EX-10.1





 Exhibit 10.1 

CHECKMATE PHARMACEUTICALS, INC. 

2015 STOCK OPTION AND GRANT PLAN 
 SECTION
1. GENERAL PURPOSE OF THE PLAN; DEFINITIONS 
 The name of the plan is the Checkmate Pharmaceuticals, Inc. 2015 Stock Option and Grant
Plan (the “Plan”). The purpose of the Plan is to encourage and enable the officers, employees, directors, Consultants and other key persons of Checkmate Pharmaceuticals, Inc., a Delaware corporation (including any successor entity, the
“Company”) and its Subsidiaries, upon whose judgment, initiative and efforts the Company largely depends for the successful conduct of its business, to acquire a proprietary interest in the Company. 

The following terms shall be defined as set forth below: 

“Affiliate” of any Person means a Person that directly or indirectly, through one or more intermediaries, controls, is
controlled by or is under common control with the first mentioned Person. A Person shall be deemed to control another Person if such first Person possesses directly or indirectly the power to direct, or cause the direction of, the management and
policies of the second Person, whether through the ownership of voting securities, by contract or otherwise. 
 “Award” or
“Awards,” except where referring to a particular category of grant under the Plan, shall include Incentive Stock Options, Non-Qualified Stock Options, Restricted Stock Awards, Unrestricted
Stock Awards, Restricted Stock Units or any combination of the foregoing. 
 “Award Agreement” means a written or
electronic agreement setting forth the terms and provisions applicable to an Award granted under the Plan. Each Award Agreement may contain terms and conditions in addition to those set forth in the Plan; provided, however, in the event of
any conflict in the terms of the Plan and the Award Agreement, the terms of the Plan shall govern. 
 “Board” means
the Board of Directors of the Company. 
 “Cause” shall have the meaning as set forth in the Award Agreement(s). In the
case that any Award Agreement does not contain a definition of “Cause,” it shall mean (i) the grantee’s dishonest statements or acts with respect to the Company or any Affiliate of the Company, or any current or prospective
customers, suppliers vendors or other third parties with which such entity does business; (ii) the grantee’s commission of (A) a felony or (B) any misdemeanor involving moral turpitude, deceit, dishonesty or fraud; (iii) the
grantee’s failure to perform his assigned duties and responsibilities to the reasonable satisfaction of the Company which failure continues, in the reasonable judgment of the Company, after written notice given to the grantee by the Company;
(iv) the grantee’s gross negligence, willful misconduct or insubordination with respect to the Company or any Affiliate of the Company; or (v) the grantee’s material violation of any provision of any agreement(s) between the
grantee and the Company relating to noncompetition, nonsolicitation, nondisclosure and/or assignment of inventions. 












 “Chief Executive Officer” means the Chief Executive Officer of the Company
or, if there is no Chief Executive Officer, then the President of the Company. 
 “Code” means the Internal Revenue Code of
1986, as amended, and any successor Code, and related rules, regulations and interpretations. 
 “Committee” means the
Committee of the Board referred to in Section 2. 
 “Consultant” means any natural person that provides bona fide
services to the Company (including a Subsidiary), and such services are not in connection with the offer or sale of securities in a capital-raising transaction and do not directly or indirectly promote or maintain a market for the Company’s
securities. 
 “Disability” means “disability” as defined in Section 422(c) of the Code. 

“Effective Date” means the date on which the Plan is adopted as set forth on the final page of the Plan. 

“Exchange Act” means the Securities Exchange Act of 1934, as amended, and the rules and regulations thereunder. 

“Fair Market Value” of the Stock on any given date means the fair market value of the Stock determined in good faith by the
Committee based on the reasonable application of a reasonable valuation method not inconsistent with Section 409A of the Code. If the Stock is admitted to trade on a national securities exchange, the determination shall be made by reference to
the closing price reported on such exchange. If there is no closing price for such date, the determination shall be made by reference to the last date preceding such date for which there is a closing price. If the date for which Fair Market Value is
determined is the first day when trading prices for the Stock are reported on a national securities exchange, the Fair Market Value shall be the “Price to the Public” (or equivalent) set forth on the cover page for the final prospectus
relating to the Company’s Initial Public Offering. 
 “Good Reason” shall have the meaning as set forth in the Award
Agreement(s). In the case that any Award Agreement does not contain a definition of “Good Reason,” it shall mean (i) a material diminution in the grantee’s base salary except for across-the-board salary reductions similarly affecting all or substantially all similarly situated employees of the Company or (ii) a change of more than 50 miles in the geographic location at which the
grantee provides services to the Company, so long as the grantee provides at least 90 days notice to the Company following the initial occurrence of any such event and the Company fails to cure such event within 30 days thereafter. 

“Grant Date” means the date that the Committee designates in its approval of an Award in accordance with applicable law as
the date on which the Award is granted, which date may not precede the date of such Committee approval. 
 “Holder” means,
with respect to an Award or any Shares, the Person holding such Award or Shares, including the initial recipient of the Award or any Permitted Transferee. 

  
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 “Incentive Stock Option” means any Stock Option designated and qualified as
an “incentive stock option” as defined in Section 422 of the Code. 
 “Initial Public Offering” means the
consummation of the first firm commitment underwritten public offering pursuant to an effective registration statement under the Securities Act covering the offer and sale by the Company of its equity securities, as a result of or following which
the Stock shall be publicly held. 
 “Non-Qualified Stock Option” means any Stock
Option that is not an Incentive Stock Option. 
 “Option” or “Stock Option” means any option to purchase
shares of Stock granted pursuant to Section 5. 
 “Permitted Transferees” shall mean any of the following to whom a
Holder may transfer Shares hereunder (as set forth in Section 9(a)(ii)(A)): the Holder’s child, stepchild, grandchild, parent, stepparent, grandparent, spouse, former spouse, sibling, niece, nephew, mother-in-law, father-in-law, son-in-law, daughter-in-law, brother-in-law, or sister-in-law, including adoptive relationships, any person sharing the Holder’s household (other than a tenant or employee), a trust in which these persons have more than fifty percent of the beneficial
interest, a foundation in which these persons control the management of assets, and any other entity in which these persons own more than fifty percent of the voting interests; provided, however, that any such trust does not require or permit
distribution of any Shares during the term of the Award Agreement unless subject to its terms. Upon the death of the Holder, the term Permitted Transferees shall also include such deceased Holder’s estate, executors, administrators, personal
representatives, heirs, legatees and distributees, as the case may be. 
 “Person” shall mean any individual, corporation,
partnership (limited or general), limited liability company, limited liability partnership, association, trust, joint venture, unincorporated organization or any similar entity. 

“Restricted Stock Award” means Awards granted pursuant to Section 6 and “Restricted Stock” means Shares
issued pursuant to such Awards. 
 “Restricted Stock Unit” means an Award of phantom stock units to a grantee, which may be
settled in cash or Shares as determined by the Committee, pursuant to Section 8. 
 “Sale Event” means the
consummation of (i) the dissolution or liquidation of the Company, (ii) the sale of all or substantially all of the assets of the Company on a consolidated basis to an unrelated person or entity, (iii) a merger, reorganization or
consolidation pursuant to which the holders of the Company’s outstanding voting power immediately prior to such transaction do not own a majority of the outstanding voting power of the surviving or resulting entity (or its ultimate parent, if
applicable), (iv) the acquisition of all or a majority of the outstanding voting stock of the Company in a single transaction or a series of related transactions by a Person or group of Persons, or (v) any other acquisition of the business of
the Company, as determined by the Board; provided, however, that the Company’s Initial Public Offering, any subsequent public offering or another capital raising event, or a merger effected solely to change the Company’s domicile
shall not constitute a “Sale Event.” 

