Document:

EX-10.3

 Exhibit 10.3 

DYNE THERAPEUTICS, INC. 

RESTRICTED STOCK AGREEMENT 

GRANTED UNDER 2018 STOCK INCENTIVE PLAN 

This Restricted Stock Agreement (the “Agreement”) is made this [    ] day of
[            ], 2018, between Dyne Therapeutics, Inc., a Delaware corporation (the “Company”), and
[                    ] (the “Recipient”). 

For valuable consideration, receipt of which is acknowledged, the parties hereto agree as follows: 

1. Issuance of Shares. 

The Company hereby issues to the Recipient in consideration of services rendered and to be rendered by the Recipient to the Company, subject
to the terms and conditions set forth in this Agreement and in the Company’s 2018 Stock Incentive Plan (the “Plan”), [                ] shares (the
“Shares”) of common stock, $0.0001 par value per share, of the Company (the “Common Stock”). Promptly following the execution of this Agreement by the Recipient and, to the extent required, the payment of amounts
due under Section 11(a) of this Agreement, the Company shall issue to the Recipient one or more certificates in the name of the Recipient for that number of Shares issued to the Recipient. The Recipient agrees that the Shares shall be subject
to forfeiture in accordance with Section 3 of this Agreement and the restrictions on transfer set forth in Sections 4 and 5 of this Agreement. 

2. Certain Definitions. 

(a) If the Recipient is party to an employment, consulting or severance agreement with the Company that contains a definition of
“cause” for termination of employment, “Cause” shall have the meaning ascribed to such term in such agreement. Otherwise, “Cause” shall exist upon (i) a good faith finding by the Board of Directors of the
Company (A) of repeated and willful failure of the Recipient after written notice to perform the Recipient’s reasonably assigned duties for the Company, or (B) that the Recipient has engaged in dishonesty, gross negligence or
misconduct, which dishonesty, gross negligence or misconduct has had a material adverse effect on the business affairs of the Company; (ii) the conviction of the Recipient of, or the entry of a pleading of guilty or nolo contendere by the
Recipient to, any crime involving moral turpitude or any felony; or (iii) a breach by the Recipient of any material provision of any invention and non-disclosure agreement or non-competition and non-solicitation agreement with the Company, which breach is not cured within ten days written notice thereof. 

(b) “Change in Control” shall mean the sale of all or substantially all of the outstanding shares of capital stock, assets or
business of the Company, by merger, consolidation, sale of assets or otherwise (other than a merger or consolidation in which all or substantially all of the individuals and entities who were beneficial owners of the Company’s voting securities
immediately prior to such transaction beneficially own, directly or indirectly, more than 50% (determined on an as-converted basis) of the outstanding securities entitled to vote generally in the election of
directors of the resulting, surviving or acquiring corporation in such transaction).” 

 (c) “Code” shall mean the Internal Revenue Code of 1986, as amended. 

(d) “Service” shall mean employment by or the provision of services to the Company or a parent or subsidiary thereof as an
advisor, officer, consultant or member of the Board of Directors. 
 (e) “Vesting Commencement Date” shall mean
[                    ]. 
 3. Vesting
and Forfeiture of Unvested Shares. 
 (a) All of the Shares shall initially be subject to forfeiture. The Recipient shall acquire a
vested interest in (i) twenty-five percent (25%) of the upon Recipient’s completion of one year of Service measured from the Vesting Commencement Date and (ii) the balance of the in a series of successive equal quarterly installments
of six and one-quarter percent (6.25%) of the upon Recipient’s completion of each additional quarter of Service over the three year period measured from the first anniversary of the Vesting Commencement
Date. 
 (b) Subject to the terms of the [Offer Letter/Consulting Agreement/Consulting and Scientific Advisory Board Agreement] dated as of
            , 2018 between the Recipient and the Company (the “[Offer Letter/Consulting Agreement]”), in the event that the Recipient ceases to provide Service for
any reason or no reason, with or without Cause, prior to the fourth (4th) anniversary of the Vesting Commencement Date, vesting shall cease and all of the Shares that have not vested pursuant to
this Agreement shall be forfeited immediately and automatically to the Company without payment to the Recipient. 
 4. Restrictions on
Transfer. 
 (a) The Recipient shall not sell, assign, transfer, pledge, hypothecate or otherwise dispose of, by operation of law or
otherwise (collectively “transfer”) any Shares that have not vested, or any interest therein, except that the Recipient may transfer such Shares (i) to or for the benefit of any spouse, children, parents, uncles, aunts,
siblings, grandchildren and any other relatives approved by the Board of Directors (collectively, “Approved Relatives”) or to a trust established solely for the benefit of the Recipient and/or Approved Relatives; provided
that such Shares shall remain subject to this Agreement (including without limitation the restrictions on transfer set forth in this Section 4 and the right of first refusal set forth in Section 5) and such permitted transferee
shall, as a condition to such transfer, deliver to the Company a written instrument confirming that such transferee shall be bound by all of the terms and conditions of this Agreement or (ii) as part of the sale of all or substantially all of
the shares of capital stock of the Company (including pursuant to a merger or consolidation); provided that, in accordance with the Plan, the securities or other property received by the Recipient in connection with such transaction
shall remain subject to this Agreement. 
 (b) The Recipient shall not transfer any vested Shares, or any interest therein, except in
accordance with Section 5 below. 

  
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 5. Right of First Refusal. 

(a) If the Recipient proposes to transfer any vested Shares, then the Recipient shall first give written notice of the proposed transfer (the
“Transfer Notice”) to the Company. The Transfer Notice shall name the proposed transferee and state the number of such Shares the Recipient proposes to transfer (the “Offered Shares”), the price per share and all
other material terms and conditions of the transfer. 
 (b) For thirty (30) days following its receipt of such Transfer Notice, the
Company shall have the option to purchase all or part of the Offered Shares at the price and upon the terms set forth in the Transfer Notice. In the event the Company elects to purchase all or part of the Offered Shares, it shall give written notice
of such election to the Recipient within such 30-day period. Within ten (10) days after the Recipient’s receipt of such notice, the Recipient shall tender to the Company at its principal offices the
certificate or certificates representing the Offered Shares to be purchased by the Company, duly endorsed in blank by the Recipient or with duly endorsed stock powers attached thereto, all in a form suitable for transfer of the Offered Shares to the
Company. Promptly following receipt of such certificate or certificates, the Company shall deliver or mail to the Recipient a check in payment of the purchase price for such Offered Shares; provided that if the terms of payment set
forth in the Transfer Notice were other than cash against delivery, the Company may pay for the Offered Shares on the same terms and conditions as were set forth in the Transfer Notice; and provided further that any delay in making
such payment shall not invalidate the Company’s exercise of its option to purchase the Offered Shares. 
 (c) If the Company does not
elect to acquire all of the Offered Shares, the Recipient may, within the 30-day period following the expiration of the option granted to the Company under subsection (b) above, transfer the Offered
Shares which the Company has not elected to acquire to the proposed transferee; provided that such transfer shall not be on terms and conditions more favorable to the transferee than those contained in the Transfer Notice.
Notwithstanding any of the above, all Offered Shares transferred pursuant to this Section 5 shall remain subject to this Agreement (including without limitation the restrictions on transfer set forth in Section 4 and the right of first
refusal set forth in this Section 5) and such transferee shall, as a condition to such transfer, deliver to the Company a written instrument confirming that such transferee shall be bound by all of the terms and conditions of this Agreement.

 (d) After the time at which the Offered Shares are required to be delivered to the Company for transfer to the Company pursuant to
subsection (b) above, the Company shall not pay any dividend to the Recipient on account of such Offered Shares or permit the Recipient to exercise any of the privileges or rights of a stockholder with respect to such Offered Shares, but shall,
insofar as permitted by law, treat the Company as the owner of such Offered Shares. 
 (e) The following transactions shall be exempt from
the provisions of this Section 5: 
 (1) a transfer of Shares to or for the benefit of any Approved Relatives, or to a trust
established solely for the benefit of the Recipient and/or Approved Relatives; 

  
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 (2) any transfer pursuant to an effective registration statement filed by the Company under
the Securities Act of 1933, as amended (the “Securities Act”); and 
 (3) the sale of all or substantially all of the
outstanding shares of capital stock of the Company (including pursuant to a merger or consolidation); 
 provided, however, that in the case of a
transfer pursuant to clause (1) above, such Shares shall remain subject to this Agreement (including without limitation the restrictions on transfer set forth in Section 4 and the right of first refusal set forth in this Section 5)
and such transferee shall, as a condition to such transfer, deliver to the Company a written instrument confirming that such transferee shall be bound by all of the terms and conditions of this Agreement. 

(f) The Company may assign its rights to purchase Offered Shares in any particular transaction under this Section 5 to one or more
persons or entities. 
 (g) The provisions of this Section 5 shall terminate upon the earlier of the following events: 

(1) the closing of the sale of shares of Common Stock in an underwritten public offering pursuant to an effective registration statement
filed by the Company under the Securities Act; or 
 (2) a Change in Control. 

(h) The Company shall not be required (1) to transfer on its books any of the Shares which shall have been sold or transferred in
violation of any of the provisions set forth in this Agreement, or (2) to treat as owner of such Shares or to pay dividends to any transferee to whom any such Shares shall have been so sold or transferred. 

6. Agreement in Connection with Initial Public Offering. 

The Recipient agrees, in connection with the initial underwritten public offering of the Common Stock pursuant to a registration statement
under the Securities Act, (i) not to (a) offer, pledge, announce the intention to sell, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to
purchase, or otherwise transfer or dispose of, directly or indirectly, any shares of Common Stock or any securities convertible into or exercisable or exchangeable for shares of Common Stock or (b) enter into any swap or other agreement that
transfers, in whole or in part, any of the economic consequences of ownership of shares of Common Stock, whether any transaction described in clause (a) or (b) is to be settled by delivery of shares of Common Stock or other securities, in cash
or otherwise, during the period beginning on the date of the filing of such registration statement with the Securities and Exchange Commission and ending 180 days from the date of the final prospectus relating to the offering (plus up to an
additional 34 days to the extent requested by the managing underwriters for such offering in order to address NASD Rule 2711(f)(4) or NYSE Rule 472(f)(4) or any similar successor provision), and (ii) to execute any agreement reflecting clause
(i) above as may be requested by the Company or the managing underwriters at the time of such offering. The Company may impose stop-transfer instructions with respect to the shares of Common Stock or other securities subject to the foregoing
restriction until the end of the “lock-up” period. 

  
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 7. Escrow. 

The Recipient shall, upon the execution of this Agreement, execute Joint Escrow Instructions in the form attached to this Agreement as
Exhibit A. The Joint Escrow Instructions shall be delivered to the Secretary of the Company, as escrow agent thereunder. The Recipient shall deliver to such escrow agent a stock assignment duly endorsed in blank, in the form attached to this
Agreement as Exhibit B, and hereby instructs the Company to deliver to such escrow agent, on behalf of the Recipient, the certificate(s) evidencing the Shares issued hereunder. Such materials shall be held by such escrow agent pursuant to the
terms of such Joint Escrow Instructions. 
 8. Restrictive Legends. 

All certificates representing Shares shall have affixed thereto legends in substantially the following form, in addition to any other legends
that may be required under federal or state securities laws: 
 “The shares of stock represented by this certificate are subject to
restrictions on transfer and forfeiture under a certain Restricted Stock Agreement between the corporation and the registered owner of these shares (or such owner’s predecessor in interest), and such Agreement is available for inspection
without charge at the office of the Secretary of the corporation.” 
 “The shares represented by this certificate have not been
registered under the Securities Act of 1933, as amended, and may not be sold, transferred or otherwise disposed of in the absence of an effective registration statement under such Act or an opinion of counsel satisfactory to the corporation to the
effect that such registration is not required.” 
 9. Investment Representations. 

The Recipient represents, warrants and covenants as follows: 

(a) The Recipient is acquiring the Shares for the Recipient’s own account for investment only, and not with a view to, or for sale in
connection with, any distribution of the Shares in violation of the Securities Act, or any rule or regulation under the Securities Act. 

(b) The Recipient has had such opportunity as the Recipient has deemed adequate to obtain from representatives of the Company such information
as is necessary to permit the Recipient to evaluate the merits and risks of Recipient’s investment in the Company. 

  
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 (c) The Recipient has sufficient experience in business, financial and investment matters to
be able to evaluate the risks involved in the receipt of the Shares and to make an informed investment decision with respect to such receipt. 

