EX-10.2



 Exhibit 10.2 

HOMOLOGY MEDICINES, INC. 

2018 INCENTIVE AWARD PLAN 

ARTICLE I. 
 PURPOSE

 The Plan’s purpose is to enhance the Company’s ability to attract, retain and motivate persons who make (or are expected to
make) important contributions to the Company by providing these individuals with equity ownership opportunities. Capitalized terms used in the Plan are defined in Article XI. 

ARTICLE II. 
 ELIGIBILITY

 Service Providers are eligible to be granted Awards under the Plan, subject to the limitations described herein. 

ARTICLE III. 

ADMINISTRATION AND DELEGATION 

3.1 Administration. The Plan is administered by the Administrator. The Administrator has authority to determine which Service Providers
receive Awards, grant Awards and set Award terms and conditions, subject to the conditions and limitations in the Plan. The Administrator also has the authority to take all actions and make all determinations under the Plan, to interpret the Plan
and Award Agreements and to adopt, amend and repeal Plan administrative rules, guidelines and practices as it deems advisable. The Administrator may correct defects and ambiguities, supply omissions and reconcile inconsistencies in the Plan or any
Award as it deems necessary or appropriate to administer the Plan and any Awards. The Administrator’s determinations under the Plan are in its sole discretion and will be final and binding on all persons having or claiming any interest in the
Plan or any Award. 
 3.2 Appointment of Committees. To the extent Applicable Laws permit, the Board may delegate any or all of its
powers under the Plan to one or more Committees or officers of the Company or any of its Subsidiaries. The Board may abolish any Committee or re-vest in itself any previously delegated authority at any time.

 ARTICLE IV. 
 STOCK
AVAILABLE FOR AWARDS 
 4.1 Number of Shares. Subject to adjustment under Article VIII and the terms of this Article IV,
Awards may be made under the Plan covering up to the Overall Share Limit. As of the Plan’s effective date under Section 10.3, the Company will cease granting awards under the Prior Plans; however, Prior Plan Awards will remain subject to
the terms of the applicable Prior Plan. Shares issued under the Plan may consist of authorized but unissued Shares, Shares purchased on the open market or treasury Shares. 

4.2 Share Recycling. If all or any part of an Award or Prior Plan Award expires, lapses or is terminated, exchanged for cash,
surrendered, repurchased, canceled without having been fully exercised or forfeited, in any case, in a manner that results in the Company acquiring Shares covered by the Award or Prior Plan Award at a price not greater than the price (as adjusted to
reflect any Equity Restructuring) paid by the Participant for such Shares or not issuing any Shares covered by the Award or Prior Plan 







 
Award, the unused Shares covered by the Award or Prior Plan Award will, as applicable, become or again be available for Award grants under the Plan. Further, Shares delivered (either by actual
delivery or attestation) to the Company by a Participant to satisfy the applicable exercise or purchase price of an Award or Prior Plan Award and/or to satisfy any applicable tax withholding obligation (including Shares retained by the Company from
the Award or Prior Plan Award being exercised or purchased and/or creating the tax obligation) will, as applicable, become or again be available for Award grants under the Plan. The payment of Dividend Equivalents in cash in conjunction with any
outstanding Awards or Prior Plan Awards shall not count against the Overall Share Limit. 
 4.3 Incentive Stock Option Limitations.
Notwithstanding anything to the contrary herein, no more than 20,887,347 Shares may be issued pursuant to the exercise of Incentive Stock Options. 

4.4 Substitute Awards. In connection with an entity’s merger or consolidation with the Company or the Company’s acquisition
of an entity’s property or stock, the Administrator may grant Awards in substitution for any options or other stock or stock-based awards granted before such merger or consolidation by such entity or its affiliate. Substitute Awards may be
granted on such terms as the Administrator deems appropriate, notwithstanding limitations on Awards in the Plan. Substitute Awards will not count against the Overall Share Limit (nor shall Shares subject to a Substitute Award be added to the Shares
available for Awards under the Plan as provided above), except that Shares acquired by exercise of substitute Incentive Stock Options will count against the maximum number of Shares that may be issued pursuant to the exercise of Incentive Stock
Options under the Plan. Additionally, in the event that a company acquired by the Company or any Subsidiary or with which the Company or any Subsidiary combines has shares available under a pre-existing plan
approved by stockholders and not adopted in contemplation of such acquisition or combination, the shares available for grant pursuant to the terms of such pre-existing plan (as adjusted, to the extent
appropriate, using the exchange ratio or other adjustment or valuation ratio or formula used in such acquisition or combination to determine the consideration payable to the holders of common stock of the entities party to such acquisition or
combination) may be used for Awards under the Plan and shall not reduce the Shares authorized for grant under the Plan (and Shares subject to such Awards shall not be added to the Shares available for Awards under the Plan as provided above);
provided that Awards using such available shares shall not be made after the date awards or grants could have been made under the terms of the pre-existing plan, absent the acquisition or combination, and
shall only be made to individuals who were not Employees or Directors prior to such acquisition or combination. 
 4.5 Non-Employee Director Compensation. Notwithstanding any provision to the contrary in the Plan, the Administrator may establish compensation for non-employee Directors from
time to time, subject to the limitations in the Plan. The Administrator will from time to time determine the terms, conditions and amounts of all such non-employee Director compensation in its discretion and
pursuant to the exercise of its business judgment, taking into account such factors, circumstances and considerations as it shall deem relevant from time to time, provided that the sum of any cash compensation, or other compensation, and the value
(determined as of the grant date in accordance with Financial Accounting Standards Board Accounting Standards Codification Topic 718, or any successor thereto) of Awards granted to a non-employee Director as
compensation for services as a non-employee Director during any fiscal year of the Company may not exceed $500,000 increased to $750,000 in the fiscal year of a
non-employee Director’s initial service as a non-employee Director. The Administrator may make exceptions to this limit for individual non-employee Directors in extraordinary circumstances, as the Administrator may determine in its discretion, provided that the non-employee Director receiving such additional
compensation may not participate in the decision to award such compensation or in other contemporaneous compensation decisions involving non-employee Directors. 

  
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 ARTICLE V. 

STOCK OPTIONS AND STOCK APPRECIATION RIGHTS 

5.1 General. The Administrator may grant Options or Stock Appreciation Rights to Service Providers subject to the limitations in the
Plan, including any limitations in the Plan that apply to Incentive Stock Options. The Administrator will determine the number of Shares covered by each Option and Stock Appreciation Right, the exercise price of each Option and Stock Appreciation
Right and the conditions and limitations applicable to the exercise of each Option and Stock Appreciation Right. A Stock Appreciation Right will entitle the Participant (or other person entitled to exercise the Stock Appreciation Right) to receive
from the Company upon exercise of the exercisable portion of the Stock Appreciation Right an amount determined by multiplying the excess, if any, of the Fair Market Value of one Share on the date of exercise over the exercise price per Share of the
Stock Appreciation Right by the number of Shares with respect to which the Stock Appreciation Right is exercised, subject to any limitations of the Plan or that the Administrator may impose and payable in cash, Shares valued at Fair Market Value or
a combination of the two as the Administrator may determine or provide in the Award Agreement. 
 5.2 Exercise Price. The
Administrator will establish each Option’s and Stock Appreciation Right’s exercise price and specify the exercise price in the Award Agreement. The exercise price will not be less than 100% of the Fair Market Value on the grant date of the
Option or Stock Appreciation Right. 
 5.3 Duration. Each Option or Stock Appreciation Right will be exercisable at such times and as
specified in the Award Agreement, provided that the term of an Option or Stock Appreciation Right will not exceed ten years. Notwithstanding the foregoing and unless determined otherwise by the Company, in the event that on the last business day of
the term of an Option or Stock Appreciation Right (other than an Incentive Stock Option) (i) the exercise of the Option or Stock Appreciation Right is prohibited by Applicable Law, as determined by the Company, or (ii) Shares may not be
purchased or sold by the applicable Participant due to any Company insider trading policy (including blackout periods) or a “lock-up” agreement undertaken in connection with an issuance of securities
by the Company, the term of the Option or Stock Appreciation Right shall be extended until the date that is thirty (30) days after the end of the legal prohibition, black-out period or lock-up agreement, as determined by the Company; provided, however, in no event shall the extension last beyond the ten year term of the applicable Option or Stock Appreciation Right. Notwithstanding the foregoing,
if the Participant, prior to the end of the term of an Option or Stock Appreciation Right, violates the non-competition, non-solicitation, confidentiality or other
similar restrictive covenant provisions of any employment contract, confidentiality and nondisclosure agreement or other agreement between the Participant and the Company or any of its Subsidiaries, the right of the Participant and the
Participant’s transferees to exercise any Option or Stock Appreciation Right issued to the Participant shall terminate immediately upon such violation, unless the Company otherwise determines. In addition, if, prior to the end of the term of an
Option or Stock Appreciation Right, the Participant is given notice by the Company or any of its Subsidiaries of the Participant’s Termination of Service by the Company or any of its Subsidiaries for Cause, and the effective date of such
Termination of Service is subsequent to the date of the delivery of such notice, the right of the Participant and the Participant’s transferees to exercise any Option or Stock Appreciation Right issued to the Participant shall be suspended from
the time of the delivery of such notice until the earlier of (i) such time as it is determined or otherwise agreed that the Participant’s service as a Service Provider will not be terminated for Cause as provided in such notice or
(ii) the effective date of the Participant’s Termination of Service by the Company or any of its Subsidiaries for Cause (in which case the right of the Participant and the Participant’s transferees to exercise any Option or Stock
Appreciation Right issued to the Participant will terminate immediately upon the effective date of such termination of Service). 

  
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 5.4 Exercise. Options and Stock Appreciation Rights may be exercised by delivering to the
Company a written notice of exercise, in a form the Administrator approves (which may be electronic), signed by the person authorized to exercise the Option or Stock Appreciation Right, together with, as applicable, payment in full (i) as
specified in Section 5.5 for the number of Shares for which the Award is exercised and (ii) as specified in Section 9.5 for any applicable taxes. Unless the Administrator otherwise determines, an Option or Stock Appreciation Right may
not be exercised for a fraction of a Share. 
 5.5 Payment Upon Exercise. Subject to Section 10.8, any Company
insider trading policy (including blackout periods) and Applicable Laws, the exercise price of an Option must be paid by: 
 (a) cash, wire
transfer of immediately available funds or by check payable to the order of the Company, provided that the Company may limit the use of one of the foregoing payment forms if one or more of the payment forms below is permitted; 

(b) if there is a public market for Shares at the time of exercise, unless the Company otherwise determines, (A) delivery (including
telephonically to the extent permitted by the Company) of an irrevocable and unconditional undertaking by a broker acceptable to the Company to deliver promptly to the Company sufficient funds to pay the exercise price, or (B) the
Participant’s delivery to the Company of a copy of irrevocable and unconditional instructions to a broker acceptable to the Company to deliver promptly to the Company cash or a check sufficient to pay the exercise price; provided that such
amount is paid to the Company at such time as may be required by the Administrator; 
 (c) to the extent permitted by the Administrator,
delivery (either by actual delivery or attestation) of Shares owned by the Participant valued at their Fair Market Value; 
 (d) to the
extent permitted by the Administrator, surrendering Shares then issuable upon the Option’s exercise valued at their Fair Market Value on the exercise date; 

(e) to the extent permitted by the Administrator, delivery of a promissory note or any other property that the Administrator determines is
good and valuable consideration; or 
 (f) to the extent permitted by the Company, any combination of the above payment forms approved by
the Administrator. 
 ARTICLE VI. 

