Hurley Street, Cambridge, MA/Editas Medicine, Inc. LEASE AGREEMENT THIS LEASE AGREEMENT is made as of this 12th day of February, 2016 between ARE-MA REGION NO. 55 EXCHANGE HOLDING LLC, a Massachusetts limited liability c

11 Hurley Street, Cambridge, MA/Editas Medicine, Inc.

THIS LEASE AGREEMENT is made as of this 12th day of February, 2016 between ARE-MA REGION NO. 55 EXCHANGE HOLDING LLC, a Massachusetts limited liability company ( Landlord ), and EDITAS MEDICINE, INC., a Delaware corporation ( Tenant ).

BASIC LEASE PROVISIONS

CONFIDENTIAL DO NOT COPY OR DISTRIBUTE

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

1. Lease of Premises. Upon and subject to all of the terms and conditions hereof, Landlord hereby leases the Premises to Tenant and Tenant hereby leases the Premises from Landlord. The portions of the Project which are for the non-exclusive use of tenants of the Project are collectively referred to herein as the Common Areas. Landlord reserves the right to modify Common Areas, provided that such modifications do not materially adversely affect Tenant s use of the Premises for the Permitted Use. Notwithstanding any provision hereof to the contrary, so long as 100% of the Building is demised to Tenant hereunder, the entirety of the Project shall be deemed to be the Premises , and there shall be no Common Areas for all purposes of this Lease.

2. Delivery; Acceptance of Premises; Commencement Date. Landlord shall use reasonable efforts to deliver the Premises to Tenant on or before the Target Commencement Date, with Landlord s Work, if any, Substantially Completed ( Delivery or Deliver ). If Landlord fails to timely Deliver the Premises, Landlord shall not be liable to Tenant for any loss or damage resulting therefrom, and this Lease shall not be void or voidable except as provided herein. If Landlord does not Deliver the Premises within 135 days of the Target Commencement Date for any reason other than Force Majeure Delays (but in no event more than 120 days in the aggregate of Force Majeure Delays) and Tenant Delays, this Lease may be terminated by Landlord or Tenant by written notice to the other (except that Landlord shall not have the right to terminate this Lease under this Section 2 other than in the event of Force Majeure or Tenant Delays), and if so terminated by either: (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 other sums paid by Tenant to Landlord pursuant to this Lease, 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. As used herein, the terms Landlord s Work, Tenants Work, Force Majeure Delays, Tenant Delays and Substantially Completed shall have the meanings set forth for such terms in the Work Letter. If neither Landlord nor Tenant elects to void this Lease within 5 business days of the lapse of such 180 day period, such right to void this Lease shall be waived and this Lease shall remain in full force and effect.

The Commencement Date shall be the earliest of: (i) the date Landlord Delivers the Premises to Tenant; (ii) the date Landlord could have Delivered the Premises but for Tenant Delays; and (iii) the date

Tenant conducts any business in the Premises or any part thereof. Upon request of Landlord, Tenant shall execute and deliver a written acknowledgment of the Commencement Date, the Rent 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 in the Basic Lease Provisions and any Extension Terms which Tenant may elect pursuant to Section 41 hereof. Notwithstanding that the Commencement Date may occur by reason of clause (ii) above, (a) Tenant shall not be required to perform any obligations under this Lease that cannot be performed without having possession of the Premises; and (b) Landlord shall complete Landlord s Work in accordance with the Work Letter.

Except as set forth in the Work Letter: (i) Tenant shall accept the Premises in their condition as of the Commencement Date, subject to all applicable Legal Requirements (as defined in Section 7 hereof); (ii) Landlord shall have no obligation for any defects in the Premises; and (iii) Tenant s taking possession of the Premises shall be conclusive evidence that Tenant accepts the Premises and that the Premises were in good condition at the time possession was taken. Any occupancy of the Premises by Tenant before the Commencement Date for the conduct of its business (which shall not include the performance of any Tenant Work) shall be subject to all of the terms and conditions of this Lease, including the obligation to pay Rent.

Landlord hereby represents to Tenant that the Premises may be used for the Permitted Uses in accordance with the terms of the provisions of the Cambridge Zoning Ordinance. Tenant agrees and acknowledges that, except as expressly provided in this Lease, 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. 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.

(a) Project Accounting. Landlord shall provide to Tenant (a) on a quarterly basis within 15 days of the end of each quarter, an updated report as to certain costs of the Landlord s Base Building Work and the Tenant Improvements (each as defined in the Work Letter) for the categories of expense identified in the attached Exhibit D-1 (collectively, Reported Project Costs ), in the format attached hereto as Exhibit D-1, and (b) after final confirmation of the completion of the Landlord s Base Building Work and the Tenant Improvements, a final report with respect to the Reported Project Costs in the format attached hereto as Exhibit D-1 (such documents, and any others Landlord may consent to provide including invoices, supporting schedules, and any other document provided or subject to physical inspection, collectively, the Disclosed Documents ). Tenant intends to use the Disclosed Documents for the preparation and audit of certain financial statements that may be filed by Tenant with the Securities and Exchange Commission ( SEC ) pursuant to applicable law (the Special Permitted Use ). Any Disclosed Documents so provided shall be subject to the following terms and conditions:

a. Any Disclosed Documents provided to Tenant shall be used by Tenant only for the Special Permitted Use and for no other use. Specifically, the Disclosed Documents shall be used only to prepare the Tenant financial statements and shall not themselves be disclosed to third parties, unless required solely for the purpose of the preparation or audit of such financial statements (the Preparing/Auditing Parties ).

b. Any Disclosed Documents provided to Tenant shall be considered Confidential Information and Tenant shall not copy, duplicate, deliver, disclose or transmit the Disclosed Documents or their content to any third party without Landlord s express prior written approval, except to the Preparing/Auditing Parties solely for the purpose of the preparation or audit of such financial statements, provided, however, that Landlord may require any of the Preparing/Auditing Parties (other than Tenant s independent registered public accounting firm) and any other third party inspecting or receiving any of the

Disclosed Documents to sign a non-disclosure agreement, in a form reasonably acceptable to Landlord and such other third party, prior to such inspection or receipt.

