Document:

EX-4.2

 Exhibit 4.2 
 FORM OF COMMON STOCK WARRANT 
 THIS WARRANT AND THE SHARES OF COMMON STOCK ISSUED UPON
ANY EXERCISE HEREOF HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED (THE “SECURITIES ACT”), OR ANY APPLICABLE STATE SECURITIES LAWS AND MAY NOT BE SOLD OR OTHERWISE TRANSFERRED BY ANY PERSON, INCLUDING A PLEDGEE,
UNLESS (1) EITHER (A) A REGISTRATION WITH RESPECT THERETO SHALL BE EFFECTIVE UNDER THE SECURITIES ACT, OR (B) THE COMPANY SHALL HAVE RECEIVED AN OPINION OF COUNSEL REASONABLY SATISFACTORY TO THE COMPANY THAT AN EXEMPTION FROM
REGISTRATION UNDER THE SECURITIES ACT IS AVAILABLE, AND (2) THERE SHALL HAVE BEEN COMPLIANCE WITH ALL APPLICABLE STATE SECURITIES OR “BLUE SKY” LAWS. THERE IS NO AND THERE IS NOT EXPECTED TO BE A PUBLIC MARKET FOR THE SHARES OF COMMON
STOCK ISSUABLE UPON ANY EXERCISE HEREOF. INVESTORS SHOULD BE AWARE THAT THEY WILL BE REQUIRED TO BEAR THE FINANCIAL RISKS OF THIS INVESTMENT FOR AN INDEFINITE PERIOD OF TIME. 

 

			
	Void After [                    ]	  	 Right to Purchase [                ] Shares
of

 Common Stock of bluebird bio, Inc.

 BLUEBIRD BIO, INC. 
 Common Stock Purchase Warrant 
 bluebird bio, Inc., a Delaware corporation (the
“Company”), hereby certifies that for value received, [                ] or assigns (the “Warrantholder”), is entitled to purchase, subject to
the terms and conditions hereinafter set forth, an aggregate of [                ] shares of Common Stock, par value $.01 per share of the Company (subject to
adjustment as hereinafter provided) at a purchase price of $.01 per share (subject to adjustment as hereinafter provided), payable as hereinafter provided. 
 1. Definitions. As used herein, the following terms shall have the following meanings, unless the context otherwise requires: 

 

	 	(a)	“Common Stock” shall mean the Company’s Common Stock, $.01 par value per share. 

 

	 	(b)	“Stated Purchase Price” shall mean the purchase price to be paid upon exercise of this Warrant in accordance with the terms hereof, which price
initially shall be $.01 per share of Common Stock. The Stated Purchase Price shall be subject to adjustment from time to time pursuant to the provisions of Section 6 hereof. 

 

	 	(c)	“Warrant Expiration Date” shall mean [            ] p.m., Eastern Time, on
[                    ]; provided that if such date shall be a holiday or a day on which banks are authorized to close in the Commonwealth of
Massachusetts, then [            ] p.m., Eastern Time, on the next following day which in the Commonwealth of Massachusetts is not a holiday or a day on which banks are authorized to
close. 

 2. Notice. In case at any time: (a) the Company shall pay any dividend or make any
distribution (other than regular cash dividends from earnings or earned surplus paid at an established rate) to the holders of the Common Stock; (b) there shall be any capital reorganization or reclassification of the capital stock of the
Company or consolidation or merger 

 
of the Company with or sale of all or substantially all of its assets to another corporation; or (c) there shall be a voluntary or involuntary dissolution, liquidation or winding-up of the
Company; then, in any one or more of such cases, the Company shall give written notice, by first class mail, postage prepaid, addressed to the registered holder at the address of such registered holder as shown on the books of the Company of the
date on which (i) the books of the Company shall close or a record date shall be fixed for determining the shareholders entitled to such dividend or distribution, or (ii) such reorganization, reclassification, consolidation, merger, sale,
dissolution, liquidation, winding-up, conversion, redemption or other event shall take place, as the case may be. Such notice shall also provide reasonable details of the proposed transaction and specify the date as of which the holders of Common
Stock of record shall participate in such dividend or distribution, or shall be entitled to exchange their Common Stock for securities or other property deliverable upon such reorganization, reclassification, consolidation, merger, sale,
dissolution, liquidation, winding-up, conversion, redemption or other event, as the case may be. Such written notice shall be given at least fifteen days prior to the action in question and not less than fifteen days prior to the record date or the
date on which the Company’s transfer books are closed in respect thereto. 
 3. Exercise. 

