Document:

EX-10.15

 Exhibit 10.15 

EXECUTIVE EMPLOYMENT AGREEMENT 

This Employment Agreement (the “Agreement”), made and entered into this 14th day of October 2019 (the “Effective Date”),
by and between Checkmate Pharmaceuticals, Inc., a Delaware corporation (“Company”), and Kleem Chaudhary, Ph.D. (“Executive”). 

WHEREAS, Company wishes to employ Executive as its Chief Business Officer. 

WHEREAS, Executive represents that Executive possesses the necessary skills to perform the duties of this position and that Executive
has no obligation to any other person or entity which would prevent, limit or interfere with Executive’s ability to do so; and 

WHEREAS, Executive and Company desire to enter into a formal Employment Agreement to assure the harmonious performance of the affairs
of Company. 
 NOW, THEREFORE, in consideration of the mutual promises, terms, provisions, and conditions contained herein, the
parties agree as follows: 
 1.    Roles and Duties. Subject to the terms and conditions of this
Agreement, Company shall employ Executive as its Chief Business Officer reporting to the CEO. Executive’s duties will include responsibility for the Company’s Business Development, Corporate Strategy and Planning, Investor Relations and
Corporate Communications functions; and other duties as assigned by the CEO. Executive accepts such employment upon the terms and conditions set forth herein and agrees to perform to the best of Executive’s ability the duties normally
associated with such position and as determined by Company in its sole discretion. During Executive’s employment. Executive shall devote all of Executive’s business time and energies to the business and affairs of Company, provided that
nothing contained in this Section 1 shall prevent or limit Executive’s right to manage Executive’s personal investments on Executive’s own personal time, including the right to make passive investments in the securities
of: (a) any entity which Executive does not control, directly or indirectly, and which does not compete with Company, or (b) any publicly held entity so long as Executive’s aggregate direct and indirect interest does not
exceed two percent (2%) of the issued and outstanding securities of any class of securities of such publicly held entity. 

2.    Term of Employment. 

(a)    Term. Subject to the terms hereof, Executive’s employment hereunder shall commence on
November 1, 2019 (the “Commencement Date”) and shall continue until terminated hereunder by either party (such term of employment referred to herein as the “Term”). 

(b)    Termination. Notwithstanding anything else contained in this Agreement, Executive’s employment
hereunder shall terminate upon the earliest to occur of the following: 
 (i)    Death. Immediately upon
Executive’s death: 
 (ii)    Termination by Company. 

 (A)    If because of Executive’s Disability (as
defined in Section 2(c)). upon written notice by Company to Executive that Executive’s employment is being terminated as a result of Executive’s Disability, which termination shall be effective on the date of such notice or such later
date as specified in writing by Company; 
 (B)    If for Cause (as defined in Section 2(d)), upon
written notice by Company to Executive that Executive’s employment is being terminated for Cause, which termination shall be effective on the date of such notice or such later date as specified in writing by Company; or 

(C)    If by Company for reasons other than Disability or Cause, upon written notice by Company to
Executive that Executive’s employment is being terminated, which termination shall be effective immediately after the date of such notice or such later date as specified in writing by Company. 

(iii)    Termination by Executive. 

(A)    If for Good Reason (as defined in Section 2(e)), upon written notice by Executive to
Company that Executive is terminating Executive’s employment for Good Reason and that sets forth the factual basis supporting the alleged Good Reason, which termination shall be effective thirty (30) days after the date of such
notice; provided that if Company has cured the circumstances giving rise to the Good Reason, then such termination shall not be effective; see Section 4 for Severance Payment provisions or 

(B)    If without Good Reason, written notice by Executive to Company that Executive is terminating
Executive’s employment, which termination shall be effective at least thirty’ (30) days after the date of such notice. 

Notwithstanding anything in this Section 2(b), Company may at any point terminate Executive’s employment for Cause prior to the
effective date of any other termination contemplated hereunder. 
 (c)    Definition of “Disability”.
For purposes of this Agreement, “Disability” shall mean Executive’s incapacity or inability to perform Executive’s duties and responsibilities as contemplated herein for one hundred twenty (120) days or more within
any one (1) year period (cumulative or consecutive), because Executive’s physical or mental health has become so impaired as to make it impossible or impractical for Executive to perform the duties and responsibilities contemplated
hereunder. Determination of Executive’s physical or mental health shall be determined by Company after consultation with a medical expert appointed by mutual agreement between Company and Executive who has examined Executive. Executive hereby
consents to such examination and consultation regarding Executive’s health and ability to perform as aforesaid. 

