Lease Agreement between Omega Therapeutics, Inc. and ARE-MA Region No, 94, LLC

DocuSign Envelope ID: 95812A0E-597B-4C31-9F12-CB594CA06309

Exhibit 10.13

LEASE AGREEMENT

THIS LEASE AGREEMENT (this “Lease”) is made this 4 day of November, 2021, between ARE-MA REGION NO. 94, LLC, a Delaware limited liability company (“Landlord”), and OMEGA THERAPEUTICS, INC., a Delaware corporation (“Tenant”).

Premises: That portion of the Building containing approximately 89,246 rentable square feet, consisting of (i) approximately 78,380 rentable square feet in Suite 501, chemical storage rooms CC5 and RC5, and penthouse storage room PH5 (collectively, the “Phase 1 Premises”), and (ii) approximately 10,866 rentable square feet in Suite 105 (the “Phase 2 Premises”), all as determined by Landlord, as shown on Exhibit A. The rentable square footage of the Premises has been determined in accordance with the Standard Method of Measuring Floor Area in Office Buildings as adopted by the Building Owners and Managers Association International (ANSI/BOMA Z65.1- 2017, Method B), as customarily modified for laboratory properties in the Cambridge, Massachusetts market.

Building: That certain building in the Project currently being redeveloped and known as One Charles Park, Cambridge, Massachusetts, and located on the real property owned by Landlord and described on Exhibit B.

Project: The real property on which the Building in which the Premises are located, together with all improvements thereon and appurtenances thereto as described on Exhibit B.

Base Rent: $115.00 per rentable square foot of the Premises per year, subject to adjustment pursuant to Section 4 hereof.

Rentable Area of Premises: 89,246 sq. ft. Rentable Area of Building: 408,259 sq. ft. Rentable Area of Project: 408,259 sq. ft.

Tenant’s Share of Operating Expenses of Building: 21.86% (19.20% with respect to the Phase 1 Premises and 2.66% with respect to the Phase 2 Premises)

Security Deposit: None

Phase 1 Target Commencement Date: December 15, 2022

Phase 2 Target Commencement Date: March 15, 2023

Rent Adjustment Percentage: 3%

Base Term: Beginning on the Commencement Date and ending 180 months from the first day of the first full month following the Commencement Date. For clarity, if the Commencement Date occurs on the first day of a month, the expiration of the Base Term shall be measured from that date. If the Commencement Date occurs on a day other than the first day of a month, the expiration of the Base Term shall be measured from the first day of the following month.

Permitted Use: Research and development laboratory, general office and other related uses consistent with the character of the Project and otherwise in compliance with the provisions of Section 7 hereof.

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In all events with a copy to:

VentureLabs VI, Inc. c/o Flagship Pioneering

55 Cambridge Parkway, Suite 800E Cambridge, MA 02142

Attn: One Charles Park Coordinator

As a courtesy, copies of notices provided by Landlord to Tenant under this Lease shall be sent to ***@*** and ***@***.

The following Exhibits and Addenda are attached hereto and incorporated herein by this reference:

[X] EXHIBIT A - PREMISES DESCRIPTION [X] EXHIBIT B - DESCRIPTION OF PROJECT

[X] EXHIBIT C - WORK LETTER [X] EXHIBIT D - COMMENCEMENT DATE

[X] EXHIBIT E - RULES AND REGULATIONS [X] EXHIBIT F - TENANT’S PERSONAL PROPERTY

[X] EXHIBIT G - SHARED SPACE CONSENT

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The “Commencement Date” shall be the earlier of: (i) the date Landlord Delivers the Phase 1 Premises to Tenant; and (ii) the date Landlord could have Delivered the Phase 1 Premises but for Tenant Delays.

Except as set forth in the Work Letter or as otherwise expressly set forth in this Lease: (i) Tenant shall accept the Phase 1 Premises in their condition as of the Commencement Date; (ii) Landlord shall have no obligation for any defects in the Phase 1 Premises; and (iii) Tenant’s taking possession of the Phase 1 Premises shall be conclusive evidence that Tenant accepts the Phase 1 Premises and that the Phase 1 Premises were in good condition at the time possession was taken. Any occupancy of the Phase 1 Premises by Tenant before the Commencement Date shall be subject to all of the terms and conditions of this Lease, excluding, so long as Tenant is not conducting business in any portion of the Phase 1 Premises, the obligation to pay Base Rent and Operating Expenses with respect to the Phase 1 Premises.

For the period of 90 consecutive days after the Commencement Date, Landlord shall, at its sole cost and expense (which shall not constitute an Operating Expense), be responsible for any repairs that are required to be made to the Building or Building Systems (as defined in Section 13) serving the Phase 1 Premises, unless Tenant or any Tenant Party was responsible for the cause of such repair, in which case Tenant shall pay the cost. Tenant shall also have the benefit of any warranties issued to Landlord in connection with Landlord’s Work related to the Phase 1 Premises.

“Phase 2 Commencement Date” shall be the earlier of: (i) the date Landlord Delivers the Phase 2 Premises to Tenant; and (ii) the date Landlord could have Delivered the Phase 2 Premises but for Tenant Delays.

Except as set forth in the Work Letter or as otherwise expressly set forth in this Lease: (i) Tenant

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shall accept the Phase 2 Premises in their condition as of the Phase 2 Commencement Date; (ii) Landlord shall have no obligation for any defects in the Phase 2 Premises; and (iii) Tenant’s taking possession of the Phase 2 Premises shall be conclusive evidence that Tenant accepts the Phase 2 Premises and that the Phase 2 Premises were in good condition at the time possession was taken. Any occupancy of the Phase 2 Premises by Tenant before the Phase 2 Commencement Date shall be subject to all of the terms and conditions of this Lease, excluding, so long as Tenant is not conducting business in any portion of the Phase 2 Premises, the obligation to pay Base Rent and Operating Expenses with respect to the Phase 2 Premises.

For the period of 90 consecutive days after the Phase 2 Commencement Date, Landlord shall, at its sole cost and expense (which shall not constitute an Operating Expense), be responsible for any repairs that are required to be made to the Building or Building Systems serving the Phase 2 Premises, unless Tenant or any Tenant Party was responsible for the cause of such repair, in which case Tenant shall pay the cost. Tenant shall also have the benefit of any warranties issued to Landlord in connection with Landlord’s Work related to the Phase 2 Premises.

Upon request of Landlord, Tenant shall execute and deliver a written acknowledgment of the Commencement Date, the Phase 2 Commencement Date, and the expiration date of the Term when such are established in the form of the “Acknowledgement of Commencement Date” attached to this Lease as Exhibit D; provided, however, Tenant’s failure to execute and deliver such acknowledgment shall not affect Landlord’s rights hereunder. The “Term” of this Lease shall be the Base Term, as defined above on the first page of this Lease and any Extension Terms which Tenant may elect pursuant to Section 39 hereof.

Tenant agrees and acknowledges that neither Landlord nor any agent of Landlord has made any representation or warranty with respect to the condition of all or any portion of the Premises or the Project, and/or the suitability of the Premises or the Project for the conduct of Tenant’s business, and Tenant waives any implied warranty that the Premises or the Project are suitable for the Permitted Use. Landlord represents and warrants that the person signing this Lease on behalf of Landlord is duly authorized to execute and deliver this Lease on behalf of Landlord as a legally binding contract of Landlord. Tenant represents and warrants that the person signing this Lease on behalf of Tenant is duly authorized to execute and deliver this Lease on behalf of Tenant as a legally binding contract of Tenant. This Lease constitutes the complete agreement of Landlord and Tenant with respect to the subject matter hereof and supersedes any and all prior representations, inducements, promises, agreements, understandings and negotiations which are not contained herein. Landlord in executing this Lease does so in reliance upon Tenant’s representations, warranties, acknowledgments and agreements contained herein.

