EXHIBIT 2.1.1

ASSET CONTRIBUTION AGREEMENT

by and between

Maxygen, Inc., a Delaware Corporation

and Perseid Therapeutics LLC, a Limited Liability Company

Dated as of September 18, 2009

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EXHIBITS AND SCHEDULES

Exhibits

The registrant agrees to furnish to the Securities and Exchange Commission upon request a copy of any omitted schedule or exhibit.

ASSET CONTRIBUTION AGREEMENT

This Asset Contribution Agreement (this “ Agreement ”) is made and entered into as of this 18 ^th day of September, 2009, by and between Maxygen, Inc., a Delaware corporation, having its principal offices at 515 Galveston Drive, Redwood City, CA 94063 (together with its Affiliates, “ Contributor ”), and Perseid Therapeutics LLC, a Delaware limited liability company, having its principal offices at 515 Galveston Drive, Redwood City, CA 94063 (“ Company ”). Contributor and Company are collectively referred to herein as the “ Parties. ”

RECITALS

WHEREAS , Contributor has conducted discovery, research and development of certain proteins, including certain CTLA-4 proteins, with potential usefulness as human pharmaceutical products, and owns or possesses certain patents and know-how with respect thereto;

WHEREAS , Company desires to discover, develop, manufacture and commercialize protein pharmaceutical products utilizing among other things the core team of personnel currently employed by Contributor in connection with the conduct of such activities, and in connection therewith desires to obtain certain assets and licenses from Contributor related to Contributor’s programs for discovery, research and development of CTLA-4 proteins and, subject to certain exceptions, other protein therapeutics (including assignment to Company of Contributor’s rights and obligations under the Astellas Agreement);

WHEREAS , Contributor desires to contribute to Company, and Company desires to acquire from Contributor, certain assets, properties, rights, claims, liabilities and obligations on the terms and conditions set forth herein in exchange for shares of Series A Preferred Stock of Company to be issued to Contributor therefor (the “ Issued Units ”) upon the terms and subject to the conditions set forth in the Purchase Agreement (as defined below), which represent the first issuance of Units by the Company;

WHEREAS , immediately following the contribution of assets, properties, rights, claims, liabilities and obligations by Contributor to Company, each of Contributor and Astellas Bio Inc., a Delaware corporation (“ Bio ”), intends to make a $10,000,000 cash investment in Company in exchange for preferred units of Company pursuant to the Series A and Series B Preferred Unit Purchase Agreement of even date herewith, by and among Company, on the one hand, and Contributor, and Bio, on the other hand (the “ Purchase Agreement ”);

WHEREAS , concurrently herewith Astellas Pharma Inc., a corporation formed under the laws of Japan (“ Astellas ”), Astellas US Holding, Inc., a Delaware corporation, Bio, Contributor and Company have entered into other Transaction Agreements;

WHEREAS , the contribution of assets to, and the assumption of the Assumed Liabilities, as defined below, by, Company and the issuance of the Issued Units to Contributor, are each intended to be effected on a tax-free basis pursuant to Section 721 of the Code (and any comparable provisions of applicable state or local tax laws);

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NOW, THEREFORE , in consideration of the foregoing recitals and the mutual representations, warranties, covenants and promises contained herein, the adequacy and sufficiency of which are hereby acknowledged, the Parties hereto agree as follows:

ARTICLE 1

DEFINITIONS

1.1 “ Books and Records ” means all books, files, papers, correspondence, databases, electronic files, documents (including originals or copies of agreements) and records in Contributor’s possession or control, in whatever medium, excluding (a) originals and drafts of Contracts that are not Contributor Contracts assigned to Company, (b) electronic mail correspondence that are no longer in existence as of the Closing Date or which are deleted in the ordinary course of business under Contributor’s standard retention policy, (c) minutes of meetings of the Board of Contributor and (d) books, files, papers, correspondence, databases, electronic files, documents and records produced in connection with the negotiation of the potential sale of the Business or Contributed Assets to Third Parties (including originals or copies of agreements with such Third Parties with respect to such negotiations) to the extent containing the contents of, or correspondence regarding, such negotiation with such Third Party.

1.2 “ Business ” means the conduct of the Programs by or for Contributor, including, without limitation, the exploitation of assets and rights and the performance of activities and obligations relevant to the Programs and the discovery, research, development, manufacture, commercialization and other exploitation of Products within the Programs.

1.3 “ Code ” means the Internal Revenue Code of 1986, as amended.

1.4 “ Company Business ” means the conduct of the Programs by or for Company or its Affiliates or its licensees, including, without limitation, the exploitation of assets and rights and the performance of activities and obligations relevant to the Programs and the discovery, research, development, manufacture, commercialization and other exploitation of Products within the Programs.