c. To the extent that any Disclosed Document is based upon information received from or prepared by a third party, such Disclosed Document may be subject to specific limitations regarding its use by third parties, including Tenant.

d. Disclosed Documents should be prepared on an accrual basis.

e. Neither Landlord nor any of its affiliates, employees, agents, successors or assigns (collectively, the Landlord Preparers ), nor any third party that prepared any Disclosed Document, has made or shall be deemed to have made any representations, statements or warranties of any kind as to (i) the accuracy or validity of the information contained in any Disclosed Document; or (ii) the condition or cost of construction of the Project in any respect as a consequence of providing the Disclosed Documents.

f. Tenant is responsible for making its own independent assessment and investigation of the condition and cost of construction of the Project in connection with the preparation and audit of Tenant s financial statements.

g. To the extent permitted under applicable law, Tenant agrees to indemnify, defend and hold the Landlord Preparers harmless from and against losses, costs, damages, claims or causes of action (including, without limitation, any actions initiated by Tenant shareholders) arising out of any use of the Disclosed Information by Tenant or the Preparing/Auditing Parties, or their respective agents, employees or representatives, including, without limitation, the Special Permitted Use and any use in violation of paragraphs (a) and (b) above.

h. Within 15 days of the end of each quarter, Landlord shall provide: (a) a complete copy of all approved General Contractor form AIA 702 s for such quarter (to the extent received), (b) updated report in a format consistent with Exhibit D-1, (c) a copy of all invoices received related to architecture and design costs incurred for such quarter (summary pages only), and (d) the dollar value by category type (e.g. insurance, taxes, etc.) of all other non-General Contractor and non-architecture-and-design building costs as reasonably determined by Landlord. To the extent that any non-General Contractor and non-architecture-and-design building cost category represents greater than 2% of the cumulative Reported Project Costs for the most recent quarter end, as reasonably determined by Landlord, Tenant shall have the right to inspect supporting summary invoices for such cost incurred for the most recent quarter related to such cost category, provided however that Landlord may limit access to this information to physical inspection only. Landlord shall be available to answer reasonable questions necessary for the Tenant to gain comfort over any cost balances through inquiry and analytics. Tenant may request additional information with respect to Reported Project Costs directed through Landlord s Chief Financial Officer, provided that the release of any such information shall be in the Landlord s sole discretion.

i. Tenant s employees, affiliates or agents shall be entitled to at least one meeting per quarter, within 15 days after Tenant s receipt of the Disclosed Documents, with Landlord Preparers to review and discuss the methods and key assumptions used to prepare the reported information in Disclosed Documents. Such meeting shall be either by telephone or in-person. Any requested in-person meeting shall be at a location determined by the Landlord Preparers.

j. Upon 10 days advance written notice within 15 days after Tenant s receipt of the Disclosed Documents during each quarter, Tenant s employees, affiliates or agents shall be entitled to physically inspect the 11 Hurley Building not more than once per quarter for the purposes of independently corroborating the reported costs on Exhibit D-1. Tenant shall use reasonable efforts to limit each such inspection to no more than one hour.

k. Tenant s employees, affiliates or agents may request, and Landlord shall reasonably cooperate to provide, additional information reasonably necessary for Tenant to complete a land appraisal as required for the preparation and audit of certain financial statements that will be filed by Tenant with the SEC, provided, however, that Landlord may limit access to this information to oral discussions or physical inspection only.

l. Tenant may engage a third party firm to assist with review of Reported Project Costs, provided that such third party inspecting or receiving any of the Disclosed Documents shall sign a non-disclosure agreement, in a form reasonably acceptable to Landlord and such other third party, prior to such inspection or receipt.

Tenant, for itself and its agents, affiliates, successors and assigns, hereby releases and forever discharges each of the Landlord Preparers from any and all rights, claims and demands at law or in equity, whether direct or indirect, known or unknown, foreseen or unforeseen, at the time of execution of this Lease, which Tenant has or may have in the future, arising out of the financial information provided by Landlord in the Disclosed Documents. With respect to the waiver and release set forth herein relating to unknown and unsuspected claims, Tenant hereby acknowledges that such waiver and release is being made after obtaining the advice of counsel and with full knowledge and understanding of the consequences and effects of such waiver. Nothing set forth herein shall in any way waive or limit any right or obligation of Landlord or of Tenant as otherwise set forth in the Lease which either party now has or may have in the future. Tenant s agents shall only have access to the Disclosed Documents and other provisions under this Section 2(a) to the extent such agents are real estate consultants, the Tenant s independent registered public accounting firm, or other agents reasonably related to the Special Permitted Use. Any Tenant agents for which Tenant desires to share Disclosed Documents or otherwise subject to this Section 2(a) shall be subject to reasonable approval rights by Landlord, except for Tenant s independent registered public accounting firm and PricewaterhouseCoopers in connection with the matters described herein. Such approval shall be subject to the required non-disclosure agreement for any Tenant agents as required above in Subsection b of this Section.

(a) Base Rent. Tenant shall pay to Landlord in advance, without demand, abatement (except as expressly provided in Section 11(c), Section 18, or Section 19 hereof), deduction or set-off, monthly installments of Base Rent on or before the Rent Commencement Date and on or before the first day of each calendar month during the Term thereafter, in lawful money of the United States of America, at the office of Landlord for payment of Rent set forth above, or to such other person or at such other place as Landlord may from time to time designate in writing. Payments of Base Rent for any fractional calendar month shall be prorated. The obligation of Tenant to pay Base Rent and other sums to Landlord and the obligations of Landlord under this Lease are independent obligations. Tenant shall have no right at any time to abate, reduce, or set-off any Rent (as defined in Section 5) due hereunder except for any abatement as may be expressly provided in this Lease.

(b) Additional Rent. In addition to Base Rent, Tenant agrees to pay to Landlord as additional rent ( Additional Rent ): (i) from and after the Rent Commencement Date, Tenant s Share of Operating Expenses (as defined in Section 5), and (ii) any and all other amounts Tenant assumes or agrees to pay under the provisions of this Lease, including, without limitation, any and all other sums that may become due by reason of any default of Tenant or failure to comply with the agreements, terms, covenants and conditions of this Lease to be performed by Tenant, after any applicable notice and cure period.

