Exhibit 10.1

EXCHANGE AGREEMENT

THIS EXCHANGE AGREEMENT (this Agreement) is dated as of
February 25, 2009, by and between Arrowhead Research Corporation, a Delaware corporation (the Corporation), and each of Bob G. Gower, Allison Gower Trust, Rachel Gower Trust, Morganne Gower Trust, William A. McMinn (each, a
Holder and collectively, the Holders). The Corporation and each Holder are referred to as a Party and collectively as the Parties.

W I T N E S S E T H:

WHEREAS, the Corporation and each of the Holders are shareholders of Unidym, Inc., a Delaware corporation (Unidym);

WHEREAS, the Holders own shares of Series A Preferred Stock, $0.0001 par value per share, of Unidym ( each, a Unidym Share and,
collectively, the Unidym Shares) in the amounts set forth on Exhibit A, attached hereto;

WHEREAS, the Holders
each desire to exchange all their Unidym Shares (including any such Holders Unidym Shares held or previously held in escrow but reduced by the number of shares that are subject to the proper exercise of any right of first refusal) for common
stock of the Corporation, $0.001 par value per share (each, an Arrowhead Share and, collectively the Arrowhead Shares); and

WHEREAS, the Corporation desires to exchange (the Exchange) one newly issued and unregistered Arrowhead Share for each Unidym Share and the agreement of each Holder to certain restrictions on the
transfer and sale of any Arrowhead Shares they receive pursuant to this Agreement (the Arrowhead Shares received in the Exchange, referred to in this Agreement as the Exchanged Shares).

NOW, THEREFORE, for good and valuable consideration, the receipt and sufficiency of which are hereby acknowledged, the parties hereto agree as follows:

1. Exchange.

(a)
Exchange Ratio. The Corporation and each Holder hereby agree to exchange at the Closing the Unidym Shares in the amounts set forth on Exhibit A, attached hereto, for Arrowhead Shares in the following ratio: one Unidym Share for one
Arrowhead Share (1:1).

(b) Exchange. To effect this exchange, each Holder will deliver to the Corporation the stock certificate or
certificates representing the pro-rata number of Unidym Shares together with duly executed stock powers related thereto and the Corporation will deliver to each Holder a stock certificate or certificates representing the pro-rata number of Exchanged
Shares.



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2. The Closing.

(a) Closing Date. The closing of the transactions contemplated by this Agreement (the Closing) shall take place at the offices of Neal, Gerber & Eisenberg, LLP, Two North LaSalle
Street, Suite 2200, Chicago, Illinois at 10:00 a.m., Chicago time, on such date as agreed to by the parties on or after the date the conditions to closing set forth in this Agreement are satisfied (Closing Date), or at such other
place, date or time as the parties may mutually agree in writing.

(b) Conditions to Closing of Holders. The obligation of Holders
to consummate the transactions on the Closing Date as contemplated by this Agreement shall be subject to the satisfaction or waiver on or prior to the Closing Date of the following conditions:

(i) the Corporation shall have performed and complied in all material respects with all obligations and agreements required to be
performed and complied with by the Corporation hereunder on or prior to the Closing Date;

(ii) the representations and
warranties of the Corporation contained in this Agreement shall be true and correct in all material respects as of the Closing Date as if made as of such date;

(iii) the Corporation shall have delivered to each Holder one or more stock certificates evidencing such Holders ownership of the
Exchanged Shares to be delivered on the Closing Date duly executed by the Corporation;

(iv) the Corporation shall have
delivered to the Transfer Agent the instructions and pre-authorizations described in Section 5(b) of this Agreement relating to the acceptance of the opinion of counsel satisfactory to the Corporation authorizing the removal of the legends from
the Exchanged Shares after the expiration of the Prohibited Period (as defined herein); and

(v) the Corporation shall have
received all third party consents and all authorizations, consents and approvals of any Governmental Authority necessary to consummate the transactions contemplated hereby.

