AVALANCHE BIOTECHNOLOGIES, INC. (a Delaware corporation) WARRANT TO PURCHASE SHARES OF COMMON STOCK

Exhibit 4.3

THIS WARRANT AND THE SECURITIES ISSUABLE UPON THE EXERCISE HEREOF HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED. THEY MAY NOT BE SOLD, OFFERED FOR SALE, PLEDGED, HYPOTHECATED, OR OTHERWISE TRANSFERRED EXCEPT PURSUANT TO AN EFFECTIVE REGISTRATION STATEMENT UNDER THE SECURITIES ACT OF 1933, AS AMENDED, OR AN OPINION OF COUNSEL SATISFACTORY TO THE COMPANY THAT REGISTRATION IS NOT REQUIRED UNDER SUCH ACT OR UNLESS SOLD PURSUANT TO RULE 144 UNDER SUCH ACT.

AVALANCHE BIOTECHNOLOGIES, INC.

(a Delaware corporation)

WARRANT TO PURCHASE SHARES OF

COMMON STOCK

This Warrant is issued to Cowen and Company, LLC (the “Holder”) by Avalanche Biotechnologies, Inc. a Delaware corporation (the “Company”).

1. Purchase of Shares.

(a) Number of Shares. Subject to the terms and conditions set forth herein, the Holder is entitled, upon surrender of this Warrant at the principal office of the Company (or at such other place as the Company shall notify the Holder in writing), to purchase from the Company up to 63,415 fully paid and nonassessable shares of the Company’s Common Stock, par value $0.0001 per share (the “Common Stock”).

(b) Exercise Price. The exercise price for the shares of Common Stock issuable pursuant to this Section 1 (the “Shares”) shall be $6.83 per share (the “Exercise Price”). The Shares and the Exercise Price shall be subject to adjustment pursuant to Section 8 hereof.

2. Exercise Period. This Warrant shall be exercisable, in whole or in part, during the term commencing on the Issue Date and ending at 5:00 p.m. Pacific Time on May 14, 2019 (the “Exercise Period”); provided, however, that this Warrant shall no longer be exercisable and become null and void upon the consummation of any “Termination Event” defined as (a) the consummation of the Company’s sale of its Common Stock or other securities pursuant to a registration statement under the Securities Act of 1933, as amended (the “Securities Act”) (other than a registration statement relating either to sale of securities to employees of the Company pursuant to its stock option, stock purchase or similar plan or a SEC Rule 145 transaction) (an “IPO”) and (b) the consummation of a Liquidation Event, as such term is defined in the Company’s Amended and Restated Certificate of Incorporation on file with the Secretary of State of the State of Delaware, as amended from time to time. In the event of a Termination Event, the Company shall notify the Holder at least ten (10) days prior to the consummation of such Termination Event.

3. Method of Exercise.

(a) While this Warrant remains outstanding and exercisable in accordance with Section 2 above, the Holder may exercise, in whole or in part, the purchase rights evidenced hereby. Such exercise shall be effected by:

(i) the surrender of the Warrant, together with a duly executed copy of the Notice of Exercise attached hereto, to the Secretary of the Company at its principal office (or at such other place as the Company shall notify the Holder in writing); and

(ii) the payment to the Company of an amount equal to the aggregate Exercise Price for the number of Shares being purchased, which amount may be paid, at the election of the Holder, by wire transfer of immediately available funds or certified check payable to the order of the Company or by cancellation of indebtedness.

(b) Each exercise of this Warrant shall be deemed to have been effected immediately prior to the close of business on the day on which this Warrant is surrendered to the Company as provided in Section 3(a) above. At such time, the person or persons in whose name or names any certificate for the Shares shall be issuable upon such exercise as provided in Section 3(c) below shall be deemed to have become the holder or holders of record of the Shares represented by such certificate.

(c) Within a reasonable time after the exercise of this Warrant in whole or in part, the Company at its expense will cause to be issued in the name of, and delivered to, the Holder, or as such Holder (upon payment by such Holder of any applicable transfer taxes) may direct:

(i) a certificate or certificates for the number of Shares to which such Holder shall be entitled; and

(ii) in case such exercise is in part only, a new warrant or warrants (dated the date hereof) of like tenor, calling in the aggregate on the face or faces thereof for the number of Shares equal to the number of such Shares described in this Warrant minus the number of such Shares purchased by the Holder upon all exercises made in accordance with Section 3(a) above or Section 4 below.

