SENSEI BIOTHERAPEUTICS, INC. [AMENDED AND RESTATED] WARRANT TO PURCHASE COMMON STOCK VOID AFTER

Exhibit 4.2

THIS WARRANT AND THE SECURITIES ISSUABLE UPON THE EXERCISE HEREOF HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED (THE “ACT”), OR UNDER THE SECURITIES LAWS OF ANY STATES IN THE UNITED STATES. THESE SECURITIES ARE SUBJECT TO RESTRICTIONS ON TRANSFERABILITY AND RESALE AND MAY NOT BE TRANSFERRED OR RESOLD EXCEPT AS PERMITTED UNDER THE ACT AND THE APPLICABLE STATE SECURITIES LAWS, PURSUANT TO REGISTRATION OR EXEMPTION THEREFROM. THE ISSUER OF THESE SECURITIES MAY REQUIRE AN OPINION OF COUNSEL IN FORM AND SUBSTANCE SATISFACTORY TO THE ISSUER TO THE EFFECT THAT ANY PROPOSED TRANSFER OR RESALE IS IN COMPLIANCE WITH THE ACT AND ANY APPLICABLE STATE SECURITIES LAWS.

SENSEI BIOTHERAPEUTICS, INC.

[AMENDED AND RESTATED] WARRANT TO PURCHASE COMMON STOCK

VOID AFTER

THIS CERTIFIES THAT, for value received,                 , or [its][his][her] assigns (the “Holder”), is entitled to subscribe for and purchase from SENSEI BIOTHERAPEUTICS, INC., a Delaware corporation (the “Company”), the Exercise Shares at the Exercise Price (each subject to adjustment as provided herein). [This Warrant is issued pursuant to that certain Convertible Promissory Note issued by the Company to the Holder, dated as of the date hereof][(the “Note”)]. [This Amended and Restated Warrant amends and restates and supersedes in its entirety that certain Warrant to Purchase Common Stock dated as of April 1, 2019 (the “Prior Warrant”) which was issued to Holder pursuant to that certain Convertible Promissory Note issued by the Company to the Holder, dated as April 1, 2019 (the “Note”). Upon acceptance of this Warrant by Holder, Holder hereby agrees that the Prior Warrant is terminated in its entirety. ]

1. DEFINITIONS. As used herein, the following terms shall have the following respective meanings:

(a) “Exercise Price” shall mean $                  per Exercise Share.

(b) “Exercise Period” shall mean the period commencing on the date hereof and ending ten (10) years later, unless sooner terminated as provided below.

(c) “Exercise Shares” shall mean shares of the Company’s Common Stock, subject to adjustment pursuant to the terms hereof, including but not limited to adjustments pursuant to Section 5 below, issuable upon exercise of this Warrant.

2. EXERCISE OF WARRANT.

2.1 Exercise. The rights represented by this Warrant may be exercised in whole or in part at any time during the Exercise Period, by delivery of the following to the Company at its address set forth in Section 11 (or at such other address as it may designate by notice in writing to the Holder):

(a) An executed Notice of Exercise in the form attached hereto as EXHIBIT A;

(b) Payment of the Exercise Price either (i) in cash or by check, (ii) by cancellation of indebtedness or (iii) pursuant to Section 2.2; and

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(c) This Warrant.

2.2 Net Exercise. Notwithstanding any provisions herein to the contrary, if the fair market value of one Exercise Share is greater than the Exercise Price (at the date of calculation as set forth below), then, in lieu of exercising this Warrant as provided in Section 2.1, the Holder may, by surrender of this Warrant at the principal office of the Company together with the properly endorsed Notice of Exercise, elect to receive the number of Exercise Shares computed using the following formula:

For purposes of the above calculation, the fair market value of one Exercise Share shall be determined by the Company’s Board of Directors in good faith; provided, however, that in the event that this Warrant is exercised pursuant to this Section 2.2 in connection with the Company’s initial public offering of its Common Stock, the fair market value per share shall be the per share offering price to the public of the Company’s initial public offering.