4. Base Rent Adjustments.

(a) Annual Adjustment. Base Rent shall be increased on each annual anniversary of the first day of the first full month during the Term of this Lease (each an Adjustment Date ) by multiplying the Base Rent payable immediately before such Adjustment Date by the Rent Adjustment Percentage and adding the resulting amount to the Base Rent payable immediately before such

Adjustment Date. Base Rent, as so adjusted, shall thereafter be due as provided herein. Base Rent adjustments for any fractional calendar month shall be prorated.

(b) Base Rent/Additional Tenant Improvement Allowance. Tenant shall pay with Base Rent from and after the Rent Commencement Date an amount ( TIA Rent ) equal to $0.186 per annum for each dollar or portion thereof of the Additional Tenant Improvement Allowance elected to be used by Tenant pursuant to Section 5(b)(ii) of the Work Letter. Amounts payable under this Section 4(b) shall not be subject to adjustment pursuant to Section 4(a) above.

5. Operating Expense Payments. Landlord shall deliver to Tenant a written estimate of Operating Expenses for each calendar year during the Term (the Annual Estimate ), which may be revised by Landlord from time to time during such calendar year. During each month of the Term, on the same date that Base Rent is due, Tenant shall pay Landlord an amount equal to 1/12th of Tenant s Share of the Annual Estimate. Payments for any fractional calendar month shall be prorated.

The term Operating Expenses means all costs and expenses incurred or accrued each calendar year by Landlord with respect to the operation, repair, maintenance and management of the Project (including, without duplication, Taxes (as defined in Section 9), and, to the extent of Eligible Capital Items (as defined below), capital repairs and replacements and improvements amortized the useful life of such capital items using generally accepted accounting principles consistently applied ( GAAP ), and the costs of Landlord s third party property manager (which management fee shall not exceed management fees customarily paid for comparable buildings in the Cambridge/Boston market), or, if there is no third party property manager, administration rent in the amount of 3% of Base Rent, excluding only:

(a) the original construction costs of renovation of the Project prior to the date of the Lease and costs of correcting defects in such renovation;

(b) except for Eligible Capital Items, the cost of any items that, under GAAP, are properly classified as capital expenditures;

(c) lease payments for rental equipment (other than equipment for which depreciation is properly charged as an expense) that would constitute a capital expenditure not expressly permitted above if the equipment were purchased;

(d) reserves for capital expenditures;

(e) interest, principal payments of Mortgage (as defined in Section 27) debts of Landlord, financing costs and amortization of funds borrowed by Landlord, whether secured or unsecured and all payments of base rent (but not taxes or operating expenses) under any ground lease or other underlying lease of all or any portion of the Project;

(f) depreciation of the Project (except for capital improvements, the cost of which are includable in Operating Expenses);

(g) advertising, legal and space planning expenses and leasing commissions and other costs and expenses incurred in procuring and leasing space to tenants for the Project, including any leasing office maintained in the Project, free rent and construction allowances for tenants;

(h) legal and other expenses incurred in the negotiation or enforcement of leases;

(i) completing, fixturing, improving, renovating, painting, redecorating or other work, which Landlord pays for or performs for other tenants within their premises, and costs of correcting defects in such work;

(j) costs of utilities outside normal business hours sold to tenants of the Project;

(k) costs to be reimbursed by other tenants of the Project or Taxes to be paid directly by Tenant or other tenants of the Project, whether or not actually paid;

(l) salaries, wages, benefits and other compensation paid to officers and employees of Landlord who are not assigned in whole or in part to the operation, management, maintenance or repair of the Project;

(m) general organizational, administrative and overhead costs relating to maintaining Landlord s existence, either as a corporation, partnership, or other entity, including general corporate, legal and accounting expenses;

(n) costs (including attorneys fees and costs of settlement, judgments and payments in lieu thereof) incurred in connection with disputes with tenants, other occupants, or prospective tenants, and costs and expenses, including legal fees, incurred in connection with negotiations or disputes with employees, consultants, management agents, leasing agents, purchasers or mortgagees of the Building;

(o) costs incurred by Landlord due to the violation by Landlord, its employees, agents or contractors or any tenant of the terms and conditions of any lease of space in the Project or any Legal Requirement (as defined in Section 7);

(p) penalties, fines or interest incurred as a result of Landlord s inability or failure to make payment of Taxes and/or to file any tax or informational returns when due, or from Landlord s failure to make any payment of Taxes required to be made by Landlord hereunder before delinquency;

(q) overhead and profit increment paid to Landlord or to subsidiaries or affiliates of Landlord for goods and/or services in or to the Project to the extent the same exceeds the costs of such goods and/or services rendered by unaffiliated third parties on a competitive basis;

(r) costs of Landlord s charitable or political contributions, or of fine art maintained at the Project;

(s) costs in connection with services (including electricity), items or other benefits of a type which are not standard for the Project and which are not available to Tenant without specific charges therefor, but which are provided to another tenant or occupant of the Project, whether or not such other tenant or occupant is specifically charged therefor by Landlord;

(t) costs incurred in the sale or refinancing of the Project;

(u) net income taxes of Landlord or the owner of any interest in the Project, franchise, capital stock, gift, estate or inheritance taxes or any federal, state or local documentary taxes imposed against the Project or any portion thereof or interest therein;

(v) 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; and

(w) costs and expenses of remediating Hazardous Substances on, under or about the Project or in the Premises, and related fines or penalties, in each case imposed by reason of Landlord s failure to comply with any Environmental Requirement.

Eligible Capital Items shall mean: (i) all capital repairs, replacements and improvements made or installed during the Term for the Project, which are either: (x) for the purpose of reducing the amount of Operating Expenses; or (y) required by applicable Legal Requirements first enacted after the Delivery Date of the Premises, and (ii) all other capital repairs, replacements and improvements for the

Building after the third anniversary of the Delivery Date reasonably required for the proper operation of the Project. Notwithstanding the foregoing, the cost of any capital repair, replacement or improvement of any Building structure, exterior walls or foundation shall not constitute an Eligible Capital Item during the Term. Eligible Capital Items shall be amortized over the useful life of the particular item in accordance with GAAP, together with interest at the 10-year U.S. Treasury rate plus 5.25%.

