10,000,000 Shares SEATTLE GENETICS, INC. Common Stock ($0.001 par value per Share) UNDERWRITING AGREEMENT February 2, 2011

Exhibit 1.1

EXECUTION COPY

10,000,000 Shares

SEATTLE GENETICS, INC.

Common Stock

($0.001 par value per Share)

UNDERWRITING AGREEMENT

February 2, 2011

▇▇▇▇▇▇▇▇▇ & COMPANY, INC.

▇.▇. ▇▇▇▇▇▇ Securities LLC

As Representatives of the

several Underwriters listed

in Schedule 1 hereto

c/▇ ▇▇▇▇▇▇▇▇▇ & COMPANY, INC.

▇▇▇ ▇▇▇▇▇▇▇ ▇▇▇▇▇▇

▇▇▇ ▇▇▇▇, ▇▇▇ ▇▇▇▇ ▇▇▇▇▇

c/o ▇.▇. ▇▇▇▇▇▇ Securities LLC

▇▇▇ ▇▇▇▇▇▇▇ ▇▇▇▇▇▇

▇▇▇ ▇▇▇▇, ▇▇▇ ▇▇▇▇ ▇▇▇▇▇

Ladies and Gentlemen:

Seattle Genetics, Inc., a Delaware corporation (the “Company”), proposes to issue and sell to the several Underwriters listed in Schedule 1 hereto (the “Underwriters”), for whom you are acting as representatives (the “Representatives”), an aggregate of 10,000,000 shares of common stock, par value $0.001 per share, of the Company (the “Underwritten Shares”) and, at the option of the Underwriters, up to an additional 1,500,000 shares of common stock of the Company (the “Option Shares”). The Underwritten Shares and the Option Shares are herein referred to as the “Shares”. The shares of common stock of the Company to be outstanding after giving effect to the sale of the Shares are herein referred to as the “Stock”.

The Company hereby confirms its agreement with the several Underwriters concerning the purchase and sale of the Shares, as follows:

1. Registration Statement. The Company has prepared and filed with the Securities and Exchange Commission (the “Commission”) under the Securities Act of 1933, as amended, and the rules and regulations of the Commission thereunder (collectively, the “Securities Act”), a registration statement on Form S-3 (File No. 333-159457), including a prospectus, relating to the Shares. Such registration statement, as amended at the time it became effective, including the information, if any, deemed pursuant to Rule 430A, 430B or 430C under the Securities Act to be part of the registration statement at the time of its effectiveness (“Rule 430 Information”), is referred

to herein as the “Registration Statement”; and as used herein, the term “Preliminary Prospectus” means any prospectus filed with the Commission pursuant to Rule 424(a) under the Securities Act describing the Shares and the public offer and sale thereof together with the prospectus included in the Registration Statement at the time of its effectiveness that omits Rule 430 Information, and the term “Prospectus” means the prospectus in the form first used (or made available upon request of purchasers pursuant to Rule 173 under the Securities Act) in connection with confirmation of sales of the Shares. Any reference in this Agreement to the Registration Statement, any Preliminary Prospectus or the Prospectus shall be deemed to refer to and include the documents incorporated by reference therein pursuant to Item 12 of Form S-3 under the Securities Act, as of the effective date of the Registration Statement or the date of such Preliminary Prospectus or the Prospectus, as the case may be, and any reference to “amend”, “amendment” or “supplement” with respect to the Registration Statement, any Preliminary Prospectus or the Prospectus shall be deemed to refer to and include any documents filed after such date under the Securities Exchange Act of 1934, as amended, and the rules and regulations of the Commission thereunder (collectively, the “Exchange Act”) that are deemed to be incorporated by reference therein. Capitalized terms used but not defined herein shall have the meanings given to such terms in the Registration Statement and the Prospectus.

At or prior to the Applicable Time (as defined below), the Company had prepared the following information (collectively with the pricing information set forth on Annex B hereto, the “Time of Sale Information”): a Preliminary Prospectus dated February 1, 2011 and each “free-writing prospectus” (as defined pursuant to Rule 405 under the Securities Act) listed on Annex A hereto.

“Applicable Time” means 8:45 A.M., New York City time, on February 2, 2011.

2. Purchase of the Shares by the Underwriters. (a) The Company agrees to issue and sell the Underwritten Shares to the several Underwriters as provided in this Agreement, and each Underwriter, on the basis of the representations, warranties and agreements set forth herein and subject to the conditions set forth herein, agrees, severally and not jointly, to purchase from the Company the respective number of Underwritten Shares set forth opposite such Underwriter’s name in Schedule 1 hereto at a price per share (the “Purchase Price”) of $14.6475.

In addition, the Company agrees to issue and sell the Option Shares to the several Underwriters as provided in this Agreement, and the Underwriters, on the basis of the representations, warranties and agreements set forth herein and subject to the conditions set forth herein, shall have the option to purchase, severally and not jointly, from the Company the Option Shares at the Purchase Price less an amount per share equal to any dividends or distributions declared by the Company and payable on the Underwritten Shares but not payable on the Option Shares.

If any Option Shares are to be purchased, the number of Option Shares to be purchased by each Underwriter shall be the number of Option Shares which bears the

same ratio to the aggregate number of Option Shares being purchased as the number of Underwritten Shares set forth opposite the name of such Underwriter in Schedule 1 hereto (or such number increased as set forth in Section 10 hereof) bears to the aggregate number of Underwritten Shares being purchased from the Company by the several Underwriters, subject, however, to such adjustments to eliminate any fractional Shares as the Representatives in their sole discretion shall make.

The Underwriters may exercise the option to purchase the Option Shares at any time in whole, or from time to time in part, on or before the thirtieth (30^th) day following the date of this Agreement, by written notice from the Representatives to the Company. Such notice shall set forth the aggregate number of Option Shares as to which the option is being exercised and the date and time when the Option Shares are to be delivered and paid for which may be the same date and time as the Closing Date (as hereinafter defined) but shall not be earlier than the Closing Date nor later than the tenth full business day (as hereinafter defined) after the date of such notice (unless such time and date are postponed in accordance with the provisions of Section 10 hereof). Any such notice shall be given at least two Business Days prior to the date and time of delivery specified therein, or such shorter time period as is agreed upon by the Company and Representatives.

(b) The Company understands that the Underwriters intend to make a public offering of the Shares as soon after the effectiveness of this Agreement as in the judgment of the Representatives is advisable, and initially to offer the Shares on the terms set forth in the Prospectus. The Company acknowledges and agrees that the Underwriters may offer and sell Shares to or through any affiliate of an Underwriter and that any such affiliate may offer and sell Shares purchased by it to or through any Underwriter.

(c) Payment of the Purchase Price for the Underwritten Shares shall be made by wire transfer in immediately available funds to the account specified by the Company to the Representatives at the offices of ▇▇▇▇▇▇ & ▇▇▇▇▇▇▇ LLP, ▇▇▇▇▇ ▇▇▇▇ ▇▇▇▇▇ ▇▇▇▇▇, ▇▇▇▇▇ ▇▇▇, ▇▇▇ ▇▇▇▇▇, ▇▇▇▇▇▇▇▇▇▇ ▇▇▇▇▇, at 10:00 A.M. New York City time on February 7, 2011, or at such other time or place on the same or such other date, not later than the fifth business day thereafter, as the Representatives and the Company may agree upon in writing or, in the case of the Option Shares, on the date and at the time and place specified by the Representatives in the written notice of the Underwriters’ election to purchase such Option Shares. The time and date of such payment for the Underwritten Shares is referred to herein as the “Closing Date” and the time and date for such payment for the Option Shares, if other than the Closing Date, is herein referred to as the “Additional Closing Date”.

Payment for the Shares to be purchased on the Closing Date or the Additional Closing Date, as the case may be, shall be made against delivery to the Representatives for the respective accounts of the several Underwriters of the Shares to be purchased on such date or the Additional Closing Date, as the case may be, with any transfer taxes payable in connection with the sale of such Shares duly paid by the Company. Delivery

of the Shares shall be made through the facilities of The Depository Trust Company unless the Representatives shall otherwise instruct.

(d) The Company acknowledges and agrees that the Underwriters are acting solely in the capacity of an arm’s length contractual counterparty to the Company with respect to the offering of Shares contemplated hereby (including in connection with determining the terms of the offering) and not as a financial advisor or a fiduciary to, or an agent of, the Company or any other person. The Company also acknowledges and agrees that the Underwriters may be engaged in a broad range of transactions that involve interests that differ from those of the Company. Additionally, neither the Representatives nor any other Underwriter is advising the Company or any other person as to any legal, tax, investment, accounting or regulatory matters in any jurisdiction. The Company shall consult with its own advisors concerning such matters and shall be responsible for making its own independent investigation and appraisal of the transactions contemplated hereby, and the Underwriters shall have no responsibility or liability to the Company with respect thereto. No Underwriter has any obligation to the Company with respect to the offering of Shares except the obligations expressly set forth in this Agreement. Any review by the Underwriters of the Company, the transactions contemplated hereby or other matters relating to such transactions will be performed solely for the benefit of the Underwriters and shall not be on behalf of the Company.

3. Representations and Warranties of the Company. The Company represents and warrants to each Underwriter that:

(a) Preliminary Prospectus. No order preventing or suspending the use of any Preliminary Prospectus has been issued by the Commission, and each Preliminary Prospectus included in the Time of Sale Information, at the time of filing thereof, complied in all material respects with the Securities Act, and no Preliminary Prospectus, at the time of filing thereof, contained any untrue statement of a material fact or omitted to state a material fact required to be stated therein or necessary in order to make the statements therein, in the light of the circumstances under which they were made, not misleading; provided that the Company makes no representation and warranty with respect to any statements or omissions made in reliance upon and in conformity with information relating to any Underwriter furnished to the Company in writing by such Underwriter through the Representatives expressly for use in any Preliminary Prospectus, it being understood and agreed that the only such information furnished by any Underwriter consists of the information described as such in Section 7(b) hereof.

(b) Time of Sale Information. The Time of Sale Information, at the Applicable Time, did not, and at the Closing Date and as of the Additional Closing Date, as the case may be, will not, contain any untrue statement of a material fact or omit to state a material fact required to be stated therein or necessary in order to make the statements therein, in the light of the circumstances under which they were made, not misleading; provided that the Company makes no representation and warranty with respect to any statements or omissions made in reliance upon and in conformity with information relating to any Underwriter furnished to the Company in writing by such Underwriter

through the Representatives expressly for use in such Time of Sale Information, it being understood and agreed that the only such information furnished by any Underwriter consists of the information described as such in Section 7(b) hereof. No statement of material fact included in the Prospectus has been omitted from the Time of Sale Information and no statement of material fact included in the Time of Sale Information that is required to be included in the Prospectus has been omitted therefrom.

(c) Issuer Free Writing Prospectus. Other than the Registration Statement, the Preliminary Prospectus and the Prospectus, the Company (including its agents and representatives, other than the Underwriters in their capacity as such) has not made, used, prepared, authorized, approved or referred to and will not prepare, make, use, authorize, approve or refer to any “written communication” (as defined in Rule 405 under the Securities Act) that constitutes an offer to sell or solicitation of an offer to buy the Shares (each such communication by the Company or its agents and representatives (other than a communication referred to in clause (i) below) an “Issuer Free Writing Prospectus”) other than (i) any document not constituting a prospectus pursuant to Section 2(a)(10)(a) of the Securities Act or Rule 134 under the Securities Act or (ii) the documents listed on Annex A hereto, each electronic road show and any other written communications approved in writing in advance by the Representatives. Each such Issuer Free Writing Prospectus complied in all material respects with the Securities Act, has been or will be (within the time period specified in Rule 433) filed in accordance with the Securities Act (to the extent required thereby) and, when taken together with the Preliminary Prospectus filed prior to the first use of such Issuer Free Writing Prospectus, did not, and at the Closing Date and as of the Additional Closing Date, as the case may be, will not, contain any untrue statement of a material fact or omit to state a material fact necessary in order to make the statements therein, in the light of the circumstances under which they were made, not misleading; provided that the Company makes no representation and warranty with respect to any statements or omissions made in each such Issuer Free Writing Prospectus in reliance upon and in conformity with information relating to any Underwriter furnished to the Company in writing by or on behalf of such Underwriter through the Representatives expressly for use in such Issuer Free Writing Prospectus, it being understood and agreed that the only such information furnished by any Underwriter consists of the information described as such in Section 7(b) hereof. Each such Issuer Free Writing Prospectus, as of its issue date and at all subsequent times through the completion of the public offer and sale of the Shares or until any earlier date that the Company notified or notifies the Representatives as described in Section 4(e), did not, does not and will not include any information that conflicted, conflicts or will conflict with the information contained in the Registration Statement or the Prospectus, including any document incorporated by reference therein and any Preliminary Prospectus deemed to be a part thereof that has not been superseded or modified.