(d)    Definition of “Cause”. As used herein, “Cause” shall include: (i) Executive’s
willful engagement in illegal conduct or gross misconduct, which, in each case, is materially injurious to Company; (ii) Executive’s insubordination or substantial malfeasance or nonfeasance of duty, which, in each case, is
materially injurious to Company; (iii) Executive’s embezzlement, misappropriation or fraud; (iv) Executive’s unauthorized disclosure of confidential 

 
information; or (v) Executive’s breach of a material provision of any employment, non-disclosure, invention assignment, non-competition,
or similar agreement between Executive and Company; provided that (A) Company provides Executive with written notice that Company intends to terminate Executive’s employment hereunder for one of the circumstances set forth in
this Section 2(d) within thirty (30) days of such circumstance occurring, (B) if such circumstance is capable of being cured, Executive has failed to cure such circumstance within a period of thirty
(30) days from the date of such written notice, and (C) Company terminates Executive’s employment within sixty five (65) days from the date that Cause first occurs. For purposes of clarification, the
above-listed conditions shall apply separately to each occurrence of Cause, and failure to adhere to such conditions in the event of Cause shall not disqualify Company from asserting Cause for any subsequent occurrence of Cause. 

(e)    Definition of “Good Reason”. As used herein, “Good Reason” shall mean:
(i) relocation of Executive’s principal business location to a location more than fifty (50) miles from Executive’s then-current business location; (ii) a material diminution in Executive’s duties,
authority or responsibilities; or (iii) a material reduction in Executive’s Base Salary; provided that (A) Executive provides Company with written notice that Executive intends to terminate Executive’s
employment hereunder for one of the circumstances set forth in this Section 2(e) within thirty (30) days of such circumstance occurring, (B) if such circumstance is capable of being cured, Company has failed to
cure such circumstance within a period of thirty (30) days from the date of such written notice, and (C) Executive terminates Executive’s employment within sixty five (65) days from the date that Good Reason
first occurs. For purposes of clarification, the above-listed conditions shall apply separately to each occurrence of Good Reason and failure to adhere to such conditions in the event of Good Reason shall not disqualify Executive from asserting Good
Reason for any subsequent occurrence of Good Reason. For purposes of this Agreement, “Good Reason” shall be interpreted in a manner, and limited to the extent necessary, so that it shall not cause adverse tax consequences for either party
with respect to Section 409A (“Section 409A”) of the Internal Revenue Code of 1986, as amended (the “Code”), and any successor statute, regulation and guidance thereto. 

3.    Compensation. 

(a)    Base Salary. Company shall pay Executive a base salary (the “Base Salary”) at the annual rate of
three hundred and fifty thousand dollars ($350,000), as of the Commencement Date. The Base Salary’ shall be payable in substantially equal periodic installments in accordance with Company’s payroll practices as in effect from time to time.
Company shall deduct from each such installment all amounts required to be deducted or withheld under applicable law or under any employee benefit plan in which Executive participates. The Company shall review the Base Salary on an annual basis and
may increase, but not decrease, the Base Salary. 
 (b)    Annual Performance Bonus. Executive shall be eligible
to receive an annual cash bonus (the “Annual Performance Bonus”), with the target amount of such Annual Performance Bonus equal to Thirty Percent (30%) of Executive’s Base Salary in the year to which the Annual Performance Bonus
relates; provided that the actual amount of the Annual Performance Bonus may be greater or less than such target amount. The amount of the Annual Performance Bonus shall be determined by the Board or an appropriate committee thereof in its sole
discretion, 

 
and shall be paid to Executive no later than March 15th of the calendar year immediately following the calendar year in which it was earned.
Executive must be employed by Company on the last day of the fiscal year on which the Annual Performance Bonus is based in order to be eligible for such Annual Performance Bonus. Company shall deduct from the Annual Performance Bonus all amounts
required to be deducted or withheld under applicable law or under any employee benefit plan in which Executive participates. For the current calendar year, Executive shall be eligible for a prorated Annual Performance Bonus subject to the terms and
conditions described above. 
 (c)    Paid Time Off. Executive may take up to twenty (20) days of paid time
off (“PTO”) per year, to be scheduled to minimize disruption to Company’s operations, pursuant to the terms and conditions of Company policy and practices as applied to Company senior executives. 