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.

The Annual Statement shall be final and binding upon Tenant unless Tenant, within 90 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 90 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 an independent public accounting firm selected by Tenant from among the 5 largest in the United States, working pursuant to a fee arrangement other than a contingent fee (at Tenant s sole cost and expense) and approved by Landlord (which approval shall not be unreasonably withheld or delayed), 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 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.

Tenant s Share shall be the percentage set forth in the Basic Lease Provisions as Tenant s Share, and shall be subject to further adjustment for changes in the physical size of the Premises or the Project occurring thereafter. Landlord shall cause the Design/Builder (as defined in the Work Letter) to perform a remeasurement of the rentable square footage of the Building within 30 days of the Commencement Date, or as soon as reasonably possible thereafter, and the rentable square footage of the Premises shall be rentable square footage of the Building as determined by such measurement, for all purposes of this Lease. Such measurement shall be performed in accordance with the 1996 Standard Method of Measuring Floor Area in Office Buildings as adopted by the Building Owners and Managers Association (ANSI/BOMA Z65.1-1996), modified for laboratory premises. Base Rent, TIA Rent, Tenant s Share of Operating Expenses and all other amounts payable by Tenant to Landlord hereunder are collectively referred to herein as Rent.

6. Security Deposit. Tenant shall deposit with Landlord, upon delivery of an executed copy of this Lease to Landlord, a security deposit (the Security Deposit ) for the performance of all of Tenant s obligations hereunder in the amount set forth in the Basic Lease Provisions, which Security Deposit shall be in the form of an unconditional and irrevocable letter of credit (the Letter of Credit ): (i) in form and substance satisfactory to Landlord, (ii) naming Landlord as beneficiary, (iii) expressly allowing Landlord to draw upon it at any time from time to time by delivering to the issuer notice that Landlord is entitled to draw thereunder, (iv) issued by an FDIC-insured financial institution satisfactory to Landlord, and (v) redeemable by presentation of a sight draft (which may be presented by delivery by overnight courier) at the financial institution s offices in the United States). If Tenant does not provide Landlord with a substitute Letter of Credit complying with all of the requirements hereof at least 10 days before the stated expiration date of any then current Letter of Credit, Landlord shall have the right to draw the full amount of the current Letter of Credit and hold the funds drawn in cash without obligation for interest thereon as the Security Deposit. The Security Deposit shall be held by Landlord as security for the performance of Tenant s obligations under this Lease. The Security Deposit is not an advance rental deposit or a measure of Landlord s damages in case of Tenant s default. Upon each occurrence of a Default (as defined in Section 20), Landlord may use all or any part of the Security Deposit to pay delinquent payments due under this Lease, and the cost of any damage, injury, expense or liability caused by such Default, without prejudice to any other remedy provided herein or provided by law. Upon any such use of all or any portion of the Security Deposit, Tenant shall pay Landlord within 5 days after demand the amount that will restore the Security Deposit to the amount set forth in the Basic Lease Provisions. Tenant hereby waives the provisions of any law, now or hereafter in force, which provide that Landlord may claim from a security deposit only those sums reasonably necessary to remedy defaults in the payment of Rent, to repair damage caused by Tenant or to clean the Premises, it being agreed that Landlord may, in addition, claim those sums reasonably necessary to compensate Landlord for any other loss or damage, foreseeable or unforeseeable, caused by the act or omission of Tenant or any officer, employee, agent or invitee of Tenant. Upon bankruptcy or other debtor-creditor proceedings against Tenant, the Security Deposit shall be deemed to be applied first to the payment of Rent and other charges due Landlord for periods prior to the filing of such proceedings. Upon any such use of all or any portion of the Security Deposit, Tenant shall, within 5 days after demand from Landlord, restore the Security Deposit to its original amount. If Tenant shall fully perform every provision of this Lease to be performed by Tenant, 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), shall be returned to Tenant (or, at Landlord s option, to the last assignee of Tenant s interest hereunder) within 45 days after the expiration or earlier termination of this Lease.

If Landlord transfers its interest in the Project or this Lease, Landlord shall either (a) transfer any Security Deposit then held by Landlord to a person or entity assuming Landlord s obligations under this Section 6, or (b) return to Tenant any Security Deposit then held by Landlord and remaining after the deductions permitted herein. Upon such transfer to such transferee or the return of the Security Deposit to Tenant, Landlord shall have no further obligation with respect to the Security Deposit, and Tenant s right to the return of the Security Deposit shall apply solely against Landlord s transferee. The Security Deposit is not an advance rental deposit or a measure of Landlord s damages in case of Tenant s default. Landlord s obligation respecting the Security Deposit is that of a debtor, not a trustee, and no interest shall accrue thereon.

If at any time during the Term of this Lease Tenant meets or exceeds the requirements listed below (collectively, the Reduction Requirements and each a Reduction Requirement ), then the Security Deposit shall be reduced to an amount equal to 4 months of the Base Rent effective during Lease Year 1 (the Reduced Security Deposit ). The Reduction Requirements are: (a) the absence of any Event of Default at the time of such reduction; and (b) Tenant shall have a net worth of at least $500,000,000, as determined in accordance with generally accepted accounting principles, and certified by a nationally recognized, independent public accounting firm or as demonstrated in Tenant s annual audited financial statements. If Tenant provides Landlord with written evidence reasonably satisfactory to Landlord Tenant has met the Reduction Requirements and provides Landlord with a replacement Letter of Credit in the amount of the Reduction Requirements and otherwise in accordance with the requirements of this Section 6, then Landlord shall return the original Letter of Credit then held by Landlord to Tenant within 30 days of Tenant s delivery of such replacement Letter of Credit. If Landlord returns to Tenant any portion of the

Security Deposit in accordance with this Section, then from and after the date such monies are returned to Tenant, the Security Deposit shall be deemed to be the Reduced Security Deposit for all purposes of this Lease.