(d) Registration Statement and Prospectus. The Registration Statement is an “automatic shelf registration statement” as defined under Rule 405 of the Securities Act that has been filed with the Commission not earlier than three years prior to the date hereof; and no notice of objection of the Commission to the use of such registration statement or any post-effective amendment thereto pursuant to Rule 401(g)(2) under the

Securities Act has been received by the Company. No order suspending the effectiveness of the Registration Statement has been issued by the Commission and no proceeding for that purpose or pursuant to Section 8A of the Securities Act against the Company or related to the offering has been initiated or, to the best knowledge of the Company, threatened by the Commission; as of the applicable effective date of the Registration Statement and any post-effective amendment thereto, the Registration Statement complied and will comply in all material respects with the Securities Act, and did not and will not contain any untrue statement of a material fact or omit to state a material fact required to be stated therein or necessary in order to make the statements therein not misleading; and as of the date of the Prospectus and any amendment or supplement thereto and as of the Closing Date and as of the Additional Closing Date, as the case may be, the Prospectus does not and will not contain any untrue statement of a material fact or omit to state a material fact required to be stated therein or necessary in order to make the statements therein, in the light of the circumstances under which they were made, not misleading; provided that the Company makes no representation and warranty with respect to any statements or omissions made in reliance upon and in conformity with information relating to any Underwriter furnished to the Company in writing by such Underwriter through the Representatives expressly for use in the Registration Statement and the Prospectus and any amendment or supplement thereto, it being understood and agreed that the only such information furnished by any Underwriter consists of the information described as such in Section 7(b) hereof.

(e) Incorporated Documents. The documents incorporated by reference in the Registration Statement, the Prospectus or the Time of Sale Information, when they became effective or were filed with the Commission, as the case may be, conformed in all material respects to the requirements of the Securities Act or the Exchange Act, as applicable, and none of such documents contained any untrue statement of a material fact or omitted to state a material fact required to be stated therein or necessary to make the statements therein, in the light of the circumstances under which they were made, not misleading; and any further documents so filed and incorporated by reference in the Registration Statement, the Prospectus or the Time of Sale Information, when such documents become effective or are filed with the Commission, as the case may be, will conform in all material respects to the requirements of the Securities Act or the Exchange Act, as applicable, and will not contain any untrue statement of a material fact or omit to state a material fact required to be stated therein or necessary to make the statements therein, in the light of the circumstances under which they were made, not misleading.

(f) Financial Statements. The financial statements and the related notes thereto of the Company and its consolidated subsidiary included or incorporated by reference in the Registration Statement, the Time of Sale Information and the Prospectus comply in all material respects with the applicable requirements of the Securities Act and the Exchange Act, as applicable, and present fairly the financial position of the Company and its consolidated subsidiary as of the dates indicated and the results of their operations and the changes in their cash flows for the periods specified, it being understood that unaudited interim financial statements are subject to normal, year-end audit adjustments; such financial statements have been prepared in conformity with U.S. generally accepted

accounting principles applied on a consistent basis throughout the periods covered thereby, except as may be otherwise specified therein or to the extent unaudited interim financial statements exclude footnotes or may be condensed or summary statements, and the supporting schedules included or incorporated by reference in the Registration Statement present fairly the information required to be stated therein; and the other financial information included or incorporated by reference in the Registration Statement, the Time of Sale Information and the Prospectus has been derived from the accounting records of the Company and its consolidated subsidiary and presents fairly the information shown thereby.

(g) No Material Adverse Change. Since the date of the most recent financial statements of the Company included or incorporated by reference in the Registration Statement, the Time of Sale Information and the Prospectus, (i) there has not been any change in the capital stock (except for grants, exercises, terminations, or forfeitures of equity awards under the Company’s stock option plans and employee stock purchase plan described in the Registration Statement, the Time of Sale Information or the Prospectus, and except for exercises and terminations of warrants described as outstanding in the Registration Statement, the Time of Sale Information or the Prospectus), long-term debt, notes payable or current portion of long-term debt of the Company or its consolidated subsidiary, or any dividend or distribution of any kind declared, set aside for payment, paid or made by the Company on any class of capital stock, or any material adverse change, or any development involving a prospective material adverse change, in or affecting the business, properties, management, financial position, stockholders’ equity, results of operations or prospects of the Company and its subsidiary taken as a whole; (ii) neither the Company nor its subsidiary has entered into any transaction or agreement that is material to the Company and its subsidiary taken as a whole or incurred any liability or obligation, direct or contingent, that is material to the Company and its subsidiary taken as a whole; and (iii) neither the Company nor its subsidiary has sustained any material loss or interference with its business from fire, explosion, flood or other calamity, whether or not covered by insurance, or from any labor disturbance or dispute or any action, order or decree of any court or arbitrator or governmental or regulatory authority, except in each case as otherwise disclosed in the Registration Statement, the Time of Sale Information and the Prospectus.

(h) Organization and Good Standing. The Company and its subsidiary have been duly organized or formed, as applicable, and are validly existing and in good standing (where such concept is recognized under the laws of the jurisdiction in which they are organized or formed) under the laws of their respective jurisdictions of organization, are duly qualified to do business and are in good standing (where such concept is recognized under the laws of the jurisdiction in which they are organized or formed) in each jurisdiction in which their respective ownership or lease of property or the conduct of their respective businesses requires such qualification, and have all power and authority necessary to own or hold their respective properties and to conduct the businesses in which they are engaged, except where the failure to be so qualified or in good standing, as applicable, or have such power or authority would not, individually or in the aggregate, have a material adverse effect on the business, properties, management, financial position, stockholders’ equity,

results of operations or prospects of the Company and its subsidiary taken as a whole or on the performance by the Company of its obligations under this Agreement (a “Material Adverse Effect”).

(i) Capitalization. The Company has an authorized capitalization as set forth in the Registration Statement, under the heading “Description of Capital Stock”; all the outstanding shares of capital stock of the Company have been duly and validly authorized and issued and are fully paid and non-assessable and are not subject to any pre-emptive or similar rights; except as described in or expressly contemplated by the Time of Sale Information and the Prospectus, there are no outstanding rights (including, without limitation, pre-emptive rights), warrants or options to acquire, or instruments convertible into or exchangeable for, any shares of capital stock or other equity interest in the Company or its subsidiary, or any contract, commitment, agreement, understanding or arrangement of any kind relating to the issuance of any capital stock of the Company or any such subsidiary, any such convertible or exchangeable securities or any such rights, warrants or options; the capital stock of the Company conforms in all material respects to the description thereof contained in the Registration Statement, the Time of Sale Information and the Prospectus; and all the outstanding shares of capital stock or other equity interests of each subsidiary owned, directly or indirectly, by the Company have been duly and validly authorized and issued, are fully paid and non-assessable (to the extent such concepts are applicable to the equity interest owned) and are owned directly or indirectly by the Company, free and clear of any lien, charge, encumbrance, security interest, restriction on voting or transfer or any other claim of any third party. Seattle Genetics UK, Ltd. has no material assets or operations.

(j) Stock Options. With respect to the stock options (the “Stock Options”) granted pursuant to the stock-based compensation plans of the Company and its subsidiary (the “Company Stock Plans”), (i) to the Company’s knowledge, each Stock Option intended to qualify as an “incentive stock option” under Section 422 of the Code so qualifies, (ii) each grant of a Stock Option was duly authorized no later than the date on which the grant of such Stock Option was by its terms to be effective (the “Grant Date”) by all necessary corporate action, including, as applicable, approval by the board of directors of the Company (or a duly constituted and authorized committee thereof) and any required stockholder approval by the necessary number of votes or written consents, and the award agreement governing such grant (if any) was duly executed and delivered by each party thereto, and (iii) since March 12, 2001 (a) to the Company’s knowledge, each such grant was made in accordance with the terms of the Company Stock Plans, the Exchange Act and all other applicable laws and regulatory rules or requirements, including the rules of the Nasdaq Stock Market (“Nasdaq Market”) and any other exchange on which Company securities are traded, (b) the per share exercise price of each Stock Option was greater than or equal to the fair market value of a share of Common Stock on the applicable Grant Date (as determined in accordance with the Company Stock Plans) and (c) to the Company’s knowledge, each such grant was properly accounted for in accordance with GAAP in the financial statements (including the related notes) of the Company and disclosed in the Company’s filings with the Commission in accordance with the Exchange Act and all other applicable laws. The Company has not knowingly granted, and there is no and has been no

policy or practice of the Company of granting, Stock Options prior to, or otherwise coordinate the grant of Stock Options with, the release or other public announcement of material information regarding the Company or its subsidiary or their results of operations or prospects.

(k) Due Authorization. The Company has full right, power and authority to execute and deliver this Agreement and to perform its obligations hereunder; and all action required to be taken for the due and proper authorization, execution and delivery by it of each of this Agreement and the consummation by it of the transactions contemplated hereby have been duly and validly taken.

(l) Underwriting Agreement. This Agreement has been duly authorized, executed and delivered by the Company.

(m) The Shares. The Shares to be issued and sold by the Company hereunder have been duly authorized by the Company and, when issued and delivered and paid for as provided herein, will be duly and validly issued and will be fully paid and nonassessable and will conform to the descriptions thereof in the Registration Statement, the Time of Sale Information and the Prospectus; and the issuance of the Shares is not subject to any preemptive or similar rights.

(n) No Violation or Default. Neither the Company nor its subsidiary is (i) in violation of its charter or by-laws or similar organizational documents; (ii) in default, and no event has occurred that, with notice or lapse of time or both, would constitute such a default, in the due performance or observance of any term, covenant or condition contained in any indenture, mortgage, deed of trust, loan agreement or other agreement or instrument to which the Company or its subsidiary is a party or by which the Company or its subsidiary is bound or to which any of the property or assets of the Company or its subsidiary is subject; or (iii) in violation of any law or statute or any judgment, order, rule or regulation of any court or arbitrator or governmental or regulatory authority having jurisdiction over the Company and its subsidiary or any of their respective properties, except, in the case of clauses (ii) and (iii) above, for any such default or violation that would not, individually or in the aggregate, have a Material Adverse Effect.

(o) No Conflicts. The execution, delivery and performance by the Company of this Agreement, the issuance and sale of the Shares and the consummation of the transactions contemplated hereby or by the Time of Sale Information and the Prospectus will not (i) conflict with or result in a breach or violation of any of the terms or provisions of, or constitute a default under, or result in the creation or imposition of any lien, charge or encumbrance upon any property or assets of the Company or its subsidiary pursuant to, any indenture, mortgage, deed of trust, loan agreement or other agreement or instrument to which the Company or its subsidiary is a party or by which the Company or its subsidiary is bound or to which any of the property or assets of the Company or its subsidiary is subject, (ii) result in any violation of the provisions of the charter or by-laws or similar organizational documents of the Company or its subsidiary or (iii) result in the violation of any law or statute or any judgment, order, rule or regulation of any court or

arbitrator or governmental or regulatory authority, except, in the case of clauses (i) and (iii) above, for any such conflict or violation that would not, individually or in the aggregate, have a Material Adverse Effect.

(p) No Consents Required. No consent, approval, authorization, order, registration or qualification of or with any court or arbitrator or governmental or regulatory authority is required for the execution, delivery and performance by the Company of this Agreement, the issuance and sale of the Shares and the consummation of the transactions contemplated by this Agreement or the Time of Sale Information and the Prospectus, except for the registration of the Shares under the Securities Act and such consents, approvals, authorizations, orders and registrations or qualifications as may be required under applicable state securities laws in connection with the purchase and distribution of the Shares by the Underwriters.