 

	 	(a)	Manner of Exercise. This Warrant may be exercised at any time or from time to time, on any day which is not a Saturday, Sunday or holiday under the laws of the
State of Delaware, for all or any part of the number of shares of Common Stock purchasable upon its exercise; provided, however, that this Warrant shall be void and all rights represented hereby shall cease unless exercised before the Warrant
Expiration Date. In order to exercise this Warrant, in whole or in part, the holder hereof shall deliver to the Company at its principal executive offices, or at such other office as the Company may designate by notice in writing, (i) this
Warrant, (ii) a written notice of such holder’s election to exercise its Warrant substantially in the form of Exhibit A attached hereto, and (iii) the documents described in Section 10, and shall pay to the Company by
check made payable to the order of the Company or wire transfer of funds to a bank account designated by the Company an amount equal to the aggregate purchase price for all shares of Common Stock as to which this Warrant is exercised. In lieu of
such exercise of this Warrant, the holder may from time to time convert this Warrant, in whole or in part, into a number of shares of Common Stock determined by using the following formula: 

X=((P)(Y)(A-B))/A 
 where 
  

			
	X  =	 	the number of shares of Common Stock to be issued to the holder for the portion of this Warrant being exercised;
	P  =	 	the percentage of this Warrant being exercised;
	Y  =	 	the total number of shares of Common Stock issuable upon exercise of this Warrant in full;
	A  =	 	the Fair Market Value of one share of Common Stock as of the exercise date; and
	B  =	 	the Stated Purchase Price as in effect on the exercise date.

  
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 Any portion of this Warrant that is exercised shall be immediately canceled. For purposes of
the foregoing, “Fair Market Value” shall be determined pursuant to Section 8 hereof. 
  

	 	(b)	Issuance of Common Stock. Upon receipt of the documents and payments described in Section 3(a), the Company shall, as promptly as practicable, and in any
event within 30 days thereafter, execute or cause to be executed, and deliver to such holder a certificate or certificates representing the aggregate number of full shares of Common Stock (or such other stock or securities that may be issuable upon
exercise of the Warrant) issuable upon such exercise, together with an amount in cash in lieu of any fraction of a share, as hereinafter provided. The stock certificate or certificates so delivered shall be in the denomination specified in said
notice and shall be registered in the name of the holder hereof. This Warrant shall be deemed to have been exercised and a certificate or certificates for shares of Common Stock shall be deemed to have been issued, and the holder hereof or any other
person so designated to be named therein shall be deemed to have become a holder of record of such shares for all purposes as of the date said notice, together with this Warrant and the documents and payments described in Section 3(a), are
received by the Company as aforesaid. If this Warrant shall have been exercised in part, the Company shall, at the time of delivery of said certificate or certificates, deliver to the holder hereof a new Warrant evidencing the rights of such holder
to purchase the unpurchased shares of Common Stock called for by this Warrant, which new Warrant shall in all other respects be identical with this Warrant. 

 4. Reservation of Shares; State Securities Laws. The Company covenants that it will at all times until the Warrant Expiration Date reserve and keep available out of its authorized and unissued
Common Stock and its authorized and unissued Common Stock (“Common Stock”), solely for the purpose of issue upon exercise of this Warrant or conversion of Common Stock issued upon such exercise, such number of shares of Common Stock as
shall then be issuable upon the exercise of this Warrant and such number of shares of Common Stock as shall then be issuable upon conversion of such Common Stock. If any securities to be reserved for the purpose of exercise of this Warrant require
approvals or registrations under applicable state “blue sky” or federal securities laws, the Company will use its reasonable efforts to obtain such approvals or registrations as may be appropriate. 

5. Loss or Mutilation. Upon receipt of evidence satisfactory to the Company of the loss, theft, destruction or mutilation of this
Warrant (including a reasonably detailed affidavit with respect to the circumstances of any loss, theft or destruction of such Warrant), and, in the case of any such mutilation, upon surrender and cancellation of this Warrant, the Company at its
expense will execute and deliver, in lieu hereof, a new Warrant of like tenor. 

  
 -3-

 6. Subdivision or Combination of Common Stock. If the Company at any time subdivides
(by any stock split, stock dividend, recapitalization or otherwise) its outstanding shares of Common Stock into a greater number of shares, the Stated Purchase Price in effect immediately prior to such subdivision will be proportionately reduced and
the number of shares issuable upon exercise of this Warrant will be proportionately increased, and if the Company at any time combines (by reverse stock split, recapitalization or otherwise) its outstanding shares of Common Stock into a smaller
number of shares, the Stated Purchase Price in effect immediately prior to such combination will be proportionately increased and the number of shares issuable upon exercise of this Warrant will be proportionately decreased. 

