information which is not privileged or otherwise protected from disclosure and which is reasonably available to Indemnitee
and reasonably necessary to such determination. Any Independent Counsel, member of the Board or stockholder of the Company shall act reasonably and in good faith in making a determination regarding the Indemnitee’s entitlement to
indemnification under this Agreement. Any costs or expenses (including attorneys’ fees and disbursements) incurred by Indemnitee in so cooperating with the person, persons or entity making such determination shall be borne by the Company
(irrespective of the determination as to Indemnitee’s entitlement to indemnification) and the Company hereby indemnifies and agrees to hold Indemnitee harmless therefrom. 

(h) The Company acknowledges that a settlement or other disposition short of final judgment may be successful if it permits a party to avoid
expense, delay, distraction, disruption and uncertainty. In the event that any action, claim or proceeding to which Indemnitee is a party is resolved in any manner other than by adverse judgment against Indemnitee (including, without limitation,
settlement of such action, claim or proceeding with or without payment of money or other consideration) it shall be presumed that Indemnitee has been successful on the merits or otherwise in such action, suit or proceeding. Anyone seeking to
overcome this presumption shall have the burden of proof and the burden of persuasion by clear and convincing evidence. 

  
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 (i) The termination of any Proceeding or of any claim, issue or matter therein, by judgment,
order, settlement or conviction, or upon a plea of nolo contendere or its equivalent, shall not (except as otherwise expressly provided in this Agreement) of itself adversely affect the right of Indemnitee to indemnification or create a presumption
that Indemnitee did not act in good faith and in a manner which he reasonably believed to be in or not opposed to the best interests of the Company or, with respect to any criminal Proceeding, that Indemnitee had reasonable cause to believe that his
conduct was unlawful. 
 7. Remedies of Indemnitee. 

(a) In the event that (i) a determination is made pursuant to Section 6 of this Agreement that Indemnitee is not entitled to
indemnification under this Agreement, (ii) advancement of Expenses is not timely made pursuant to Section 5 of this Agreement, (iii) no determination of entitlement to indemnification is made pursuant to
Section 6(b) of this Agreement within ninety (90) days after the conclusion of the Proceeding giving rise to the request for indemnification, (iv) payment of indemnification required by Section 4 is not made pursuant to
this Agreement within thirty (30) days after receipt by the Company of a written request therefor or (v) payment of indemnification is not made within ten (10) days after a determination has been made that Indemnitee is entitled to
indemnification or such determination is deemed to have been made pursuant to Section 6 of this Agreement, Indemnitee shall be entitled to an adjudication in Court of Chancery of the State of Delaware of Indemnitee’s entitlement to
such indemnification. Indemnitee shall commence such proceeding seeking an adjudication within one hundred eighty (180) days following the date on which Indemnitee first has the right to commence such proceeding pursuant to this
Section 7(a). The Company shall not oppose Indemnitee’s right to seek any such adjudication. 
 (b) In the event that a
determination shall have been made pursuant to Section 6(b) of this Agreement that Indemnitee is not entitled to indemnification, any judicial proceeding commenced pursuant to this Section 7 shall be conducted in all respects
as a de novo trial on the merits, and Indemnitee shall not be prejudiced by reason of the adverse determination under Section 6(b). 

(c) If a determination shall have been made pursuant to Section 6(b) of this Agreement that Indemnitee is entitled to
indemnification, the Company shall be bound by such determination in any judicial proceeding commenced pursuant to this Section 7, absent (i) a misstatement by Indemnitee of a material fact, or an omission of a material fact
necessary to make Indemnitee’s misstatement not materially misleading in connection with the application for indemnification, or (ii) a prohibition of such indemnification under applicable law. 

(d) In the event that Indemnitee, pursuant to this Section 7, seeks a judicial adjudication of his rights under, or to recover
damages for breach of, this Agreement, or to recover under any directors’ and officers’ liability insurance policies maintained by the Company, the Company shall pay on his behalf, in advance, any and all expenses (of the types described
in the definition of Expenses in Section 13 of this Agreement) actually and reasonably incurred by him in such judicial adjudication, regardless of whether Indemnitee ultimately is determined to be entitled to such indemnification,
advancement of expenses or insurance recovery. 