  
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 “Section 409A” means Section 409A of the Code and
the regulations and other guidance promulgated thereunder. 
 “Securities Act” means the Securities Act of 1933, as
amended, and the rules and regulations thereunder. 
 “Service Relationship” means any relationship as a full-time
employee, part-time employee, director or other key person (including Consultants) of the Company or any Subsidiary or any successor entity (e.g., a Service Relationship shall be deemed to continue without interruption in the event an
individual’s status changes from full-time employee to part-time employee or Consultant). 
 “Shares” means shares of
Stock. 
 “Stock” means the Common Stock, par value $0.0001 per share, of the Company. 

“Subsidiary” means any corporation or other entity (other than the Company) in which the Company has more than a
50 percent interest, either directly or indirectly. 
 “Ten Percent Owner” means an employee who owns or is deemed to
own (by reason of the attribution rules of Section 424(d) of the Code) more than 10 percent of the combined voting power of all classes of stock of the Company or any parent of the Company or any Subsidiary. 

“Termination Event” means the termination of the Award recipient’s Service Relationship with the Company and its
Subsidiaries for any reason whatsoever, regardless of the circumstances thereof, and including, without limitation, upon death, disability, retirement, discharge or resignation for any reason, whether voluntarily or involuntarily. The following
shall not constitute a Termination Event: (i) a transfer to the service of the Company from a Subsidiary or from the Company to a Subsidiary, or from one Subsidiary to another Subsidiary or (ii) an approved leave of absence for military
service or sickness, or for any other purpose approved by the Committee, if the individual’s right to re-employment is guaranteed either by a statute or by contract or under the policy pursuant to which
the leave of absence was granted or if the Committee otherwise so provides in writing. 
 “Unrestricted Stock Award” means
any Award granted pursuant to Section 7 and “Unrestricted Stock” means Shares issued pursuant to such Awards. 
 SECTION 2.
ADMINISTRATION OF PLAN; COMMITTEE AUTHORITY TO SELECT GRANTEES AND DETERMINE AWARDS 
 (a) Administration of Plan. The
Plan shall be administered by the Board, or at the discretion of the Board, by a committee of the Board, comprised of not less than two directors. All references herein to the “Committee” shall be deemed to refer to the group then
responsible for administration of the Plan at the relevant time (i.e., either the Board of Directors or a committee or committees of the Board, as applicable). 

(b) Powers of Committee. The Committee shall have the power and authority to grant Awards consistent with the terms of the Plan,
including the power and authority: 
 (i) to select the individuals to whom Awards may from time to time be granted; 

  
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 (ii) to determine the time or times of grant, and the amount, if any, of Incentive Stock
Options, Non-Qualified Stock Options, Restricted Stock Awards, Unrestricted Stock Awards, Restricted Stock Units, or any combination of the foregoing, granted to any one or more grantees; 

(iii) to determine the number of Shares to be covered by any Award and, subject to the provisions of the Plan, the price, exercise price,
conversion ratio or other price relating thereto; 
 (iv) to determine and, subject to Section 12, to modify from time to time the terms
and conditions, including restrictions, not inconsistent with the terms of the Plan, of any Award, which terms and conditions may differ among individual Awards and grantees, and to approve the form of Award Agreements; 

(v) to accelerate at any time the exercisability or vesting of all or any portion of any Award; 

(vi) to impose any limitations on Awards, including limitations on transfers, repurchase provisions and the like, and to exercise repurchase
rights or obligations; 
 (vii) subject to Section 5(a)(ii) and any restrictions imposed by Section 409A, to extend at any time the
period in which Stock Options may be exercised; and 
 (viii) at any time to adopt, alter and repeal such rules, guidelines and practices for
administration of the Plan and for its own acts and proceedings as it shall deem advisable; to interpret the terms and provisions of the Plan and any Award (including Award Agreements); to make all determinations it deems advisable for the
administration of the Plan; to decide all disputes arising in connection with the Plan; and to otherwise supervise the administration of the Plan. 
 All
decisions and interpretations of the Committee shall be binding on all persons, including the Company and all Holders. 
 (c) Award
Agreement. Awards under the Plan shall be evidenced by Award Agreements that set forth the terms, conditions and limitations for each Award. 

(d) Indemnification. Neither the Board nor the Committee, nor any member of either or any delegate thereof, shall be liable for
any act, omission, interpretation, construction or determination made in good faith in connection with the Plan, and the members of the Board and the Committee (and any delegate thereof) shall be entitled in all cases to indemnification and
reimbursement by the Company in respect of any claim, loss, damage or expense (including, without limitation, reasonable attorneys’ fees) arising or resulting therefrom to the fullest extent permitted by law and/or under the Company’s
governing documents, including its certificate of incorporation or bylaws, or any directors’ and officers’ liability insurance coverage which may be in effect from time to time and/or any indemnification agreement between such individual
and the Company. 

  
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 (e) Foreign Award Recipients. Notwithstanding any provision of the Plan to the
contrary, in order to comply with the laws in other countries in which the Company and any Subsidiary operate or have employees or other individuals eligible for Awards, the Committee, in its sole discretion, shall have the power and authority to:
(i) determine which Subsidiaries, if any, shall be covered by the Plan; (ii) determine which individuals, if any, outside the United States are eligible to participate in the Plan; (iii) modify the terms and conditions of any Award
granted to individuals outside the United States to comply with applicable foreign laws; (iv) establish subplans and modify exercise procedures and other terms and procedures, to the extent the Committee determines such actions to be necessary
or advisable (and such subplans and/or modifications shall be attached to the Plan as appendices); provided, however, that no such subplans and/or modifications shall increase the share limitation contained in Section 3(a) hereof; and
(v) take any action, before or after an Award is made, that the Committee determines to be necessary or advisable to obtain approval or comply with any local governmental regulatory exemptions or approvals. 