(c) Conditions to Closing of Corporation. The obligation of the Corporation to consummate the transactions on the Closing Date shall be subject to
the satisfaction or waiver on or prior to the Closing Date of the following conditions:

(i) Each Holder shall have each
performed and complied in all material respects with all obligations and agreements required to be performed and complied with by each Holder hereunder on or prior to the Closing Date;

(ii) Holders shall have delivered to Corporation evidence and supporting documents satisfactory to Corporation that the Holders have
complied with or obtained all necessary consents under the terms and conditions of the Amended and Restated Right of first Refusal and Co-Sale Agreement, (the ROFR and Co-Sale Agreement) to exchange all the Unidym Shares free and
clear of any Claims as required under this Agreement and with the requested assistance of the Corporation in obtaining such consents as set forth in Section 10(c) of this Agreement;



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(iii) the representations and warranties of each Holder contained in this Agreement shall
be true and correct in all material respects as of the Closing Date as if made as of such date;

(iv) Holders shall have
delivered to the Corporation a certificate or the certificates representing all the Unidym Shares owned by Holder to be exchanged on such date and related executed stock powers; and

(v) Holders shall have received all third party consents and all authorizations, consents and approvals of any Governmental Authority
necessary to consummate the transactions contemplated hereby.

3. Representations and Warranties of the Corporation. The
Corporation represents and warrants to Holder as follows:

(a) Corporate Status. The Corporation is a corporation incorporated,
validly existing and in good standing under the laws of the State of Delaware with full right, power and authority to execute, deliver and perform this Agreement.

(b) Authorization/Enforceability. This Agreement has been duly authorized, executed and delivered by the Corporation and constitutes the valid and legally binding obligation of the Corporation, enforceable in
accordance with its terms and conditions. The Corporation need not give any notice to, make any filing with, or obtain any authorization, consent, or approval of any Governmental Authority in order to consummate the transactions contemplated by this
Agreement.

(c) Non-Contravention. Neither the execution and the delivery of this Agreement, nor the consummation of the
transactions contemplated hereby, will (i) violate any constitution, statute, regulation, rule, injunction, judgment, order, decree, ruling, charge, or other restriction of any Governmental Authority to which the Corporation is subject, or
(ii) conflict with, result in a breach of, constitute a default under, result in the acceleration of, create in any party the right to accelerate, terminate, modify, or cancel, or require any notice under the certificate of incorporation or
bylaws of the Corporation, or any agreement, contract, lease, license, instrument, or other arrangement to which the Corporation is a party or by which it is bound or to which any of its assets is subject.

(d) Consents/Approvals. No consent, approval, authorization, order, registration or qualification of or with any Governmental Authority or other
Person or entity is required for the issuance and sale of the Exchanged Shares by the Corporation to Holder or the consummation by the Corporation of the transactions contemplated by this Agreement.

(e) Exchanged Shares Authorization. The Exchanged Shares have been duly authorized and, when issued and delivered, will be duly and validly issued
and fully paid and nonassessable. Upon consummation of the transactions contemplated hereby, good and valid title to the Exchanged Shares, free and clear of all Claims, will be transferred by the Corporation to Holder.



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4. Representations and Warranties of Holder. Each Holder represents and warrants to the
Corporation as follows:

(a) Legal Capacity. Each Holder has full legal right, power and capacity to execute and deliver this
Agreement and to perform his, her or its obligations hereunder. This Agreement constitutes the valid and legally binding obligation of Holder, enforceable in accordance with its terms and conditions. Holder need not give any notice to, make any
filing with, or obtain any authorization, consent, or approval of any third party or Governmental Authority in order to consummate the transactions contemplated by this Agreement. Except as set forth on attached Schedule 4(a), no Person has
any community property rights by virtue of marriage or otherwise in any of the Unidym Shares owned by such Holder. Any such Person with community property rights has duly executed and delivered to the Corporation at or prior to the Closing a copy of
the consent attached hereto as Exhibit C. If such Holder is not a natural person, it has been duly organized, and is validly existing and in good standing, under the laws of its jurisdiction of formation, and it has properly taken all
corporate, limited liability, partnership or other action required to be taken by such Holder with respect to the execution and delivery of this Agreement and consummate the transactions contemplated by this Agreement.