4. Net Exercise. In lieu of exercising this Warrant for cash, from and after the Issue Date, the Holder may elect to receive shares equal to the value of this Warrant (or the portion thereof being exercised) by surrender of this Warrant at the principal office of the Company together with a Notice of Exercise indicating such election (a “Net Exercise”). A Holder who Net Exercises shall have the rights described in Section 3(b) and Section 3(c) hereof, and the Company shall issue to such Holder a number of Shares computed using the following formula:

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Where

For purposes of this Section 4, the fair market value of one Share shall be determined by the Company’s Board of Directors in good faith.

5. Representations and Warranties of the Company. In connection with the transactions provided for herein, the Company hereby represents and warrants to the Holder that:

(a) Organization, Good Standing, and Qualification. The Company is a corporation duly organized, validly existing, and in good standing under the laws of the State of Delaware and has all requisite corporate power and authority to carry on its business as now conducted. The Company is duly qualified to transact business and is in good standing in each jurisdiction in which the failure to so qualify would have a material adverse effect on its business or properties.

(b) Authorization. Except as may be limited by applicable bankruptcy, insolvency, reorganization or similar laws relating to or affecting the enforcement of creditors’ rights, all corporate action has been taken on the part of the Company, its officers, directors, and stockholders necessary for the authorization, execution and delivery of this Warrant. The Company has taken all corporate action required to make all the obligations of the Company reflected in the provisions of this Warrant the valid and enforceable obligations they purport to be. The issuance of this Warrant will not be subject to preemptive rights of any stockholders of the Company. The Company has authorized sufficient shares of Common Stock to allow for the exercise of this Warrant.

(c) Compliance with Other Instruments. The authorization, execution and delivery of the Warrant will not constitute or result in a material default or violation of any law or regulation applicable to the Company or any material term or provision of the Company’s current Certificate of Incorporation or bylaws, or any material agreement or instrument by which it is bound or to which its properties or assets are subject.

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(d) Valid Issuance of Common Stock. The Shares, when issued, sold, and delivered in accordance with the terms of the Warrant for the consideration expressed therein, will be duly and validly issued, fully paid and nonassessable and, based in part upon the representations and warranties of the Holders in this Warrant, will be issued in compliance with all applicable federal and state securities laws.

6. Representations and Warranties of the Holder. In connection with the transactions provided for herein, the Holder hereby represents and warrants to the Company that:

(a) Authorization. The Holder has full right, power, authority and capacity to enter into this Warrant, and this Warrant constitutes its valid and legally binding obligation, enforceable in accordance with its terms except (i) as limited by applicable bankruptcy, insolvency, reorganization, moratorium or similar laws relating to or affecting the enforcement of creditors’ rights generally, (ii) as limited by equitable principles generally, including any specific performance, and (iii) as to any provisions relating to indemnity or contribution.

(b) Investment Experience. The Holder represents that it has substantial experience in evaluating and investing in securities of companies similar to the Company so that it is capable of evaluating the merits and risks of its investment in the Warrant, and has the capacity to protect its own interests.

(c) Accredited Investor. The Holder is an “accredited investor” within the meaning of Rule 501 of Regulation D, as presently in effect, as promulgated by the Securities and Exchange Commission (the “SEC”) under the Act.

(d) Acquired Entirely for Own Account. This Warrant is issued to the Holder in reliance upon the Holder’s representation to the Company, which by the Holder’s execution of this Warrant the Holder hereby confirms, that the Shares to be received by the Holder will be acquired for investment for the Holder’s own account, not as a nominee or agent, and not with a view to the resale or distribution of any part thereof, and that the Holder has no present intention of selling, granting any participation in, or otherwise distributing the same. The Holder further represents that it does not have any contract, undertaking, agreement or arrangement with any person to sell, transfer or grant participations, to such person or to any third person, with respect to the Shares.