(d)    Fringe Benefits. Executive shall be entitled to participate in all benefit/welfare plans and fringe benefits
provided to Company senior executives. Executive understands that, except when prohibited by applicable law, Company’s benefit plans and fringe benefits may be amended by Company from time to time in its sole discretion. 

(e)    Equity Incentive Awards. Executive will eligible to participate in the Company’s equity incentive
program and, subject to approval by the Company’s Board of Directors, to be obtained no later than the Commencement Date, receive a stock option grant equal to 1.1% of the Company’s fully diluted stock vesting over four years, with the
first twenty-five percent (25%) vesting on the twelve (12) month anniversary of your Commencement Date, and the remaining vesting in equal monthly installments over the following thirty-six
(36) months. In the case of a Sale Event, as defined in the Company’s 2015 Stock Option and Grant Plan (“the Plan”), this option shall be treated as provided in Section 3(c) of the Plan and all of the shares
shall vest immediately upon the Completion of a Sale Event (as defined in the Plan). 
 (f)    Sign-On Bonus. Company shall pay Executive a sign-on bonus payment of one hundred thousand dollars ($100,000) within one month after the Commencement Date and an
additional payment of sixty-five thousand dollars ($65,000) within one month after either (i) the twelve (12) month anniversary of the Commencement Date provided that Executive is employed by the Company on the twelve
(12) month anniversary of the Commencement Date or (ii) a change of control of the Company provided that Executive is employed by the Company on the date of the change of control of the Company. 

(g)    Reimbursement of Expenses. Company shall reimburse Executive for all ordinary and reasonable out-of-pocket business expenses incurred by Executive in furtherance of Company’s business in accordance with Company’s policies with respect thereto as in effect
from time to time. Executive must submit any request for reimbursement no later than ninety (90) days following the date that such business expense is incurred. All reimbursements provided under this Agreement shall be made or provided in
accordance with the requirements of Section 409A including, where applicable, the requirement that (i) any reimbursement is for expenses incurred during Executive’s lifetime (or during a shorter period of time specified
in this Agreement); (ii) the amount of expenses eligible for reimbursement during a calendar year may not affect the expenses eligible for reimbursement in any other calendar year; (iii) the reimbursement of an eligible
expense shall be made no later than the last day of the calendar year following the year in which the expense is incurred; and (iv) the right to reimbursement or in kind benefits is not subject to liquidation or exchange for another
benefit. 

 (h)    Indemnification. Executive shall be entitled to
indemnification with respect to Executive’s sendees provided hereunder pursuant to Delaware law, the terms and conditions of Company’s certificate of incorporation and/or by-laws, Company’s
directors and officers (“D&O”) liability insurance policy, and Company’s standard indemnification agreement for directors and officers as executed by Company and Executive. 

(i)    Initial Public Offering. If the Company completes an initial public offering, Executive’s cash
compensation (base salary’ plus target bonus) shall be set at least the median for the Chief Business Officer at comparable public companies as determined by the Company’s Board of Directors. 

4.    Payments Upon Termination. 

(a)    Definition of Accrued Obligations. For purposes of this Agreement, “Accrued Obligations” means the
portion of Executive’s Base Salary that has accrued prior to any termination of Executive’s employment with Company and has not yet been paid, and the amount of any expenses properly incurred by Executive on behalf of Company prior to any
such termination and not yet reimbursed. Executive’s entitlement to any other compensation or benefit under any plan of Company shall be governed by and determined in accordance with the terms of such plans, except as otherwise specified in
this Agreement. 
 (b)    Termination by Company for Cause, by Executive Without Good Reason, or as a Result of
Executive’s Disability or Death. If Executive’s employment hereunder is terminated by Company for Cause, by Executive without Good Reason, or as a result of Executive’s Disability or death, then Company shall pay the Accrued
Obligations to Executive promptly following the effective date of such termination. 
 (c)    Termination by Company
Without Cause or by Executive For Good Reason. In the event that Executive’s employment is terminated by action of Company other than for Cause, or Executive terminates Executive’s employment for Good Reason, then, in addition to the
Accrued Obligations, Executive shall receive the following, subject to the terms and conditions of Section 4(d): 