(d) The Recipient can afford a complete loss of the value of the Shares and is able to bear the economic risk of holding such Shares for an
indefinite period. 
 (e) The Recipient understands that (i) the Shares have not been registered under the Securities Act and are
“restricted securities” within the meaning of Rule 144 under the Securities Act; (ii) the Shares cannot be sold, transferred or otherwise disposed of unless they are subsequently registered under the Securities Act or an
exemption from registration is then available; (iii) in any event, the exemption from registration under Rule 144 will not be available for at least one year and even then will not be available unless a public market then exists for the
Common Stock, adequate information concerning the Company is then available to the public, and other terms and conditions of Rule 144 are complied with; and (iv) there is now no registration statement on file with the Securities and
Exchange Commission with respect to any stock of the Company and the Company has no obligation or current intention to register the Shares under the Securities Act. 

10. Voting Proxy 
 The
Recipient hereby constitutes and appoints as the proxy of the Recipient, and hereby grants a power of attorney to, the Chairman of the Board of the Company, with full power of substitution, with respect to any election of directors and any other
matter submitted to a vote of the stockholders of the Company (whether taken at an annual or special meeting of stockholders or by written action), and hereby authorizes each of them to represent and to vote all voting securities held by the
Recipient as of the applicable record date in such manner as such person shall determine in his sole discretion. The proxy and power of attorney granted by this Section 10 shall terminate and be of no further force or effect upon the earlier of
(i) such time as the Company has issued and sold securities having an aggregate purchase price of $30,000,000 (the “Completed Financing Date”), or (ii) such time as the Board of Directors determines. Each of the proxy and
power of attorney granted hereby is given in consideration of the issuance of the Shares hereunder and, as such, each is coupled with an interest and shall be irrevocable until the Completed Financing Date. 

11. Withholding Taxes; Section 83(b) Election. 

(a) The Recipient acknowledges and agrees that the Company has the right to deduct from payments of any kind otherwise due to the Recipient
any federal, state or local taxes of any kind required by law to be withheld with respect to the issuance of the Shares to the Recipient or vesting of the Shares. The Recipient further acknowledges and agrees that, as a condition to the issuance of
Shares to the Recipient hereunder, the Company may require the Recipient to satisfy the Company’s tax withholding obligations by making a cash payment to the Company in the amount of the Company’s withholding obligation as determined in
good faith by the Company. 

  
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 (b) The Recipient has reviewed with the Recipient’s own tax advisors the federal,
state, local and foreign tax consequences of this investment and the transactions contemplated by this Agreement. The Recipient is relying solely on such advisors and not on any statements or representations of the Company or any of its agents. The
Recipient understands that the Recipient (and not the Company) shall be responsible for the Recipient’s own tax liability that may arise as a result of this investment or the transactions contemplated by this Agreement. The Recipient
understands that it may be beneficial in many circumstances to elect to be taxed at the time the Shares are granted by the Company rather than when and as the Shares vest by filing an election under Section 83(b) of the Code with the I.R.S.
within 30 days from the date of grant by the Company. 
 THE RECIPIENT ACKNOWLEDGES THAT IT IS SOLELY THE RECIPIENT’S RESPONSIBILITY
AND NOT THE COMPANY’S TO FILE TIMELY THE ELECTION UNDER SECTION 83(b), EVEN IF THE RECIPIENT REQUESTS THE COMPANY OR ITS REPRESENTATIVES TO MAKE THIS FILING ON THE RECIPIENT’S BEHALF. 

12. Miscellaneous. 
 (a)
No Rights to Employment. The Recipient acknowledges and agrees that the vesting of the Shares pursuant to Section 3 hereof is earned only by the Recipient’s continuous Service (not through the act of being hired or purchasing the
Shares hereunder). The Recipient further acknowledges and agrees that the transactions contemplated hereunder and the vesting schedule set forth herein do not constitute an express or implied promise of continued engagement as an employee or
consultant for the vesting period, for any period, or at all. 
 (b) Severability. The invalidity or unenforceability of any
provision of this Agreement shall not affect the validity or enforceability of any other provision of this Agreement, and each other provision of this Agreement shall be severable and enforceable to the extent permitted by law. 

(c) Waiver. Any provision for the benefit of the Company contained in this Agreement may be waived, either generally or in any
particular instance, by the Board of Directors of the Company. 
 (d) Binding Effect. This Agreement shall be binding upon and inure
to the benefit of the Company and the Recipient and their respective heirs, executors, administrators, legal representatives, successors and assigns, subject to the restrictions on transfer set forth in Sections 4 and 5 of this Agreement. 

(e) Notice. All notices required or permitted hereunder shall be in writing and deemed effectively given upon personal delivery or five
days after deposit in the United States Post Office, by registered or certified mail, postage prepaid, addressed to the other party hereto at the address shown beneath his or her or its respective signature to this Agreement, or at such other
address or addresses as either party shall designate to the other in accordance with this Section 12(e). 

  
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 (f) Pronouns. Whenever the context may require, any pronouns used in this Agreement
shall include the corresponding masculine, feminine or neuter forms, and the singular form of nouns and pronouns shall include the plural, and vice versa. 

(g) Entire Agreement. This Agreement constitutes the entire agreement between the parties, and supersedes all prior agreements and
understandings, relating to the subject matter of this Agreement. 
 (h) Amendment. This Agreement may be amended or modified only by
a written instrument executed by both the Company and the Recipient. 
 (i) Governing Law. This Agreement shall be construed,
interpreted and enforced in accordance with the internal laws of the State of Delaware without regard to any applicable conflict of law principles. 

(j) Recipient’s Acknowledgments. The Recipient acknowledges that he or she: (i) has read this Agreement; (ii) has been
represented in the preparation, negotiation, and execution of this Agreement by legal counsel of the Recipient’s own choice or has voluntarily declined to seek such counsel; (iii) understands the terms and consequences of this Agreement;
(iv) is fully aware of the legal and binding effect of this Agreement; and (v) understands that the law firm of WilmerHale is acting as counsel to the Company in connection with the transactions contemplated by the Agreement, and is not
acting as counsel for the Recipient. 
 [Remainder of Page Intentionally Left Blank] 

  
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 IN WITNESS WHEREOF, the parties hereto have executed the Restricted Stock Agreement as of
the date and year first above written. The Recipient hereby agrees to the terms and conditions thereof. The Participant hereby acknowledges receipt of a copy of the Company’s 2018 Stock Incentive Plan. 

 

					
	COMPANY:
	
	DYNE THERAPEUTICS, INC.
		
	By:	 	  

		 	Name:	 	  

		 	Title:	 	  

		
	 Address:
	 	400 Technology Square, 10th Floor Cambridge, MA 02139
	
	RECIPIENT:
		
	By:	 	  

		 	Name:	 	  

		
	Address:	 	  

		 		 	  

 SIGNATURE PAGE TO RESTRICTED STOCK AGREEMENT GRANTED UNDER STOCK INCENTIVE PLAN 

 EXHIBIT A 

JOINT ESCROW INSTRUCTIONS 

 DYNE THERAPEUTICS, INC. 

JOINT ESCROW INSTRUCTIONS 

[            ], 2018 

Dyne Therapeutics, Inc. 
 400 Technology Square, 10th Floor 
 Cambridge, MA 02139 

Attention: Secretary 
 Dear Secretary: 

As Escrow Agent for Dyne Therapeutics, Inc., a Delaware corporation (the “Company”), and its successors in interest under the
Restricted Stock Agreement (the “Agreement”) of even date herewith, to which a copy of these Joint Escrow Instructions is attached, and the undersigned person (“Holder”), you are hereby authorized and directed to
hold the documents delivered to you pursuant to the terms of the Agreement in accordance with the following instructions: 

1. Appointment. Holder irrevocably authorizes the Company to deposit with you any certificates evidencing Shares (as
defined in the Agreement) to be held by you hereunder and any additions and substitutions to said Shares. For purposes of these Joint Escrow Instructions, “Shares” shall be deemed to include any additional or substitute property.
Holder does hereby irrevocably constitute and appoint you as his or her attorney-in-fact and agent for the term of this escrow to execute with respect to such Shares all
documents necessary or appropriate to make such Shares negotiable and to complete any transaction herein contemplated. Subject to the provisions of this Section 1 and the terms of the Agreement, Holder shall exercise all rights and privileges
of a stockholder of the Company while the Shares are held by you. 
 2. Forfeiture of Shares. 

(a) Upon any forfeiture by the Holder of the Shares pursuant to the Agreement, the Company shall give to Holder and you a
written notice specifying the number of Shares to be forfeited and the time for a closing hereunder (the “Closing”) at the principal office of the Company. Holder and the Company hereby irrevocably authorize and direct you to close
the transaction contemplated by such notice in accordance with the terms of said notice. 
 (b) At the Closing, you are
directed (i) to date the stock assignment form or forms necessary for the transfer of the Shares, (ii) to fill in on such form or forms the number of Shares being transferred, and (iii) to deliver the same, together with the
certificate or certificates evidencing the Shares to be transferred, to the Company. 

  
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 3. Withdrawal. The Holder shall have the right to withdraw from this
escrow any Shares that have vested pursuant to the Agreement. 
 4. Duties of Escrow Agent. 

(a) Your duties hereunder may be altered, amended, modified or revoked only by a writing signed by all of the parties hereto.

 (b) You shall be obligated only for the performance of such duties as are specifically set forth herein and may rely and
shall be protected in relying or refraining from acting on any instrument reasonably believed by you to be genuine and to have been signed or presented by the proper party or parties. You shall not be personally liable for any act you may do or omit
to do hereunder as Escrow Agent or as attorney-in-fact of Holder while acting in good faith and in the exercise of your own good judgment, and any act done or omitted by
you pursuant to the advice of your own attorneys shall be conclusive evidence of such good faith. 
 (c) You are hereby
expressly authorized to disregard any and all warnings given by any of the parties hereto or by any other person or entity, excepting only orders or process of courts of law, and are hereby expressly authorized to comply with and obey orders,
judgments or decrees of any court. If you are uncertain of any actions to be taken or instructions to be followed, you may refuse to act in the absence of an order, judgment or decrees of a court. In case you obey or comply with any such order,
judgment or decree of any court, you shall not be liable to any of the parties hereto or to any other person or entity, by reason of such compliance, notwithstanding any such order, judgment or decree being subsequently reversed, modified, annulled,
set aside, vacated or found to have been entered without jurisdiction. 
 (d) You shall not be liable in any respect on
account of the identity, authority or rights of the parties executing or delivering or purporting to execute or deliver the Agreement or any documents or papers deposited or called for hereunder. 

(e) You shall be entitled to employ such legal counsel and other experts as you may deem necessary properly to advise you in
connection with your obligations hereunder and may rely upon the advice of such counsel. 
 (f) Your rights and
responsibilities as Escrow Agent hereunder shall terminate if (i) you cease to be Secretary of the Company or (ii) you resign by written notice to each party. In the event of a termination under clause (i), your successor as Secretary
shall become Escrow Agent hereunder; in the event of a termination under clause (ii), the Company shall appoint a successor Escrow Agent hereunder. 

(g) If you reasonably require other or further instruments in connection with these Joint Escrow Instructions or obligations in
respect hereto, the necessary parties hereto shall join in furnishing such instruments. 
 (h) It is understood and agreed
that if you believe a dispute has arisen with respect to the delivery and/or ownership or right of possession of the securities held 

  
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by you hereunder, you are authorized and directed to retain in your possession without liability to anyone all or any part of said securities until such dispute shall have been settled either by
mutual written agreement of the parties concerned or by a final order, decree or judgment of a court of competent jurisdiction after the time for appeal has expired and no appeal has been perfected, but you shall be under no duty whatsoever to
institute or defend any such proceedings. 
 (i) These Joint Escrow Instructions set forth your sole duties with respect to
any and all matters pertinent hereto and no implied duties or obligations shall be read into these Joint Escrow Instructions against you. 

(j) The Company shall indemnify you and hold you harmless against any and all damages, losses, liabilities, costs, and
expenses, including attorneys’ fees and disbursements, (including without limitation the fees of counsel retained pursuant to Section 4(e) above, for anything done or omitted to be done by you as Escrow Agent in connection with this
Agreement or the performance of your duties hereunder, except such as shall result from your gross negligence or willful misconduct. 

5. Notice. Any notice required or permitted hereunder shall be given in writing and shall be deemed effectively given
upon personal delivery or upon deposit in the United States Post Office, by registered or certified mail with postage and fees prepaid, addressed to each of the other parties thereunto entitled at the following addresses, or at such other addresses
as a party may designate by ten days’ advance written notice to each of the other parties hereto. 
  