The Reduced Security Deposit shall be increased in accordance with the terms of this Section 6 if (i) Tenant is in Default hereunder, or (ii) Tenant fails at any time after reduction of the Security Deposit to continue to meet the Reduction Requirements. Landlord shall have the right from time to time to request written evidence from Tenant that Tenant continues to meet the Reduction Requirements. If Tenant is in Default under the Lease or fails to continue to meet the Reduction Requirements, the Security Deposit shall be increased to its original amount. A replacement Letter of Credit in the amount of the increased Security Deposit shall be delivered to Landlord within 15 days of Landlord s written demand, in the case of Tenant s Default under the Lease, or within 15 days of Landlord s written demand, in the case of Tenant s failure to meet the Reduction Requirements. If Tenant is required to increase the Reduced Security Deposit in accordance with this Section, then from and after the date such monies are deposited with Landlord, the Security Deposit shall be deemed to be the amount then held by Landlord hereunder.

7. Use. The Premises shall be used solely for the Permitted Use set forth in the Basic Lease Provisions, and in compliance with all laws, orders, judgments, ordinances, regulations, codes, directives, permits, licenses, covenants and restrictions now or hereafter applicable to the Premises, and to the use and occupancy thereof, including, without limitation, the Americans With Disabilities Act, 42 U.S.C. 12101, et seq. (together with the regulations promulgated pursuant thereto, ADA ) (collectively, Legal Requirements and each, a Legal Requirement ). Tenant shall, upon 5 days written notice from Landlord, discontinue any use of the Premises which is declared by any Governmental Authority (as defined in Section 9) having jurisdiction to be a violation of a Legal Requirement. Tenant will not use or permit the Premises to be used for any purpose or in any manner that would void Tenant s or Landlord s insurance, increase the insurance risk, or cause the disallowance of any sprinkler or other credits. Tenant shall not permit any part of the Premises to be used as a place of public accommodation , as defined in the ADA or any similar legal requirement. Tenant shall reimburse Landlord promptly upon demand for any additional premium charged for any such insurance policy by reason of Tenant s failure to comply with the provisions of this Section or otherwise caused by Tenant s use and/or occupancy of the Premises. Tenant will use the Premises in a careful, safe and proper manner and will not commit or permit waste, overload the floor or structure of the Premises, subject the Premises to use that would damage the Premises or obstruct or interfere with the rights of Landlord or other tenants or occupants of the Project, including conducting or giving notice of any auction, liquidation, or going out of business sale on the Premises, or using or allowing the Premises to be used for any unlawful purpose. Tenant shall cause any equipment or machinery to be installed in the Premises so as to reasonably prevent sounds or vibrations from the Premises from extending into Common Areas, or other space in the Project. Tenant shall not place any machinery or equipment exceeding the structural capacity of the floor of the Premises in or upon the Premises or transport or move such items through the Common Areas of the Project or in the Project elevators without the prior written consent of Landlord. Except as may be provided under the Work Letter, Tenant shall not, without the prior written consent of Landlord (which consent shall not be unreasonably withheld, so long as Tenant bears all costs associated with such excess use), use the Premises in any manner which will require ventilation, air exchange, heating, gas, steam, electricity or water beyond the existing capacity of the Project as proportionately allocated to the Premises based upon Tenant s Share as usually furnished for the Permitted Use.

As of the Commencement Date, Landlord s Work shall comply with all Legal Requirements including ADA. From and after 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 expenses (to the extent such Legal Requirement is applicable solely by reason of Tenant s, as compared to other tenants of the Project, particular use of the Premises) make any alterations or modifications to the Common Areas or the exterior of the Building that are required by Legal Requirements, including the Americans With Disabilities Act, 42 U.S.C. 12101, et seq. (together with regulations promulgated pursuant thereto, ADA ). From and after the Commencement Date, 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.

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 Tenant s obligations to comply with the Legal Requirements, 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 Requirement, to the extent such failure is Tenant s responsibility hereunder.

8. Holding Over. If, with Landlord s express written consent, Tenant retains possession of the Premises after the termination of the Term, (i) unless otherwise agreed in such written consent, such possession shall be subject to immediate termination by Landlord at any time, (ii) all of the other terms and provisions of this Lease (including, without limitation, the adjustment of Base Rent pursuant to Section 4 hereof) shall remain in full force and effect (excluding any expansion or renewal option or other similar right or option) during such holdover period, (iii) Tenant shall continue to pay Base Rent in the amount payable upon the date of the expiration or earlier termination of this Lease or such other amount as Landlord may indicate, in Landlord s sole and absolute discretion, in such written consent, and (iv) all other payments shall continue under the terms of this Lease. If Tenant remains in possession of the Premises after the expiration or earlier termination of the Term without the express written consent of Landlord, (A) Tenant shall become a tenant at sufferance upon the terms of this Lease except that the monthly rental shall be equal to 150% of Rent in effect during the last 30 days of the Term, and (B) if such hold over continues for more than 30 days, monthly rental shall be equal to 200% of Rent in effect during the last 30 days of the Term and Tenant shall be responsible for all damages suffered by Landlord resulting from or occasioned by Tenant s holding over, including consequential damages. No holding over by Tenant, whether with or without consent of Landlord, shall operate to extend this Lease except as otherwise expressly provided, and this Section 8 shall not be construed as consent for Tenant to retain possession of the Premises. Acceptance by Landlord of Rent after the expiration of the Term or earlier termination of this Lease shall not result in a renewal or reinstatement of this Lease.