SECTION 3. STOCK ISSUABLE UNDER THE PLAN; MERGERS AND OTHER TRANSACTIONS; SUBSTITUTION 

(a) Stock Issuable. The maximum number of Shares reserved and available for issuance under the Plan shall be 5,538,676 Shares,
subject to adjustment as provided in Section 3(b). For purposes of this limitation, the Shares underlying any Awards that are forfeited, canceled, reacquired by the Company prior to vesting, satisfied without the issuance of Stock or otherwise
terminated (other than by exercise) and Shares that are withheld upon exercise of an Option or settlement of an Award to cover the exercise price or tax withholding shall be added back to the Shares available for issuance under the Plan. Subject to
such overall limitations, Shares may be issued up to such maximum number pursuant to any type or types of Award, and no more than 5,000,000 Shares may be issued pursuant to Incentive Stock Options. The Shares available for issuance under the Plan
may be authorized but unissued Shares or Shares reacquired by the Company. Beginning on the date that the Company becomes subject to Section 162(m) of the Code, Options with respect to no more than 5,000,000 Shares shall be granted to any one
individual in any calendar year period. 
 (b) Changes in Stock. Subject to Section 3(c) hereof, if, as a result of any
reorganization, recapitalization, reclassification, stock dividend, stock split, reverse stock split or other similar change in the Company’s capital stock, the outstanding Shares are increased or decreased or are exchanged for a different
number or kind of shares or other securities of the Company, or additional Shares or new or different shares or other securities of the Company or other non-cash assets are distributed with respect to such
Shares or other securities, in each case, without the receipt of consideration by the Company, or, if, as a result of any merger or consolidation, or sale of all or substantially all of the assets of the Company, the outstanding Shares are converted
into or exchanged for other securities of the Company or any successor entity (or a parent or subsidiary thereof), the Committee shall make an appropriate and proportionate adjustment in (i) the maximum number of Shares reserved for issuance
under the Plan, (ii) the number and kind of Shares or other securities subject to any then outstanding 

  
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Awards under the Plan, (iii) the repurchase price, if any, per Share subject to each outstanding Award, and (iv) the exercise price for each Share subject to any then outstanding Stock
Options under the Plan, without changing the aggregate exercise price (i.e., the exercise price multiplied by the number of Stock Options) as to which such Stock Options remain exercisable. The adjustment by the Committee shall be final, binding and
conclusive. No fractional Shares shall be issued under the Plan resulting from any such adjustment, but the Committee in its discretion may make a cash payment in lieu of fractional shares. 

(c) Sale Events. 
 (i)
Options. 
 (A) In the case of and subject to the consummation of a Sale Event, the Plan and all outstanding Options
issued hereunder shall terminate upon the effective time of any such Sale Event unless assumed or continued by the successor entity, or new stock options or other awards of the successor entity or parent thereof are substituted therefor, with an
equitable or proportionate adjustment as to the number and kind of shares and, if appropriate, the per share exercise prices, as such parties shall agree (after taking into account any acceleration hereunder and/or pursuant to the terms of any Award
Agreement). 
 (B) In the event of the termination of the Plan and all outstanding Options issued hereunder pursuant to
Section 3(c), each Holder of Options shall be permitted, within a period of time prior to the consummation of the Sale Event as specified by the Committee, to exercise all such Options which are then exercisable or will become exercisable as of
the effective time of the Sale Event; provided, however, that the exercise of Options not exercisable prior to the Sale Event shall be subject to the consummation of the Sale Event. 

(C) Notwithstanding anything to the contrary in Section 3(c)(i)(A), in the event of a Sale Event, the Company shall have
the right, but not the obligation, to make or provide for a cash payment to the Holders of Options, without any consent of the Holders, in exchange for the cancellation thereof, in an amount equal to the difference between (A) the value as
determined by the Committee of the consideration payable per share of Stock pursuant to the Sale Event (the “Sale Price”) times the number of Shares subject to outstanding Options being cancelled (to the extent then vested and exercisable,
including by reason of acceleration in connection with such Sale Event, at prices not in excess of the Sale Price) and (B) the aggregate exercise price of all such outstanding vested and exercisable Options. 

(ii) Restricted Stock and Restricted Stock Unit Awards. 

(A) In the case of and subject to the consummation of a Sale Event, all unvested Restricted Stock and unvested Restricted Stock
Unit Awards (other than those becoming vested as a result of the Sale Event) issued hereunder shall be forfeited immediately prior to the effective time of any such Sale Event unless assumed or continued by the successor entity, or awards of the
successor entity or parent thereof are substituted therefor, with an equitable or proportionate adjustment as to the number and kind of shares subject to such awards as such parties shall agree (after taking into account any acceleration hereunder
and/or pursuant to the terms of any Award Agreement). 

  
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 (B) In the event of the forfeiture of Restricted Stock pursuant to
Section 3(c)(ii)(A), such Restricted Stock shall be repurchased from the Holder thereof at a price per share equal to the original per share purchase price paid by the Holder (subject to adjustment as provided in Section 3(b)) for such
Shares. 
 (C) Notwithstanding anything to the contrary in Section 3(c)(ii)(A), in the event of a Sale Event, the
Company shall have the right, but not the obligation, to make or provide for a cash payment to the Holders of Restricted Stock or Restricted Stock Unit Awards, without consent of the Holders, in exchange for the cancellation thereof, in an amount
equal to the Sale Price times the number of Shares subject to such Awards, to be paid at the time of such Sale Event or upon the later vesting of such Awards. 

SECTION 4. ELIGIBILITY 
 Grantees under
the Plan will be such full or part-time officers and other employees, directors, Consultants and key persons of the Company and any Subsidiary who are selected from time to time by the Committee in its sole discretion; provided, however, that
Awards shall be granted only to those individuals described in Rule 701(c) of the Securities Act. 
 SECTION 5. STOCK OPTIONS 

Upon the grant of a Stock Option, the Company and the grantee shall enter into an Award Agreement. The terms and conditions of each such Award
Agreement shall be determined by the Committee, and such terms and conditions may differ among individual Awards and grantees. 
 Stock
Options granted under the Plan may be either Incentive Stock Options or Non-Qualified Stock Options. Incentive Stock Options may be granted only to employees of the Company or any Subsidiary that is a
“subsidiary corporation” within the meaning of Section 424(f) of the Code. To the extent that any Option does not qualify as an Incentive Stock Option, it shall be deemed a Non-Qualified Stock
Option. 
 (a) Terms of Stock Options. The Committee in its discretion may grant Stock 

Options to those individuals who meet the eligibility requirements of Section 4. Stock Options shall be subject to the following terms and conditions and
shall contain such additional terms and conditions, not inconsistent with the terms of the Plan, as the Committee shall deem desirable. 

(i) Exercise Price. The exercise price per share for the Shares covered by a 

Stock Option shall be determined by the Committee at the time of grant but shall not be less than 100 percent of the Fair Market Value on the Grant Date.
In the case of an Incentive Stock Option that is granted to a Ten Percent Owner, the exercise price per share for the Shares covered by such Incentive Stock Option shall not be less than 110 percent of the Fair Market Value on the Grant Date.