(e) Restricted Securities. The Holder understands that the Shares are characterized as “restricted securities” under the federal securities laws inasmuch as they are being acquired from the Company in a transaction not involving a public offering and that under such laws and applicable regulations such Shares may be resold without registration under the Securities Act only in certain limited circumstances. In this connection, the Holder represents that it is familiar with Rule 144, as presently in effect, and understands the resale limitations imposed thereby and by the Securities Act. The Holder must bear the economic risk of this investment indefinitely unless the Shares are

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registered pursuant to the Securities Act or an exemption from registration is available. The Holder understands that the Company has no present intention of registering the Shares. The Holder further acknowledges and understands that the Company is under no obligation to register the Shares. The Holder also understands that there is no assurance that any exemption from registration under the Securities Act will be available and that, even if available, such exemption may not allow the Holder to transfer all or any portion of the Shares under the circumstances, in the amounts or at the times the Holder might propose.

(f) No Public Market. The Holder understands 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 Shares.

(g) Disclosure of Information. The Holder has conducted the due diligence it determined in its sole judgment was necessary or appropriate and has received all the information it considers necessary or appropriate for deciding whether to acquire the Shares. The Holder has received and reviewed information about the Company and has had an opportunity to discuss the Company’s business, management and financial affairs with its management. The Holder understands and acknowledges that such discussions, as well as any written information provided by the Company to the Holder, (i) were intended to describe the aspects of the Company’s business which the Company believes to be material, but were not necessarily an exhaustive description, and (ii) may have contained forward-looking statements involving known and unknown risks and uncertainties which may cause the Company’s actual results in future periods or plans for future periods to differ materially from what was anticipated and that no representations or warranties were or are being made with respect to any such forward-looking statements or the probability of achieving any of the results projected in any of such forward-looking statements.

(h) Market Stand-off Agreement. The Holder hereby agrees, if so requested by the managing underwriters or the Company in connection with the IPO, that, without the prior written consent of such managing underwriters, the Holder will not (i) lend, offer, pledge, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, or otherwise transfer or dispose of, directly or indirectly, any shares of the Company’s capital stock acquired through the exercise of this Warrant, or (ii) enter into any swap or other arrangement that transfers to another, in whole or in part, any of the economic consequences of ownership of the Company’s capital stock acquired through the exercise of this Warrant, whether any such transaction described in clause (i) or (ii) above is to be settled by delivery of securities, in cash for a period of up to 180 days after the date of the final prospectus relating to the IPO. The Holder acknowledges and agrees that the Company’s managing underwriters are intended third party beneficiaries of this Section 6(h) and shall have the right, power and authority to enforce the provisions hereof as though they were a party hereto. Holder further agrees to execute such agreements as may be reasonably requested by the underwriters in the IPO that are consistent with this Section 6(h) or that are necessary to give further effect thereto.

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(i) Residence. The Holder’s principal office location is in the state identified in the address of the Holder set forth beneath its signature hereto.

(j) Legends. The Holder understands that the Shares, and any securities issued in respect thereof or exchange therefor, may bear one or all of the following legends:

(i) “THE SECURITIES REPRESENTED BY THIS CERTIFICATE HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED, AND MAY NOT BE SOLD, TRANSFERRED, ASSIGNED, PLEDGED OR HYPOTHECATED UNLESS AND UNTIL REGISTERED UNDER SUCH ACT, OR UNLESS THE COMPANY HAS RECEIVED AN OPINION OF COUNSEL OR OTHER EVIDENCE, SATISFACTORY TO THE COMPANY AND ITS COUNSEL, THAT SUCH REGISTRATION IS NOT REQUIRED.”

(ii) Any legend required by the blue sky laws of any state to the extent such laws are applicable to the securities represented by the certificate or other document so legended.

(iii) Any legend required by the Company’s bylaws.

(k) Representations on Exercise. Upon exercise of this Warrant and as a condition thereof, the Holder hereof shall confirm in writing, in a form of Attachment A, that the representations and warranties in this Section 5 are true and correct as of the date of exercise. In addition, the Holder shall provide such additional information regarding such Holder’s financial and investment background, as the Company may reasonably request, as is relevant for purposes of determining the accuracy of such representations and warranties.

7. Covenants of the Company.

(a) Notices of Record Date. In the event of any taking by the Company of a record of the holders of any class of securities for the purpose of determining the holders thereof who are entitled to receive any dividend (other than a cash dividend which is the same as cash dividends paid in previous quarters or any stock dividend) or other distribution, the Company shall mail to the Holder, at least ten (10) days prior to such record date, a notice specifying the date on which any such record is to be taken for the purpose of such dividend or distribution.