Notwithstanding anything to the contrary contained in this Lease, Tenant and Landlord acknowledge and agree that as of the date of this Lease, Landlord does not own the Project and that the effectiveness of this Lease and the delivery of the Premises to Tenant is conditioned upon Landlord acquiring fee title to the Project or entering into a master lease to become the master lessee of the Project pursuant to the existing purchase and sale agreement (as the same may be amended) between Landlord and the current owner of the Project (“Condition Precedent”). Neither Landlord nor Tenant shall have any liability whatsoever to each other relating to or arising from Landlord’s inability or failure for any reason to cause the Condition Precedent to be satisfied. If the Condition Precedent is not satisfied by January 26, 2022, then this Lease may be terminated by Landlord or Tenant by delivery of written notice to the other delivered on or before February 2, 2022. If this Lease terminates pursuant to the

immediately preceding sentence, neither Landlord nor Tenant shall have any further rights, duties or obligations under this Lease: (a) the Security Deposit, or any balance thereof (i.e., after deducting therefrom all amounts to which Landlord is entitled under the provisions of this Lease), and any prepaid Base Rent shall be returned to Tenant, and (b) neither Landlord nor Tenant shall have any further rights, duties or obligations under this Lease, except with respect to provisions which expressly survive termination of this Lease.

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prepay the then-outstanding TI Rent (including applicable interest remaining unpaid) in full at any time without penalty.

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The term “Operating Expenses” means all costs and expenses of any kind or description whatsoever incurred or accrued each calendar year by Landlord with respect to the Building including, without duplication, (i) Taxes (as defined in Section 9), (ii) the cost of upgrades to the Building or Project or enhanced services provided at the Building and/or Project which are intended to encourage social distancing, promote and protect health and physical well-being and/or intended to limit the spread of communicable diseases and/or viruses of any kind or nature (collectively, “Infectious Conditions”), (iii) the cost (including, without limitation, any commercially reasonable subsidies which Landlord may provide in connection with the Project Amenities) of the Project Amenities, (iv) costs related to the parking structures and/or other parking areas serving the Project and transportation costs (including costs associated with Landlord’s operation of or participation in a shuttle service serving the Project, if any), (v) capital repairs, improvements and replacements amortized over the lesser of 10 years and the useful life of such capital repairs, improvements and replacements, and (vi) the costs of Landlord’s third party property manager (not to exceed 3% of Base Rent) or, if there is no third party property manager, administration rent in the amount of 3% of Base Rent, excluding only:

Project;

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Project;

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(aa) the costs of signs at the Project identifying Landlord or any other tenants of the Project;

(bb) any expenses applicable to applying and reporting for the Building or the Project solely for the purpose of seeking or maintaining a Leadership in Energy and Environmental Design (LEED), WELL Building Standard, or other similar “green” certification rating above a gold standard or its equivalent;

(cc) costs associated with the maintenance or operation of the Charles Park Garage (as defined in Section 10) or other parking facilities serving the Building or the Project or any portion thereof; and

(dd) any expenses otherwise includable within Operating Expenses to the extent actually reimbursed by persons other than tenants of the Project under leases for space in the Project.

In addition, notwithstanding anything to the contrary contained in this Lease, Operating Expenses incurred or accrued by Landlord with respect to any capital improvements which are reasonably expected by Landlord to reduce overall Operating Expenses (for example, without limitation, by reducing energy usage at the Project) (the “Energy Savings Costs”) shall be amortized over a period of years equal to the least of (A) 10 years, (B) the useful life of such capital items, or (C) the quotient of (i) the Energy Savings Costs, divided by (ii) the annual amount of Operating Expenses reasonably expected by Landlord to be saved as a result of such capital improvements.

Within 90 days after the end of each calendar year (or such longer period as may be reasonably required), Landlord shall furnish to Tenant a statement (an “Annual Statement”) showing in reasonable detail: (a) the total and Tenant’s Share of actual Operating Expenses for the previous calendar year, and

(b) the total of Tenant’s payments in respect of Operating Expenses for such year. If Tenant’s Share of actual Operating Expenses for such year exceeds Tenant’s payments of Operating Expenses for such year, the excess shall be due and payable by Tenant as Rent within 30 days after delivery of such Annual Statement to Tenant. If Tenant’s payments of Operating Expenses for such year exceed Tenant’s Share of actual Operating Expenses for such year Landlord shall pay the excess to Tenant within 30 days after delivery of such Annual Statement, except that after the expiration, or earlier termination of the Term or if Tenant is delinquent in its obligation to pay Rent, Landlord shall pay the excess to Tenant after deducting all other amounts due Landlord.

Following the date that is 18 months after Landlord’s delivery of an Annual Statement to Tenant, Tenant shall not be responsible for the payment of items of Operating Expenses not reflected in such Annual Statement, except for Taxes for which Tenant is responsible under this Lease and/or any costs for which Landlord is billed after the expiration of such 18 month period.

The Annual Statement shall be final and binding upon Tenant unless Tenant, within 120 days after Tenant’s receipt thereof, shall contest any item therein by giving written notice to Landlord, specifying each item contested and the reason therefor. If, during such 120 day period, Tenant reasonably and in good faith questions or contests the accuracy of Landlord’s statement of Tenant’s Share of Operating Expenses, Landlord will provide Tenant with access to Landlord’s books and records relating to the operation of the Project and such information as Landlord reasonably determines to be responsive to Tenant’s questions (the “Expense Information”). If after Tenant’s review of such Expense Information, Landlord and Tenant cannot agree upon the amount of Tenant’s Share of Operating Expenses, then Tenant shall have the right to have a regionally or nationally recognized independent public accounting firm or an auditing firm selected by Tenant and approved by Landlord (which approval shall not be unreasonably withheld or delayed), working pursuant to a fee arrangement other than a contingent fee (at Tenant’s sole cost and expense), audit and/or review the Expense Information for the year in question (the “Independent Review”). The results of any such Independent Review shall be binding on Landlord and Tenant. If the Independent Review shows that the payments actually made by Tenant with respect to Operating Expenses for the calendar year in question exceeded Tenant’s Share of Operating Expenses for such calendar year, Landlord shall at Landlord’s option either (i) credit the excess amount to the next succeeding installments

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of estimated Operating Expenses or (ii) pay the excess to Tenant within 30 days after delivery of such statement, except that after the expiration or earlier termination of this Lease or if Tenant is delinquent in its obligation to pay Rent, Landlord shall pay the excess to Tenant after deducting all other amounts due Landlord. If the Independent Review shows that Tenant’s payments with respect to Operating Expenses for such calendar year were less than Tenant’s Share of Operating Expenses for the calendar year, Tenant shall pay the deficiency to Landlord within 30 days after delivery of such statement. If the Independent Review shows that Tenant has overpaid with respect to Operating Expenses by more than 5% then Landlord shall reimburse Tenant for all costs incurred by Tenant for the Independent Review. Operating Expenses for the calendar years in which Tenant’s obligation to share therein begins and ends shall be prorated. Notwithstanding anything set forth herein to the contrary, if the Building is not at least 95% occupied on average during any year of the Term, Tenant’s Share of Operating Expenses for such year that vary with the level of occupancy of the Building shall be computed as though the Building had been 95% occupied on average during such year.

“Tenant’s Share” shall be the percentage set forth in the Basic Lease Provisions as “Tenant’s Share of Operating Expenses of Building,” as may be reasonably adjusted by Landlord for changes in the physical size of the Premises, Building, and/or Project occurring thereafter. Landlord may equitably increase Tenant’s Share for any Operating Expenses that relate to any item of expense or cost (1) equitably and reasonably allocated only to the Premises, the Building or Property, (2) equitably and reasonably allocated to only a portion of the Building, Property or Project that includes the Premises, or

(3) a greater proportion of which is equitably and reasonably allocated to the Premises, or a portion of the Building, Property or Project that includes the Premises, as reasonably determined by Landlord. Base Rent, Tenant’s Share of Operating Expenses and all other amounts payable by Tenant to Landlord hereunder are collectively referred to herein as “Rent.”

Tenant shall have the right, within 30 days after the TI Construction Drawings (as defined in the Work Letter) with respect to the entire Premises (including the Phase 2 Premises) have been finalized, to have the TI Architect verify the rentable square footage of the Premises (“RSF Verification”). Such RSF Verification shall be performed in accordance with the Measurement Standard, using the same methodologies and assumptions as applied by Stevenson Systems in connection with its determination of the rentable square footage of the Premises reflected on page 1 of this Lease. Upon the completion of the RSF Verification, Tenant shall deliver a copy of the results of the RSF Verification to Landlord. If the RSF Verification reflects a deviation from the rentable square footage of the Premises reflected in the definitions of “Premises” and “Rentable Area of Premises,” on page 1 of this Lease then, promptly following Tenant’s delivery of the results of the RSF Verification to Landlord, the definitions of “Premises” and “Rentable Area of Premises” (and, if applicable, as reasonably determined by Landlord, “Rentable Area of Building” and/or “Rentable Area of Project”) on page 1 of this Lease, shall be amended so as to (i) reflect the actual rentable square footage thereof in the definitions of “Premises” and “Rentable Area of Premises” (and, if applicable, as reasonably determined by Landlord, “Rentable Area of Building” and/or “Rentable Area of Project”), and (ii) appropriately adjust the amount set forth in the definition of “Tenant’s Share of Operating Expenses of Building,” which were calculated based on the rentable square footages of the Premises, Building and Project originally set forth on page 1 of this Lease.