7. Consolidation, Merger, etc. If any consolidation or merger of the Company with another corporation that involves a transfer of
more than 50% of the voting power of the Company, any transfer of shares representing more than 50% of the voting power of the Company are transferred to any person that is not, on the date hereof, a holder of stock of any class or preference of the
Company or the sale of all or substantially all of the Company’s assets to another entity (each an “Extraordinary Event”) shall be effected, then, while this Warrant remains outstanding, the Company may terminate this Warrant as of
the effective date of such Extraordinary Event, provided that written notice of such termination shall be given to the Warrantholder and the Warrantholder shall have the right to exercise this Warrant during the twenty (20) day period preceding
the effective date of such Extraordinary Event. 
 8. Fractional Shares. If the number of shares of Common Stock
purchasable upon the exercise of this Warrant is adjusted pursuant to Section 6 hereof, the Company shall nevertheless not be required to issue fractions of shares, upon exercise of this Warrant or otherwise, or to distribute certificates that
evidence fractional shares. With respect to any fraction of a share called for upon any exercise hereof, such fraction shall neither be issued nor extinguished until the final exercise of this Warrant, in which event if a fraction is issuable, the
Company shall pay to the holder hereof an amount in cash equal to such fraction multiplied by the current “Fair Market Value” of the security into which such fractional share is convertible, determined as follows: 

 

	 	(a)	If the security is listed on a National Securities Exchange or admitted to unlisted trading privileges on such exchange or quoted in the NASDAQ System, the current fair
market value shall be the last reported sale price of the security on such exchange or market system on the last business day prior to the date of exercise of this Warrant or, if no such sale is made on such day, the average closing bid and asked
price for such day on such exchange or market system; or 

  

	 	(b)	If the security is not listed or admitted to unlisted trading privileges, the current fair market value shall be the mean of the last reported bid and asked prices
reported by the National Quotation Bureau, on the last business day prior to the date of the exercise of this Warrant; or 

  

	 	(c)	If the security is not so listed or admitted to unlisted trading privileges and bid and asked prices are not so reported, the current fair market value shall be an
amount determined in good faith by the Board of Directors of the Company. 

  
 -4-

 9. Transfers by Warrantholder. If the Warrantholder proposes to Transfer any shares
of Common Stock issued upon exercise of the Warrant (the “Warrant Shares”), then the Warrantholder shall comply with the terms and provisions of that certain Right of First Refusal and Co-Sale Agreement by and among the Company and certain
of its stockholders, as may be amended from time to time. 
 10. Agreements. As a condition precedent to any exercise of
this Warrant, the holder hereof understands and agrees that it may be required to execute certain documents and agreements (in form and substance substantially identical to those governing the sale of Common Stock) relating to the purchase and sale
of such Common Stock as well as registration, co-sale and voting rights, if any, relating to such Common Stock. Upon the execution and delivery of such documents and agreements, the holder will become a party to, and bound by, such agreements, as so
amended or restated, as to the shares of Common Stock acquired upon exercise of this Warrant. 
 Each holder of this Warrant,
and each holder of shares of Common Stock acquired upon the exercise of this Warrant, by acceptance hereof and thereof, agrees to furnish to the Company such information concerning such holder as may be requested by the Company which is necessary in
connection with any registration or qualification of shares of Common Stock purchasable hereunder. 
 11. Lock-Up. If, in
connection with a registration statement filed by the Company pursuant to the 1933 Act, the Company or its underwriter so requests, the Warrantholder will agree not to sell any Warrant Shares for a period not to exceed (i) in the event of an
initial public offering, 180 days following the effectiveness of such registration and (ii) in connection with any additional registration statement filed after the closing date of the initial public offering, 90 days following the
effectiveness of such registration, unless such period is extended to the extent required by any FINRA rules, for an additional period of up to thirty-four (34) days if the Company issues or proposes to issue an earnings or other public release
within fifteen (15) days of the expiration of such lockup period. 
 12. Warrant Holder Not Deemed Stockholder. The
holder of this Warrant shall not, as such, be entitled to vote or to receive dividends or be deemed the holder of Common Stock that may at any time be issuable upon exercise of this Warrant for any purpose whatsoever, nor shall anything contained
herein be construed to confer upon the holder of this Warrant, as such, any of the rights of a stockholder of the Company or any right to vote for the election of directors or upon any matter submitted to stockholders at any meeting thereof, or to
receive dividends or subscription rights, until such holder shall have exercised this Warrant and been issued shares of Common Stock in accordance with the provisions hereof. 
 13. Rights of Action; Remedies. All rights of action with respect to this Warrant are vested in the holder of this Warrant, and the holder may enforce against the Company its right to exercise this
Warrant for the purchase of shares of Common Stock in the manner provided in this Warrant. The Company stipulates that the remedies at law of the holder of this Warrant in the event of any default or threatened default by the Company in the
performance of or compliance with any of the terms of this Warrant are not and will not be adequate, and that such terms may be specifically enforced by a decree for the specific performance of any agreement contained herein or by an injunction
against a violation of any of the terms hereof or otherwise. 

  
 -5-

 14. Modification of Warrant. This Warrant shall not be modified, supplemented or
altered in any respect except with the consent in writing of the holder hereof and the Company; and no change in the number or nature of the securities purchasable upon the exercise of this Warrant, or the Stated Purchase Price therefor, or the
acceleration of the Warrant Expiration Date, shall be made without the consent in writing of the holder hereof, other than such changes as are specifically prescribed by this Warrant as originally executed. 