  
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 (ii) Option Term. The term of each Stock Option shall be fixed by the
Committee, but no Stock Option shall be exercisable more than ten years from the Grant Date. In the case of an Incentive Stock Option that is granted to a Ten Percent Owner, the term of such Stock Option shall be no more than five years from the
Grant Date. 
 (iii) Exercisability; Rights of a Stockholder. Stock Options shall become exercisable and/or vested at such time
or times, whether or not in installments, as shall be determined by the Committee at or after the Grant Date. The Award Agreement may permit a grantee to exercise all or a portion of a Stock Option immediately at grant; provided that the Shares
issued upon such exercise shall be subject to restrictions and a vesting schedule identical to the vesting schedule of the related Stock Option, such Shares shall be deemed to be Restricted Stock for purposes of the Plan, and the optionee may be
required to enter into an additional or new Award Agreement as a condition to exercise of such Stock Option. An optionee shall have the rights of a stockholder only as to Shares acquired upon the exercise of a Stock Option and not as to unexercised
Stock Options. An optionee shall not be deemed to have acquired any Shares unless and until a Stock Option shall have been exercised pursuant to the terms of the Award Agreement and this Plan and the optionee’s name has been entered on the
books of the Company as a stockholder. 
 (iv) Method of Exercise. Stock Options may be exercised by an optionee in whole or in
part, by the optionee giving written or electronic notice of exercise to the Company, specifying the number of Shares to be purchased. Payment of the purchase price may be made by one or more of the following methods (or any combination thereof) to
the extent provided in the Award Agreement: 
 (A) In cash, by certified or bank check, by wire transfer of immediately
available funds, or other instrument acceptable to the Committee; 
 (B) If permitted by the Committee, by the optionee
delivering to the Company a promissory note, if the Board has expressly authorized the loan of funds to the optionee for the purpose of enabling or assisting the optionee to effect the exercise of his or her Stock Option; provided, that at
least so much of the exercise price as represents the par value of the Stock shall be paid in cash if required by state law; 

(C) If permitted by the Committee and the Initial Public Offering has occurred (or the Stock otherwise becomes
publicly-traded), through the delivery (or attestation to the ownership) of Shares that have been purchased by the optionee on the open market or that are beneficially owned by the optionee and are not then subject to restrictions under any Company
plan. To the extent required to avoid variable accounting treatment under ASC 718 or other applicable accounting rules, such surrendered Shares if originally purchased from the Company shall have been owned by the optionee for at least six months.
Such surrendered Shares shall be valued at Fair Market Value on the exercise date; 

  
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 (D) If permitted by the Committee and the Initial Public Offering has
occurred (or the Stock otherwise becomes publicly-traded), by the optionee delivering to the Company a properly executed exercise notice together with irrevocable instructions to a broker to promptly deliver to the Company cash or a check payable
and acceptable to the Company for the purchase price; provided that in the event the optionee chooses to pay the purchase price as so provided, the optionee and the broker shall comply with such procedures and enter into such agreements of
indemnity and other agreements as the Committee shall prescribe as a condition of such payment procedure; or 
 (E) If
permitted by the Committee, and only with respect to Stock Options that are not Incentive Stock Options, by a “net exercise” arrangement pursuant to which the Company will reduce the number of Shares issuable upon exercise by the largest
whole number of Shares with a Fair Market Value that does not exceed the aggregate exercise price. 
 Payment instruments will be received
subject to collection. No certificates for Shares so purchased will be issued to the optionee or, with respect to uncertificated Stock, no transfer to the optionee on the records of the Company will take place, until the Company has completed all
steps it has deemed necessary to satisfy legal requirements relating to the issuance and sale of the Shares, which steps may include, without limitation, (i) receipt of a representation from the optionee at the time of exercise of the Option
that the optionee is purchasing the Shares for the optionee’s own account and not with a view to any sale or distribution of the Shares or other representations relating to compliance with applicable law governing the issuance of securities,
(ii) the legending of the certificate (or notation on any book entry) representing the Shares to evidence the foregoing restrictions, and (iii) obtaining from optionee payment or provision for all withholding taxes due as a result of the
exercise of the Option. The delivery of certificates representing the shares of Stock (or the transfer to the optionee on the records of the Company with respect to uncertificated Stock) to be purchased pursuant to the exercise of a Stock Option
will be contingent upon (A) receipt from the optionee (or a purchaser acting in his or her stead in accordance with the provisions of the Stock Option) by the Company of the full purchase price for such Shares and the fulfillment of any other
requirements contained in the Award Agreement or applicable provisions of laws and (B) if required by the Company, the optionee shall have entered into any stockholders agreements or other agreements with the Company and/or certain other of the
Company’s stockholders relating to the Stock. In the event an optionee chooses to pay the purchase price by previously-owned Shares through the attestation method, the number of Shares transferred to the optionee upon the exercise of the Stock
Option shall be net of the number of Shares attested to. 
 (b) Annual Limit on Incentive Stock Options. To the extent required
for “incentive stock option” treatment under Section 422 of the Code, the aggregate Fair Market Value (determined as of the Grant Date) of the Shares with respect to which Incentive Stock Options granted under the Plan and any other
plan of the Company or its parent and any Subsidiary that become exercisable for the first time by an optionee during any calendar year shall not exceed $100,000 or such other limit as may be in effect from time to time under Section 422 of the
Code. To the extent that any Stock Option exceeds this limit, it shall constitute a Non-Qualified Stock Option. 

  
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 (c) Termination. Any portion of a Stock Option that is not vested and
exercisable on the date of termination of an optionee’s Service Relationship shall immediately expire and be null and void. Once any portion of the Stock Option becomes vested and exercisable, the optionee’s right to exercise such portion
of the Stock Option (or the optionee’s representatives and legatees as applicable) in the event of a termination of the optionee’s Service Relationship shall continue until the earliest of: (i) the date which is: (A) 12 months
following the date on which the optionee’s Service Relationship terminates due to death or Disability (or such longer period of time as determined by the Committee and set forth in the applicable Award Agreement), or (B) three months
following the date on which the optionee’s Service Relationship terminates if the termination is due to any reason other than death or Disability (or such longer period of time as determined by the Committee and set forth in the applicable
Award Agreement), or (ii) the Expiration Date set forth in the Award Agreement; provided that notwithstanding the foregoing, an Award Agreement may provide that if the optionee’s Service Relationship is terminated for Cause, the
Stock Option shall terminate immediately and be null and void upon the date of the optionee’s termination and shall not thereafter be exercisable. 

SECTION 6. RESTRICTED STOCK AWARDS 

(a) Nature of Restricted Stock Awards. The Committee may, in its sole discretion, grant (or sell at par value or such other
purchase price determined by the Committee) to an eligible individual under Section 4 hereof a Restricted Stock Award under the Plan. The Committee shall determine the restrictions and conditions applicable to each Restricted Stock Award at the
time of grant. Conditions may be based on continuing employment (or other Service Relationship), achievement of pre-established performance goals and objectives and/or such other criteria as the Committee may
determine. Upon the grant of a Restricted Stock Award, the Company and the grantee shall enter into an Award Agreement. The terms and conditions of each such Award Agreement shall be determined by the Committee, and such terms and conditions may
differ among individual Awards and grantees. 
 (b) Rights as a Stockholder. Upon the grant of the Restricted Stock Award and
payment of any applicable purchase price, a grantee of Restricted Stock shall be considered the record owner of and shall be entitled to vote the Restricted Stock if, and to the extent, such Shares are entitled to voting rights, subject to such
conditions contained in the Award Agreement. The grantee shall be entitled to receive all dividends and any other distributions declared on the Shares; provided, however, that the Company is under no duty to declare any such dividends or to
make any such distribution. Unless the Committee shall otherwise determine, certificates evidencing the Restricted Stock shall remain in the possession of the Company until such Restricted Stock is vested as provided in subsection (d) below of
this Section, and the grantee shall be required, as a condition of the grant, to deliver to the Company a stock power endorsed in blank and such other instruments of transfer as the Committee may prescribe. 

