EXHIBIT 4.5

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 PREFERRED STOCK

of

SUTRO BIOPHARMA, INC.

Dated as of                         

Void after the date specified in Section 8

THIS CERTIFIES THAT, in consideration of the sum of                              ($            ) and for other value received,                 , or its 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 (as defined below), 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 in connection with the transactions described in the Note and Warrant Purchase Agreement, dated as of                             , by and among the Company and the purchasers described therein (the “Purchase Agreement”).

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) Definition of Shares. “Shares” shall mean the class and series of preferred stock issued by the Company to investors in a Qualified Financing (as defined below) that occurs prior to the earlier of (i)                              or (ii) the expiration of this Warrant. If no Qualified Financing occurs prior to the earlier of (i)                      or (ii) the expiration of this Warrant, “Shares” shall mean Series B Preferred Stock of the Company. A “Qualified Financing” is a transaction or series of transactions pursuant to which the Company issues and sells shares of its preferred stock, with the principal purpose of raising capital, for aggregate gross proceeds of at least $                     (including any and all amounts received upon the conversion or cancellation of indebtedness).

(b) Number of Shares. Subject to any previous exercise of the Warrant, the Holder shall have the right to purchase up to the number of Shares that equals the quotient obtained by dividing (x) $                         by (y) the Exercise Price (as defined below), prior to (or in connection with) the expiration of this Warrant as provided in Section 8.

(c) Exercise Price. The exercise price per Share shall be equal to the lowest price per share of the Shares issued in a Qualified Financing; provided, however, that if no Qualified Financing has occurred on or prior to the earlier of (i) September 20, 2011 or (ii) the expiration of this Warrant, and if the Shares subject to this Warrant are deemed to be Series B Preferred Stock of the Company in accordance with Section 1(a), the exercise price for the Shares subject to this Warrant shall be                  per Share, subject to adjustment pursuant hereto (the “Exercise Price”).

(d) Exercise Period. This Warrant shall be exercisable, in whole or in part, after the earlier of (i) the closing date of a Qualified Financing or (ii)                              and 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:

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For purposes of the calculation above, the fair market value of one Share shall be determined by the Board of Directors of the Company, acting in good faith; provided, however, that:

(i) where a public market exists for the Company’s common stock at the time of such exercise, the fair market value per Share shall be the product of (x) the average of the closing bid and asked prices of the common stock or the closing price quoted on the national securities exchange on which the common stock is listed as published in the Wall Street Journal, as applicable, for the ten (10) trading day period ending five (5) trading days prior to the date of determination of fair market value and (y) the number of shares of common stock into which each Share is convertible at the time of such exercise, as applicable; and

(ii) 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 product of (x) the per share offering price to the public of the Company’s initial public offering and (y) the number of shares of common stock into which each Share is convertible at the time of such exercise, as applicable.

(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) 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 preferred stock for the purpose of effecting the exercise of this Warrant such number of shares (and shares of common stock for issuance on conversion of such 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 preferred stock (and shares of common stock for issuance on conversion of such shares) shall not be sufficient for purposes of the exercise of this Warrant in accordance with its terms and the conversion of the Shares, 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 preferred stock (and shares of common stock for issuance on conversion of such shares) 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.

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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.

(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) 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. Subject to Section 5(b), 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 or the shares of common stock issuable upon conversion of 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) Permitted Transfers. Permitted transfers include (i) a transfer not involving a change in beneficial ownership, or (ii) transactions involving the distribution without consideration of Securities by any Holder to (x) a parent, subsidiary or other affiliate of a Holder that is a corporation, (y) any of the Holder’s partners, members or other equity owners, or retired partners or members, or to the estate of any of its partners, members or other equity owners or retired partners or members, or (z) a venture capital fund that is controlled by or under common control with one or more general partners or managing members of, or shares the same management company with, the Holder; provided, in each case, that the Holder shall give written notice to the Company of the Holder’s intention to effect such disposition and shall have furnished the Company with a detailed description of the manner and circumstances of the proposed disposition.

(c) 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.

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(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.

(e) Market Stand-off Legend. The Shares and common stock issued upon exercise hereof or conversion thereof shall also be stamped or imprinted with a legend in substantially the following form:

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 common stock issuable upon conversion thereof) 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.