RESTRICTED STOCK; RESTRICTED STOCK UNITS 

6.1 General. The Administrator may grant Restricted Stock, or the right to purchase Restricted Stock, to any Service Provider, subject
to the Company’s right to repurchase all or part of such shares at their issue price or other stated or formula price from the Participant (or to require forfeiture of such shares) if conditions the Administrator specifies in the Award
Agreement are not satisfied before the end of the applicable restriction period or periods that the Administrator establishes for such Award. In addition, the Administrator may grant to Service Providers Restricted Stock Units, which may be subject
to vesting and forfeiture conditions during the applicable restriction period or periods, as set forth in an Award Agreement. The Administrator will determine and set forth in the Award Agreement the terms and conditions for each Restricted Stock
and Restricted Stock Unit Award, subject to the conditions and limitations contained in the Plan. 

  
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 6.2 Restricted Stock. 

(a) Dividends. Participants holding shares of Restricted Stock will be entitled to all ordinary cash dividends paid with respect to
such Shares, unless the Administrator provides otherwise in the Award Agreement. In addition, unless the Administrator provides otherwise, if any dividends or distributions are paid in Shares, or consist of a dividend or distribution to holders of
Common Stock of property other than an ordinary cash dividend, the Shares or other property will be subject to the same restrictions on transferability and forfeitability as the shares of Restricted Stock with respect to which they were paid. 

(b) Stock Certificates. The Company may require that the Participant deposit in escrow with the Company (or its designee) any stock
certificates issued in respect of shares of Restricted Stock, together with a stock power endorsed in blank. 
 6.3 Restricted Stock
Units. 
 (a) Settlement. The Administrator may provide that settlement of Restricted Stock Units will occur upon or as soon as
reasonably practicable after the Restricted Stock Units vest or will instead be deferred, on a mandatory basis or at the Participant’s election, in a manner intended to comply with Section 409A. 

(b) Stockholder Rights. A Participant will have no rights of a stockholder with respect to Shares subject to any Restricted Stock Unit
unless and until the Shares are delivered in settlement of the Restricted Stock Unit. 
 (c) Dividend Equivalents. If the
Administrator provides, a grant of Restricted Stock Units may provide a Participant with the right to receive Dividend Equivalents. Dividend Equivalents may be paid currently or credited to an account for the Participant, settled in cash or Shares
and subject to the same restrictions on transferability and forfeitability as the Restricted Stock Units with respect to which the Dividend Equivalents are granted and subject to other terms and conditions as set forth in the Award Agreement. 

ARTICLE VII. 
 OTHER
STOCK OR CASH BASED AWARDS 
 Other Stock or Cash Based Awards may be granted to Participants, including Awards entitling Participants
to receive Shares to be delivered in the future and including annual or other periodic or long-term cash bonus awards (whether based on specified Performance Criteria or otherwise), in each case subject to any conditions and limitations in the Plan.
Such Other Stock or Cash Based Awards will also be available as a payment form in the settlement of other Awards, as standalone payments and as payment in lieu of compensation to which a Participant is otherwise entitled. Other Stock or Cash Based
Awards may be paid in Shares, cash or other property, as the Administrator determines. Subject to the provisions of the Plan, the Administrator will determine the terms and conditions of each Other Stock or Cash Based Award, including any purchase
price, performance goal (which may be based on the Performance Criteria), transfer restrictions, and vesting conditions, which will be set forth in the applicable Award Agreement. 

  
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 ARTICLE VIII. 

ADJUSTMENTS FOR CHANGES IN COMMON STOCK 

AND CERTAIN OTHER EVENTS 

8.1 Equity Restructuring. In connection with any Equity Restructuring, notwithstanding anything to the contrary in this Article VIII,
the Administrator will equitably adjust each outstanding Award as it deems appropriate to reflect the Equity Restructuring, which may include adjusting the number and type of securities subject to each outstanding Award and/or the Award’s
exercise price or grant price (if applicable), granting new Awards to Participants, and making a cash payment to Participants. The adjustments provided under this Section 8.1 will be nondiscretionary and final and binding on the affected
Participant and the Company; provided that the Administrator will determine whether an adjustment is equitable. 
 8.2 Corporate
Transactions. In the event of any dividend or other distribution (whether in the form of cash, Common Stock, other securities, or other property), reorganization, merger, consolidation, combination, amalgamation, repurchase, recapitalization,
liquidation, dissolution, or sale, transfer, exchange or other disposition of all or substantially all of the assets of the Company, or sale or exchange of Common Stock or other securities of the Company, Change in Control, issuance of warrants or
other rights to purchase Common Stock or other securities of the Company, other similar corporate transaction or event, other unusual or nonrecurring transaction or event affecting the Company or its financial statements or any change in any
Applicable Laws or accounting principles, the Administrator, on such terms and conditions as it deems appropriate, either by the terms of the Award or by action taken prior to the occurrence of such transaction or event (except that action to give
effect to a change in Applicable Law or accounting principles may be made within a reasonable period of time after such change) and either automatically or upon the Participant’s request, is hereby authorized to take any one or more of the
following actions whenever the Administrator determines that such action is appropriate in order to (x) prevent dilution or enlargement of the benefits or potential benefits intended by the Company to be made available under the Plan or with
respect to any Award granted or issued under the Plan, (y) to facilitate such transaction or event or (z) give effect to such changes in Applicable Laws or accounting principles: 

(a) To provide for the cancellation of any such Award in exchange for either an amount of cash or other property with a value equal to the
amount that could have been obtained upon the exercise or settlement of the vested portion of such Award or realization of the Participant’s rights under the vested portion of such Award, as applicable; provided that, if the amount that could
have been obtained upon the exercise or settlement of the vested portion of such Award or realization of the Participant’s rights, in any case, is equal to or less than zero, then the Award may be terminated without payment; 

(b) To provide that such Award shall vest and, to the extent applicable, be exercisable as to all shares covered thereby, notwithstanding
anything to the contrary in the Plan or the provisions of such Award; 
 (c) To provide that such Award be assumed by the successor or
survivor corporation, or a parent or subsidiary thereof, or shall be substituted for by awards covering the stock of the successor or survivor corporation, or a parent or subsidiary thereof, with appropriate adjustments as to the number and kind of
shares and/or applicable exercise or purchase price, in all cases, as determined by the Administrator; 
 (d) To make adjustments in the
number and type of shares of Common Stock (or other securities or property) subject to outstanding Awards and/or with respect to which Awards may be granted under the Plan (including, but not limited to, adjustments of the limitations in Article IV
hereof on the maximum number and kind of shares which may be issued) and/or in the terms and conditions of (including the grant or exercise price), and the criteria included in, outstanding Awards; 

(e) To replace such Award with other rights or property selected by the Administrator; and/or 

  
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 (f) To provide that the Award will terminate and cannot vest, be exercised or become payable
after the applicable event. 
 8.3 Administrative Stand Still. In the event of any pending stock dividend, stock split, combination
or exchange of shares, merger, consolidation or other distribution (other than normal cash dividends) of Company assets to stockholders, or any other extraordinary transaction or change affecting the Shares or the share price of Common Stock,
including any Equity Restructuring or any securities offering or other similar transaction, for administrative convenience, the Administrator may refuse to permit the exercise of any Award for up to sixty days before or after such transaction. 

8.4 General. Except as expressly provided in the Plan or the Administrator’s action under the Plan, no Participant will have any
rights due to any subdivision or consolidation of Shares of any class, dividend payment, increase or decrease in the number of Shares of any class or dissolution, liquidation, merger, or consolidation of the Company or other corporation. Except as
expressly provided with respect to an Equity Restructuring under Section 8.1 above or the Administrator’s action under the Plan, no issuance by the Company of Shares of any class, or securities convertible into Shares of any class, will
affect, and no adjustment will be made regarding, the number of Shares subject to an Award or the Award’s grant or exercise price. The existence of the Plan, any Award Agreements and the Awards granted hereunder will not affect or restrict in
any way the Company’s right or power to make or authorize (i) any adjustment, recapitalization, reorganization or other change in the Company’s capital structure or its business, (ii) any merger, consolidation dissolution or
liquidation of the Company or sale of Company assets or (iii) any sale or issuance of securities, including securities with rights superior to those of the Shares or securities convertible into or exchangeable for Shares. The Administrator may
treat Participants and Awards (or portions thereof) differently under this Article VIII. 
 ARTICLE IX. 

GENERAL PROVISIONS APPLICABLE TO AWARDS 

9.1 Transferability. Except as the Administrator may determine or provide in an Award Agreement or otherwise for Awards other than
Incentive Stock Options, Awards may not be sold, assigned, transferred, pledged or otherwise encumbered, either voluntarily or by operation of law, except by will or the laws of descent and distribution, or, subject to the Administrator’s
consent, pursuant to a domestic relations order, and, during the life of the Participant, will be exercisable only by the Participant. References to a Participant, to the extent relevant in the context, will include references to a
Participant’s authorized transferee that the Administrator specifically approves. 
 9.2 Documentation. Each Award will be
evidenced in an Award Agreement, which may be written or electronic, as the Administrator determines. Each Award may contain terms and conditions in addition to those set forth in the Plan. 

9.3 Discretion. Except as the Plan otherwise provides, each Award may be made alone or in addition or in relation to any other Award.
The terms of each Award to a Participant need not be identical, and the Administrator need not treat Participants or Awards (or portions thereof) uniformly. 

9.4 Termination of Status. The Administrator will determine how the disability, death, retirement, authorized leave of absence or any
other change or purported change in a Participant’s Service Provider status affects an Award and the extent to which, and the period during which, the Participant, the Participant’s legal representative, conservator, guardian or Designated
Beneficiary may exercise rights under the Award, if applicable. 