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Landlord shall be responsible, (i) subject to the terms of the Work Letter, for the compliance of the Phase 1 Premises with Legal Requirements (including the ADA) as of the Commencement Date, (ii) subject to the terms of the Work Letter, for the compliance of the Phase 2 Premises with Legal Requirements (including the ADA) as of the Phase 2 Commencement Date, and (iii) at Landlord’s cost, for the compliance of the Common Areas of the Project with Legal Requirements (including the ADA) as of the Commencement Date. Following the Commencement Date, Landlord shall, as an Operating Expense (to the extent such Legal Requirement is generally applicable to similar buildings in the area in which the Project is located) or at Tenant’s expense (to the extent such Legal Requirement is triggered by reason of Tenant’s, as compared to other tenants of the Project, specific use of the Premises or Tenant’s Alterations) make any alterations or modifications to the Common Areas or the exterior of the Building that are required by Legal Requirements. Except as otherwise expressly provided in the 2 immediately preceding sentences, Tenant, at its sole expense, shall make any alterations or modifications to the interior of the Premises that are required by Legal Requirements (including, without limitation, compliance of the Premises with the ADA) related to Tenant’s particular use or occupancy of the Premises. Notwithstanding any other provision herein to the contrary, Tenant shall be responsible for any and all demands, claims, liabilities, losses, costs, expenses, actions, causes of action, damages or judgments, and all reasonable expenses incurred in investigating or resisting the same (including, without limitation, reasonable attorneys’ fees, charges and disbursements and costs of suit) (collectively, “Claims”) arising out of or in connection with Legal Requirements related to Tenant’s particular use or occupancy of the Premises or Tenant’s Alterations, and Tenant shall indemnify, defend, hold and save Landlord harmless from and against any and all Claims arising out of or in connection with any failure of the Premises to comply with any Legal Requirements related to Tenant’s particular use or occupancy of the Premises or Tenant’s Alterations.

Tenant acknowledges that Landlord may, but shall not be obligated to, seek to obtain Leadership in Energy and Environmental Design (LEED), WELL Building Standard, or other similar “green” certification with respect to the Project and/or the Premises, and Tenant agrees to reasonably cooperate with Landlord, at no material cost to Tenant, and to provide such information and/or documentation as Landlord may reasonably request, in connection therewith.

8.67.010 et seq. of the Municipal Code of the City of Cambridge (as the same may be amended, the “Cambridge Building Energy Use Disclosure Ordinance”), and other such energy or sustainability

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requirements as may be adopted from time to time by the City of Cambridge or any other governmental authority with jurisdiction over the Building, which information shall include without limitation usage at or by the Premises of electricity, natural gas, steam, hot or chilled water or other energy. Landlord shall report to the applicable governmental authority such energy usage for the Building and other Building information as required by the Cambridge Building Energy Use Disclosure Ordinance.

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(ii) the number of parking spaces allocated, as determined by Landlord in its sole and absolute discretion, for “guest” parking, shall be designated as a “Surplus Parking Pool” and parking spaces from the Surplus Parking Pool shall be proportionately allocated to tenants of the Building, subject to each tenant’s payment of Monthly Parking Charges for all such additional parking spaces from the Surplus Parking Pool. Notwithstanding the foregoing, Landlord shall have the right at any time upon written notice to the tenants of the Building, including Tenant, to reduce the number of parking spaces included as part of the Surplus Parking Pool or to eliminate the Surplus Parking Pool, in connection with any development or redevelopment by Landlord or any affiliate of Landlord at the Project, including any expansion thereof. Landlord shall not be responsible for enforcing Tenant’s parking rights against any third parties, including other tenants of the Project. The “Monthly Parking Charge” shall mean the market rate monthly charge therefor designated by Landlord, adjusted reasonably and no more frequently than once in any 12-month period, based upon the rates charged by comparable parking facilities in the vicinity of the Project, which Monthly Parking Charge is anticipated as of the Commencement Date to be equal to $450.00 per space per month, plus applicable taxes.

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Notwithstanding anything to the contrary set forth herein, if (i) a stoppage of an Essential Service (as defined below) to the Premises shall occur and such stoppage is due solely to the gross negligence or willful misconduct of Landlord and not due in any part to any act or omission on the part of Tenant or any Tenant Party or any matter beyond Landlord’s reasonable control (any such stoppage of an Essential Service being hereinafter referred to as a “Service Interruption”), and (ii) such Service Interruption continues for more than 5 consecutive business days after Landlord shall have received written notice thereof from Tenant, and (iii) as a result of such Service Interruption, the conduct of Tenant’s normal operations in the Premises are materially and adversely affected, then, there shall be an abatement of one day’s Base Rent for each day during which such Service Interruption continues after such 5 business day period; provided, however, that if any part of the Premises is reasonably useable for Tenant’s normal business operations or if Tenant conducts all or any part of its operations in any portion of the Premises notwithstanding such Service Interruption, then the amount of each daily abatement of Base Rent shall only be proportionate to the nature and extent of the interruption of Tenant’s normal operations or ability to use the Premises. The rights granted to Tenant under this paragraph shall be Tenant’s sole and exclusive remedy resulting from a failure of Landlord to provide services, and Landlord shall not otherwise be liable for any loss or damage suffered or sustained by Tenant resulting from any failure or cessation of services. For purposes hereof, the term “Essential Services” shall mean the following services: HVAC service, water, sewer and electricity, but in each case only to the extent that Landlord has an obligation to provide same to Tenant under this Lease.

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Tenant agrees to provide Landlord with access to Tenant’s water and/or energy usage data on a monthly basis, either by providing Tenant’s applicable utility login credentials to Landlord’s Measurabl online portal, or by another delivery method reasonably agreed to by Landlord and Tenant. The costs and expenses incurred by Landlord in connection with receiving and analyzing such water and/or energy usage data (including, without limitation, as may be required pursuant to applicable Legal Requirements) shall be included as part of Operating Expenses.

the Massachusetts Water Resources Authority for discharge through the Acid Neutralization System (the “Discharge Permit”), provided that Tenant reasonably cooperates with Landlord and provides all information and documents reasonably necessary in connection with the Discharge Permit; and (ii) contract with a third party to maintain the Acid Neutralization System as operating as per the manufacturer’s standard maintenance guidelines. Notwithstanding anything herein to the contrary, if the Acid Neutralization System must be replaced and the cost thereof is not included in such third party maintenance contract, then, Landlord shall replace the Acid Neutralization System, it being acknowledged, however, that Tenant shall be responsible for its share of all costs incurred in connection therewith as an Operating Expense, as provided in Section 5 above (subject to amortization set forth therein relating to capital improvements).