(c) Restrictions. Restricted Stock may not be sold, assigned, transferred, pledged or otherwise encumbered or disposed of except
as specifically provided herein or in the Award Agreement. Except as may otherwise be provided by the Committee either in the Award Agreement or, subject to Section 12 below, in writing after the Award Agreement is issued, if a grantee’s
Service Relationship with the Company and any Subsidiary terminates, the Company or its assigns shall have the right, as may be specified in the relevant instrument, to repurchase some or all of the Shares subject to the Award at such purchase price
as is set forth in the Award Agreement. 

  
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 (d) Vesting of Restricted Stock. The Committee at the time of grant shall
specify in the Award Agreement the date or dates and/or the attainment of pre-established performance goals, objectives and other conditions on which the substantial risk of forfeiture imposed shall lapse and
the Restricted Stock shall become vested, subject to such further rights of the Company or its assigns as may be specified in the Award Agreement. 

SECTION 7. UNRESTRICTED STOCK AWARDS 
 The
Committee may, in its sole discretion, grant (or sell at par value or such other purchase price determined by the Committee) to an eligible person under Section 4 hereof an Unrestricted Stock Award under the Plan. Unrestricted Stock Awards may
be granted in respect of past services or other valid consideration, or in lieu of cash compensation due to such grantee. 
 SECTION 8. RESTRICTED STOCK
UNITS 
 (a) Nature of Restricted Stock Units. The Committee may, in its sole discretion, grant to an eligible person under
Section 4 hereof Restricted Stock Units under the Plan. The Committee shall determine the restrictions and conditions applicable to each Restricted Stock Unit at the time of grant. Vesting conditions may be based on continuing employment (or
other Service Relationship), achievement of pre-established performance goals and objectives and/or other such criteria as the Committee may determine. Upon the grant of Restricted Stock Units, the grantee and
the Company shall enter into an Award Agreement. The terms and conditions of each such Award Agreement shall be determined by the Committee and may differ among individual Awards and grantees. On or promptly following the vesting date or dates
applicable to any Restricted Stock Unit, but in no event later than March 15 of the year following the year in which such vesting occurs, such Restricted Stock Unit(s) shall be settled in the form of cash or shares of Stock, as specified in the
Award Agreement. Restricted Stock Units may not be sold, assigned, transferred, pledged, or otherwise encumbered or disposed of. 

(b) Rights as a Stockholder. A grantee shall have the rights of a stockholder only as to Shares, if any, acquired upon settlement
of Restricted Stock Units. A grantee shall not be deemed to have acquired any such Shares unless and until the Restricted Stock Units shall have been settled in Shares pursuant to the terms of the Plan and the Award Agreement, the Company shall have
issued and delivered a certificate representing the Shares to the grantee (or transferred on the records of the Company with respect to uncertificated stock), and the grantee’s name has been entered in the books of the Company as a stockholder.

 (c) Termination. Except as may otherwise be provided by the Committee either in the Award Agreement or in writing after the
Award Agreement is issued, a grantee’s right in all Restricted Stock Units that have not vested shall automatically terminate upon the grantee’s cessation of Service Relationship with the Company and any Subsidiary for any reason. 

  
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 SECTION 9. TRANSFER RESTRICTIONS; COMPANY RIGHT OF FIRST REFUSAL; COMPANY REPURCHASE RIGHTS 

(a) Restrictions on Transfer. 

(i) Non-Transferability of Stock Options. Stock Options and, prior to exercise, the
Shares issuable upon exercise of such Stock Option, shall not be transferable by the optionee otherwise than by will, or by the laws of descent and distribution, and all Stock Options shall be exercisable, during the optionee’s lifetime, only
by the optionee, or by the optionee’s legal representative or guardian in the event of the optionee’s incapacity. Notwithstanding the foregoing, the Committee, in its sole discretion, may provide in the Award Agreement regarding a given
Stock Option that the optionee may transfer by gift, without consideration for the transfer, his or her Non-Qualified Stock Options to his or her family members (as defined in Rule 701 of the Securities Act),
to trusts for the benefit of such family members, or to partnerships in which such family members are the only partners (to the extent such trusts or partnerships are considered “family members” for purposes of Rule 701 of the Securities
Act), provided that the transferee agrees in writing with the Company to be bound by all of the terms and conditions of this Plan and the applicable Award Agreement, including the execution of a stock power upon the issuance of Shares. Stock
Options, and the Shares issuable upon exercise of such Stock Options, shall be restricted as to any pledge, hypothecation, or other transfer, including any short position, any “put equivalent position” (as defined in the Exchange Act) or
any “call equivalent position” (as defined in the Exchange Act) prior to exercise. 
 (ii) Shares. No Shares shall be
sold, assigned, transferred, pledged, hypothecated, given away or in any other manner disposed of or encumbered, whether voluntarily or by operation of law, unless (i) the transfer is in compliance with the terms of the applicable Award
Agreement, all applicable securities laws (including, without limitation, the Securities Act), and with the terms and conditions of this Section 9, (ii) the transfer does not cause the Company to become subject to the reporting requirements of
the Exchange Act, and 
 (iii) the transferee consents in writing to be bound by the provisions of the Plan and the Award Agreement,
including this Section 9. In connection with any proposed transfer, the Committee may require the transferor to provide at the transferor’s own expense an opinion of counsel to the transferor, satisfactory to the Committee, that such
transfer is in compliance with all foreign, federal and state securities laws (including, without limitation, the Securities Act). Any attempted transfer of Shares not in accordance with the terms and conditions of this Section 9 shall be null
and void, and the Company shall not reflect on its records any change in record ownership of any Shares as a result of any such transfer, shall otherwise refuse to recognize any such transfer and shall not in any way give effect to any such transfer
of Shares. The Company shall be entitled to seek protective orders, injunctive relief and other remedies available at law or in equity including, without limitation, seeking specific performance or the rescission of any transfer not made in strict
compliance with the provisions of this Section 9. Subject to the foregoing general provisions, and unless otherwise provided in the applicable Award Agreement, Shares may be transferred pursuant to the following specific terms and conditions
(provided that with respect to any transfer of Restricted Stock, all vesting and forfeiture provisions shall continue to apply with respect to the original recipient): 

  
 13 













 (A) Transfers to Permitted Transferees. The Holder may
transfer any or all of the Shares to one or more Permitted Transferees; provided, however, that following such transfer, such Shares shall continue to be subject to the terms of this Plan (including this Section 9) and such Permitted
Transferee(s) shall, as a condition to any such transfer, deliver a written acknowledgment to that effect to the Company and shall deliver a stock power to the Company with respect to the Shares. Notwithstanding the foregoing, the Holder may not
transfer any of the Shares to a Person whom the Company reasonably determines is a direct competitor or a potential competitor of the Company or any of its Subsidiaries. 

(B) Transfers Upon Death. Upon the death of the Holder, any Shares then held by the Holder at the time of such
death and any Shares acquired after the Holder’s death by the Holder’s legal representative shall be subject to the provisions of this Plan, and the Holder’s estate, executors, administrators, personal representatives, heirs, legatees
and distributees shall be obligated to convey such Shares to the Company or its assigns under the terms contemplated by the Plan and the Award Agreement. 