  
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 9.5 Withholding. Each Participant must pay the Company, or make provision satisfactory to
the Administrator for payment of, any taxes required by law to be withheld in connection with such Participant’s Awards by the date of the event creating the tax liability. The Company may deduct an amount sufficient to satisfy such tax
obligations based on the applicable statutory withholding rates (or such other rate as may be determined by the Company after considering any accounting consequences or costs) from any payment of any kind otherwise due to a Participant. Subject to
Section 10.8 and any Company insider trading policy (including blackout periods), Participants may satisfy such tax obligations (i) in cash, by wire transfer of immediately available funds, by check made payable to the order of the
Company, provided that the Company may limit the use of the foregoing payment forms if one or more of the payment forms below is permitted, (ii) to the extent permitted by the Administrator, in whole or in part by delivery of Shares, including
Shares retained from the Award creating the tax obligation, valued at their Fair Market Value, (iii) if there is a public market for Shares at the time the tax obligations are satisfied, unless the Company otherwise determines,
(A) delivery (including telephonically to the extent permitted by the Company) of an irrevocable and unconditional undertaking by a broker acceptable to the Company to deliver promptly to the Company sufficient funds to satisfy the tax
obligations, or (B) delivery by the Participant to the Company of a copy of irrevocable and unconditional instructions to a broker acceptable to the Company to deliver promptly to the Company cash or a check sufficient to satisfy the tax
withholding; provided that such amount is paid to the Company at such time as may be required by the Administrator, or (iv) to the extent permitted by the Company, any combination of the foregoing payment forms approved by the Administrator. If
any tax withholding obligation will be satisfied under clause (ii) of the immediately preceding sentence by the Company’s retention of Shares from the Award creating the tax obligation and there is a public market for Shares at the time
the tax obligation is satisfied, the Company may elect to instruct any brokerage firm determined acceptable to the Company for such purpose to sell on the applicable Participant’s behalf some or all of the Shares retained and to remit the
proceeds of the sale to the Company or its designee, and each Participant’s acceptance of an Award under the Plan will constitute the Participant’s authorization to the Company and instruction and authorization to such brokerage firm to
complete the transactions described in this sentence. 
 9.6 Amendment of Award; Repricing. The Administrator may amend, modify or
terminate any outstanding Award, including by substituting another Award of the same or a different type, changing the exercise or settlement date, and converting an Incentive Stock Option to a Non-Qualified
Stock Option. The Participant’s consent to such action will be required unless (i) the action, taking into account any related action, does not materially and adversely affect the Participant’s rights under the Award, or (ii) the
change is permitted under Article VIII or pursuant to Section 10.6. Notwithstanding the foregoing or anything in the Plan to the contrary, the Administrator may not except pursuant to Article VIII, without the approval of the stockholders of
the Company, reduce the exercise price per share of outstanding Options or Stock Appreciation Rights or cancel outstanding Options or Stock Appreciation Rights in exchange for cash, other Awards or Options or Stock Appreciation Rights with an
exercise price per share that is less than the exercise price per share of the original Options or Stock Appreciation Rights. 
 9.7
Conditions on Delivery of Stock. The Company will not be obligated to deliver any Shares under the Plan or remove restrictions from Shares previously delivered under the Plan until (i) all Award conditions have been met or removed to the
Company’s satisfaction, (ii) as determined by the Company, all other legal matters regarding the issuance and delivery of such Shares have been satisfied, including any applicable securities laws and stock exchange or stock market rules
and regulations, and (iii) the Participant has executed and delivered to the Company such representations or agreements as the Administrator deems necessary or appropriate to satisfy any Applicable Laws. The Company’s inability to obtain
authority from any regulatory body having jurisdiction, which the Administrator determines is necessary to the lawful issuance and sale of any securities, will relieve the Company of any liability for failing to issue or sell such Shares as to which
such requisite authority has not been obtained. 

  
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 9.8 Acceleration. The Administrator may at any time provide that any Award will become
immediately vested and fully or partially exercisable, free of some or all restrictions or conditions, or otherwise fully or partially realizable. 

9.9 Additional Terms of Incentive Stock Options. The Administrator may grant Incentive Stock Options only to employees of the Company,
any of its present or future parent or subsidiary corporations, as defined in Sections 424(e) or (f) of the Code, respectively, and any other entities the employees of which are eligible to receive Incentive Stock Options under the Code.
If an Incentive Stock Option is granted to a Greater Than 10% Stockholder, the exercise price will not be less than 110% of the Fair Market Value on the Option’s grant date, and the term of the Option will not exceed five years. All Incentive
Stock Options will be subject to and construed consistently with Section 422 of the Code. By accepting an Incentive Stock Option, the Participant agrees to give prompt notice to the Company of dispositions or other transfers (other than in
connection with a Change in Control) of Shares acquired under the Option made within (i) two years from the grant date of the Option or (ii) one year after the transfer of such Shares to the Participant, specifying the date of the
disposition or other transfer and the amount the Participant realized, in cash, other property, assumption of indebtedness or other consideration, in such disposition or other transfer. Neither the Company nor the Administrator will be liable to a
Participant, or any other party, if an Incentive Stock Option fails or ceases to qualify as an “incentive stock option” under Section 422 of the Code. Any Incentive Stock Option or portion thereof that fails to qualify as an
“incentive stock option” under Section 422 of the Code for any reason, including becoming exercisable with respect to Shares having a fair market value exceeding the $100,000 limitation under Treasury Regulation Section 1.422-4, will be a Non-Qualified Stock Option. 

ARTICLE X. 

MISCELLANEOUS 
 10.1 No
Right to Employment or Other Status. No person will have any claim or right to be granted an Award, and the grant of an Award will not be construed as giving a Participant the right to continued employment or any other relationship with the
Company. The Company expressly reserves the right at any time to dismiss or otherwise terminate its relationship with a Participant free from any liability or claim under the Plan or any Award, except as expressly provided in an Award Agreement.

 10.2 No Rights as Stockholder; Certificates. Subject to the Award Agreement, no Participant or Designated Beneficiary will have
any rights as a stockholder with respect to any Shares to be distributed under an Award until becoming the record holder of such Shares. Notwithstanding any other provision of the Plan, unless the Administrator otherwise determines or Applicable
Laws require, the Company will not be required to deliver to any Participant certificates evidencing Shares issued in connection with any Award and instead such Shares may be recorded in the books of the Company (or, as applicable, its transfer
agent or stock plan administrator). The Company may place legends on stock certificates issued under the Plan that the Administrator deems necessary or appropriate to comply with Applicable Laws. 

10.3 Effective Date and Term of Plan. Unless earlier terminated by the Board, the Plan will become effective on the day prior to the
Public Trading Date and will remain in effect until the tenth anniversary of the earlier of (i) the date the Board adopted the Plan or (ii) the date the Company’s stockholders approved the Plan, but Awards previously granted may
extend beyond that date in accordance with the Plan. If the Plan is not approved by the Company’s stockholders, the Plan will not become effective, no Awards will be granted under the Plan and the Prior Plans will continue in full force and
effect in accordance with their terms. 

  
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 10.4 Amendment of Plan. The Administrator may amend, suspend or terminate the Plan at any
time; provided that no amendment, other than an increase to the Overall Share Limit, may materially and adversely affect any Award outstanding at the time of such amendment without the affected Participant’s consent. No Awards may be granted
under the Plan during any suspension period or after Plan termination. Awards outstanding at the time of any Plan suspension or termination will continue to be governed by the Plan and the Award Agreement, as in effect before such suspension or
termination. The Board will obtain stockholder approval of any Plan amendment to the extent necessary to comply with Applicable Laws. 

10.5 Provisions for Foreign Participants. The Administrator may modify Awards granted to Participants who are foreign nationals or
employed outside the United States or establish subplans or procedures under the Plan to address differences in laws, rules, regulations or customs of such foreign jurisdictions with respect to tax, securities, currency, employee benefit or other
matters. 
 10.6 Section 409A. 

(a) General. The Company intends that all Awards be structured to comply with, or be exempt from, Section 409A, such that no
adverse tax consequences, interest, or penalties under Section 409A apply. Notwithstanding anything in the Plan or any Award Agreement to the contrary, the Administrator may, without a Participant’s consent, amend this Plan or Awards,
adopt policies and procedures, or take any other actions (including amendments, policies, procedures and retroactive actions) as are necessary or appropriate to preserve the intended tax treatment of Awards, including any such actions intended to
(A) exempt this Plan or any Award from Section 409A, or (B) comply with Section 409A, including regulations, guidance, compliance programs and other interpretative authority that may be issued after an Award’s grant date.
The Company makes no representations or warranties as to an Award’s tax treatment under Section 409A or otherwise. The Company will have no obligation under this Section 10.6 or otherwise to avoid the taxes, penalties or interest
under Section 409A with respect to any Award and will have no liability to any Participant or any other person if any Award, compensation or other benefits under the Plan are determined to constitute noncompliant “nonqualified deferred
compensation” subject to taxes, penalties or interest under Section 409A. 
 (b) Separation from Service. If an Award
constitutes “nonqualified deferred compensation” under Section 409A, any payment or settlement of such Award upon a termination of a Participant’s Service Provider relationship will, to the extent necessary to avoid taxes under
Section 409A, be made only upon the Participant’s “separation from service” (within the meaning of Section 409A), whether such “separation from service” occurs upon or after the termination of the
Participant’s Service Provider relationship. For purposes of this Plan or any Award Agreement relating to any such payments or benefits, references to a “termination,” “termination of employment” or like terms means a
“separation from service.” 
 (c) Payments to Specified Employees. Notwithstanding any contrary provision in the Plan or
any Award Agreement, any payment(s) of “nonqualified deferred compensation” required to be made under an Award to a “specified employee” (as defined under Section 409A and as the Administrator determines) due to his or her
“separation from service” will, to the extent necessary to avoid taxes under Section 409A(a)(2)(B)(i) of the Code, be delayed for the six-month period immediately following such “separation
from service” (or, if earlier, until the specified employee’s death) and will instead be paid (as set forth in the Award Agreement) on the day immediately following such six-month period or as soon
as administratively practicable thereafter (without interest). Any payments of “nonqualified deferred compensation” under such Award payable more than six months following the Participant’s “separation from service” will be
paid at the time or times the payments are otherwise scheduled to be made. 