2.3 Mechanics of Exercise. Upon the exercise of the rights represented by this Warrant, a certificate or certificates for the Exercise Shares so purchased, registered in the name of the Holder or persons affiliated with the Holder, if the Holder so designates, shall be issued and delivered to the Holder within a reasonable time after the rights represented by this Warrant shall have been so exercised. In the event that this Warrant is being exercised for less than all of the then-current number of Exercise Shares purchasable hereunder, then the Company shall, concurrently with the issuance by the Company of the number of Exercise Shares for which this Warrant is then being exercised, issue a new Warrant exercisable for the remaining number of Exercise Shares purchasable hereunder. The person in whose name any certificate or certificates for Exercise Shares are to be issued upon exercise of this Warrant shall be deemed to have become the holder of record of such shares on the date on which this Warrant was surrendered and payment of the Exercise Price was made, irrespective of the date of delivery of such certificate or certificates, except that, if the date of such surrender and payment is a date when the stock transfer books of the Company are closed, such person shall be deemed to have become the holder of such shares at the close of business on the next succeeding date on which the stock transfer books are open.

3. COVENANTS OF THE COMPANY. The Company covenants and agrees that all Exercise Shares that may be issued upon the exercise of the rights represented by this Warrant will, upon issuance, be validly issued and outstanding, fully paid and nonassessable, and free from all taxes, liens and charges with respect to the issuance thereof. The Company further covenants and agrees that the Company will at all times during the Exercise Period, have authorized and reserved a sufficient number of shares of the series of equity securities comprising the Exercise Shares to provide for the exercise of the rights represented by this Warrant. The issuance of the Exercise Shares will not be subject to any preemptive rights that have not been properly waived or complied with. If at any time during the Exercise Period the number of authorized but unissued shares of such series of the Company’s equity securities shall not be sufficient to permit exercise of this Warrant, the Company will take such corporate action as may, in the opinion of its counsel, be necessary to increase its authorized but unissued shares of such series of the Company’s equity securities to such number of shares as shall be sufficient for such purposes.

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4. REPRESENTATIONS OF HOLDER.

4.1 Acquisition of Warrant for Personal Account. The Holder represents and warrants that it is acquiring the Warrant and the Exercise Shares solely for its account for investment and not with a view to or for sale or distribution of said Warrant or Exercise Shares or any part thereof. The Holder also represents that the entire legal and beneficial interests of the Warrant and Exercise Shares the Holder is acquiring is being acquired for, and will be held for, its account only.

4.2 Securities Are Not Registered.

(a) The Holder understands that the Warrant and the Exercise Shares have not been registered under the Securities Act of 1933, as amended (the “Act”) on the basis that no distribution or public offering of the stock of the Company is to be effected. The Holder realizes that the basis for the exemption may not be present if, notwithstanding its representations, the Holder has a present intention of acquiring the securities for a fixed or determinable period in the future, selling (in connection with a distribution or otherwise), granting any participation in, or otherwise distributing the securities. The Holder has no such present intention.

(b) The Holder recognizes that the Warrant and the Exercise Shares must be held indefinitely unless they are subsequently registered under the Act or an exemption from such registration is available. The Holder recognizes that the Company has no obligation to register the Warrant or the Exercise Shares of the Company, or to comply with any exemption from such registration.

(c) The Holder is aware that neither the Warrant nor the Exercise Shares may be sold pursuant to Rule 144 adopted under the Act unless certain conditions are met. These conditions may include, among other things, the existence of a public market for the shares, the availability of certain current public information about the Company, the resale following the required holding period under Rule 144 and the number of shares being sold during any three month period not exceeding specified limitations. Holder is aware that the conditions for resale set forth in Rule 144 have not been satisfied and that the Company presently has no plans to satisfy these conditions in the foreseeable future.

4.3 Disposition of Warrant and Exercise Shares.

(a) The Holder further agrees not to make any disposition of all or any part of the Warrant or Exercise Shares in any event unless and until:

(i) The Company shall have received a letter secured by the Holder from the Securities and Exchange Commission stating that no action will be recommended to the Commission with respect to the proposed disposition;

(ii) There is then in effect a registration statement under the Act covering such proposed disposition and such disposition is made in accordance with said registration statement; or

(iii) The Holder shall have notified the Company of the proposed disposition and shall have furnished the Company with a detailed statement of the circumstances surrounding the proposed disposition, and if reasonably requested by the Company, the Holder shall have furnished the Company with an opinion of counsel, reasonably satisfactory to the Company, for the Holder to the effect that such disposition will not require registration of such Warrant or Exercise Shares under the Act or any applicable state securities laws. The Company agrees that it will not require an opinion of counsel with respect to transactions under Rule 144 of the Act except in unusual circumstances.