(q) Legal Proceedings. Except as described in the Registration Statement, the Time of Sale Information and the Prospectus, there are no legal, governmental or regulatory investigations, actions, suits or proceedings pending to which the Company or its subsidiary is or may be a party or to which any property of the Company or its subsidiary is or may be the subject that, individually or in the aggregate, if determined adversely to the Company or its subsidiary, could reasonably be expected to have a Material Adverse Effect; no such investigations, actions, suits or proceedings are threatened or, to the best knowledge of the Company, contemplated by any governmental or regulatory authority or threatened by others; and (i) there are no current or pending legal, governmental or regulatory actions, suits or proceedings that are required under the Securities Act to be described in the Registration Statement or the Prospectus that are not so described in the Registration Statement, the Time of Sale Information and the Prospectus and (ii) there are no statutes, regulations or contracts or other documents that are required under the Securities Act to be filed as exhibits to the Registration Statement or described in the Registration Statement, the Time of Sale Information or the Prospectus that are not so filed as exhibits to the Registration Statement or described in the Registration Statement, the Time of Sale Information and the Prospectus.

(r) Independent Accountants. PricewaterhouseCoopers LLP, who has certified certain financial statements of the Company and its consolidated subsidiary is an independent registered public accounting firm with respect to the Company and its consolidated subsidiary within the applicable rules and regulations adopted by the Commission and the Public Company Accounting Oversight Board (United States) and as required by the Securities Act.

(s) Title to Real and Personal Property. The Company and its subsidiary have good and marketable title in fee simple to, or have valid rights to lease or otherwise use, all items of real and personal property that are material to the respective businesses of the Company and its subsidiary, in each case free and clear of all liens, encumbrances, claims and defects and imperfections of title except those that (i) do not materially interfere with the use made and proposed to be made of such property by the Company and its

subsidiary or (ii) could not reasonably be expected, individually or in the aggregate, to have a Material Adverse Effect.

(t) Intellectual Property. The Company and its subsidiary own, or have obtained valid and enforceable licenses for, or other rights to use, or can acquire on commercially reasonable terms rights to use all Intellectual Property (as defined below) described in the Registration Statement, the Time of Sale Information and the Prospectus as either being owned or licensed by them or necessary for the conduct of their respective businesses, except where the failure to own, license, have or acquire such rights would not, individually or in the aggregate, have a Material Adverse Effect, and (i) to the knowledge of the Company, there is no infringement, misappropriation or violation by third parties of any such Intellectual Property; (ii) except as specifically described in the Registration Statement, the Time of Sale Information and the Prospectus, there is no pending or, to the knowledge of the Company, threatened action, suit, proceeding or claim by others challenging the rights of the Company or its subsidiary in or to any such Intellectual Property, and the Company is unaware of any facts which it believes would form a reasonable basis for a successful challenge to the rights in such Intellectual Property that would have a Material Adverse Effect on the Company; (iii) the Intellectual Property owned by the Company and its subsidiary and, to the knowledge of the Company, the Intellectual Property licensed to the Company and its subsidiary have not been adjudged invalid or unenforceable, in whole or in part, and except as specifically described in the Registration Statement, the Time of Sale Information and the Prospectus, there is no pending or, to the knowledge of the Company, threatened action, suit, proceeding or claim by others challenging the validity or scope of any such Intellectual Property, and the Company is unaware of any facts which it believes would form a reasonable basis for a successful challenge to the validity, enforceability or scope of such Intellectual Property that would have a Material Adverse Effect on the Company; (iv) to the knowledge of the Company, there is no pending or threatened action, suit, proceeding or claim by others that the Company or its subsidiary infringes, misappropriates or otherwise violates any Intellectual Property or other proprietary rights of others, the Company has not received any written notice of such claim and the Company is unaware of any facts which it believes would form a reasonable basis for a successful claim of such infringement, misappropriation or violation that would have a Material Adverse Effect on the Company; (v) the Company is unaware of any facts which it believes would form a reasonable basis for a successful challenge that any of its employees are in or have ever been in material violation of any term of any employment contract, patent disclosure agreement, invention assignment agreement, non-competition agreement, non-solicitation agreement, nondisclosure agreement or any restrictive covenant to or with a former employer where the basis of such violation relates to such employee’s employment with the Company or its subsidiary, or actions undertaken by the employee while employed with the Company or its subsidiary; (vi) to the knowledge of the Company, the Company is assignee of or is the recipient of an obligation to assign each of the Company’s rights in its patents and patent applications; and (vii) the Company is not a party to or bound by any options, licenses or other agreements, with respect to the Company’s or any third party’s Intellectual Property, that are required to be set forth in the Registration Statement, the Time of Sale Information and the Prospectus, and that are not described in all material respects in such documents. The term “Intellectual Property” as used herein means all patents, patent

applications, trade and service marks, trade and service ▇▇▇▇ registrations, trade names, copyrights, licenses, inventions, trade secrets, technology, know-how and other intellectual property.

(u) No Undisclosed Relationships. No relationship, direct or indirect, exists between or among the Company or its subsidiary, on the one hand, and the directors, officers, stockholders, customers or suppliers of the Company or its subsidiary, on the other, that is required by the Securities Act to be described in the Registration Statement and the Prospectus and that is not so described in such documents and in the Time of Sale Information.

(v) Investment Company Act. The Company is not and, after giving effect to the offering and sale of the Shares and the application of the proceeds thereof as described in the Registration Statement, the Time of Sale Information and the Prospectus, will not be required to register as an “investment company” or an entity “controlled” by an “investment company” within the meaning of the Investment Company Act of 1940, as amended, and the rules and regulations of the Commission thereunder (collectively, the “Investment Company Act”).

(w) Taxes. The Company and its subsidiary have paid all federal, state, local and foreign taxes and filed all tax returns required to be paid or filed through the date hereof; and except as otherwise disclosed in the Registration Statement, the Time of Sale Information and the Prospectus, there is no tax deficiency that has been, or could reasonably be expected to be, asserted against the Company or its subsidiary or any of their respective properties or assets.

(x) Licenses and Permits. The Company and its subsidiary possess all licenses, certificates, permits and other authorizations issued by, and have made all declarations and filings with, the appropriate federal, state, local or foreign governmental or regulatory authorities that are necessary for the ownership or lease of their respective properties or the conduct of their respective businesses as described in the Registration Statement, the Time of Sale Information and the Prospectus, except where the failure to possess or make the same would not, individually or in the aggregate, have a Material Adverse Effect; and except as described in the Registration Statement, the Time of Sale Information and the Prospectus, neither the Company nor its subsidiary has received notice of any revocation or modification of any such license, certificate, permit or authorization or has any reason to believe that any such license, certificate, permit or authorization will not be renewed in the ordinary course.

(y) No Labor Disputes. No labor disturbance by or dispute with employees of the Company or its subsidiary exists or, to the best knowledge of the Company, is contemplated or threatened and the Company is not aware of any existing or imminent labor disturbance by, or dispute with, the employees of any of its or its subsidiary’s principal suppliers, contractors or customers, except as would not have a Material Adverse Effect.

(z) Compliance With Environmental Laws. (i) The Company and its subsidiary (x) are, and at all prior times were, in compliance with any and all applicable federal, state, local and foreign laws, rules, regulations, requirements, decisions and orders relating to the protection of human health or safety, the environment, natural resources, hazardous or toxic substances or wastes, pollutants or contaminants (collectively, “Environmental Laws”), (y) have received and are in compliance with all permits, licenses, certificates or other authorizations or approvals required of them under applicable Environmental Laws to conduct their respective businesses, and (z) have not received notice of any actual or potential liability under or relating to any Environmental Laws, including for the investigation or remediation of any disposal or release of hazardous or toxic substances or wastes, pollutants or contaminants, and have no knowledge of any event or condition that would reasonably be expected to result in any such notice, and (ii) there are no costs or liabilities associated with Environmental Laws of or relating to the Company or its subsidiary, except in the case of each of (i) and (ii) above, for any such failure to comply, or failure to receive required permits, licenses or approvals, or cost or liability, as would not, individually or in the aggregate, have a Material Adverse Effect; and (iii) except as described in each of the Time of Sale Information and the Offering Memorandum, (x) there are no proceedings that are pending, or that are known by the Company or its subsidiary to be contemplated, against the Company or its subsidiary under any Environmental Laws in which a governmental entity is also a party, other than such proceedings regarding which it is reasonably believed no monetary sanctions of $100,000 or more will be imposed, (y) the Company and its subsidiary are not aware of any issues regarding compliance with Environmental Laws, or liabilities or other obligations under Environmental Laws or concerning hazardous or toxic substances or wastes, pollutants or contaminants, that could reasonably be expected to have a material effect on the capital expenditures, earnings or competitive position of the Company and its subsidiary, and (z) none of the Company and its subsidiary anticipates material capital expenditures relating to any Environmental Laws.

(aa) Hazardous Substances. There has been no storage, generation, transportation, handling, treatment, disposal, discharge, emission, or other release of any kind of toxic wastes or hazardous substances, including, but not limited to, any naturally occurring radioactive materials, brine, drilling mud, crude oil, natural gas liquids and other petroleum materials, by, due to or caused by the Company or its subsidiary (or, to the best of the Company’s knowledge, any other entity (including any predecessor) for whose acts or omissions the Company or its subsidiary is or could reasonably be expected to be liable) upon any of the property now or previously owned or leased by the Company or its subsidiary, or upon any other property, in violation of any Environmental Laws or in a manner or to a location that could reasonably be expected to give rise to any liability under the Environmental Laws, except for any violation or liability which would not, individually or in the aggregate, have a Material Adverse Effect.

(bb) Compliance With ERISA. (i) Each employee benefit plan, within the meaning of Section 3(3) of the Employee Retirement Income Security Act of 1974, as amended (“ERISA”), for which the Company or any member of its “Controlled Group”

(defined as any organization which is a member of a controlled group of corporations within the meaning of Section 414 of the Internal Revenue Code of 1986, as amended (the “Code”)) would have any liability (each, a “Plan”) has been maintained in compliance in all material respects with its terms and the requirements of any applicable statutes, orders, rules and regulations, including but not limited to ERISA and the Code; (ii) no prohibited transaction, within the meaning of Section 406 of ERISA or Section 4975 of the Code, has occurred with respect to any Plan excluding transactions effected pursuant to a statutory or administrative exemption; (iii) for each Plan that is subject to the funding rules of Section 412 of the Code or Section 302 of ERISA, no “accumulated funding deficiency” as defined in Section 412 of the Code, whether or not waived, has occurred or is reasonably expected to occur; (iv) with respect to each Plan that is subject to Title IV of ERISA, the fair market value of the assets of each Plan are at least equal in value to the present value of all benefits accrued under such Plan (determined based on those assumptions used to fund such Plan); (v) no “reportable event” (within the meaning of Section 4043(c) of ERISA) has occurred or is reasonably expected to occur with respect to any Plan; and (vi) neither the Company nor any member of the Controlled Group has incurred, nor reasonably expects to incur, any liability under Title IV of ERISA (other than contributions to the Plan or premiums to the PBGC, in the ordinary course and without default) in respect of a Plan (including a “multiemployer plan”, within the meaning of Section 4001(a)(3) of ERISA).

(cc) Disclosure Controls. The Company maintains, on its behalf and on behalf of its subsidiary, an effective system of “disclosure controls and procedures” (as defined in Rule 13a-15(e) of the Exchange Act) that is designed to ensure that information required to be disclosed by the Company in reports that it files or submits under the Exchange Act is recorded, processed, summarized and reported within the time periods specified in the Commission’s rules and forms, including controls and procedures designed to ensure that such information is accumulated and communicated to the Company’s management as appropriate to allow timely decisions regarding required disclosure. The Company has carried out evaluations of the effectiveness of its disclosure controls and procedures as required by Rule 13a-15 of the Exchange Act.

(dd) Accounting Controls. The Company maintains, on its behalf and on behalf of its subsidiary, systems of “internal control over financial reporting” (as defined in Rule 13a-15(f) of the Exchange Act) that comply with the requirements of the Exchange Act and have been designed by, or under the supervision of, the Company’s principal executive and principal financial officers, or persons performing similar functions, to provide reasonable assurance regarding the reliability of financial reporting and the preparation of financial statements for external purposes in accordance with generally accepted accounting principles, including, but not limited to internal accounting controls sufficient to provide reasonable assurance that (i) transactions are executed in accordance with management’s general or specific authorizations; (ii) transactions are recorded as necessary to permit preparation of financial statements in conformity with generally accepted accounting principles and to maintain asset accountability; (iii) access to assets is permitted only in accordance with management’s general or specific authorization; and (iv) the recorded accountability for assets is compared with the existing assets at reasonable intervals and

appropriate action is taken with respect to any differences. Except as disclosed in the Registration Statement, the Time of Sale Information and the Prospectus, there are no material weaknesses in the Company’s internal controls. The Company’s auditors and the Audit Committee of the Board of Directors of the Company have been advised of: (i) all significant deficiencies and material weaknesses in the design or operation of internal controls over financial reporting which are reasonably likely to adversely affect the Company’s ability to record, process, summarize and report financial information; and (ii) any fraud, whether or not material, that involves management or other employees who have a significant role in the Company’s internal controls over financial reporting.