Tenant shall be solely responsible for the use of the Acid Neutralization System by Tenant and all Tenant Parties or any party other than Landlord or Landlord’s contractors, and Tenant shall be jointly and severally responsible for the use of the Acid Neutralization System with the other user tenants. Tenant shall use, and cause other parties under its control or for which it is responsible to use, the Acid Neutralization System in accordance with this Lease and in accordance with all applicable Legal Requirements, the Discharge Permit and any permits and approvals from Governmental Authorities for or applicable to Tenant’s use of the Acid Neutralization System. Tenant shall not take any action or make any omission that would result in a violation of the Discharge Permit or any other permit or Legal Requirements applicable to the Acid Neutralization System. Tenant’s compliance with applicable permits and Legal Requirements shall include but not be limited to posting signs at all sinks located in the Premises containing applicable notices regarding the use of sink drains for the disposal of chemicals and other Hazardous Materials. Tenant shall maintain a chemical management plan prohibiting the improper discharge or disposal of chemicals. Tenant shall train all laboratory personnel in the Premises on the proper disposal of chemicals and other Hazardous Materials. Landlord reserves the right, at any time and from time to time, to require reasonable limitations and restrictions on discharges by Tenant to the Acid Neutralization System as Landlord may reasonably determine to be necessary for the operation of the Acid Neutralization System. Landlord and its contractors and consultants shall be permitted to perform periodic sampling of all substances regulated under permits applicable to the Acid Neutralization System, including without limitation the discharge permit issued by the Massachusetts Water Resources Authority (“MWRA”), or as otherwise deemed appropriate by Landlord in

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its sole discretion. Landlord and its contractors and consultants shall be permitted to perform periodic inspections of the Acid Neutralization System and the discharge points and connections thereto located in the Premises. If requested by Landlord based on conditions pertaining to the Acid Neutralization System, Tenant shall promptly provide updates to its Hazardous Materials List (as defined in Section 30(b) below) to Landlord. Tenant shall promptly notify Landlord of any changes in the flow volume or properties that could impact the operation of the Acid Neutralization System or compliance with applicable permits or Legal Requirements, including without limitation a discharge known or reasonably believed to be non-compliant, changes in Tenant’s operations in the Premises and addition of new equipment by Tenant such as cage washers, glass washers or autoclaves.

The scope of the Decommissioning and HazMat Closure Plan (as defined in Section 28 of this Lease) shall include all actions for the proper cleaning, decommissioning and cessation of Tenant’s use of the Acid Neutralization System, and all requirements under this Lease for the surrender of the Premises shall also apply to Tenant’s cessation of use of the Acid Neutralization System, in each case whether at Lease expiration, termination or prior thereto (but Tenant shall not be required to complete the decommissioning of the Acid Neutralization System if other tenants or occupants will continue to use the same after the expiration or earlier termination of this Lease, nor shall Tenant be responsible for or bear any costs of decommissioning arising from the use of the Acid Neutralization System by any party other than Tenant; it being agreed that if multiple tenants use the Acid Neutralization System, then Landlord shall be responsible for completing the decommissioning thereof, and Tenant shall pay to Landlord within thirty (30) days after invoice therefor Tenant’s share of the reasonable, actual costs of decommissioning based on the ratio of the rentable square footage of the Premises to the rentable square footage of the Premises and the premises of all other user tenants). The obligations of Tenant under this Lease with respect to the Acid Neutralization System shall be joint and several with such other tenants as aforesaid,

except in the event that Tenant can prove to Landlord’s reasonable satisfaction that neither Tenant nor any Tenant Party caused, contributed to or exacerbated the matter for which Tenant would otherwise be jointly and severally responsible but for this exception. Without in any way limiting the Acid Neutralization Obligations, Landlord shall have no obligation to provide Tenant with operational emergency or back-up acid neutralization facilities or to supervise, oversee or confirm that the third party maintaining the Acid Neutralization System is maintaining such system as per the manufacturer’s standard guidelines or otherwise. During any period of replacement, repair or maintenance of the Acid Neutralization System when such system is not operational, including any delays thereto due to the inability to obtain parts or replacement equipment, Landlord shall have no obligation to provide Tenant with an alternative back-up system or facilities. Tenant expressly acknowledges and agrees that Landlord does not guaranty that such Acid Neutralization System will be operational at all times or that such system will be available to the Premises when needed. Without in any way limiting the Acid Neutralization Obligations, in no event shall Landlord be liable to Tenant or any other party for any damages of any type, whether actual or consequential, suffered by Tenant or any such other person in the event that the Acid Neutralization System or back-up system, if any, or any replacement thereof fails or does not operate in a manner that meets Tenant’s requirements. For the avoidance of doubt, the foregoing shall not abrogate Landlord’s responsibilities under this Lease.

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In connection with any Alteration the cost of which is expected to exceed $5,000,000.00, Landlord may require Tenant to furnish security or make other arrangements satisfactory to Landlord to assure payment for the completion of all Alterations work free and clear of liens. Tenant shall, with respect to all Alterations, shall provide (and cause each contractor or subcontractor to provide) certificates of insurance for workers’ compensation and other coverage in amounts and from an insurance company satisfactory to Landlord protecting Landlord against liability for personal injury or property damage during construction. Upon completion of any Alterations, Tenant shall deliver to Landlord: (i) sworn statements setting forth the names of all contractors and subcontractors who did the work and final lien waivers from all such contractors and subcontractors; and (ii) “as built” plans for any such Alteration. Notwithstanding anything to the contrary set forth herein, in no event shall Tenant be required to provide Landlord with a payment or performance bond with respect to the Tenant Improvements.

Other than (i) the items, if any, listed on Exhibit F attached hereto, (ii) any items agreed by Landlord in writing to be included on Exhibit F in the future, and (iii) any trade fixtures, machinery, equipment and other personal property not paid for out of the TI Fund (as defined in the Work Letter) which may be removed without material damage to the Premises, which damage shall be repaired (including capping or terminating utility hook-ups behind walls) by Tenant during the Term (collectively, “Tenant’s Property”), all property of any kind paid for with the TI Fund, all Alterations, real property fixtures, built-in machinery and equipment, built-in casework and cabinets and other similar additions and improvements built into the Premises so as to become an integral part of the Premises, such as fume hoods which penetrate the roof or plenum area, built-in cold rooms, built-in warm rooms, walk-in cold rooms, walk-in warm rooms, deionized water systems, glass washing equipment, autoclaves, chillers, built-in plumbing, electrical and mechanical equipment and systems, and any power generator and transfer switch (collectively, “Installations”) shall be and shall remain the property of Landlord during the Term and following the expiration or earlier termination of the Term, shall not be removed by Tenant at any time during the Term and shall remain upon and be surrendered with the Premises as a part thereof in accordance with Section 28 following the expiration or earlier termination of this Lease; provided, however, that Landlord shall, at the time its approval of such Installation is requested, or at the time it receives notice of a Notice-Only Alteration, notify Tenant if it has elected to cause Tenant to remove such Installation upon the expiration or earlier termination of this Lease, except that Landlord shall not require removal of customary office cabling unless otherwise required by Legal Requirements. If Landlord so elects, Tenant shall remove such Installation upon the expiration or

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earlier termination of this Lease and restore any damage caused by or occasioned as a result of such removal, including, when removing any of Tenant’s Property which was plumbed, wired or otherwise connected to any of the Building Systems, capping off all such connections behind the walls of the Premises and repairing any holes. During any such restoration period, Tenant shall pay Rent to Landlord as provided herein as if said space were otherwise occupied by Tenant.

Notwithstanding anything to the contrary contained herein, Tenant shall not be required to remove or restore any Tenant Improvements that are generic in nature and reusable by future tenants of the Premises for laboratory/life science purposes, as reasonably determined by Landlord at the time of Landlord’s approval of the Space Plans (as defined in the Work Letter) (and with respect to any Changes (as such term is defined in the Work Letter), at the time Landlord’s approval of any such Change), nor shall Tenant have the right to remove such Tenant Improvements at any time during the Term, other than in accordance with the terms of this Section 12. Notwithstanding anything to the contrary contained in this Lease or the Work Letter, Tenant may during the Term, replace components of furniture, fixtures and equipment paid for out of the Additional Tenant Improvement Allowance with “like-kind” furniture, fixtures and equipment reasonably acceptable to Landlord, which replacement components shall become Landlord’s property at remain in the Premises at the expiration or earlier termination of the Term.

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Subject to all of the other provisions of this Lease including, without limitation, the waivers provided in Sections 17 and 36, Landlord hereby indemnifies and agrees to defend, save and hold Tenant harmless from and against any and all third party Claims for injury or death to persons or damage to property occurring within the Common Areas of the Project caused by Landlord’s willful misconduct or negligence, except to the extent caused by the willful misconduct or negligence of Tenant or its employees or agents.