(b) Title to Unidym Shares. Holder is the lawful record and beneficial owner of the Unidym Shares that will be transferred pursuant to
Section 1 of this Agreement with good and marketable title thereto, and the Holder has the right to sell, assign, convey, transfer and deliver the Unidym Shares and any and all rights and benefits incident to the ownership thereof (including,
without limitation, any registration or other rights pertaining to the Unidym Shares and the shares of common stock underlying such securities), all of which rights and benefits are transferable by the Holder to the Corporation pursuant to this
Agreement, free and clear of all Claims, except as set forth on the attached Schedule 4(b). The exchange of the securities as contemplated herein will (i) pass good and marketable title to all the Unidym Shares transferred pursuant to
Section 1 of this Agreement to the Corporation, free and clear of all Claims, and (ii) convey, free and clear of all Claims, any and all rights and benefits incident to the ownership of such securities (including, without limitation, any
registration or other rights pertaining to the securities and the shares of common stock underlying such securities).

(c)
Non-Contravention. Neither the execution and the delivery of this Agreement, nor the consummation of the transactions contemplated hereby, will (i) violate any constitution, statute, regulation, rule, injunction, judgment, order, decree,
ruling, charge, or other restriction of any Governmental Authority to which Holder is subject, or (ii) conflict with, result in a breach of, constitute a default under, result in the acceleration of, create in any party the right to accelerate,
terminate, modify, or cancel, or require any notice under any agreement, organizational document, bylaws, partnership agreement, trust agreement, agreement any trust is bound by, contract, lease, license, instrument, or other arrangement to which
Holder, as applicable, is a party or by which it is bound or to which any of its assets is subject.

(d) Consents/Approvals. No
consent, approval, authorization, order, registration or qualification of or with any Governmental Authority or other entity or Person is required for the Exchange or the consummation by Holder of the transactions contemplated by this Agreement.



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(e) Investment Representations.

(i) Holder qualifies as an accredited investor (as defined in Rule 501(a) of Regulation D under the Securities Act of 1933, as
amended (the Securities Act)) and is acquiring the Exchanged Shares hereunder for its own account and with no intention of distributing or selling the Exchanged Shares except pursuant to a registration or an available exemption
under applicable law. Holder understands that the Exchanged Shares have not been (and are not being) registered under the Securities Act by reason of their contemplated issuance in transaction(s) exempt from the registration and prospectus delivery
requirements of the Securities Act pursuant to Section 4(2) thereof (including the rules and regulations promulgated thereunder), and that the reliance of the Corporation on such exemption from registration is predicated in part on the
representations and warranties of Holder hereunder.

(ii) Holder agrees that it will not sell or otherwise dispose of any of
the Exchanged Shares unless such sale or other disposition has been registered or is exempt from registration under the Securities Act and has been registered or qualified or is exempt from registration or qualification under applicable securities
laws of any State.

(iii) Holder understands that a restrictive legend consistent with the foregoing set forth in
Section 10(a) of this Agreement has been or will be placed on the certificates evidencing the Exchanged Shares to be issued to it hereunder, and related stop transfer instructions will be noted in the transfer records of the Corporation and/or
its transfer agent for the Exchanged Shares during the Prohibited Period.

(iv) Each Holder represents that it is not an
Affiliate (as defined herein) of the Corporation and will covenant and agree that if it becomes an Affiliate, it will promptly provide notice to the Corporation of such status and comply with insider trading laws and policies and the applicable
control securities provisions of Rule 144 in addition to any other obligations set forth in this Agreement.

(v)
Each Holder has such knowledge and experience in financial and business matters so as to be capable of evaluating the merits and risk of an investment in the Exchanged Shares. Each Holder acknowledges that it has had access to all information
concerning the Corporation and Unidym and their respective businesses, assets, liabilities, financial statements, and obligations which have been requested and has been provided the opportunity to ask questions of and receive answers from the
Corporation and/or Unidym to fully and effectively evaluate the Exchange and the transactions contemplated herein. Each Holder understands that a new holding period for purposes of Rule 144 under the Securities Act will be triggered with respect to
the Exchanged Shares, and such Holder is able to bear the economic risk of loss of the investment in such Exchanged Shares and is able to afford a complete loss of such investment.



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5. Covenants.

(a) Current Public Information. The Corporation agrees to keep current in the filing of its quarterly and annual reports as required under the Securities and Exchange Act of 1934, as amended (Exchange
Act), for at least 12 months from the Closing Date in order to allow resales under Rule 144 of the Securities Act, it being understood that the Holders shall remain subject to the contractual lock-up and prohibited sales period set forth
in this Agreement. The Corporation shall notify Holders during any period it is not current with any such filing and shall take all commercially reasonable steps to cure any such late filing in a timely fashion.