			
	COMPANY:	  	Notices to the Company shall be sent to the address set forth in the salutation hereto, Attn: President
		
	HOLDER:	  	Notices to Holder shall be sent to the address set forth below Holder’s signature below.
		
	ESCROW AGENT:	  	Notices to the Escrow Agent shall be sent to the address set forth in the salutation hereto.

 6. Miscellaneous. 

(a) By signing these Joint Escrow Instructions, you become a party hereto only for the purpose of said Joint Escrow
Instructions, and you do not become a party to the Agreement. 
 (b) This instrument shall be binding upon and inure to the
benefit of the parties hereto and their respective successors and permitted assigns. 
 [Remainder of Page Intentionally Left
Blank] 

  
 A - 3 

 IN WITNESS WHEREOF, the parties hereto have executed these Joint Escrow Instructions as of
the day and year first above written. 
  

					
	Very truly yours,
	
	COMPANY:
	
	DYNE THERAPEUTICS, INC.
		
	By:	 	  

		 	Name:	 	  

		 	Title:	 	  

	
	HOLDER:
		
	By:	 	  

		 	Name:	 	  

		
	Address:	 	  

		 	  

	
	ESCROW AGENT:
		
	By:	 	  

		 	Name:	 	  

		 	Title:	 	

 SIGNATURE PAGE TO JOINT ESCROW INSTRUCTIONS 

 EXHIBIT B 

STOCK ASSIGNMENT SEPARATE FROM CERTIFICATE 

 STOCK ASSIGNMENT SEPARATE FROM
CERTIFICATE 
 FOR VALUE RECEIVED, I hereby sell, assign and transfer unto Dyne Therapeutics, Inc. (the
“Corporation”)                     
(                ) shares of Common Stock, $0.0001 par value per share, of the Corporation standing in my name on the books of the Corporation represented by
Certificate(s) Number              herewith, and do hereby irrevocably constitute and appoint Wilmer Cutler Pickering Hale and Dorr LLP attorney to transfer the said stock on the books of
the Corporation with full power of substitution in the premises. 
  

			
	Dated:	 	  

  

	
	RECIPIENT:
	
	  

	[Name]
	
	  

	Name of Spouse (if any):

 Instructions to Recipient: Please do not fill in any blanks other than the signature line(s). The purpose
of the Stock Assignment Separate from Certificate is to enable the Company to acquire the Shares upon forfeiture by Recipient or exercise of its Right of First Refusal without requiring additional signatures on the part of the Recipient or
Recipient’s spouse, if any. The signature(s) to this assignment must correspond with the name as written upon the face of the certificate, in every particular, without alteration, enlargement, or any change whatever. 

 NOTICE ON 83(B) ELECTIONS

 IF YOU WISH TO MAKE A SECTION 83(B) ELECTION, THE FILING OF SUCH ELECTION IS YOUR RESPONSIBILITY. 

THE FORM FOR MAKING THIS SECTION 83(B) ELECTION IS ATTACHED TO THIS AGREEMENT. YOU MUST FILE THIS FORM WITHIN 30 DAYS OF THE GRANT DATE. 

YOU (AND NOT THE COMPANY, ANY OF ITS AGENTS OR ANY OTHER PERSON) SHALL BE SOLELY RESPONSIBLE FOR FILING SUCH FORM WITH THE IRS, EVEN IF YOU REQUEST THE
COMPANY, ITS AGENTS OR ANY OTHER PERSON TO MAKE THIS FILING ON YOUR BEHALF AND EVEN IF THE COMPANY, ANY OF ITS AGENTS OR ANY OTHER PERSON HAS PREVIOUSLY MADE THIS FILING ON YOUR BEHALF. 

The 83(b) election should be filed by mailing a signed election form by certified mail, return receipt requested to the IRS Service Center where you file your
tax returns. See www.irs.gov. 

 SECTION 83(B) ELECTION 

The undersigned hereby makes an election pursuant to Section 83(b) of the Internal Revenue Code of 1986, as amended, with respect to the property
described below and supplies the following information in accordance with Treas. Reg. § 1.83-2: 
  

	 	1.	 The name, address, and taxpayer identification number of the undersigned are: 

[Name] 
 [Address] 

[City, State Zip] 
 Taxpayer
Identification Number:
                                         

 

	 	2.	 The property with respect to which this election is being made is
[                ] shares of common stock, $0.0001 par value per share, of Dyne Therapeutics, Inc., a Delaware corporation (the “Company”).

  

	 	3.	 The date on which the property was transferred or the date on which the restrictions on such property were
imposed, whichever is later, is [            ], 2018 and the taxable year for which this election is being made is the calendar year 2018. 

 

	 	4.	 The property is subject to vesting provisions and may be forfeited under the terms of a stock restriction
agreement executed between the undersigned and the Company. 

  

	 	5.	 The fair market value of the property at the time of the transfer or the date on which the restrictions on such
property were imposed, whichever is later, (determined without regard to any lapse restriction, as defined in Treas. Reg. § 1.83-3(i)) is $[        ], equal
to a fair market value of $0.001 per share. 

  

	 	6.	 The amount paid for the property by the undersigned is $0.00. 

 

	 	7.	 This statement is executed on             , 2018.

 In accordance with Treas. Reg. § 1.83-2(d) & (e)(7), a copy of this statement has
been furnished to the Company. 
  

									
	  
	 		 		 	  
	 	
	Signature of Taxpayer	 		 		 	Signature of Spouse (if any)	 	

 SECTION 83(B) ELECTION 

BACKGROUND INFORMATION 

Section 83(b) of the Internal Revenue Code permits persons who receive restricted property, such as restricted stock, in connection with
the performance of services to include the value of such property in their gross income for the year the property is received. Such persons who purchase stock of the company subject to a stock restriction agreement providing for the vesting of such
stock over a period of time are entitled to make this election. Any person who makes a timely Section 83(b) election will recognize compensation income on the date of grant (the date listed in item 3 of the election form) equal to the
difference, if any, between the fair market value of the stock and the amount paid for the stock. A person who pays taxes in connection with an election and subsequently forfeits the stock, however, will not receive a refund or other tax benefit for
the taxes previously paid. 
 Any person who does not make the election will be required to include the value of the stock in gross income
in the year in which the stock vests. In particular, when the stock vests, the person will recognize compensation income in an amount equal to the difference between the fair market value of the stock on the vesting date and the amount paid for the
stock. As a result, if the value of the stock increases, a person who does not make a timely Section 83(b) election will have compensation income at the time each installment of stock vests. 

Each person should consult with his or her tax or legal advisor regarding the advisability and timing of filing the election. The original,
signed and dated Section 83(b) election must be filed within 30 days of the grant date but may be filed prior to the grant date. The election should be filed by certified mail, return receipt requested, with the Internal
Revenue Service at the service center where the electing person ordinarily files his or her annual tax return. A copy of the Section 83(b) election, as filed, must be returned to the company. A copy of the Section 83(b) election must also
be included with the person’s federal income tax return for the year of grant (each person should check with his or her tax preparer regarding this and any state, local, foreign or other filing requirements). 

Please also note that the certified mailing receipt for the Section 83(b) election should be retained. This receipt is essential if
the Internal Revenue Service does not receive the Section 83(b) election and challenges the election.EX-10.9

 Exhibit 10.9 

SUBLEASE AGREEMENT 
 This
Sublease Agreement (the “Sublease”) is made as of May 20, 2019 (the “Effective Date”) by and between ARRAKIS THERAPEUTICS, INC., a Delaware corporation (“Sublandlord”) and
DYNE THERAPEUTICS, INC., a Delaware corporation (“Subtenant”), in the following factual context: 
 A. CRP/King 830
Winter, L.L.C., a Delaware limited liability company (“Master Landlord”), and Sublandlord are the parties to that certain Lease dated as of June 29, 2018 (the “Master Lease”). The Master Lease
covers certain premises consisting in the aggregate of 40,628 rentable square feet of space (the “Premises”) in that certain building located at 830 Winter Street, Waltham, Massachusetts (the
“Building”). 
 B. Sublandlord desires to sublease to Subtenant and Subtenant desires to sublease from Sublandlord
the entirety of the portion of the Premises comprising 14,122 rentable square feet located on the second (2nd) floor of the Building and approximately as shown on the diagram attached as
Exhibit A (the “Prime Premises”) and the Appurtenant Areas (as hereinafter defined) (collectively, the “Subleased Space”), on the terms and conditions set forth in this
Sublease. The parties agree that the Prime Premises comprises 14,122 rentable square feet, and that such figure is not subject to remeasurement or modification. 

C. Reference is made to that certain Consent, Nondisturbance and Attornment Agreement (the “CNDA”), dated as of
May 20, 2019, by and among PPF OFF 828-830 WINTER STREET, LLC (as successor in interest to Master Landlord), Sublandlord and Subtenant, which is incorporated herein by reference. 

NOW THEREFORE, for valuable consideration, the receipt and sufficiency of which is acknowledged, the parties agree as follows: 

1. Sublease 
 1.1 Grant.
Sublandlord hereby subleases the Subleased Space to Subtenant and Subtenant hereby subleases the Subleased Space from Sublandlord on the terms and conditions set forth in this Sublease and, to the extent applicable, the Master Lease. Except to the
extent directly contradicted by the provisions of this Sublease, any capitalized terms not otherwise defined in this Sublease shall have the meanings ascribed thereto in the Master Lease. The parties agree that the Subleased Space is 15,000 rentable
square feet, comprised of (i) the Prime Premises of 14,122 rentable square feet and (ii) the Appurtenant Areas comprised of, in the aggregate, 878 rentable square feet as per the breakdown below. 

“Appurtenant Areas” collectively shall mean: 
  

	 	(a)	 PH System and Acid Neutralization Tank comprising 315 rentable square feet located on the basement floor of the
Building; 

  

	 	(b)	 Chemical Storage Premises comprising 114 rentable square feet located on the basement floor of the Building;

  

	 	(c)	 Nitrogen Tank Premises comprising 0 rentable square feet located outside of the Building.

	 	(d)	 Hazardous Waste Storage Premises comprising 114 rentable square feet located on the basement floor of the
Building; 

  

	 	(e)	 Generator comprising 0 rentable square feet located outside of the Building; and 

 

	 	(f)	 Mechanical System Premises comprising 335 rentable square feet located on the basement floor of the Building.

 1.2 Incorporation of Master Lease by Reference 

(a) Except to the extent such terms and provisions are inconsistent with or are specifically contrary to the express written provisions of
this Sublease and except as provided in this Section 1.2, all of the terms, covenants and conditions of the Master Lease are by this reference incorporated herein and made a part of this Sublease with the same force and effect as if fully set
forth herein, provided, however, that for purposes of such incorporation, (i) the term “Lease” as used in the Master Lease shall refer to this Sublease; (ii) the term “Landlord” (and other defined terms
containing the term “Landlord” or any derivative thereof) as used in the Master Lease, and subject to the limitations of Sublandlord’s responsibilities to Subtenant under the Master Lease set forth in Section 5 below of this
Sublease, shall refer to Sublandlord; (iii) the term “Tenant” (and other defined terms containing the term “Tenant” or any derivative thereof) as used in the Master Lease shall refer to Subtenant; (iv) the term
“Term” as used in the Master Lease shall refer to the Term defined herein; (v) the term “Expiration Date” as used in the Master Lease shall mean the Termination Date of this Sublease; (vi) the term “Premises,”
as used in the Master Lease shall refer to the Subleased Space; (vii) the term “Base Rent” as used in the Master Lease shall refer to the Base Rent due under this Sublease; and (viii) the terms “Tenant’s Share”
shall refer to Subtenant’s Share under this Sublease. In the event of any inconsistency between the provisions set forth in this Sublease and the provisions of the Master Lease, as incorporated herein, the provisions of this Sublease shall
control as between Sublandlord and Subtenant. Notwithstanding the foregoing, the following provisions of the Master Lease are expressly not incorporated into this Sublease: (1) the definitions of Premises, Term Commencement Date, Estimated Term
Commencement Date, Expiration Date, Term, Extension Term, Base Rent, Security Deposit/Letter of Credit and any and all definitions and terms which are defined in or included in any of the Excluded Master Lease Provisions (as hereinafter defined) set
forth in Article 1 of the Master Lease (except to the extent used or referred to in this Sublease), (2) all of the following within the Master Lease: Articles 3 and 7, Sections 1.2, 1.3(b), 1.4(b), 2.4(b), 5.2(h) 10.7(b), 11.1(c), 12.2(but without
limiting the effect of Section 6.1 of this Sublease Agreement), 12.3, 17.9, 21.1(a), 21.1(e), 26.3 and 26.7(b) the following provision in Section 9.1 “with such metering equipment to be installed as part of the Landlord’s
Work”, those provisions in Sections 9.1, 9.2 and 9.3 regarding Tenant’s obligations regarding payment for the utilities referenced in such sections (payment obligations for the same instead being addressed in Article 3 of this Sublease),
the last three sentences of Section 22.1, Exhibits 4, 6 and 12, and (3) such other terms of the Master Lease which are inapplicable, inconsistent with, or specifically modified by the terms of this Sublease (collectively, the
“Excluded Master Lease Provisions”). Any reference to an allowance in the Master Lease is not incorporated herein. For the avoidance of doubt, in the event of a casualty, condemnation or Service Interruption, Subtenant shall
be entitled to an abatement of rent only to the extent that Sublandlord actually receives such abatement from Master Landlord in accordance with the Master Lease. 