(b) Stock Fully Paid; Reservation of Shares. All shares of stock which may be issued upon the exercise of the rights represented by this Warrant will, upon issuance, be fully paid and nonassessable, and free from all taxes, liens and charges with respect to the issue thereof. During the period within which the rights represented by this Warrant may be exercised, the Company will at all times have authorized and reserved for the purpose of issue upon exercise of the purchase rights evidenced by this Warrant, a sufficient number of shares of its Common Stock to provide for the exercise of the rights represented by this Warrant.

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8. Adjustment of Exercise Price and Number of Shares.

(a) Subdivision or Combination of Shares. If the Company at any time while this Warrant remains outstanding and unexpired shall subdivide or combine its stock, including without limitation through a reverse stock split, the Exercise Price shall be proportionately decreased in the case of a subdivision or increased in the case of a combination.

(b) Reclassification, Reorganization and Consolidation. In case of any reclassification, capital reorganization or change in the capital stock of the Company (other than as a result of a subdivision, combination or stock dividend provided for in Section 8(a) above or Section 8(c) below), then, as a condition of such reclassification, reorganization or change, lawful provision shall be made, and duly executed documents evidencing the same from the Company or its successor shall be delivered to the Holder, so that the Holder shall have the right at any time prior to the expiration of this Warrant to purchase, at a total price equal to that payable upon the exercise of this Warrant, the kind and amount of shares of stock and other securities or property receivable in connection with such reclassification, reorganization or change by a holder of the same number and type of securities as were purchasable as Shares by the Holder immediately prior to such reclassification, reorganization or change. In any such case appropriate provisions shall be made with respect to the rights and interest of the Holder so that the provisions hereof shall thereafter be applicable with respect to any shares of stock or other securities or property deliverable upon exercise hereof, and appropriate adjustments shall be made to the Exercise Price per Share payable hereunder, provided the aggregate Exercise Price shall remain the same.

(c) Stock Dividends. If the Company at any time while this Warrant is outstanding and unexpired shall pay a dividend with respect to stock payable in, or make any other distribution with respect to stock (except any distribution specifically provided for in the foregoing Sections 8(a) or 8(b)) of, stock, then the Exercise Price shall be adjusted, from and after the date of determination of stockholders entitled to receive such dividend or distribution, to that price determined by multiplying the Exercise Price in effect immediately prior to such date of determination by a fraction (a) the numerator of which shall be the total number of shares of stock outstanding immediately prior to such dividend or distribution, and (b) the denominator of which shall be the total number of shares of stock outstanding immediately after such dividend or distribution.

(d) Adjustment of Number of Shares. Upon each adjustment in the Exercise Price, the number of shares of stock purchasable hereunder shall be adjusted, to the nearest whole share, to the product obtained by multiplying the number of Shares purchasable immediately prior to such adjustment in the Exercise Price by a fraction, the numerator of which shall be the Exercise Price immediately prior to such adjustment and the denominator of which shall be the Exercise Price immediately thereafter.

(e) Fractional Shares. No fractional Shares or scrip representing fractional Shares will be issued in connection with any exercise hereunder, but in lieu of such fractional shares the Company shall make a cash payment therefor upon the basis of the Exercise Price then in effect.

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9. No Stockholder Rights. Prior to exercise of this Warrant, the Holder shall not be entitled to any rights of a stockholder with respect to the Shares, including (without limitation) the right to vote such Shares, receive dividends or other distributions thereon, exercise preemptive rights or be notified of stockholder meetings, and except as otherwise provided in this Warrant or the Note, such Holder shall not be entitled to any stockholder notice or other communication concerning the business or affairs of the Company.

10. Transfer of Warrant. Other than a surrender of this Warrant to the Company and reissuance of a new warrant to the transferee pursuant to Sections 2 or 3 of this Warrant, any attempted transfer, assignment, delegation or otherwise by the Holder of this Warrant, or of any right, interest or obligation hereunder, shall be null and void. Nothing in this Warrant, express or implied, is intended to confer upon any party other than the parties hereto or their respective successors and assigns any rights, remedies, obligations or liabilities under or by reason of this Warrant, except as expressly provided in this Warrant.

11. Governing Law. The terms and conditions of this Warrant shall be governed by and construed in accordance with California law, without giving effect to principles of conflicts of law.

12. 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.

13. Amendments and Waivers. Any term of this Warrant may be amended or waived with the written consent of the Company and the Holder.