  
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 (e) The Company shall be precluded from asserting in any judicial proceeding commenced pursuant
to this Section 7 that the procedures and presumptions of this Agreement are not valid, binding and enforceable and shall stipulate in any such court that the Company is bound by all the provisions of this Agreement. The Company shall
indemnify Indemnitee against any and all Expenses and, if requested by Indemnitee, shall (within ten (10) days after receipt by the Company of a written request therefore) advance, to the extent not prohibited by law, such expenses to
Indemnitee, which are incurred by Indemnitee in connection with any action brought by Indemnitee for indemnification or advance of Expenses from the Company under this Agreement or under any directors’ and officers’ liability insurance
policies maintained by the Company, regardless of whether Indemnitee ultimately is determined to be entitled to such indemnification, advancement of Expenses or insurance recovery, as the case may be. 

(f) Notwithstanding anything in this Agreement to the contrary, no determination as to entitlement to indemnification under this Agreement
shall be required to be made prior to the final disposition of the Proceeding. 
 8. Non-Exclusivity; Survival of Rights; Insurance;
Primacy of Indemnification; Subrogation. 
 (a) The rights of indemnification as provided by this Agreement shall not be deemed
exclusive of any other rights to which Indemnitee may at any time be entitled under applicable law, the Bylaws, any agreement, a vote of stockholders, a resolution of directors of the Company, or otherwise. No amendment, alteration or repeal of this
Agreement or of any provision hereof shall limit or restrict any right of Indemnitee under this Agreement in respect of any action taken or omitted by such Indemnitee in his Corporate Status prior to such amendment, alteration or repeal. To the
extent that a change in the DGCL, whether by statute or judicial decision, permits greater indemnification than would be afforded currently under the Bylaws and this Agreement, it is the intent of the parties hereto that Indemnitee shall enjoy by
this Agreement the greater benefits so afforded by such change. No right or remedy herein conferred is intended to be exclusive of any other right or remedy, and every other right and remedy shall be cumulative and in addition to every other right
and remedy given hereunder or now or hereafter existing at law or in equity or otherwise. The assertion or employment of any right or remedy hereunder, or otherwise, shall not prevent the concurrent assertion or employment of any other right or
remedy. 
 (b) To the extent that the Company maintains an insurance policy or policies providing liability insurance for directors,
officers, employees, or agents or fiduciaries of the Company or of any other corporation, partnership, joint venture, trust, employee benefit plan or other enterprise that such person serves at the request of the Company, Indemnitee shall be covered
by such policy or policies in accordance with its or their terms to the maximum extent of the coverage available for any director, officer, employee, agent or fiduciary under such policy or policies. If, at the time of the receipt of a notice of a
claim pursuant to the terms hereof, the Company has directors’ and officers’ liability insurance in effect, the Company shall give prompt notice of the commencement of such proceeding to the insurers in accordance with the procedures set
forth in the respective policies. The Company shall thereafter take all necessary or desirable action to cause such insurers to pay, on behalf of the Indemnitee, all amounts payable as a result of such proceeding in accordance with the terms of such
policies. 

  
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 (c) [The Company hereby acknowledges that Indemnitee has certain rights to
indemnification, advancement of expenses and/or insurance provided by [●] and certain of its affiliates (collectively, the “Fund Indemnitors”). The Company hereby agrees (i) that it is the indemnitor of first
resort (i.e., its obligations to Indemnitee are primary and any obligation of the Fund Indemnitors to advance expenses or to provide indemnification for the same expenses or liabilities incurred by Indemnitee are secondary), (ii) that it shall
be required to advance the full amount of expenses incurred by Indemnitee and shall be liable for the full amount of all Expenses, judgments, penalties, fines and amounts paid in settlement to the extent legally permitted and as required by the
terms of this Agreement and the Bylaws of the Company (or any other agreement between the Company and Indemnitee), without regard to any rights Indemnitee may have against the Fund Indemnitors, and, (iii) that it irrevocably waives,
relinquishes and releases the Fund Indemnitors from any and all claims against the Fund Indemnitors for contribution, subrogation or any other recovery of any kind in respect thereof. The Company further agrees that no advancement or payment by the
Fund Indemnitors on behalf of Indemnitee with respect to any claim for which Indemnitee has sought indemnification from the Company shall affect the foregoing and the Fund Indemnitors shall have a right of contribution and/or be subrogated to the
extent of such advancement or payment to all of the rights of recovery of Indemnitee against the Company. The Company and Indemnitee agree that the Fund Indemnitors are express third party beneficiaries of the terms of this Section 8(c).]