(ee) Insurance. The Company and its subsidiary have insurance covering their respective properties, operations, personnel and businesses, including business interruption insurance, which insurance is in amounts and insures against such losses and risks in accordance with customary industry practice for companies of comparable size, market capitalization and stage of business and clinical development to protect the Company and its subsidiary and their respective businesses; and neither the Company nor its subsidiary has (i) received notice from any insurer or agent of such insurer that capital improvements or other expenditures are required or necessary to be made in order to continue such insurance or (ii) any reason to believe that it will not be able to renew its existing insurance coverage as and when such coverage expires or to obtain similar coverage at reasonable cost from similar insurers as may be necessary to continue its business.

(ff) No Unlawful Payments. Neither the Company nor its subsidiary nor, to the best knowledge of the Company, any director, officer, agent, employee or other person associated with or acting on behalf of the Company or its subsidiary has (i) used any corporate funds for any unlawful contribution, gift, entertainment or other unlawful expense relating to political activity; (ii) made any direct or indirect unlawful payment to any foreign or domestic government official or employee from corporate funds; (iii) violated or is in violation of any provision of the Foreign Corrupt Practices Act of 1977; or (iv) made any bribe, rebate, payoff, influence payment, kickback or other unlawful payment.

(gg) Compliance with Money Laundering Laws. The operations of the Company and its subsidiary are and have been conducted at all times in compliance with applicable financial recordkeeping and reporting requirements of the Currency and Foreign Transactions Reporting Act of 1970, as amended, the money laundering statutes of all jurisdictions, the rules and regulations thereunder and any related or similar rules, regulations or guidelines, issued, administered or enforced by any governmental agency (collectively, the “Money Laundering Laws”) and no action, suit or proceeding by or before any court or governmental agency, authority or body or any arbitrator involving the Company or its subsidiary with respect to the Money Laundering Laws is pending or, to the best knowledge of the Company, threatened.

(hh) Compliance with OFAC. None of the Company, its subsidiary or, to the knowledge of the Company, any director, officer, agent, employee or Affiliate of the Company or its subsidiary is currently subject to any U.S. sanctions administered by the Office of Foreign Assets Control of the U.S. Department of the Treasury (“OFAC”); and

the Company will not directly or indirectly use the proceeds of the offering of the Shares hereunder, or lend, contribute or otherwise make available such proceeds to any subsidiary, joint venture partner or other person or entity, for the purpose of financing the activities of any person currently subject to any U.S. sanctions administered by OFAC.

(ii) Affiliations. To the Company’s knowledge, there are no affiliations or associations between (i) the Underwriters and (ii) the Company or any of the Company’s officers, directors or 5% or greater security holders or any beneficial owner of the Company’s unregistered equity securities that were acquired at any time on or after the 180th day immediately preceding the date the Registration Statement was initially filed with the Commission, except as disclosed in the Registration Statement, the Time of Sale Information and the Prospectus.

(jj) No Broker’s Fees. Neither the Company nor its subsidiary is a party to any contract, agreement or understanding with any person (other than this Agreement) that would give rise to a valid claim against the Company or its subsidiary or any Underwriter for a brokerage commission, finder’s fee or like payment in connection with the offering and sale of the Shares.

(kk) No Registration Rights. No person has the right to require the Company or its subsidiary to register any securities for sale under the Securities Act by reason of the filing of the Registration Statement with the Commission or the issuance and sale of the Shares, except as otherwise have been waived in connection with the filing of the Registration Statement with the Commission (and which waivers are effective as to the issuance and sale of the Shares contemplated hereby).

(ll) No Stabilization. The Company has not taken, directly or indirectly, any action designed to or that could reasonably be expected to cause or result in any stabilization or manipulation of the price of the Shares.

(mm) Business With Cuba. The Company has complied with all provisions of Section 517.075, Florida Statutes (Chapter 92-198, Laws of Florida) relating to doing business with the Government of Cuba or with any person or affiliate located in Cuba.

(nn) Margin Rules. Neither the issuance, sale and delivery of the Shares nor the application of the proceeds thereof by the Company as described in the Registration Statement, the Time of Sale Information and the Prospectus will violate Regulation T, U or X of the Board of Governors of the Federal Reserve System or any other regulation of such Board of Governors.

(oo) Forward-Looking Statements. No forward-looking statement (within the meaning of Section 27A of the Securities Act and Section 21E of the Exchange Act) contained in the Registration Statement, the Time of Sale Information and the Prospectus has been made or reaffirmed without a reasonable basis or has been disclosed other than in good faith. The statements and financial information (including the assumptions described therein) included in the Registration Statement, the Time of Sale Information and the

Prospectus under the Heading “Use of Proceeds” or incorporated by reference therein from the Company’s Annual Report on Form 10-K for the year ended December 31, 2009 and Quarterly Reports on Form 10-Q for the periods ending on March 31, 2010, June 30, 2010 and September 30, 2010 (in each case under the heading “Management’s Discussion and Analysis of Financial Condition and Results of Operations—Liquidity and Capital Resources”) (collectively, the “Projections”) (i) are within the coverage of the safe harbor for forward looking statements set forth in Section 27A of the Securities Act, Rule 175(b) under the Securities Act or Rule 3b-6 under the Exchange Act, as applicable, (ii) were made by the Company with a reasonable basis and in good faith and reflect the Company’s good faith best estimate of the matters described therein, and (iii) have been prepared in accordance with Item 10 of Regulation S-K under the Securities Act; all assumptions material to the Projections are set forth in the Registration Statement, the Time of Sale Information and the Prospectus; the assumptions used in the preparation of the Projections are reasonable; and none of the Company or its subsidiary are aware of any business, economic or industry developments inconsistent with the assumptions underlying the Projections.

(pp) Statistical and Market Data. Nothing has come to the attention of the Company that has caused the Company to believe that the statistical and market-related data included in the Registration Statement, the Time of Sale Information and the Prospectus is not based on or derived from sources that are reliable and accurate in all material respects.

(qq) ▇▇▇▇▇▇▇▇-▇▇▇▇▇ Act. There is and has been no material failure on the part of the Company or any of the Company’s directors or officers, in their capacities as such, to comply with any applicable provision of the ▇▇▇▇▇▇▇▇-▇▇▇▇▇ Act of 2002 and the rules and regulations promulgated in connection therewith (the “▇▇▇▇▇▇▇▇-▇▇▇▇▇ Act”), including Section 402 related to loans and Sections 302 and 906 related to certifications.

(rr) Status under the Securities Act. At the time of filing the Registration Statement and any post-effective amendments thereto, at the earliest time thereafter that the Company or any offering participant made a bona fide offer (within the meaning of Rule 164(h)(2) under the Securities Act) of the Shares and at the date hereof, the Company was not and is not an “ineligible issuer,” as defined in Rule 405 under the Securities Act.

(ss) Termination or Nonrenewal of Contracts. Except for the termination of the Collaboration Agreement dated February 7, 2007 between the Company and Genentech, Inc., which is described in the Registration Statement, the Time of Sale Information and the Prospectus and except as would not, individually or the aggregate, have a Material Adverse Effect, neither the Company nor its subsidiary has sent or received any communication regarding termination of, or intent not to renew, any of the contracts or agreements to which the Company or its subsidiary are a party referred to or described in, or filed as an exhibit to, the Registration Statement or as incorporated by reference in the Registration Statement, and no such termination or nonrenewal has been threatened by, to the Company’s knowledge, any other party to any such contract or agreement.

(tt) Clinical Trials. The clinical and pre-clinical trials conducted by or on behalf of or sponsored by the Company or its subsidiary, or in which the Company or its subsidiary have participated, that are described in the Registration Statement, the Time of Sale Information and the Prospectus or the results of which are referred to in the Registration Statement, the Time of Sale Information and the Prospectus were and, if still pending, are being conducted in all material respects in accordance with standard medical and scientific research procedures and all applicable statutes, rules, regulations and policies of the U.S. Food and Drug Administration (the “FDA”) and comparable drug regulatory agencies outside of the United States to which it is subject (collectively, the “Regulatory Authorities”), including, without limitation, 21 C.F.R. Parts 50, 54, 56, 58, and 312, and current Good Clinical Practices and Good Laboratory Practices; the descriptions in the Registration Statement, the Time of Sale Information and the Prospectus of the results of such studies and tests are accurate and complete in all material respects and fairly present the data derived from such trials and the Company has no knowledge of any other trials the results of which are inconsistent with or otherwise call into question the results described or referred to in the Registration Statement, the Time of Sale Information and the Prospectus; the Company and its subsidiary have operated and are currently in compliance in all material respects with all applicable statutes, rules, regulations and policies of the Regulatory Authorities; and neither the Company nor its subsidiary have received any notices, correspondence or other communication from the Regulatory Authorities or any other governmental agency which could lead to the termination or suspension of any clinical or pre-clinical trials that are described in the Registration Statement, the Time of Sale Information and the Prospectus or the results of which are referred to in the Registration Statement, Time or Sale Information and the Prospectus and, to the Company’s knowledge, there are no grounds for the same.

(uu) Compliance with Applicable Laws; Authorizations. The Company and its subsidiary: (i) are and at all times have been in material compliance with all statutes, rules and regulations applicable to the ownership, testing, development, manufacture, packaging, processing, use, distribution, marketing, labeling, promotion, sale, offer for sale, storage, import, export or disposal of any product manufactured or distributed by the Company (“Applicable Laws”); (ii) have not received any FDA Form 483, notice of adverse finding, warning letter, untitled letter or other correspondence or notice from any court or arbitrator or governmental or regulatory authority or third party alleging or asserting material noncompliance with any Applicable Laws or any licenses, exemptions, certificates, approvals, clearances, authorizations, permits and supplements or amendments thereto required by any such Applicable Laws (“Authorizations”); (iii) possess all material Authorizations and such Authorizations are valid and in full force and effect and are not in violation of any term of any such Authorizations; (iv) have not received notice of any claim, action, suit, proceeding, hearing, enforcement, investigation, arbitration or other action from any court or arbitrator or governmental or regulatory authority or third party alleging that any product operation or activity is in violation of any Applicable Laws or Authorizations and have no knowledge that any such court or arbitrator or governmental or regulatory authority or third party is considering

any such claim, litigation, arbitration, action, suit, investigation or proceeding; (v) have not received notice that any court or arbitrator or governmental or regulatory authority has taken, is taking or intends to take action to materially limit, suspend, materially modify or revoke any Authorizations and have no knowledge that any such court or arbitrator or governmental or regulatory authority is considering such action; and (vi) have filed, obtained, maintained or submitted all material reports, documents, forms, notices, applications, records, claims, submissions and supplements or amendments as required by any Applicable Laws or Authorizations and that all such reports, documents, forms, notices, applications, records, claims, submissions and supplements or amendments were complete and correct on the date filed in all material respects (or were corrected or supplemented by a subsequent submission).

(vv) No Restrictions on Subsidiaries. No subsidiary of the Company is currently prohibited, directly or indirectly, under any agreement or other instrument to which it is a party or is subject, from paying any dividends to the Company, from making any other distribution on such subsidiary’s capital stock, from repaying to the Company any loans or advances to such subsidiary from the Company or from transferring any of such subsidiary’s properties or assets to the Company or any other subsidiary of the Company.

(ww) No Ratings. There are no securities or preferred stock of or guaranteed by the Company or its subsidiary that are rated by a “nationally recognized statistical rating organization,” as such term is defined by the Commission for purposes of Rule 436(g)(2) under the Securities Act.

