EX-4.3





 Exhibit 4.3 

Description of the Registrant’s Securities 

Registered Pursuant to Section 12 of the Securities Exchange Act of 1934, as amended 

The summary of the general terms and provisions of the registered securities of Checkmate Pharmaceuticals, Inc. (“Checkmate,”
“we,” or “our”) set forth below does not purport to be complete and is subject to and qualified in its entirety by reference to our Fourth Amended and Restated Certificate of Incorporation (our “certificate of
incorporation”) and our Second Amended and Restated By-laws (our “by-laws” and, together with our certificate of incorporation, our “Charter
Documents”), each of which is incorporated by reference as an exhibit to our most recent Annual Report on Form 10-K filed with the Securities and Exchange Commission. We encourage you to read our Charter
Documents and the applicable provisions of the General Corporation Law of the State of Delaware (the “DGCL”) for additional information. 

Authorized capital stock 
 Our authorized capital stock
will consist of 300,000,000 shares of common stock, par value $0.0001 per share, and 10,000,000 shares of preferred stock, par value $0.0001 per share, all of which shares of preferred stock will be undesignated. 

Common stock 
 The holders of our common stock are
entitled to one vote for each share held on all matters submitted to a vote of the stockholders. The holders of our common stock do not have any cumulative voting rights. Holders of our common stock are entitled to receive ratably any dividends
declared by our board of directors out of funds legally available for that purpose, subject to any preferential dividend rights of any outstanding convertible preferred stock. Our common stock has no preemptive rights, conversion rights or other
subscription rights or redemption or sinking fund provisions. 
 In the event of our liquidation, dissolution or winding up, holders of our common stock
will be entitled to share ratably in all assets remaining after payment of all debts and other liabilities and any liquidation preference of any outstanding convertible preferred stock. The shares to be issued by us in this offering will be, when
issued and paid for, validly issued, fully paid and non-assessable. The rights, preferences and privileges of holders of common stock are subject to and may be adversely affected by the rights of the holders
of shares of any series of preferred stock that we may designate and issue in the future. 
 Preferred stock 

Our board of directors has the authority, without further action by our stockholders, to issue up to 10,000,000 shares of preferred stock in one or more series
and to fix the rights, preferences, privileges and restrictions thereof. These rights, preferences and privileges could include dividend rights, conversion rights, voting rights, terms of redemption, liquidation preferences, sinking fund terms and
the number of shares constituting, or the designation of, such series, any or all of which may be greater than the rights of common stock. The issuance of our preferred stock could adversely affect the voting power of holders of common stock and the
likelihood that such holders will receive dividend payments and payments upon our liquidation. In addition, the issuance of preferred stock could have the effect of delaying, deferring or preventing a change in control of our company or other
corporate action. 
 Registration rights 
 Certain
holders of our common stock are entitled to rights with respect to the registration of these securities under the Securities Act. These rights are provided under the terms of an amended and restated investors’ rights agreement between us and
holders of our convertible preferred stock. The amended and restated investors’ rights agreement includes demand registration rights, short-form registration rights and piggyback registration rights. All fees, costs and expenses of underwritten
registrations under this agreement will be borne by us and all selling expenses, including underwriting discounts and selling commissions, will be borne by the holders of the shares being registered. 












 Demand registration rights 

Certain holders of our common stock are entitled to demand registration rights. Under the terms of the amended and restated investors’ rights agreement,
we will be required, upon the written request of a majority of the holders of convertible preferred stock, to file a registration statement and use best efforts to effect the registration of all or a portion of these shares for public resale at
an aggregate price of at least $5.0 million. We are required to effect only two registrations pursuant to this provision of the amended and restated investors’ rights agreement. 

Short-Form registration rights 
 Pursuant to the
amended and restated investors’ rights agreement, if we are eligible to file a registration statement on Form S-3, upon the written request of at least 10% of these holders to sell registrable
securities at an aggregate price of at least $1.0 million, we will be required to use best efforts to effect a registration of such shares. We are required to effect only two registrations in any twelve-month period pursuant to this provision
of the investors’ rights agreement. The right to have such shares registered on Form S-3 is further subject to other specified conditions and limitations. 