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(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, conversion of all outstanding shares of the relevant class or series (other than as would cause the expiration of this Warrant pursuant to Section 8) or otherwise (other than as otherwise provided for herein) (a “Reclassification”), 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 the securities issuable upon exercise of this Warrant 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 the securities issuable upon exercise of this Warrant 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

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(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 Warrants.

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

(a) ____ p.m., Pacific time, on                     ;

(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

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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.

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.

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(g) Residency. The residency of the Holder (or, in the case of a partnership or corporation, 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 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. 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

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a majority of the Shares issuable upon exercise of any and all outstanding 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 12(a) shall be binding upon each holder of the Warrants, each future holder of such 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 Stock issuable upon exercise of the Warrants. The Company shall promptly give notice to all holders of Warrants of any amendment effected in accordance with this Section 12(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 address as the Company shall have furnished to the Holder, with a copy to Kenneth A. Clark, Wilson Sonsini Goodrich & Rosati, P.C., 650 Page Mill Road, Palo Alto, CA 94301.

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 Santa Clara 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.

(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.

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(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 Santa Clara 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 supersede 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 of Preferred Stock of Sutro Biopharma, Inc.)

EXHIBIT A

NOTICE OF EXERCISE

A-1

(Signature page to the Notice of Exercise)

A-2

EXHIBIT A-1

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

A-1-1

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.

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 or corporation, 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.

(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., maintained for the purpose, with full power of substitution in the premises.

B-1

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

B-2

THIS WARRANT AND THE SHARES ISSUABLE HEREUNDER HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED (THE “ACT”), OR THE SECURITIES LAWS OF ANY STATE AND, EXCEPT AS SET FORTH IN SECTIONS 5.3 AND 5.4 BELOW, MAY NOT BE OFFERED, SOLD, PLEDGED OR OTHERWISE TRANSFERRED UNLESS AND UNTIL REGISTERED UNDER SAID ACT AND LAWS OR IN THE OPINION OF LEGAL COUNSEL IN FORM AND SUBSTANCE SATISFACTORY TO THE COMPANY, SUCH OFFER, SALE, PLEDGE OR OTHER TRANSFER IS EXEMPT FROM SUCH REGISTRATION.

WARRANT TO PURCHASE STOCK

THIS WARRANT CERTIFIES THAT, for good and valuable consideration,                                     (together with any successor or permitted assignee or transferee of this Warrant or of any shares issued upon exercise hereof, “Holder”) is entitled to purchase the number of fully paid and non-assessable shares (the “Shares”) of the above-stated Type/Series of Stock (the “Class”) of the above-named company (the “Company”) at the above-stated Warrant Price, all as set forth above and as adjusted pursuant to Section 2 of this Warrant, subject to the provisions and upon the terms and conditions set forth in this Warrant. Reference is made to Section 5.4 of this Warrant whereby                                      shall transfer this Warrant to its parent company,                                     .

SECTION 1. EXERCISE.

1.1 Method of Exercise. Holder may at any time and from time to time exercise this Warrant, in whole or in part, by delivering to the Company the original of this Warrant together with a duly executed Notice of Exercise in substantially the form attached hereto as Appendix 1 and, unless Holder is exercising this Warrant pursuant to a cashless exercise as set forth in Section 1.2, a check, wire transfer of same-day funds (to an account designated by the Company), or other form of payment acceptable to the Company for the aggregate Warrant Price for the Shares being purchased.

1.2 Cashless Exercise. On any exercise of this Warrant, in lieu of payment of the aggregate Warrant Price in the manner as specified in Section 1.1 above, but otherwise in accordance with the requirements of Section 1.1, Holder may elect to receive Shares equal to the value of this Warrant, or portion hereof as to which this Warrant is being exercised. Thereupon, the Company shall issue to the Holder such number of fully paid and non-assessable Shares as are computed using the following formula:

X = Y(A-B)/A

1

where:

1.3 Fair Market Value. If the Company’s common stock is then traded or quoted on a nationally recognized securities exchange, inter-dealer quotation system or over-the-counter market (a “Trading Market”) and the Class is common stock, the fair market value of a Share shall be the closing price or last sale price of a share of common stock reported for the Business Day immediately before the date on which Holder delivers this Warrant together with its Notice of Exercise to the Company. If the Company’s common stock is then traded in a Trading Market and the Class is a series of the Company’s convertible preferred stock, the fair market value of a Share shall be the closing price or last sale price of a share of the Company’s common stock reported for the Business Day immediately before the date on which Holder delivers this Warrant together with its Notice of Exercise to the Company multiplied by the number of shares of the Company’s common stock into which a Share is then convertible. If the Company’s common stock is not traded in a Trading Market, the Board of Directors of the Company shall determine the fair market value of a Share in its reasonable good faith judgment.