  
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 10.7 Limitations on Liability. Notwithstanding any other provisions of the Plan, no
individual acting as a director, officer, other employee or agent of the Company or any Subsidiary will be liable to any Participant, former Participant, spouse, beneficiary, or any other person for any claim, loss, liability, or expense incurred in
connection with the Plan or any Award, and such individual will not be personally liable with respect to the Plan because of any contract or other instrument executed in his or her capacity as an Administrator, director, officer, other employee or
agent of the Company or any Subsidiary. The Company will indemnify and hold harmless each director, officer, other employee and agent of the Company or any Subsidiary that has been or will be granted or delegated any duty or power relating to the
Plan’s administration or interpretation, against any cost or expense (including attorneys’ fees) or liability (including any sum paid in settlement of a claim with the Administrator’s approval) arising from any act or omission
concerning this Plan unless arising from such person’s own fraud or bad faith. 
 10.8
Lock-Up Period. The Company may, at the request of any underwriter representative or otherwise, in connection with registering the offering of any Company securities under the Securities Act, prohibit
Participants from, directly or indirectly, selling or otherwise transferring any Shares or other Company securities during a period of up to one hundred eighty days following the effective date of a Company registration statement filed under the
Securities Act, or such longer period as determined by the underwriter. 
 10.9 Data Privacy. As a condition for receiving any Award,
each Participant explicitly and unambiguously consents to the collection, use and transfer, in electronic or other form, of personal data as described in this section by and among the Company and its Subsidiaries and affiliates exclusively for
implementing, administering and managing the Participant’s participation in the Plan. The Company and its Subsidiaries and affiliates may hold certain personal information about a Participant, including the Participant’s name, address and
telephone number; birthdate; social security, insurance number or other identification number; salary; nationality; job title(s); any Shares held in the Company or its Subsidiaries and affiliates; and Award details, to implement, manage and
administer the Plan and Awards (the “Data”). The Company and its Subsidiaries and affiliates may transfer the Data amongst themselves as necessary to implement, administer and manage a Participant’s participation in the
Plan, and the Company and its Subsidiaries and affiliates may transfer the Data to third parties assisting the Company with Plan implementation, administration and management. These recipients may be located in the Participant’s country, or
elsewhere, and the Participant’s country may have different data privacy laws and protections than the recipients’ country. By accepting an Award, each Participant authorizes such recipients to receive, possess, use, retain and transfer
the Data, in electronic or other form, to implement, administer and manage the Participant’s participation in the Plan, including any required Data transfer to a broker or other third party with whom the Company or the Participant may elect to
deposit any Shares. The Data related to a Participant will be held only as long as necessary to implement, administer, and manage the Participant’s participation in the Plan. A Participant may, at any time, view the Data that the Company holds
regarding such Participant, request additional information about the storage and processing of the Data regarding such Participant, recommend any necessary corrections to the Data regarding the Participant or refuse or withdraw the consents in this
Section 10.9 in writing, without cost, by contacting the local human resources representative. The Company may cancel Participant’s ability to participate in the Plan and, in the Administrator’s discretion, the Participant may forfeit
any outstanding Awards if the Participant refuses or withdraws the consents in this Section 10.9. For more information on the consequences of refusing or withdrawing consent, Participants may contact their local human resources representative.


  
 11 








 10.10 Severability. If any portion of the Plan or any action taken under it is held
illegal or invalid for any reason, the illegality or invalidity will not affect the remaining parts of the Plan, and the Plan will be construed and enforced as if the illegal or invalid provisions had been excluded, and the illegal or invalid action
will be null and void. 
 10.11 Governing Documents. If any contradiction occurs between the Plan and any Award Agreement or other
written agreement between a Participant and the Company (or any Subsidiary) that the Administrator has approved, the Plan will govern, unless it is expressly specified in such Award Agreement or other written document that a specific provision of
the Plan will not apply. 
 10.12 Governing Law. The Plan and all Awards will be governed by and interpreted in accordance with the
laws of the State of Delaware, disregarding any state’s choice-of-law principles requiring the application of a jurisdiction’s laws other than the State of
Delaware. 
 10.13 Claw-back Provisions. All Awards (including any proceeds, gains or other economic benefit the Participant actually
or constructively receives upon receipt or exercise of any Award or the receipt or resale of any Shares underlying the Award) will be subject to any Company claw-back policy, including any claw-back policy adopted to comply with Applicable Laws
(including the Dodd-Frank Wall Street Reform and Consumer Protection Act and any rules or regulations promulgated thereunder) as set forth in such claw-back policy or the Award Agreement. 

10.14 Titles and Headings. The titles and headings in the Plan are for convenience of reference only and, if any conflict, the
Plan’s text, rather than such titles or headings, will control. 
 10.15 Conformity to Securities Laws. Participant acknowledges
that the Plan is intended to conform to the extent necessary with Applicable Laws. Notwithstanding anything herein to the contrary, the Plan and all Awards will be administered only in conformance with Applicable Laws. To the extent Applicable Laws
permit, the Plan and all Award Agreements will be deemed amended as necessary to conform to Applicable Laws. 
 10.16 Relationship to
Other Benefits. No payment under the Plan will be taken into account in determining any benefits under any pension, retirement, savings, profit sharing, group insurance, welfare or other benefit plan of the Company or any Subsidiary except as
expressly provided in writing in such other plan or an agreement thereunder. 
 10.17 Broker-Assisted Sales. In the event of a
broker-assisted sale of Shares in connection with the payment of amounts owed by a Participant under or with respect to the Plan or Awards, including amounts to be paid under the final sentence of Section 9.5: (a) any Shares to be sold through
the broker-assisted sale will be sold on the day the payment first becomes due, or as soon thereafter as practicable; (b) such Shares may be sold as part of a block trade with other Participants in the Plan in which all participants receive an
average price; (c) the applicable Participant will be responsible for all broker’s fees and other costs of sale, and by accepting an Award, each Participant agrees to indemnify and hold the Company harmless from any losses, costs, damages,
or expenses relating to any such sale; (d) to the extent the Company or its designee receives proceeds of such sale that exceed the amount owed, the Company will pay such excess in cash to the applicable Participant as soon as reasonably
practicable; (e) the Company and its designees are under no obligation to arrange for such sale at any particular price; and (f) in the event the proceeds of such sale are insufficient to satisfy the Participant’s applicable
obligation, the Participant may be required to pay immediately upon demand to the Company or its designee an amount in cash sufficient to satisfy any remaining portion of the Participant’s obligation. 

  
 12 








 ARTICLE XI. 

DEFINITIONS 
 As used in
the Plan, the following words and phrases will have the following meanings: 
 11.1 “Administrator” means the Board
or a Committee to the extent that the Board’s powers or authority under the Plan have been delegated to such Committee. 
 11.2
“Applicable Laws” means the requirements relating to the administration of equity incentive plans under U.S. federal and state securities, tax and other applicable laws, rules and regulations, the applicable rules of any
stock exchange or quotation system on which the Common Stock is listed or quoted and the applicable laws and rules of any foreign country or other jurisdiction where Awards are granted. 

11.3 “Award” means, individually or collectively, a grant under the Plan of Options, Stock Appreciation Rights,
Restricted Stock, Restricted Stock Units or Other Stock or Cash Based Awards. 
 11.4 “Award Agreement” means a
written agreement evidencing an Award, which may be electronic, that contains such terms and conditions as the Administrator determines, consistent with and subject to the terms and conditions of the Plan. 

11.5 “Board” means the Board of Directors of the Company. 

11.6 “Cause” means (i) if a Participant is a party to a written employment or consulting agreement with the
Company or any of its Subsidiaries or an Award Agreement in which the term “cause” is defined (a “Relevant Agreement”), “Cause” as defined in the Relevant Agreement, and (ii) if no Relevant Agreement
exists, (A) the Administrator’s determination that the Participant failed to substantially perform the Participant’s duties (other than a failure resulting from the Participant’s Disability); (B) the Administrator’s
determination that the Participant failed to carry out, or comply with any lawful and reasonable directive of the Board or the Participant’s immediate supervisor; (C) the occurrence of any act or omission by the Participant that could
reasonably be expected to result in (or has resulted in) the Participant’s conviction, plea of no contest, plea of nolo contendere, or imposition of unadjudicated probation for any felony or indictable offense or crime involving moral
turpitude; (D) the Participant’s unlawful use (including being under the influence) or possession of illegal drugs on the premises of the Company or any of its Subsidiaries or while performing the Participant’s duties and
responsibilities for the Company or any of its Subsidiaries; or (E) the Participant’s commission of an act of fraud, embezzlement, misappropriation, misconduct, or breach of fiduciary duty against the Company or any of its Subsidiaries.

 11.7 “Change in Control” means and includes each of the following: 

(a) A transaction or series of transactions (other than an offering of Common Stock to the general public through a registration statement
filed with the Securities and Exchange Commission or a transaction or series of transactions that meets the requirements of clauses (i) and (ii) of subsection (c) below) whereby any “person” or related “group” of
“persons” (as such terms are used in Sections 13(d) and 14(d)(2) of the Exchange Act) (other than the Company, any of its Subsidiaries, an employee benefit plan maintained by the Company or any of its Subsidiaries or a
“person” that, prior to such transaction, directly or indirectly controls, is controlled by, or is under common control with, the Company) directly or indirectly acquires beneficial ownership (within the meaning of Rule 13d-3 under the Exchange Act) of securities of the Company possessing more than 50% of the total combined voting power of the Company’s securities outstanding immediately after such acquisition; or 

  
 13 








 (b) During any period of two consecutive years, individuals who, at the beginning of such period,
constitute the Board together with any new Director(s) (other than a Director designated by a person who shall have entered into an agreement with the Company to effect a transaction described in subsections (a) or (c)) whose election by the
Board or nomination for election by the Company’s stockholders was approved by a vote of at least two-thirds of the Directors then still in office who either were Directors at the beginning of the two-year period or whose election or nomination for election was previously so approved, cease for any reason to constitute a majority thereof; or 

(c) The consummation by the Company (whether directly involving the Company or indirectly involving the Company through one or more
intermediaries) of (x) a merger, consolidation, reorganization, or business combination or (y) a sale or other disposition of all or substantially all of the Company’s assets in any single transaction or series of related transactions
or (z) the acquisition of assets or stock of another entity, in each case other than a transaction: 
 (i) which results in the
Company’s voting securities outstanding immediately before the transaction continuing to represent (either by remaining outstanding or by being converted into voting securities of the Company or the person that, as a result of the transaction,
controls, directly or indirectly, the Company or owns, directly or indirectly, all or substantially all of the Company’s assets or otherwise succeeds to the business of the Company (the Company or such person, the “Successor
Entity”)) directly or indirectly, at least a majority of the combined voting power of the Successor Entity’s outstanding voting securities immediately after the transaction, and 

(ii) after which no person or group beneficially owns voting securities representing 50% or more of the combined voting power of the
Successor Entity; provided, however, that no person or group shall be treated for purposes of this clause (ii) as beneficially owning 50% or more of the combined voting power of the Successor Entity solely as a result of the
voting power held in the Company prior to the consummation of the transaction. 
 Notwithstanding the foregoing, if a Change in Control
constitutes a payment event with respect to any Award (or portion of any Award) that provides for the deferral of compensation that is subject to Section 409A, to the extent required to avoid the imposition of additional taxes under
Section 409A, the transaction or event described in subsection (a), (b) or (c) with respect to such Award (or portion thereof) shall only constitute a Change in Control for purposes of the payment timing of such Award if such
transaction also constitutes a “change in control event,” as defined in Treasury Regulation Section 1.409A-3(i)(5). 

The Administrator shall have full and final authority, which shall be exercised in its discretion, to determine conclusively whether a Change
in Control has occurred pursuant to the above definition, the date of the occurrence of such Change in Control and any incidental matters relating thereto; provided that any exercise of authority in conjunction with a determination of whether a
Change in Control is a “change in control event” as defined in Treasury Regulation Section 1.409A-3(i)(5) shall be consistent with such regulation. 

11.8 “Code” means the Internal Revenue Code of 1986, as amended, and the regulations issued thereunder. 