15. Miscellaneous. This Warrant shall be governed by, and construed and enforced in accordance with, the laws of the Commonwealth
of Massachusetts, without regard to its principles of conflicts of laws. The headings in this Warrant are for purposes of reference only, and shall not limit or otherwise affect any of the terms hereof. This Warrant is being executed as an
instrument under seal. The invalidity or unenforceability of any provision hereof shall in no way affect the validity or enforceability of any other provision. 
 [Remainder of page intentionally left blank.] 

  
 -6-

 IN WITNESS WHEREOF, the Company has caused this Warrant to be duly executed as of
                , 2011. 
  

			
	BLUEBIRD BIO, INC.
		
	By:	 	  
		 	 Nick Leschly
 President and
Chief Executive Officer

 EXHIBIT A 
 EXERCISE FORM 
 (To be signed only on exercise of Warrant) 

bluebird bio, Inc. 
 840 Memorial Drive

 Cambridge, MA 02139 

The undersigned hereby irrevocably elects to exercise the right to purchase represented by the within Warrant for, and to purchase
thereunder,                  shares of the stock provided for therein, and requests that certificates for such shares be issued in the name of: 

 

			
	(Please print name, address, and social security number)	  	
		
	 	  	

 and, if said number of shares shall not be all the shares purchasable thereunder, that a new Warrant for the balance
remaining of the shares purchasable under the within Warrant be registered in the name of the undersigned holder of the within Warrant or his Assignee as below indicated and delivered to the address stated below. 

NAME OF HOLDER OR
ASSIGNEE:                                       
                                         
         

                         
                                         
          (Please print) 
 ADDRESS OF HOLDER 

OR
ASSIGNEE:                                       
                                         
                                         
    
 SIGNATURE OF
HOLDER:                                        
                                         
                        

DATED:                        
         
 Note: The above signature must correspond with the name exactly as written upon the face
of the within Warrant in every particular, without alteration or enlargement or any change whatever, unless the within Warrant has been assigned.EX-4.3

 Exhibit 4.3 
 FORM OF SERIES A-1 PREFERRED WARRANT 
 NEITHER THIS WARRANT NOR ANY
SECURITIES THAT MAY BE ISSUED UPON EXERCISE HEREOF HAVE BEEN REGISTERED OR QUALIFIED UNDER THE SECURITIES ACT OF 1933, AS AMENDED, OR APPLICABLE STATE SECURITIES LAWS. THIS WARRANT AND SUCH SECURITIES MAY NOT BE TRANSFERRED OR OTHERWISE DISPOSED OF
UNLESS THEY HAVE BEEN SO REGISTERED AND QUALIFIED OR AN OPINION OF COUNSEL SATISFACTORY TO THE COMPANY TO THE EFFECT THAT SUCH REGISTRATION AND QUALIFICATION IS NOT REQUIRED HAS BEEN DELIVERED TO THE COMPANY. 

STOCK PURCHASE WARRANT 
  

					
	 No. [__]
	  	 	[                    	] 

 Genetix Pharmaceuticals Inc., a Delaware corporation (the “Company”), hereby certifies
that, subject to the terms and conditions set forth herein, [                    ] (the “Holder”), is entitled to purchase
the Warrant Share Number of shares of Warrant Stock (both as defined below) from the Company at any time or from time to time before the earlier of (i) [            ] p.m.
([                ] time) on [                    ] or
(ii) the effective time of an Extraordinary Event (as defined in the Notes (as defined below)), for the Exercise Price (as defined below), subject to adjustments as set forth in Sections 4 and 6. 

This Stock Purchase Warrant (this “Warrant”) is being issued in connection with the purchase by the Holder of a
Convertible Term Note (the “Note”) of the Company in the principal amount set forth on the signature page hereto. The Note is one of a series of similar Convertible Term Notes (the Note and such Convertible Term Notes shall
collectively be referred to as the “Notes”) being issued by the Company to certain investors in the aggregate principal amount of up to
$[                ] pursuant to the terms of a Convertible Note and Warrant Purchase Agreement dated as of
[                    ] (the “Purchase Agreement”), by and among the Company and certain Investors named therein (the
“Investors”) including the Holder, and this Warrant is one of a series of similar Stock Purchase Warrants (this Warrant and such Stock Purchase Warrants shall collectively be referred to as the “Warrants”)
being issued by the Company to such Investors in connection with the issuance of the Notes. 
 1. Determination of Warrant
Stock, Warrant Share Number and Warrant Exercise Price. 
 (a) Warrant Stock. “Warrant Stock” shall
mean Series A-1 Convertible Preferred Stock, $.01 par value per share, of the Company (the “Series A-l Preferred Stock”). 
 (b) Warrant Share Number. This Warrant shall be exercisable for a number of shares of Warrant Stock (the “Warrant Share Number”) equal to a fraction, the numerator of which is the
product of the original principal amount of such Note (the “Principal Amount”) times twenty-five hundredths (0.25) and the denominator of which is the Exercise Price described in Section 1(c) below, such Warrant Share Number to
be rounded to the nearest whole number. 