4. Further Agreements of the Company. The Company covenants and agrees with each Underwriter that:

(a) Required Filings. The Company will file the final Prospectus with the Commission within the time periods specified by Rule 424(b) and Rule 430A, 430B or 430C under the Securities Act, will file any Issuer Free Writing Prospectus to the extent required by Rule 433 under the Securities Act; will file promptly all reports and any definitive proxy or information statements required to be filed by the Company with the Commission pursuant to Section 13(a), 13(c), 14 or 15(d) of the Exchange Act subsequent to the date of the Prospectus and for so long as the delivery of a prospectus is required in connection with the offering or sale of the Shares; and will furnish copies of the Prospectus and each Issuer Free Writing Prospectus (to the extent not previously delivered) to the Underwriters in New York City prior to 10:00 A.M., New York City time, on the business day next succeeding the date of this Agreement in such quantities as the Representatives may reasonably request. The Company will pay the registration fee for this offering within the time period required by Rule 456(b)(1) under the Securities Act (without giving effect to the proviso therein) and in any event prior to the Closing Date.

(b) Delivery of Copies. Upon the request of the Representatives, the Company will deliver, without charge, (i) to the Representatives, two signed copies of the

Registration Statement as originally filed and each amendment thereto, in each case including all exhibits and consents filed therewith; and (ii) to each Underwriter (A) a conformed copy of the Registration Statement as originally filed and each amendment thereto (without exhibits) and (B) during the Prospectus Delivery Period (as defined below), as many copies of the Prospectus (including all amendments and supplements thereto and documents incorporated by reference therein) and each Issuer Free Writing Prospectus as the Representatives may reasonably request. As used herein, the term “Prospectus Delivery Period” means such period of time after the first date of the public offering of the Shares as in the opinion of counsel for the Underwriters a prospectus relating to the Shares is required by law to be delivered (or required to be delivered but for Rule 172 under the Securities Act) in connection with sales of the Shares by any Underwriter or dealer.

(c) Amendments or Supplements, Issuer Free Writing Prospectuses. Before preparing, using, authorizing, approving, referring to or filing any Issuer Free Writing Prospectus, and before filing any amendment or supplement to the Registration Statement or the Prospectus, whether before or after the time that the Registration Statement becomes effective, the Company will furnish to the Representatives and counsel for the Underwriters a copy of the proposed Issuer Free Writing Prospectus, amendment or supplement for review and will not prepare, use, authorize, approve, refer to or file any such Issuer Free Writing Prospectus or file any such proposed amendment or supplement to which the Representatives reasonably object.

(d) Notice to the Representatives. The Company will advise the Representatives promptly, and confirm such advice in writing, (i) when any amendment to the Registration Statement has been filed or becomes effective; (ii) when any supplement to the Prospectus or any Issuer Free Writing Prospectus or any amendment to the Prospectus has been filed; (iii) of any request by the Commission for any amendment to the Registration Statement or any amendment or supplement to the Prospectus or the receipt of any comments from the Commission relating to the Registration Statement or any other request by the Commission for any additional information; (iv) of the issuance by the Commission of any order suspending the effectiveness of the Registration Statement or preventing or suspending the use of any Preliminary Prospectus, any of the Time of Sale Information or the Prospectus or the initiation or threatening of any proceeding for that purpose or pursuant to Section 8A of the Securities Act; (v) of the occurrence of any event within the Prospectus Delivery Period as a result of which the Prospectus, the Time of Sale Information or any Issuer Free Writing Prospectus as then amended or supplemented would include any untrue statement of a material fact or omit to state a material fact required to be stated therein or necessary in order to make the statements therein, in the light of the circumstances existing when the Prospectus, the Time of Sale Information or any such Issuer Free Writing Prospectus is delivered to a purchaser, not misleading; (vi) of the receipt by the Company of any notice with respect to any suspension of the qualification of the Shares for offer and sale in any jurisdiction or the initiation or threatening of any proceeding for such purpose; and (vii) of the receipt by the Company of any notice of objection of the Commission to the use of the Registration Statement or any post-effective amendment thereto pursuant to Rule

401(g)(2) under the Securities Act; and the Company will use its best efforts to prevent the issuance of any such order suspending the effectiveness of the Registration Statement, preventing or suspending the use of any Preliminary Prospectus, any of the Time of Sale Information or the Prospectus or suspending any such qualification of the Shares and, if any such order is issued, will use its best efforts to obtain as soon as possible the withdrawal thereof.

(e) Ongoing Compliance. (1) If during the Prospectus Delivery Period (i) any event shall occur or condition shall exist as a result of which the Prospectus as then amended or supplemented would include any untrue statement of a material fact or omit to state any material fact required to be stated therein or necessary in order to make the statements therein, in the light of the circumstances existing when the Prospectus is delivered to a purchaser, not misleading or (ii) it is necessary to amend or supplement the Prospectus to comply with law, the Company will immediately notify the Underwriters thereof and forthwith prepare and, subject to paragraph (c) above, file with the Commission and furnish to the Underwriters and to such dealers as the Representatives may designate, such amendments or supplements to the Prospectus as may be necessary so that the statements in the Prospectus as so amended or supplemented will not, in the light of the circumstances existing when the Prospectus is delivered to a purchaser, be misleading or so that the Prospectus will comply with law and (2) if at any time prior to the Closing Date (i) any event shall occur or condition shall exist as a result of which the Time of Sale Information as then amended or supplemented would include any untrue statement of a material fact or omit to state any material fact necessary in order to make the statements therein, in the light of the circumstances existing when the Time of Sale Information is delivered to a purchaser, not misleading or (ii) it is necessary to amend or supplement the Time of Sale Information to comply with law, the Company will immediately notify the Underwriters thereof and forthwith prepare and, subject to paragraph (c) above, file with the Commission (to the extent required) and furnish to the Underwriters and to such dealers as the Representatives may designate, such amendments or supplements to the Time of Sale Information as may be necessary so that the statements in the Time of Sale Information as so amended or supplemented will not, in the light of the circumstances under which they were made, be misleading or so that the Time of Sale Information will comply with law.

(f) Blue Sky Compliance. The Company will qualify the Shares for offer and sale under the securities or Blue Sky laws of such jurisdictions as the Representatives shall reasonably request and will continue such qualifications in effect so long as required for distribution of the Shares; provided that the Company shall not be required to (i) qualify as a foreign corporation or other entity or as a dealer in securities in any such jurisdiction where it would not otherwise be required to so qualify, (ii) file any general consent to service of process in any such jurisdiction or (iii) subject itself to taxation in any such jurisdiction if it is not otherwise so subject.

(g) Earning Statement. The Company will make generally available to its security holders and the Representatives as soon as practicable an earnings statement that satisfies the provisions of Section 11(a) of the Securities Act and Rule 158 of the

Commission promulgated thereunder covering a period of at least twelve months beginning with the first fiscal quarter of the Company occurring after the “effective date” (as defined in Rule 158) of the Registration Statement.

(h) Clear Market. For a period of 90 days after the date of the Prospectus, the Company will not (i) offer, pledge, announce the intention to sell, 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 Stock or any securities convertible into or exercisable or exchangeable for Stock or (ii) enter into any swap or other agreement that transfers, in whole or in part, any of the economic consequences of ownership of the Stock, whether any such transaction described in clause (i) or (ii) above is to be settled by delivery of Stock or such other securities, in cash or otherwise, without the prior written consent of the Representatives, other than (x) the Shares to be sold hereunder, (y) the issuance of shares of Stock of the Company upon the exercise of options or warrants disclosed in the Registration Statement and the Time of Sale Information as outstanding or (z) the issuance of shares of Stock of the Company, or the issuance or grant of options, rights to purchase, restricted stock units or other equity awards, in each case under existing employee stock option or other equity compensation plans and the Company’s employee stock purchase plan, and in each case to the extent that such plans are disclosed in the Registration Statement and Time of Sale Information. Notwithstanding the foregoing, if (1) during the last 17 days of the 90-day restricted period, the Company issues an earnings release or material news or a material event relating to the Company occurs; or (2) prior to the expiration of the 90-day restricted period, the Company announces that it will release earnings results during the 16-day period beginning on the last day of the 90-day period, the restrictions imposed by this Agreement shall continue to apply until the expiration of the 18-day period beginning on the issuance of the earnings release or the occurrence of the material news or material event; provided that, such extension will not apply if (a) the shares of Stock of the Company are “actively traded securities” (as defined in Regulation M of the Exchange Act), (b) the Company meets the applicable requirements of paragraph (a)(1) of Rule 139 under the Securities Act in the manner contemplated by NASD Conduct Rule 2711(f)(4), and (c) the provisions of NASD Conduct Rule 2711(f)(4) do not restrict the publishing or distribution of any research reports relating to the Company by any of the Underwriters during the 15 days before or after the last day of the 90-day period (before giving effect to such extension).

(i) Use of Proceeds. The Company will apply the net proceeds from the sale of the Shares as described in the Registration Statement, the Time of Sale Information and the Prospectus under the heading “Use of Proceeds”.

(j) No Stabilization. The Company will not take, directly or indirectly, any action designed to or that could reasonably be expected to cause or result in any stabilization or manipulation of the price of the Shares.

(k) Exchange Listing. The Company will use its best efforts to list for quotation the Shares on the Nasdaq Global Select Market.

(l) Reports. For a period of two years from the date of this Agreement, the Company will furnish to the Representatives, as soon as they are available, copies of all reports or other communications (financial or other) furnished to holders of the Shares generally, and copies of any reports and financial statements furnished to or filed with the Commission or any national securities exchange or automatic quotation system, provided, however, that the Company shall not be required to furnish any such reports or other communications pursuant to this paragraph that are filed with or furnished to the Commission and accessible through the ▇▇▇▇▇ database.

(m) Record Retention. The Company will, pursuant to reasonable procedures developed in good faith, retain copies of each Issuer Free Writing Prospectus that is not filed with the Commission in accordance with Rule 433 under the Securities Act.

(n) ▇▇▇▇▇▇▇▇-▇▇▇▇▇ Act. For a period of one year from the date of this Agreement, the Company will use commercially reasonable efforts to comply with all effective applicable provisions of the ▇▇▇▇▇▇▇▇-▇▇▇▇▇ Act.

5. Certain Agreements of the Underwriters. Each Underwriter hereby represents and agrees that:

(a) It has not and will not use, authorize use of, refer to, or participate in the planning for use of, any “free writing prospectus”, as defined in Rule 405 under the Securities Act (which term includes use of any written information furnished to the Commission by the Company and not incorporated by reference into the Registration Statement and any press release issued by the Company) other than (i) a free writing prospectus that contains no “issuer information” (as defined in Rule 433(h)(2) under the Securities Act) that was not included (including through incorporation by reference) in the Preliminary Prospectus or a previously filed Issuer Free Writing Prospectus, (ii) any Issuer Free Writing Prospectus listed on Annex A hereto or prepared pursuant to Section 3(c) or Section 4(c) above (including any electronic road show), or (iii) any free writing prospectus prepared by such Underwriter and approved by the Company in advance in writing (each such free writing prospectus referred to in clauses (i) or (iii), an “Underwriter Free Writing Prospectus”).

(b) It has not and will not, without the prior written consent of the Company, use any free writing prospectus that contains the final terms of the Shares unless such terms have previously been included in a free writing prospectus filed with the Commission; provided that Underwriters may use a term sheet substantially in the form of Annex C hereto without the consent of the Company; provided further that any Underwriter using such term sheet shall notify the Company, and provide a copy of such term sheet to the Company, prior to, or substantially concurrently with, the first use of such term sheet.

(c) It is not subject to any pending proceeding under Section 8A of the Securities Act with respect to the offering (and will promptly notify the Company if any such proceeding against it is initiated during the Prospectus Delivery Period).

6. Conditions of Underwriters’ Obligations. The obligation of each Underwriter to purchase the Underwritten Shares on the Closing Date or the Option Shares on the Additional Closing Date, as the case may be as provided herein is subject to the performance by the Company of its covenants and other obligations hereunder and to the following additional conditions:

(a) Registration Compliance; No Stop Order. No order suspending the effectiveness of the Registration Statement shall be in effect, and no proceeding for such purpose or pursuant to Rule 401(g)(2) or pursuant to Section 8A under the Securities Act shall be pending before or threatened by the Commission; the Prospectus and each Issuer Free Writing Prospectus shall have been timely filed with the Commission under the Securities Act (in the case of an Issuer Free Writing Prospectus, to the extent required by Rule 433 under the Securities Act) and in accordance with Section 4(a) hereof; and all requests by the Commission for additional information shall have been complied with to the reasonable satisfaction of the Representatives.