11.9 “Committee” means one or more committees or subcommittees of the Board, which may include one or more Company
directors or executive officers, to the extent Applicable Laws permit. To the extent required to comply with the provisions of Rule 16b-3, it is intended that each member of the Committee will be, at the time
the Committee takes any action with respect to an Award that is subject to Rule 16b-3, a “non-employee director” within the meaning of Rule 16b-3; however, a Committee member’s failure to qualify as a “non-employee director” within the meaning of Rule 16b-3
will not invalidate any Award granted by the Committee that is otherwise validly granted under the Plan. 

  
 14 








 11.10 “Common Stock” means the common stock of the Company. 

11.11 “Company” means Homology Medicines, Inc., a Delaware corporation, or any successor. 

11.12 “Consultant” means any person, including any adviser, engaged by the Company or its parent or Subsidiary to
render services to such entity if the consultant or adviser: (i) renders bona fide services to the Company; (ii) renders services not in connection with the offer or sale of securities in a capital-raising transaction and does not directly
or indirectly promote or maintain a market for the Company’s securities; and (iii) is a natural person. 
 11.13
“Designated Beneficiary” means the beneficiary or beneficiaries the Participant designates, in a manner the Administrator determines, to receive amounts due or exercise the Participant’s rights if the Participant dies or
becomes incapacitated. Without a Participant’s effective designation, “Designated Beneficiary” will mean the Participant’s estate. 

11.14 “Director” means a Board member. 

11.15 “Disability” means a permanent and total disability under Section 22(e)(3) of the Code, as amended. 

11.16 “Dividend Equivalents” means a right granted to a Participant under the Plan to receive the equivalent value (in
cash or Shares) of dividends paid on Shares. 
 11.17 “Employee” means any employee of the Company or its
Subsidiaries. 
 11.18 “Equity Restructuring” means a nonreciprocal transaction between the Company and its
stockholders, such as a stock dividend, stock split, spin-off or recapitalization through a large, nonrecurring cash dividend, that affects the number or kind of Shares (or other Company securities) or the
share price of Common Stock (or other Company securities) and causes a change in the per share value of the Common Stock underlying outstanding Awards. 

11.19 “Exchange Act” means the Securities Exchange Act of 1934, as amended. 

11.20 “Fair Market Value” means, as of any date, the value of Common Stock determined as follows: (i) if the
Common Stock is listed on any established stock exchange, its Fair Market Value will be the closing sales price for such Common Stock as quoted on such exchange for such date, or if no sale occurred on such date, the last day preceding such date
during which a sale occurred, as reported in The Wall Street Journal or another source the Administrator deems reliable; (ii) if the Common Stock is not traded on a stock exchange but is quoted on a national market or other quotation system,
the closing sales price on such date, or if no sales occurred on such date, then on the last date preceding such date during which a sale occurred, as reported in The Wall Street Journal or another source the Administrator deems reliable; or
(iii) without an established market for the Common Stock, the Administrator will determine the Fair Market Value in its discretion. Notwithstanding the foregoing, with respect to any Award granted on the pricing date of the Company’s
initial public offering, the Fair Market Value shall mean the initial public offering price of a Share as set forth in the Company’s final prospectus relating to its initial public offering filed with the Securities and Exchange Commission.


  
 15 








 11.21 “Greater Than 10% Stockholder” means an individual then owning
(within the meaning of Section 424(d) of the Code) more than 10% of the total combined voting power of all classes of stock of the Company or its parent or subsidiary corporation, as defined in Section 424(e) and (f) of the Code,
respectively. 
 11.22 “Incentive Stock Option” means an Option intended to qualify as an “incentive stock
option” as defined in Section 422 of the Code. 
 11.23 “Non-Qualified Stock
Option” means an Option not intended or not qualifying as an Incentive Stock Option. 
 11.24 “Option”
means an option to purchase Shares. 
 11.25 “Other Stock or Cash Based Awards” means cash awards, awards of Shares,
and other awards valued wholly or partially by referring to, or are otherwise based on, Shares or other property. 
 11.26
“Overall Share Limit” means the sum of (i) 3,186,205 Shares; (ii) any shares of Common Stock which are subject to Prior Plan Awards which become available for issuance under the Plan pursuant to Article IV and
(iii) an annual increase on the first day of each calendar year beginning January 1, 2019 and ending on and including January 1, 2028, equal to the lesser of (A) 4% of the aggregate number of shares of Common Stock outstanding on the
final day of the immediately preceding calendar year and (B) such smaller number of Shares as is determined by the Board. 
 11.27
“Participant” means a Service Provider who has been granted an Award. 
 11.28 “Performance
Criteria” mean the criteria (and adjustments) that the Administrator may select for an Award to establish performance goals for a performance period, which may include the following: net earnings or losses (either before or after one or
more of interest, taxes, depreciation, amortization, and non-cash equity-based compensation expense); gross or net sales or revenue or sales or revenue growth; net income (either before or after taxes) or
adjusted net income; profits (including but not limited to gross profits, net profits, profit growth, net operation profit or economic profit), profit return ratios or operating margin; budget or operating earnings (either before or after taxes or
before or after allocation of corporate overhead and bonus); cash flow (including operating cash flow and free cash flow or cash flow return on capital); return on assets; return on capital or invested capital; cost of capital; return on
stockholders’ equity; total stockholder return; return on sales; costs, reductions in costs and cost control measures; expenses; working capital; earnings or loss per share; adjusted earnings or loss per share; price per share or dividends per
share (or appreciation in or maintenance of such price or dividends); regulatory achievements or compliance; implementation, completion or attainment of objectives relating to research, development, regulatory, commercial, or strategic milestones or
developments; market share; economic value or economic value added models; division, group or corporate financial goals; customer satisfaction/growth; customer service; employee satisfaction; recruitment and maintenance of personnel; human resources
management; supervision of litigation and other legal matters; strategic partnerships and transactions; financial ratios (including those measuring liquidity, activity, profitability or leverage); debt levels or reductions; sales-related goals;
financing and other capital raising transactions; cash on hand; acquisition activity; investment sourcing activity; and marketing initiatives, any of which may be measured in absolute terms or as compared to any incremental increase or decrease.
Such performance goals also may be based solely by reference to the Company’s performance or the performance of a Subsidiary, division, business segment or business unit of the Company or a Subsidiary, or based upon performance relative to
performance of other companies or upon comparisons of any of the indicators of performance relative to performance of other companies. The 

  
 16 








 
Committee may provide for exclusion of the impact of an event or occurrence which the Committee determines should appropriately be excluded, including (a) restructurings, discontinued
operations, extraordinary items, and other unusual, infrequently occurring or non-recurring charges or events, (b) asset write-downs, (c) litigation or claim judgments or settlements,
(d) acquisitions or divestitures, (e) reorganization or change in the corporate structure or capital structure of the Company, (f) an event either not directly related to the operations of the Company, Subsidiary, division, business
segment or business unit or not within the reasonable control of management, (g) foreign exchange gains and losses, (h) a change in the fiscal year of the Company, (i) the refinancing or repurchase of bank loans or debt securities,
(j) unbudgeted capital expenditures, (k) the issuance or repurchase of equity securities and other changes in the number of outstanding shares, (l) conversion of some or all of convertible securities to Common Stock, (m) any
business interruption event (n) the cumulative effects of tax or accounting changes in accordance with U.S. generally accepted accounting principles, or (o) the effect of changes in other laws or regulatory rules affecting reported
results. 
 11.29 “Plan” means this 2018 Incentive Award Plan. 

11.30 “Prior Plans” means, collectively, the Homology Medicines, Inc. 2015 Stock Incentive Plan and any prior equity
incentive plans of the Company or its predecessor. 
 11.31 “Prior Plan Award” means an award outstanding under the
Prior Plans as of the Plan’s effective date in Section 10.3. 
 11.32 “Public Trading Date” means the
first date upon which the Common Stock is listed (or approved for listing) upon notice of issuance on any securities exchange or designated (or approved for designation) upon notice of issuance as a national market security on an interdealer
quotation system, or, if earlier, the date on which the Company becomes a “publicly held corporation” for purposes of Treasury Regulation Section 1.162-27(c)(1). 

11.33 “Restricted Stock” means Shares awarded to a Participant under Article VI subject to certain vesting
conditions and other restrictions. 
 11.34 “Restricted Stock Unit” means an unfunded, unsecured right to receive,
on the applicable settlement date, one Share or an amount in cash or other consideration determined by the Administrator to be of equal value as of such settlement date, subject to certain vesting conditions and other restrictions. 

11.35 “Rule 16b-3” means Rule 16b-3
promulgated under the Exchange Act. 
 11.36 “Section 409A” means Section 409A
of the Code and all regulations, guidance, compliance programs and other interpretative authority thereunder. 
 11.37
“Securities Act” means the Securities Act of 1933, as amended. 
 11.38 “Service Provider”
means an Employee, Consultant or Director. 
 11.39 “Shares” means shares of Common Stock. 

11.40 “Stock Appreciation Right” means a stock appreciation right granted under Article V. 

11.41 “Subsidiary” means any entity (other than the Company), whether domestic or foreign, in an unbroken chain of
entities beginning with the Company if each of the entities other than the last entity in the unbroken chain beneficially owns, at the time of the determination, securities or interests representing at least 50% of the total combined voting power of
all classes of securities or interests in one of the other entities in such chain. 

  
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 11.42 “Substitute Awards” shall mean Awards granted or Shares issued by
the Company in assumption of, or in substitution or exchange for, awards previously granted, or the right or obligation to make future awards, in each case by a company acquired by the Company or any Subsidiary or with which the Company or any
Subsidiary combines. 
 11.43 “Termination of Service” means the date the Participant ceases to be a Service
Provider. 
 * * * * * 

  
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 HOMOLOGY MEDICINES, INC. 

2018 INCENTIVE AWARD PLAN 

STOCK OPTION GRANT NOTICE 

Capitalized terms not specifically defined in this Stock Option Grant Notice (the “Grant Notice”) have the meanings
given to them in the 2018 Incentive Award Plan (as amended from time to time, the “Plan”) of Homology Medicines, Inc. (the “Company”). 

The Company has granted to the participant listed below (“Participant”) the stock option described in this Grant
Notice (the “Option”), subject to the terms and conditions of the Plan and the Stock Option Agreement attached as Exhibit A (the “Agreement”), both of which are incorporated into this Grant
Notice by reference. 
  

			
	Participant:	  	
		
	Grant Date:	  	
		
	Exercise Price per Share:	  	
		
	Shares Subject to the Option:	  	
		
	Final Expiration Date:	  	
		
	Vesting Commencement Date:	  	
		
	Vesting Schedule:	  	[To be specified in individual award agreements]
		
	Type of Option	  	[Incentive Stock Option/Non-Qualified Stock Option]

 By Participant’s signature below, Participant agrees to be bound by the terms of this Grant Notice, the
Plan and the Agreement. Participant has reviewed the Plan, this Grant Notice and the Agreement in their entirety, has had an opportunity to obtain the advice of counsel prior to executing this Grant Notice and fully understands all provisions of the
Plan, this Grant Notice and the Agreement. Participant hereby agrees to accept as binding, conclusive and final all decisions or interpretations of the Administrator upon any questions arising under the Plan, this Grant Notice or the Agreement. 