9. Taxes. Landlord shall pay, as part of Operating Expenses, all taxes, levies, fees, assessments and governmental charges of any kind, existing as of the Commencement Date or thereafter enacted (collectively referred to as Taxes ), imposed by any federal, state, regional, municipal, local or other governmental authority or agency, including, without limitation, quasi-public agencies (collectively, Governmental Authority ) during the Term, including, without limitation, all Taxes: (i) imposed on or measured by or based, in whole or in part, on rent payable to (or gross receipts received by) Landlord under this Lease and/or from the rental by Landlord of the Project or any portion thereof, or (ii) based on the square footage, assessed value or other measure or evaluation of any kind of the Premises or the Project, or (iii) assessed or imposed by or on the operation or maintenance of any portion of the Premises or the Project, including parking, or (iv) assessed or imposed by, or at the direction of, or resulting from Legal Requirements, or interpretations thereof, promulgated by, any Governmental Authority, or (v) imposed as a license or other fee, charge, tax or assessment on Landlord s business or occupation of leasing space in the Project. Landlord may contest by appropriate legal proceedings the amount, validity, or application of any Taxes or liens securing Taxes. If Tenant in good faith believes that the Project is over-assessed, Landlord shall, at Tenant s expense, file and prosecute an abatement application for such Taxes, or at Landlord s election permit Tenant to do so on behalf of Landlord, and any abatement received by Landlord with respect to Taxes paid by Tenant shall be promptly refunded to Tenant (after Landlord deducts its third-party costs and expenses incurred in connection with the same). Taxes shall not include any net income taxes, excess profit taxes, franchise taxes, transfer taxes, capital stock taxes, gift taxes or estate, inheritance or succession taxes imposed on Landlord except to the extent such taxes are in substitution for any Taxes payable hereunder, or interest and penalties assessed by reason of Landlord s failure to pay such Taxes when due (except to the extent that Landlord s failure to pay such Taxes is due to the failure of Tenant to pay timely Taxes payable by Tenant hereunder). If any such Tax is levied or assessed directly against Tenant, then Tenant shall be responsible for and shall pay the same at such times and in such manner as the taxing authority shall require. Operating Expenses hereunder shall also include the cost of tax monitoring services provided to Landlord with respect to the Project. Tenant shall pay, prior to delinquency, any and all Taxes levied or assessed against any personal property or trade fixtures placed

by Tenant in the Premises, whether levied or assessed against Landlord or Tenant. If any Taxes on Tenant s personal property or trade fixtures are levied against Landlord or Landlord s property, or if the assessed valuation of the Project is increased by a value attributable to improvements in or alterations to the Premises, whether owned by Landlord or Tenant and whether or not affixed to the real property so as to become a part thereof, higher than the base valuation on which Landlord from time-to-time allocates Taxes to all tenants in the Project, Landlord shall have the right, but not the obligation, to pay such Taxes. Landlord s determination of any excess assessed valuation shall be binding and conclusive, absent manifest error. The amount of any such payment by Landlord shall constitute Additional Rent due from Tenant to Landlord immediately upon demand.

10. Parking. Subject to all matters of record, Force Majeure, a Taking (as defined in Section 19 below) and the exercise by Landlord of its rights hereunder, Tenant shall have the right to park in all of the areas of the Project designated for parking, subject in each case to Landlord s rules and regulations. On the Rent Commencement Date and thereafter on the first day of each month of the Term, Tenant shall pay to Landlord, together with payments of Base Rent hereunder, the market parking rate for the parking spaces (currently $275 per parking space per month), adjusted at the beginning of each Lease Year based upon the rates charged by comparable parking facilities in the vicinity of the Project. Landlord shall not be responsible for enforcing Tenant s parking rights against any third parties.

11. Utilities and Services; Emergency Generator; Service Interruptions.

(a) Utilities and Services. Landlord shall provide, subject to the terms of this Section 11, water, electricity, heat, air conditioning, ventilation, light, power, elevator, telephone, sewer, and other utilities (including gas and fire sprinklers to the extent the Project is plumbed for such services), refuse and trash collection (collectively, Utilities ). Landlord shall be responsible, as part of Operating Expenses, for maintenance of the exterior of the Project, including snow plowing and shoveling and maintenance of landscaped areas, which shall be consistent with the comparable first-class buildings used for comparable purposes in Cambridge, Massachusetts. Tenant shall be responsible, at Tenant s expense, for all janitorial services for the interior of the Building consistent with the comparable first-class buildings used for comparable purposes in Cambridge, Massachusetts, provided that such services shall conform with the minimum janitorial specifications set forth in Exhibit I. Landlord shall pay, as Operating Expenses or subject to Tenant s reimbursement obligation, for all Utilities used on the Premises, all maintenance charges for Utilities, and any storm sewer charges or other similar charges for Utilities imposed by any Governmental Authority or Utility provider, and any taxes, penalties, surcharges or similar charges thereon. Landlord may cause, at Tenant s expense, any Utilities to be separately metered or charged directly to Tenant by the provider. Tenant shall pay directly to the Utility provider, prior to delinquency, any separately metered Utilities and services which may be furnished to Tenant or the Premises during the Term. Tenant shall pay, as part of Operating Expenses, its share of all charges for jointly metered Utilities based upon consumption, as reasonably determined by Landlord. No interruption or failure of Utilities, from any cause whatsoever, shall result in eviction or constructive eviction of Tenant, termination of this Lease or the abatement of Rent. Tenant agrees to limit use of water and sewer with respect to lavatories to normal restroom use.

(b) Emergency Generator. Landlord s sole obligation for either providing emergency generators or providing emergency back-up power to Tenant shall be: (i) to provide the emergency generator required in accordance with terms of the Work Letter, and (ii) to contract with a third party to maintain the emergency generators as per the manufacturer s standard maintenance guidelines. Landlord shall have no obligation to provide Tenant with operational emergency generators or back-up power or to supervise, oversee or confirm that the third party maintaining the emergency generators is maintaining the generators as per the manufacturer s standard guidelines or otherwise. During any period of replacement, repair or maintenance of the emergency generators when the emergency generators are 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 generator or generators or alternative sources of back-up power. Tenant expressly acknowledges and agrees that Landlord does not guaranty that such emergency generators will be operational at all times or that emergency power will be available to the Premises when needed. 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 any emergency generator or back-up power or any replacement thereof fails or does not provide sufficient power.

(c) Service Interruptions.