(b) Representations and Warranties. The representations and warranties of the Company contained herein shall be true and correct on the date hereof and on and as of the Closing Date or the Additional Closing Date, as the case may be (except to the extent expressly made as of an earlier date, in which case as of such earlier date); and the statements of the Company and its officers made in any certificates delivered pursuant to this Agreement shall be true and correct on and as of the Closing Date or the Additional Closing Date, as the case may be.

(c) No Material Adverse Change. No event or condition of a type described in Section 3(g) hereof shall have occurred or shall exist, which event or condition is not described in the Time of Sale Information (excluding any amendment or supplement thereto) and the Prospectus (excluding any amendment or supplement thereto) and the effect of which in the judgment of the Representatives makes it impracticable or inadvisable to proceed with the offering, sale or delivery of the Shares on the Closing Date or the Additional Closing Date, as the case may be, on the terms and in the manner contemplated by this Agreement, the Time of Sale Information and the Prospectus.

(d) Officer’s Certificate. The Representatives shall have received on and as of the Closing Date or the Additional Closing Date, as the case may be, a certificate of the chief financial officer or chief accounting officer of the Company and one additional senior executive officer of the Company who is satisfactory to the Representatives (i) confirming that such officers have carefully reviewed the Registration Statement, the Time of Sale Information and the Prospectus and, to the knowledge of such officers, the representations set forth in Sections 3(b) and 3(d) hereof are true and correct, (ii) confirming that the other representations and warranties of the Company in this Agreement are true and correct, that the statements of the Company and its officers made in any certificates delivered pursuant to this Agreement shall be true and correct on and as of the Closing Date and that the Company has complied with all agreements and satisfied all conditions on its part to be performed or satisfied hereunder at or prior to the

Closing Date or the Additional Closing Date, as the case may be, and (iii) to the effect set forth in paragraphs (a) and (c) above.

(e) Comfort Letters. On the date of this Agreement and on the Closing Date or the Additional Closing Date, as the case may be, PricewaterhouseCoopers LLP shall have furnished to the Representatives, at the request of the Company, letters, dated the respective dates of delivery thereof and addressed to the Underwriters, in form and substance reasonably satisfactory to the Representatives, containing statements and information of the type customarily included in accountants’ “comfort letters” to underwriters with respect to the financial statements and certain financial information contained or incorporated by reference in the Registration Statement, the Time of Sale Information and the Prospectus; provided, that the letter delivered on the Closing Date or the Additional Closing Date, as the case may be shall use a “cut-off” date no more than three business days prior to such Closing Date or such Additional Closing Date, as the case may be.

(f) Opinion and Negative Assurance Letter of Counsel for the Company. ▇▇▇▇▇▇ LLP, counsel for the Company, shall have furnished to the Representatives, at the request of the Company, their written opinion and negative assurance letter, dated the Closing Date or the Additional Closing Date, as the case may be, and addressed to the Underwriters, in form and substance stating in effect the matters set forth on Annex D hereto (with appropriate modifications reasonably acceptable to the Representatives for any opinion or negative assurance letter delivered on any Additional Closing Date).

(g) Opinion of Regulatory Counsel for the Company. ▇▇▇▇▇▇ LLP, regulatory counsel for the Company, shall have furnished to the Representatives, at the request of the Company, their written opinion, dated the Closing Date or the Additional Closing Date, as the case may be, and addressed to the Underwriters, in form and substance stating in effect the matters set forth on Annex E hereto (with appropriate modifications reasonably acceptable to the Representatives for any opinion delivered on any Additional Closing Date).

(h) Opinion of Intellectual Property Counsel for the Company. ▇▇▇▇▇▇▇▇▇▇ ▇▇▇▇▇▇▇▇ & ▇▇▇▇▇▇▇▇ LLP and ▇▇▇▇▇▇ & Bird LLP, intellectual property counsel for the Company, shall have furnished to the Representatives, at the request of the Company, their respective written opinions, dated the Closing Date or the Additional Closing Date, as the case may be, and addressed to the Underwriters, in form and substance stating in effect the matters set forth on Annexes F-1 and F-2 hereto, respectively, (with appropriate modifications reasonably acceptable to the Representatives for any opinion delivered on any Additional Closing Date).

(i) Opinion of General Counsel of the Company. The Company shall have furnished to the Representatives, at the request of the Company, the written opinion of is General Counsel, dated the Closing Date and addressed to the Underwriters, in form and substance stating in effect the matters set forth on Annex G hereto.

(j) Opinion of General Counsel and Senior Director of Intellectual Property of the Company. The Company shall have furnished to the Representatives, at the request of the Company, the written opinion signed by its General Counsel and Senior Director of Intellectual Property, dated the Closing Date and addressed to the Underwriters, in form and substance stating in effect the matters set forth on Annex H hereto.

(k) Opinion of Counsel for the Underwriters. The Representatives shall have received on and as of the Closing Date or the Additional Closing Date, as the case may be, an opinion of ▇▇▇▇▇▇ & ▇▇▇▇▇▇▇ LLP, counsel for the Underwriters, with respect to such matters as the Representatives may reasonably request, and such counsel shall have received such documents and information as they may reasonably request to enable them to pass upon such matters.

(l) No Legal Impediment to Issuance. No action shall have been taken and no statute, rule, regulation or order shall have been enacted, adopted or issued by any federal, state or foreign governmental or regulatory authority that would, as of the Closing Date or the Additional Closing Date, as the case may be, prevent the issuance or sale of the Shares; and no injunction or order of any federal, state or foreign court shall have been issued that would, as of the Closing Date or the Additional Closing Date, as the case may be, prevent the issuance or sale of the Shares.

(m) Good Standing. The Representatives shall have received on and as of the Closing Date or the Additional Closing Date, as the case may be, satisfactory evidence of the good standing of the Company and its subsidiary in their respective jurisdictions of organization and their good standing as foreign entities in such other jurisdictions as the Representatives may reasonably request, in each case in writing or any standard form of telecommunication from the appropriate governmental authorities of such jurisdictions and in each case only where the concept of good standing is recognized under the laws of the applicable jurisdiction.

(n) Exchange Listing. The Shares to be delivered on the Closing Date or Additional Closing Date, as the case may be, shall have been approved for listing on the Nasdaq Market, subject to official notice of issuance.

(o) Lock-up Agreements. The “lock-up” agreements, each substantially in the form of Exhibit A hereto, between you and certain stockholders, executive officers and directors of the Company relating to sales and certain other dispositions of shares of Stock or certain other securities, delivered to you on or before the date hereof, shall be full force and effect on the Closing Date or Additional Closing Date, as the case may be.

(p) Additional Documents. On or prior to the Closing Date or the Additional Closing Date, as the case may be, the Company shall have furnished to the Representatives such further certificates and documents as the Representatives may reasonably request.

All opinions, letters, certificates and evidence mentioned above or elsewhere in this Agreement shall be deemed to be in compliance with the provisions hereof only if they are in form and substance reasonably satisfactory to counsel for the Underwriters.

7. Indemnification and Contribution.

(a) Indemnification of the Underwriters. The Company agrees to indemnify and hold harmless each Underwriter, its affiliates, directors and officers and each person, if any, who controls such Underwriter within the meaning of Section 15 of the Securities Act or Section 20 of the Exchange Act, from and against any and all losses, claims, damages and liabilities (including, without limitation, legal fees and other expenses incurred in connection with any suit, action or proceeding or any claim asserted, as such fees and expenses are incurred), joint or several, that arise out of, or are based upon, (i) any untrue statement or alleged untrue statement of a material fact contained in the Registration Statement or caused by any omission or alleged omission to state therein a material fact required to be stated therein or necessary in order to make the statements therein, not misleading, (ii) any untrue statement or alleged untrue statement of a material fact included in any materials or information provided to investors by, or with the written approval of, the Company in connection with the marketing of the offering of the Shares, including any road show or investor presentations made to the investors by the Company (whether in person or electronically), or the omission or alleged omission therefrom of a material fact necessary in order to make the statements therein, when taken together with the Time of Sale Information, in the light of the circumstances under which they are made, not misleading or (iii) any untrue statement or alleged untrue statement of a material fact contained in the Prospectus (or any amendment or supplement thereto), any Issuer Free Writing Prospectus or any Time of Sale Information (including any Time of Sale Information that has subsequently been amended), or caused by any omission or alleged omission to state therein a material fact required to be stated therein or necessary in order to make the statements therein, in light of the circumstances under which they were made, not misleading, in each case except insofar as such losses, claims, damages or liabilities arise out of, or are based upon, any untrue statement or omission or alleged untrue statement or omission made in reliance upon and in conformity with any information relating to any Underwriter furnished to the Company in writing by such Underwriter through the Representatives expressly for use therein, it being understood and agreed that the only such information furnished by any Underwriter consists of the information described as such in subsection (b) below.

(b) Indemnification of the Company. Each Underwriter agrees, severally and not jointly, to indemnify and hold harmless the Company, its directors, its officers who signed the Registration Statement and each person, if any, who controls the Company within the meaning of Section 15 of the Securities Act or Section 20 of the Exchange Act to the same extent as the indemnity set forth in paragraph (a) above, but only with respect to any losses, claims, damages or liabilities that arise out of, or are based upon, any untrue statement or omission or alleged untrue statement or omission made in reliance upon and in conformity with any information relating to such Underwriter furnished to the Company in writing by such Underwriter through the Representatives expressly for

use in the Registration Statement, the Prospectus (or any amendment or supplement thereto), any Issuer Free Writing Prospectus or any Time of Sale Information, it being understood and agreed upon that the only such information furnished by any Underwriter consists of the following information in the Prospectus furnished on behalf of each Underwriter: the statements set forth in the first two sentences of the first paragraph under the title “Commissions and Expenses” and the statements in the paragraph immediately below the title “Stabilization” (other than the third sentence, the sixth sentence and the last two sentences of such paragraph), in each case under the caption “Underwriting” in the Prospectus.

(c) Notice and Procedures. If any suit, action, proceeding (including any governmental or regulatory investigation), claim or demand shall be brought or asserted against any person in respect of which indemnification may be sought pursuant to either paragraph (a) or (b) above, such person (the “Indemnified Person”) shall promptly notify the person against whom such indemnification may be sought (the “Indemnifying Person”) in writing; provided that the failure to notify the Indemnifying Person shall not relieve it from any liability that it may have under paragraph (a) or (b) above except to the extent that it has been materially prejudiced (through the forfeiture of substantive rights or defenses) by such failure; and provided, further, that the failure to notify the Indemnifying Person shall not relieve it from any liability that it may have to an Indemnified Person otherwise than under paragraph (a) or (b) above. If any such proceeding shall be brought or asserted against an Indemnified Person and it shall have notified the Indemnifying Person thereof, the Indemnifying Person shall retain counsel reasonably satisfactory to the Indemnified Person (who shall not, without the consent of the Indemnified Person, be counsel to the Indemnifying Person) to represent the Indemnified Person in such proceeding and shall pay the fees and expenses of such counsel related to such proceeding, as incurred. In any such proceeding, any Indemnified Person shall have the right to retain its own counsel, but the fees and expenses of such counsel shall be at the expense of such Indemnified Person unless (i) the Indemnifying Person and the Indemnified Person shall have mutually agreed to the contrary; (ii) the Indemnifying Person has failed within a reasonable time to retain counsel reasonably satisfactory to the Indemnified Person; (iii) the Indemnified Person shall have reasonably concluded that there may be legal defenses available to it that are different from or in addition to those available to the Indemnifying Person; or (iv) the named parties in any such proceeding (including any impleaded parties) include both the Indemnifying Person and the Indemnified Person and representation of both parties by the same counsel would be inappropriate due to actual or potential differing interest between them. It is understood and agreed that the Indemnifying Person shall not, in connection with any proceeding or related proceeding in the same jurisdiction, be liable for the fees and expenses of more than one separate firm (in addition to any local counsel) for all Indemnified Persons, and that all such fees and expenses shall be paid or reimbursed as they are incurred. Any such separate firm for any Underwriter, its affiliates, directors and officers and any control persons of such Underwriter shall be designated in writing by the Representatives and any such separate firm for the Company, its directors, its officers who signed the Registration Statement and any control persons of the Company shall be designated in writing by the Company. The Indemnifying Person shall not be liable for any settlement

of any proceeding effected without its written consent, but if settled with such consent or if there be a final judgment for the plaintiff for which the Indemnified Person is entitled to indemnification pursuant to this Section 7, the Indemnifying Person agrees to indemnify each Indemnified Person from and against any loss or liability by reason of such settlement or judgment. Notwithstanding the foregoing sentence, if at any time an Indemnified Person shall have requested that an Indemnifying Person reimburse the Indemnified Person for fees and expenses of counsel as contemplated by this paragraph, the Indemnifying Person shall be liable for any settlement of any proceeding effected without its written consent if (i) such settlement is entered into more than 30 days’ after receipt by the Indemnifying Person of such request, (ii) such Indemnified Person shall have given the Indemnifying Person at least 30 days prior notice of its intention to settle and (iii) the Indemnifying Person shall not have reimbursed the Indemnified Person in accordance with such request prior to the date of such settlement. No Indemnifying Person shall, without the written consent of the Indemnified Person, effect any settlement of any pending or threatened proceeding in respect of which any Indemnified Person is or could have been a party and indemnification could have been sought hereunder by such Indemnified Person, unless such settlement (x) includes an unconditional release of such Indemnified Person, in form and substance reasonably satisfactory to such Indemnified Person, from all liability on claims that are the subject matter of such proceeding and (y) does not include any statement as to or any admission of fault, culpability or a failure to act by or on behalf of any Indemnified Person.