(b) Pre-Authorization to Transfer Agent. The Corporation shall give instructions to the Transfer Agent authorizing it on or after the date 12
months after the Closing Date (i) to accept the form of opinion of counsel pre-approved by the Corporation regarding the removal of the non-registered securities legend set forth in Section 10(a) of this Agreement from any or all of the
Exchanged Shares and (ii) to remove the legend set forth in Section 10(a) of this Agreement referencing the restrictions imposed by this Agreement from any or all of the Exchanged Shares. The Corporations instructions and
pre-authorization to the Transfer Agent may not be revoked by the Corporation with respect to the opinion for so long as the assumptions set forth therein are reasonably believed by the Corporation to be correct and the form of opinion complies with
applicable law on the date it is to be relied upon by the Transfer Agent to remove the legend. In the event the assumptions set forth in any such form of opinion are not reasonably believed by the Corporation to be correct or no longer comply with
applicable law, the Corporation may rescind its pre-approval and instructions until approved counsel has submitted an acceptable opinion. In the event that the Corporation changes to a successor Transfer Agent, it shall give such pre-authorization
at the time of the appointment of the successor for as long as any Exchanged Shares remain outstanding with restricted legends.

(c)
Removal of Legend. The Corporation shall use commercially reasonable efforts with the assistance of the Holders to facilitate removal of the restrictive legends set forth in Section 10(a) of this Agreement from the Exchanged Shares
within ten (10) business days after expiration of the Prohibited Period (provided certificates have been submitted to the Transfer Agent prior to the end of the Prohibited Period). If for any reason the Legend cannot be removed as contemplated
by this section, the Corporation shall use commercially reasonable efforts to work with the Holders to find an alternative solution that does not require any extraordinary or material costs to be incurred by the Corporation and the liquidated
damages contemplated by this section shall not apply.



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6. Restrictions on Exchanged Shares.

(a) Prohibited Sale Period. For a period of twelve (12) months from the Closing Date (the Prohibited Period), each Holder
agrees that he, she or it shall not (i) offer, sell, contract to sell, pledge or otherwise dispose of any of such Holders Exchanged Shares (or securities convertible into or exchangeable for such Exchanged Shares) received in the
Exchange, whether held directly or indirectly, or (ii) enter into a transaction which would have the same effect, or enter into any swap, option, contract to purchase or sell, hedge or other arrangement that transfers, in whole or in part, any
economic consequences of owning any such security.

(b) Permitted Sales. For the purpose of clarification, the Corporation
acknowledges that nothing contained in Section 6(a) of this Agreement is intended to restrict a Holders ability to sell Arrowhead Shares that are not Exchanged Shares that are held or acquired by the Holder in transactions outside of this
Agreement in the open market (unless as part of a plan or scheme to evade the terms and conditions of this Agreement). Notwithstanding the foregoing, each Holder acknowledges that they may be subject to other restrictions imposed on them by the
federal or state securities laws of the United States.

7. Termination.

(a) In the event the Closing Date does not occur on or before June 1, 2009, this Agreement may be terminated in writing after such date (i) by
the Corporation or (ii) by any Holder as to itself only (but not with respect to the other Holders) and withdraw all of such Holders portion of Unidym Shares from the Exchange, upon two (2) days prior written notice to the
Corporation.

(b) In the event that any Person exercises its co-sale rights under the ROFR and Co-Sale Agreement, and the number of Unidym
Shares to be exchanged is reduced, any Holder shall have the option to terminate this Agreement as to itself only, and withdraw all of such Holders Unidym Shares from the Exchange, upon two (2) days prior written notice to the
Corporation.

8. Indemnification.

(a) Each Holder understands and acknowledges that the Corporation is relying on representations, warranties, covenants and agreements made by such Holder to the Corporation in this Agreement. Each Holder, as
applicable, hereby agrees to indemnify, defend and hold harmless the Corporation and its directors, officers, shareholders, principals, Affiliates, representatives, agents and employees (each, a Corporation Indemnified Party),
against any and all loss, damage, liability or expense (including, but not limited to, expenses related to the investigation and enforcement of any provisions of this Agreement and/or any reasonable attorneys fees) (collectively,
Losses) which any Corporation Indemnified Party may suffer, sustain or incur by reason of or in connection with or arising under (i) any inaccuracy or breach of representation or warranty of such Holder contained in this
Agreement; (ii) the breach of this Agreement or any covenant or agreement made by such Holder in this Agreement; or (iii) the sale or distribution by such Holder of the Exchanged Shares in violation of this Agreement and/or the Securities
Act or any other applicable law. This right to indemnification is in addition to any other remedy available to the Corporation under this Agreement.