(A) Service Interruptions. If all or a material portion of the Premises is rendered untenantable such that Tenant cannot occupy such portion of the Premises as a proximate result of Landlord s negligence or willful misconduct, or as a proximate result of Landlord s failure to perform any covenant or provision of this Lease on its part to be performed (except to the extent that such failure is caused in whole or in part by the action or inaction of Tenant) or by reason of the performance of any work in or about the Premises by or on behalf of Landlord, such that the foregoing conditions materially and adversely interfere with the conduct of Tenant s operations in the Premises ( Material Services Failure ), then Tenant shall have the rights hereinafter set forth. During such period of Material Services Failure, Landlord will, if reasonably practical, cooperate with Tenant to arrange for the provision of any interrupted Utilities on an interim basis via temporary measures until final corrective measures can be accomplished and Tenant shall permit Landlord the necessary access to the Premises to remedy such Material Service Failure. In the event a Material Services Failure is not remedied by Landlord within 5 consecutive business days after receiving written notice thereof from Tenant (an MSF Notice ) and provided that Tenant has given Landlord all access to the Premises necessary for the remedy of such Material Service Failure, then Tenant shall have the right to an equitable abatement of Base Rent and Tenant s Pro Rata Share of Operating Expenses under this Lease in proportion to the extent of interference with Tenant s operations until the Material Services Failure is remedied

(B) Exclusive Remedies. This Section 11(c) sets forth Tenant s sole and exclusive remedies on account of an interruption of services or Landlord s default resulting in an interruption of services. This Section 11(c) shall not apply to casualty or a Taking, which are governed by the terms of Section 18 and Section 19, respectively, nor shall it apply to any failure of a utility or other third party service provider to provide any utility or service (unless caused by Landlord s negligence or willful misconduct).

(C) Nonapplicability to Tenant Standby Emergency Generators. Notwithstanding any provision hereof to the contrary, this Section 11(c) shall be inapplicable to any Tenant standby emergency generators servicing the Premises or the Buildings, which are solely governed by the provisions of Section 11(b) above.

12. Alterations and Tenant s Property. Any alterations, additions, or improvements made to the Premises by or on behalf of Tenant, including additional locks or bolts of any kind or nature upon any doors or windows in the Premises, but excluding installation, removal or realignment of furniture systems (other than removal of furniture systems owned or paid for by Landlord) not involving any modifications to the structure or to Building Systems (as defined in Section 13) ( Alterations ) shall be subject to Landlord s prior written consent, which may be given or withheld in Landlord s sole discretion if any such Alteration affects the structure or Building Systems, but which shall otherwise not be unreasonably withheld or delayed. Tenant may construct nonstructural Alterations in the Premises without Landlord s prior approval if the aggregate cost of all such work in any 12 month period does not exceed $50,000.00 (a Notice-Only Alteration ), provided Tenant notifies Landlord in writing of such intended Notice-Only Alteration, and such notice shall be accompanied by plans, specifications, work contracts and such other information concerning the nature and cost of the Notice-Only Alteration as may be reasonably requested by Landlord, which notice and accompanying materials shall be delivered to Landlord not less than 15 business days in advance of any proposed construction. If Landlord approves any Alterations, Landlord may impose such conditions on Tenant in connection with the commencement, performance and completion of such Alterations as Landlord may deem appropriate in Landlord s reasonable discretion. Any request for approval shall be in writing, delivered not less than 15 business days in advance of any proposed construction, and accompanied by plans, specifications, bid proposals, work contracts and such other information concerning the nature and

cost of the alterations as may be reasonably requested by Landlord, including the identities and mailing addresses of all persons performing work or supplying materials. Landlord s right to review plans and specifications and to monitor construction shall be solely for its own benefit, and Landlord shall have no duty to ensure that such plans and specifications or construction comply with applicable Legal Requirements. Tenant shall cause, at its sole cost and expense, all Alterations to comply with insurance requirements and with Legal Requirements and shall implement at its sole cost and expense any alteration or modification required by Legal Requirements as a result of any Alterations. Tenant shall not be required to pay to Landlord any cost, charge or fee of Landlord in connection with any proposed Alterations, but Tenant shall pay to Landlord, as Additional Rent, within 20 days after invoice therefor, Landlord s reasonable out-of-pocket expenses for plan review in connection with any such Alterations. Before Tenant begins any Alteration, Landlord may post on and about the Premises notices of non-responsibility pursuant to applicable law. Tenant shall reimburse Landlord for, and indemnify and hold Landlord harmless from, any expense incurred by Landlord by reason of faulty work done by Tenant or its contractors, delays caused by such work, or inadequate cleanup.

If the expected costs of such Alterations exceed $100,000.00, Tenant shall furnish security or make other arrangements satisfactory to Landlord to assure payment for the completion of all Alterations work free and clear of liens, and in all cases 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.

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, provided, however, that, subject to the provisions of Section 28 below, Landlord shall not require the removal of customary lab and general office improvements. If Landlord so elects, Tenant shall remove such Installation upon the expiration or 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 herein to the contrary, in no event shall Landlord elect to cause Tenant to remove Landlord s Work (except for any equipment not permanently attached to Building Systems which Landlord may require Tenant to remove).

13. Landlord s Repairs. Landlord, as an Operating Expense, shall maintain all of the structural, exterior, roof, parking and other Common Areas of the Project, including HVAC, plumbing, electrical, fire sprinklers, elevators and all other building systems serving the Premises and other portions of the Project ( Building Systems ), in good operating order and repair, reasonable wear and tear and

uninsured losses and damages caused by Tenant, or by any of Tenant s agents, servants, employees, invitees and contractors (collectively, Tenant Parties ) excluded (and otherwise in conformity with the standards that are customary for comparable first-class buildings used for comparable purposes in Cambridge, Massachusetts). Losses and damages caused by Tenant or any Tenant Party shall be repaired by Landlord, to the extent not covered by insurance, at Tenant s sole cost and expense. Landlord reserves the right to stop Building Systems services when necessary (i) by reason of accident or emergency, or (ii) for planned repairs, alterations or improvements, which are, in the judgment of Landlord, desirable or necessary to be made, until said repairs, alterations or improvements shall have been completed. Landlord shall have no responsibility or liability for failure to supply Building Systems services during any such period of interruption; provided, however, that Landlord shall, except in case of emergency, make a commercially reasonable effort to give Tenant 24 hours advance notice of any planned stoppage of Building Systems services for routine maintenance, repairs, alterations or improvements. Tenant shall promptly give Landlord written notice of any repair required by Landlord pursuant to this Section, after which Landlord shall have a reasonable opportunity to effect such repair. Landlord shall not be liable for any failure to make any repairs or to perform any maintenance unless such failure shall persist for an unreasonable time after Tenant s written notice of the need for such repairs or maintenance. Tenant waives its rights under any state or local law to terminate this Lease or to make such repairs at Landlord s expense and agrees that the parties respective rights with respect to such matters shall be solely as set forth herein. Repairs required as the result of fire, earthquake, flood, vandalism, war, or similar cause of damage or destruction shall be controlled by Section 18.