1.5 “ Constructive Knowledge ” of a Party means, with respect to any fact, circumstance, event or other matter in question, (a) the actual knowledge of such fact, circumstance, event or other matter, or (b) the knowledge of such fact, circumstance, event or other matter that would have been ascertained after reasonable inquiry, consistent with such Person’s title and responsibilities, in either case, by any of the following individuals with respect to such Party or the Party’s employees who directly report to such individuals: Russell Howard, Larry Briscoe, Elliot Goldstein, John Borkholder, Grant Yonehiro, Sridhar Viswanathan, Erik Karrer and Norm Kruse.

1.6 “ Contributor Benefit Plans ” means every material written, unwritten, formal or informal plan, agreement, program, policy or other arrangement providing for direct or indirect compensation (other than workers’ compensation, unemployment compensation and other government programs), employment, severance, consulting, disability benefits, supplemental unemployment benefits, vacation benefits, retirement benefits, deferred compensation,

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profit-sharing, bonuses, stock options, stock appreciation rights, other forms of incentive compensation, post-retirement insurance benefits, or other benefits, including, without limitation, each “employee benefit plan,” as defined in Section 3(3) of ERISA, which is maintained or contributed to by Contributor or any Member of the Controlled Group for the benefit of any Employee, or pursuant to which the Contributor has or may have any liability with respect to any Employee.

1.7 “ Contributor Intellectual Property ” means all Intellectual Property included within the Contributed Assets, collectively, the 4 Program Intellectual Property, Other Program Intellectual Property and Other Contributor Intellectual Property. Contributor Intellectual Property does not include any Licensed Intellectual Property.

1.8 “ Control ” means, with respect to any particular Patent, Intellectual Property Right, Know-How, Technology, Intellectual Property, or other particular asset and any and all rights therein, (a) ownership by the applicable Party or (b) possession by the Party granting the applicable right, license or sublicense to the other Party as provided herein, of the power and authority, whether arising by ownership, license, or other authorization, to disclose, and, if applicable, to deliver the particular Know-How or asset to the other Party, and to grant and to authorize under such Patent or Know-How or asset the right, license or sublicense, as applicable, to such other Party without giving rise to a violation of terms of any written agreement with any Third Party. “ Controlled ” and “ Controlling ” shall have their correlative meanings.

1.9 “ Copyrights ” means all copyrights, and all rights, title and interests in all copyrights, copyright registrations and applications for copyright registration, certificates of copyright and copyrighted interests throughout the world, and all rights, title and interests in related applications and registrations throughout the world.

1.10 “ CTLA-4 Variant ” has the meaning assigned to it in the Astellas Agreement.

1.11 “ Defined Benefit Plan ” means either a plan described in Section 3(35) of ERISA or a plan subject to the minimum funding standards set forth in Section 302 of ERISA and Section 412 of the Code.

1.12 “ Employee ” means the employees of Contributor substantially related to the Programs, who are set forth on Schedule 1.12 attached hereto.

1.13 “ Enabling Intellectual Property ” means the Enabling Technology as defined under the Technology Licensed Agreement. For clarity, Enabling Technology excludes (a) any Patents listed on Schedules 2.1(a) , 2.1(b)(2) , or 2.1(e) attached hereto, and (b) any CTLA-4 Variants and Other Protein Variants resulting from the use of the Enabling Technology, together with genetic materials encoding, and cell lines expressing, any such CTLA-4 Variant or Other Protein Variant.

1.14 “ Environment ” means any ambient workplace, indoor or outdoor air, surface water, drinking water supply, groundwater, or other waterways, land surface or subsurface strata, soil, wildlife, plants, or other natural resources, or buildings, structures and fixtures.

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1.15 “ Environmental Claim ” means any legal proceeding, order or written notice of violation from any Governmental Authority or any Person alleging liability under any Environmental Law.

1.16 “ Environmental Law ” means any applicable Legal Requirement concerning: (a) the Environment, including pollution, contamination, cleanup, preservation, protection, and reclamation thereof; (b) human health or safety related to the exposure to a Regulated Substances; (c) any Release or threatened Release of any Regulated Substance; or (d) the management of any Regulated Substance, including the presence, manufacture, generation, use, labeling, warning, notification, treatment, handling, storage, disposal, transportation, re-use, recycling or reclamation of any Regulated Substance.

1.17 “ Environmental Permit ” means any permit, registration, approval, identification number, license or other authorization required under or issued pursuant to any Environmental Law.

1.18 “ ERISA ” means the Employee Retirement Income Security Act of 1974, as amended.

1.19 “ Excluded Books and Records ” means Books and Records other than Assigned Books and Records.