(i)    Severance Payments. Payment in an amount equal to Executive’s then-current Base Salary for a nine
(9) month period plus any Annual Performance Bonus accrued prior to any termination of Executive’s employment with Company and has not yet been paid (prorated based on the date of termination) less customary and required taxes and
employment-related deductions, paid in one lump sum amount on the first payroll date following the date on which the separation agreement under Section 4(d) becomes effective and non-revocable;
provided that such payment shall be made within seventy (70) days following the effective date of termination from employment, and further provided that if the 70th day falls in the calendar year following the year during
which the termination or separation from service occurred, then the payments will commence in such subsequent calendar year, and further provided that if such payments commence in such subsequent year, the first such payment shall be a lump
sum in an 

 
amount equal to the payments that would have come due since Employee’s separation from service. For the avoidance of doubt, the severance payments in this Section 4(c)(i) apply in the
event of a change of control of the Company. 
 (ii)    Benefits Payments. Upon completion of appropriate forms
and subject to applicable terms and conditions under the Consolidated Omnibus Budget Reconciliation Act of 1985, as amended (“COBRA”), Company shall continue to provide Executive medical insurance coverage at no cost to Executive to the
same extent that such insurance continues to be provided to similarly situated executives at the time of Executive’s termination, until the earlier to occur of twelve (12) months following Executive’s termination date or the date
Executive begins employment with another employer. Executive shall bear responsibility for applying for COBRA continuation coverage. 

(d)    Execution of Separation Agreement. Company shall not be obligated to pay Executive severance payments or
benefits described in this Section 4 unless Executive has executed (without revocation) a timely separation agreement in a form acceptable to Company, which shall include a release of claims and standard terms regarding non-disparagement,
confidentiality, cooperation and the like, which shall be provided to Executive within ten (10) days following separation from service, and signed by Executive and returned to Company no later than sixty (60) days following
Executive’s separation from service (the “Review Period”). 
 (e)    COBRA. If the payment of any
COBRA or health insurance premiums by Company on behalf of Executive as described herein would otherwise violate any applicable nondiscrimination rules or cause the reimbursement of claims to be taxable under the Patient Protection and Affordable
Care Act of 2010, together with the Health Care and Education Reconciliation Act of 2010 (collectively, the “Act”) or Section 105(h) of the Code, the COBRA premiums paid by Company shall be treated as taxable payments (subject to
customary and required taxes and employment-related deductions) and be subject to imputed income tax treatment to the extent necessary to eliminate any discriminatory treatment or taxation under the Act or Section 105(h) of the Code. If
Company determines in its sole discretion that it cannot provide the COBRA benefits described herein under Company’s health insurance plan without potentially violating applicable law (including, without limitation, Section 2716 of
the Public Health Service Act), Company shall in lieu thereof provide to Executive a taxable lump-sum payment in an amount equal to the sum of the monthly (or then remaining) COBRA premiums that Executive would be required to pay to maintain
Executive’s group health insurance coverage in effect on the separation date for the remaining portion of the period for which Executive shall receive the payments described in Sections 4(b) or 4(c) above. 

5.    Prohibited Competition And Solicitation. In light of the competitive and proprietary aspects of
the business of Company, and as a condition of employment hereunder, Executive agrees to execute and abide by Company’s Confidentiality, Assignment of Inventions and Non-Competition Agreement. 

6.    Property and Records. Upon the termination of Executive’s employment hereunder, or if
Company otherwise requests, Executive shall: (a) return to Company all tangible business information and copies thereof (regardless how such Confidential Information or copies are maintained), and (b) deliver to Company any
property of Company which may be in Executive’s possession, including, but not limited to, cell phones, smart phones, laptops, products, materials, memoranda, notes, records, reports or other documents or photocopies of the same. 

 7.    Code Sections 409A and 280G. 

(a)    In the event that the payments or benefits set forth in Section 4 of this Agreement constitute
“non-qualified deferred compensation” subject to Section 409A, then the following conditions apply to such payments or benefits: 