14. Severability. If any provision of this Warrant is held to be unenforceable under applicable law, such provision shall be excluded from this Warrant and the balance of the Warrant shall be interpreted as if such provision were so excluded and shall be enforceable in accordance with its terms.

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15. Notices. All notices and other communications given or made pursuant hereto shall be in writing and shall be deemed effectively given: (a) upon personal delivery to the party to be notified, (b) when sent by confirmed electronic mail or facsimile if sent during normal business hours of the recipient, and if not so confirmed, then on the next business day, (c) five (5) days after having been sent by registered or certified mail, return receipt requested, postage prepaid, or (d) one (1) day after deposit with a nationally recognized overnight courier, specifying next day delivery, with written verification of receipt. All communications shall be sent to the respective parties at the following addresses (or at such other addresses as shall be specified by notice given in accordance with this Section 15):

If to the Company:

Avalanche Biotechnologies, Inc.

1035 O’Brien Drive

Menlo Park, CA 94025

Attention: Chief Executive Officer

with a copy (which shall not constitute notice) to:

Latham & Watkins LLP

140 Scott Drive

Menlo Park, California 94025

Attn: Alan C. Mendelson

Facsimile: (650)  ###-###-####

If to Holder:

Cowen and Company, LLC

599 Lexington Avenue

New York, NY 10022

Attention: General Counsel

16. Counterparts. This Warrant may be executed in two or more counterparts, each of which shall be deemed an original and all of which together shall constitute one instrument. Any counterpart delivered electronically (including without limitation by .pdf transmission) or by facsimile shall be binding to the same extent as an original counterpart with regard to any agreement subject to the terms hereof or any amendment thereto

17. Finder’s Fee. Each party represents that it neither is or will be obligated for any finder’s fee or commission in connection with this transaction. The Holder agrees to indemnify and to hold harmless the Company from any liability for any commission or compensation in the nature of a finder’s fee (and the costs and expenses of defending against such liability or asserted liability) for which the Holder or any of its officers, partners, employees or representatives is responsible. The Company agrees to indemnify and hold harmless the Holder from any liability for any commission or compensation in the nature of a finder’s fee (and the costs and expenses of defending against such liability or asserted liability) for which the Company or any of its officers, employees or representatives is responsible.

18. Expenses. If any action at law or in equity is necessary to enforce or interpret the terms of this Warrant, the prevailing party shall be entitled to reasonable attorneys’ fees, costs and necessary disbursements in addition to any other relief to which such party may be entitled.

19. Entire Agreement; Amendments and Waivers. This Warrant and any other documents delivered pursuant hereto constitute the full and entire understanding and agreement between the parties with regard to the subjects hereof and thereof. Nonetheless, any term of this Warrant may be amended and the observance of any term

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of this Agreement may be waived (either generally or in a particular instance and either retroactively or prospectively), with the written consent of the Company and the Holder; or if this Warrant has been assigned in part, by the holders or rights to purchase a majority of the shares originally issuable pursuant to this Warrant.

(Signature Page Follows)

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IN WITNESS WHEREOF, the parties have executed this Warrant as of the date above written.

SIGNATURE PAGE TO WARRANT

ATTACHMENT A

NOTICE OF EXERCISE

TO: [                    ]

1. The undersigned hereby elects to purchase                  Shares pursuant to the terms of the attached Warrant, and tenders herewith payment of the purchase price of such shares in full, together with all applicable transfer taxes, if any.

1. The undersigned hereby elects to convert the attached Warrant into Shares in the manner specified in Section 4 of the Warrant. This conversion is exercised with respect to                  of the shares covered by the Warrant.

[Strike paragraph above that does not apply.]

2. Please issue a certificate or certificates representing said shares of stock in the name of the undersigned or in such other name as is specified below:

3. The undersigned represents that the aforesaid shares of stock are being acquired for the account of the undersigned for investment and not with a view to, or for resale in connection with, the distribution thereof and that the undersigned has no present intention of distributing or reselling such shares. In support thereof, the undersigned hereby represents and warrants to the Company that the representations and warranties contained in Section 6 of the Warrant are true and correct as of the date of exercise.

4. The undersigned further acknowledges that it has reviewed the market stand-off provisions set forth in Section 6(h) of the Warrant and agrees to be bound by such provisions.