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(b) The Corporation understands and acknowledges that each Holder is relying on representations,
warranties, covenants and agreements made by the Corporation to such Holder in this Agreement. The Corporation hereby agrees to indemnify, defend and hold harmless each Holder and its officers, principals, Affiliates, trustees, agents and
representatives, as applicable, (each, a Holder Indemnified Party), against any and all Losses which any Holder Indemnified Party may suffer, sustain or incur by reason of or in connection with or arising under (i) any
inaccuracy or breach of representation or warranty of the Corporation contained in this Agreement; or (ii) the breach of this Agreement or any covenant or agreement made by the Corporation in this Agreement. This right to indemnification is in
addition to any other remedy available to each Holder under this Agreement.

9. Certain Definitions.

(a) Affiliate (and, with a correlative meaning, affiliated) means, with respect to any Person, any direct or
indirect subsidiary of such Person, and any other Person that directly, or through one or more intermediaries, Controls or is Controlled by or is under common Control with such first Person. As used in this definition, Control
(and, with correlative meanings, Controlled by and under common Control with) means the possession, directly or indirectly, of the power to direct the management or policies of a Person (whether through
ownership of securities or partnership or other ownership interests, by contract or otherwise).

(b) Claims shall mean
the following of any nature whatsoever: security interests, liens, deeds of trust, hypothecations, pledges, claims (pending or threatened), charges, escrows, encumbrances, lock-up arrangements, options, rights of first offer or refusal, community
property rights, mortgages, indentures, security agreements or other agreements, arrangements, contracts, commitments, understandings or obligations, whether written or oral and whether or not relating in any way to credit or the borrowing of money.

(c) Governmental Authority means any entity exercising executive, legislative, judicial, regulatory or administrative
functions of or pertaining to government, including any governmental authority, independent or autonomous official authority, agency, department, board, commission or instrumentality of the United States or any other country, or any political
subdivision thereof, whether federal, state or local, and any tribunal, court or arbitrator(s) of competent jurisdiction.

(d)
Person(s) means and includes any natural persons, sole proprietorships, corporations, limited partnerships, limited liability companies, general partnerships, joint stock companies, joint ventures, associations, companies, trusts,
banks, trust companies, land trusts, business trusts or other organizations, whether or not legal entities, all Governmental Authorities and all other entities.

(e) Transfer Agent shall mean Computershare Limited, 350 Indiana St., Suite 800, Golden, CO 80401, in its capacity as transfer agent to the Corporation, or any successor transfer agent to the
Corporation.



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10. Miscellaneous.

(a) Legend Requirement. Each certificate representing Exchanged Shares held or acquired by a Holder will contain legends acknowledging that the shares represented by such certificate are restricted securities
and are subject to this Agreement, as follows:

THE SECURITIES REPRESENTED BY THIS INSTRUMENT HAVE NOT BEEN REGISTERED UNDER THE
SECURITIES ACT OF 1933, AS AMENDED (THE SECURITIES ACT), OR ANY STATE SECURITIES LAWS, AND NO SALE, ASSIGNMENT, PLEDGE, HYPOTHECATION, GIFT, TRANSFER OR OTHER DISPOSITION OR OFFER TO DO ANY OF THE FOREGOING MAY BE MADE UNLESS A
REGISTRATION STATEMENT UNDER THE SECURITIES ACT AND OTHER APPLICABLE SECURITIES LAWS WITH RESPECT TO SUCH SECURITIES IS THEN IN EFFECT, OR IN THE OPINION OF COUNSEL ACCEPTABLE TO THE ISSUER, SUCH REGISTRATION UNDER THE SECURITIES ACT AND OTHER
APPLICABLE SECURITIES LAWS IS NOT REQUIRED.