Piggyback registration rights 
 Pursuant to the
amended and restated investors’ rights agreement, if we register any of our securities either for our own account or for the account of other security holders, the holders of these shares are entitled to include their shares in the
registration. Subject to certain exceptions contained in the amended and restated investors’ rights agreement, we and the underwriters may terminate or withdraw any registration initiated before the effective date of such registration in our
sole discretion. 
 Indemnification 
 Our amended
and restated investors’ rights agreement contains customary cross-indemnification provisions, under which we are obligated to indemnify holders of registrable securities in the event of material misstatements or omissions in the registration
statement attributable to us, and they are obligated to indemnify us for material misstatements or omissions attributable to them. 
 Expiration of
registration rights 
 The demand registration rights and short form registration rights granted under the investors’ rights agreement will
terminate on the fifth anniversary of the completion of this offering or at such time after this offering when the holders’ shares may be sold without restriction pursuant to Rule 144 within a three-month period. 

Anti-Takeover effects of our certificate of incorporation and bylaws and Delaware law 

Our certificate of incorporation and bylaws include a number of provisions that may have the effect of delaying, deferring or preventing another party from
acquiring control of us and encouraging persons considering unsolicited tender offers or other unilateral takeover proposals to negotiate with our board of directors rather than pursue non-negotiated takeover
attempts. These provisions include the items described below. 
 Board composition and filling vacancies 

Our certificate of incorporation provides for the division of our board of directors into three classes serving staggered three-year terms, with one class
being elected each year. Our certificate of incorporation also provides that directors may be removed only for cause and then only by the affirmative vote of the holders of 66 2/3% or more of the shares then entitled to vote at an election of
directors. Furthermore, any vacancy on our board of directors, however occurring, including a vacancy resulting from an increase in the size of our board, may only be filled by the affirmative vote of
two-thirds of our directors then in office even if less than a quorum. The classification of directors, together with the limitations on removal of directors and treatment of vacancies, has the effect of
making it more difficult for stockholders to change the composition of our board of directors. 












 No written consent of stockholders 

Our certificate of incorporation provides that all stockholder actions are required to be taken by a vote of the stockholders at an annual or special meeting,
and that stockholders may not take any action by written consent in lieu of a meeting. This limit may lengthen the amount of time required to take stockholder actions and would prevent the amendment of our bylaws or removal of directors by our
stockholders without holding a meeting of stockholders. 
 Meetings of stockholders 

Our certificate of incorporation and bylaws provide that only a majority of the members of our board of directors then in office may call special meetings of
stockholders and only those matters set forth in the notice of the special meeting may be considered or acted upon at a special meeting of stockholders. Our bylaws limit the business that may be conducted at an annual meeting of stockholders to
those matters properly brought before the meeting. 
 Advance notice requirements 

Our bylaws establish advance notice procedures with regard to stockholder proposals relating to the nomination of candidates for election as directors or new
business to be brought before meetings of our stockholders. These procedures provide that notice of stockholder proposals must be timely given in writing to our corporate secretary prior to the meeting at which the action is to be taken. Generally,
to be timely, notice must be received at our principal executive offices not less than 90 days nor more than 120 days prior to the first anniversary date of the annual meeting for the preceding year. Our bylaws specify the requirements as
to form and content of all stockholders’ notices. These requirements may preclude stockholders from bringing matters before the stockholders at an annual or special meeting. 

Amendment to certificate of incorporation and bylaws 

Any amendment of our certificate of incorporation must first be approved by a majority of our board of directors, and if required by law or our certificate of
incorporation, must thereafter be approved by a majority of the outstanding shares entitled to vote on the amendment and a majority of the outstanding shares of each class entitled to vote thereon as a class, except that the amendment of the
provisions relating to stockholder action, board composition, limitation of liability and certificate of incorporation must be approved by not less than two-thirds of the outstanding shares entitled to vote on
the amendment, and not less than 66 2/3% of the outstanding shares of each class entitled to vote thereon as a class. Our bylaws may be amended by the affirmative vote of a majority of the directors then in office, subject to any limitations set
forth in the bylaws; and may also be amended by the affirmative vote of a majority of the outstanding shares entitled to vote on the amendment. 