 (c) Exercise Price. The exercise price per share of Warrant Stock (the
“Exercise Price”) shall be (i) $0.6619 per share if the Warrant Stock is Series A-l Preferred Stock or (ii) the lowest price per share paid by any purchaser of Next Round Preferred Stock in the Qualified Financing if
the Warrant Stock is Next Round Preferred Stock. 
 2. Exercise of Warrant. 

(a) Mechanics of Exercise. This Warrant may be exercised by the Holder by surrender to the Company of this Warrant, with the
attached form of subscription agreement duly executed by the Holder, accompanied by payment equal to the aggregate purchase price for the securities for which this Warrant is then being exercised according to Section 3 hereof. 

(b) Warrant Agent. In the event that a bank or trust company is appointed as trustee for the Holder pursuant to Section 4(b)
hereof, such bank or trust company will have all the powers and duties of a warrant agent appointed pursuant to Section 9 hereof and will accept, in its own name for the account of the Company or such successor entity as may be entitled
thereto, all amounts otherwise payable to the Company or such successor, as the case may be, upon exercise of this Warrant. 

(c) Expiration. This Warrant and the Holder’s rights hereunder will expire at the earlier of
(i) [            ] P.M. ([                ] time) on
[                    ] or (ii) the effective time of an Extraordinary Event (the “Expiration Date”); provided, however,
that if the Holder has not previously exercised the Warrant, this Warrant shall be automatically exercised by the net issuance method upon the effective time of an Extraordinary Event; and provided further that upon and after the Warrant Stock
Conversion Effective Time (as defined in Section 6), the right to purchase shares of Warrant Stock granted herein shall terminate, and this Warrant shall represent the right to purchase shares of the Common Stock, $0.01 par value per share, of
the Company (“Common Stock”) as provided in Section 6 hereof. 
 (d) Delivery of Certificates. As
soon as is practicable after any exercise of this Warrant, the Company, at its own expense, will deliver to the Holder one or more certificates representing the securities to which the Holder is entitled in respect of such exercise, together, in the
case of any partial exercise, with a new Warrant representing the unexercised portion hereof. 
 (e) Fractional Shares.
In the event that any exercise of this Warrant would, but for the provisions of this Section 2(e), result in the issuance of any fractional share of capital stock, then in lieu of such fractional share the Holder will be entitled to cash equal
to the fair market value of such fractional share, as determined in good faith by the Company’s Board of Directors. 

  
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 3. Payment of Exercise Price. The Exercise Price may be paid at the Holder’s
election either: 
 (a) by cash, certified or official bank check payable to the order of the Company, or wire transfer to its
account, or 
 (b) by the net issuance method as described below: 

(i) Prior to the Warrant Stock Conversion Effective Time (as defined in Section 6 hereof), the Company shall issue
Warrant Stock under the net issuance method in accordance with the following formula: 
  

									
		 		  	X	  	=	  	(Y)(A-B)/A
					
		 	 Where
	  	X	  	  =  	  	the number of shares of Warrant Stock to be issued to the Holder
					
		 		  	Y	  	=	  	the number of shares of Warrant Stock requested to be exercised under this Warrant
					
		 		  	A	  	=	  	the current fair market value of one (1) share of Warrant Stock
					
		 		  	B	  	=	  	the Exercise Price

 As used herein, the current fair market value of a share of Warrant Stock shall mean the price per share
which the Company could obtain from a willing buyer (not a current employee or director) for shares of Warrant Stock, as determined in good faith by the Company’s Board of Directors, unless the Company shall become subject to a merger,
consolidation or other acquisition pursuant to which the holders of Warrant Stock receive securities and/or other property in exchange for their Warrant Stock, in which case the fair market value of Warrant Stock shall be deemed to be the value
(determined in good faith by the Company’s Board of Directors) of the securities and other property received by the holders of the Warrant Stock per share of Warrant Stock pursuant to such merger, consolidation or other acquisition. 

(ii) Upon and after the Warrant Stock Conversion Effective Time, the Company shall issue Common Stock under the net
issuance method in accordance with the following formula: 
  

									
		 		  	X	  	  =  	  	(Y)(A-B)/A
					
		 	 Where
	  	X	  	=	  	the number of shares of Common Stock to be issued to the Holder
					
		 		  	Y	  	=	  	the number of shares of Common Stock requested to be exercised under this Warrant
					