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Tenant, at its sole cost and expense, shall maintain during the Term: all risk property insurance with business interruption and extra expense coverage, covering the full replacement cost of all property and improvements installed or placed in the Premises by Tenant at Tenant’s expense; workers’ compensation insurance with no less than the minimum limits required by law; employer’s liability insurance with employers liability limits of $1,000,000 bodily injury by accident – each accident,

$1,000,000 bodily injury by disease – policy limit, and $1,000,000 bodily injury by disease – each employee; and commercial general liability insurance, with a minimum limit of not less than $5,000,000 per occurrence for bodily injury and property damage with respect to the Premises (the “Umbrella Policy”). The commercial general liability insurance maintained by Tenant shall name Alexandria Real Estate Equities, Inc., and Landlord, its officers, directors, employees, managers, agents, sub-agents, constituent entities and lease signatories (collectively, “Landlord Insured Parties”), as additional insureds; insure on an occurrence and not a claims-made basis; be issued by insurance companies which have a rating of not less than policyholder rating of A and financial category rating of at least Class X in “Best’s Insurance Guide”; not contain a hostile fire exclusion; contain a contractual liability endorsement; and provide primary coverage to Landlord Insured Parties (any policy issued to Landlord Insured Parties providing duplicate or similar coverage shall be deemed excess over Tenant’s policies, regardless of limits). Tenant shall (i) provide Landlord with 30 days advance written notice of cancellation of such commercial general liability policy, and (ii) request Tenant’s insurer to endeavor to provide advance written notice to Landlord of cancellation of such commercial general liability policy. Copies of such policies (if requested by Landlord), or certificates of insurance showing the limits of coverage required hereunder and showing Landlord as an additional insured, along with reasonable evidence of the payment of premiums for the applicable period, shall be delivered to Landlord by Tenant prior to (i) the earlier to occur of (x) the Commencement Date, or (y) the date that Tenant accesses the Premises under this Lease, and (ii) each renewal of said insurance. Tenant’s policy may be a “blanket policy” with an aggregate per location endorsement which specifically provides that the amount of insurance shall not be prejudiced by other losses covered by the policy. Tenant shall, prior to the expiration of such policies, furnish Landlord with renewal certificates.

In each instance where insurance is to name Landlord as an additional insured, Tenant shall upon written request of Landlord also designate and furnish certificates so evidencing Landlord as additional insured to: (i) any lender of Landlord holding a security interest in the Building, Property or Project or any portion thereof and any servicer in connection therewith, (ii) the landlord under any lease wherein Landlord is tenant of the real property on which the Building, Property or Project is located, if the interest of Landlord is or shall become that of a tenant under a ground or other underlying lease rather than that of a fee owner, and/or (iii) any management company retained by Landlord to manage the Project.

The property insurance obtained by Landlord and Tenant shall include a waiver of subrogation by the insurers and all rights based upon an assignment from its insured, against Landlord or Tenant, and their respective officers, directors, employees, managers, agents, invitees and contractors (“Related Parties”), in connection with any loss or damage thereby insured against. Notwithstanding anything in this Lease to the contrary, neither party nor its respective Related Parties shall be liable to the other for loss or damage caused by any risk insured against (or required to be insured against pursuant to this Lease) under property insurance required to be maintained hereunder, and each party waives any claims against the other party, and its respective Related Parties, for such loss or damage. The failure of a party to insure its property shall not void this waiver. Landlord and its respective Related Parties shall not be liable for, and Tenant hereby waives all claims against such parties for, business interruption and losses occasioned thereby sustained by Tenant or any person claiming through Tenant resulting from any accident or occurrence in or upon the Premises, Building, Property or Project from any cause whatsoever. If the foregoing waivers shall contravene any law with respect to exculpatory agreements, the liability of Landlord or Tenant shall be deemed not released but shall be secondary to the other’s insurer.

Landlord may require insurance policy limits to be raised to conform with requirements of Landlord’s lender and/or to bring coverage limits to levels then being generally required of new tenants within the Project; provided, however, that the increased amount of coverage is consistent with coverage amounts then being required by institutional owners of similar projects with tenants occupying similar size premises

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in the geographical area in which the Project is located.

Tenant, at its expense, following the date that Landlord makes the Premises available to Tenant for Tenant’s repairs or restoration, shall promptly perform, subject to delays arising from the collection of insurance proceeds, from Force Majeure (as defined in Section 34) events or to obtain Hazardous Materials Clearances, all repairs or restoration not required to be done by Landlord and shall promptly reenter the Premises and commence doing business in accordance with this Lease. Notwithstanding the foregoing, Landlord or Tenant may terminate this Lease if the Premises are damaged during the last year of the Term and Landlord reasonably estimates that it will take more than 2 months to repair such damage; provided, however, that such notice is delivered within 10 business days after the date that Landlord delivers notice to Tenant of the estimated Restoration Period. Notwithstanding anything to the contrary contained in this Lease, Landlord shall also have the right to terminate this Lease if insurance proceeds are not available for such restoration, provided that such unavailability of insurance proceeds is not the result of Landlord’s failure to maintain the insurance policies required to be maintained by Landlord under Section 17. Rent shall be abated from the date all required Hazardous Materials Clearances are obtained until the Premises are repaired and restored, in the proportion which the area of the Premises, if any, which is not usable by Tenant bears to the total area of the Premises, unless Landlord provides Tenant with other space during the period of repair that is suitable for the temporary conduct of Tenant’s business. In the event that no Hazardous Materials Clearances are required to be obtained with respect to such fire or other casualty, the rent abatement shall commence as of the date of discovery of the damage or destruction. Such abatement shall be the sole remedy of Tenant, and except as provided in this Section 18, Tenant waives any right to terminate the Lease by reason of damage or casualty loss.

The provisions of this Lease, including this Section 18, constitute an express agreement between Landlord and Tenant with respect to any and all damage to, or destruction of, all or any part of the Premises, or any other portion of the Building, Property or Project, and any statute or regulation which is now or may hereafter be in effect shall have no application to this Lease or any damage or destruction to all or any part

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of the Premises or any other portion of the Building, Property or Project, the parties hereto expressly agreeing that this Section 18 sets forth their entire understanding and agreement with respect to such matters.

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Any notice given under Section 20(h) hereof shall: (i) specify the alleged default, (ii) demand that Tenant cure such default, (iii) be in lieu of, and not in addition to, or shall be deemed to be, any notice required under any provision of applicable law, and (iv) not be deemed a forfeiture or a termination of this Lease unless Landlord elects otherwise in such notice; provided that if the nature of Tenant’s default pursuant to Section 20(h) is such that it cannot be cured by the payment of money and reasonably requires more than 30 days to cure, then Tenant shall not be deemed to be in default if Tenant commences such cure within said 30 day period and thereafter diligently prosecutes the same to completion; provided, however, that such cure shall be completed no later than 90 days from the date of Landlord’s notice.

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Actions, proceedings or suits for the recovery of damages, whether liquidated or other damages, under this Lease, or any installments thereof, may be brought by Landlord from time to time at its election, and nothing contained herein shall be deemed to require Landlord to postpone suit until the date when the Term of this Lease would have expired if it had not been terminated hereunder.

Landlord’s recovery under its Lump Sum Election shall be in addition to Tenant’s obligations to pay Base Rent and Additional Rent due and costs incurred prior to the date of Landlord’s Lump Sum Election, and in lieu of any Base Rent and Additional Rent which would otherwise have been due under this Section from and after the date of Landlord’s Lump Sum Election. The yield to maturity on United States Treasury Notes having a maturity date that is nearest the date that would have been the last day of the Term of this Lease, as reported in the Wall Street Journal or a comparable publication if it ceases to publish such yields, shall be used in calculating present values for purposes of Landlord’s Lump Sum Election. For the purposes of this Section, if Landlord makes the Lump Sum Election to recover liquidated damages in accordance with this Section, the total Additional Rent shall be computed based upon Landlord’s reasonable estimate of Tenant’s Share of Operating Expenses and other Additional Rent for each 12-month period in what would have been the remainder of the Term of this Lease and any part thereof at the end of such remainder of the Term, but in no event less than the amounts therefor payable for the twelve (12) calendar months (or if less than twelve (12) calendar months have elapsed since the date hereof, the partial year) immediately preceding the date of Landlord’s Lump Sum Election. Amounts of Tenant’s Share of Operating Expenses and any other Additional Rent for any partial year at the beginning of the Term or at the end of what would have been the remainder of the Term shall be prorated.

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(b) in any other case if such default continues after any applicable notice and cure period provided in Section 20. All reasonable costs and expenses incurred by Landlord in connection with any such performance by it for the account of Tenant and also all reasonable costs and expenses, including attorneys’ fees and disbursements incurred by Landlord in any action or proceeding (including any summary dispossess proceeding) brought by Landlord to enforce any obligation of Tenant under this Lease and/or right of Landlord in or to the Premises, shall be paid by Tenant to Landlord within 10 days after demand.

