EX-4.3





 Exhibit 4.3 

DESCRIPTION OF REGISTRANT’S SECURITIES 

REGISTERED PURSUANT TO SECTION 12 OF THE 

SECURITIES EXCHANGE ACT OF 1934, AS AMENDED 

The following description of the capital stock and provisions of Generation Bio Co.’s (the “Company,” “we,” “us” and/or
“our”) restated certificate of incorporation and amended and restated bylaws are summaries and are qualified by reference to our restated certificate of incorporation and amended and restated bylaws, each of which is filed as an exhibit to
our most recent Annual Report on Form 10-K filed with the Securities and Exchange Commission. For additional information, please read our restated certificate of incorporation and amended and restated bylaws
and the applicable provisions of the Delaware General Corporation Law. 
 General 

Our authorized capital stock consists of 150,000,000 shares of our common stock, par value $0.0001 per share, and 5,000,000 shares of our preferred stock, par
value $0.0001 per share, all of which preferred stock is undesignated. Our common stock is registered under Section 12(b) of the Securities Exchange Act of 1934, as amended (the “Exchange Act”). 

Common stock 
 Holders of our common stock are entitled to
one vote for each share held on all matters submitted to a vote of stockholders and do not have cumulative voting rights. Each election of directors by our stockholders will be determined by a plurality of the votes cast by the stockholders entitled
to vote on the election. Holders of common stock are entitled to receive proportionately any dividends as may be declared by our board of directors, subject to any preferential dividend rights of outstanding preferred stock that we may designate and
issue in the future. 
 In the event of our liquidation or dissolution, the holders of our common stock are entitled to receive proportionately all assets
available for distribution to stockholders after the payment of all debts and other liabilities and subject to the prior rights of any of our outstanding preferred stock. Holders of our common stock have no preemptive, subscription, redemption or
conversion rights. The rights, preferences and privileges of holders of our common stock are subject to and may be adversely affected by the rights of the holders of shares of any series of our preferred stock that we may designate and issue in the
future. 
 The transfer agent and registrar for our common stock is Computershare Trust Company, N.A. Our common stock is listed on the Nasdaq Global Select
Market under the symbol “GBIO.” 
 Preferred stock 

Under the terms of our restated certificate of incorporation, our board of directors is authorized to issue shares of preferred stock in one or more series
without stockholder approval. Our board of directors has the discretion to determine the rights, preferences, privileges and restrictions, including voting rights, dividend rights, conversion rights, redemption privileges and liquidation
preferences, of each series of preferred stock. 
 The purpose of authorizing our board of directors to issue preferred stock and determine its rights and
preferences is to eliminate delays associated with a stockholder vote on specific issuances. The issuance of preferred stock, while providing flexibility in connection with possible acquisitions, future financings and other corporate purposes, could
have the effect of making it more difficult for a third party to acquire, or could discourage a third party from seeking to acquire, a majority of our outstanding voting stock. There are no shares of preferred stock currently outstanding, and we
have no present plans to issue any shares of preferred stock. 
 Delaware anti-takeover law and certain charter and bylaw provisions 

Delaware law 
 We are subject to Section 203 of
the Delaware General Corporation Law. Subject to certain exceptions, Section 203 prevents a publicly held Delaware corporation from engaging in a “business combination” with any “interested stockholder” for three years
following the date that the person became an interested stockholder, unless either the interested stockholder attained such status with the approval of our board of directors, the business combination is


  
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approved by our board of directors and stockholders in a prescribed manner or the interested stockholder acquired at least 85% of our outstanding voting stock in the transaction in which it
became an interested stockholder. A “business combination” includes, among other things, a merger or consolidation involving us and the “interested stockholder” and the sale of more than 10% of our assets. In general, an
“interested stockholder” is any entity or person beneficially owning 15% or more of our outstanding voting stock and any entity or person affiliated with or controlling or controlled by such entity or person. 

Staggered board; removal of directors 
 Our
restated certificate of incorporation and our amended and restated bylaws divide our board of directors into three classes with staggered three-year terms. In addition, our restated certificate of incorporation and our amended and restated bylaws
provide that directors may be removed only for cause and only by the affirmative vote of the holders of at least 75% of our shares of capital stock present in person or by proxy and entitled to vote. Under our restated certificate of incorporation
and our amended and restated bylaws, any vacancy on our board of directors, including a vacancy resulting from an enlargement of our board of directors, may be filled only by vote of a majority of our directors then in office. 