1.4 Delivery of Certificate and New Warrant. Within a reasonable time after Holder exercises this Warrant in the manner set forth in Section 1.1 or 1.2 above, the Company shall deliver to Holder a certificate representing the Shares issued to Holder upon such exercise and, if this Warrant has not been fully exercised and has not expired, a new warrant of like tenor representing the Shares not so acquired.

1.5 Replacement of Warrant. On 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, substance and amount to the Company or, in the case of mutilation, on surrender of this Warrant to the Company for cancellation, the Company shall, within a reasonable time, execute and deliver to Holder, in lieu of this Warrant, a new warrant of like tenor and amount.

1.6 Treatment of Warrant Upon Acquisition of Company.

(a) Acquisition. For the purpose of this Warrant, “Acquisition” means any transaction or series of related transactions involving: (i) the sale, lease, exclusive license, or other disposition of all or substantially all of the assets of the Company; (ii) any merger or consolidation of the Company into or with another person or entity (other than a merger or consolidation effected exclusively to change the Company’s domicile), or any other corporate reorganization, in which the stockholders of the Company in their capacity as such immediately prior to such merger, consolidation or reorganization, own less than a majority of the Company’s (or the surviving or successor entity’s) outstanding voting power immediately after such merger, consolidation or reorganization; or (iii) any sale or other transfer by the stockholders of the Company of shares representing at least a majority of the Company’s then-total outstanding combined voting power.

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(b) Treatment of Warrant at Acquisition. In the event of an Acquisition in which the consideration to be received by the Company’s stockholders consists solely of cash, solely of Marketable Securities or a combination of cash and Marketable Securities (a “Cash/Public Acquisition”), either (i) Holder shall exercise this Warrant pursuant to Section 1.1 and/or 1.2 and such exercise will be deemed effective immediately prior to and contingent upon the consummation of such Acquisition or (ii) if Holder elects not to exercise the Warrant, this Warrant will expire immediately prior to the consummation of such Acquisition.

(c) The Company shall provide Holder with written notice of its request relating to the Cash/Public Acquisition (together with such reasonable information as Holder may reasonably require regarding the treatment of this Warrant in connection with such contemplated Cash/Public Acquisition giving rise to such notice), which is to be delivered to Holder not less than seven (7) Business Days prior to the closing of the proposed Cash/Public Acquisition. In the event the Company does not provide such notice, then if, immediately prior to the Cash/Public Acquisition, the fair market value of one Share (or other security issuable upon the exercise hereof) as determined in accordance with Section 1.3 above would be greater than the Warrant Price in effect on such date, then this Warrant shall automatically be deemed on and as of such date to be exercised pursuant to Section 1.2 above as to all Shares (or such other securities) for which it shall not previously have been exercised, and the Company shall promptly notify the Holder of the number of Shares (or such other securities) issued upon such exercise to the Holder and Holder shall be deemed to have restated each of the representations and warranties in Section 4 of the Warrant as the date thereof.

(d) Upon the closing of any Acquisition other than a Cash/Public Acquisition defined above, the acquiring, surviving or successor entity shall assume the obligations of this Warrant, and this Warrant shall thereafter be exercisable for the same securities and/or other property as would have been paid for the Shares issuable upon exercise of the unexercised portion of this Warrant as if such Shares were outstanding on and as of the closing of such Acquisition, subject to further adjustment from time to time in accordance with the provisions of this Warrant.

(e) As used in this Warrant, “Marketable Securities” means securities meeting all of the following requirements: (i) the issuer thereof is then subject to the reporting requirements of Section 13 or Section 15(d) of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), and is then current in its filing of all required reports and other information under the Act and the Exchange Act; (ii) the class and series of shares or other security of the issuer that would be received by Holder in connection with the Acquisition were Holder to exercise this Warrant on or prior to the closing thereof is then traded in a Trading Market, and (iii) Holder would not be restricted by contract or by applicable federal and state securities laws from publicly re-selling, within six (6) months following the closing of such Acquisition, all of the issuer’s shares and/or other securities that would be received by Holder in such Acquisition were Holder to exercise this Warrant in full on or prior to the closing of such Acquisition.