 

									
	HOMOLOGY MEDICINES, INC.	 		 	PARTICIPANT
				
	By:	 	 	 		 	 
				
	Name:	 	 	 		 	[Participant Name]
				
	Title:	 	 	 		 	








 Exhibit A 

STOCK OPTION AGREEMENT 

Capitalized terms not specifically defined in this Agreement have the meanings specified in the Grant Notice or, if not defined in the Grant
Notice, in the Plan. 
 ARTICLE I. 

GENERAL 
 1.1 Grant of
Option. The Company has granted to Participant the Option effective as of the grant date set forth in the Grant Notice (the “Grant Date”). 

1.2 Incorporation of Terms of Plan. The Option is subject to the terms and conditions set forth in this Agreement and the Plan, which
is incorporated herein by reference. In the event of any inconsistency between the Plan and this Agreement, the terms of the Plan will control. 

ARTICLE II. 
 PERIOD OF
EXERCISABILITY 
 2.1 Commencement of Exercisability. The Option will vest and become exercisable according to the vesting
schedule in the Grant Notice (the “Vesting Schedule”) except that any fraction of a Share as to which the Option would be vested or exercisable will be accumulated and will vest and become exercisable only when a whole Share
has accumulated. Notwithstanding anything in the Grant Notice, the Plan or this Agreement to the contrary, unless the Administrator otherwise determines, the Option will immediately expire and be forfeited as to any portion that is not vested and
exercisable as of Participant’s Termination of Service for any reason. 
 2.2 Duration of Exercisability. The Vesting Schedule
is cumulative. Any portion of the Option which vests and becomes exercisable will remain vested and exercisable until the Option expires. The Option will be forfeited immediately upon its expiration. 

2.3 Expiration of Option. The Option may not be exercised to any extent by anyone after, and will expire on, the first of the following
to occur: 
 (a) The final expiration date in the Grant Notice; 

(b) Except as the Administrator may otherwise approve, the expiration of three (3) months from the date of Participant’s Termination
of Service, unless Participant’s Termination of Service is for Cause or by reason of Participant’s death or Disability; 
 (c)
Except as the Administrator may otherwise approve, the expiration of one (1) year from the date of Participant’s Termination of Service by reason of Participant’s death or Disability; and 

(d) Except as the Administrator may otherwise approve, Participant’s Termination of Service for Cause. 







 ARTICLE III. 

EXERCISE OF OPTION 
 3.1
Person Eligible to Exercise. During Participant’s lifetime, only Participant may exercise the Option. After Participant’s death, any exercisable portion of the Option may, prior to the time the Option expires, be exercised by
Participant’s Designated Beneficiary as provided in the Plan. 
 3.2 Partial Exercise. Any exercisable portion of the Option or
the entire Option, if then wholly exercisable, may be exercised, in whole or in part, according to the procedures in the Plan at any time prior to the time the Option or portion thereof expires, except that the Option may only be exercised for whole
Shares. 
 3.3 Tax Withholding. 

(a) The Company has the right and option, but not the obligation, to treat Participant’s failure to provide timely payment in accordance
with the Plan of any withholding tax arising in connection with the Option as Participant’s election to satisfy all or any portion of the withholding tax by requesting the Company retain Shares otherwise issuable under the Option. 

(b) Participant acknowledges that Participant is ultimately liable and responsible for all taxes owed in connection with the Option,
regardless of any action the Company or any Subsidiary takes with respect to any tax withholding obligations that arise in connection with the Option. Neither the Company nor any Subsidiary makes any representation or undertaking regarding the
treatment of any tax withholding in connection with the awarding, vesting or exercise of the Option or the subsequent sale of Shares. The Company and the Subsidiaries do not commit and are under no obligation to structure the Option to reduce or
eliminate Participant’s tax liability. 
 ARTICLE IV. 

OTHER PROVISIONS 
 4.1
Adjustments. Participant acknowledges that the Option is subject to adjustment, modification and termination in certain events as provided in this Agreement and the Plan. 

4.2 Notices. Any notice to be given under the terms of this Agreement to the Company must be in writing and addressed to the Company in
care of the Company’s Secretary at the Company’s principal office or the Secretary’s then-current email address or facsimile number. Any notice to be given under the terms of this Agreement to Participant must be in writing and
addressed to Participant (or, if Participant is then deceased, to the person entitled to exercise the Option) at Participant’s last known mailing address, email address or facsimile number in the Company’s personnel files. By a notice
given pursuant to this Section, either party may designate a different address for notices to be given to that party. Any notice will be deemed duly given when actually received, when sent by email, when sent by certified mail (return receipt
requested) and deposited with postage prepaid in a post office or branch post office regularly maintained by the United States Postal Service, when delivered by a nationally recognized express shipping company or upon receipt of a facsimile
transmission confirmation. 
 4.3 Titles. Titles are provided herein for convenience only and are not to serve as a basis for
interpretation or construction of this Agreement. 
 4.4 Conformity to Securities Laws. Participant acknowledges that the Plan, the
Grant Notice and this Agreement are intended to conform to the extent necessary with all Applicable Laws and, to the extent Applicable Laws permit, will be deemed amended as necessary to conform to Applicable Laws. 

  
 A-2 








 4.5 Successors and Assigns. The Company may assign any of its rights under this Agreement
to single or multiple assignees, and this Agreement will inure to the benefit of the successors and assigns of the Company. Subject to the restrictions on transfer set forth in the Plan, this Agreement will be binding upon and inure to the benefit
of the heirs, legatees, legal representatives, successors and assigns of the parties hereto. 
 4.6 Limitations Applicable to
Section 16 Persons. Notwithstanding any other provision of the Plan or this Agreement, if Participant is subject to Section 16 of the Exchange Act, the Plan, the Grant Notice, this Agreement and the Option will be subject
to any additional limitations set forth in any applicable exemptive rule under Section 16 of the Exchange Act (including any amendment to Rule 16b-3) that are requirements for the application of such
exemptive rule. To the extent Applicable Laws permit, this Agreement will be deemed amended as necessary to conform to such applicable exemptive rule. 

4.7 Entire Agreement. The Plan, the Grant Notice and this Agreement (including any exhibit hereto) constitute the entire agreement
of the parties and supersede in their entirety all prior undertakings and agreements of the Company and Participant with respect to the subject matter hereof. 

4.8 Agreement Severable. In the event that any provision of the Grant Notice or this Agreement is held illegal or invalid, the
provision will be severable from, and the illegality or invalidity of the provision will not be construed to have any effect on, the remaining provisions of the Grant Notice or this Agreement. 

4.9 Limitation on Participant’s Rights. Participation in the Plan confers no rights or interests other than as herein provided.
This Agreement creates only a contractual obligation on the part of the Company as to amounts payable and may not be construed as creating a trust. Neither the Plan nor any underlying program, in and of itself, has any assets. Participant will have
only the rights of a general unsecured creditor of the Company with respect to amounts credited and benefits payable, if any, with respect to the Option, and rights no greater than the right to receive the Shares as a general unsecured creditor with
respect to the Option, as and when exercised pursuant to the terms hereof. 
 4.10 Not a Contract of Employment. Nothing in the Plan,
the Grant Notice or this Agreement confers upon Participant any right to continue in the employ or service of the Company or any Subsidiary or interferes with or restricts in any way the rights of the Company and its Subsidiaries, which rights are
hereby expressly reserved, to discharge or terminate the services of Participant at any time for any reason whatsoever, with or without Cause, except to the extent expressly provided otherwise in a written agreement between the Company or a
Subsidiary and Participant. 
 4.11 Counterparts. The Grant Notice may be executed in one or more counterparts, including by way of
any electronic signature, subject to Applicable Law, each of which will be deemed an original and all of which together will constitute one instrument. 

4.12 Incentive Stock Options. If the Option is designated as an Incentive Stock Option: 

(a) Participant acknowledges that to the extent the aggregate fair market value of shares (determined as of the time the option with respect to
the shares is granted) with respect to which stock options intended to qualify as “incentive stock options” under Section 422 of the Code, including the Option, are exercisable for the first time by Participant during any calendar
year exceeds $100,000 or if for any other reason such stock options do not qualify or cease to qualify for treatment as “incentive stock options” under Section 422 of the Code, such stock options (including the Option) will be treated
as non-qualified stock options. Participant further acknowledges that the rule set forth in the preceding sentence will be applied by taking the Option and other stock options into account in the order in
which they were granted, as determined under Section 422(d) of the Code. Participant acknowledges that amendments or modifications made to the Option pursuant to the Plan that would cause the Option to become a
Non-Qualified Stock Option will not materially or adversely affect Participant’s rights under the Option, and that any such amendment or modification shall not require Participant’s consent.
Participant also acknowledges that if the Option is exercised more than three (3) months after Participant’s Termination of Service as an Employee, other than by reason of death or disability, the Option will be taxed as a Non-Qualified Stock Option. 

  
 A-3 








 (b) Participant will give prompt written notice to the Company of any disposition or other
transfer of any Shares acquired under this Agreement if such disposition or other transfer is made (a) within two (2) years from the Grant Date or (b) within one (1) year after the transfer of such Shares to Participant. Such
notice will specify the date of such disposition or other transfer and the amount realized, in cash, other property, assumption of indebtedness or other consideration, by Participant in such disposition or other transfer. 

* * * * * 

  
 A-4 








 HOMOLOGY MEDICINES, INC. 

2018 INCENTIVE AWARD PLAN 

RESTRICTED STOCK GRANT NOTICE 

Capitalized terms not specifically defined in this Restricted Stock Grant Notice (the “Grant Notice”) have the
meanings given to them in the 2018 Incentive Award Plan (as amended from time to time, the “Plan”) of Homology Medicines, Inc. (the “Company”). 

The Company has granted to the participant listed below (“Participant”) the shares of Restricted Stock
described in this Grant Notice (the “Restricted Shares”), subject to the terms and conditions of the Plan and the Restricted Stock Agreement attached as Exhibit A (the “Agreement”), both of
which are incorporated into this Grant Notice by reference. 
  

			
	Participant:	  	
		
	Grant Date:	  	
		
	Number of Restricted Shares:	  	
		
	Vesting Commencement Date:	  	
		
	Vesting Schedule:	  	[To be specified in individual award agreements]

 By Participant’s signature below, Participant agrees to be bound by the terms of this Grant Notice, the
Plan and the Agreement. Participant has reviewed the Plan, this Grant Notice and the Agreement in their entirety, has had an opportunity to obtain the advice of counsel prior to executing this Grant Notice and fully understands all provisions of the
Plan, this Grant Notice and the Agreement. Participant hereby agrees to accept as binding, conclusive and final all decisions or interpretations of the Administrator upon any questions arising under the Plan, this Grant Notice or the Agreement. 