(d) Contribution. If the indemnification provided for in paragraphs (a) and (b) above is unavailable to an Indemnified Person or insufficient in respect of any losses, claims, damages or liabilities referred to therein, then each Indemnifying Person under such paragraph, in lieu of indemnifying such Indemnified Person thereunder, shall contribute to the amount paid or payable by such Indemnified Person as a result of such losses, claims, damages or liabilities (i) in such proportion as is appropriate to reflect the relative benefits received by the Company, on the one hand, and the Underwriters, on the other, from the offering of the Shares or (ii) if the allocation provided by clause (i) is not permitted by applicable law, in such proportion as is appropriate to reflect not only the relative benefits referred to in clause (i) but also the relative fault of the Company, on the one hand, and the Underwriters, on the other, in connection with the statements or omissions that resulted in such losses, claims, damages or liabilities, as well as any other relevant equitable considerations. The relative benefits received by the Company, on the one hand, and the Underwriters, on the other, shall be deemed to be in the same respective proportions as the net proceeds (before deducting expenses) received by the Company from the sale of the Shares and the total underwriting discounts and commissions received by the Underwriters in connection therewith, in each case as set forth in the table on the cover of the Prospectus, bear to the aggregate offering price of the Shares. The relative fault of the Company, on the one hand, and the Underwriters, on the other, shall be determined by reference to, among other things, whether the untrue or alleged untrue statement of a material fact or the omission or alleged omission to state a material fact relates to information supplied by the Company or by the Underwriters and the parties’ relative intent, knowledge, access to information and opportunity to correct or prevent such statement or omission.

(e) Limitation on Liability. The Company and the Underwriters agree that it would not be just and equitable if contribution pursuant to this Section 7 were determined by pro rata allocation (even if the Underwriters were treated as one entity for such purpose) or by any other method of allocation that does not take account of the equitable considerations referred to in paragraph (d) above. The amount paid or payable by an Indemnified Person as a result of the losses, claims, damages and liabilities referred to in paragraph (d) above shall be deemed to include, subject to the limitations set forth above, any legal or other expenses incurred by such Indemnified Person in connection with any such action or claim. Notwithstanding the provisions of this Section 7, in no event shall an Underwriter be required to contribute any amount in excess of the amount by which the total underwriting discounts and commissions received by such Underwriter with respect to the offering of the Shares exceeds the amount of any damages that such Underwriter has otherwise been required to pay by reason of such untrue or alleged untrue statement or omission or alleged omission. No person guilty of fraudulent misrepresentation (within the meaning of Section 11(f) of the Securities Act) shall be entitled to contribution from any person who was not guilty of such fraudulent misrepresentation. The Underwriters’ obligations to contribute pursuant to this Section 7 are several in proportion to their respective purchase obligations hereunder and not joint.

(f) Non-Exclusive Remedies. The remedies provided for in this Section 7 are not exclusive and shall not limit any rights or remedies which may otherwise be available to any Indemnified Person at law or in equity.

8. Effectiveness of Agreement. This Agreement shall become effective upon the execution and delivery hereof by the parties hereto.

9. Termination. This Agreement may be terminated in the absolute discretion of the Representatives, by notice to the Company, if after the execution and delivery of this Agreement and prior to the Closing Date or, solely in the case of the Option Shares, prior to the Additional Closing Date (i) trading generally shall have been suspended or materially limited on or by any of the New York Stock Exchange, the American Stock Exchange, the Nasdaq Stock Market, the Chicago Board Options Exchange, the Chicago Mercantile Exchange or the Chicago Board of Trade; (ii) trading of any securities issued or guaranteed by the Company shall have been suspended on any exchange or in any over-the-counter market; (iii) a general moratorium on commercial banking activities shall have been declared by federal or New York State authorities; or (iv) there shall have occurred any outbreak or escalation of hostilities or any change in financial markets or any calamity or crisis, either within or outside the United States, that, in the judgment of the Representatives, is material and adverse and makes it impracticable or inadvisable to proceed with the offering, sale or delivery of the Shares on the Closing Date or the Additional Closing Date, as the case may be, on the terms and in the manner contemplated by this Agreement, the Time of Sale Information and the Prospectus.

10. Defaulting Underwriter. (a) If, on the Closing Date or the Additional Closing Date, as the case may be, any Underwriter defaults on its obligation to purchase the Shares that it has agreed to purchase hereunder on such date, the non-defaulting Underwriters may in their discretion arrange for the purchase of such Shares by other persons satisfactory to the Company on the terms contained in this Agreement. If, within 36 hours after any such default by any Underwriter, the non-defaulting Underwriters do not arrange for the purchase of such Shares, then the Company shall be entitled to a further period of 36 hours within which to procure other persons satisfactory to the non-defaulting Underwriters to purchase such Shares on such terms. If other persons become obligated or agree to purchase the Shares of a defaulting Underwriter, either the non-defaulting Underwriters or the Company may postpone the Closing Date or the Additional Closing Date, as the case may be, for up to five full business days in order to effect any changes that in the opinion of counsel for the Company or counsel for the Underwriters may be necessary in the Registration Statement and the Prospectus or in any other document or arrangement, and the Company agrees to promptly prepare any amendment or supplement to the Registration Statement and the Prospectus that effects any such changes. As used in this Agreement, the term “Underwriter” includes, for all purposes of this Agreement unless the context otherwise requires, any person not listed in Schedule 1 hereto that, pursuant to this Section 10, purchases Shares that a defaulting Underwriter agreed but failed to purchase.

(b) If, after giving effect to any arrangements for the purchase of the Shares of a defaulting Underwriter or Underwriters by the non-defaulting Underwriters and the Company as provided in paragraph (a) above, the aggregate number of Shares that remain unpurchased on the Closing Date or the Additional Closing Date, as the case may be does not exceed one-eleventh of the aggregate number of Shares to be purchased on such date, then the Company shall have the right to require each non-defaulting Underwriter to purchase the number of Shares that such Underwriter agreed to purchase hereunder on such date plus such Underwriter’s pro rata share (based on the number of Shares that such Underwriter agreed to purchase on such date) of the Shares of such defaulting Underwriter or Underwriters for which such arrangements have not been made.

(c) If, after giving effect to any arrangements for the purchase of the Shares of a defaulting Underwriter or Underwriters by the non-defaulting Underwriters and the Company as provided in paragraph (a) above, the aggregate number of Shares that remain unpurchased on the Closing Date or the Additional Closing Date, as the case may be, exceeds one-eleventh of the aggregate amount of Shares to be purchased on such date, or if the Company shall not exercise the right described in paragraph (b) above, then this Agreement or, with respect to any Additional Closing Date, the obligation of the Underwriters to purchase Shares on the Additional Closing Date, as the case may be, shall terminate without liability on the part of the non-defaulting Underwriters. Any termination of this Agreement pursuant to this Section 10 shall be without liability on the part of the Company, except that the Company will continue to be liable for the payment of expenses as set forth in Section 11 hereof and except that the provisions of Section 7 hereof shall not terminate and shall remain in effect.

(d) Nothing contained herein shall relieve a defaulting Underwriter of any liability it may have to the Company or any non-defaulting Underwriter for damages caused by its default.

11. Payment of Expenses. (a) Whether or not the transactions contemplated by this Agreement are consummated or this Agreement is terminated, the Company will pay or cause to be paid all costs and expenses incident to the performance of its obligations hereunder, including without limitation, (i) the costs incident to the authorization, issuance, sale, preparation and delivery of the Shares and any taxes payable in that connection; (ii) the costs incident to the preparation, printing and filing under the Securities Act of the Registration Statement, the Preliminary Prospectus, any Issuer Free Writing Prospectus, any Time of Sale Information and the Prospectus (including all exhibits, amendments and supplements thereto) and the distribution thereof; (iii) the costs of reproducing and distributing this Agreement; (iv) the fees and expenses of the Company’s counsel and independent accountants; (v) the fees and expenses incurred in connection with the registration or qualification and determination of eligibility for investment of the Shares under the laws of such jurisdictions as the Representatives may designate and the preparation, printing and distribution of a Blue Sky Memorandum (including the related fees and expenses of counsel for the Underwriters); (vi) the cost of preparing stock certificates; (vii) the costs and charges of any transfer agent and any registrar; (viii) all expenses and application fees incurred in connection with any filing with, and clearance of the offering by, the Financial Industry Regulatory Authority; (ix) all expenses incurred by the Company in connection with any “road show” presentation to potential investors; and (x) all expenses and application fees related to the listing of the Shares on the Nasdaq Global Select Market. It is understood, however, that except as expressly provided in Section 7 and this Section 11, the Underwriters will pay all of their costs and expenses, including fees and expenses of their counsel and transfer taxes payable on resale of any of the Shares by them.

(b) If (i) this Agreement is terminated prior to the Closing Date pursuant to Section 9(ii), (ii) the Company for any reason fails to tender the Underwritten Shares for delivery to the Underwriters, (iii) this Agreement is terminated as a result of the failure by the Company to satisfy the conditions in Section 6 (other than the condition set forth in Section 6(k)) or (iv) the Underwriters decline to purchase the Underwritten Shares for any reason permitted under this Agreement (other than pursuant to Sections 9(i), 9(iii), 9(iv) or 10(c) above), the Company agrees to reimburse the Underwriters for all out-of-pocket costs and expenses (including the fees and expenses of their counsel) reasonably incurred by the Underwriters in connection with this Agreement and the offering contemplated hereby.

12. Persons Entitled to Benefit of Agreement. This Agreement shall inure to the benefit of and be binding upon the parties hereto and their respective successors and the officers and directors and any controlling persons referred to in Section 7 hereof. Nothing in this Agreement is intended or shall be construed to give any other person any legal or equitable right, remedy or claim under or in respect of this Agreement or any

provision contained herein. No purchaser of Shares from any Underwriter shall be deemed to be a successor merely by reason of such purchase.

13. Survival. The respective indemnities, rights of contribution, representations, warranties and agreements of the Company and the Underwriters contained in this Agreement or made by or on behalf of the Company or the Underwriters pursuant to this Agreement or any certificate delivered pursuant hereto shall survive the delivery of and payment for the Shares and shall remain in full force and effect, regardless of any termination of this Agreement or any investigation made by or on behalf of the Company or the Underwriters.

14. Certain Defined Terms. For purposes of this Agreement, (a) except where otherwise expressly provided, the term “affiliate” has the meaning set forth in Rule 405 under the Securities Act; (b) the term “business day” means any day other than a day on which banks are permitted or required to be closed in New York City; and (c) the term “subsidiary” has the meaning set forth in Rule 405 under the Securities Act

15. Miscellaneous. (a) Authority of the Representatives. Any action by the Underwriters hereunder may be taken by the Representatives. on behalf of the Underwriters, and any such action taken by the Representatives shall be binding upon the Underwriters.