		 		  	A	  	=	  	the current fair market value of one (1) share of Common Stock
					
		 		  	B	  	=	  	the Exercise Price

  
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 As used herein, current fair market value of Common Stock shall mean with respect to each
share of Common Stock: 
 (A) if the exercise is in connection with the Company’s initial public offering of
Common Stock, and if the Company’s registration statement relating to such public offering, has been declared effective by the Securities and Exchange Commission, then the initial “Price to Public” specified in the final prospectus
with respect to the offering; 
 (B) if this Warrant is exercised after, and not in connection with, the
Company’s initial public offering of Common Stock and 
 (1) if the Common Stock is traded on an
internationally recognized securities exchange that publishes closing prices, the fair market value shall be deemed to be the average of the closing prices over a fourteen (14) day period ending three (3) days before the day the current
fair market value of the Common Stock is being determined; or 
 (2) if the Common Stock is not listed on an
internationally recognized securities exchange that publishes closing prices but is actively traded over-the-counter, the fair market value shall be deemed to be the average of the closing bid and asked prices reported by the National Quotation
Bureau (or similar system) over the twenty-one (21) day period ending three (3) days before the day the current fair market value of the Common Stock is being determined; 

(3) if at any time the Common Stock is not listed on an internationally recognized securities exchange that publishes
closing prices or actively traded over-the-counter, the current fair market value of Common Stock shall be the price per share which the Company could obtain from a willing buyer (not a current employee or director) for shares of Common Stock sold
by the Company, from authorized but unissued shares, as determined in good faith by its Board of Directors, unless the Company shall become subject to a merger, consolidation or other acquisition pursuant to which the holders of Common Stock receive
securities and/or other property in exchange for their Common Stock, in which case the fair market value of Common Stock shall be deemed to be the value of the securities and other property received by the holders of the Common Stock per share of
Common Stock pursuant to such merger, consolidation or other acquisition. 
 4. Adjustment for Reorganizations, Etc.

 (a) Certain Adjustments. 
 (i) If at any time or from time to time prior to the exercise of this Warrant but before the Warrant Stock Conversion Effective Time, the Company effects a “Warrant Stock Adjustment Event” (as
hereafter defined), then in each such case, (A) the number of shares of Warrant Stock purchasable hereunder shall be adjusted to the number obtained by multiplying the number of shares of Warrant Stock purchasable

  
 4 

 
hereunder immediately before such Warrant Stock Adjustment Event by a fraction, the numerator of which shall be the number of shares of Warrant Stock outstanding (excluding treasury stock)
immediately after such Warrant Stock Adjustment Event and the denominator of which shall be the number of shares of Warrant Stock outstanding (excluding treasury stock) immediately before such Warrant Stock Adjustment Event, and (B) the
Exercise Price shall be adjusted to the number obtained by multiplying the Exercise Price in effect immediately before such Warrant . Stock Adjustment Event by a fraction, the numerator of which shall be the number of shares of Warrant Stock
outstanding (excluding treasury stock) immediately before such Warrant Stock Adjustment Event and the denominator of which shall be the number of shares of Warrant Stock outstanding (excluding treasury stock) immediately after such Warrant Stock
Adjustment Event, in each case subject to further adjustment thereafter as provided herein. The term “Warrant Stock Adjustment Event” shall mean (x) the issuance of additional shares of Warrant Stock as a dividend or other
distribution on outstanding Warrant Stock, (y) the subdivision of outstanding shares of Warrant Stock into a greater number of shares of Warrant Stock, or (z) the combination of outstanding shares of Warrant Stock into a smaller number of
shares of Warrant Stock, but shall not include the Recapitalization as defined in the Company’s Third Amended and Restated Certificate of Incorporation, adjustments with respect to which have already been made. 

(ii) If at any time or from time to time prior to the exercise of this Warrant but after the Warrant Stock Conversion
Effective Time, the Company effects a “Common Stock Adjustment Event” (as hereafter defined), then in each such case, (A) the number of shares of Common Stock purchasable hereunder shall be adjusted to the number obtained by
multiplying the number of shares of Common Stock purchasable hereunder immediately before such Common Stock Adjustment Event by a fraction, the numerator of which shall be the number of shares of Common Stock outstanding (excluding treasury stock)
immediately after such Common Stock Adjustment Event and the denominator of which shall be the number of shares of Common Stock outstanding (excluding treasury stock) immediately before such Common Stock Adjustment Event, and (B) the Exercise
Price shall be adjusted to the number obtained by multiplying the Exercise Price in effect immediately before such Common Stock Adjustment Event by a fraction, the numerator of which shall be the number of shares of Common Stock outstanding
(excluding treasury stock) immediately before such Common Stock Adjustment Event and the denominator of which shall be the number, of shares of Common Stock outstanding (excluding treasury stock) immediately after such Common Stock Adjustment Event,
in each case subject to further adjustment thereafter as provided herein. The term “Common Stock Adjustment Event” shall mean (x) the issuance of additional shares of Common Stock as a dividend or other distribution on
outstanding Common Stock, (y) the subdivision of outstanding shares of Common Stock into a greater number of shares of Common Stock, or (z) the combination of outstanding shares of Common Stock into a smaller number of shares of Common
Stock. 
 (iii) Subject to earlier termination of this Warrant upon the effective time of an Extraordinary Event,
at any time or from time to time prior to the exercise of this Warrant, the Company (A) effects a capital reorganization, reclassification or recapitalization, or (B) consolidates with or merges with or into any other person or

  
 5 

 
entity, then in each such case, the Holder, upon exercise hereof at any time after or simultaneously with the consummation of such reorganization, reclassification, recapitalization,
consolidation or merger, as the case may be, will receive, in lieu of the securities issuable upon such exercise before such consummation or effective date, the other securities, cash, and/or property to which the Holder would have been entitled
upon such consummation or in connection with such dissolution, as the case may be, if the Holder had exercised this Warrant immediately prior thereto, all subject to further adjustment thereafter as provided herein. 