 

									
	HOMOLOGY MEDICINES, INC.	 		 	PARTICIPANT
				
	By:	 	 	 		 	 
				
	Name:	 	 	 		 	[Participant Name]
				
	Title:	 	 	 		 	








 Exhibit A 

RESTRICTED STOCK AGREEMENT 

Capitalized terms not specifically defined in this Agreement have the meanings specified in the Grant Notice or, if not defined in the Grant
Notice, in the Plan. 
 ARTICLE I. 

GENERAL 
 1.1 Issuance
of Restricted Shares. The Company will issue the Restricted Shares to the Participant effective as of the grant date set forth in the Grant Notice and will cause (a) a stock certificate or certificates representing the Restricted Shares to
be registered in Participant’s name or (b) the Restricted Shares to be held in book-entry form. If a stock certificate is issued, the certificate will be delivered to, and held in accordance with this Agreement by, the Company or its
authorized representatives and will bear the restrictive legends required by this Agreement. If the Restricted Shares are held in book-entry form, then the book-entry will indicate that the Restricted Shares are subject to the restrictions of this
Agreement. 
 1.2 Incorporation of Terms of Plan. The Restricted Shares are subject to the terms and conditions set forth in this
Agreement and the Plan, which is incorporated herein by reference. In the event of any inconsistency between the Plan and this Agreement, the terms of the Plan will control.  

ARTICLE II. 
 VESTING,
FORFEITURE AND ESCROW 
 2.1 Vesting. The Restricted Shares will become vested Shares (the “Vested
Shares”) according to the vesting schedule in the Grant Notice except that any fraction of a Share that would otherwise become a Vested Share will be accumulated and will become a Vested Share only when a whole Vested Share has
accumulated. 
 2.2 Forfeiture. In the event of Participant’s Termination of Service for any reason, Participant will
immediately and automatically forfeit to the Company any Shares that are not Vested Shares (the “Unvested Shares”) at the time of Participant’s Termination of Service, except as otherwise determined by the Administrator
or provided in a binding written agreement between Participant and the Company. Upon forfeiture of Unvested Shares, the Company will become the legal and beneficial owner of the Unvested Shares and all related interests and Participant will have no
further rights with respect to the Unvested Shares. 
 2.3 Escrow. 

(a) Unvested Shares will be held by the Company or its authorized representatives until (i) they are forfeited, (ii) they become
Vested Shares or (iii) this Agreement is no longer in effect. By accepting this Award, Participant appoints the Company and its authorized representatives as Participant’s
attorney(s)-in-fact to take all actions necessary to effect any transfer of forfeited Unvested Shares (and Retained Distributions (as defined below), if any, paid on
such forfeited Unvested Shares) to the Company as may be required pursuant to the Plan or this Agreement and to execute such representations or other documents or assurances as the Company or such representatives deem necessary or advisable in
connection with any such transfer. The Company, or its authorized representative, will not be liable for any good faith act or omission with respect to the holding in escrow or transfer of the Restricted Shares. 







 (b) All cash dividends and other distributions made or declared with respect to Unvested Shares
(“Retained Distributions”) will be held by the Company until the time (if ever) when the Unvested Shares to which such Retained Distributions relate become Vested Shares. The Company will establish a separate Retained
Distribution bookkeeping account (“Retained Distribution Account”) for each Unvested Share with respect to which Retained Distributions have been made or declared in cash and credit the Retained Distribution Account (without
interest) on the date of payment with the amount of such cash made or declared with respect to the Unvested Share. Retained Distributions (including any Retained Distribution Account balance) will immediately and automatically be forfeited upon
forfeiture of the Unvested Share with respect to which the Retained Distributions were paid or declared. 
 (c) As soon as reasonably
practicable following the date on which an Unvested Share becomes a Vested Share, the Company will (i) cause the certificate (or a new certificate without the legend required by this Agreement, if Participant so requests) representing the Share
to be delivered to Participant or, if the Share is held in book-entry form, cause the notations indicating the Share is subject to the restrictions of this Agreement to be removed and (ii) pay to Participant the Retained Distributions relating
to the Share. 
 2.4 Rights as Stockholder. Except as otherwise provided in this Agreement or the Plan, upon issuance of the
Restricted Shares by the Company, Participant will have all the rights of a stockholder with respect to the Restricted Shares, including the right to vote the Restricted Shares and to receive dividends or other distributions paid or made with
respect to the Restricted Shares. 
 ARTICLE III. 

TAXATION AND TAX WITHHOLDING 

3.1 Representation. Participant represents to the Company that Participant has reviewed with Participant’s own tax advisors the
tax consequences of the Restricted Shares and the transactions contemplated by the Grant Notice and this Agreement. Participant is relying solely on such advisors and not on any statements or representations of the Company or any of its agents. 

3.2 Section 83(b) Election. If Participant makes an election under Section 83(b) of the Code with respect to the Restricted
Shares, Participant will deliver a copy of the election to the Company promptly after filing the election with the Internal Revenue Service. 

3.3 Tax Withholding. 

(a) The Company has the right and option, but not the obligation, to treat Participant’s failure to provide timely payment in accordance
with the Plan of any withholding tax arising in connection with the Restricted Shares as Participant’s election to satisfy all or any portion of the withholding tax by requesting the Company retain Shares otherwise deliverable under the Award.

 (b) Participant acknowledges that Participant is ultimately liable and responsible for all taxes owed in connection with the Restricted
Shares, regardless of any action the Company or any Subsidiary takes with respect to any tax withholding obligations that arise in connection with the Restricted Shares. Neither the Company nor any Subsidiary makes any representation or undertaking
regarding the treatment of any tax withholding in connection with the awarding, vesting or payment of the Restricted Shares or the subsequent sale of the Restricted Shares. The Company and the Subsidiaries do not commit and are under no obligation
to structure this Award to reduce or eliminate Participant’s tax liability. 

  
 A-2 








 ARTICLE IV. 

RESTRICTIVE LEGENDS AND TRANSFERABILITY 

4.1 Legends. Any certificate representing a Restricted Share will bear the following legend until the Restricted Share becomes a Vested
Share: 
 THE SHARES REPRESENTED BY THIS CERTIFICATE ARE SUBJECT TO FORFEITURE IN FAVOR OF THE COMPANY AND MAY BE TRANSFERRED ONLY IN
ACCORDANCE WITH THE TERMS OF A RESTRICTED STOCK AGREEMENT BETWEEN THE COMPANY AND THE STOCKHOLDER, A COPY OF WHICH IS ON FILE WITH THE SECRETARY OF THE COMPANY. 

4.2 Transferability. The Restricted Shares and any Retained Distributions are subject to the restrictions on transfer in the Plan and
may not be sold, assigned or transferred in any manner unless and until they become Vested Shares. Any attempted transfer or disposition of Unvested Shares or related Retained Distributions prior to the time the Unvested Shares become Vested Shares
will be null and void. The Company will not be required to (a) transfer on its books any Restricted Share that has been sold or otherwise transferred in violation of this Agreement or (b) treat as owner of such Restricted Share or accord
the right to vote or pay dividends to any purchaser or other transferee to whom such Restricted Share has been so transferred. The Company may issue appropriate “stop transfer” instructions to its transfer agent, if any, or make
appropriate notations to the same effect in its records. 
 ARTICLE V. 

OTHER PROVISIONS 
 5.1
Adjustments. Participant acknowledges that the Restricted Shares are subject to adjustment, modification and termination in certain events as provided in this Agreement and the Plan. 

5.2 Notices. Any notice to be given under the terms of this Agreement to the Company must be in writing and addressed to the Company in
care of the Company’s Secretary at the Company’s principal office or the Secretary’s then-current email address or facsimile number. Any notice to be given under the terms of this Agreement to Participant must be in writing and
addressed to Participant at Participant’s last known mailing address, email address or facsimile number in the Company’s personnel files. By a notice given pursuant to this Section, either party may designate a different address for
notices to be given to that party. Any notice will be deemed duly given when actually received, when sent by email, when sent by certified mail (return receipt requested) and deposited with postage prepaid in a post office or branch post office
regularly maintained by the United States Postal Service, when delivered by a nationally recognized express shipping company or upon receipt of a facsimile transmission confirmation. 

5.3 Titles. Titles are provided herein for convenience only and are not to serve as a basis for interpretation or construction of this
Agreement. 
 5.4 Conformity to Securities Laws. Participant acknowledges that the Plan, the Grant Notice and this Agreement are
intended to conform to the extent necessary with all Applicable Laws and, to the extent Applicable Laws permit, will be deemed amended as necessary to conform to Applicable Laws. 

5.5 Successors and Assigns. The Company may assign any of its rights under this Agreement to single or multiple assignees, and this
Agreement will inure to the benefit of the successors and assigns of the Company. Subject to the restrictions on transfer set forth in this Agreement or the Plan, this Agreement will be binding upon and inure to the benefit of the heirs, legatees,
legal representatives, successors and assigns of the parties hereto. 

  
 A-3 








 5.6 Limitations Applicable to Section 16 Persons. Notwithstanding any other provision of
the Plan or this Agreement, if Participant is subject to Section 16 of the Exchange Act, the Plan, the Grant Notice, this Agreement and the Restricted Shares will be subject to any additional limitations set forth in any applicable exemptive rule
under Section 16 of the Exchange Act (including any amendment to Rule 16b-3) that are requirements for the application of such exemptive rule. To the extent Applicable Laws permit, this Agreement will be deemed amended as necessary to conform to
such applicable exemptive rule. 
 5.7 Entire Agreement. The Plan, the Grant Notice and this Agreement (including any
exhibit hereto) constitute the entire agreement of the parties and supersede in their entirety all prior undertakings and agreements of the Company and Participant with respect to the subject matter hereof. 

5.8 Agreement Severable. In the event that any provision of the Grant Notice or this Agreement is held illegal or invalid, the
provision will be severable from, and the illegality or invalidity of the provision will not be construed to have any effect on, the remaining provisions of the Grant Notice or this Agreement. 

5.9 Limitation on Participant’s Rights. Participation in the Plan confers no rights or interests other than as herein provided.
This Agreement creates only a contractual obligation on the part of the Company as to amounts payable and may not be construed as creating a trust. Neither the Plan nor any underlying program, in and of itself, has any assets. Participant will have
only the rights of a general unsecured creditor of the Company with respect to amounts credited and benefits payable, if any, with respect to the Award. 

5.10 Not a Contract of Employment. Nothing in the Plan, the Grant Notice or this Agreement confers upon Participant any right to
continue in the employ or service of the Company or any Subsidiary or interferes with or restricts in any way the rights of the Company and its Subsidiaries, which rights are hereby expressly reserved, to discharge or terminate the services of
Participant at any time for any reason whatsoever, with or without cause, except to the extent expressly provided otherwise in a written agreement between the Company or a Subsidiary and Participant. 