1.7 Additional Shares. In addition to the Initial Shares granted to Holder on the Issue Date, at the time of the funding of the Tranche Two Equipment Advance (as defined in the Loan Agreement), the Company shall be deemed to have automatically granted to Holder, in addition to the number of Shares which this Warrant can otherwise be exercised for by Holder, the right to purchase that number of additional Shares (rounded down to the nearest whole number) which could be purchased by taking $                                    , divided by the Warrant Price (such additional Shares being called the “Additional Shares”).

3

SECTION 2. ADJUSTMENTS TO THE SHARES AND WARRANT PRICE.

2.1 Stock Dividends, Splits, Etc. If the Company declares or pays a dividend or distribution on the outstanding shares of the Class payable in common stock or other securities or property (other than cash), then upon exercise of this Warrant, for each Share acquired, Holder shall receive, without additional cost to Holder, the total number and kind of securities and property which Holder would have received had Holder owned the Shares of record as of the date the dividend or distribution occurred. If the Company subdivides the outstanding shares of the Class by reclassification or otherwise into a greater number of shares, the number of Shares purchasable hereunder shall be proportionately increased and the Warrant Price shall be proportionately decreased. If the outstanding shares of the Class are combined or consolidated, by reclassification or otherwise, into a lesser number of shares, the Warrant Price shall be proportionately increased and the number of Shares shall be proportionately decreased.

2.2 Reclassification, Exchange, Combinations or Substitution. Upon any event whereby all of the outstanding shares of the Class are reclassified, exchanged, combined, substituted, or replaced for, into, with or by Company securities of a different class and/or series, then from and after the consummation of such event, this Warrant will be exercisable for the number, class and series of Company securities that Holder would have received had the Shares been outstanding on and as of the consummation of such event, and subject to further adjustment thereafter from time to time in accordance with the provisions of this Warrant. The provisions of this Section 2.2 shall similarly apply to successive reclassifications, exchanges, combinations substitutions, replacements or other similar events.

2.3 Conversion of Preferred Stock. If the Class is a class and series of the Company’s convertible preferred stock, in the event that all outstanding shares of the Class are converted, automatically or by action of the holders thereof, into common stock pursuant to the provisions of the Company’s Certificate of Incorporation, including, without limitation, in connection with the Company’s initial, underwritten public offering and sale of its common stock pursuant to an effective registration statement under the Act (the “IPO”), then from and after the date on which all outstanding shares of the Class have been so converted, this Warrant shall be exercisable for such number of shares of common stock into which the Shares would have been converted had the Shares been outstanding on the date of such conversion, and the Warrant Price shall equal the Warrant Price in effect as of immediately prior to such conversion divided by the number of shares of common stock into which one Share would have been converted, all subject to further adjustment thereafter from time to time in accordance with the provisions of this Warrant.

2.4 Adjustments for Diluting Issuances. Without duplication of any adjustment otherwise provided for in this Section 2, the number of shares of common stock issuable upon conversion of the Shares shall be subject to anti-dilution adjustment from time to time in the manner set forth in the Company’s Articles or Certificate of Incorporation as if the Shares were issued and outstanding on and as of the date of any such required adjustment.

2.5 No Fractional Share. No fractional Share shall be issuable upon exercise of this Warrant and the number of Shares to be issued shall be rounded down to the nearest whole Share. If a fractional Share interest arises upon any exercise of the Warrant, the Company shall eliminate such fractional Share interest by paying Holder in cash the amount computed by multiplying the fractional interest by the fair market value (as determined in accordance with Section 1.3 above) of a full Share.

2.6 Notice/Certificate as to Adjustments. Upon each adjustment of the Warrant Price, Class and/or number of Shares, the Company, at the Company’s expense, shall notify Holder in writing within a reasonable time setting forth the adjustments to the Warrant Price, Class and/or number of Shares and facts upon which such adjustment is based. The Company shall, upon written request from Holder, furnish Holder with a certificate of its Chief Financial Officer, including computations of such adjustment and the Warrant Price, Class and number of Shares in effect upon the date of such adjustment.

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SECTION 3. REPRESENTATIONS AND COVENANTS OF THE COMPANY.