(b) Appointment of Trustee for Warrant Holders Upon Dissolution. In the event of any dissolution of the Company, the Company, prior
to such dissolution, will, at its expense, deliver or cause to be delivered the securities, property, and/or cash receivable by the. Holder after the effective date of such dissolution pursuant to this Section 4 to a bank or trust company, as
trustee for the Holder. 
 (c) Continuation of Terms. Subject to earlier termination of this Warrant upon a sale of the
Company, upon any reorganization, consolidation or merger referred to in this Section 4, this Warrant will continue in full force and effect, and the terms hereof will be applicable to the securities, cash, and/or property receivable on the
exercise of this Warrant after or simultaneously with the consummation of such reorganization, consolidation or merger and will be binding upon the issuer of any such stock or other securities. 

5. No Dilution or Impairment. The Company will not, by amendment of its Certificate of Incorporation (as amended from time to
time, the “Certificate of Incorporation”) or through any reorganization, transfer of assets, consolidation, merger, dissolution, issue or sale of securities, or any other action, avoid or seek to avoid the observance or performance
of any of the terms of this Warrant, but will at all times in good faith assist in the carrying out of all such terms and in the taking of all such action as may be necessary or appropriate in order to protect the rights of the Holder against
dilution. Without limiting the generality of the foregoing, the Company will seek to take all such action as may be necessary or appropriate in order that the Company may validly and legally issue fully paid and nonassessable shares of stock upon
exercise of this Warrant from time to time. 
 6. Automatic Conversion of the Warrant Stock. If at any time the issued
and outstanding shares of the Warrant Stock shall be automatically converted into shares of Common Stock under the terms of the Certificate of Incorporation, then upon and after the effective time of such automatic conversion of the Warrant Stock
(the “Warrant Stock Conversion Effective Time”), the right to purchase Warrant Stock granted herein shall terminate, and this Warrant shall represent the right to purchase a number of shares of Common Stock calculated as follows:

  

									
		 		  	X	  	  =  	  	(Y)(Z)
					
		 	Where	  	X	  	=	  	the number of shares of Common Stock purchasable under this Warrant upon and after the Warrant Stock Conversion Effective Time

  
 6 

									
		 		 	Y	  	=	  	the number of shares of Warrant Stock purchasable under this Warrant immediately prior to the Warrant Stock Conversion Effective Time
					
		 		 	Z	  	  =  	  	the number of shares of Common Stock issuable upon conversion of each share of Warrant Stock immediately prior to the Warrant Stock Conversion Effective Time

 and the Exercise Price per share of Common Stock shall be a price calculated as follows: 

 

									
		 		  	A	  	=	  	(B)(X)/Y
					
		 	Where	  	A	  	=	  	the Exercise Price per share of Common Stock upon and after the Warrant Stock Conversion Effective Time
					
		 		  	B	  	=	  	the Exercise Price per share of Warrant Stock immediately prior to the Warrant Stock Conversion Effective Time
					
		 		  	X	  	=	  	the number of shares of Warrant Stock purchasable under this Warrant immediately prior to the Warrant Stock Conversion Effective Time
					
		 		  	Y	  	  =  	  	the number of shares of Common Stock purchasable under this Warrant upon and after the Warrant Preferred Stock Conversion Effective Time

 Thereafter, the number of shares of Common Stock purchasable hereunder and the Exercise Price per share shall be subject
to adjustment for the types of events described in Section 4 above that occur with respect to the Common Stock. 
 7.
Notices of Record Date, Etc. In the event from time to time of any proposed or contemplated: 
 (a) taking by the Company
of a record of the holders of any class of securities for the purpose of determining the holders thereof who are entitled to receive any dividend or other distribution, or any right to subscribe for, purchase, or otherwise acquire any shares of
stock of any class or any other securities or property, or to receive any other right; 
 (b) capital reorganization of the
Company, any reclassification or recapitalization of the capital stock of the Company, or any transfer of all or substantially all the assets of the Company to, or any consolidation or merger of the Company with or into, any other person or entity;
or 
 (c) voluntary or involuntary dissolution, liquidation, or winding-up of the Company; 