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(b) The Holder understands and agrees that all certificates evidencing the shares to be issued to the Holder may bear the following legend:

4.4 Accredited Investor Status. The Holder is an “accredited investor” as defined in Regulation D promulgated under the Act.

5. ADJUSTMENT OF EXERCISE PRICE AND NUMBER OF EXERCISE SHARES.

5.1 Changes in Securities. In the event of changes in the class of equity securities of the Company comprising the Exercise Shares by reason of stock dividends, splits, recapitalizations, reclassifications, combinations or exchanges of such class of equity securities, then the number and class of Exercise Shares available under the Warrant in the aggregate and the Exercise Price shall be correspondingly adjusted to give the Holder of the Warrant, on exercise for the same aggregate Exercise Price, the total number, class, and kind of shares as the Holder would have owned had the Warrant been exercised prior to the event and had the Holder continued to hold such shares until after the event requiring adjustment. For purposes of this Section 5, the “aggregate Exercise Price” shall mean the aggregate Exercise Price payable in connection with the exercise in full of this Warrant. The form of this Warrant need not be changed because of any adjustment in the number of Exercise Shares subject to this Warrant.

6. FRACTIONAL SHARES. No fractional shares shall be issued upon the exercise of this Warrant as a consequence of any adjustment pursuant hereto. All Exercise Shares (including fractions) to be issued upon exercise of this Warrant shall be aggregated for purposes of determining whether the exercise would result in the issuance of any fractional share. If, after aggregation, the exercise would result in the issuance of a fractional share, the Company shall, in lieu of issuance of any fractional share, pay the Holder otherwise entitled to such fraction a sum in cash equal to the product resulting from multiplying the then current fair market value of one Exercise Share by such fraction.

7. MARKET STANDOFF. To the extent requested by the Company or an underwriter of securities of the Company, Holder and any permitted transferee thereof shall not, without the prior written consent of the managing underwriters in the IPO (as hereafter defined), offer, sell, make any short sale of, grant or sell any option for the purchase of, lend, pledge, otherwise transfer or dispose of (directly or indirectly), enter into any swap or other arrangement that transfers to another, in whole or in part, any of the economic consequences of ownership (whether any such transaction is described above or is to be settled by delivery of Exercise Shares or other securities, in cash, or otherwise), any Exercise Shares or other shares of stock of the Company then owned by such Holder or any transferee thereof, or enter into an agreement to do any of the foregoing, for up to 180 days following the effective date of the registration statement of the initial public offering of the Company (the “IPO”) filed under the Act. For purposes of this paragraph, “Company” includes any wholly owned subsidiary of the Company into which the Company merges or consolidates. The Company may place restrictive legends on the certificates representing the shares subject to this paragraph and may impose stop transfer instructions with respect to this Warrant and the Exercise Shares and such other shares of stock of Holder and any transferee thereof (and the shares or securities of every other person subject to the foregoing restriction) until the end of such period. Holder

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and any transferee thereof shall enter into any agreement reasonably required by the underwriters to the IPO to implement the foregoing within any reasonable timeframe so requested. The underwriters for any IPO are intended third party beneficiaries of this paragraph and shall have the right, power and authority to enforce the provisions of this paragraph as though they were parties hereto.

8. NO STOCKHOLDER RIGHTS. This Warrant in and of itself shall not entitle the Holder to any voting rights or other rights as a stockholder of the Company.

9. TRANSFER OF WARRANT. Subject to applicable laws and the restriction on transfer set forth on the first page of this Warrant, this Warrant and all rights hereunder are transferable, by the Holder in person or by duly authorized attorney, upon delivery of this Warrant and the form of assignment attached hereto as EXHIBIT B to any transferee designated by Holder. The transferee shall sign an investment letter in form and substance reasonably satisfactory to the Company.

