EXHIBIT 4.3

THIS WARRANT AND THE UNDERLYING SECURITIES HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED (THE “ACT”), OR UNDER THE SECURITIES LAWS OF ANY STATE. THESE SECURITIES MAY NOT BE OFFERED, SOLD OR OTHERWISE TRANSFERRED, PLEDGED OR HYPOTHECATED EXCEPT AS PERMITTED UNDER THE ACT AND APPLICABLE STATE SECURITIES LAWS IN ACCORDANCE WITH APPLICABLE REGISTRATION REQUIREMENTS OR AN EXEMPTION THEREFROM. THE ISSUER OF THESE SECURITIES MAY REQUIRE AN OPINION OF COUNSEL REASONABLY SATISFACTORY TO THE ISSUER THAT SUCH OFFER, SALE, TRANSFER, PLEDGE OR HYPOTHECATION OTHERWISE COMPLIES WITH THE ACT AND ANY APPLICABLE STATE SECURITIES LAWS. THIS WARRANT MUST BE SURRENDERED TO THE COMPANY OR ITS TRANSFER AGENT AS A CONDITION PRECEDENT TO THE SALE, TRANSFER, PLEDGE OR HYPOTHECATION OF ANY INTEREST IN ANY OF THE SECURITIES REPRESENTED HEREBY.

WARRANT TO PURCHASE SHARES OF COMMON STOCK

of

SUTRO BIOPHARMA, INC.

Dated as of                     

Void after the date specified in Section 8

                     Shares of

Common Stock

(subject to adjustment)

THIS CERTIFIES THAT, for value received,                      or his registered assigns (the “Holder”), is entitled, subject to the provisions and upon the terms and conditions set forth herein, to purchase from Sutro Biopharma, Inc., a Delaware corporation (the “Company”), shares of the Company’s Common Stock, $0.001 par value per share (“Common Stock”), in the amounts, at such times and at the price per share set forth in Section 1. The term “Warrant” as used herein shall include this Warrant and any warrants delivered in substitution or exchange therefor as provided herein. This Warrant is issued to the Holder in consideration for the services rendered by                     , at the request of                      as its designee, under the letter agreement between                      and the Company, dated                     , in accordance with the terms set forth therein, and is one of a series of warrants issued pursuant thereto (the “Common Warrants”).

The following is a statement of the rights of the Holder and the conditions to which this Warrant is subject, and to which Holder, by acceptance of this Warrant, agrees:

1. Number and Price of Shares; Exercise Period.

(a) Number of Shares. Subject to any previous exercise of the Warrant, the Holder shall have the right to purchase up to                      shares of Common Stock, as may be adjusted pursuant hereto (the “Shares”), prior to (or in connection with) the expiration of this Warrant as provided in Section 8.

(b) Exercise Price. The exercise price per Share shall be equal to $                    , subject to adjustment pursuant hereto (the “Exercise Price”).

(c) Exercise Period. This Warrant shall be exercisable, in whole or in part, prior to (or in connection with) the expiration of this Warrant as set forth in Section 8.

2. Exercise of the Warrant.

(a) Exercise. The purchase rights represented by this Warrant may be exercised at the election of the Holder, in whole or in part, in accordance with Section 1, by:

(i) the tender to the Company at its principal office (or such other office or agency as the Company may designate) of a notice of exercise in the form of Exhibit A (the “Notice of Exercise”), duly completed and executed by or on behalf of the Holder, together with the surrender of this Warrant; and

(ii) the payment to the Company of an amount equal to (x) the Exercise Price multiplied by (y) the number of Shares being purchased, by wire transfer or certified, cashier’s or other check acceptable to the Company and payable to the order of the Company.

(b) Net Issue Exercise. In lieu of exercising this Warrant pursuant to Section 2(a)(ii), if the fair market value of one Share is greater than the Exercise Price (at the date of calculation as set forth below), the Holder may elect to receive a number of Shares equal to the value of this Warrant (or of any portion of this Warrant being canceled) by surrender of this Warrant at the principal office of the Company (or such other office or agency as the Company may designate) together with a properly completed and executed Notice of Exercise reflecting such election, in which event the Company shall issue to the Holder that number of Shares computed using the following formula:

Where:

For purposes of the calculation above, the fair market value of one Share shall be determined as follows:

(i) If the Company’s common stock is listed on any established stock exchange or a national market system, including without limitation the Nasdaq National Market or The Nasdaq SmallCap Market of The Nasdaq Stock Market, its fair market value shall be the closing sales price for such stock (or the closing bid, if no sales were reported) as quoted on such exchange or system on the day of determination, as reported in The Wall Street Journal or such other source as the Board of Directors deems reliable;

(ii) If the Company’s common stock is regularly quoted by a recognized securities dealer but selling prices are not reported, its fair market value shall be the mean between the high bid and low asked prices for the Company’s common stock on the day of determination;

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(iii) If the Warrant is exercised in connection with the Company’s initial public offering of 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; or

(iv) In the absence of an established market for the Company’s common stock and if the Warrant is not exercised in connection with the Company’s initial public offering of common stock, the fair market value thereof shall be determined in good faith by the Board of Directors of the Company.

(c) Stock Certificates. The rights under this Warrant shall be deemed to have been exercised and the Shares issuable upon such exercise shall be deemed to have been issued immediately prior to the close of business on the date this Warrant is exercised in accordance with its terms, and the person entitled to receive the Shares issuable upon such exercise shall be treated for all purposes as the holder of record of such Shares as of the close of business on such date. As promptly as reasonably practicable on or after such date, the Company shall issue and deliver to the person or persons entitled to receive the same a certificate or certificates for that number of shares issuable upon such exercise. In the event that the rights under this Warrant are exercised in part and have not expired, the Company shall execute and deliver a new Warrant reflecting the number of Shares that remain subject to this Warrant.