  
 7 

 
then, and in each such event the Company will mail or cause to be mailed to the Holder a notice specifying (i) the date on which any such record is to be taken for the purpose of such
dividend, distribution, or right, and stating the amount and character of such dividend, distribution, or right, or (ii) the date on which any such reorganization, reclassification, recapitalization, transfer, consolidation, merger,
dissolution, liquidation, or winding-up is anticipated to take place and the time, if any is to be fixed, as of which the holders of record of any class or series of the Company’s capital stock or other securities will be entitled to exchange
such stock or other securities for other securities, cash, and/or other property deliverable on such reorganization, reclassification, recapitalization, transfer, consolidation, merger, dissolution, liquidation, or winding-up. Such notice will be
mailed at least twenty (20) days prior to the earliest date specified in such notice on which any such action or transaction is to be taken or consummated 
 8. Reservation of Securities Issuable on Exercise of Warrant. The Company at all times and from time to time will reserve and keep available, solely for issuance and delivery on the exercise of
this Warrant, the quality and quantities of securities from time to time issuable upon exercise of this Warrant. If at any time the Company does not have sufficient authorized securities to comply with the foregoing sentence, the Company promptly
will take all steps (including, without limitation, amending the Certificate of Incorporation) necessary to provide the quality and quantity of securities sufficient to effect the exercise in full of this Warrant. 

9. Warrant Agent. The Company may, by written notice to the Holder, appoint an agent for the purpose of issuing securities upon
exercise of this Warrant, exchanging or replacing this Warrant, or any of the foregoing, and thereafter any such issuance, exchange, or replacement as the case may be, will be made at such office by such agent. 

10. Transfer and Exchange of Warrant. 
 (a) Transfer. Subject to evidence of compliance with the Securities Act of 1933, as amended, and applicable state securities laws, this Warrant may be transferred or succeeded to by any person;
provided, however, that the Company is given written notice at the time of such transfer stating the name and address of the transferee. 
 (b) Exchange. Upon surrender of this Warrant for transfer or exchange, a new Warrant or new Warrants of the same tenor and exercisable for the same aggregate number of shares, of Warrant Stock as
the Warrant so surrendered will be issued to, and registered in the name of, the transferee or transferees. The Company may treat the person in whose name this Warrant is registered as the Holder for all purposes. 

11. Captions. The captions of sections or subsections of this Warrant are for reference only and will not affect the
interpretation or construction of this Warrant. 
 12. Equitable Relief. The Company hereby acknowledges that any breach
by it of its obligations under this Warrant would cause substantial and irreparable damage to the Holder and that money damages would be an inadequate remedy therefor, and accordingly, acknowledges and agrees that, in addition to any other rights
and remedies to which the Holder may be entitled in respect of any breach of such obligations, the Holder will be entitled to an injunction, specific performance and/or other equitable relief to prevent the breach of such obligations. 

13. No Waiver. No failure or other delay by the Holder exercising any right, power, or privilege hereunder will be or operate as a
waiver thereof, nor will any single or partial exercise thereof preclude any other or further exercise thereof or the exercise of any other right, power, or privilege. 

  
 8 

 14. Governing Law. This Warrant will be governed by and interpreted and construed in
accordance, with the internal laws of The Commonwealth of Massachusetts (without reference to principles of conflicts or choice of law). 
 15. Amendment/Waiver. This Warrant and the other Warrants may be amended by the written agreement of the Company and holders of outstanding Warrants that when exercised could be exercised into at
least two-thirds of the aggregate number of shares of Warrant Stock into which all then outstanding Warrants could then be exercised. Any provision of this Warrant and the other Warrants may be waived with the written agreement of the holders of
outstanding Warrants that when exercised could be exercised into at least two-thirds of the aggregate number of shares of Warrant Stock into which all then outstanding Warrants could then be exercised. Notwithstanding the foregoing, no amendment of
or waiver with respect to any provision of this Warrant or the other Warrants shall be effected unless the holders of all then outstanding Warrants are treated similarly as a class and not disproportionately. 

[Remainder of page intentionally left blank.] 

  
 9 

 Executed and delivered under seal on and as of the date first above written. 

 

							
	 Original Principal Amount of Note:
 $[                                
    ]
	 		 	GENETIX PHARMACEUTICALS INC.
				
		 		 	By:	 	 
		 		 	Name:	 	
		 		 	Its:	 	

 SUBSCRIPTION FORM 

The undersigned, the Holder of the within Stock Purchase Warrant, hereby elects to exercise the purchase right represented by such
Warrant as follows: 
 The undersigned hereby elects to purchase shares of Warrant Stock (as defined in this Warrant) and
herewith makes payment of $             therefor. 
 The
undersigned hereby elects to exercise this Warrant by the net issuance method described in Section 3 of this Warrant and to exercise for that purpose              shares of
Warrant Stock (as defined in this Warrant). 
 The undersigned further requests that the certificates representing such shares
be issued in the name of and delivered to              and if such shares shall not include all of the shares issuable under this Warrant, that a new Warrant of like tenor and date
be delivered to the undersigned for the shares not issued. 
  

							
				
	Dated:
                                        
	 		 		 	 
		 		 		 	Name of Holder

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