(i)    Any termination of Executive’s employment triggering payment of benefits under Section 4 must constitute
a “separation from service” under Section 409A(a)(2)(A)(i) of the Code and Treas. Reg. §1.409A-l(h) before distribution of such benefits can commence. To the extent that the termination of Executive’s employment does
not constitute a separation of service under Section 409A(a)(2)(A)(i) of the Code and Treas. Reg. § 1.409A-1 (h) (as the result of further services that are reasonably anticipated to be provided by Executive to Company
at the time Executive’s employment terminates), any such payments under Section 4 that constitute deferred compensation under Section 409A shall be delayed until after the date of a subsequent event constituting a
separation of service under Section 409A(a)(2)(A)(i) of the Code and Treas. Reg. §1.409A-l(h). For purposes of clarification, this Section 7(a) shall not cause any forfeiture of benefits on Executive’s part, but
shall only act as a delay until such time as a “separation from service” occurs. 
 (ii)    Notwithstanding
any other provision with respect to the timing of payments under Section 4 if, at the time of Executive’s termination, Executive is deemed to be a “specified employee” of Company (within the meaning of
Section 409A(a)(2)(B)(i) of the Code), then limited only to the extent necessary to comply with the requirements of Section 409A, any payments to which Executive may become entitled under Section 4 which are
subject to Section 409A (and not otherwise exempt from its application) shall be withheld until the first (1st) business day of the seventh (7th) month following the termination of Executive’s employment, at which time Executive shall be paid an aggregate amount equal to the accumulated, but unpaid, payments otherwise due to Executive
under the terms of Section 4. 
 (b)    It is intended that each installment of the payments and benefits
provided under Section 4 of this Agreement shall be treated as a separate “payment” for purposes of Section 409A. Neither Company nor Executive shall have the right to accelerate or defer the delivery of any such payments
or benefits except to the extent specifically permitted or required by Section 409A. 

(c)    Notwithstanding any other provision of this Agreement to the contrary, this Agreement shall be interpreted and at
all times administered in a manner that avoids the inclusion of compensation in income under Section 409A, or the payment of increased taxes, excise taxes or other penalties under Section 409A. The parties intend this Agreement to
be in compliance with Section 409A. Executive acknowledges and agrees that Company does not guarantee the tax treatment or tax consequences associated with any payment or benefit arising under this Agreement, including but not limited to
consequences related to Section 409A. 

 (d)    If any payment or benefit Executive would receive under this
Agreement, when combined with any other payment or benefit Executive receives pursuant to a change of control (for purposes of this section, a “Payment”) would: (i) constitute a “parachute payment” within the meaning of
Section 280G the Code; and (ii) but for this sentence, be subject to the excise tax imposed by Section 4999 of the Code (the “Excise Tax”), then such Payment shall be either: (A) the full
amount of such Payment; or (B) such lesser amount as would result in no portion of the Payment being subject to the Excise Tax, whichever of the foregoing amounts, taking into account the applicable federal, state and local employments
taxes, income taxes and the Excise Tax, results in Executive’s receipt, on an after-tax basis, of the greater amount of the Payment notwithstanding that all or some portion of the Payment may be subject to the Excise Tax. With respect to
subsection (B), if there is more than one method of reducing the payment as would result in no portion of the Payment being subject to the Excise Tax, then Executive shall determine which method shall be followed, provided that if Executive
fails to make such determination within thirty (30) days after Company has sent Executive written notice of the need for such reduction, Company may determine the amount of such reduction in its sole discretion. 

8.    General. 

(a)    Notices. Except as otherwise specifically provided herein, any notice required or permitted by this Agreement
shall be in writing and shall be delivered as follows with notice deemed given as indicated: (i) by personal delivery when delivered personally; (ii) by overnight courier upon written verification of receipt; (iii) by
telecopy or facsimile transmission upon acknowledgment of receipt of electronic transmission; or (iv) by certified or registered mail, return receipt requested, upon verification of receipt. 

 

	 	•	 	 Notices to Executive shall be sent to: 

The last known address in Company’s records or such other address as Executive may specify in writing. 

 

	 	•	 	 Notices to Company shall be sent to: 

Checkmate Pharmaceuticals, Inc. 

245 Main St., 4th Floor 

Cambridge, MA 02142 
 Attn:
President and CEO 
 or to such other Company representative as Company may specify in writing, with a copy to: 

Goodwin Procter LLP 
 100 Northern
Avenue 
 Boston, MA 02210 

(b)    Modifications: Amendments: Waivers: Consents. The terms of this Agreement may be modified or amended only by
written agreement executed by the parties hereto. The terms of this Agreement may be waived, or consent for the departure therefrom granted, only 

 
by written document executed by the party entitled to the benefits of such terms or provisions. No such waiver or consent shall be deemed to be or shall constitute a waiver or consent with
respect to any other terms of this Agreement, whether or not similar. Each such waiver or consent shall be effective only in the specific instance and for the purpose for which it was given, and shall not constitute a continuing waiver or consent.