(d) No Fractional Shares or Scrip. No fractional shares or scrip representing fractional shares shall be issued upon the exercise of the rights under this Warrant. In lieu of such fractional share to which the Holder would otherwise be entitled, the Company shall make a cash payment equal to the Exercise Price multiplied by such fraction.

(e) Conditional Exercise. The Holder may exercise this Warrant conditioned upon (and effective immediately prior to) consummation of any transaction that would cause the expiration of this Warrant pursuant to Section 8 by so indicating in the notice of exercise.

(f) Reservation of Stock. The Company agrees during the term the rights under this Warrant are exercisable to reserve and keep available from its authorized and unissued shares of common stock for the purpose of effecting the exercise of this Warrant such number of shares as shall from time to time be sufficient to effect the exercise of the rights under this Warrant; and if at any time the number of authorized but unissued shares of common stock shall not be sufficient for purposes of the exercise of this Warrant in accordance with its terms, without limitation of such other remedies as may be available to the Holder, the Company will use its best efforts to take such corporate action as may be necessary to increase its authorized and unissued shares of its common stock to a number of shares as shall be sufficient for such purposes.

3. Replacement of the Warrant. Subject to the receipt of evidence reasonably satisfactory to the Company of the loss, theft, destruction or mutilation of this Warrant and, in the case of loss, theft or destruction, on delivery of an indemnity agreement reasonably satisfactory in form and substance to the Company or, in the case of mutilation, on surrender and cancellation of this Warrant, the Company at the expense of the Holder shall execute and deliver, in lieu of this Warrant, a new warrant of like tenor and amount.

4. Transfer of the Warrant.

(a) Warrant Register. The Company shall maintain a register (the “Warrant Register”) containing the name and address of the Holder or Holders. Until this Warrant is transferred on the Warrant Register in accordance herewith, the Company may treat the Holder as shown on the Warrant Register as the absolute owner of this Warrant for all purposes, notwithstanding any notice to the contrary. Any Holder of this Warrant (or of any portion of this Warrant) may change its address as shown on the Warrant Register by written notice to the Company requesting a change.

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(b) Warrant Agent. The Company may appoint an agent for the purpose of maintaining the Warrant Register referred to in Section 4(a), issuing the Shares or other securities then issuable upon the exercise of the rights under this Warrant, exchanging this Warrant, replacing this Warrant or conducting related activities.

(c) Transferability of the Warrant. Subject to the provisions of this Warrant with respect to compliance with the Securities Act of 1933, as amended (the “Securities Act”) and limitations on assignments and transfers, including without limitation compliance with the restrictions on transfer set forth in Section 5, title to this Warrant may be transferred by endorsement (by the transferor and the transferee executing the assignment form attached as Exhibit B (the “Assignment Form”)) and delivery in the same manner as a negotiable instrument transferable by endorsement and delivery.

(d) Exchange of the Warrant upon a Transfer. On surrender of this Warrant (and a properly endorsed Assignment Form) for exchange, subject to the provisions of this Warrant with respect to compliance with the Securities Act and limitations on assignments and transfers, the Company shall issue to or on the order of the Holder a new warrant or warrants of like tenor, in the name of the Holder or as the Holder (on payment by the Holder of any applicable transfer taxes) may direct, for the number of shares issuable upon exercise hereof, and the Company shall register any such transfer upon the Warrant Register. This Warrant (and the securities issuable upon exercise of the rights under this Warrant) must be surrendered to the Company or its warrant or transfer agent, as applicable, as a condition precedent to the sale, pledge, hypothecation or other transfer of any interest in any of the securities represented hereby.

(e) Minimum Transfer. This Warrant may not be transferred in part unless such transfer is to a transferee who, pursuant to such transfer, receives the right to purchase at least                              (                ) Shares hereunder (as adjusted from time to time in accordance with Section 6).

(f) Taxes. In no event shall the Company be required to pay any tax which may be payable in respect of any transfer involved in the issue and delivery of any certificate in a name other than that of the Holder, and the Company shall not be required to issue or deliver any such certificate unless and until the person or persons requesting the issue thereof shall have paid to the Company the amount of such tax or shall have established to the satisfaction of the Company that such tax has been paid or is not payable.

5. Restrictions on Transfer of the Warrant and Shares; Compliance with Securities Laws. By acceptance of this Warrant, the Holder agrees to comply with the following:

(a) Restrictions on Transfers. This Warrant may not be transferred or assigned in whole or in part without the Company’s prior written consent (which shall not be unreasonably withheld), and any attempt by Holder to transfer or assign any rights, duties or obligations that arise under this Warrant without such permission shall be void. Any transfer of this Warrant or the Shares (the “Securities”) must be in compliance with all applicable federal and state securities laws. The Holder agrees not to make any sale, assignment, transfer, pledge or other disposition of all or any portion of the Securities, or any beneficial interest therein, unless and until the transferee thereof has agreed in writing for the benefit of the Company to take and hold such Securities subject to, and to be bound by, the terms and conditions set forth in this Warrant to the same extent as if the transferee were the original Holder hereunder, and

(i) there is then in effect a registration statement under the Securities Act covering such proposed disposition and such disposition is made in accordance with such registration statement, or

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(ii) (A) such Holder shall have given prior written notice to the Company of such Holder’s intention to make such disposition and shall have furnished the Company with a detailed description of the manner and circumstances of the proposed disposition, (B) the transferee shall have confirmed to the satisfaction of the Company in writing, substantially in the form of Exhibit A-1, that the Securities are being acquired (i) solely for the transferee’s own account and not as a nominee for any other party, (ii) for investment and (iii) not with a view toward distribution or resale, and shall have confirmed such other matters related thereto as may be reasonably requested by the Company, and (C) such Holder shall have furnished the Company, at the Holder’s expense, with (i) an opinion of counsel, reasonably satisfactory to the Company, to the effect that such disposition will not require registration of such Securities under the Securities Act or (ii) a “no action” letter from the Securities and Exchange Commission to the effect that the transfer of such Securities without registration will not result in a recommendation by the staff of the Securities and Exchange Commission that action be taken with respect thereto, whereupon such Holder shall be entitled to transfer such Securities in accordance with the terms of the notice delivered by the Holder to the Company.