(b) Right of First Refusal. In the event that a Holder desires at any time to sell or otherwise transfer all or any part of his or her
Shares (other than shares of Restricted Stock which by their terms are not transferrable), the Holder first shall give written notice to the Company of the Holder’s intention to make such transfer. Such notice shall state the number of Shares
that the Holder proposes to sell (the “Offered Shares”), the price and the terms at which the proposed sale is to be made and the name and address of the proposed transferee. At any time within 30 days after the receipt of such notice by
the Company, the Company or its assigns may elect to purchase all or any portion of the Offered Shares at the price and on the terms offered by the proposed transferee and specified in the notice. The Company or its assigns shall exercise this right
by mailing or delivering written notice to the Holder within the foregoing 30-day period. If the Company or its assigns elect to exercise its purchase rights under this Section 9(b), the closing for such
purchase shall, in any event, take place within 45 days after the receipt by the Company of the initial notice from the Holder. In the event that the Company or its assigns do not elect to exercise such purchase right, or in the event that the
Company or its assigns do not pay the full purchase price within such 45-day period, the Holder shall be required to pay a transaction processing fee of $10,000 to the Company (unless waived by the Committee)
and then may, within 60 days thereafter, sell the Offered Shares to the proposed transferee and at the same price and on the same terms as specified in the Holder’s notice. Any Shares not sold to the proposed transferee shall remain subject to
the Plan. If the Holder is a party to any stockholders agreements or other agreements with the Company and/or certain other of the Company’s stockholders relating to the Shares, (i) the transferring Holder shall comply with the
requirements of such stockholders agreements or other agreements relating to any proposed transfer of the Offered Shares, and (ii) any proposed transferee that purchases Offered Shares shall enter into such stockholders agreements or other
agreements with the Company and/or certain of the Company’s stockholders relating to the Offered Shares on the same terms and in the same capacity as the transferring Holder. 

  
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 (c) Company’s Right of Repurchase. 

(i) Right of Repurchase for Unvested Shares Issued Upon the Exercise of an Option. Upon a Termination Event, the Company or its
assigns shall have the right and option to repurchase from a Holder of Shares acquired upon exercise of a Stock Option which are still subject to a risk of forfeiture as of the Termination Event. Such repurchase rights may be exercised by the
Company within the later of (A) six months following the date of such Termination Event or (B) seven months after the acquisition of Shares upon exercise of a Stock Option. The repurchase price shall be equal to the lower of the original
per share price paid by the Holder, subject to adjustment as provided in Section 3(b) of the Plan, or the current Fair Market Value of such Shares as of the date the Company elects to exercise its repurchase rights. 

(ii) Right of Repurchase With Respect to Restricted Stock. Upon a Termination Event, the Company or its assigns shall have the
right and option to repurchase from a Holder of Shares received pursuant to a Restricted Stock Award any Shares that are still subject to a risk of forfeiture as of the Termination Event. Such repurchase right may be exercised by the Company within
six months following the date of such Termination Event. The repurchase price shall be the lower of the original per share purchase price paid by the Holder, subject to adjustment as provided in Section 3(b) of the Plan, or the current Fair
Market Value of such Shares as of the date the Company elects to exercise its repurchase rights. 
 (iii) Procedure. Any
repurchase right of the Company shall be exercised by the Company or its assigns by giving the Holder written notice on or before the last day of the repurchase period of its intention to exercise such repurchase right. Upon such notification, the
Holder shall promptly surrender to the Company, free and clear of any liens or encumbrances, any certificates representing the Shares being purchased, together with a duly executed stock power for the transfer of such Shares to the Company or the
Company’s assignee or assignees. Upon the Company’s or its assignee’s receipt of the certificates from the Holder, the Company or its assignee or assignees shall deliver to him, her or them a check for the applicable repurchase price;
provided, however, that the Company may pay the repurchase price by offsetting and canceling any indebtedness then owed by the Holder to the Company. 

(d) Reserved. 
 (e)
Escrow Arrangement. 
 (i) Escrow. In order to carry out the provisions of this Section 9 of this Plan more effectively,
the Company shall hold any Shares issued pursuant to Awards granted under the Plan in escrow together with separate stock powers executed by the Holder in blank for transfer. The Company shall not dispose of the Shares except as otherwise provided
in this Plan. In the event of any repurchase by the Company (or any of its assigns), the Company is hereby authorized by the Holder, as the Holder’s
attorney-in-fact, to date and complete the stock powers necessary for the transfer of the Shares being purchased and to transfer such Shares in accordance with the terms
hereof. At such time as any Shares are no longer subject to the Company’s repurchase and first refusal rights, the Company shall, at the written request of the Holder, deliver to the Holder a certificate representing such Shares with the
balance of the Shares to be held in escrow pursuant to this Section. 

  
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 (ii) Remedy. Without limitation of any other provision of this Plan or other rights,
in the event that a Holder or any other Person is required to sell a Holder’s Shares pursuant to the provisions of Sections 9(b) or (c) hereof and in the further event that he or she refuses or for any reason fails to deliver to the
Company or its designated purchaser of such Shares the certificate or certificates evidencing such Shares together with a related stock power, the Company or such designated purchaser may deposit the applicable purchase price for such Shares with a
bank designated by the Company, or with the Company’s independent public accounting firm, as agent or trustee, or in escrow, for such Holder or other Person, to be held by such bank or accounting firm for the benefit of and for delivery to him,
her, them or it, and/or, in its discretion, pay such purchase price by offsetting any indebtedness then owed by such Holder as provided above. Upon any such deposit and/or offset by the Company or its designated purchaser of such amount and upon
notice to the Person who was required to sell the Shares to be sold pursuant to the provisions of Sections 9(b) or (c), such Shares shall at such time be deemed to have been sold, assigned, transferred and conveyed to such purchaser, such Holder
shall have no further rights thereto (other than the right to withdraw the payment thereof held in escrow, if applicable), and the Company shall record such transfer in its stock transfer book or in any appropriate manner. 

(f) Lockup Provision. If requested by the Company, a Holder shall not sell or otherwise transfer or dispose of any Shares
(including, without limitation, pursuant to Rule 144 under the Securities Act) held by him or her for such period following the effective date of a public offering by the Company of Shares as the Company shall specify reasonably and in good faith.
If requested by the underwriter engaged by the Company, each Holder shall execute a separate letter confirming his or her agreement to comply with this Section. 

(g) Adjustments for Changes in Capital Structure. If, as a result of any reorganization, recapitalization, reclassification,
stock dividend, stock split, reverse stock split or other similar change in the Common Stock, the outstanding Shares are increased or decreased or are exchanged for a different number or kind of securities of the Company, the restrictions contained
in this Section 9 shall apply with equal force to additional and/or substitute securities, if any, received by Holder in exchange for, or by virtue of his or her ownership of, Shares. 