10. LOST, STOLEN, MUTILATED OR DESTROYED WARRANT. If this Warrant is lost, stolen, mutilated or destroyed, the Company may, on such terms as to indemnity or otherwise as it may reasonably impose (which shall, in the case of a mutilated Warrant, include the surrender thereof), issue a new Warrant of like denomination and tenor as the Warrant so lost, stolen, mutilated or destroyed. Any such new Warrant shall constitute an original contractual obligation of the Company, whether or not the allegedly lost, stolen, mutilated or destroyed Warrant shall be at any time enforceable by anyone.

11. NOTICES, ETC. [All notices required or permitted hereunder shall be in writing and shall be deemed effectively given: (a) upon personal delivery to the party to be notified, (b) when sent by electronic transmission or facsimile if sent during normal business hours of the recipient, if not, then on the next business day, (c) five (5) days after having been sent by registered or certified mail, return receipt requested, postage prepaid, or (d) one (1) day after deposit with a nationally recognized overnight courier, specifying next day delivery, with written verification of receipt. All communications shall be sent to the Company at ▇▇▇ ▇▇▇▇▇▇▇▇▇▇▇▇ ▇▇▇▇▇, ▇▇▇▇▇▇▇▇▇▇▇▇, ▇▇▇▇▇▇▇▇ ▇▇▇▇▇, Attn: Chief Executive Officer, and to Holder at                     , or at such other address as the Company or Holder may designate by ten (10) days advance written notice to the other parties hereto.][All notices required or permitted hereunder shall be in writing and shall be deemed effectively given in accordance with the provisions of Section 6(j) of the Note.]

12. SUCCESSOR AND ASSIGNS. This Warrant and the rights evidenced hereby shall be binding upon and shall inure to the benefit of the parties hereto and the successors of the Company and the successors and permitted assigns of the Holder. Such successors and/or permitted assigns of the Holder shall be deemed to be a Holder for all purposes hereunder.

13. NO THIRD-PARTY BENEFICIARIES. This Warrant is for the sole benefit of the Company and the Holder and their respective successors and, in the case of the Holder, permitted assigns and nothing herein, express or implied, is intended to or shall confer upon any other Person any legal or equitable right, benefit or remedy of any nature whatsoever, under or by reason of this Warrant.

14. HEADINGS. The headings in this Warrant are for reference only and shall not affect the interpretation of this Warrant.

15. AMENDMENT AND MODIFICATION; WAIVER. [Except as otherwise provided herein, this Warrant may be amended, modified or supplemented only by an agreement in writing signed by the Holder and the Company. No waiver by the Company or the Holder of any of the provisions hereof shall be effective unless explicitly set forth in writing and signed by the party so waiving. No waiver by any party shall operate or be construed as a waiver in respect of any failure, breach or default not expressly identified by such written waiver, whether of a similar or different character, and whether occurring before or after

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that waiver. No failure to exercise, or delay in exercising, any rights, remedy, power or privilege arising from this Warrant shall operate or be construed as a waiver thereof; nor shall any single or partial exercise of any right, remedy, power or privilege hereunder preclude any other or further exercise thereof or the exercise of any other right, remedy, power or privilege.][Except as otherwise provided herein, this Warrant may be amended, modified or supplemented only by an agreement in writing signed by the Holder or the Majority Holders (as defined in the Note), on the one hand, and the Company, on the other hand. Upon the effectuation of such amendment, modification or supplement with the consent of the Majority Holders in conformance with this paragraph, such amendment, modification or supplement shall be effective as to, and binding against, the holders of all warrants issued pursuant to the Notes (as defined in the Note), and the Company shall promptly give written notice thereof to the Holder if the Holder has not previously consented to such amendment, modification or waiver in writing; provided that the failure to give such notice shall not affect the validity of such amendment, modification or waiver. No waiver by the Company, the Majority Holders, or the Holder of any of the provisions hereof shall be effective unless explicitly set forth in writing and signed by the party or parties so waiving. No waiver by any party shall operate or be construed as a waiver in respect of any failure, breach or default not expressly identified by such written waiver, whether of a similar or different character, and whether occurring before or after that waiver. No failure to exercise, or delay in exercising, any rights, remedy, power or privilege arising from this Warrant shall operate or be construed as a waiver thereof; nor shall any single or partial exercise of any right, remedy, power or privilege hereunder preclude any other or further exercise thereof or the exercise of any other right, remedy, power or privilege.]