(b) Investment Representation Statement. Unless the rights under this Warrant are exercised pursuant to an effective registration statement under the Securities Act that includes the Shares with respect to which the Warrant was exercised, it shall be a condition to any exercise of the rights under this Warrant that the Holder shall have confirmed to the satisfaction of the Company in writing, substantially in the form of Exhibit A-1, that the Shares so purchased are being acquired solely for the Holder’s own account and not as a nominee for any other party, for investment and not with a view toward distribution or resale and that the Holder shall have confirmed such other matters related thereto as may be reasonably requested by the Company.

(c) Company’s Right of First Refusal. Notwithstanding anything to the contrary herein, before any Shares held by Holder (which, for the purposes of this Section 5(c), shall include any transferee of Shares) may be sold or otherwise transferred (including transfer by gift or operation of law), the Company or its assignee(s) shall have a right of first refusal to purchase the Shares on the terms and conditions set forth in this Section (the “Right of First Refusal”).

(i) Notice of Proposed Transfer. The Holder of the Shares shall deliver to the Company a written notice (the “Notice”) stating: (A) the Holder’s bona fide intention to sell or otherwise transfer such Shares; (B) the name of each proposed purchaser or other transferee (“Proposed Transferee”); (C) the number of Shares to be transferred to each Proposed Transferee; and (D) the bona fide cash price or other consideration for which the Holder proposes to transfer the Shares (the “Offered Price”), and the Holder shall offer the Shares at the Offered Price to the Company or its assignee(s).

(ii) Exercise of Right of First Refusal. At any time within thirty (30) days after receipt of the Notice, the Company and/or its assignee(s) may, by giving written notice to the Holder, elect to purchase all, but not less than all, of the Shares proposed to be transferred to any one or more of the Proposed Transferees, at the purchase price determined in accordance with subsection (iii) below.

(iii) Purchase Price. The purchase price (“Purchase Price”) for the Shares purchased by the Company or its assignee(s) under this Section shall be the Offered Price. If the Offered Price includes consideration other than cash, the cash equivalent value of the non-cash consideration shall be determined by the Board of Directors of the Company in good faith.

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(iv) Payment. Payment of the Purchase Price shall be made, at the option of the Company or its assignee(s), in cash (by check), by cancellation of all or a portion of any outstanding indebtedness of the Holder to the Company (or, in the case of repurchase by an assignee, to the assignee), or by any combination thereof within thirty (30) days after receipt of the Notice or in the manner and at the times set forth in the Notice.

(v) Holder’s Right to Transfer. If all of the Shares proposed in the Notice to be transferred to a given Proposed Transferee are not purchased by the Company and/or its assignee(s) as provided in this Section, then the Holder may sell or otherwise transfer such Shares to that Proposed Transferee at the Offered Price or at a higher price, provided that such sale or other transfer is consummated within 120 days after the date of the Notice, that any such sale or other transfer is effected in accordance with any applicable securities laws and that the Proposed Transferee agrees in writing that the provisions of this Section shall continue to apply to the Shares in the hands of such Proposed Transferee. If the Shares described in the Notice are not transferred to the Proposed Transferee within such period, a new Notice shall be given to the Company, and the Company and/or its assignees shall again be offered the Right of First Refusal before any Shares held by the Holder may be sold or otherwise transferred.

(vi) Exception for Certain Family Transfers. Anything to the contrary contained in this Section notwithstanding, the transfer of any or all of the Shares during the Holder’s lifetime or on the Holder’s death by will or intestacy to the Holder’s immediate family or a trust for the benefit of the Holder’s immediate family shall be exempt from the provisions of this Section. “Immediate Family” as used herein shall mean spouse, lineal descendant or antecedent, father, mother, brother or sister. In such case, the transferee or other recipient shall receive and hold the Shares so transferred subject to the provisions of this Section, and there shall be no further transfer of such Shares except in accordance with the terms of this Section.

(vii) Termination of Right of First Refusal. The Right of First Refusal shall terminate as to any Shares upon the expiration of this Warrant or the occurrence of any event specified in Section 8.

(d) Securities Law Legend. The Securities shall (unless otherwise permitted by the provisions of this Warrant) be stamped or imprinted with a legend substantially similar to the following (in addition to any legend required by state securities laws):

THE SECURITIES REPRESENTED HEREBY HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED (THE “ACT”), OR UNDER THE SECURITIES LAWS OF CERTAIN STATES. THESE SECURITIES MAY NOT BE OFFERED, SOLD OR OTHERWISE TRANSFERRED, PLEDGED OR HYPOTHECATED EXCEPT AS PERMITTED UNDER THE ACT AND APPLICABLE STATE SECURITIES LAWS IN ACCORDANCE WITH APPLICABLE REGISTRATION REQUIREMENTS OR AN EXEMPTION THEREFROM. THE ISSUER OF THESE SECURITIES MAY REQUIRE AN OPINION OF COUNSEL REASONABLY SATISFACTORY TO THE ISSUER THAT SUCH OFFER, SALE OR TRANSFER, PLEDGE OR HYPOTHECATION OTHERWISE COMPLIES WITH THE ACT AND ANY APPLICABLE STATE SECURITIES LAWS. THIS CERTIFICATE MUST BE SURRENDERED TO THE COMPANY OR ITS TRANSFER AGENT AS A CONDITION PRECEDENT TO THE SALE, TRANSFER, PLEDGE OR HYPOTHECATION OF ANY INTEREST IN ANY OF THE SECURITIES REPRESENTED HEREBY.