3.1 Representations and Warranties. The Company represents and warrants to, and agrees with, the Holder as follows:

(a) The initial Warrant Price referenced on the first page of this Warrant is not greater than the price per share at which shares of the Class were last sold and issued prior to the Issue Date hereof in an arms-length transaction in which at least $                     of such shares were sold.

(b) All Shares which may be issued upon the exercise of this Warrant, and all securities, if any, issuable upon conversion of the Shares, shall, upon issuance, be duly authorized, validly issued, fully paid and non-assessable, and free of any liens and encumbrances except for restrictions on transfer provided for herein or under applicable federal and state securities laws. The Company covenants that it shall at all times cause to be reserved and kept available out of its authorized and unissued capital stock such number of shares of the Class, common stock and other securities as will be sufficient to permit the exercise in full of this Warrant and the conversion of the Shares into common stock or such other securities.

(c) The Company’s capitalization table attached hereto as Schedule 1 is true and complete, in all material respects, as of the Issue Date.

3.2 Notice of Certain Events. If the Company proposes at any time to:

(a) declare any dividend or distribution upon the outstanding shares of the Class or common stock, whether in cash, property, stock, or other securities and whether or not a regular cash dividend;

(b) offer for subscription or sale pro rata to the holders of the outstanding shares of the Class any additional shares of any class or series of the Company’s stock (other than pursuant to contractual pre-emptive rights);

(c) effect any reclassification, exchange, combination, substitution, reorganization or recapitalization of the outstanding shares of the Class;

(d) effect an Acquisition or to liquidate, dissolve or wind up; or

(e) effect an IPO;

then, in connection with each such event, the Company shall give Holder:

(1) at least seven (7) Business Days prior written notice of the date on which a record will be taken for such dividend, distribution, or subscription rights (and specifying the date on which the holders of outstanding shares of the Class will be entitled thereto) or for determining rights to vote, if any, in respect of the matters referred to in (a) and (b) above;

(2) in the case of the matters referred to in (c) and (d) above at least seven (7) Business Days prior written notice of the date when the same will take place (and specifying the date on which the holders of outstanding shares of the Class will be entitled to exchange their shares for the securities or other property deliverable upon the occurrence of such event); and

5

(3) with respect to the IPO, at least seven (7) Business Days prior written notice of the date on which the Company proposes to file its registration statement in connection therewith.

Reference is made to Section 1.6(c) whereby this Warrant will be deemed to be exercised pursuant to Section 1.2 hereof if the Company does not give written notice to Holder of a Cash/Public Acquisition as required by the terms hereof. Company will also provide information requested by Holder that is reasonably necessary to enable Holder to comply with Holder’s accounting or reporting requirements.

3.3 Registration Under Securities Act of 1933, as amended. The Company agrees that the Shares or, if the Shares are convertible into common stock of the Company, such common stock, shall have certain “piggyback” and “S-3” registration rights in parity with the investors pursuant to and as set forth in the Company’s Amended and Restated Investors’ Rights Agreement dated November 5, 2010 (the “Rights Agreement”), which rights shall be effective as of the date that the Company receives the requisite investor consent and an executed amendment to the Rights Agreement from Holder substantially in the form attached hereto as Exhibit A, joining the Holder as a party to the Rights Agreement, which shall occur no later than the earlier of (a) the Company’s next financing round, or (b) upon any exercise or conversion of this Warrant. The provisions set forth in the Rights Agreement or similar agreement relating to the above in effect as of the Issue Date may not be amended, modified or waived without the prior written consent of Holder unless such amendment, modification or waiver affects the rights associated with the Shares in the same manner as such amendment, modification, or waiver affects the rights associated with all other shares of the same series and class as the Shares granted to Holder.

SECTION 4. REPRESENTATIONS, WARRANTIES OF THE HOLDER.

The Holder represents and warrants to the Company as follows:

4.1 Purchase for Own Account. This Warrant and the securities to be acquired upon exercise of this Warrant by Holder are being acquired for investment for Holder’s account, not as a nominee or agent, and not with a view to the public resale or distribution within the meaning of the Act. Holder also represents that it has not been formed for the specific purpose of acquiring this Warrant or the Shares.

4.2 Disclosure of Information. Holder is aware of the Company’s business affairs and financial condition and has received or has had full access to all the information it considers necessary or appropriate to make an informed investment decision with respect to the acquisition of this Warrant and its underlying securities. Holder further has had an opportunity to ask questions and receive answers from the Company regarding the terms and conditions of the offering of this Warrant and its underlying securities and to obtain additional information (to the extent the Company possessed such information or could acquire it without unreasonable effort or expense) necessary to verify any information furnished to Holder or to which Holder has access.