16. SEVERABILITY. If any term or provision of this Warrant is invalid, illegal or unenforceable in any jurisdiction, such invalidity, illegality or unenforceability shall not affect any other term or provision of this Warrant or invalidate or render unenforceable such term or provision in any other jurisdiction.

17. ACCEPTANCE. Receipt of this Warrant by the Holder shall constitute acceptance of and agreement to all of the terms and conditions contained herein.

18. GOVERNING LAW. This Warrant and all rights, obligations and liabilities hereunder shall be governed by and construed under the laws of the State of Delaware as applied to agreements among Delaware residents, made and to be performed entirely within the State of Delaware without giving effect to conflicts of laws principles.

[SIGNATURE PAGE FOLLOWS]

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IN WITNESS WHEREOF, the Company has caused this Warrant to be executed by its duly authorized officer as of the date first written above.

[WARRANT TO PURCHASE COMMON STOCK]

EXHIBIT A

NOTICE OF EXERCISE

TO: SENSEI BIOTHERAPEUTICS, INC.

(1) ☐ The undersigned hereby elects to purchase __________ shares of Common Stock (the “Exercise Shares”) of Sensei Biotherapeutics, Inc. (the “Company”) pursuant to the terms of the attached Warrant, and tenders herewith payment of the exercise price in full, together with all applicable transfer taxes, if any.

      ☐ The undersigned hereby elects to purchase __________ shares of Common Stock (the “Exercise Shares”) of Sensei Biotherapeutics, Inc. (the “Company”) pursuant to the terms of the net exercise provisions set forth in Section 2.2 of the attached Warrant, and shall tender payment of all applicable transfer taxes, if any.

(2) Please issue a certificate or certificates representing said Exercise Shares in the name of the undersigned or in such other name as is specified below:

(3) The undersigned represents that (i) the aforesaid Exercise Shares are being acquired for the account of the undersigned for investment and not with a view to, or for resale in connection with, the distribution thereof and that the undersigned has no present intention of distributing or reselling such shares; (ii) the undersigned is aware of the Company’s business affairs and financial condition and has acquired sufficient information about the Company to reach an informed and knowledgeable decision regarding its investment in the Company; (iii) the undersigned is experienced in making investments of this type and has such knowledge and background in financial and business matters that the undersigned is capable of evaluating the merits and risks of this investment and protecting the undersigned’s own interests; (iv) the undersigned understands that Exercise Shares issuable upon exercise of this Warrant have not been registered under the Act by reason of a specific exemption from the registration provisions of the Act, which exemption depends upon, among other things, the bona fide nature of the investment intent as expressed herein, and, because such securities have not been registered under the Act, they must be held indefinitely unless subsequently registered under the Act or an exemption from such registration is available; (v) the undersigned is aware that the aforesaid Exercise Shares may not be sold pursuant to Rule 144 adopted under the Act unless certain conditions are met and until the undersigned has held the shares for the number of years prescribed by Rule 144, that the conditions for use of the Rule may include the availability of current information to the public about the Company and the Company has not made such information available and has no present plans to do so; and (vi) the undersigned agrees not to make any disposition of all or any part of the aforesaid shares of Exercise Shares unless and until there is then in effect a registration statement under the Act covering such proposed disposition and such disposition is made in accordance with said registration statement, or, if reasonably requested by the Company, the undersigned has provided the Company with an opinion of counsel satisfactory to the Company, stating that such registration is not required.

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EXHIBIT B

ASSIGNMENT FORM

FOR VALUE RECEIVED, the foregoing Warrant and all rights evidenced thereby are hereby assigned to

Name: ______________________________________________________________________________________________________

(Please Print)

Address: _____________________________________________________________________________________________________

(Please Print)

Dated: ____________, 20__

Holder’s

Signature: _______________________________________________________

Holder’s

Address: ________________________________________________________

NOTE: The signature to this Assignment Form must correspond with the name as it appears on the face of the Warrant, without alteration or enlargement or any change whatever. Officers of corporations and those acting in a fiduciary or other representative capacity should file proper evidence of authority to assign the foregoing Warrant.

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