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(e) Additional Share Legend. The Shares issued upon exercise hereof shall also be stamped or imprinted with a legend in substantially the following form:

THE SHARES REPRESENTED BY THIS CERTIFICATE ARE SUBJECT TO CERTAIN RESTRICTIONS ON TRANSFER AND A RIGHT OF FIRST REFUSAL HELD BY THE ISSUER OR ITS ASSIGNEE(S) AS SET FORTH IN THE WARRANT TO PURCHASE SHARES OF COMMON STOCK BETWEEN THE ISSUER AND THE ORIGINAL HOLDER OF THESE SHARES, A COPY OF WHICH MAY BE OBTAINED AT THE PRINCIPAL OFFICE OF THE ISSUER. SUCH TRANSFER RESTRICTIONS AND RIGHT OF FIRST REFUSAL ARE BINDING ON TRANSFEREES OF THESE SHARES.

THE SHARES REPRESENTED BY THIS CERTIFICATE ARE SUBJECT TO RESTRICTIONS ON TRANSFERABILITY AND RESALE, INCLUDING A LOCK-UP PERIOD IN THE EVENT OF A PUBLIC OFFERING, AS SET FORTH IN THE WARRANT PURSUANT TO WHICH THESE SHARES WERE ISSUED, A COPY OF WHICH MAY BE OBTAINED AT THE PRINCIPAL OFFICE OF THE COMPANY.

(f) Instructions Regarding Transfer Restrictions. The Holder consents to the Company making a notation on its records and giving instructions to any transfer agent in order to implement the restrictions on transfer established in this Section 5.

(g) Removal of Legend. The legend referring to federal and state securities laws identified in Section 5(d) stamped on a certificate evidencing the Shares and the stock transfer instructions and record notations with respect to such securities shall be removed and the Company shall issue a certificate without such legend to the holder of such securities if (i) such securities are registered under the Securities Act, or (ii) such holder provides the Company with an opinion of counsel reasonably acceptable to the Company to the effect that a sale or transfer of such securities may be made without registration or qualification.

6. Adjustments. Subject to the expiration of this Warrant pursuant to Section 8, the number and kind of shares purchasable hereunder and the Exercise Price therefor are subject to adjustment from time to time, as follows:

(a) Merger or Reorganization. If at any time there shall be any reorganization, recapitalization, merger or consolidation (a “Reorganization”) involving the Company (other than as otherwise provided for herein or as would cause the expiration of this Warrant under Section 8) in which shares of the Company’s stock are converted into or exchanged for securities, cash or other property, then, as a part of such Reorganization, lawful provision shall be made so that the Holder shall thereafter be entitled to receive upon exercise of this Warrant, the kind and amount of securities, cash or other property of the successor corporation resulting from such Reorganization, equivalent in value to that which a holder of the Shares deliverable upon exercise of this Warrant would have been entitled in such Reorganization if the right to purchase the Shares hereunder had been exercised immediately prior to such Reorganization. In any such case, appropriate adjustment (as determined in good faith by the Board of Directors of the successor corporation) shall be made in the application of the provisions of this Warrant with respect to the rights and interests of the Holder after such Reorganization to the end that the provisions of this Warrant shall be applicable after the event, as near as reasonably may be, in relation to any shares or other securities deliverable after that event upon the exercise of this Warrant.

(b) Reclassification of Shares. If the securities issuable upon exercise of this Warrant are changed into the same or a different number of securities of any other class or classes by reclassification, capital reorganization or otherwise (other than as otherwise provided for herein) (a “Reclassification”),

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then, in any such event, in lieu of the number of Shares which the Holder would otherwise have been entitled to receive, the Holder shall have the right thereafter to exercise this Warrant for a number of shares of such other class or classes of stock that a holder of the number of securities deliverable upon exercise of this Warrant immediately before that change would have been entitled to receive in such Reclassification, all subject to further adjustment as provided herein with respect to such other shares.

(c) Subdivisions and Combinations. In the event that the outstanding shares of common stock are subdivided (by stock split, by payment of a stock dividend or otherwise) into a greater number of shares of such securities, the number of Shares issuable upon exercise of the rights under this Warrant immediately prior to such subdivision shall, concurrently with the effectiveness of such subdivision, be proportionately increased, and the Exercise Price shall be proportionately decreased, and in the event that the outstanding shares of common stock are combined (by reclassification or otherwise) into a lesser number of shares of such securities, the number of Shares issuable upon exercise of the rights under this Warrant immediately prior to such combination shall, concurrently with the effectiveness of such combination, be proportionately decreased, and the Exercise Price shall be proportionately increased.

(d) Notice of Adjustments. Upon any adjustment in accordance with this Section 6, the Company shall give notice thereof to the Holder, which notice shall state the event giving rise to the adjustment, the Exercise Price as adjusted and the number of securities or other property purchasable upon the exercise of the rights under this Warrant, setting forth in reasonable detail the method of calculation of each. The Company shall, upon the written request of any Holder, furnish or cause to be furnished to such Holder a certificate setting forth (i) such adjustments, (ii) the Exercise Price at the time in effect and (iii) the number of securities and the amount, if any, of other property that at the time would be received upon exercise of this Warrant.

7. Notification of Certain Events. Prior to the expiration of this Warrant pursuant to Section 8, in the event that the Company shall authorize:

(a) the issuance of any dividend or other distribution on the capital stock of the Company (other than (i) dividends or distributions otherwise provided for in Section 6, (ii) repurchases of common stock issued to or held by employees, officers, directors or consultants of the Company or its subsidiaries upon termination of their employment or services pursuant to agreements providing for the right of said repurchase; (iii) repurchases of common stock issued to or held by employees, officers, directors or consultants of the Company or its subsidiaries pursuant to rights of first refusal or first offer contained in agreements providing for such rights; or (iv) repurchases of capital stock of the Company in connection with the settlement of disputes with any stockholder), whether in cash, property, stock or other securities;

(b) the voluntary liquidation, dissolution or winding up of the Company; or

(c) any transaction resulting in the expiration of this Warrant pursuant to Section 8(b) or 8(c);

the Company shall send to the Holder of this Warrant at least ten (10) days prior written notice of the date on which a record shall be taken for any such dividend or distribution specified in clause (a) or the expected effective date of any such other event specified in clause (b) or (c), as applicable. The notice provisions set forth in this section may be shortened or waived prospectively or retrospectively by the consent of the holders of a majority of the Shares issuable upon exercise of the rights under the Common Warrants.