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Notwithstanding anything to the contrary contained in this Lease, Tenant may from time to time enter into license agreements (each, a “Shared Space Arrangement”) with affiliates of any Flagship Pioneering Entity (each, a “Space Occupant”) to use portions of the Premises as “Shared Space Area” for a period not to exceed 12 months in the aggregate, and such Share Space Arrangements shall not require Landlord’s consent under Section 22 of this Lease but Tenant shall be required to provide Landlord with a copy of each such Shared Space Arrangement and, prior to the effective date of each such Shared Space Arrangement and prior to any use of the Premises by such Space Occupant, Tenant

and each licensee shall be required to execute Landlord’s consent in the form attached hereto as Exhibit G. The rights set forth in this paragraph are personal to Omega Therapeutics, Inc., and any assignee of Omega Therapeutics, Inc. pursuant to a Permitted Assignment and, except with respect to such assignee pursuant to a Permitted Assignment, shall not inure to the benefit of any successor, assignee or subtenant of Omega Therapeutics, Inc. Tenant shall be fully responsible for the conduct of all Space Occupants and the agents, servants, employees, invitees and contractors of each Space Occupant within the Shared Space Area and the Project, and Tenant’s indemnification obligations set forth in the Lease shall apply with respect to the conduct of such parties within the Shared Space Area and Project.

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If Tenant shall fail to prepare or submit a Decommissioning and HazMat Closure Plan approved by Landlord, or if Tenant shall fail to complete the approved Decommissioning and HazMat Closure Plan, or if such Decommissioning and HazMat Closure Plan, whether or not approved by Landlord, shall fail to adequately address any residual effect of Tenant HazMat Operations in, on or about the Premises, Landlord shall have the right to take such actions as Landlord may deem reasonable or appropriate to assure that the Premises and the Project are surrendered free from any residual impact from Tenant HazMat Operations, the actual cost of which actions shall be reimbursed by Tenant as Additional Rent, without regard to the limitation set forth in the first paragraph of this Section 28.

Upon the expiration or earlier termination of the Term, Tenant shall immediately return to Landlord all keys and/or access cards to parking, the Building, restrooms or all or any portion of the Premises, Building or Project furnished to or otherwise procured by Tenant. If any such access card or key is lost, Tenant shall pay to Landlord, at Landlord’s election, either the cost of replacing such lost access card or key or the cost of reprogramming the access security system in which such access card was used or changing the lock or locks opened by such lost key. Any Tenant’s Property, Alterations and other property of Tenant not so removed by Tenant as permitted or required herein shall be deemed abandoned and may be stored, removed, and disposed of by Landlord at Tenant’s expense, and Tenant waives all claims against Landlord for any damages resulting from Landlord’s retention and/or disposition of such property. All obligations of Tenant hereunder not fully performed as of the termination of the Term, including the obligations of Tenant under Section 30 hereof, shall survive the expiration or earlier termination of the Term, including, without limitation, indemnity obligations, payment obligations with respect to Rent and obligations concerning the condition and repair of the Premises.

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All obligations of Landlord under this Lease will be binding upon Landlord only during the period of its ownership of the Premises and not thereafter. The term “Landlord” in this Lease shall mean only the owner for the time being of the Premises. Upon the transfer by such owner of its interest in the Premises, such owner shall thereupon be released and discharged from all obligations of Landlord thereafter accruing, but such obligations shall be binding during the Term upon each new owner for the duration of such owner’s ownership.

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Notwithstanding the foregoing, Tenant shall have the right to designate (on plans provided by Tenant to Landlord, which may be reasonably updated by Tenant from time to time upon notice to Landlord) certain areas of the Premises as limited access areas required to protect the health of persons or security of confidential and proprietary information (“Limited Access Areas”), which Limited Access Areas shall not be entered into by Landlord or Landlord’s representatives without a Tenant representative, except in the case of an emergency. Notwithstanding anything to the contrary contained in this Lease, Landlord shall not provide janitorial services any area designated by Tenant as a Limited Access Area and shall only enter such Limited Access Areas to perform maintenance and repairs (i) for which Landlord is responsible under this Lease, or (ii) in response to specific requests by Tenant, which requests remain subject to Landlord’s approval.

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NOTWITHSTANDING ANYTHING TO THE CONTRARY CONTAINED IN THIS LEASE, IN NO EVENT SHALL PERSONAL LIABILITY FOR TENANT’S OBLIGATIONS UNDER THIS LEASE BE ASSERTED AGAINST ANY OF TENANT’S OFFICERS, DIRECTORS, EMPLOYEES OR AGENTS.

Tenant acknowledges and agrees that measures and/or services implemented at the Project, if any, intended to encourage social distancing, promote and protect health and physical well-being and/or intended to limit the spread of Infectious Conditions, may not prevent the spread of such Infectious Conditions. Neither Landlord nor any Landlord Indemnified Parties shall have any liability and Tenant waives any claims against Landlord and the Landlord Indemnified Parties with respect to any loss, damage or injury in connection with (x) the implementation, or failure of Landlord or any Landlord Indemnified Parties to implement, any measures and/or services at the Project intended to encourage social distancing, promote and protect health and physical well-being and/or intended to limit the spread of Infectious Conditions, or (y) the failure of any measures and/or services implemented at the Project, if any, to limit the spread of any Infectious Conditions.

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Upon the commencement of the Extension Term, Base Rent shall be payable at the Market Rate (as defined below). Base Rent shall thereafter be adjusted on each annual anniversary of the commencement of the Extension Term by a percentage as determined by Landlord and agreed to by Tenant at the time the Market Rate is determined. As used herein, “Market Rate” shall mean the rate that comparable landlords of comparable buildings have accepted in current transactions from non-equity (i.e., not being offered equity in the buildings) and nonaffiliated tenants of similar financial strength for space of comparable size, quality (including all Tenant Improvements, Alterations and other improvements) and floor height in Class A laboratory/office buildings in the East Cambridge and Kendall Square market area of Cambridge, Massachusetts for a comparable term, with the determination of the Market Rate to take into account all relevant factors, including tenant inducements, views, parking costs, available amenities (including the Project Amenities), leasing commissions, allowances or concessions, if any. Notwithstanding the foregoing, the Market Rate shall in no event be less than the Base Rent payable as of the date immediately preceding the commencement of such Extension Term. In addition, Landlord may impose a market rent for the parking rights provided hereunder.

If, on or before the date which is 270 days prior to the expiration of the Base Term of this Lease or the expiration of the prior Extension Term, as applicable, Tenant has not agreed with Landlord’s determination of the Market Rate and the rent escalations during the applicable Extension Term after negotiating in good faith, Tenant shall be deemed to have elected arbitration as described in Section 39(b). Tenant acknowledges and agrees that, if Tenant has elected to exercise an Extension Right by delivering notice to Landlord as required in this Section 39(a), Tenant shall have no right thereafter to rescind or elect not to extend the term of this Lease for the Extension Term.

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(B) a licensed commercial real estate broker with not less than 15 years’ experience representing landlords and/or tenants in the leasing of life sciences and office space in the greater Boston, Massachusetts metropolitan area, (ii) devoting substantially all of their time to professional appraisal or brokerage work, as applicable, at the time of appointment and (iii) be in all respects impartial and disinterested.

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“Submarket Amenities”) within the following geographical area surrounding the Project: Spring Street to the north, Atheneum Street to south, Third Street to the west and Edwin H Land Boulevard to the east (the “Amenities Area”), for non-exclusive use by tenants of (i) tenants of the projects owned or operated by any Amenity Affiliates, (ii) tenants of the Project, (iii) other affiliates of Landlord, Amenity Affiliates and Alexandria Real Estate Equities, Inc. (“ARE”), and (iv) any other parties permitted by Amenity Affiliates (collectively, “Users”). Landlord, Amenity Affiliates, ARE, and all affiliates of Landlord, Amenity Affiliates and ARE may be referred to collectively herein as the “ARE Parties.” Any project within the Amenities Area at which Submarket Amenities are located may be referred to herein as a “Submarket Amenities Project.” Notwithstanding anything to the contrary contained herein, Tenant acknowledges and agrees that the Amenity Affiliates shall have the right, in their sole respective discretion, to construct any Submarket Amenities desired by such Amenity Affiliates but not make all or a portion of such Submarket Amenities available for use by some or all currently contemplated Users. Amenity Affiliates shall, respectively have the sole right to determine all matters related to the Submarket Amenities including, without limitation, relating to the type, design and construction thereof. Tenant acknowledges and agrees that Landlord has not made any representations or warranties regarding the development of any of the Submarket Amenities and that Tenant is not entering into this Lease relying on the construction and completion of the Submarket Amenities or with an expectation that the Submarket Amenities will ever be constructed and/or made available to Tenant.