  
 2 

 (b) Sublandlord shall permit Subtenant to operate under Sublandlord’s MWRA Permit at no
additional cost to Subtenant except as explicitly set forth herein, and Subtenant will take all such actions as may be reasonably necessary to facilitate this. In the event Sublandlord is required to move to a higher level permit than the current
low flow MWRA Permit, due solely to the increased discharge from Subtenant, Subtenant shall be responsible for any increased costs associated with such higher level MWRA Permit. Subtenant shall be responsible for Subtenant’s Share (as
hereinafter defined) for the daily monitoring costs related to the discharge under the MWRA Permit, which amount shall be paid as Additional Rent a set forth herein. Any indemnifications for the acts, omissions, negligence and willful misconduct of
Subtenant and any of Subtenant’s employees, agents, contractors or invitees shall also apply to Subtenant’s use of Sublandlord’s MWRA Permit. Subtenant shall have the non-exclusive right to use
its proportionate share of the Acid Neutralization Tank and Acid Neutralization Tank Premises under Section 1.7(b) of the Master Lease; provided, however, any Tank Costs shall be Sublandlord’s responsibility, except to the extent such Tank
Costs are necessitated as a result of any acts, omissions, negligence or willful misconduct of Subtenant or any of Subtenant’s employees, agents, contractors or invitees. Subtenant’s use of the Acid Neutralization Tank shall be in
accordance with applicable laws. Further, it is agreed that the obligations of Tenant in relation to Lab Services Equipment, as indicated in Section 10.1 of the Master Lease, do not apply to Subtenant, unless and to the extent any repair,
replacement or maintenance is necessitated as a result of the acts, omissions, negligence or willful misconduct of Subtenant or any of Subtenant’s employees, agents, contractors or invitees. In the event that the Master Lease is terminated
prior to the Termination Date of this Sublease, this Section 1.2(b) shall be superseded in its entirety by the provisions of Sections III.1 and III.2 of the CNDA. 

(c) Sublandlord shall have all of the same rights and remedies with respect to the Subleased Space as Master Landlord has with respect thereto
under the Master Lease, including, without limitation, the access rights (and limitations thereon) set forth in Section 2.4 of the Master Lease. This Sublease is expressly subject and subordinate to any mortgages or deeds of trust and all
matters of record, ground leases and underlying leases to which the Master Lease is now or hereafter subject and subordinate pursuant to the Master Lease without the requirement of delivering any subordination, attornment and non-disturbance agreement or other agreements to Subtenant. 
 (d) Subtenant shall be entitled to exercise
those rights of termination, if any, provided to the Sublandlord, as Tenant, in Article 15 of the Master Lease; provided, however, in no event shall Subtenant have the right to terminate this Sublease as set forth in Section 15.2(c). 

(e) With respect to any of Subtenant’s obligations to be performed under this Sublease, when the Master Lease grants Sublandlord a
specific number of days to perform its obligations thereunder, Subtenant shall perform such obligation not later than the date that is three (3) business days prior to the date Sublandlord is obligated under the Master Lease to perform such
obligation; provided, however, in no event shall Subtenant have less than three (3) days with which to perform any monetary obligations prior to a default being claimed under this Sublease. Wherever in the Master Lease there is a specific
number of days for Master Landlord to respond to a request from Tenant for consent or approval, Sublandlord shall have an additional two (2) business days to respond to any such request (including a second notice) from Subtenant

  
 3 

 
under this Sublease. In the event of any conflict between the provisions of the Master Lease and this Sublease, the Master Lease shall govern and control except to the extent directly
contradicted by the provisions of this Sublease. 
 2. Term. The term of this Sublease (the “Term”) shall commence on the
later date to occur of (i) the date Sublandlord delivers the Subleased Space to Subtenant free and clear of all tenants and occupants and free of all personal property, except as expressly set forth herein and in the condition indicated in
Section 8 hereof with Sublandlord’s Furniture available, consistent with the terms of Section 9 hereof, and (ii) the date Sublandlord delivers to Subtenant a fully executed copy of the Consent to Sublease (as hereinafter defined)
(the “Term Commencement Date”) and shall expire at 11:59 p.m. EST on the last day of the thirtieth (30th) full calendar month after the Term Commencement Date (the
“Termination Date”), unless extended or sooner terminated pursuant to any provision of the Master Lease or this Sublease. Subject to the CNDA, this Sublease shall immediately terminate as of the date the Master Lease is
terminated, for any reason, prior to the Termination Date. Promptly after the Term Commencement Date is determined, Sublandlord and Subtenant, following Sublandlord’s request, will execute a customary form of commencement date letter with
respect to any or each of the above dates. Subtenant’s or Sublandlord’s failure or refusal to sign the same shall in no event affect the determination of such dates or either party’s obligations hereunder. 

Notwithstanding the foregoing to the contrary, subject to Sublandlord’s right to reject Subtenant’s extension election and recapture
the Subleased Space or any portion thereof after the initial thirty (30) month term for Sublandlord’s own use, provided that Subtenant shall not be in Default (as hereinafter defined) either at the time Sublandlord receives the Extension
Notice (as hereinafter defined) or at the commencement of the Extension Term (as hereinafter defined), Subtenant shall have one (1) option to extend the Term for a period of six (6) months, but in any event not to exceed the term of the
Master Lease (the “Extension Term”). Subtenant must exercise its right to extend the Term by providing written notice of the election to Sublandlord (the “Extension Notice”) at least nine
(9) months prior to the Termination Date. In the event of such renewal, the “Term” shall include the Extension Term and such renewal shall be upon the same provisions as for the initial Term. In the event that the Master Lease is
terminated prior to the Termination Date of this Sublease, the provisions of Section III.4 of the CNDA shall apply to this Section 2. 
 3. Rent

 3.1 Base Rent. 
 (a)
During the Term, Subtenant shall pay to Sublandlord, base rent (“Base Rent”) as outlined in the foregoing chart: 
  

									
	 Period:
	  	Monthly Base Rent:	 	  	Yearly Base Rent:	 
	 Sublease Year 1
	  	$	63,750.00	 	  	$	765,000.00	* 
	 Sublease Year 2
	  	$	65,662.50	 	  	$	787,950.00	 
	 Sublease Year 3
	  	$	67,637.50	 	  	$	811,650.00	** 

  
 4 

	*	 Notwithstanding anything to the contrary contained herein, provided and only so long as there is no Default in
existence, the monthly payment of Base Rent due under this Sublease will be abated for the first (1) full month of the Term (the “Abated Month”). The foregoing rent abatement shall apply to and affect only the monthly
installment of Base Rent due under this Sublease during the Abated Month and Subtenant shall be obligated to pay all Additional Rent and all other charges which accrue and are due under this Sublease with respect to the Subleased Space during the
Abated Month. If at any time following the Effective Date there occurs any Default under this Sublease, Tenant’s right to abate the monthly installments of Base Rent during any future Abated Month shall immediately terminate and be of no
further force and effect. 

	**	 Annualized. 

For purposes of this Sublease, “Sublease Year” shall mean each successive twelve (12) month period during the
Term, with the first such Sublease Year commencing on the Term Commencement Date and each successive Sublease Year commencing on the next succeeding anniversary of the Term Commencement Date; provided, however, (i) the final Sublease Year shall
expire on the Termination Date, and (ii) if the Term Commencement Date does not occur on the first day of a calendar month, then the first Sublease Year shall include the partial calendar month in which the first anniversary of the Term
Commencement Date occurs and will end on the last day of the first full calendar month following the Term Commencement Date (creating a Sublease Year of slightly longer than 12 full months), and the remaining Sublease Years shall be the successive
twelve (12) month periods following the end of the first Sublease Year. 
 (b) Base Rent and recurring payments of Additional Rent
shall be payable in equal monthly installments, in advance, on the second to last business day of each and every calendar month during the term of this Sublease immediately preceding the date that payment of Base Rent for the corresponding month is
due from Sublandlord to Master Landlord under the Master Lease. Payments of Base Rent shall be paid to Sublandlord at Sublandlord’s address set forth above or at such other place as Sublandlord shall from time to time designate, in immediately
available funds, without notice, demand, deduction or offset. Base Rent and Additional Rent for any partial month shall be pro-rated on a daily basis. Notwithstanding anything herein to the contrary, Subtenant
shall deliver the first monthly installment of Base Rent due hereunder to Sublandlord simultaneously with Subtenant’s execution and delivery of this Sublease. 

3.2 Additional Rent. 

(a) All amounts other than Base Rent that are due to Sublandlord from Subtenant under this Sublease are hereinafter referred to collectively
as “Additional Rent,” and Base Rent and Additional Rent may be referred to collectively as “Rent.” 

(b) During the Term, Subtenant shall pay to Sublandlord, as Additional Rent in the manner and at the same time as set forth in
Section 3.1 above with respect to Base Rent, 

  
 5 

 
Subtenant’s Share (as hereinafter defined) of (i) Operating Costs (the “Sublease Operating Costs”) and (ii) Taxes (the “Sublease
Taxes”), all based upon the amounts billed to Sublandlord pursuant to Article 5 of the Master Lease. As used herein, the term “Subtenant’s Share” shall mean 36.92% of Tenant’s
Share, as such term is defined within the Master Lease. Sublandlord shall, within a reasonable period of time after Sublandlord receives corresponding notices or statements from Master Landlord of the estimated monthly payments of Additional Rent
due under Article 5 of the Master Lease for the Premises, provide to Subtenant a good faith estimate of the Additional Rent payable from Subtenant under this Section 3.2 for any calendar year (or part thereof) during the Term of this Sublease
that such amounts are due and Subtenant shall pay to Sublandlord, at the times and in the manner set forth in Section 3.1 above with respect to Base Rent, an amount equal to 1/12th of such
estimated Additional Rent due for such calendar year or part thereof. Within ninety (90) days following receipt by Sublandlord of Master Landlord’s annual reconciliation statement of Operating Costs or Taxes, as applicable, Sublandlord
will send to Subtenant a statement together with relevant, non-confidential documentation, establishing the actual Sublease Operating Costs payment or Sublease Taxes payment, as applicable, for such year. If
Subtenant has paid more in estimated Additional Rent under this Section than the actual amount due from Subtenant for the applicable year, Sublandlord shall credit such excess against subsequent obligations of Subtenant for Additional Rent (or
refund such excess to Subtenant within thirty (30) days if the Term of this Sublease has ended and Subtenant has no further obligation to Sublandlord). If Subtenant has paid less than the actual Additional Rent due under this Section 3.2,
Subtenant shall pay any deficiency to Sublandlord within thirty (30) days following receipt of the reconciliation documentation from Sublandlord. 

If Subtenant has questions or good faith concerns regarding any amounts or items billed to Sublandlord pursuant to Article 5 of the Master
Lease, Sublandlord will use its commercially reasonable efforts to provide further requested information to Subtenant, including from Master Landlord. 

3.3 Electricity. Commencing on the Term Commencement Date, and continuing throughout the remainder of the Term or such later date as
Subtenant or anyone claiming by, through or under Subtenant remains in occupancy, Subtenant shall pay to Sublandlord, as Additional Rent, an amount equal to Subtenant’s electricity billed to Sublandlord pursuant to Section 9.1 of the
Master Lease for any separately metered or check-metered electricity charges for the Subleased Space, or, if the Subleased Space is not separately metered or check-metered at any time during the Term, Subtenant shall pay to Sublandlord
Subtenant’s Share of the electricity charges billed to Sublandlord for the Premises, within fourteen (14) days after delivery to Subtenant of an invoice therefor, for the supply of electricity to the Subleased Space. In the event that the
Master Lease is terminated prior to the Termination Date of this Sublease, the provisions of Section III.5 of the CNDA shall apply to this Section 3.3. 