4.3 Investment Experience. Holder understands that the purchase of this Warrant and its underlying securities involves substantial risk. Holder has experience as an investor in securities of companies in the development stage and acknowledges that Holder can bear the economic risk of such Holder’s investment in this Warrant and its underlying securities and has such knowledge and experience in financial or business matters that Holder is capable of evaluating the merits and risks of its investment in this Warrant and its underlying securities and/or has a preexisting personal or business relationship with the Company and certain of its officers, directors or controlling persons of a nature and duration that enables Holder to be aware of the character, business acumen and financial circumstances of such persons.

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4.4 Accredited Investor Status. Holder is an “accredited investor” within the meaning of Regulation D promulgated under the Act.

4.5 The Act. Holder understands that this Warrant and the Shares issuable upon exercise hereof have not been registered under the Act in reliance upon a specific exemption therefrom, which exemption depends upon, among other things, the bona fide nature of the Holder’s investment intent as expressed herein. Holder understands that this Warrant and the Shares issued upon any exercise hereof must be held indefinitely unless subsequently registered under the Act and qualified under applicable state securities laws, or unless exemption from such registration and qualification are otherwise available. Holder is aware of the provisions of Rule 144 promulgated under the Act.

4.6 Lock-Up Agreement. The Holder agrees that the Shares shall be subject to the Lock-Up provisions in Section 11 of the Rights Agreement.

4.7 No Voting Rights. Holder, as a Holder of this Warrant, will not have any voting rights until the exercise of this Warrant.

SECTION 5. MISCELLANEOUS.

5.1 Term and Automatic Conversion Upon Expiration.

(a) Term. Subject to the provisions of Section 1.6 above, this Warrant is exercisable in whole or in part at any time and from time to time on or before 6:00 PM, Pacific time, on the Expiration Date and shall be void thereafter.

(b) Automatic Cashless Exercise upon Expiration. In the event that, upon the Expiration Date, the fair market value of one Share (or other security issuable upon the exercise hereof) as determined in accordance with Section 1.3 above is greater than the Warrant Price in effect on such date, then this Warrant shall automatically be deemed on and as of such date to be exercised pursuant to Section 1.2 above as to all Shares (or such other securities) for which it shall not previously have been exercised, and the Company shall, within a reasonable time, deliver a certificate representing the Shares (or such other securities) issued upon such exercise to Holder.

5.2 Legends. The Shares (and the securities issuable, directly or indirectly, upon conversion of the Shares, if any) shall be imprinted with a legend in substantially the following form:

THE SHARES EVIDENCED BY THIS CERTIFICATE HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED (THE “ACT”), OR THE SECURITIES LAWS OF ANY STATE AND, EXCEPT AS SET FORTH IN THAT CERTAIN WARRANT TO PURCHASE STOCK ISSUED BY THE ISSUER TO                          DATED                                     MAY NOT BE OFFERED, SOLD, PLEDGED OR OTHERWISE TRANSFERRED UNLESS AND UNTIL REGISTERED UNDER SAID ACT AND LAWS OR IN THE OPINION OF LEGAL COUNSEL IN FORM AND SUBSTANCE SATISFACTORY TO THE ISSUER, SUCH OFFER, SALE, PLEDGE OR OTHER TRANSFER IS EXEMPT FROM SUCH REGISTRATION.

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The Shares issuable upon exercise of this Warrant (and the securities issuable, directly or indirectly, upon conversion of the Shares, if any) shall also be imprinted with the legends described in, and required by, the Rights Agreement.

5.3 Compliance with Securities Laws on Transfer. This Warrant and the Shares issuable upon exercise of this Warrant (and the securities issuable, directly or indirectly, upon conversion of the Shares, if any) may not be transferred or assigned in whole or in part except in compliance with applicable federal and state securities laws by the transferor and the transferee (including, without limitation, the delivery of investment representation letters and legal opinions reasonably satisfactory to the Company, as reasonably requested by the Company). The Company shall not require                                      to provide an opinion of counsel if the transfer is to                                      (                                         parent company) or any other affiliate of Holder, provided that any such transferee is an “accredited investor” as defined in Regulation D promulgated under the Act. Additionally, the Company shall also not require an opinion of counsel if there is no material question as to the availability of Rule 144 promulgated under the Act.