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Notwithstanding the foregoing, for the period during the Base Term commencing on the Amenities Commencement Date through the expiration of the first full calendar year following the Amenities Commencement Date, Tenant shall not be responsible for Tenant’s Amenities Share of Submarket Amenities Costs in excess of $2.25 per rentable square foot of the Premises per year (the “Cap Amount”). The Cap Amount shall increase on each January 1st thereafter during the Base Term by multiplying the Cap Amount applicable during the immediately preceding calendar year by 3% and adding the resulting amount to the Cap Amount applicable during the immediately preceding calendar year. For the avoidance of doubt, the cost of Submarket Amenities Costs subject to the Cap Amount shall not include costs relating to Shuttle Service or the cost of ancillary services or items payable by Tenant in connection with its use of the Submarket Amenities which may include without limitation, conference center booking fees (to the extent one or more conference centers are included as part of the Submarket Amenities), costs for food and beverage/catering services, personal training, fitness classes and/or wellness clinics.

(iii) the payment of additional costs in connection with the after-hours usage of facilities, and (iv) access card entry requirements. The use of the Submarket Amenities by employees of Tenant shall be in accordance with the terms and conditions of the standard licenses, indemnification and waiver agreements required by applicable Amenities Affiliate or the operator of the applicable Submarket Amenities to be executed by all persons wishing to use such Submarket Amenities. Neither the Amenities Affiliates nor Landlord (nor, if applicable, any other affiliate of Landlord) shall have any liability or obligation for the breach of any rules or regulations by other Users with respect to the Submarket Amenities. Tenant shall not make any alterations, additions, or improvements of any kind to the Submarket Amenities or any Submarket Amenities Project.

Tenant acknowledges and agrees that the Amenities Affiliates shall have the right at any time and from time to time to reconfigure, relocate, modify or remove any of the Submarket Amenities, and/or to revise, expand or discontinue any of the services (if any) provided in connection with the Submarket Amenities.

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(i) upon Landlord’s written request on an annual basis, Tenant’s most recent audited annual financial statements, provided, however, that Tenant shall not be required to deliver to Landlord such annual financial statements for any particular year sooner than the date that is 90 days after the end of each of Tenant’s fiscal years during the Term, (ii) upon Landlord’s written request on a quarterly basis, Tenant’s most recent unaudited quarterly financial statements; provided, however, that Tenant shall not be required to deliver to Landlord such quarterly financial statements for any particular quarter sooner that the date that is 45 days after the end of each of Tenant’s fiscal quarters during the Term, (iii) upon Landlord’s written request from time to time, updated business plans, including cash flow projections and/or pro forma balance sheets and income statements, all of which shall be treated by Landlord as confidential information belonging to Tenant, (iv) upon Landlord’s written request from time to time, corporate brochures and/or profiles prepared by Tenant for prospective investors, and (v) upon Landlord’s written request from time to time, any other financial information or summaries that Tenant typically provides to its lenders or shareholders. Notwithstanding anything to the contrary contained in this Lease, Landlord’s written request for financial information pursuant to this Section 42(c) may delivered to Tenant via email. So long as Tenant is a “public company” and its financial information is publicly available, then the foregoing delivery requirements of this Section 42(c) shall not apply.

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Lease.

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[ Signatures on next page ]

DocuSign Envelope ID: 95812A0E-597B-4C31-9F12-CB594CA06309

Net Multi-Tenant Laboratory

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IN WITNESS WHEREOF, Landlord and Tenant have executed this Lease as of the day and year first above written.

TENANT:

OMEGA THERAPEUTICS, INC.,

a Delaware corporation

X I hereby certify that the signature, name, and title above are my signature, name and title.

LANDLORD:

ARE-MA REGION NO. 94, LLC,

a Delaware limited liability company

By: ALEXANDRIA REAL ESTATE EQUITIES, L.P.,

a Delaware limited partnership,

managing member

By: ARE-QRS CORP.,

a Maryland corporation

general partner

DocuSign Envelope ID: 95812A0E-597B-4C31-9F12-CB594CA06309

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EXHIBIT A TO LEASE DESCRIPTION OF PREMISES

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EXHIBIT B TO LEASE DESCRIPTION OF PROJECT

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Work Letter – Tenant Build

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EXHIBIT C TO LEASE WORK LETTER

THIS WORK LETTER dated November 4 , 2021 (this “Work Letter”) is made and entered into by and between ARE-MA REGION NO. 94, LLC, a Delaware limited liability company (“Landlord”), and OMEGA THERAPEUTICS, INC., a Delaware corporation (“Tenant”), and is attached to and made a part of the Lease Agreement dated November 4 , 2021 (the “Lease”), by and between Landlord and Tenant. Any initially capitalized terms used but not defined herein shall have the meanings given them in the Lease.

DocuSign Envelope ID: 95812A0E-597B-4C31-9F12-CB594CA06309

Work Letter – Tenant Build

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Work Letter – Tenant Build

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Tenant shall be solely responsible for ensuring that the design and specifications for Landlord’s Work are consistent with Tenant’s requirements. Landlord shall be responsible for obtaining all permits, approvals and entitlements necessary for Landlord’s Work, but shall have no obligation to, and shall not, secure any permits, approvals or entitlements related to Tenant’s specific use of the Premises or Tenant’s business operations therein.

(iii) will materially delay the construction of Landlord’s Work, Landlord and Tenant shall reasonably and in good faith seek means by which to mitigate or eliminate any such adverse terms and conditions.

DocuSign Envelope ID: 95812A0E-597B-4C31-9F12-CB594CA06309

Work Letter – Tenant Build

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Tenant shall be entitled to receive the benefit of all construction warranties and manufacturer’s equipment warranties relating to equipment installed in the Premises. If requested by Tenant, Landlord shall attempt to obtain extended warranties from manufacturers and suppliers of such equipment, but the cost of any such extended warranties shall be borne solely out of the TI Fund. Landlord shall promptly undertake and complete, or cause to be completed, all punch list items.

DocuSign Envelope ID: 95812A0E-597B-4C31-9F12-CB594CA06309

Work Letter – Tenant Build

One Charles Park – Suite 501/Omega Therapeutics - Page 5

If Delivery is delayed for any of the foregoing reasons, then Landlord shall cause the TI Architect to certify the date on which the Tenant Improvements would have been Substantially Completed but for such Tenant Delay and such certified date shall be the date of Delivery.

(ii) the architectural and engineering fees and costs that will be incurred, to analyze such Change Request (which costs shall be paid from the TI Fund to the extent actually incurred, whether or not such change is implemented). Landlord shall thereafter submit to Tenant in writing, within 5 business days of receipt of the Change Request (or such longer period of time as is reasonably required depending on the extent of the Change Request), an analysis of the additional cost or savings involved, including, without limitation, architectural and engineering costs and the period of time, if any, that the Change will extend the date on which Landlord’s Work in the Phase 1 Premises or the Phase 2 Premises, as applicable, will be Substantially Complete. Any such delay in the completion of Landlord’s Work caused by a Change, including any suspension of Landlord’s Work while any such Change is being evaluated and/or designed, shall be Tenant Delay.

and estimate of Tenant Delay. Notwithstanding any approval or disapproval by Tenant of any estimate of the delay caused by such proposed Change to the Base Building Improvements, the architect’s determination of the amount of Tenant Delay in connection with such Change to the Base Building

DocuSign Envelope ID: 95812A0E-597B-4C31-9F12-CB594CA06309

Work Letter – Tenant Build

One Charles Park – Suite 501/Omega Therapeutics - Page 6

Improvements shall be final and binding on Landlord and Tenant.

Landlord and Tenant hereby acknowledge and agree that Tenant has agreed to use and apply not less than 50% of the Additional Tenant Improvement Allowance toward TI Costs. Following the disbursement of the full amount of the Tenant Improvement Allowance, Tenant shall notify Landlord if Tenant has elected to use any additional portion of the Additional Tenant Improvement Allowance Tenant. Such election shall be final and binding on Tenant, and may not thereafter be modified without Landlord’s consent, which may be granted or withheld in Landlord’s sole and absolute subjective discretion. The TI Allowance shall be disbursed in accordance with this Work Letter.