1.20 “ Excluded Laboratory Notebooks ” means laboratory notebook no. 2183 of Contributor.

1.21 “ Excluded Machinery and Equipment ” means all tools, machinery and equipment (including manufacturing assembly and test equipment) that are listed on Schedule 1.21 attached hereto.

1.22 “ Excluded Personal Property ” means all personal property, office furnishings, supplies and other tangible personal listed on Schedule 1.22 attached hereto.

1.23 “ Excluded Protein Variant or Vaccine ” means (i) any amino acid (including any natural, synthetic, modified or other amino acid analogue) chain that is a (A) granulocyte colony stimulating factor (G-CSF), (B) Exclusively Out-Licensed Protein, (C) MaxyBody (which, for the avoidance of doubt, shall not include any Ig portion of a CTLA-4 Variant or Other Protein Variant), (D) a protein from an infectious agent or a polynucleotide encoding such protein that in each case is intended to be used as a Vaccine (including infectious agents or other constructs incorporating a Vaccine and/or genetic material encoding a Vaccine (including live-attenuated or whole killed virus), but solely when such agent, construct or material is included with or otherwise incorporates a protein from an infectious agent (or variant, homolog, derivative, mutant or fragment of such protein as described in (E), below) or a polynucleotide encoding such protein (or such variant, homolog, derivative, mutant or fragment) and is intended to be used as a Vaccine), or (E) any variant, homolog, derivative, mutant, or fragment of subsection (A) or (B) or (D), which in the case of (D) is intended to be used as a vaccine (each, an “ Excluded Protein Molecule ”) and (ii) any Excluded Protein Molecule that is conjugated or otherwise coupled to any other molecule (e.g., polyethylene glycol, immunoglobulin domain, sialylation, pegylated, or glycosylation). In no event shall Excluded Protein Variants or Vaccines include any CTLA-4 Variants or (x) any

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amino acid (including any natural, synthetic, modified or other amino acid analogue) chain that is a protein or polypeptide listed on Schedule 2.1(b)(1) attached hereto, or (y) any variant, homolog, derivative, mutant, or fragment of subsection of (x), provided that in the case of (y) such variant, homolog, derivative, mutant, or fragment has not been altered or modified in such a way as to cause such variant, homolog, derivative, mutant, or fragment to fall within (A), (B), (C), or (D) of the definition of Excluded Protein Variant or Vaccine set forth in the first sentence of this Section 1.23 , or to fall within (E) above such that a reasonable, independent expert knowledgeable and experienced in working with protein pharmaceuticals would primarily consider such variant, homolog, derivative, mutant, or fragment to be a variant of a protein or polypeptide within (A), (B) or (D) above or a material portion thereof (rather than as a variant of some other protein or material portion thereof). For purposes of this definition of Excluded Protein Variant or Vaccine:

(a) “ Exclusively Out-Licensed Protein ” has the meaning set forth in Schedule 1.23(a) attached hereto; and

(b) “ MaxyBody ” shall have the meaning set forth on Schedule 1.23(b) attached hereto.

1.24 “ Facility ” means, collectively, the laboratory and offices located at 515 Galveston Drive, Redwood City, California 94063 (the “ Lab Facility ”), and 301 Galveston Drive, Redwood City, California 94063 (the “ Office Facility ”).

1.25 “ Field ” shall have the meaning set forth in the Technology License Agreement.

1.26 “ G&A Function ” means a general and administrative function as is reasonably required to operate the Business consistent with past practice, which shall consist, in all material respects, of those assets and agreements specified on Schedule 1.26 attached hereto.

1.27 “ Governmental Approval ” means any: permit, license, certificate, concession, approval, consent, ratification, permission, clearance, confirmation, exemption, waiver, franchise, certification, designation, rating, registration, variance, qualification, accreditation or authorization issued, granted, given or otherwise made available by or under the authority of any Governmental Authority or pursuant to any Legal Requirement including, without limitation, any filing or application with the U.S. Food and Drug Administration (the “ FDA ”), or any foreign counterpart thereof, including investigational new drug applications filed with the FDA as more fully defined in 21 C.F.R. §312.3, and foreign equivalents thereof, but excluding Environmental Permits.

1.28 “ Intellectual Property ” means (a) Technology and (b) Intellectual Property Rights therein and thereto.

1.29 “ Intellectual Property Rights ” means any and all rights in and to Technology, including without limitation, Patents, Trade Secrets, Copyrights, Trademarks, moral rights, and mask work rights.

1.30 “ Joint Venture Agreement ” means the Master Joint Venture Agreement among the Contributor, Bio and Astellas, dated as of June 30, 2009.