8. Expiration of the Warrant. This Warrant shall expire and shall no longer be exercisable as of the earlier of:

(a)                 , Pacific time, on                     ;

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(b) (i) the acquisition of the Company by another entity by means of any transaction or series of related transactions to which the Company is a party (including, without limitation, any stock acquisition, reorganization, merger or consolidation, but excluding any sale of stock for capital raising purposes and any transaction effected primarily for purposes of changing the Company’s jurisdiction of incorporation) other than a transaction or series of related transactions in which the holders of the voting securities of the Company outstanding immediately prior to such transaction or series of related transactions retain, immediately after such transaction or series of transactions, as a result of shares in the Company held by such holders prior to such transaction or series of transactions, at least a majority of the total voting power represented by the outstanding voting securities of the Company or such other surviving or resulting entity (or if the Company or such other surviving or resulting entity is a wholly-owned subsidiary immediately following such acquisition, its parent), or (ii) a sale, lease or other disposition of all or substantially all of the assets of the Company and its subsidiaries taken as a whole by means of any transaction or series of related transactions, except where such sale, lease or other disposition is to a wholly-owned subsidiary of the Company; or

(c) Immediately prior to the closing of a firm commitment underwritten public offering pursuant to an effective registration statement filed under the Securities Act covering the offering and sale of the Company’s common stock.

9. No Rights as a Stockholder. Nothing contained herein shall entitle the Holder to any rights as a stockholder of the Company or to be deemed the holder of any securities that may at any time be issuable on the exercise of the rights hereunder for any purpose nor shall anything contained herein be construed to confer upon the Holder, as such, any right to vote for the election of directors or upon any matter submitted to stockholders at any meeting thereof, or to give or withhold consent to any corporate action (whether upon any recapitalization, issuance of stock, reclassification of stock, change of par value or change of stock to no par value, consolidation, merger, conveyance or otherwise) or to receive notice of meetings, or to receive dividends or subscription rights or any other rights of a stockholder of the Company until the rights under the Warrant shall have been exercised and the Shares purchasable upon exercise of the rights hereunder shall have become deliverable as provided herein.

10. Market Stand-off. The Holder of this Warrant hereby agrees that such Holder shall not sell or otherwise transfer, make any short sale of, grant any option for the purchase of, or enter into any hedging or similar transaction with the same economic effect as a sale, of any common stock (or other securities) of the Company held by the Holder (other than those included in the registration) during the one hundred eighty (180) day period following the effective date of the registration statement for the Company’s initial public offering filed under the Securities Act (or such other period as may be requested by the Company or an underwriter to accommodate regulatory restrictions on (i) the publication or other distribution of research reports and (ii) analyst recommendations and opinions, including, but not limited to, the restrictions contained in NASD Rule 2711(f)(4) or NYSE Rule 472(f)(4), or any successor provisions or amendments thereto). The obligations described in this section shall not apply to a registration relating solely to employee benefit plans on Form S-1 or Form S-8 or similar forms that may be promulgated in the future, or a registration relating solely to a transaction on Form S-4 or similar forms that may be promulgated in the future. The Company may impose stop-transfer instructions and may stamp each certificate with a legend as substantially set forth in Section 5(e) with respect to the shares of common stock (or other securities) subject to the foregoing restriction until the end of such one hundred eighty (180) day (or other) period. The Holder agrees to execute a market stand-off agreement with the underwriters in the offering in customary form consistent with the provisions of this section.

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11. Representations and Warranties of the Holder. By acceptance of this Warrant, the Holder represents and warrants to the Company as follows:

(a) No Registration. The Holder understands that the Securities have not been, and will not be, registered under the Securities Act by reason of a specific exemption from the registration provisions of the Securities Act, the availability of which depends upon, among other things, the bona fide nature of the investment intent and the accuracy of the Holder’s representations as expressed herein or otherwise made pursuant hereto.

(b) Investment Intent. The Holder is acquiring the Securities for investment for its own account, not as a nominee or agent, and not with a view to, or for resale in connection with, any distribution thereof. The Holder has no present intention of selling, granting any participation in, or otherwise distributing the Securities, nor does it have any contract, undertaking, agreement or arrangement for the same.

(c) Investment Experience. The Holder has substantial experience in evaluating and investing in private placement transactions of securities in companies similar to the Company, and has such knowledge and experience in financial or business matters so that it is capable of evaluating the merits and risks of its investment in the Company and protecting its own interests.

(d) Speculative Nature of Investment. The Holder understands and acknowledges that the Company has a limited financial and operating history and that its investment in the Company is highly speculative and involves substantial risks. The Holder can bear the economic risk of its investment and is able, without impairing its financial condition, to hold the Securities for an indefinite period of time and to suffer a complete loss of its investment.

(e) Access to Data. The Holder has had an opportunity to ask questions of officers of the Company, which questions were answered to its satisfaction. The Holder believes that it has received all the information that it considers necessary or appropriate for deciding whether to acquire the Securities. The Holder understands that any such discussions, as well as any information issued by the Company, were intended to describe certain aspects of the Company’s business and prospects, but were not necessarily a thorough or exhaustive description. The Holder acknowledges that any business plans prepared by the Company have been, and continue to be, subject to change and that any projections included in such business plans or otherwise are necessarily speculative in nature, and it can be expected that some or all of the assumptions underlying the projections will not materialize or will vary significantly from actual results.

(f) Accredited Investor. The Holder is an “accredited investor” within the meaning of Regulation D, Rule 501(a), promulgated by the Securities and Exchange Commission and agrees to submit to the Company such further assurances of such status as may be reasonably requested by the Company.