 (d) [Except as provided in paragraph (c) above,] in the event of any payment under this Agreement, the Company shall be
subrogated to the extent of such payment to all of the rights of recovery of Indemnitee (other than against the Fund Indemnitors), who shall execute all papers required and take all action necessary to secure such rights, including execution of such
documents as are necessary to enable the Company to bring suit to enforce such rights. 
 (e) [Except as provided in paragraph
(c) above,] the Company shall not be liable under this Agreement to make any payment of amounts otherwise indemnifiable hereunder if and to the extent that Indemnitee has otherwise actually received such payment under any insurance policy,
contract, agreement or otherwise. 
 (f) [Except as provided in paragraph (c) above,] the Company’s obligation to indemnify or
advance Expenses hereunder to Indemnitee who is or was serving at the request of the Company as a director, officer, employee or agent of any other corporation, partnership, joint venture, trust, employee benefit plan or other enterprise shall be
reduced by any amount Indemnitee has actually received as indemnification or advancement of expenses from such other corporation, partnership, joint venture, trust, employee benefit plan or other enterprise. 

9. Exception to Right of Indemnification. Notwithstanding any provision in this Agreement, the Company shall not be obligated under
this Agreement to make any indemnity in connection with any claim made against Indemnitee: 
 (a) for which payment has actually been made
to or on behalf of Indemnitee under any insurance policy or other indemnity provision, except with respect to any excess beyond the amount paid under any insurance policy or other indemnity provision[, provided, that the foregoing shall not affect
the rights of Indemnitee or the Fund Indemnitors set forth in Section 8(c) above]; or 

  
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 (b) for an accounting of profits made from the purchase and sale (or sale and purchase) by
Indemnitee of securities of the Company within the meaning of Section 16(b) of the Securities Exchange Act of 1934, as amended, or similar provisions of state statutory law or common law; or 

(c) in connection with any Proceeding (or any part of any Proceeding) initiated by Indemnitee, including any Proceeding (or any part of any
Proceeding) initiated by Indemnitee against the Company or its directors, officers, employees or other indemnitees, unless (i) the Board authorized the Proceeding (or any part of any Proceeding) prior to its initiation or (ii) the Company
provides the indemnification, in its sole discretion, pursuant to the powers vested in the Company under applicable law. 
 10. Duration
of Agreement. All agreements and obligations of the Company contained herein shall continue during the period Indemnitee is an officer or director of the Company (or is or was serving at the request of the Company as a director, officer,
employee or agent of another corporation, partnership, joint venture, trust or other enterprise) and shall continue thereafter so long as Indemnitee shall be subject to any Proceeding (or any proceeding commenced under Section 7 hereof)
by reason of his Corporate Status, whether or not he is acting or serving in any such capacity at the time any liability or expense is incurred for which indemnification can be provided under this Agreement. This Agreement shall be binding upon and
inure to the benefit of and be enforceable by the parties hereto and their respective successors (including any direct or indirect successor by purchase, merger, consolidation or otherwise to all or substantially all of the business or assets of the
Company), assigns, spouses, heirs, executors and personal and legal representatives. 
 11. Security. To the extent requested by
Indemnitee and approved by the Board, the Company may at any time and from time to time provide security to Indemnitee for the Company’s obligations hereunder through an irrevocable bank line of credit, funded trust or other collateral. Any
such security, once provided to Indemnitee, may not be revoked or released without the prior written consent of the Indemnitee. 
 12.
Enforcement. 
 (a) The Company expressly confirms and agrees that it has entered into this Agreement and assumes the obligations
imposed on it hereby in order to induce Indemnitee to serve as an officer or director of the Company, and the Company acknowledges that Indemnitee is relying upon this Agreement in serving as an officer or director of the Company. 