(h) Termination. The terms and provisions of Section 9(b) and Section 9(c) (except for the Company’s right to
repurchase Shares still subject to a risk of forfeiture upon a Termination Event) shall terminate upon the closing of the Company’s Initial Public Offering or upon consummation of any Sale Event, in either case as a result of which Shares are
registered under Section 12 of the Exchange Act and publicly-traded on any national security exchange. 
 SECTION 10. TAX WITHHOLDING 

(a) Payment by Grantee. Each grantee shall, no later than the date as of which the value of an Award or of any Shares or other amounts
received thereunder first becomes includable in the gross income of the grantee for income tax purposes, pay to the Company, or make arrangements satisfactory to the Committee regarding payment of, any Federal, state, or local taxes of any kind
required by law to be withheld by the Company with respect to such income. The Company and any Subsidiary shall, to the extent permitted by law, have the right to deduct any such taxes from any payment of any kind otherwise due to the grantee. The
Company’s obligation to deliver stock certificates (or evidence of book entry) to any grantee is subject to and conditioned on any such tax withholding obligations being satisfied by the grantee. 

  
 16 













 (b) Payment in Stock. The Company’s minimum required tax withholding obligation
may be satisfied, in whole or in part, by the Company withholding from Shares to be issued pursuant to an Award a number of Shares having an aggregate Fair Market Value (as of the date the withholding is effected) that would satisfy the minimum
withholding amount due. 
 SECTION 11. SECTION 409A AWARDS.  

To the extent that any Award is determined to constitute “nonqualified deferred compensation” within the meaning of Section 409A
(a “409A Award”), the Award shall be subject to such additional rules and requirements as may be specified by the Committee from time to time. In this regard, if any amount under a 409A Award is payable upon a “separation from
service” (within the meaning of Section 409A) to a grantee who is considered a “specified employee” (within the meaning of Section 409A), then no such payment shall be made prior to the date that is the earlier of
(i) six months and one day after the grantee’s separation from service, or (ii) the grantee’s death, but only to the extent such delay is necessary to prevent such payment from being subject to interest, penalties and/or
additional tax imposed pursuant to Section 409A. The Company makes no representation or warranty and shall have no liability to any grantee under the Plan or any other Person with respect to any penalties or taxes under Section 409A that
are, or may be, imposed with respect to any Award. 
 SECTION 12. AMENDMENTS AND TERMINATION 

The Board may, at any time, amend or discontinue the Plan and the Committee may, at any time, amend or cancel any outstanding Award for the
purpose of satisfying changes in law or for any other lawful purpose, but no such action shall adversely affect rights under any outstanding Award without the consent of the holder of the Award. The Committee may exercise its discretion to reduce
the exercise price of outstanding Stock Options or effect repricing through cancellation of outstanding Stock Options and by granting such holders new Awards in replacement of the cancelled Stock Options. To the extent determined by the Committee to
be required either by the Code to ensure that Incentive Stock Options granted under the Plan are qualified under Section 422 of the Code or otherwise, Plan amendments shall be subject to approval by the Company stockholders entitled to vote at
a meeting of stockholders. Nothing in this Section 12 shall limit the Board’s or Committee’s authority to take any action permitted pursuant to Section 3(c). The Board reserves the right to amend the Plan and/or the terms of any
outstanding Stock Options to the extent reasonably necessary to comply with the requirements of the exemption pursuant to paragraph (f)(4) of Rule 12h-1 of the Exchange Act. 

SECTION 13. STATUS OF PLAN 
 With respect
to the portion of any Award that has not been exercised and any payments in cash, Stock or other consideration not received by a grantee, a grantee shall have no rights greater than those of a general creditor of the Company unless the Committee
shall otherwise expressly so determine in connection with any Award. 

  
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 SECTION 14. GENERAL PROVISIONS 

(a) No Distribution; Compliance with Legal Requirements. The Committee may require each person acquiring Shares pursuant to an
Award to represent to and agree with the Company in writing that such person is acquiring the Shares without a view to distribution thereof. No Shares shall be issued pursuant to an Award until all applicable securities law and other legal and stock
exchange or similar requirements have been satisfied. The Committee may require the placing of such stop-orders and restrictive legends on certificates for Stock and Awards as it deems appropriate. 

(b) Delivery of Stock Certificates. Stock certificates to grantees under the Plan shall be deemed delivered for all purposes when
the Company or a stock transfer agent of the Company shall have mailed such certificates in the United States mail, addressed to the grantee, at the grantee’s last known address on file with the Company; provided that stock certificates to be
held in escrow pursuant to Section 9 of the Plan shall be deemed delivered when the Company shall have recorded the issuance in its records. Uncertificated Stock shall be deemed delivered for all purposes when the Company or a stock transfer
agent of the Company shall have given to the grantee by electronic mail (with proof of receipt) or by United States mail, addressed to the grantee, at the grantee’s last known address on file with the Company, notice of issuance and recorded
the issuance in its records (which may include electronic “book entry” records). 
 (c) No Employment
Rights. The adoption of the Plan and the grant of Awards do not confer upon any Person any right to continued employment or Service Relationship with the Company or any Subsidiary. 

(d) Trading Policy Restrictions. Option exercises and other Awards under the Plan shall be subject to the Company’s insider
trading policy-related restrictions, terms and conditions as may be established by the Committee, or in accordance with policies set by the Committee, from time to time. 

(e) Designation of Beneficiary. Each grantee to whom an Award has been made under the Plan may designate a beneficiary or
beneficiaries to exercise any Award on or after the grantee’s death or receive any payment under any Award payable on or after the grantee’s death. Any such designation shall be on a form provided for that purpose by the Committee and
shall not be effective until received by the Committee. If no beneficiary has been designated by a deceased grantee, or if the designated beneficiaries have predeceased the grantee, the beneficiary shall be the grantee’s estate. 

(f) Legend. Any certificate(s) representing the Shares shall carry substantially the following legend (and with respect to
uncertificated Stock, the book entries evidencing such shares shall contain the following notation): 
 The transferability of this
certificate and the shares of stock represented hereby are subject to the restrictions, terms and conditions (including repurchase and restrictions against transfers) contained in the Checkmate Pharmaceuticals, Inc. 2015 Stock Option and Grant Plan
and any agreements entered into thereunder by and between the company and the holder of this certificate (a copy of which is available at the offices of the company for examination). 

  
 18 













 (g) Information to Holders of Options. In the event the Company is relying on the
exemption from the registration requirements of Section 12(g) of the Exchange Act contained in paragraph (f)(1) of Rule 12h-1 of the Exchange Act, the Company shall provide the information described in
Rule 701(e)(3), (4) and (5) of the Securities Act to all holders of Options in accordance with the requirements thereunder. The foregoing notwithstanding, the Company shall not be required to provide such information unless the optionholder has
agreed in writing, on a form prescribed by the Company, to keep such information confidential. 
 SECTION 15. EFFECTIVE DATE OF PLAN 

The Plan shall become effective upon adoption by the Board and shall be approved by stockholders in accordance with applicable state law and
the Company’s articles of incorporation and bylaws within 12 months thereafter. If the stockholders fail to approve the Plan within 12 months after its adoption by the Board of Directors, then any Awards granted or sold under the Plan shall be
rescinded and no additional grants or sales shall thereafter be made under the Plan. Subject to such approval by stockholders and to the requirement that no Shares may be issued hereunder prior to such approval, Stock Options and other Awards may be
granted hereunder on and after adoption of the Plan by the Board. No grants of Stock Options and other Awards may be made hereunder after the tenth anniversary of the date the Plan is adopted by the Board or the date the Plan is approved by the
Company’s stockholders, whichever is earlier. 
 SECTION 16. GOVERNING LAW 

This Plan, all Awards and any controversy arising out of or relating to this Plan and all Awards shall be governed by and construed in
accordance with the General Corporation Law of the State of Delaware as to matters within the scope thereof, and as to all other matters shall be governed by and construed in accordance with the internal laws of the Commonwealth of Massachusetts,
without regard to conflict of law principles that would result in the application of any law other than the law of the Commonwealth of Massachusetts. 