(g) Residency. The residency of the Holder (or, in the case of a partnership, corporation or other business entity, such entity’s principal place of business) is correctly set forth on the signature page hereto.

(h) Restrictions on Resales. The Holder acknowledges that the Securities must be held indefinitely unless subsequently registered under the Securities Act or an exemption from such registration is available. The Holder is aware of the provisions of Rule 144 promulgated under the Securities Act, which permit resale of shares purchased in a private placement subject to the satisfaction of certain conditions, which may include, among other things, the availability of certain current public information about the Company; the resale occurring not less than a specified period after a party has

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purchased and paid for the security to be sold; the number of shares being sold during any three-month period not exceeding specified limitations; the sale being effected through a “broker’s transaction,” a transaction directly with a “market maker” or a “riskless principal transaction” (as those terms are defined in the Securities Act or the Securities Exchange Act of 1934, as amended, and the rules and regulations promulgated thereunder); and the filing of a Form 144 notice, if applicable. The Holder acknowledges and understands that the Company may not be satisfying the current public information requirement of Rule 144 at the time the Holder wishes to sell the Securities and that, in such event, the Holder may be precluded from selling the Securities under Rule 144 even if the other applicable requirements of Rule 144 have been satisfied. The Holder acknowledges that, in the event the applicable requirements of Rule 144 are not met, registration under the Securities Act or an exemption from registration will be required for any disposition of the Securities. The Holder understands that, although Rule 144 is not exclusive, the Securities and Exchange Commission has expressed its opinion that persons proposing to sell restricted securities received in a private offering other than in a registered offering or pursuant to Rule 144 will have a substantial burden of proof in establishing that an exemption from registration is available for such offers or sales and that such persons and the brokers who participate in the transactions do so at their own risk.

(i) No Public Market. The Holder understands and acknowledges that no public market now exists for any of the securities issued by the Company and that the Company has made no assurances that a public market will ever exist for the Company’s securities.

(j) Brokers and Finders. The Holder has not engaged any brokers, finders or agents in connection with the Securities, and the Company has not incurred nor will incur, directly or indirectly, as a result of any action taken by the Holder, any liability for brokerage or finders’ fees or agents’ commissions or any similar charges in connection with the Securities.

(k) Legal Counsel. The Holder has had the opportunity to review this Warrant, the exhibits and schedules attached hereto and the transactions contemplated by this Warrant with its own legal counsel. The Holder is not relying on any statements or representations of the Company or its agents for legal advice with respect to this investment or the transactions contemplated by this Warrant.

(l) Tax Advisors. The Holder has reviewed with its own tax advisors the U.S. federal, state and local and non-U.S. tax consequences of this investment and the transactions contemplated by this Warrant. With respect to such matters, the Holder relies solely on any such advisors and not on any statements or representations of the Company or any of its agents, written or oral. The Holder understands that it (and not the Company) shall be responsible for its own tax liability that may arise as a result of this investment and the transactions contemplated by this Warrant.

12. Code Section 409A. Under Code Section 409A, a warrant that vests after                      (or that vested on or prior to such date but which was materially modified after                     ) that was granted with a per Share exercise price that is determined by the Internal Revenue Service (the “IRS”) to be less than the fair market value of a Share on the date of grant (a “discount warrant”) may be considered “deferred compensation.” A warrant that is a “discount warrant” may result in (i) income recognition by the holder of the warrant prior to the exercise of the warrant, (ii) an additional twenty percent (20%) federal income tax, and (iii) potential penalty and interest charges. The “discount warrant” may also result in additional state income, penalty and interest tax to the holder of the warrant. Holder acknowledges that the Company cannot guarantee and has not guaranteed that the IRS will agree that the per Share exercise price of this Warrant equals or exceeds the fair market value of a Share on the date of grant in a later examination. Holder agrees that if the IRS determines that the Warrant was granted with a per Share exercise price that was less than the fair market value of a Share on the date of grant, Holder will be solely responsible for Holder’s costs related to such a determination.

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13. Miscellaneous.

(a) Amendments. Except as expressly provided herein, neither this Warrant nor any term hereof may be amended, waived, discharged or terminated other than by a written instrument referencing this Warrant and signed by the Company and the holders of warrants representing not less than a majority of the Shares issuable upon exercise of any and all outstanding Common Warrants, which majority does not need to include the consent of the Holder. Any amendment, waiver, discharge or termination effected in accordance with this Section 13(a) shall be binding upon each holder of the Common Warrants, each future holder of such Common Warrants and the Company; provided, however, that no special consideration or inducement may be given to any such holder in connection with such consent that is not given ratably to all such holders, and that such amendment must apply to all such holders equally and ratably in accordance with the number of shares of Common Stock issuable upon exercise of the Common Warrants. The Company shall promptly give notice to all holders of Common Warrants of any amendment effected in accordance with this Section 13(a).

(b) Waivers. No waiver of any single breach or default shall be deemed a waiver of any other breach or default theretofore or thereafter occurring.

(c) Notices. All notices and other communications required or permitted hereunder shall be in writing and shall be mailed by registered or certified mail, postage prepaid, sent by facsimile or electronic mail (if to the Holder) or otherwise delivered by hand, messenger or courier service addressed:

(i) if to the Holder, to the Holder at the Holder’s address, facsimile number or electronic mail address as shown in the Company’s records, as may be updated in accordance with the provisions hereof, or until any such Holder so furnishes an address, facsimile number or electronic mail address to the Company, then to and at the address, facsimile number or electronic mail address of the last holder of this Warrant for which the Company has contact information in its records; or

(ii) if to the Company, to the attention of the President or Chief Financial Officer of the Company at the Company’s address as shown on the signature page hereto, or at such other current address as the Company shall have furnished to the Holder, with a copy (which shall not constitute notice) to                             ,                         .