Furthermore, our restated certificate of incorporation provides that the authorized number of directors may be changed only by the resolution of our board of
directors. The classification of our board of directors and the limitations on the ability of our stockholders to remove directors, change the authorized number of directors and fill vacancies could make it more difficult for a third party to
acquire, or discourage a third party from seeking to acquire, control of our company. 
 Super-majority voting 

The Delaware General Corporation Law provides generally that the affirmative vote of a majority of the shares entitled to vote on any matter is required to
amend a corporation’s certificate of incorporation or bylaws, unless a corporation’s certificate of incorporation or bylaws, as the case may be, requires a greater percentage. Our amended and restated bylaws may be amended or repealed by a
majority vote of our board of directors or the affirmative vote of the holders of at least 75% of the votes that all our stockholders would be entitled to cast in any annual election of directors. In addition, the affirmative vote of the holders of
at least 75% of the votes that all our stockholders would be entitled to cast in any election of directors is required to amend or repeal or to adopt any provisions inconsistent with any of the provisions of our restated certificate of incorporation
described above. 
 Stockholder action; special meeting of stockholders; advance notice requirements for stockholder proposals and director
nominations 
 Our restated certificate of incorporation and our amended and restated bylaws provide that any action required or permitted to be
taken by our stockholders at an annual meeting or special meeting of stockholders may only be taken if it is properly brought before such meeting and may not be taken by written action in lieu of a meeting. Our restated certificate of incorporation
and our amended and restated bylaws also provide that, except as otherwise required by law, special meetings of the stockholders can only be called by our board of directors. In addition, our amended and restated bylaws establish an advance notice
procedure for stockholder proposals to be brought before an annual meeting of stockholders, including proposed nominations of candidates for election to our board of directors. Stockholders at an annual meeting may only consider proposals or
nominations specified in the notice of meeting or brought before the meeting by or at the direction of our board of directors, or by a stockholder of record on the record date for the meeting who is entitled to vote at the meeting and who has
delivered timely written notice in proper form to our secretary of the stockholder’s intention to bring such business before the meeting. These provisions could have the effect of delaying until the next stockholder meeting stockholder actions
that are favored by the holders of a majority of our outstanding voting securities. These provisions also could discourage a third party from making a tender offer for our common stock because even if the third party acquired a majority of our
outstanding voting stock, it would be able to take action as a stockholder, such as electing new directors or approving a merger, only at a duly called stockholders meeting and not by written consent. 

Exclusive forum provision 
 Our restated
certificate of incorporation provides that, unless we consent in writing to the selection of an alternative forum, the Court of Chancery of the State of Delaware (or, if the Court of Chancery of the State of Delaware does not


  
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have jurisdiction, the federal district court for the District of Delaware) shall be the sole and exclusive forum for the following types of proceedings: (1) any derivative action or
proceeding brought on behalf of our company, (2) any action asserting a claim of breach of a fiduciary duty owed by any of our directors, officers, employees or stockholders to our company or our stockholders, (3) any action asserting a
claim arising pursuant to any provision of the General Corporation Law of the State of Delaware or as to which the General Corporation Law of the State of Delaware confers jurisdiction on the Court of Chancery of the State of Delaware, or
(4) any action asserting a claim arising pursuant to any provision of our restated certificate of incorporation or our amended and restated bylaws (in each case, as they may be amended from time to time) or governed by the internal affairs
doctrine. These choice of forum provisions will not apply to suits brought to enforce a duty or liability created by the Securities Act, the Exchange Act or any other claim for which federal courts have exclusive jurisdiction. Furthermore, our
restated certificate of incorporation provides that, unless we consent in writing to the selection of an alternative forum, the federal district courts of the United States of America shall, to the fullest extent permitted by law, be the sole and
exclusive forum for the resolution of any claims arising under the Securities Act. Although our restated certificate of incorporation contains the choice of forum provisions described above, it is possible that a court could rule that such
provisions are inapplicable for a particular claim or action or that such provisions are unenforceable. 

  
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