Undesignated preferred stock 
 Our certificate of
incorporation provides for 10,000,000 authorized shares of preferred stock. The existence of authorized but unissued shares of preferred stock may enable our board of directors to discourage an attempt to obtain control of us by means of a merger,
tender offer, proxy contest or otherwise. For example, if in the due exercise of its fiduciary obligations, our board of directors were to determine that a takeover proposal is not in the best interests of our stockholders, our board of directors
could cause shares of preferred stock to be issued without stockholder approval in one or more private offerings or other transactions that might dilute the voting or other rights of the proposed acquirer or insurgent stockholder or stockholder
group. In this regard, our certificate of incorporation grants our board of directors broad power to establish the rights and preferences of authorized and unissued shares of preferred stock. The issuance of shares of preferred stock could decrease
the amount of earnings and assets available for distribution to holders of shares of common stock. The issuance may also adversely affect the rights and powers, including voting rights, of these holders and may have the effect of delaying, deterring
or preventing a change in control of us. 












 Section 203 of the Delaware general corporation law 

We are subject to the provisions of Section 203 of the Delaware General Corporation Law. In general, Section 203 prohibits a publicly held Delaware
corporation from engaging in a “business combination” with an “interested stockholder” for a three-year period following the time that this stockholder becomes an interested stockholder, unless the business combination is
approved in a prescribed manner. Under Section 203, a business combination between a corporation and an interested stockholder is prohibited unless it satisfies one of the following conditions: 

 

	 	•	 before the stockholder became interested, our board of directors approved either the business combination or
the transaction which resulted in the stockholder becoming an interested stockholder; 


  

	 	•	 upon consummation of the transaction which resulted in the stockholder becoming an interested stockholder, the
interested stockholder owned at least 85% of the voting stock of the corporation outstanding at the time the transaction commenced, excluding for purposes of determining the voting stock outstanding, shares owned by persons who are directors and
also officers, and 


 employee stock plans, in some instances, but not the outstanding voting stock owned by the interested
stockholder; or 
  

	 	•	 at or after the time the stockholder became interested, the business combination was approved by our board of
directors and authorized at an annual or special meeting of the stockholders by the affirmative vote of at least two-thirds of the outstanding voting stock which is not owned by the interested stockholder.



 Section 203 defines a business combination to include: 
  

	 	•	 any merger or consolidation involving the corporation and the interested stockholder; 



 

	 	•	 any sale, transfer, lease, pledge or other disposition involving the interested stockholder of 10% or more of
the assets of the corporation; 


  

	 	•	 subject to exceptions, any transaction that results in the issuance or transfer by the corporation of any stock
of the corporation to the interested stockholder; 


  

	 	•	 subject to exceptions, any transaction involving the corporation that has the effect of increasing the
proportionate share of the stock of any class or series of the corporation beneficially owned by the interested stockholder; and 


  

	 	•	 the receipt by the interested stockholder of the benefit of any loans, advances, guarantees, pledges or other
financial benefits provided by or through the corporation. 


  

	 	•	 In general, Section 203 defines an interested stockholder as any entity or person beneficially owning 15%
or more of the outstanding voting stock of the corporation and any entity or person affiliated with or controlling or controlled by the entity or person. 














 Choice of forum 

Pursuant to our amended and restated bylaws, unless we consent in writing to the selection of an alternative forum, the Court of Chancery of the State of
Delaware will be the sole and exclusive forum for any state law claims for (i) any derivative action or proceeding brought on our behalf, (ii) any action asserting a claim of breach of fiduciary duty owed by any of our directors, officers,
employees or agents to us or our stockholders, (iii) any action asserting a claim arising pursuant to any provision of the Delaware General Corporation Law, our amended and restated certificate of incorporation and our amended and restated
bylaws, (iv) any action to interpret, apply, enforce or determine the validity of our certificate of incorporation or by-laws or (v) any action asserting a claim that is governed by the internal
affairs doctrine, in each case subject to the Court of Chancery having personal jurisdiction over the indispensable parties named as defendants therein, or the Delaware Forum Provision. The Delaware Exclusive Forum Provision will not apply to any
causes of action arising under the Securities Act or the Exchange Act or any other claim for which the federal courts have exclusive jurisdiction. Unless we consent in writing to the selection of an alternate forum, the United Stated District Court
for the District of Massachusetts shall be the sole and exclusive forum for resolving any complaint asserting a cause of action arising under the Securities Act, or the Federal Forum Provision, as our principal office is located in Cambridge,
Massachusetts. These forum provisions may impose additional costs on stockholders, may limit our stockholders’ ability to bring a claim in a forum they find favorable, and the designated courts may reach different judgments or results than
other courts. In addition, there is uncertainty as to whether the Federal Forum Provision will be enforced, which may impose additional costs on us and stockholders.