Each such notice or other communication shall for all purposes of this Warrant be treated as effective or having been given (i) if delivered by hand, messenger or courier service, when delivered, or (ii) if sent by mail, at the earlier of its receipt or 72 hours after the same has been deposited in a regularly-maintained receptacle for the deposit of the United States mail, addressed and mailed as aforesaid, or (iii) if sent by facsimile, upon confirmation of facsimile transfer or, if sent by electronic mail, upon confirmation of delivery when directed to the relevant electronic mail address. In the event of any conflict between the Company’s books and records and this Warrant or any notice delivered hereunder, the Company’s books and records will control absent fraud or error.

(d) Governing Law. This Warrant and all actions arising out of or in connection with this Warrant shall be governed by and construed in accordance with the laws of the State of California, without regard to the conflicts of law provisions of the State of California, or of any other state.

(e) Jurisdiction and Venue. Each of the Holder and the Company irrevocably consents to the exclusive jurisdiction and venue of any court within San Mateo County, State of California, in connection with any matter based upon or arising out of this Warrant or the matters contemplated herein, and agrees that process may be served upon them in any manner authorized by the laws of the State of California for such persons.

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(f) Titles and Subtitles. The titles and subtitles used in this Warrant are used for convenience only and are not to be considered in construing or interpreting this Warrant. All references in this Warrant to sections, paragraphs and exhibits shall, unless otherwise provided, refer to sections and paragraphs hereof and exhibits attached hereto.

(g) Severability. If any provision of this Warrant becomes or is declared by a court of competent jurisdiction to be illegal, unenforceable or void, portions of such provision, or such provision in its entirety, to the extent necessary, shall be severed from this Warrant, and such illegal, unenforceable or void provision shall be replaced with a valid and enforceable provision that will achieve, to the extent possible, the same economic, business and other purposes of the illegal, unenforceable or void provision. The balance of this Warrant shall be enforceable in accordance with its terms.

(h) Waiver of Jury Trial. EACH OF THE HOLDER AND THE COMPANY WAIVES, TO THE FULLEST EXTENT PERMITTED BY LAW, ANY AND ALL RIGHT TO TRIAL BY JURY IN ANY LEGAL PROCEEDING (WHETHER BASED ON CONTRACT, TORT OR OTHERWISE) ARISING OUT OF OR RELATED TO THIS WARRANT. If the waiver of jury trial set forth in this paragraph is not enforceable, then any claim or cause of action arising out of or relating to this Warrant shall be settled by judicial reference pursuant to California Code of Civil Procedure Section 638 et seq. before a referee sitting without a jury, such referee to be mutually acceptable to the parties or, if no agreement is reached, by a referee appointed by the Presiding Judge of the California Superior Court for San Mateo County. This paragraph shall not restrict the Holder or the Company from exercising remedies under the Uniform Commercial Code or from exercising pre-judgment remedies under applicable law.

(i) California Corporate Securities Law. THE SALE OF THE SECURITIES THAT ARE THE SUBJECT OF THIS WARRANT HAS NOT BEEN QUALIFIED WITH THE COMMISSIONER OF CORPORATIONS OF THE STATE OF CALIFORNIA AND THE ISSUANCE OF SUCH SECURITIES OR THE PAYMENT OR RECEIPT OF ANY PART OF THE CONSIDERATION THEREFOR PRIOR TO SUCH QUALIFICATION IS UNLAWFUL, UNLESS THE SALE OF SECURITIES IS EXEMPT FROM QUALIFICATION BY SECTION 25100, 25102, OR 25105 OF THE CALIFORNIA CORPORATIONS CODE. THE RIGHTS OF ALL PARTIES TO THIS WARRANT ARE EXPRESSLY CONDITIONED UPON THE QUALIFICATION BEING OBTAINED, UNLESS THE SALE IS SO EXEMPT.

(j) Rights and Obligations Survive Exercise of the Warrant. Except as otherwise provided herein, the rights and obligations of the Company and the Holder under this Warrant shall survive exercise of this Warrant.

(k) Entire Agreement. Except as expressly set forth herein, this Warrant (including the exhibits attached hereto) constitutes the entire agreement and understanding of the Company and the Holder with respect to the subject matter hereof and supersedes all prior agreements and understandings relating to the subject matter hereof.

(signature page follows)

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The Company and the Holder sign this Warrant as of the date stated on the first page.

(Signature Page to Warrant to Purchase Shares Common Stock of Sutro Biopharma, Inc.)

EXHIBIT A

NOTICE OF EXERCISE

A-1

(Signature page to the Notice of Exercise)

A-2

EXHIBIT A-l

INVESTMENT REPRESENTATION STATEMENT

AND

MARKET STAND-OFF AGREEMENT

In connection with the purchase or acquisition of the above-listed Securities, the undersigned Investor represents and warrants to, and agrees with, the Company as follows:

1. No Registration. The Investor understands that the Securities have not been, and will not be, registered under the Securities Act of 1933, as amended (the “Securities Act”), by reason of a specific exemption from the registration provisions of the Securities Act, the availability of which depends upon, among other things, the bona fide nature of the investment intent and the accuracy of the Investor’s representations as expressed herein or otherwise made pursuant hereto.

2. Investment Intent. The Investor is acquiring the Securities for investment for its own account, not as a nominee or agent, and not with a view to, or for resale in connection with, any distribution thereof. The Investor has no present intention of selling, granting any participation in, or otherwise distributing the Securities, nor does it have any contract, undertaking, agreement or arrangement for the same.

3. Investment Experience. The Investor has substantial experience in evaluating and investing in private placement transactions of securities in companies similar to the Company, and has such knowledge and experience in financial or business matters so that it is capable of evaluating the merits and risks of its investment in the Company and protecting its own interests.

4. Speculative Nature of Investment. The Investor understands and acknowledges that the Company has a limited financial and operating history and that its investment in the Company is highly speculative and involves substantial risks. The Investor can bear the economic risk of its investment and is able, without impairing its financial condition, to hold the Securities for an indefinite period of time and to suffer a complete loss of its investment.