3.4 Water. Commencing on the Term Commencement Date, and continuing throughout the remainder of the Term or such later date as
Subtenant or anyone claiming by, through or under Subtenant remains in occupancy, Subtenant shall pay to Sublandlord, as Additional Rent, an amount equal to Subtenant’s Share of water billed to Sublandlord pursuant to Section 9.2 of the
Master Lease for any separately metered or check-metered water charges which are attributable to the Subleased Space, if any, within fourteen (14) days after delivery to 

  
 6 

 
Subtenant of an invoice therefor, for the supply of water to the Subleased Space. In the event that the Master Lease is terminated prior to the Termination Date of this Sublease, the provisions
of Section III.5 of the CNDA shall apply to this Section 3.4. 
 3.5 Gas. If Subtenant requires gas service for the operation of
Subtenant’s laboratory equipment in the Subleased Space, Subtenant shall pay to Sublandlord, as Additional Rent, all charges for gas furnished to the Subleased Space and/or any equipment exclusively serving the Subleased Space based on
(i) Master Landlord’s reasonable estimate of such gas usage for the Premises and Sublandlord’s reasonable estimate of such gas usage for the Subleased Space or (ii) metering or submetering equipment installed by Master Landlord.
In the event that the Master Lease is terminated prior to the Termination Date of this Sublease, the provisions of Section III.5 of the CNDA shall apply to this Section 3.5. 

3.6 Additional Charges. Subtenant shall also be responsible for its own utilities, including telephone, facsimile transmitter, internet
access, photocopier, and its other business expenses. In addition, if Subtenant shall procure any additional services from Master Landlord, or if additional rent or other sums are incurred for Subtenant’s sole benefit, including, without
limitation, repairs and replacements to the Subleased Space caused or permitted by Subtenant, Subtenant shall make such payment to Sublandlord within thirty (30) days after Subtenant’s receipt of an invoice. Any rent or other sums payable
by Subtenant to Sublandlord under this Section 3.8 shall constitute and be due as “Rent.” 
 3.7 Abatement of Rent Under
Master Lease. Notwithstanding anything in this Sublease to the contrary, if the rent due under the Master Lease with respect to the Subleased Space is abated in whole or in part during the Term pursuant to the terms of Section 10.7 or
Article 15 of the Master Lease, or any other applicable provision of the Master Lease, then the Base Rent and Additional Rent due under this Sublease shall abate for the same period and to the same extent as the rent for the Premises is abated
pursuant to such Section 10.7 or Article 15 of the Master Lease, or any other provision of the Master Lease, as applicable. 
 4. Intentionally
omitted. 
 5. Master Lease 
 5.1
Compliance. Except to the extent otherwise provided in this Sublease, Subtenant covenants and agrees to assume, perform and observe all the terms, covenants and conditions required to be performed by Sublandlord, as Tenant under the Master
Lease, with respect to the Subleased Space and to the extent such Master Lease provisions are incorporated herein, except to the extent such terms, covenants and conditions conflict with the terms of this Sublease and specifically excluding the
obligations to pay the Base Rent due under the Master Lease. Subtenant further agrees that Subtenant’s performance of all such obligations shall be performed by Subtenant for the benefit of Sublandlord as well as for the benefit of Master
Landlord, and that Sublandlord shall have, with respect to Subtenant, this Sublease and the Subleased Space, all of the rights and benefits provided to Master Landlord by the Master Lease. 

  
 7 

 5.2 Sublandlord’s Covenants. Sublandlord covenants to Subtenant to perform all
of the terms and provisions required of it under the Master Lease and to promptly pay when due all rents due and accruing to Master Landlord, provided Subtenant timely complies with its obligations under this Sublease. Nothing contained in this
Sublease shall be construed as a guarantee by Sublandlord of any of the obligations, covenants, warranties, agreements or undertakings of Master Landlord in the Master Lease, nor as an undertaking by Sublandlord to Subtenant on the same or similar
terms as are contained in the Master Lease. Sublandlord agrees, upon Subtenant’s request, to use reasonable efforts at Subtenant’s expense to obtain Master Landlord’s consent or approval wherever required by the Master Lease.
Sublandlord agrees that if under the Master Lease any right or remedy of Sublandlord or any duty or obligation of Master Landlord is subject to or conditioned upon Sublandlord making any demand upon Master Landlord or giving any notice or request to
Master Landlord then, if Subtenant shall so request, Sublandlord, at Subtenant’s expense, shall make such demand or give such notice or request on Sublandlord’s behalf, except that Sublandlord shall not be required to do so with respect to
any act or thing as to which Sublandlord shall have determined in accordance with this Sublease to withhold its consent or approval. 
 5.3
Subordination. Subtenant covenants and agrees that this Sublease is expressly made subject and subordinate in all respects to (i) the Master Lease and to all of its terms, covenants and conditions (including without limitation those
provisions not incorporated herein by reference, as set forth in Section 1.2 above of this Sublease); and (ii) any and all matters to which the tenancy of Sublandlord, as tenant under the Master Lease, is or may be subordinate. Subtenant
agrees that Subtenant has reviewed and is familiar with the Master Lease, and shall not do, or permit or suffer to be done, any act or omission by Subtenant, its agents, employees, contractors or invitees which is prohibited by the Master Lease, or
which would constitute a violation or default thereunder, or result in a forfeiture or termination of the Master Lease or render Sublandlord liable for damages, fines, or penalties under the Master Lease. Should the Master Lease expire or terminate
during the Term for any reason, this Sublease shall terminate on the date of such expiration or termination of the Master Lease, with the same force and effect as if such expiration or termination date had been specified in this Sublease as the
Termination Date and Sublandlord shall have no liability to Subtenant in the event of any such expiration or termination unless such termination is solely and directly caused by the gross negligence or willful misconduct of Sublandlord. 

5.4 Benefits of Master Lease. As long as this Sublease is in full force and effect, Subtenant shall be entitled, with respect to the
Subleased Space, to the benefit of Master Landlord’s obligations and agreements to furnish utilities and other services to the Subleased Space (and to the tenant thereof) and to repair and maintain the Building and all other obligations of
Master Landlord under the Master Lease. Notwithstanding anything provided herein or the Master Lease to the contrary, including the incorporation into this Sublease of the relevant sections of the Master Lease, Subtenant acknowledges and agrees that
Sublandlord shall not be obligated to furnish any services or utilities of any nature whatsoever or be responsible for the performance of any of Master Landlord’s covenants or obligations under the Master Lease, and without limitation to
Sublandlord’s obligations under Section 5.2 of this Sublease, Sublandlord shall not be liable in damages or otherwise for any negligence of Master Landlord or for any damage or injury suffered by Subtenant as a result of any act or failure
to act by Master 

  
 8 

 
Landlord, or any default by Master Landlord in the performance of its obligations under the Master Lease. Sublandlord shall not be bound by and expressly does not make any of the
indemnifications, representations or warranties, if any, made by Master Landlord under the Master Lease. If Master Landlord shall default in the performance of its obligations under the Master Lease, or if, prior to default, Subtenant seeks
Sublandlord’s reasonable assistance to cause or assure Landlord’s performance of an obligation, Sublandlord, upon receipt of written notice thereof from Subtenant, shall use commercially reasonable efforts to cause Master Landlord to
perform its obligations under the Master Lease and to enforce the terms thereof, provided such commercially reasonable efforts shall not require Sublandlord to expend any money or commence any litigation to cause Master Landlord to perform its
obligations under the Master Lease. As a condition to Sublandlord exercising any efforts to enforce Master Landlord’s obligations, Sublandlord may require Subtenant to make an advance deposit with Sublandlord of an amount reasonably estimated
to reimburse Sublandlord for its costs in connection with such efforts. 
 5.5 Liability of Sublandlord. 

(a) Sublandlord shall not incur any liability whatsoever to Subtenant for any injury, inconvenience, incidental or consequential damages
incurred or suffered by Subtenant solely as a result of the exercise by Master Landlord of any of the rights reserved to Master Landlord under the Master Lease, nor shall such exercise constitute a constructive eviction or a default by Sublandlord
hereunder. Except as otherwise set forth herein, Subtenant’s obligations to pay Base Rent, Additional Rent and any other charges due under this Sublease shall not be reduced or abated in the event that Master Landlord fails to provide any
service, to perform any maintenance or repairs, or to perform any other obligation of Master Landlord under the Master Lease, except if and only to the extent that Sublandlord’s obligation to pay Base Rent, Additional Rent and other charges
under the Master Lease with respect to the Subleased Space is actually reduced or abated as a result of Master Landlord’s failure. 

(b) Notwithstanding anything contained in this Sublease to the contrary but subject to the last sentence of Section 20.8 of this Sublease
with respect to a holdover by Subtenant, neither Sublandlord nor Subtenant shall be liable to the other in connection with any matter arising from or relating to this Sublease for any consequential, punitive, special or indirect damages. 

5.6 Approvals and Consents. In all provisions of the Master Lease requiring the approval or consent of, or notice to, Master Landlord,
Subtenant shall be required to obtain the approval or consent of, or provide notice to, both Master Landlord and Sublandlord. If Sublandlord is obligated to be reasonable with respect to any approval or consent required under the terms of this
Sublease, in addition to and without limitation of any reasons set forth in the Master Lease for which Sublandlord may withhold consent, Sublandlord shall not be deemed to be unreasonable in withholding such consent if Master Landlord withholds its
consent thereto and Sublandlord shall have no liability to Subtenant for any loss, damage or injury in the event that Master Landlord withholds its consent. 

  
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 5.7 Quiet Enjoyment. Sublandlord covenants that, subject to the terms and conditions
of the Master Lease and this Sublease, if and so long as Subtenant keeps and performs each term and condition herein contained on its part to be kept and performed, Subtenant shall not be disturbed in the enjoyment of the Subleased Space by
Sublandlord or by anyone claiming by, through or under Sublandlord. 
 5.8 Copies of Notices. Whenever a notice is given or received
pursuant to the Master Lease by or to Sublandlord or Subtenant which has relevance to the Subleased Space, Sublandlord and Subtenant each agree promptly to provide the other with a copy of such notice. 

6. Signage; Telecommunications; Services. 

6.1 Signage. Subtenant, at Subtenant’s sole cost and expense, shall be entitled to (i) building standard signage on the
directory board in the Building lobby, and (ii) a building standard identification sign at the entrance to the Subleased Space, subject to Sublandlord’s and Master Landlord’s prior written consent, which consent will not be
unreasonably withheld, conditioned or delayed. Subject to Master Landlord consenting thereto in the Consent to Sublease, Subtenant also will have the benefit of Sublandlord’s rights under Section 12.2 of the Master Lease regarding Monument
Signage, provided that Subtenant shall be responsible for all costs associated with the same, regardless of whether those charges are included in Operating Costs or as a direct charge. All signage shall comply with the terms of the Master Lease and
with all federal, state and local rules, regulations, statutes, and ordinances at all times during the Term. 
 6.2
Telecommunications. Subtenant shall be responsible, at Subtenant’s sole cost and expense, for arranging for all telecommunications and data transmission services to the Subleased Space with the approved service providers for the
Building. Subtenant shall, at Subtenant’s sole cost and expense, remove all wiring, cabling and other installations made by Subtenant in the Building on or before the expiration or earlier termination of the Term of this Sublease. 

6.3 Supply Cleaning. Subtenant shall have the right to use the glasswash and autoclave in the Premises on the third (3rd) floor for no
additional fee. A schedule regarding the use and access of the glasswash and autoclave shall be mutually agreed upon by the Sublandlord and the Subtenant. Service of the glasswash and autoclave shall be coordinated through a vendor mutually agreed
upon by the Sublandlord and the Subtenant, the cost of which will be borne by Sublandlord. In the event that the Master Lease is terminated prior to the Termination Date of this Sublease, the provisions of Section III.6 of the CNDA shall apply to
this Section 6.3. 
 6.4 Cleaning of Sublease Space. Subtenant is responsible for and will pay directly for all janitorial
services it may require for the Subleased Space. Subtenant may, but is not required to, contract for this service with the same provider that cleans the common areas. 