14. Tenant s Repairs. Subject to Section 13, Section 18, and Section 19 hereof, Tenant, at its expense, shall repair, replace and maintain in good condition (reasonable wear and tear and damage by fire or other casualty excepted, provided that Tenant shall maintain the Premises in conformity with the standards that are customary for comparable first-class buildings used for comparable purposes in Cambridge, Massachusetts) all portions of the Premises, including, without limitation, entries, doors, ceilings, interior windows, interior walls, and the interior side of demising walls. Such repair and replacement may include capital expenditures and repairs whose benefit may extend beyond the Term. Should Tenant fail to make any such repair or replacement or fail to maintain the Premises, Landlord shall give Tenant notice of such failure. If Tenant fails to commence cure of such failure within 10 days of Landlord s notice, and thereafter diligently prosecute such cure to completion, Landlord may perform such work and shall be reimbursed by Tenant within 10 days after demand therefor; provided, however, that if such failure by Tenant creates or could create an emergency, Landlord may immediately commence cure of such failure and shall thereafter be entitled to recover the costs of such cure from Tenant. Subject to Sections 17 and 18, Tenant shall bear the full uninsured cost of any repair or replacement to any part of the Project that results from damage caused by Tenant or any Tenant Party and any repair that benefits only the Premises.

15. Mechanic s Liens. Tenant shall discharge, by bond or otherwise, any mechanic s lien filed against the Premises or against the Project for work claimed to have been done for, or materials claimed to have been furnished to, Tenant within 10 days after written notice of the filing thereof, at Tenant s sole cost and shall otherwise keep the Premises and the Project free from any liens arising out of work performed, materials furnished or obligations incurred by Tenant. Should Tenant fail to discharge any lien described herein, Landlord shall have the right, but not the obligation, to pay such claim or post a bond or otherwise provide security to eliminate the lien as a claim against title to the Project and the cost thereof shall be immediately due from Tenant as Additional Rent. If Tenant shall lease or finance the acquisition of office equipment, furnishings, or other personal property of a removable nature utilized by Tenant in the operation of Tenant s business, Tenant warrants that any Uniform Commercial Code Financing Statement filed as a matter of public record by any lessor or creditor of Tenant will upon its face or by exhibit thereto indicate that such Financing Statement is applicable only to removable personal property of Tenant located within the Premises. In no event shall the address of the Project be furnished on the statement without qualifying language as to applicability of the lien only to removable personal property, located in an identified suite held by Tenant.

16. Indemnification. Tenant hereby indemnifies and agrees to defend, save and hold Landlord harmless from and against any and all Claims for injury or death to persons or damage to property

occurring within or about the Premises, arising directly or indirectly out use or occupancy of the Premises or a breach or default by Tenant in the performance of any of its obligations hereunder, except to the extent caused by the willful misconduct or negligence of Landlord. Landlord shall not be liable to Tenant for, and Tenant assumes all risk of damage to, personal property (including, without limitation, loss of records kept within the Premises). Tenant further hereby irrevocably waives any and all Claims for injury to Tenant s business or loss of income relating to any such damage or destruction of personal property (including, without limitation, any loss of records). Landlord shall not be liable for any damages arising from any act, omission or neglect of any tenant in the Project or of any other third party.

17. Insurance. Landlord shall maintain all risk property and, if applicable, sprinkler damage insurance covering the full replacement cost of the Project (including, without limitation, Landlord s Work (as defined in the Work Letter) and any approved Alterations), or such lesser coverage amount as Landlord may elect provided such coverage amount is not less than 90% of such full replacement cost]. Landlord shall further procure and maintain commercial general liability insurance with a single loss limit of not less than $2,000,000 for bodily injury and property damage with respect to the Project. Landlord may, but is not obligated to, maintain such other insurance and additional coverages as it may deem necessary, including, but not limited to, flood, environmental hazard and earthquake, loss or failure of building equipment, errors and omissions, rental loss during the period of repair or rebuilding, workers compensation insurance and fidelity bonds for employees employed to perform services and insurance for any improvements installed by Tenant or which are in addition to the standard improvements customarily furnished by Landlord without regard to whether or not such are made a part of the Project. All such insurance shall be included as part of the Operating Expenses. The Project may be included in a blanket policy (in which case the cost of such insurance allocable to the Project will be determined by Landlord based upon the insurer s cost calculations). Tenant shall also reimburse Landlord for any increased premiums or additional insurance which Landlord reasonably deems necessary as a result of Tenant s use of the Premises.

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 such limits as required by law; commercial general liability insurance, with a minimum limit of not less than $2,000,000 per occurrence for bodily injury and property damage with respect to the Premises and pollution legal liability insurance with a minimum limit of not less than $2,000,000 per occurrence. The commercial general liability insurance policy shall name Landlord, its officers, directors, employees, managers, agents, invitees and contractors (collectively, Landlord Parties ), as additional insureds. The commercial general liability and pollution legal liability insurance policies shall insure on an occurrence and not a claims-made basis; shall 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 ; shall not be cancelable for nonpayment of premium unless 30 days prior written notice shall have been given to Landlord from the insurer; contain a hostile fire endorsement and a contractual liability endorsement; and provide primary coverage to Landlord (any policy issued to Landlord providing duplicate or similar coverage shall be deemed excess over Tenant s policies).] 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 upon commencement of the Term and upon 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, at least 5 days 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 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 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. Neither party nor its respective Related Parties shall be liable to the other for loss or damage caused by any risk insured against 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 or the 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.