DATE ADOPTED BY THE BOARD OF DIRECTORS: August 10, 2015 

DATE APPROVED BY THE STOCKHOLDERS: August 10, 2015 












 CHECKMATE PHARMACEUTICALS, INC. 

AMENDMENT NO. 1 TO 2015 STOCK OPTION AND
GRANT PLAN 
 This Amendment to the Checkmate Pharmaceuticals, Inc. 2015 Stock Option and Grant Plan,
attached hereto as Exhibit A, (the “Plan”) is effective as of May 1, 2018. 
 1. Section 5(a)(i) of the Plan is hereby amended by
deleting it in its entirety and replacing such section with the following: 
 “Exercise Price. The exercise price per share for
the Shares covered by a Stock Option shall be determined by the Committee at the time of grant but shall not be less than 100 percent of the Fair Market Value on the Grant Date; provided, that the exercise price may be less than Fair Market
Value, if the terms of such Option comply with the requirements of Section 409A of the Code or granted to a Consultant to whom Section 409A of the Code does not apply. In the case of an Incentive Stock Option that is granted to a Ten
Percent Owner, the exercise price per share for the Shares covered by such Incentive Stock Option shall not be less than 110 percent of the Fair Market Value on the Grant Date.” 

2. Except as expressly amended hereby, the Plan shall remain in full force and effect. 

IN WITNESS WHEREOF, the Chief Executive Officer of Checkmate Pharmaceuticals, Inc. has duly executed this Amendment to be effective as the
date first above written. 
  

			
	CHECKMATE PHARMACEUTICALS, INC.
		
	By:	 	 /s/ Arthur Krieg

	Name:	 	Arthur Krieg
	Title:	 	Chief Executive Officer














 CHECKMATE PHARMACEUTICALS, INC. 

AMENDMENT NO. 2 TO 2015 STOCK OPTION AND
GRANT PLAN 
 This Amendment to the Checkmate Pharmaceuticals, Inc. 2015 Stock Option and Grant Plan,
attached hereto as Exhibit A (the “Plan”), is effective as of November 28, 2018. 
 1. Section 3(a) of the Plan is hereby amended by
deleting it in its entirety and replacing such section with the following: 
 Stock Issuable. The maximum number of Shares reserved
and available for issuance under the Plan shall be 10,972,938 Shares, subject to adjustment as provided in Section 3(b). For purposes of this limitation, the Shares underlying any Awards that are forfeited, canceled, reacquired by the Company
prior to vesting, satisfied without the issuance of Stock or otherwise terminated (other than by exercise) and Shares that are withheld upon exercise of an Option or settlement of an Award to cover the exercise price or tax withholding shall be
added back to the Shares available for issuance under the Plan. Subject to such overall limitations, Shares may be issued up to such maximum number pursuant to any type or types of Award, and no more than 10,000,000 Shares may be issued pursuant to
Incentive Stock Options. The Shares available for issuance under the Plan may be authorized but unissued Shares or Shares reacquired by the Company. Beginning on the date that the Company becomes subject to Section 162(m) of the Code, Options
with respect to no more than 10,000,000 Shares shall be granted to any one individual in any calendar year period. 
 2. Except as expressly amended hereby,
the Plan shall remain in full force and effect. 
 IN WITNESS WHEREOF, the Chief Executive Officer of Checkmate Pharmaceuticals, Inc. has
duly executed this Amendment to be effective as the date first above written. 
 [Remainder of Page Intentionally Left Blank; Signature
Page Follows 
  

			
	CHECKMATE PHARMACEUTICALS, INC.
		
	By:	 	 /s/ Arthur Krieg

	Name:	 	Arthur Krieg
	Title:	 	Chief Executive Officer














 CHECKMATE PHARMACEUTICALS, INC. 

AMENDMENT NO. 3 TO 2015 STOCK OPTION AND
GRANT PLAN 
 This Amendment to the Checkmate Pharmaceuticals, Inc. 2015 Stock Option and Grant Plan,
attached hereto as Exhibit A, (the “Plan”) is effective as of June 9, 2020. 
 3. Section 3(a) of the Plan is hereby amended by
deleting it in its entirety and replacing such section with the following: 
 Stock Issuable. The maximum number of Shares reserved
and available for issuance under the Plan shall be 13,059,889 Shares, subject to adjustment as provided in Section 3(b). For purposes of this limitation, the Shares underlying any Awards that are forfeited, canceled, reacquired by the Company
prior to vesting, satisfied without the issuance of Stock or otherwise terminated (other than by exercise) and Shares that are withheld upon exercise of an Option or settlement of an Award to cover the exercise price or tax withholding shall be
added back to the Shares available for issuance under the Plan. Subject to such overall limitations, Shares may be issued up to such maximum number pursuant to any type or types of Award, and no more than 10,000,000 Shares may be issued pursuant to
Incentive Stock Options. The Shares available for issuance under the Plan may be authorized but unissued Shares or Shares reacquired by the Company. Beginning on the date that the Company becomes subject to Section 162(m) of the Code, Options
with respect to no more than 10,000,000 Shares shall be granted to any one individual in any calendar year period. 
 4. Except as expressly amended hereby,
the Plan shall remain in full force and effect. 












 CHECKMATE PHARMACEUTICALS, INC. 

AMENDMENT NO. 4 TO 2015 STOCK OPTION AND
GRANT PLAN 
 This Amendment to the Checkmate Pharmaceuticals, Inc. 2015 Stock Option and Grant Plan,
attached hereto as Exhibit A, (the “Plan”) is effective as of June 16, 2020. 
 5. Section 3(a) of the Plan is hereby amended by
deleting it in its entirety and replacing such section with the following: 
 Stock Issuable. The maximum number of Shares reserved
and available for issuance under the Plan shall be 15,146,840 Shares, subject to adjustment as provided in Section 3(b). For purposes of this limitation, the Shares underlying any Awards that are forfeited, canceled, reacquired by the Company
prior to vesting, satisfied without the issuance of Stock or otherwise terminated (other than by exercise) and Shares that are withheld upon exercise of an Option or settlement of an Award to cover the exercise price or tax withholding shall be
added back to the Shares available for issuance under the Plan. Subject to such overall limitations, Shares may be issued up to such maximum number pursuant to any type or types of Award, and no more than 10,000,000 Shares may be issued pursuant to
Incentive Stock Options. The Shares available for issuance under the Plan may be authorized but unissued Shares or Shares reacquired by the Company. Beginning on the date that the Company becomes subject to Section 162(m) of the Code, Options
with respect to no more than 10,000,000 Shares shall be granted to any one individual in any calendar year period. 
 6. Except as expressly amended hereby,
the Plan shall remain in full force and effect.