6.5 Access and Security. For the avoidance of doubt, it is expressly acknowledged that Subtenant will have the benefit of the terms of
Section 1.4(a) of the Master Lease. After-hours access to the Building is provided by a card reader access system. Access to the Subleased 

  
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Space is also limited via a card reader system. During the Term of this Sublease, upon Subtenant’s reasonable request, Sublandlord shall provide card reader access cards for each of
Subtenant’s employees and designated independent contractors, for Subtenant’s exclusive use, a list of which shall be submitted to Sublandlord and maintained by Subtenant. Sublandlord will facilitate and enable an individual or individuals
authorized by Subtenant to add and drop access for specific cardholders directly. In the event that the Master Lease is terminated prior to the Termination Date of this Sublease, the provisions of Section III.7 of the CNDA shall apply to this
Section 6.5. 
 6.6 Lab Services Equipment. Sublandlord expressly acknowledges that its obligations under Section 10.1 of
the Master Lease in relation to the Lab Services Equipment and Lab Services will continue to apply with respect to this Sublease and Subtenant’s use of the Subleased Space. Sublandlord’s obligations in relation thereto in the Master Lease
are not passed to Subtenant, and instead, Subtenant is expressly a third party beneficiary of Sublandlord’s obligations thereunder; unless and to the extent any repair, replacement or maintenance is necessitated as a result of the acts,
omissions, negligence or willful misconduct of Subtenant or any of Subtenant’s employees, agents, contractors or invitees, in which case Subtenant shall be responsible for the same in accordance with the terms and conditions of this Sublease.
In the event that the Master Lease is terminated prior to the Termination Date of this Sublease, this Section 6.6 shall be superseded in its entirety by the provisions of Section III.2 of the CNDA. 

7. Security Deposit. 
 7.1 Amount.
Simultaneously with the execution of this Sublease by Subtenant, Subtenant shall deliver to Sublandlord either (i) cash in the amount of $191,250.00 (the “Cash Security Deposit”), which shall be held by Sublandlord in
accordance with this Section 7, or (ii) in the form of an unconditional, irrevocable, absolutely “clean” letter of credit in a face amount equal to 191,250.00 in form and substance reasonably satisfactory to Sublandlord and
otherwise reasonably satisfactory to Sublandlord and issued by a banking corporation reasonably satisfactory to Sublandlord and either having its principal place of business or a duly licensed branch or agency in Waltham, Massachusetts (such letter
of credit and any replacement thereof, the “Letter of Credit”). Sublandlord shall hold the Cash Security Deposit or the Letter of Credit (each hereinafter referred to as the “Security Deposit”) as
security for the faithful performance and observance by Subtenant thereafter of the terms, provisions, and conditions of this Sublease. Sublandlord has no obligation to pay interest on the Cash Security Deposit and may
co-mingle the Cash Security Deposit with Sublandlord’s funds. Neither the Security Deposit, any proceeds therefrom shall be deemed an advance rent deposit or an advance payment of any other kind, or a
measure or limitation of Sublandlord’s damages or constitute a bar or defense to any of the Sublandlord’s other remedies under this Sublease or at law or in equity upon Subtenant’s default. 

7.2 Letter of Credit. If Subtenant elects to deliver the Security Deposit in the form of a Letter of Credit, the Letter of Credit shall
have an expiration date no earlier than the first anniversary of the date of issuance thereof and shall be automatically renewed from year to year unless terminated by the issuer thereof by notice to Sublandlord given not less than forty-five
(45) days prior to the expiration thereof. Subtenant shall, throughout the Term of this Sublease, 

  
 11 

 
deliver to Sublandlord, in the event of the termination of any such letter of credit, replacement letters of credit in lieu thereof no later than thirty (30) days prior to the expiration
date of the preceding Letter of Credit. The term of each such Letter of Credit shall be not less than one year and shall be automatically renewable from year to year as aforesaid. Notwithstanding the foregoing, if Sublandlord shall elect, in its
sole discretion, to accept a Letter of Credit which is subject to a final expiration date, Subtenant shall deliver a replacement of or amendment to such Letter of Credit no later than thirty (30) days prior to such final expiration date, and
the final Letter of Credit delivered to Sublandlord pursuant to this Section 7 shall have a final expiration date occurring not earlier than sixty (60) days following the expiration date of this Sublease. If Subtenant shall fail to obtain
any replacement of or amendment to a Letter of Credit within any of the applicable time limits set forth in this Section 7, Subtenant shall be in default of its obligations under this Section 7 immediately and without need for any
additional notice or cure period, and Sublandlord shall have the right (but not the obligation), at its option, to draw down the full amount of the existing Letter of Credit and use, apply and retain the same as security, and notwithstanding such
draw by Sublandlord, Sublandlord shall have the right (but not the obligation), at its option, to give written notice to Subtenant stating that such failure by Subtenant to deliver such replacement of or amendment to the Letter of Credit constitutes
a continuing default by Subtenant of its obligations under this Section 7, and in the event that Subtenant shall not have delivered such replacement or amendment to Sublandlord within fifteen (15) business days after Subtenant’s
receipt of such notice, Sublandlord may give to Subtenant a notice of intention to end the Term of this Sublease at the expiration of five (5) days from the date of the service of such notice of intention, and upon the expiration of said five
(5) days, this Sublease and the term and estate hereby granted, whether or not the Term shall theretofore have commenced, shall terminate with the same effect as if that day was the day herein definitely fixed for the end and expiration of this
Sublease, but Subtenant shall remain liable for damages as provided in Section 15 hereof. Upon delivery to Sublandlord of any such replacement of or amendment to the Letter of Credit within the fifteen (15) business day period described in
the preceding sentence, such default shall be deemed cured and Sublandlord shall return to Subtenant the proceeds of the Letter of Credit which had been drawn by Sublandlord pursuant to the preceding sentence (or any balance thereof to which
Subtenant is entitled). 
 7.3 Use. In the event Subtenant Defaults in respect of the full and prompt payment and performance of any
of the terms, provisions, covenants and conditions of this Sublease beyond notice (the delivery of which shall not be required for purposes of this Section 7 if Sublandlord is prevented or prohibited from delivering the same under applicable
law, including, but not limited to, all applicable bankruptcy and insolvency laws) and the expiration of any applicable cure periods, including, but not limited to, the payment of Base Rent and Additional Rent, Sublandlord may, at its election, (but
shall not be obligated to) apply the Cash Security Deposit or draw down the entire Letter of Credit or any portion thereof and use, apply or retain the whole or any part of the security represented by the Security Deposit to the extent required for
the payment of: (i) Base Rent and Additional Rent or any other sum as to which Subtenant is in default, (ii) any sum which Sublandlord may expend or may be required to expend by reason of Subtenant’s default in respect of any of the
terms, provisions, covenants, and conditions of this Sublease, including but not limited to, any reletting costs or expenses (including, without limitation, any free rent, Subtenant improvement allowance, leasing commissions, attorneys’ fees,
costs and expenses, and other fees, costs and expenses relating to the reletting of all or any 

  
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portion of the Subleased Space), (iii) any damages or deficiency in the reletting of the Subleased Space, whether such damages or deficiency accrued before or after summary proceedings or other re-entry by Sublandlord, or (iv) any damages awarded to Sublandlord in accordance with the terms and conditions of Section 15 hereof, it being understood that any use of the whole or any part of the
security represented by the Letter of Credit shall not constitute a bar or defense to any of Sublandlord’s other remedies under this Sublease or any law, rule or regulation. To insure that Sublandlord may utilize the security represented by the
Letter of Credit in the manner, for the purpose, and to the extent provided in this Section 7, each Letter of Credit shall provide that the full amount or any portion thereof may be drawn down by Sublandlord upon the presentation to the issuing
bank (or the advising bank, if applicable) of Sublandlord’s draft drawn on the issuing bank without accompanying memoranda or statement of beneficiary. In no event shall the Letter of Credit require Sublandlord to submit evidence to the issuing
(or advising) bank of the truth or accuracy of any such written statement and in no event shall the issuing bank or Subtenant have the right to dispute the truth or accuracy of any such statement nor shall the issuing (or advising) bank have the
right to review the applicable provisions of this Sublease. In no event and under no circumstance shall the draw down on or use of any amounts under the Letter of Credit constitute a basis or defense to the exercise of any other of
Sublandlord’s rights and remedies under this Sublease or under any law, rule or regulation. 
 7.4 Restoration. In the event
that Subtenant defaults in respect of any of the terms, provisions, covenants and conditions of the Sublease beyond notice and the expiration of any applicable cure periods and Sublandlord utilizes all or any part of the security represented by the
Security Deposit but does not terminate this Sublease as provided in Section 15.2 hereof, Sublandlord may, in addition to exercising its rights as provided in Section 7.2 hereof, retain the unapplied and unused balance of the portion of
the Letter of Credit drawn down by Sublandlord as a Cash Security Deposit as security for the faithful performance and observance by Subtenant thereafter of the terms, provisions, and conditions of this Sublease, and may use, apply, or retain the
whole or any part of any such Cash Security Deposit to the extent required for payment of Base Rent and Additional Rent, or any other sum as to which Subtenant is in default or for any sum which Sublandlord may expend or be required to expend by
reason of Subtenant’s default in respect of any of the terms, covenants, and conditions of this Sublease. In the event Sublandlord uses, applies or retains any portion or all of the security represented by the Security Deposit, Subtenant shall
forthwith restore the amount so used, applied or retained (at Sublandlord’s option, either by the deposit with Sublandlord of cash or the provision of a replacement Letter of Credit) so that at all times the amount of the security represented
by the Security Deposit shall be not less than the security required herein, failing which Subtenant shall be in default of its obligations under this Section 7 and Sublandlord shall have the same rights and remedies as for the non-payment of Base Rent beyond the applicable grace period. 
 7.5 Return. Sublandlord shall
return the Security Deposit, whether in the form of cash or Letter of Credit, or so much thereof as shall not have theretofore been applied in accordance with the terms of this Section, to Subtenant within thirty (30) days of the Termination
Date or earlier termination of this Sublease and surrender of possession of the Subleased Space by Subtenant to Sublandlord at such time, provided that there is then existing no Default of Subtenant (nor any circumstance which, with the passage of
time or the giving of notice, or both, would constitute a Default of Subtenant). 

  
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 7.6 In the event that the Master Lease is terminated prior to the Termination Date of this
Sublease, Sections 7.1 through 7.5 shall be superseded in their entirety by the provisions of Section II.3 of the CNDA. 
 8. Delivery Condition of the
Subleased Space. Sublandlord delivers the Subleased Space to Subtenant in their “AS IS” condition with all faults and without any obligation on the part of Sublandlord to modify, improve or otherwise prepare the Subleased Space for
Subtenant’s occupancy or to pay any money to prepare the Subleased Space for Subtenant’s occupancy, except that Sublandlord is responsible to ensure that all base building systems, including but not limited to HVAC, electrical, life safety
and plumbing systems are in good working condition and suitable for laboratory uses. Without limiting Sublandlord’s obligations per the preceding sentence, Subtenant acknowledges that Sublandlord has made no warranty or representation, express
or implied, as to the present or future condition of the Subleased Space or the fitness and availability of the Subleased Space for any particular use or any other matter relating to this Sublease by Sublandlord, Master Landlord, Sublandlord’s
or Subtenant’s Brokers or any other parties and Subtenant has relied upon its own examination of the Subleased Space in entering into this Sublease. By taking possession of the Subleased Space, Subtenant accepts the Subleased Space in their
“AS IS” condition, subject to all applicable zoning, municipal, county, state and federal laws, ordinances, and regulations governing and regulating the use of the Subleased Space and any covenants or restrictions of record. In the event
that the Master Lease is terminated prior to the Termination Date of this Sublease, the provisions of Section III.3 of the CNDA shall apply to this Section 8. 