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1.31 “ Know-How ” means any and all data, information and tangible materials including (a) ideas, discoveries, inventions or improvements; (b) research and development data, such as medicinal chemistry data, nonclinical data, preclinical data, pharmacology data, chemistry data (including analytical, product characterization, manufacturing, and stability data), toxicology data, clinical data (including investigator reports (both preliminary and final), statistical analyses, expert opinions and reports, safety and other electronic databases), analytical and quality control data and stability data, in each case together with supporting data; (c) databases, specifications, formulations, formulae; (d) practices, knowledge, techniques, methods, formulas, processes, manufacturing information; and (e) research materials and compositions of matter, including compounds, reagents, clinical candidates, chemical and biological material, cell lines, assays, compound libraries, animal models, and other physical, biological, or chemical material, in each of the foregoing cases, that is Controlled by Contributor. Know-How excludes any Patent rights with respect thereto (but does include information in unpublished patent applications).

1.32 “ Laboratory Notebooks ” means laboratory notebooks that qualify as Shared Books and Records.

1.33 “ Leased Real Property ” means all of the Contributor’s rights in the Real Property Lease and the leasehold estate created thereby, together with all of Contributor’s right, title and interest in all land, buildings, structures, easements, appurtenances, improvements (including construction in progress) and fixtures located on the premises described therein;

1.34 “ Licensed Intellectual Property ” means the Licensed Technology as defined under the Technology License Agreement, which definition, for the avoidance of doubt, includes the Enabling Intellectual Property.

1.35 “ Member of the Controlled Group ” means each trade or business, whether or not incorporated, that would be treated as a single employer with Contributor under Section 4001 of ERISA or Section 414(b), (c), (m) or (o) of the Code.

1.36 “ Multiemployer Plan ” means a plan described in Section 3(37) of ERISA.

1.37 “ Other Protein Variant ” means (a) any amino acid (including any natural, synthetic, modified or other amino acid analogue) chain that is a human or animal protein including, without limitation, any protein or polypeptide listed on Schedule 2.1(b)(1) attached hereto, or any variant, homolog, derivative, mutant or fragment of the foregoing subsection (a), including, without limitation, amino acid chains resulting from the use of Shuffling, in each case other than any (i) CTLA-4 Variant or (ii) Excluded Protein Variant or Vaccine, (each such protein or variant, homolog, derivative, mutant or fragment thereof, an “ Other Protein Molecule ”) and (b) any Other Protein Molecule that is conjugated or otherwise coupled to any other molecule (e.g., polyethylene glycol, immunoglobulin domain, sialylation, pegylated, or glycosylation).

1.38 “ Patents ” means all patent rights and all rights, title and interests in all patent applications and patents to issue on them, all letters patent or equivalent rights and applications, including utility patents, design patents, plant patents, statutory invention registrations, and any reissue, re-examination, renewal, supplementary protection certificates, extension, division, provisional, substitution, continuation, or continuation-in-part applications thereto throughout the world.

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1.39 “ PP&E ” means, collectively, (a) Personal Property, (b) Machinery and Equipment and (c) all buildings, structures, improvements, furnishings, furniture, fixtures, displays, appliances and other personal property of every kind and nature owned or leased by the Contributor in connection with the Contributed Assets or the Facility.

1.40 “ Programs ” mean, collectively, (i) the 4 Program and (ii) the Other Programs.

(a) “ 4 Program ” means any and all activities performed by or on behalf of Contributor, Company or any of their licensees or Affiliates, (i) pursuant to the Astellas Agreement, or (ii) otherwise directed to any CTLA-4 Variant including, without limitation, activities for the discovery, research, development, manufacture, commercialization or other exploitation of any CTLA-4 Variant or CTLA-4 Product intended for use in the Field.

(b) “ Other Programs ” means, individually and collectively, any and all activities performed by or on behalf of Contributor, Company or any of their licensees or Affiliates, directed to any Other Protein Variant including, without limitation, activities for the discovery, research, development, manufacture, commercialization or other exploitation of any Other Protein Variant or Other Protein Product intended for use in the Field.

1.41 “ Products ” mean, collectively, (i) any CTLA-4 Product and (ii) any Other Protein Product.

(a) “ CTLA-4 Product ” means any pharmaceutical product that contains a CTLA-4 Variant as an ingredient. For the avoidance of doubt, CTLA-4 Product shall include any formulation, delivery device, dispensing device or packaging required for effective use of the CTLA-4 Product.

(b) “ Other Protein Product ” means any pharmaceutical product that contains an Other Protein Variant as an ingredient. For the avoidance of doubt, Other Protein Product shall include any formulation, delivery device, dispensing device or packaging