 (c)    Assignment. Company may assign its rights and obligations hereunder to any person or entity that
succeeds to all or substantially all of Company’s business or that aspect of Company’s business in which Executive is principally involved. Executive may not assign Executive’s rights and obligations under this Agreement without the
prior written consent of Company. 
 (d)    Governing Law; Jurisdiction: Venue. This Agreement shall be
governed by and construed in accordance with the substantive laws of the Commonwealth of Massachusetts, without giving effect to any choice or conflict of law provision or rule. Any legal action permitted by this Agreement to enforce an award or for
a claimed breach shall be governed by the laws of the Commonwealth of Massachusetts and shall be commenced and maintained solely in any state or federal court located in the Commonwealth of Massachusetts, and both parties hereby submit to the
jurisdiction and venue of any such court. 
 (e)    Headings and Captions. The headings and captions of the
various subdivisions of this Agreement are for convenience of reference only and shall in no way modify or affect the meaning or construction of any of the terms or provisions hereof. 

(f)    Entire Agreement. This Agreement, together with the other agreements specifically referenced herein,
embodies the entire agreement and understanding between the parties hereto with respect to the subject matter hereof and supersedes all prior oral or written agreements and understandings relating to the subject matter hereof. No statement,
representation, warranty, covenant or agreement of any kind not expressly set forth in this Agreement shall affect, or be used to interpret, change or restrict, the express terms and provisions of this Agreement. 

This Agreement may be executed in two or more counterparts, and by different parties hereto on separate counterparts, each of which shall be
deemed an original, but all of which together shall constitute one and the same instrument. For all purposes a signature by fax shall be treated as an original. 

IN WITNESS WHEREOF, the parties hereto have executed this Agreement as of the date first written above. 

 

							
	KLEEM CHAUDHARY	 		 	CHECKMATE PHARMACEUTICALS, INC.
				
	 /s/ Kleem Chaudhary
	 		 	By:	 	 /s/ Barry Labinger

	Signature	 		 		 	 Name: Barry Labinger
 Title: President and
CEOEX-10.16

 Exhibit 10.16 

June 13, 2017 
 Karen M. Brennan 

Dear Karen: 
 On behalf of Checkmate
Pharmaceuticals, Inc. (the “Company”), I am pleased to offer you employment with the Company. The terms and conditions of your employment are set forth below in this letter (“Offer Letter”). 

1.    Position. Your initial position with the Company will be Chief Operating Officer. This is a full-time position As Chief
Operating Officer you will oversee and have responsibility for managing the Company’s clinical development efforts including quality and compliance. These responsibilities may evolve over time. You will report to me. 

2.    Start Date. Your employment will begin on June 26, 2017 (“Start Date”), unless otherwise agreed to by
you and the Company. 
 3.    Base Salary. The Company will pay you a base salary at the rate of $27,083.33 per month (which is
equivalent to an annualized rate of $325,000 per year), payable in accordance with the Company’s standard payroll schedule and subject to applicable tax and other withholdings as required by law (“Base Salary”). Your Base Salary may
be subject to periodic review (at least on an annual basis) and upward adjustments at the Company’s sole discretion. 

4.    Bonus. You will be eligible to receive an annual cash performance bonus of up to 30% of your then-existing Base Salary
(“Annual Bonus”). The award of the Annual Bonus is discretionary and will be subject to the Company’s assessment of your performance, as well as the Company’s corporate objectives and business conditions at the Company. The
Annual Bonus also will be subject to your employment for the full period covered by the bonus and on the date the bonus is to be paid, approval by and adjustment at the discretion of the Company’s Board of Directors and the terms of any
applicable bonus plan. The Company expects to review your job performance on an annual basis and to discuss with you the criteria that the Company will use to assess your performance for bonus purposes. The Company also may increase the targeted
amount of your annual performance bonus above 30% in the Company’s sole discretion. 
 5.    Incentive Equity Awards.
Subject to your acceptance of this Offer Letter and the Employee Confidentiality Agreement, the Board of Directors has approved a stock option grant to you for 539,500 shares of the Company’s common stock vesting over four years, assuming
continued employment or service, with the first twenty-five percent (25%) vesting on the twelve (12) month anniversary of your Start Date, and the remaining vesting in equal monthly installments over the following thirty-six (36) months. 
 6.    Benefits. You will be eligible to participate in
the Company’s employee benefits and insurance programs generally made available from time to time to its full-time employees, in accordance with, and provided you are eligible under, the plan documents governing those programs. You will receive
a copy of benefit plan documents and personnel policies and procedures when you begin your employment with the Company. You will also be eligible for up 