9. Furniture. 
 9.1 Sublandlord’s
Furniture. Sublandlord shall deliver the Subleased Space in its “AS IS,” where is, condition, but with the furniture identified on Exhibit B attached hereto (“Sublandlord’s
Furniture”) in the Subleased Space, which shall include the installation of two (2) Biosaftey Cabinets (“BSC”) in the tissue culture suite located in the Premises for use by Subtenant, which BSCs will have
been inspected and certified for use by appropriate authorities. Placement of the BSCs shall be reasonably coordinated with Subtenant. Subtenant agrees to take all actions necessary or appropriate to ensure that Sublandlord’s Furniture shall be
and remain personal property, and nothing in this Sublease shall be constituted as conveying to Subtenant any interest in Sublandlord’s Furniture other than its interest as a Subtenant. Subtenant shall, at its expense, protect and defend the
interest of Sublandlord in Sublandlord’s Furniture against all third party claims; keep Sublandlord’s Furniture free and clear of any mortgage, security interest, pledge, lien, charge, claim, or other encumbrance (collectively, a
“Lien”), except any Lien arising solely through acts of Sublandlord; and indemnify and defend Sublandlord against any claim, liability, loss, damage, or expense arising in connection with any of the foregoing. Sublandlord’s
Furniture shall be used by Subtenant only at the Subleased Space and in the ordinary conduct of its business. Subtenant shall, at its expense, repair, maintain and replace Sublandlord’s Furniture so that it will remain in the same condition as
when delivered to Subtenant, ordinary wear and tear from proper use excepted. In addition, Subtenant hereby assumes all other risks and liabilities, including without limitation personal injury or death and property damage, arising with respect to
Sublandlord’s Furniture (unless solely through Sublandlord’s willful misconduct), howsoever arising, in connection with any event occurring 

  
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prior to such Sublandlord’s Furniture’s return in accordance herewith. Subtenant hereby assumes liability for, and shall pay when due, and shall indemnify and defend Sublandlord
against, all fees, taxes, and governmental charges (including without limitation interest and penalties) of any nature imposed upon or in any way relating to Sublandlord’s Furniture. In addition, Sublandlord makes no other representation or
warranty, express or implied, as to any matter whatsoever, including without limitation the design or condition of Sublandlord’s Furniture, its merchantability, durability, suitability or fitness for any particular purpose, the quality of the
material or workmanship of Sublandlord’s Furniture, or the conformity of Sublandlord’s Furniture to the provisions or specifications of any purchase order relating thereto, and Sublandlord hereby disclaims any and all such representations
and warranties. Upon the expiration of the term of this Sublease, Subtenant shall surrender Sublandlord’s Furniture to Sublandlord in the condition required hereunder. In the event that the Master Lease is terminated prior to the Termination
Date of this Sublease, the provisions of Section III.3 of the CNDA shall apply to this Section 9.1. 
 9.2 Subtenant’s
FF&E. Subtenant acknowledges and agrees that Sublandlord is not obligated to provide any other furniture, furnishings, or equipment in the Subleased Space other than Sublandlord’s Furniture, and Subtenant agrees that it will be solely
responsible for providing any other furniture, furnishings, and equipment necessary for Subtenant’s occupancy (“Subtenant’s FF&E”). Prior to expiration of the Term or earlier termination of
this Sublease, unless otherwise agreed to by Sublandlord or as expressly provided in this Sublease, Subtenant shall remove all of Subtenant’s FF&E and restore the Subleased Space to the same condition as when received, excepting only
ordinary wear and tear and damage by fire or other insured Casualty. If Subtenant fails to remove Subtenant’s FF&E and restore the Subleased Space, then Sublandlord shall have the right to do so, and charge Subtenant the actual costs
therefor, plus a service charge of ten percent (10%) of the costs incurred by Sublandlord. Subtenant’s obligations under this Section 9.2 shall survive the expiration or earlier termination of this Sublease. In the event that the Master
Lease is terminated prior to the Termination Date of this Sublease, the provisions of Section III.3 of the CNDA shall apply to this Section 9.2. 
 10.
Repairs; Alterations; Maintenance 
 10.1 Approval Required. Subtenant at its own cost shall keep the Subleased Space in good
condition and repair and in accordance with the applicable terms of the Master Lease. Subtenant shall not perform or cause to be performed any interior or exterior improvements to the Subleased Space (“Subtenant Alterations”)
without the prior written consent of Master Landlord (in accordance with the terms of the Master Lease) and Sublandlord, to be granted or withheld in Sublandlord’s sole and absolute discretion. Subtenant shall reimburse Master Landlord and
Sublandlord for all costs they may incur in connection with reviewing Subtenant’s proposed Subtenant Alterations, including, without limitation, Master Landlord’s and Sublandlord’s reasonable engineers’, architects’,
attorneys’ and other consultants’ fees and costs. 
 10.2 Sublandlord Conditions to Approval. If Master Landlord and
Sublandlord do approve the proposed Subtenant Alterations in addition to all the requirements of the Master Lease, Sublandlord may impose as a condition to its consent such requirements as Sublandlord may deem reasonable and desirable, including
without limitation the requirement that 

  
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Subtenant’s contractors and subcontractors at all tiers be approved by Sublandlord and that Subtenant and/or Subtenant’s contractor(s) post a payment and/or completion bond to guarantee
the performance of its construction obligations. Subtenant shall pay the full cost of designing and constructing the Subtenant Alterations and shall keep the Subleased Space and the Building free from any liens arising out of work performed,
materials furnished or obligations incurred by or on behalf of Subtenant. In accordance with the incorporated provisions of the Master Lease, Subtenant shall provide Master Landlord and Sublandlord with: (a) copies of all permits obtained by
Subtenant in connection with performing the Subtenant Alterations, prior to commencing construction; and (b) meet all requirements provided for in the Master Lease or as may be provided by Master Landlord for construction rules and regulations.
It is expressly agreed that Subtenant will be permitted, in its discretion, to install a third BSC in the Subleased Space. To the extent that this might constitute a “Subtenant Alteration”, Sublandlord hereby consents to such installation.

 10.3 Removal. Prior to expiration of the Term or earlier termination of this Sublease, if Sublandlord so directs, Subtenant shall
remove all of the Subtenant Alterations and restore the Subleased Space to the same condition as when received, excepting only ordinary wear and tear and damage by fire or other insured Casualty. If Subtenant fails to remove the Subtenant
Alterations and restore the Subleased Space, then Sublandlord shall have the right to do so, and charge Subtenant the actual costs therefor, plus a service charge of ten percent (10%) of the costs incurred by Sublandlord. Subtenant may request in
writing to Sublandlord at the time Subtenant presents any plans to Sublandlord for review that Sublandlord designate whether Sublandlord will require that the proposed alterations shown on the plans be removed at the expiration or earlier
termination of the Term of this Sublease and, if such is so requested in writing, Sublandlord agrees, if expressly requested by Subtenant in writing, to make such designation at the time Sublandlord reviews and responds to Subtenant’s plans,
provided, however, Sublandlord may defer notification until Master Landlord responds to such request in accordance with the terms of the Master Lease. Subtenant’s obligations under this Section 10.3 shall survive the expiration or earlier
termination of this Sublease. It is expressly agreed that, if installed, a third BSC may, in Subtenant’s discretion, be left in the Subleased Space on surrender of the Subleased Space. 

11. Parking. Subtenant shall have the right, free of charge for the Term, to use up to thirty-five (35) parking spaces, located at the surface or
“828 Garage” parking areas serving the Building, all on a non-reserved, first come first served basis, and all in accordance with the terms and conditions of Section 1.3(b) of the Master Lease.

 12. Assignment or Subleasing 
 12.1
Applicability of Master Lease. Except as otherwise provided herein, Sublandlord and Subtenant shall have the rights and obligations as set forth in Article 13 of the Master Lease with respect to any assignment or sublease of the Subleased
Space. In the event that the Master Lease is terminated prior to the Termination Date of this Sublease, the provisions of Section III.11 of the CNDA shall apply to this Section 12. 

  
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 12.2 Form of Document. Every assignment, agreement, or sublease shall contain such
terms and conditions as shall be reasonably requested by Sublandlord’s attorneys, and recite that: (a) it is and shall be subject and subordinate to the provisions of this Sublease and the Master Lease; (b) the assignee or subtenant
assumes Subtenant’s obligation hereunder; and (c) the termination of this Sublease shall, at Sublandlord’s sole election, constitute a termination of every such assignment or sublease. 

12.3 No Release of Subtenant. Regardless of Sublandlord’s and Master Landlord’s consent, no subletting or assignment shall
release Subtenant of Subtenant’s obligation or alter the primary liability of Subtenant to pay the Rent and to perform all other obligations to be performed by Subtenant under this Sublease. The acceptance of Rent by Sublandlord from any other
person shall not be deemed to be a waiver by Sublandlord of any provision of this Sublease. In the event of default by Subtenant or any successor or assignee which remains uncured after any applicable notice and cure periods, if any, Sublandlord may
proceed directly against Subtenant without the necessity of exhausting remedies against such assignee, subtenant or successor. 
 12.4
Permitted Atlas Transfers. Without limitation to the applicability of the terms of Article 13 of the Master Lease, as incorporated herein per the terms of this Sublease, it is further agreed that, for purposes of Section 13.7 of the
Master Lease, any company in which an Atlas Venture fund is an investor and that meets the Financial Test (as hereinafter defined), will be considered an “Affiliated Entity”. The “Financial Test” shall mean that the
company’s total cash and cash equivalents, taken at the time of the Transfer, divided by their 12-month forward-looking net loss (as a positive number) is greater than 1.5. In the event that the Master
Lease is terminated prior to the Termination Date of this Sublease, the provisions of Section III.8 of the CNDA shall apply to this Section 12.4. 

12.5 Default. An involuntary assignment which remains uncured after the applicable notice and cure periods set forth in this Sublease
shall constitute a Default by Subtenant and in such event Sublandlord may elect, in addition to other remedies, to terminate this Sublease. If this Sublease is terminated, it shall not be treated as an asset of Subtenant. 

13. Insurance. Subtenant, at its sole cost and expense, shall procure and maintain during the Term all insurance types and coverages required to be
maintained by the Tenant under the Master Lease with respect to the Subleased Space, except that it is agreed that Subtenant’s insurance as required by Section 14(a) of the Master Lease, may exclude umbrella liability coverage if Subtenant
carries commercial general liability insurance meeting the requirements thereof, and in amounts of at least $2,000,000 per occurrence and $4,000,000 in the aggregate. Sublandlord and Master Landlord shall be named as additional insureds on all such
insurance policies except with respect to coverages solely on Subtenant’s furniture, equipment and other personal property in the Subleased Space. Subtenant hereby agrees that the property damage insurance carried by Subtenant hereunder shall
provide for the waiver by the insurance carrier of any right of subrogation against Sublandlord and Master Landlord, and Subtenant further agrees that, with respect to any damage to property, the loss of which is covered by insurance carried by
Subtenant or which would have been covered by the insurance coverages required to be carried by Subtenant under this Sublease, Subtenant releases Sublandlord and 

  
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Master Landlord from any and all claims with respect to such loss to the extent of the insurance proceeds paid with respect thereto. In the event that the Master Lease is terminated prior to the
Termination Date of this Sublease, this Section 13 shall be superseded in its entirety by the provisions of Section III.9 of the CNDA. 
 14.
Indemnity. Subtenant’s indemnity obligations under the Master Lease which are incorporated by reference herein shall protect both Sublandlord and the other parties referenced in the Master Lease. 

15. Default 
 15.1 Default
Described. The occurrence of any of the following shall constitute a material breach of this Sublease and a “Default” by Subtenant: (a) failure to pay Rent or any other amount within three (3) business days
after the date it is due (a “monetary default”); (b) all those items of default set forth in the Master Lease which remain uncured after the cure period provided in the Master Lease, less three (3) business days; and/or
(c) Subtenant’s failure to perform timely and subject to any cure periods any other material provision of this Sublease or the Master Lease as incorporated herein. Notwithstanding the provisions of clause (a) above to the contrary,
Sublandlord agrees that, with respect to the first instance per calendar year on which there is a monetary default, Sublandlord will provide Subtenant with a written notice that such payment was not received and such failure will not constitute a
Default of Subtenant unless such failure to pay is not cured within three (3) business days after receipt of such notice from Sublandlord. Other than the first monetary default per calendar year, Sublandlord will not be required to provide
Subtenant with a notice of nonpayment as to any other monetary default by Subtenant during that same calendar year before such monetary default will constitute a Default by Subtenant under this Sublease. 

15.2 Sublandlord’s Remedies. Sublandlord shall have, on account of any Default by Subtenant, all of the rights and remedies set
forth in the Master Lease as if Sublandlord is Master Landlord. These remedies are not exclusive; they are cumulative and in addition to any remedies now or later allowed by law. 

16. Brokers. Pursuant to separate agreements, Sublandlord agrees to pay a broker’s commission to CBRE and Jones Lang LaSalle
(“Brokers”). Sublandlord and Subtenant each represent and warrant to the other that, except for the Brokers, it has had no dealings with any real estate brokers or agents in connection with this Sublease, and it knows of no
real estate broker or agent who is entitled to a commission, finder’s fee or similar compensation in connection with this Sublease. Except for the Brokers, Sublandlord and Subtenant each shall defend, indemnify and hold the other harmless from
and against all liabilities and expenses (including reasonable attorneys’ fees and costs) arising from any claims for a commission, finder’s fees or similar compensation based on the indemnitor’s dealings or contacts in connection
with this Sublease. In the event that the Master Lease is terminated prior to the Termination Date of this Sublease, the provisions of Section I.9 of the CNDA shall apply to this Section 16. 