(b) This Agreement constitutes the entire agreement between the parties hereto with respect to the subject matter hereof and supersedes all
prior agreements and understandings, oral, written and implied, between the parties hereto with respect to the subject matter hereof. 

(c) The Company shall not seek from a court, or agree to, a “bar order” which would have the effect of prohibiting or limiting the
Indemnitee’s rights to receive advancement of expenses under this Agreement. 
 13. Definitions. For purposes of this Agreement:


  
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 (a) “Corporate Status” describes the status of a person
who is or was a director, officer, employee, agent or fiduciary of the Company or of any other corporation, partnership, joint venture, trust, employee benefit plan or other enterprise that such person is or was serving at the express written
request of the Company. 
 (b) “Disinterested Director” means a director of the Company
who is not and was not a party to the Proceeding in respect of which indemnification is sought by Indemnitee. 

(c) “Enterprise” shall mean the Company and any other corporation, partnership, joint venture, trust,
employee benefit plan or other enterprise that Indemnitee is or was serving at the express written request of the Company as a director, officer, employee, agent or fiduciary. 

(d) “Expenses” shall include all reasonable attorneys’ fees, retainers, court costs, transcript
costs, fees of experts, witness fees, travel expenses, duplicating costs, printing and binding costs, telephone charges, postage, delivery service fees and all other disbursements or expenses of the types customarily incurred in connection with
prosecuting, defending, preparing to prosecute or defend, investigating, participating, or being or preparing to be a witness in a Proceeding, or responding to, or objecting to, a request to provide discovery in any Proceeding. Expenses also shall
include Expenses incurred in connection with any appeal resulting from any Proceeding and any federal, state, local or foreign taxes imposed on the Indemnitee as a result of the actual or deemed receipt of any payments under this Agreement,
including without limitation the premium, security for, and other costs relating to any cost bond, supersede as bond, or other appeal bond or its equivalent. Expenses, however, shall not include amounts paid in settlement by Indemnitee or the amount
of judgments or fines against Indemnitee. 
 (e) “Independent Counsel” means a law firm,
or a member of a law firm, that is experienced in matters of corporation law and neither presently is, nor in the past five years has been, retained to represent: (i) the Company or Indemnitee in any matter material to either such party (other
than with respect to matters concerning Indemnitee under this Agreement, or of other indemnitees under similar indemnification agreements), or (ii) any other party to the Proceeding giving rise to a claim for indemnification hereunder.
Notwithstanding the foregoing, the term “Independent Counsel” shall not include any person who, under the applicable standards of professional conduct then prevailing, would have a conflict of interest in representing either the Company or
Indemnitee in an action to determine Indemnitee’s rights under this Agreement. The Company agrees to pay the reasonable fees of the Independent Counsel referred to above and to fully indemnify such counsel against any and all Expenses, claims,
liabilities and damages arising out of or relating to this Agreement or its engagement pursuant hereto. 
 (f)
“Proceeding” includes any threatened, pending or completed action, suit, arbitration, alternate dispute resolution mechanism, investigation, inquiry, administrative hearing or any other actual, threatened or completed
proceeding, whether brought by or in the right of the Company or otherwise and whether civil, criminal, administrative or investigative, in which Indemnitee was, is or will be involved as a party or otherwise, by reason of his or her Corporate
Status, by reason of any action taken by him or of any inaction on his part while acting in his or her Corporate Status; in each case whether or not he is acting or serving in 

  
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any such capacity at the time any liability or expense is incurred for which indemnification can be provided under this Agreement; including one pending on or before the date of this Agreement,
but excluding one initiated by an Indemnitee pursuant to Section 7 of this Agreement to enforce his rights under this Agreement. 

14. Severability. The invalidity or unenforceability of any provision hereof shall in no way affect the validity or enforceability of
any other provision. Further, the invalidity or unenforceability of any provision hereof as to either Indemnitee or Appointing Stockholder shall in no way affect the validity or enforceability of any provision hereof as to the other. Without
limiting the generality of the foregoing, this Agreement is intended to confer upon Indemnitee and Appointing Stockholder indemnification rights to the fullest extent permitted by applicable laws. In the event any provision hereof conflicts with any
applicable law, such provision shall be deemed modified, consistent with the aforementioned intent, to the extent necessary to resolve such conflict. 