Tenant shall have no right to the use or benefit (including any reduction to or payment of Base Rent) of any portion of the TI Allowance not required for the construction of (i) the Tenant Improvements

described in the TI Construction Drawings approved pursuant to Section 2(d) or (ii) any Changes pursuant to Section 4.

DocuSign Envelope ID: 95812A0E-597B-4C31-9F12-CB594CA06309

Work Letter – Tenant Build

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In addition to the TI Allowance, Landlord shall pay the TI Architect up to $0.12 per rentable square foot of the Premises for the preparation of test fit drawings for the Premises.

DocuSign Envelope ID: 95812A0E-597B-4C31-9F12-CB594CA06309

Work Letter – Tenant Build

One Charles Park – Suite 501/Omega Therapeutics - Page 8

DocuSign Envelope ID: 95812A0E-597B-4C31-9F12-CB594CA06309

Work Letter – Tenant Build

One Charles Park – Suite 501/Omega Therapeutics - Page 1

Schedule 1 Landlord/Tenant Matrix

DocuSign Envelope ID: 95812A0E-597B-4C31-9F12-CB594CA06309

Work Letter – Tenant Build

One Charles Park – Suite 501/Omega Therapeutics - Page 2

DocuSign Envelope ID: 95812A0E-597B-4C31-9F12-CB594CA06309

Work Letter – Tenant Build

One Charles Park – Suite 501/Omega Therapeutics - Page 3

DocuSign Envelope ID: 95812A0E-597B-4C31-9F12-CB594CA06309

Work Letter – Tenant Build

One Charles Park – Suite 501/Omega Therapeutics - Page 4

DocuSign Envelope ID: 95812A0E-597B-4C31-9F12-CB594CA06309

Work Letter – Tenant Build

One Charles Park – Suite 501/Omega Therapeutics - Page 5

DocuSign Envelope ID: 95812A0E-597B-4C31-9F12-CB594CA06309

Work Letter – Tenant Build

One Charles Park – Suite 501/Omega Therapeutics - Page 6

DocuSign Envelope ID: 95812A0E-597B-4C31-9F12-CB594CA06309

Work Letter – Tenant Build

One Charles Park – Suite 501/Omega Therapeutics - Page 7

DocuSign Envelope ID: 95812A0E-597B-4C31-9F12-CB594CA06309

Work Letter – Tenant Build

One Charles Park – Suite 501/Omega Therapeutics - Page 8

DocuSign Envelope ID: 95812A0E-597B-4C31-9F12-CB594CA06309

Work Letter – Tenant Build

One Charles Park – Suite 501/Omega Therapeutics - Page 9

DocuSign Envelope ID: 95812A0E-597B-4C31-9F12-CB594CA06309

Work Letter – Tenant Build

One Charles Park – Suite 501/Omega Therapeutics - Page 10

DocuSign Envelope ID: 95812A0E-597B-4C31-9F12-CB594CA06309

Work Letter – Tenant Build

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For the avoidance of doubt, it is understood that all wattages, pressures, volumes and other capacities referenced or specified in this Schedule 1 are included only to specify capacities for which applicable systems are designed.

DocuSign Envelope ID: 95812A0E-597B-4C31-9F12-CB594CA06309

Work Letter – Tenant Build

One Charles Park – Suite 501/Omega Therapeutics - Page 12

Schedule 2 Core Schedule

DocuSign Envelope ID: 95812A0E-597B-4C31-9F12-CB594CA06309

One Charles Park – Suite 501/Omega Therapeutics - Page 1

EXHIBIT D TO LEASE ACKNOWLEDGMENT OF COMMENCEMENT DATE

This ACKNOWLEDGMENT OF COMMENCEMENT DATE is made this ______ day of_________

,____, between ARE-MA REGION NO. 94, LLC, a Delaware limited liability company (“Landlord”), and OMEGA THERAPEUTICS, INC., a Delaware corporation (“Tenant”), and is attached to and made a part of the Lease dated ______________________, _______(the “Lease”), by and between Landlord and Tenant. Any initially capitalized terms used but not defined herein shall have the meanings given them in the Lease.

Landlord and Tenant hereby acknowledge and agree, for all purposes of the Lease, that the Commencement Date is _____________, _______, the Phase 2 Commencement Date is _______________, ________, and the termination date of the Base Term of the Lease shall be midnight on ____________________, _________. In case of a conflict between the terms of the Lease and the terms of this Acknowledgment of Commencement Date, this Acknowledgment of Commencement Date shall control for all purposes.

IN WITNESS WHEREOF, Landlord and Tenant have executed this ACKNOWLEDGMENT OF COMMENCEMENT DATE to be effective on the date first above written.

TENANT:

OMEGA THERAPEUTICS, INC.,

a Delaware corporation

[ ] I hereby certify that the signature, name, and title above are my signature, name and title.

LANDLORD:

ARE-MA REGION NO. 94, LLC,

a Delaware limited liability company

By: ALEXANDRIA REAL ESTATE EQUITIES, L.P.,

a Delaware limited partnership,

managing member

By: ARE-QRS CORP.,

a Maryland corporation

general partner

DocuSign Envelope ID: 95812A0E-597B-4C31-9F12-CB594CA06309

Rules and Regulations

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EXHIBIT E TO LEASE

Rules and Regulations

DocuSign Envelope ID: 95812A0E-597B-4C31-9F12-CB594CA06309

Rules and Regulations

One Charles Park – Suite 501/Omega Therapeutics - Page 2

DocuSign Envelope ID: 95812A0E-597B-4C31-9F12-CB594CA06309

Rules and Regulations

One Charles Park – Suite 501/Omega Therapeutics - Page 3

DocuSign Envelope ID: 95812A0E-597B-4C31-9F12-CB594CA06309

One Charles Park – Suite 501/Omega Therapeutics - Page 1

EXHIBIT F TO LEASE TENANT’S PERSONAL PROPERTY

None.

DocuSign Envelope ID: 95812A0E-597B-4C31-9F12-CB594CA06309

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EXHIBIT G TO LEASE

FORM OF SHARED SPACE CONSENT

This Consent (this “Consent”) is made as of ____________, 202__, by and among ARE-MA REGION NO. 94, LLC, a Delaware limited liability company, having an address of 26 North Euclid Avenue, Pasadena, California 91101 (“Landlord”), on the one hand, and OMEGA THERAPEUTICS, INC., a Delaware corporation (“Tenant”), having an address of _________________, and (“Space Occupant”), having an address of _______________, having an address of ____________, with reference to the following Recitals.

R E C I T A L S

, 2021 (as the same may have been amended and may be in the future be amended, the “Lease”) wherein Tenant leases certain premises consisting of approximately 89,246 rentable square feet (the “Premises”) in a building known as One Charles Park, Cambridge, Massachusetts.

NOW, THEREFORE, in consideration of the foregoing and the agreements contained herein, and for other good and valuable consideration, the receipt and sufficiency of which are hereby acknowledged, Landlord hereby consents to the license of the Licensed Premises to Space Occupant, such consent being subject to and upon the following terms and conditions to which Tenant and Space Occupant hereby agree:

DocuSign Envelope ID: 95812A0E-597B-4C31-9F12-CB594CA06309

One Charles Park – Suite 501/Omega Therapeutics - Page 3

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DocuSign Envelope ID: 95812A0E-597B-4C31-9F12-CB594CA06309

One Charles Park – Suite 501/Omega Therapeutics - Page 4

IN WITNESS WHEREOF, Landlord, Tenant and Space Occupant have caused their duly authorized representatives to execute this Consent as of the date first above written.

LANDLORD:

ARE-MA REGION NO. 94, LLC,

a Delaware limited liability company

By: ALEXANDRIA REAL ESTATE EQUITIES, L.P.,

a Delaware limited partnership,

managing member

By: ARE-QRS CORP.,

a Maryland corporation

general partner

TENANT:

OMEGA THERAPEUTICS, INC.,

a Delaware corporation

[ ] I hereby certify that the signature, name, and title above are my signature, name and title.

SPACE OCCUPANT:

__________________________, a ___________________

[ ] I hereby certify that the signature, name, and title above are my signature, name and title.