 
to 15 days of paid vacation per year, which shall accrue on a prorated basis in accordance with the Company’s vacation policy as in effect from time to time. The Company reserves the right
to modify or terminate any or all of its benefit plans or policies at any time at its discretion. 
 7.    Non-Competition, Non-Solicitation, Confidentiality and Assignment Agreement. As a condition of employment, you also will be required to sign an Employee Confidentiality
Agreement, a copy of which is enclosed. 
 8.    Representation Regarding Other Obligations. This offer of employment from the
Company is conditioned on your representation that you are not bound by the terms of any agreement with any previous employer or other party (i) to refrain from using or disclosing any trade secret or confidential or proprietary
information in the course of your employment with the Company, (ii) to refrain from competing, directly or indirectly, with the business of such previous employer or any other party, and (iii) to refrain from soliciting
employees, customers or suppliers of such previous employer or other party, in any case of (i), (ii) or (iii) that would (a) prevent or restrict you in carrying out your responsibilities for the Company,
(b) affect your ability to devote full time and attention to your work at the Company, or (c) be inconsistent in any way with the terms of this Offer Letter. If you have entered into any agreement that may restrict your
activities on behalf of the Company, please immediately notify me and then please provide me with a copy of the agreement as soon as possible. You further represent that your adherence to all the terms of this Offer Letter and the performance of
your duties as an employee of the Company do not and will not conflict with or breach any agreement with any prior employer or other party’ to which you are a party (including without limitation any nondisclosure or non-competition agreement),
and that you will not disclose to the Company or induce the Company to use any confidential or proprietary information or material belonging to any previous employer or others. 

9.    Taxes. All forms of compensation referred to in this Offer Letter are subject to all applicable federal, state and/or local
withholding and/or payroll taxes, and the Company may withhold from any amounts payable to you in order to comply with such withholding obligations. You hereby acknowledge that the Company does not have a duty to design its compensation policies in
a manner that minimizes your tax liabilities, and you will not make any claim against the Company or its board of directors related to tax liabilities arising from your compensation. 

10.    Interpretation, Amendment and Enforcement. This Offer Letter, the Employee Noncompetition, Non-Solicitation, Confidentiality
and Assignment Agreement, and any plans and agreements applicable to the incentive equity awards referred in Section 5 of this Offer Letter constitute the complete agreement between you and the Company, contain all of the terms of your
employment with the Company and supersede any prior agreements, representations or understandings (whether written, oral or implied) between you and the Company. The terms of this Offer Letter will be governed by statutes and common law of The
Commonwealth of Massachusetts. You and the Company hereby irrevocably submit to and acknowledge and recognize the exclusive personal jurisdiction of the federal and state courts located in The Commonwealth of Massachusetts in connection with any
dispute or any claim related to this Offer Letter. 
 11.    Other Terms. Your employment with the Company will be on an “at
will” basis. In other words, you or the Company may terminate your employment for any reason and at any time, with 

  
 2 

 
or without cause. Although your job duties, title, compensation and benefits, as well as the Company’s benefit plans and personnel policies and procedures, may change from time to time, the
“at will” nature of your employment may only be changed in an express written agreement signed by you and the Company. 
 In the event of the
termination of your employment for any reason, the Company shall pay you the Accrued Obligations, defined as (1) your then-existing Base Salary through the date of termination, (2) an amount equal to the value of your accrued unused
vacation days, and (3) the amount of any expenses properly incurred by you on behalf of the Company prior to any such termination and not yet reimbursed. In addition, in the event the Company terminates your employment without Cause or you
resign for Good Reason (both as defined below), the Company shall provide you with the following Termination Benefits: 
  

	 	(i)	 continuation of your then-existing Base Salary for a period of nine (9) months after the date of
termination at the salary rate then in effect (“Salary Continuation Payments”) (solely for purposes of Section 409A of the Internal Revenue Code of 1986, as amended, each Salary Continuation Payment is considered a
separate payment); and 

  

	 	(ii)	 If the date of termination occurs within the twelve (12) month period immediately following a Sale of the
Company (as defined below), one hundred percent (100%) of the then unvested incentive equity awards shall accelerate and shall become vested effective as of the date of termination. 