5. Access to Data. The Investor has had an opportunity to ask questions of officers of the Company, which questions were answered to its satisfaction. The Investor believes that it has received all the information that it considers necessary or appropriate for deciding whether to acquire the Securities. The Investor understands that any such discussions, as well as any information issued by the Company, were intended to describe certain aspects of the Company’s business and prospects, but were not necessarily a thorough or exhaustive description. The Investor acknowledges that any business plans prepared by the Company have been, and continue to be, subject to change and that any projections included in such business plans or otherwise are necessarily speculative in nature, and it can be expected that some or all of the assumptions underlying the projections will not materialize or will vary significantly from actual results.

A-1-1

6. Accredited Investor. The Investor is an “accredited investor” within the meaning of Regulation D, Rule 501(a), promulgated by the Securities and Exchange Commission and agrees to submit to the Company such further assurances of such status as may be reasonably requested by the Company.

7. Residency. The residency of the Investor (or, in the case of a partnership, corporation or other business entity, such entity’s principal place of business) is correctly set forth on the signature page hereto.

8. Restrictions on Resales. The Investor acknowledges that the Securities must be held indefinitely unless subsequently registered under the Securities Act or an exemption from such registration is available. The Investor is aware of the provisions of Rule 144 promulgated under the Securities Act, which permit resale of shares purchased in a private placement subject to the satisfaction of certain conditions, which may include, among other things, the availability of certain current public information about the Company; the resale occurring not less than a specified period after a party has purchased and paid for the security to be sold; the number of shares being sold during any three-month period not exceeding specified limitations; the sale being effected through a “broker’s transaction,” a transaction directly with a “market maker” or a “riskless principal transaction” (as those terms are defined in the Securities Act or the Securities Exchange Act of 1934, as amended, and the rules and regulations promulgated thereunder); and the filing of a Form 144 notice, if applicable. The Investor acknowledges and understands that the Company may not be satisfying the current public information requirement of Rule 144 at the time the Investor wishes to sell the Securities and that, in such event, the Investor may be precluded from selling the Securities under Rule 144 even if the other applicable requirements of Rule 144 have been satisfied. The Investor understands and acknowledges that, in the event the applicable requirements of Rule 144 are not met, registration under the Securities Act or an exemption from registration will be required for any disposition of the Securities. The Investor understands that, although Rule 144 is not exclusive, the Securities and Exchange Commission has expressed its opinion that persons proposing to sell restricted securities received in a private offering other than in a registered offering or pursuant to Rule 144 will have a substantial burden of proof in establishing that an exemption from registration is available for those offers or sales and that those persons and the brokers who participate in the transactions do so at their own risk.

9. No Public Market. The Holder understands and acknowledges that no public market now exists for any of the securities issued by the Company and that the Company has made no assurances that a public market will ever exist for the Company’s securities.

10. Brokers and Finders. The Investor has not engaged any brokers, finders or agents in connection with the Securities, and the Company has not incurred nor will incur, directly or indirectly, as a result of any action taken by the Investor, any liability for brokerage or finders’ fees or agents’ commissions or any similar charges in connection with the Securities.

11. Legal Counsel. The Investor has had the opportunity to review the Warrant, the exhibits and schedules attached thereto and the transactions contemplated by the Warrant with its own legal counsel. The Investor is not relying on any statements or representations of the Company or its agents for legal advice with respect to this investment or the transactions contemplated by the Warrant.

12. Tax Advisors. The Investor has reviewed with its own tax advisors the U.S. federal, state and local and non-U.S. tax consequences of this investment and the transactions contemplated by the Warrant. With respect to such matters, the Investor relies solely on such advisors and not on any statements or representations of the Company or any of its agents, written or oral. The Investor understands that it (and not the Company) shall be responsible for its own tax liability that may arise as a result of this investment or the transactions contemplated by the Warrant.

A-1-2

13. Market Stand-off. The Investor agrees that the Investor shall not sell or otherwise transfer, make any short sale of, grant any option for the purchase of, or enter into any hedging or similar transaction with the same economic effect as a sale, of any common stock (or other securities) of the Company held by the Investor (other than those included in the registration) during the one hundred eighty (180) day period following the effective date of the registration statement for the Company’s initial public offering filed under the Securities Act (or such other period as may be requested by the Company or an underwriter to accommodate regulatory restrictions on (i) the publication or other distribution of research reports and (ii) analyst recommendations and opinions, including, but not limited to, the restrictions contained in NASD Rule 2711(f)(4) or NYSE Rule 472(f)(4), or any successor provisions or amendments thereto. The obligations described in this section shall not apply to a registration relating solely to employee benefit plans on Form S-1 or Form S-8 or similar forms that may be promulgated in the future, or a registration relating solely to a transaction on Form S-4 or similar forms that may be promulgated in the future. The Company may impose stop-transfer instructions and may stamp each certificate with a legend with respect to the shares of common stock (or other securities) subject to the foregoing restriction until the end of such one hundred eighty (180) day (or other) period. The Investor agrees to execute a market stand-off agreement with the relevant underwriters in customary form consistent with the provisions of this section.

14. Company’s Right of First Refusal. The undersigned acknowledges and agrees to be bound, or to continue to be bound, by the Company’s right of first refusal over the securities issued or issuable upon the exercise of the Warrant, as provided for in Section 5(c) of the Warrant.

(signature page follows)

A-1-3

The Investor is signing this Investment Representation Statement and Market Stand-Off Agreement on the date first written above.

A-1-4

EXHIBIT B

ASSIGNMENT FORM

and does irrevocably constitute and appoint                                      as attorney to make such transfer on the books of Sutro Biopharma, Inc. (the “Company”), maintained for the purpose, with full power of substitution in the premises.

Assignor and Assignee are signing this Assignment Form on the date first set forth above.

B-1

B-2