5.11 Counterparts. The Grant Notice may be executed in one or more counterparts, including by way of any electronic signature, subject
to Applicable Law, each of which will be deemed an original and all of which together will constitute one instrument. 

* * * * * 

  
 A-4 








 HOMOLOGY MEDICINES, INC. 

2018 INCENTIVE AWARD PLAN 

RESTRICTED STOCK UNIT GRANT NOTICE 

Capitalized terms not specifically defined in this Restricted Stock Unit Grant Notice (the “Grant Notice”) have the
meanings given to them in the 2018 Incentive Award Plan (as amended from time to time, the “Plan”) of Homology Medicines, Inc. (the “Company”). 

The Company has granted to the participant listed below (“Participant”) the Restricted Stock Units described in this
Grant Notice (the “RSUs”), subject to the terms and conditions of the Plan and the Restricted Stock Unit Agreement attached as Exhibit A (the “Agreement”), both of which are incorporated into
this Grant Notice by reference. 
  

			
	 Participant:
	  	
		
	 Grant Date:
	  	
		
	 Number of RSUs:
	  	
		
	 Vesting Commencement Date:
	  	
		
	 Vesting Schedule:
	  	[To be specified in individual award agreements]

 By Participant’s signature below, Participant agrees to be bound by the terms of this Grant Notice, the
Plan and the Agreement. Participant has reviewed the Plan, this Grant Notice and the Agreement in their entirety, has had an opportunity to obtain the advice of counsel prior to executing this Grant Notice and fully understands all provisions of the
Plan, this Grant Notice and the Agreement. Participant hereby agrees to accept as binding, conclusive and final all decisions or interpretations of the Administrator upon any questions arising under the Plan, this Grant Notice or the Agreement. 

 

									
	HOMOLOGY MEDICINES, INC.	 		 	 PARTICIPANT
					
	By:	 	 	 		 		 	 
	Name:	 	 	 		 		 	[Participant Name]
	Title:	 	 	 		 		 	








 Exhibit A 

RESTRICTED STOCK UNIT AGREEMENT 

Capitalized terms not specifically defined in this Agreement have the meanings specified in the Grant Notice or, if not defined in the Grant
Notice, in the Plan. 
 ARTICLE I. 

GENERAL 
 1.1 Award of
RSUs and Dividend Equivalents. 
 (a) The Company has granted the RSUs to Participant effective as of the grant date set forth in the
Grant Notice (the “Grant Date”). Each RSU represents the right to receive one Share or, at the option of the Company, an amount of cash, in either case, as set forth in this Agreement. Participant will have no right to the
distribution of any Shares or payment of any cash until the time (if ever) the RSUs have vested. 
 (b) The Company hereby grants to
Participant, with respect to each RSU, a Dividend Equivalent for ordinary cash dividends paid to substantially all holders of outstanding Shares with a record date after the Grant Date and prior to the date the applicable RSU is settled, forfeited
or otherwise expires. Each Dividend Equivalent entitles Participant to receive the equivalent value of any such ordinary cash dividends paid on a single Share. The Company will establish a separate Dividend Equivalent bookkeeping account (a
“Dividend Equivalent Account”) for each Dividend Equivalent and credit the Dividend Equivalent Account (without interest) on the applicable dividend payment date with the amount of any such cash paid. 

1.2 Incorporation of Terms of Plan. The RSUs are subject to the terms and conditions set forth in this Agreement and the Plan, which is
incorporated herein by reference. In the event of any inconsistency between the Plan and this Agreement, the terms of the Plan will control. 

1.3 Unsecured Promise. The RSUs and Dividend Equivalents will at all times prior to settlement represent an unsecured Company
obligation payable only from the Company’s general assets. 
 ARTICLE II. 

VESTING; FORFEITURE AND SETTLEMENT 

2.1 Vesting; Forfeiture. The RSUs will vest according to the vesting schedule in the Grant Notice except that any fraction of an RSU
that would otherwise be vested will be accumulated and will vest only when a whole RSU has accumulated. In the event of Participant’s Termination of Service for any reason, all unvested RSUs will immediately and automatically be cancelled and
forfeited, except as otherwise determined by the Administrator or provided in a binding written agreement between Participant and the Company. Dividend Equivalents (including any Dividend Equivalent Account balance) will vest or be forfeited, as
applicable, upon the vesting or forfeiture of the RSU with respect to which the Dividend Equivalent (including the Dividend Equivalent Account) relates. 

2.2 Settlement. 
 (a)
RSUs and Dividend Equivalents (including any Dividend Equivalent Account balance) will be paid in Shares or cash at the Company’s option as soon as administratively practicable after the vesting of the applicable RSU, but in no event more than
sixty (60) days after the RSU’s vesting date. Notwithstanding the foregoing, the Company may delay any payment under this Agreement that the Company reasonably determines would violate Applicable Law until the earliest date the Company
reasonably determines the making of the payment will not cause such a violation (in accordance with Treasury Regulation Section 1.409A-2(b)(7)(ii)), provided the Company reasonably believes the delay will not result in the imposition of excise taxes
under Section 409A. 







 (b) If an RSU is paid in cash, the amount of cash paid with respect to the RSU will equal the
Fair Market Value of a Share on the day immediately preceding the payment date. If a Dividend Equivalent is paid in Shares, the number of Shares paid with respect to the Dividend Equivalent will equal the quotient, rounded down to the nearest whole
Share, of the Dividend Equivalent Account balance divided by the Fair Market Value of a Share on the day immediately preceding the payment date. 

ARTICLE III. 
 TAXATION
AND TAX WITHHOLDING 
 3.1 Representation. Participant represents to the Company that Participant has reviewed with
Participant’s own tax advisors the tax consequences of this Award and the transactions contemplated by the Grant Notice and this Agreement. Participant is relying solely on such advisors and not on any statements or representations of the
Company or any of its agents. 
 3.2 Tax Withholding. 

(a) The Company has the right and option, but not the obligation, to treat Participant’s failure to provide timely payment in accordance
with the Plan of any withholding tax arising in connection with the RSUs or Dividend Equivalents as Participant’s election to satisfy all or any portion of the withholding tax by requesting the Company retain Shares otherwise issuable under the
Award. 
 (b) Participant acknowledges that Participant is ultimately liable and responsible for all taxes owed in connection with the RSUs
and the Dividend Equivalents, regardless of any action the Company or any Subsidiary takes with respect to any tax withholding obligations that arise in connection with the RSUs or Dividend Equivalents. Neither the Company nor any Subsidiary makes
any representation or undertaking regarding the treatment of any tax withholding in connection with the awarding, vesting or payment of the RSUs or the Dividend Equivalents or the subsequent sale of Shares. The Company and the Subsidiaries do not
commit and are under no obligation to structure the RSUs or Dividend Equivalents to reduce or eliminate Participant’s tax liability. 

ARTICLE IV. 
 OTHER
PROVISIONS 
 4.1 Adjustments. Participant acknowledges that the RSUs, the Shares subject to the RSUs and the Dividend
Equivalents are subject to adjustment, modification and termination in certain events as provided in this Agreement and the Plan. 
 4.2
Notices. Any notice to be given under the terms of this Agreement to the Company must be in writing and addressed to the Company in care of the Company’s Secretary at the Company’s principal office or the Secretary’s
then-current email address or facsimile number. Any notice to be given under the terms of this Agreement to Participant must be in writing and addressed to Participant at Participant’s last known mailing address, email address or facsimile
number in the Company’s personnel files. By a notice given pursuant to this Section, either party may designate a different address for notices to be given to that party. Any notice will be deemed duly given when actually received, when sent by
email, when sent by certified mail (return receipt requested) and deposited with postage prepaid in a post office or branch post office regularly maintained by the United States Postal Service, when delivered by a nationally recognized express
shipping company or upon receipt of a facsimile transmission confirmation. 

  
 A-2 








 4.3 Titles. Titles are provided herein for convenience only and are not to serve as a
basis for interpretation or construction of this Agreement. 
 4.4 Conformity to Securities Laws. Participant acknowledges that the
Plan, the Grant Notice and this Agreement are intended to conform to the extent necessary with all Applicable Laws and, to the extent Applicable Laws permit, will be deemed amended as necessary to conform to Applicable Laws. 

4.5 Successors and Assigns. The Company may assign any of its rights under this Agreement to single or multiple assignees, and this
Agreement will inure to the benefit of the successors and assigns of the Company. Subject to the restrictions on transfer set forth in the Plan, this Agreement will be binding upon and inure to the benefit of the heirs, legatees, legal
representatives, successors and assigns of the parties hereto. 
 4.6 Limitations Applicable to Section 16 Persons. Notwithstanding
any other provision of the Plan or this Agreement, if Participant is subject to Section 16 of the Exchange Act, the Plan, the Grant Notice, this Agreement, the RSUs and the Dividend Equivalents will be subject to any additional limitations set forth
in any applicable exemptive rule under Section 16 of the Exchange Act (including any amendment to Rule 16b-3) that are requirements for the application of such exemptive rule. To the extent Applicable Laws permit, this Agreement will be deemed
amended as necessary to conform to such applicable exemptive rule. 
 4.7 Entire Agreement. The Plan, the Grant Notice and this
Agreement (including any exhibit hereto) constitute the entire agreement of the parties and supersede in their entirety all prior undertakings and agreements of the Company and Participant with respect to the subject matter hereof. 

4.8 Agreement Severable. In the event that any provision of the Grant Notice or this Agreement is held illegal or invalid, the
provision will be severable from, and the illegality or invalidity of the provision will not be construed to have any effect on, the remaining provisions of the Grant Notice or this Agreement. 

4.9 Limitation on Participant’s Rights. Participation in the Plan confers no rights or interests other than as herein provided.
This Agreement creates only a contractual obligation on the part of the Company as to amounts payable and may not be construed as creating a trust. Neither the Plan nor any underlying program, in and of itself, has any assets. Participant will have
only the rights of a general unsecured creditor of the Company with respect to amounts credited and benefits payable, if any, with respect to the RSUs and Dividend Equivalents, and rights no greater than the right to receive cash or the Shares as a
general unsecured creditor with respect to the RSUs and Dividend Equivalents, as and when settled pursuant to the terms of this Agreement. 

4.10 Not a Contract of Employment. Nothing in the Plan, the Grant Notice or this Agreement confers upon Participant any right to
continue in the employ or service of the Company or any Subsidiary or interferes with or restricts in any way the rights of the Company and its Subsidiaries, which rights are hereby expressly reserved, to discharge or terminate the services of
Participant at any time for any reason whatsoever, with or without Cause, except to the extent expressly provided otherwise in a written agreement between the Company or a Subsidiary and Participant. 

4.11 Counterparts. The Grant Notice may be executed in one or more counterparts, including by way of any electronic signature, subject
to Applicable Law, each of which will be deemed an original and all of which together will constitute one instrument. 

* * * * * 

  
 A-3