THE OWNERSHIP, ENCUMBRANCE, PLEDGE, ASSIGNMENT, SALE, TRANSFER OR OTHER DISPOSITION OF
THIS CERTIFICATE OF STOCK, OR SHARES ISSUED IN LIEU HEREOF, IS SUBJECT TO THE RESTRICTIONS CONTAINED IN AN EXCHANGE AGREEMENT (EXCHANGE AGREEMENT) BY AND AMONG THE CORPORATION AND CERTAIN STOCKHOLDERS OF THE CORPORATION THAT REMAINS IN
EFFECT UNTIL  2010. A COPY OF THE EXCHANGE AGREEMENT IS ON FILE AT THE OFFICE OF THE CORPORATION. ANY ENCUMBRANCE, PLEDGE,
ASSIGNMENT, SALE, TRANSFER OR OTHER DISPOSITION OF THIS STOCK CONTRARY TO THE EXCHANGE AGREEMENT SHALL BE NULL AND VOID AND OF NO EFFECT WHATSOEVER.

The Transfer Agent and any applicable broker shall each be instructed not to recognize any transfer by a Holder that does not comply with this Agreement.

(b) Pre-Approval. The Corporation hereby pre-approves: (i) Wong, Cabello, Lutsch, Rutherford & Brucculeri, L.L.P., counsel for certain of the Holders, as counsel acceptable to the
issuer for purpose of removing the Securities Act legend set forth in Section 10(a) of this Agreement; and (ii) the form of opinion of Wong, Cabello, Lutsch, Rutherford & Brucculeri, L.L.P. attached hereto as
Exhibit B relating to the removal of the restrictive legends set forth in Section 10(a) of this Agreement from any or all of the Exchanged Shares as long as such form of opinion and the applicable Holder complies with the terms and
conditions set forth in Section 5(b) of this Agreement.

(c) Assistance. By executing this Agreement, each of the Holders
hereby requests that the Corporation endeavor to assist Holders (without warranty of any kind) in their compliance with the right of first refusal and co-sale mechanics and requirements set forth in the ROFR and Co-Sale



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Agreement. Each such Holder agrees to fully and promptly cooperate with the Corporation and, upon request, each such Holder shall reimburse the Corporation
for such Holders pro rata amount of any expenses incurred by the Corporation in so complying up to a maximum aggregate amount of $2,000.

(d) Equitable Remedy. Each Party shall agree that in addition to any other remedy that may be available to such Party hereunder, the Party shall be entitled to specific performance. Notwithstanding anything to the contrary in this
Agreement, each Party shall be responsible for paying its own expenses, including legal fees, incurred in enforcing this Agreement.

(e)
Notices. All notices, claims, demands and other communications hereunder shall be in writing and shall be deemed given upon (i) confirmation of receipt of a facsimile transmission, (ii) confirmation of delivery when delivered by a
standard overnight carrier or (iii) the expiration of five (5) business days after the day when mailed by registered or certified mail (postage prepaid, return receipt requested), addressed to the respective Parties at the following
addresses (or such other address for a Party as shall be specified by like notice):



|                           |  |                                                                                                                                                                                               
|-------------------------- |  | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
|If to the Corporation, to: |  | Arrowhead Research Corporation                                                                                                                                                                
|                           |  | 201 South Lake Avenue, Suite 703                                                                                                                                                              
|                           |  | Pasadena, CA 91101                                                                                                                                                                            
|                           | 
|                           |  | Attention: Dr. Christopher Anzalone                                                                                                                                                           
|                           |  | Telephone: (626) 304-3400                                                                                                                                                                     
|                           |  | Fax: (626) 304-3401                                                                                                                                                                           
|                           | 
|with a copy to:            |  | Neal, Gerber & Eisenberg LLP                                                                                                                                                                  
|                           |  | 2 North LaSalle St.                                                                                                                                                                           
|                           |  | Chicago, IL 60602 Attn: Jonathan D. Wasserman
Telephone: (312) 269-8000                                                                                                                       
|                           |  | Fax: (312) 269-1747                                                                                                                                                                           
|                           | 
|If to any Holder, to:      |  | At the Holders address, phone or fax number appearing on Exhibit A, attached hereto.                                                                                                         
|                           | 
|                           |  |                                                                                                                                                                                               
|with a copy to:            |  | Wong, Cabello, Lutsch, Rutherford & Brucculeri,
L.L.P. Chasewood Bank Building 20333 SH 249 Suite 600 Houston, Texas 77070 Attn: Russell T. Wong Telephone: (832) 446-2420 Fax: (832) 446-2424



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(f) No Third-Party Beneficiaries. Unless otherwise specifically set forth herein, this Agreement
shall not confer any rights or remedies upon any Person other than the Parties hereto and their respective successors and assigns.