Notwithstanding anything to the contrary in this Offer Letter, you shall not be entitled to any Termination Benefits unless within sixty (60) days of the
date of termination, you first (i) enter into, do not revoke, and comply with the terms of a separation agreement in a form acceptable to the Company which shall include a release against the Company and related persons and entities;
(ii) resign from any and all positions, including, without implication of limitation, as a director, trustee, and officer, that you then hold with the Company and any affiliate of the Company; and (iii) return all Company property and
comply with any instructions related to deleting and purging duplicates of such Company property. The Salary Continuation Payments shall commence within thirty (30) days after the date of termination and shall be made on the Company’s
regular payroll dates; provided, however, that if the thirty (30) day period begins in one calendar year and ends in a second calendar year, the Salary Continuation Payments shall begin to be paid in the second calendar year. In the event you
miss a regular payroll period between the date of termination and first Salary Continuation Payment, the first Salary Continuation Payment shall include a “catch up” payment. For the avoidance of doubt, you shall not be entitled to any
Termination Benefits if the Company terminates you for Cause or you resign without Good Reason. 
 “Cause” means any of the following:
(i) dishonesty, embezzlement, misappropriation of assets or property of the Company; (ii) gross negligence, misconduct, neglect of duties, theft, fraud or breach of fiduciary duty to the Company; (iii) violation of federal or state
securities laws; (iv) your breach of this Offer Letter, the Confidential Information Agreement or any other agreement between you and the Company; (v) the conviction of a felony, or any crime involving moral turpitude, including a plea of
guilty or nolo contendre; 

  
 3 

 “Good Reason” means that you have complied with the “Good Reason Process” (hereinafter
defined) following the occurrence of any of the following actions undertaken by the Company without your express prior written consent: (i) the material diminution in your responsibilities, authority and function; (ii) any reduction in
your Base Salary, provided, however, that Good Reason shall not be deemed to have occurred in the event of a reduction in your Base Salary that is pursuant to a salary reduction program affecting all of the senior level management of the Company and
that does not adversely affect you to a greater extent than other similarly situated executives; (iii) a material change in the geographic location at which you must regularly report to work and perform services, except for required travel on
the Company’s business; or (iv) any breach by the Company of the Offer Letter (including, without limitation, the failure of the Company to pay any compensation or provide equity otherwise due to you). “Good Reason Process” means
that (i) you have reasonably determined in good faith that a “Good Reason” condition has occurred; (ii) you have notified the Company in writing of the first occurrence of the Good Reason condition within sixty (60) days of
the first occurrence of such condition; (iii) you have cooperated in good faith with the Company’s efforts, for a period not less than thirty (30) days following such notice (the “Cure Period”), to remedy the condition;
(iv) notwithstanding such efforts, the Good Reason condition continues to exist; and (v) you terminate your employment within sixty (60) days after the end of the Cure Period. If the Company cures the Good Reason condition during the
Cure Period, Good Reason shall be deemed not to have occurred. 
 “Sale of the Company” means either: (a) a transaction or series of related
transactions in which a Person, or a group of related Persons, acquires from the Members Units representing more than fifty percent (50%) of the outstanding voting power of the Company (a Unit Sale); or (b) a transaction that qualifies as a
Capital Transaction (terms not otherwise defined to be defined as in the Company’s Operating Agreement). 
 In addition, this offer is
subject satisfactory background and reference checks. You agree to provide to the Company, within three (3) days of your hire date, documentation of your eligibility to work in the United States of America, as required by the Immigration Reform
and Control Act of 1986. You may need to obtain a work visa in order to be able to work in the United Sates. If that is the case, your employment with the Company will be conditioned upon your obtaining a work visa in a timely manner as determined
by the Company. 
 The entire Checkmate team and I are excited about the prospect of having you join the Company and to working with you to
grow this enterprise. We look forward to receiving a response from you within one week acknowledging, by signing below, that you have accepted this offer of employment. 

  
 4 

 
	
	 Very truly yours,

	
	 /s/ Arthur M. Krieg, MD

	
	 Arthur M. Krieg, MD

President & CEO

 I have read and accept this employment offer: 
  

			
	 /s/ Karen M Brennan

	Signature	 	

			
		
	Dated:	 	 June 15, 2017

  
 5

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