15. Modification and Waiver. No supplement, modification, termination or amendment of this Agreement shall be binding unless executed
in writing by both of the parties hereto. No waiver of any of the provisions of this Agreement shall be deemed or shall constitute a waiver of any other provisions hereof (whether or not similar) nor shall such waiver constitute a continuing waiver.

 16. Notice By Indemnitee. Indemnitee agrees promptly to notify the Company in writing upon being served with or otherwise
receiving any summons, citation, subpoena, complaint, indictment, information or other document relating to any Proceeding or matter which may be subject to indemnification covered hereunder. The failure to so notify the Company shall not relieve
the Company of any obligation which it may have to Indemnitee under this Agreement or otherwise unless and only to the extent that such failure or delay materially prejudices the Company. 

17. Notices. All notices and other communications given or made pursuant to this Agreement shall be in writing and shall be deemed
effectively given: (a) upon personal delivery to the party to be notified, (b) when sent by confirmed electronic mail or facsimile if sent during normal business hours of the recipient, and if not so confirmed, then on the next business
day, (c) five (5) days after having been sent by registered or certified mail, return receipt requested, postage prepaid, or (d) one (1) day after deposit with a nationally recognized overnight courier, specifying next day
delivery, with written verification of receipt. All communications shall be sent: 
  

	 	(a)	To Indemnitee at the address set forth below Indemnitee signature hereto. 

  

	 	(b)	To the Company at: 

 Homology Medicines, Inc. 

45 Wiggins Avenue 
 Bedford, MA
01730 
 Attention: Chief Executive Officer 

  
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 or to such other address as may have been furnished to Indemnitee by the Company or to the Company by Indemnitee,
as the case may be. 
 18. Counterparts. This Agreement may be executed in two or more counterparts, each of which shall be deemed
an original, but all of which together shall constitute one and the same instrument. Counterparts may be delivered via facsimile, electronic mail (including pdf or any electronic signature complying with the U.S. federal ESIGN Act of 2000,
e.g., www.docusign.com) or any other transmission method and any counterpart so delivered shall be deemed to have been duly and validly delivered and be valid and effective for all purposes. 

19. Headings. The headings of the paragraphs of this Agreement are inserted for convenience only and shall not be deemed to constitute
part of this Agreement or to affect the construction thereof. 
 20. Governing Law and Consent to Jurisdiction. This Agreement and
the legal relations among the parties shall be governed by, and construed and enforced in accordance with, the laws of the State of Delaware, without regard to its conflict of laws rules. The Company and Indemnitee hereby irrevocably and
unconditionally (i) agree that any action or proceeding arising out of or in connection with this Agreement shall be brought only in the Chancery Court of the State of Delaware (the “Delaware Court”), and not in any
other state or federal court in the United States of America or any court in any other country, (ii) consent to submit to the exclusive jurisdiction of the Delaware Court for purposes of any action or proceeding arising out of or in connection
with this Agreement, (iii) appoint, to the extent such party is not otherwise subject to service of process in the State of Delaware, irrevocably The Corporation Trust Center, 1209 Orange Street, Wilmington, DE 19801 as its agent in the State
of Delaware as such party’s agent for acceptance of legal process in connection with any such action or proceeding against such party with the same legal force and validity as if served upon such party personally within the State of Delaware,
(iv) waive any objection to the laying of venue of any such action or proceeding in the Delaware Court, and (v) waive, and agree not to plead or to make, any claim that any such action or proceeding brought in the Delaware Court has been
brought in an improper or inconvenient forum. 
 SIGNATURE PAGE TO FOLLOW 

  
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 IN WITNESS WHEREOF, the parties hereto have executed this Indemnification Agreement on and as of
the day and year first above written. 
  

					
	HOMOLOGY MEDICINES, INC.


 
					
		
	By:	 	 


 
					
		 	    Name:	 	 


 
					
		 	    Title:	 	 


 
					
	
	INDEMNITEE
	
	   



 
					
	Name:	 	 


 
					
		
	Address:	 	
	   

	   

	   

	   




  
 Indemnification Agreement