(g)
Entire Agreement. This Agreement (including the documents referred to herein) constitutes the entire agreement among the parties hereto and supersedes any prior understandings, agreements, or representations by or among the parties, written
or oral, to the extent they relate in any way to the subject matter hereof.

(h) Counterparts. This Agreement may be executed in one
or more counterparts, each of which shall be deemed an original but all of which together will constitute one and the same instrument.

(i)
Headings. The section headings contained in this Agreement are inserted for convenience only and shall not affect in any way the meaning or interpretation of this Agreement.

(j) Governing Law. This Agreement shall be governed by and construed in accordance with the domestic laws of the State of Delaware without giving
effect to any choice or conflict of law provision or rule (whether of the State of Delaware or any other jurisdiction) that would cause the application of the laws of any jurisdiction other than the State of Delaware.

(k) Amendments and Waivers. No amendment of any provision of this Agreement shall be valid unless the same shall be in writing and signed by the
Corporation and each Holder.

(l) Gender. All pronouns and any variation thereof shall be deemed to refer to the masculine,
feminine, neuter, singular, or plural as the identity of the person or entity or the context may require.

(m) Severability. Any
term or provision of this Agreement that is invalid or unenforceable in any situation in any jurisdiction shall not affect the validity or enforceability of the remaining terms and provisions hereof or the validity or enforceability of the offending
term or provision in any other situation or in any other jurisdiction.

(n) No Presumption Against Drafter. Each of the Parties has
jointly participated in the negotiation and drafting of this Agreement. In the event of any ambiguity or a question of intent or interpretation arises, this Agreement shall be construed as if drafted jointly by each of the Parties and no
presumptions or burdens of proof shall arise favoring any Party by virtue of the authorship of any of the provisions of this Agreement.

(o) Successors and Assigns. Except as otherwise specifically provided herein, this Agreement shall be binding upon, and inure to the benefit of, the Parties hereto and their respective successors and permitted assigns.

(p) Survival. All covenants, agreements, representations and warranties made herein shall survive the Closing and the consummation of the Exchange
of the Unidym Shares.



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IN WITNESS WHEREOF, this Exchange Agreement has been duly executed by or on behalf of each of the parties
hereto on the date first above written.



ARROWHEAD RESEARCH CORPORATION, a Delaware corporationBy:

/s/    Christopher AnzaloneName:

Christopher AnzaloneTitle:

President & Chief Executive OfficerHOLDERS:Bob G. Gower/s/    Bob G. GowerBob G. GowerAllison Gower TrustBy:

/s/    Allison Gower, TrusteeAllison Gower, TrusteeAllison Gower TrustRachel Gower TrustBy:

/s/    Rachel Gower, TrusteeRachel Gower, TrusteeRachel Gower TrustMorganne Gower TrustBy:

/s/    Morganne Mathew, TrusteeMorganne Mathew, TrusteeMorganne Gower TrustWilliam A. McMinnBy:

/s/    William A. McMinnWilliam A. McMinn




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EXHIBIT A  Exchanged Shares



|                          |  |                                       |  |                                  
|------------------------- |  | ------------------------------------- |  | ---------------------------------
|Holder (Name and Address) |  | Number ofUnidymSharesPrior toExchange |  | Number ofExchangedSharesReceived1
|Bob G. Gower              |  | 480,671                               |  |                                  
|Allison Gower Trust       |  | 338,000                               |  |                                  
|Rachel Gower Trust        |  | 338,000                               |  |                                  
|Morganne Gower Trust      |  | 338,000                               |  |                                  
|William A. McMinn         |  | 5,114                                 |  |                                  



|1 | Please note that the Exchanged Shares shall include all shares beneficially
owned by such Holders, including any Unidym Shares released from escrow but reduced by any shares that are subject to the proper exercise of any right of first refusal.
|- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------