5.4 Transfer Procedure. After receipt by                                      of the executed Warrant,                                      will transfer all of this Warrant to its parent company,                                     . By its acceptance of this Warrant,                                          hereby makes to the Company each of the representations and warranties set forth in Section 4 hereof and agrees to be bound by all of the terms and conditions of this Warrant as if the original Holder hereof. Subject to the provisions of Section 5.3 and upon providing the Company with written notice,                                          and any subsequent Holder may transfer all or part of this Warrant or the Shares issuable upon exercise of this Warrant (or the securities issuable directly or indirectly, upon conversion of the Shares, if any) to any transferee, provided, however, in connection with any such transfer,                                               or any subsequent Holder will give the Company notice of the portion of the Warrant being transferred with the name, address and taxpayer identification number of the transferee and Holder will surrender this Warrant to the Company for reissuance to the transferee(s) (and Holder if applicable); and provided further, that any subsequent transferee other than                                          shall agree in writing with the Company to be bound by all of the terms and conditions of this Warrant. Notwithstanding any contrary provision herein, at all times prior to the IPO, Holder may not, without the Company’s prior written consent, transfer this Warrant or any portion hereof, or any Shares issued upon any exercise hereof, or any shares or other securities issued upon any conversion of any Shares issued upon any exercise hereof, to any person or entity who directly competes with the Company, except in connection with an Acquisition of the Company by such a direct competitor.

5.5 Notices. All notices and other communications hereunder from the Company to the Holder, or vice versa, shall be deemed delivered and effective (i) when given personally, (ii) on the third (3^rd) Business Day after being mailed by first-class registered or certified mail, postage prepaid, (iii) upon actual receipt if given by facsimile or electronic mail and such receipt is confirmed in writing by the recipient, or (iv) on the first Business Day following delivery to a reliable overnight courier service, courier fee prepaid, in any case at such address as may have been furnished to the Company or Holder, as the case may be, in writing by the Company or such Holder from time to time in accordance with the provisions of this Section 5.5. All notices to Holder shall be addressed as follows until the Company receives notice of a change of address in connection with a transfer or otherwise:

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Notice to the Company shall be addressed as follows until Holder receives notice of a change in address:

5.6 Waiver. This Warrant and any term hereof may be changed, waived, discharged or terminated (either generally or in a particular instance and either retroactively or prospectively) only by an instrument in writing signed by the party against which enforcement of such change, waiver, discharge or termination is sought.

5.7 Attorney’s Fees. In the event of any dispute between the parties concerning the terms and provisions of this Warrant, the party prevailing in such dispute shall be entitled to collect from the other party all costs incurred in such dispute, including reasonable attorneys’ fees.

5.8 Counterparts; Facsimile/Electronic Signatures. This Warrant may be executed in counterparts, all of which together shall constitute one and the same agreement. Any signature page delivered electronically or by facsimile shall be binding to the same extent as an original signature page with regards to any agreement subject to the terms hereof or any amendment thereto.

5.9 Governing Law. This Warrant shall be governed by and construed in accordance with the laws of the State of California, without giving effect to its principles regarding conflicts of law.

5.10 Headings. The headings in this Warrant are for purposes of reference only and shall not limit or otherwise affect the meaning of any provision of this Warrant.

5.11 Business Days. “Business Day” is any day that is not a Saturday, Sunday or a day on which                                  is closed.

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IN WITNESS WHEREOF, the parties have caused this Warrant to Purchase Stock to be executed by their duly authorized representatives effective as of the Issue Date written above.

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APPENDIX 1

NOTICE OF EXERCISE

1. The undersigned Holder hereby exercises its right purchase ____________ shares of the Common/Series ____ Preferred [circle one] Stock of Sutro Biopharma, Inc. (the “Company”) in accordance with the attached Warrant To Purchase Stock, and tenders payment of the aggregate Warrant Price for such shares as follows:

2. Please issue a certificate or certificates representing the Shares in the name specified below:

3. By its execution below and for the benefit of the Company, Holder hereby restates each of the representations and warranties in Section 4 of the Warrant to Purchase Stock as of the date hereof.

Appendix 1

SCHEDULE 1

Company Capitalization Table

EXHIBIT A

FORM OF AMENDMENT TO INVESTOR RIGHTS AGREEMENT

Exhibit A