  
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 17. Notices. All notices, demands, statements, designations, approvals or other communications
(collectively, “Notices”) given or required to be given by either party to the other hereunder or by law shall be in writing and shall be: (a) sent by United States certified or registered mail, postage prepaid, return
receipt requested (“Mail”); (b) transmitted by electronic mail (“email”), if such email is promptly followed by a Notice sent by one of the other methods permitted hereunder; (c) delivered by a
nationally recognized overnight courier; or (d) delivered personally. Any Notice shall be sent, transmitted, or delivered, as the case may be, to Subtenant at the addresses set forth below, or to such other place as Subtenant may from time to
time designate in a Notice to Sublandlord, or to Sublandlord at the addresses set forth below, or to such other places as Sublandlord may from time to time designate in a Notice to Subtenant. Any Notice will be deemed given: (i) five (5) days
after the date it is posted if sent by Mail; (ii) the date the email is transmitted; (iii) the date the overnight courier delivery is made; or (iv) the date personal delivery is made. Any Notice given by an attorney on behalf of
Sublandlord shall be considered as given by Sublandlord and shall be fully effective. Any Notice given by an attorney on behalf of Subtenant shall be considered as given by Subtenant and shall be fully effective. As of the date of this Sublease, any
Notices to Sublandlord must be sent, transmitted, or delivered, as the case may be, to the following addresses: 
 Arrakis Therapeutics, Inc. 

830 Winter Street 
 Waltham, Massachusetts 02451 

As of the date of this Sublease, any Notices to Subtenant must be sent, transmitted, or delivered, as the case may be, to the following addresses: 

400 Technology Square, 10th Floor 

Cambridge, Massachusetts 02139 
 From the Rent Commencement Date,
any Notices to Subtenant must be sent, transmitted, or delivered, as the case may be, to the following address: 
 830 Winter Street 

Waltham, Massachusetts 02451 
 Each party to this
Sublease shall send to the other party copies of any and all notices and other communications it shall send to and receive from Master Landlord relating to the Subleased Space. Either party may designate different addresses for notice to such party
by delivery of written notification of such changes to the other party in accordance with the notice provisions of this Sublease. 
 18. Surrender.
Subtenant shall keep the Subleased Space, and every part thereof, in good order and repair and Subtenant shall surrender the Subleased Space (including without limitation all fixed lab benches, fume hoods, electric, plumbing, heating and sprinkling
systems, fixtures and outlets, vaults, paneling, molding, shelving, radiator enclosures, cork, rubber, linoleum and composition floors, ventilating, silencing, air conditioning and cooling equipment therein and all other furniture, fixtures, and
equipment that was either provided by 

  
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Sublandlord or Master Landlord) at the expiration or earlier termination of the Term of this Sublease in the same condition as when received, excepting only ordinary wear and tear and damage by
fire or other insured Casualty, and shall comply with Section 21.1(b) of the Master Lease. Subtenant shall remove Subtenant’s FF&E and all of the Subtenant Alterations designated by Sublandlord pursuant to Section 10.3 of this
Sublease. If Subtenant fails to remove the Subtenant Alterations or Subtenant’s FF&E and restore the Subleased Space, then Sublandlord shall have the right to do so, and charge Subtenant the actual costs therefor, plus a service charge of
ten percent (10%) of the costs incurred by Sublandlord. Subtenant’s obligations under this Section 18 shall survive the expiration or earlier termination of this Sublease. 

19. Master Landlord’s Consent. This Sublease is expressly conditioned upon Master Landlord’s written consent to this Sublease (the
“Consent to Sublease”), which such Consent to Sublease Sublandlord shall use commercially reasonable efforts to obtain. In the event that Master Landlord’s Consent to Sublease has not been received within forty-five
(45) days after the date of this Sublease, then either party may elect to terminate this Sublease by delivering five (5) days prior written notice of such election to the other party within ten (10) business days following the
expiration of such forty-five (45) day period and whereupon this Sublease shall be null and void and of no further force and effect unless such Consent to Sublease is obtained prior to the expiration of such five (5) business day period.

 20. Miscellaneous 
 20.1 Time of
Essence. Time is of the essence with respect to the performance of every provision of this Sublease in which time of performance is a factor, including, without limitation, the giving of any Notice required to be given under this Sublease or by
law, the time periods for giving any such Notice and for taking of any action with respect to any such Notice. 
 20.2 Partial
Invalidity. If any term, provision or condition contained in this Sublease shall, to any extent, be invalid or unenforceable, the remainder of this Sublease, or the application of such term, provision or condition to persons or circumstances
other than those with respect to which it is invalid or unenforceable, shall not be affected thereby, and each and every other term, provision and condition of this Sublease shall be valid and enforceable to the fullest extent possible permitted by
law; provided that, if a material provision is adjudged void or unenforceable, the parties shall negotiate, in good faith, an equitable adjustment to such other provisions of this Sublease as may be necessary or appropriate to effectuate as closely
as possible the parties’ intent as evidenced by this Sublease. 
 20.3 Entire Agreement. There are no oral agreements between
the parties hereto affecting this Sublease and this Sublease constitutes the parties’ entire agreement with respect to the leasing of the Subleased Space and supersedes and cancels any and all previous negotiations, arrangements, letters of
intent, agreements and understandings, if any, between the parties, and none thereof shall be used to interpret or construe this Sublease. None of the terms, covenants, conditions or provisions of this Sublease can be modified, deleted or added to
except in writing signed by the parties. 

  
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 20.4 Authority. Subtenant represents and warrants that it is duly formed in Delaware,
and is an existing entity qualified to do business in the Commonwealth of Massachusetts and that Subtenant has full right and authority to execute, deliver and perform this Sublease. Subtenant represents and warrants to the Sublandlord that neither
its execution, delivery of performance of this Sublease shall cause it to be in violation of any agreement, instrument, contract, law, rule or regulation by which it is bound, and Subtenant shall protect, defend, indemnify and hold Sublandlord
harmless against any claims, demands, losses, damages, liabilities, costs and expenses, including, without limitation, reasonable attorneys’ fees and costs, arising from a breach of this representation and warranty by Subtenant. 

20.5 Attorneys’ Fees. In the event that either Sublandlord or Subtenant should bring suit for the possession of the Subleased
Space, for the recovery of any sum due under this Sublease, or because of the breach of any provision of this Sublease or for any other relief against the other, then all costs and expenses, including reasonable attorneys’ fees, incurred by the
prevailing party therein shall be paid by the other party. In any case where Subtenant requests permission from Sublandlord to assign, sublet, make alterations, or receive any other consent or obtain any waiver from or modification to the terms of
this Sublease, Subtenant shall pay to Sublandlord any reasonable third party review fees and Sublandlord’s reasonable out of pocket attorneys’ fees incurred by Sublandlord in reviewing such request; provided, however, Subtenant’s
liability relating to third party out of pocket legal fees for request for consent related to assignment and subletting shall not exceed $2,500 per request. 

20.6 Governing Law; WAIVER OF TRIAL BY JURY. This Sublease shall be construed and enforced in accordance with the internal laws of the
Commonwealth of Massachusetts. IN ANY ACTION OR PROCEEDING ARISING HEREFROM, SUBLANDLORD AND SUBTENANT HEREBY BY CONSENT TO: (A) THE JURISDICTION OF ANY FEDERAL, STATE, COUNTY OR MUNICIPAL COURT SITTING IN THE COMMONWEALTH OF MASSACHUSETTS;
(B) SERVICE OF PROCESS BY ANY MEANS AUTHORIZED BY MASSACHUSETTS LAW; AND (C) IN THE INTEREST OF SAVING TIME AND EXPENSE, TRIAL WITHOUT A JURY IN ANY ACTION, PROCEEDING OR COUNTERCLAIM BROUGHT BY EITHER OF THE PARTIES HERETO AGAINST THE
OTHER OR THEIR SUCCESSORS IN RESPECT OF ANY MATTER ARISING OUT OF OR IN CONNECTION WITH THIS SUBLEASE, THE RELATIONSHIP OF SUBLANDLORD AND SUBTENANT, SUBTENANT’S USE OR OCCUPANCY OF THE SUBLEASED SPACE, AND/OR ANY CLAIM FOR INJURY OR DAMAGE, OR
ANY EMERGENCY OR STATUTORY REMEDY. 
 20.7 Confidentiality. Sublandlord and Subtenant each acknowledge that the content of this
Sublease and of the Master Lease and any related documents are confidential information. Each shall keep such confidential information strictly confidential and shall not disclose such confidential information to any person or entity other than its
financial, legal, and space planning consultants, all of whom shall be subject to this confidentiality provision, and as otherwise required by law. 

20.8 Holding Over. Subtenant shall have no right to holdover. If Subtenant does not surrender and vacate the Subleased Space at the
expiration of the Term or earlier termination of 

  
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this Sublease, Subtenant shall be a tenant at sufferance and Rent shall be the monthly Base Rent at the Hold Over Percentage (as hereinafter defined) that was payable under the Master Lease for
the entire Premises as of the last month of the Term, plus, all other Additional Rent and other charges payable by Sublandlord under the Master Lease for the entire Premises during such period. The “Hold Over
Percentage” shall be 150% for the first sixty (60) days of such holdover, and 200% for any period of hold over after the first sixty (60) days. In connection with the foregoing, Sublandlord and Subtenant agree that the
reasonable rental value of the Subleased Space following the Termination Date or earlier termination of the Sublease shall be the amounts set forth above. Sublandlord and Subtenant acknowledge and agree that, under the circumstances existing as of
the Effective Date, it is impracticable and/or extremely difficult to ascertain the reasonable rental value of the Subleased Space and that the reasonable rental value established in this Section 20.8 is a reasonable estimate of the damage that
Sublandlord would suffer as the result of Subtenant’s failure to timely surrender possession of the Subleased Space. The parties acknowledge that the liquidated damages established herein is not intended as a forfeiture or penalty.
Notwithstanding the foregoing, and in addition to all other rights and remedies on the part of Sublandlord if Subtenant fails to surrender the Subleased Space upon the termination or expiration of this Sublease, in addition to any other liabilities
to Sublandlord accruing therefrom, if Subtenant’s holding over in the Subleased Space persists for more than thirty (30) days, Subtenant shall indemnify, defend and hold Sublandlord harmless from all claims, liabilities, losses and
expenses, including reasonable attorneys’ fees and costs, resulting from such failure. In the event that the Master Lease is terminated prior to the Termination Date of this Sublease, this Section 20.8 shall be superseded in its entirety
by the provisions of Section III.10 of the CNDA. 
 20.9 Successors and Assigns. Subject to the limitations set forth in
Section 12, this Sublease shall be binding upon each of the parties and their respective successors and assigns. 
 20.10
Interpretation. Preparation of this Sublease has been a joint effort of the parties and the resulting document shall not be construed more severely against one of the parties than against the other. 

20.11 Consent. In any instance in which this Sublease or the Master Lease requires the consent of either Sublandlord or Master
Landlord, the consent of both Sublandlord and Master Landlord shall be required. 
 20.12 Exhibits and Attachments. All Exhibits and
attachments to this Sublease are a part hereof. 
 20.13 Counterparts. This Sublease may be executed in counterparts with the same
effect as if both parties had executed the same document. Both counterparts shall be construed together and shall constitute a single lease. Pages may be transmitted by facsimile or electronically and each of will be deemed an original. The
signature pages of counterpart copies may be assembled to form one instrument. 
 [Remainder of page intentionally left blank; Signatures
to follow] 

  
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 The parties have executed this Sublease as of the Effective Date. 

 

							
		 	Sublandlord:	  	ARRAKIS THERAPEUTICS, INC., a Delaware corporation
				
		 		  	By:	  	 /s/ Michael Gilhan

							
				
		 		  	Name & Title:	  	 President : CEO

			
		 	Subtenant:	  	DYNE THERAPEUTICS, INC., a Delaware corporation

							
				
		 		  	By:	  	  

							
				
		 		  	Name & Title:	  	  

  
 23 

 The parties have executed this Sublease as of the Effective Date. 

 

							
		 	Sublandlord:	  	ARRAKIS THERAPEUTICS, INC., a Delaware corporation
				
		 		  	By:	  	
            

							
				
		 		  	Name & Title:	  	  

			
		 	Subtenant:	  	DYNE THERAPEUTICS, INC., a Delaware corporation

							
				
		 		  	By:	  	 /s/ Romesh R. Subramanian

							
				
		 		  	Name & Title:	  	 Romesh R. Subramanian, CEO

  
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