(b) Notices. All notices and other communications hereunder shall be in writing and shall be deemed to have been duly given if mailed or transmitted and confirmed by any standard form of telecommunication. Notices to the Underwriters shall be given to the Representatives c/▇ ▇▇▇▇▇▇▇▇▇ & Company, Inc., ▇▇▇ ▇▇▇▇▇▇▇ ▇▇▇▇▇▇, ▇▇▇ ▇▇▇▇, ▇▇▇ ▇▇▇▇ ▇▇▇▇▇, Facsimile: (▇▇▇) ▇▇▇-▇▇▇▇, Attention: General Counsel and c/o ▇.▇. ▇▇▇▇▇▇ Securities LLC, ▇▇▇ ▇▇▇▇▇▇▇ ▇▇▇▇▇▇, ▇▇▇ ▇▇▇▇, ▇▇▇ ▇▇▇▇ ▇▇▇▇▇ (fax: (▇▇▇) ▇▇▇-▇▇▇▇); Attention: Equity Syndicate Desk, with a copy to ▇▇▇▇▇▇ & ▇▇▇▇▇▇▇ LLP, ▇▇▇▇▇ ▇▇▇▇ ▇▇▇▇▇ ▇▇▇▇▇, ▇▇▇▇▇ ▇▇▇, ▇▇▇ ▇▇▇▇▇, ▇▇▇▇▇▇▇▇▇▇ ▇▇▇▇▇, (fax: (▇▇▇) ▇▇▇-▇▇▇▇) Attention: ▇▇▇▇▇▇▇ ▇. ▇▇▇▇▇▇, Esq. Notices to the Company shall be given to it at Seattle Genetics, Inc., ▇▇▇▇▇ ▇▇^▇▇ ▇▇▇▇▇ ▇▇, ▇▇▇▇▇▇▇, ▇▇▇▇▇▇▇▇▇▇ ▇▇▇▇▇ (fax: (▇▇▇) ▇▇▇-▇▇▇▇) Attention: ▇▇▇▇ ▇. ▇▇▇▇▇▇▇ Ph.D., Chief Executive Officer, with a copy to ▇▇▇▇▇▇ LLP, ▇▇▇ ▇▇▇▇▇▇ ▇▇▇▇▇▇, ▇▇▇▇▇ ▇▇▇, ▇▇▇▇▇▇▇, ▇▇▇▇▇▇▇▇▇▇ ▇▇▇▇▇ (fax: (▇▇▇) ▇▇▇-▇▇▇▇) Attention: ▇▇▇▇▇ ▇. ▇▇▇▇▇▇▇▇, Esq.

(c) Governing Law. This Agreement shall be governed by and construed in accordance with the laws of the State of New York applicable to agreements made and to be performed in such state.

(d) Counterparts. This Agreement may be signed in counterparts (which may include counterparts delivered by any standard form of telecommunication), each of which shall be an original and all of which together shall constitute one and the same instrument.

(e) Amendments or Waivers. No amendment or waiver of any provision of this Agreement, nor any consent or approval to any departure therefrom, shall in any event be effective unless the same shall be in writing and signed by the parties hereto.

(f) Headings. The headings herein are included for convenience of reference only and are not intended to be part of, or to affect the meaning or interpretation of, this Agreement.

[Signature Page Follows]

If the foregoing is in accordance with your understanding of our agreement, kindly sign and return to the Company the enclosed copies hereof, whereupon this instrument, along with all counterparts hereof, shall become a binding agreement in accordance with its terms.


Very truly yours,

SEATTLE GENETICS, INC.

By:		/s/ ▇▇▇▇ ▇. ▇▇▇▇▇▇▇

Name:		▇▇▇▇ ▇. ▇▇▇▇▇▇▇

Title:		President and CEO

The foregoing Underwriting Agreement is hereby confirmed and accepted by the Representative in New York, New York as of the date first above written.


▇▇▇▇▇▇▇▇▇ & COMPANY, INC.
▇.▇. ▇▇▇▇▇▇ SECURITIES LLC
Acting as Representatives of the several Underwriters named in the attached Schedule 1.

By:		▇▇▇▇▇▇▇▇▇ & COMPANY, INC.

By:		/s/ ▇▇▇▇ ▇▇▇▇▇
Name:		▇▇▇▇ ▇▇▇▇▇
Title:		Managing Director

By:		▇.▇. ▇▇▇▇▇▇ SECURITIES LLC

By:		/s/ ▇▇▇▇▇ ▇▇▇▇▇▇▇▇▇
Name:		▇▇▇▇▇ ▇▇▇▇▇▇▇▇▇
Title:		Executive Director

Schedule 1


Underwriter	Number of Shares

▇▇▇▇▇▇▇▇▇ & Company, Inc.		3,100,000
▇.▇. ▇▇▇▇▇▇ Securities LLC		3,100,000
Leerink ▇▇▇▇▇ LLC		1,200,000
RBC Capital Markets, LLC		1,000,000
▇▇▇▇▇▇▇ & Company, LLC		500,000
▇▇▇▇▇▇▇ ▇▇▇▇▇ & Company, LLC		500,000
▇▇▇▇▇▇▇▇▇▇▇ & Co. Inc.		300,000
ThinkEquity LLC		300,000


Total		10,000,000

Sch 1-1

Annex A

Issuer Free Writing Prospectus

None

Annex A-1

Annex B

Pricing Information

1. Price per share to the public: $15.50

2. Number of Underwritten Shares being sold: 10,000,000

3. Number of Option Shares: 1,500,000

4. Net proceeds to the Company: $146.1 million

5. Number of shares sold to ▇▇▇▇▇ entities: 1,800,000

Annex B-1

Annex C

Seattle Genetics, Inc.

Pricing Term Sheet

10,000,000 Shares


Issuer:		Seattle Genetics, Inc.
Symbol:		SGEN
Shares offered:		10,000,000 shares
Over-allotment option:		1,500,000 shares
Price per share to the public:		$15.50
Gross proceeds to the Company:		$155,000,000
Shares sold to ▇▇▇▇▇ entities:		1,800,000 shares
Pricing date:		February 2, 2011
Closing date:		On or about February 7, 2011
CUSIP:		▇▇▇▇▇▇▇▇▇

Underwriters:		▇▇▇▇▇▇▇▇▇ & Company, Inc. and ▇.▇. ▇▇▇▇▇▇ Securities LLC are acting as joint book-running managers for the offering, Leerink ▇▇▇▇▇ LLC and RBC Capital Markets, LLC are acting as co-lead managers for the offering and ▇▇▇▇▇▇▇ & Company, LLC, ▇▇▇▇▇▇▇ ▇▇▇▇▇ & Company, LLC, ▇▇▇▇▇▇▇▇▇▇▇ & Co. Inc. and ThinkEquity LLC are acting as co-managers for the offering.

A registration statement relating to the shares of common stock being issued in the offering has been filed and is effective. A final prospectus supplement relating to the offering will be filed with the SEC. Copies of the final prospectus supplement and related prospectuses, when available, may be obtained from Equity Syndicate Prospectus Department, ▇▇▇▇▇▇▇▇▇ & Company, Inc., ▇▇▇ ▇▇▇▇▇▇▇ ▇▇▇▇▇▇, ▇▇▇▇ ▇▇▇▇▇, ▇▇▇ ▇▇▇▇, ▇▇, ▇▇▇▇▇, at 877-547-6340, and at ▇▇▇▇▇▇▇▇▇▇_▇▇▇▇▇▇▇▇▇▇@▇▇▇▇▇▇▇▇▇.▇▇▇ or from ▇.▇. ▇▇▇▇▇▇ Securities LLC, c/o Broadridge Financial Solutions, ▇▇▇▇ ▇▇▇▇ ▇▇▇▇▇▇ ▇▇▇▇▇▇, ▇▇▇▇▇▇▇▇, ▇▇▇ ▇▇▇▇ ▇▇▇▇▇ or by calling ▇-▇▇▇-▇▇▇-▇▇▇▇. This term sheet shall not constitute an offer to sell or the solicitation of an offer to buy, nor shall there be any sale of, these securities in any state or other jurisdiction in which such offer, solicitation or sale would be unlawful prior to the registration or qualification under the securities laws of any such state or jurisdiction.

Annex C-1

Exhibit A

[Form of Lock-Up Agreement]

January 31, 2011

▇▇▇▇▇▇▇▇▇ & COMPANY, INC.

▇.▇. ▇▇▇▇▇▇ SECURITIES LLC

As Representatives of

the several Underwriters listed in

Schedule 1 to the Underwriting

Agreement referred to below

c/▇ ▇▇▇▇▇▇▇▇▇ & COMPANY, INC.

▇▇▇ ▇▇▇▇▇▇▇ ▇▇▇▇▇▇

▇▇▇ ▇▇▇▇, ▇▇▇ ▇▇▇▇ ▇▇▇▇▇

c/o ▇.▇. ▇▇▇▇▇▇ Securities LLC

▇▇▇ ▇▇▇▇▇▇▇ ▇▇▇▇▇▇

▇▇▇ ▇▇▇▇, ▇▇▇ ▇▇▇▇ ▇▇▇▇▇

Re:

Seattle Genetics, Inc. – Public Offering

Ladies and Gentlemen:

The undersigned understands that ▇▇▇▇▇▇▇▇▇ & Company, Inc. and ▇.▇. ▇▇▇▇▇▇ Securities LLC (together, the “Representatives”), propose to enter into an Underwriting Agreement (the “Underwriting Agreement”) with Seattle Genetics, Inc., a Delaware corporation (the “Company”), providing for the public offering (the “Public Offering”) by the several Underwriters named in Schedule 1 to the Underwriting Agreement (the “Underwriters”), of common stock, par value $0.001, of the Company (the “Securities”). Capitalized terms used herein and not otherwise defined shall have the meanings set forth in the Underwriting Agreement.

In consideration of the Underwriters’ agreement to purchase and make the Public Offering of the Securities, and for other good and valuable consideration receipt of which is hereby acknowledged, the undersigned hereby agrees that, without the prior written consent of the Representatives, on behalf of the Underwriters, the undersigned will not, during the period ending 45 days after the date of the prospectus relating to the Public Offering (the “Prospectus”), (1) offer, pledge, announce the intention to sell, 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 Common Stock, $0.001 per share par value, of the Company (the “Common Stock”) or any securities convertible into or exercisable or exchangeable for Common Stock (including without limitation, Common

Ex A-1

Stock which may be deemed to be beneficially owned by the undersigned in accordance with the rules and regulations of the Securities and Exchange Commission and securities which may be issued upon exercise of a stock option or warrant) or (2) enter into any swap or other agreement that transfers, in whole or in part, any of the economic consequences of ownership of the Common Stock, whether any such transaction described in clause (1) or (2) above is to be settled by delivery of Common Stock or such other securities, in cash or otherwise. In addition, the undersigned agrees that, without the prior written consent of the Representatives, on behalf of the Underwriters, it will not, during the period ending 45 days after the date of the Prospectus, make any demand for or exercise any right with respect to, the registration of any shares of Common Stock or any security convertible into or exercisable or exchangeable for Common Stock. Notwithstanding the foregoing, the undersigned may sell or otherwise transfer shares of Common Stock (i) as a bona fide gift or gifts or pledge, (ii) either during the undersigned’s lifetime or on death by will or intestacy to the undersigned’s immediate family or to a trust, the beneficiaries of which are the undersigned and a member or members of the undersigned’s immediate family, (iii) to an affiliate (as that term is defined in Rule 405 under the Securities Act of 1933, as amended) of the undersigned or if the undersigned is a partnership, limited liability company, trust, corporation or similar entity, as a transfer or distribution to its partners, members or stockholders or (iv) to the Company in connection with the “net” exercise of outstanding warrants to purchase Common Stock in accordance with their respective terms; provided that, in the case of clauses, (i) - (iii) that the recipient of such gift, pledge, transfer or distribution thereof agrees to be bound by the restrictions set forth herein; and provided that, in the case of clauses (i) - (iii), (a) such sales are not required to be reported in any public report or filing with the Securities and Exchange Commission (excluding a Form 3, 5 or Schedule 13G or 13D (or amendments thereof) under the Securities Exchange Act of 1934 (the “Exchange Act”)) during the 45-day restricted period and (b) the undersigned does not otherwise voluntarily effect any public filing or report regarding such sales; provided further that any Common Stock acquired upon the net exercise of warrants described in clause (iv) above (after giving effect to the settlement of such net exercise) shall be subject to the restrictions imposed by this Letter Agreement. For the purposes of this paragraph, “immediate family” shall mean spouse, domestic partner, lineal descendant (including adopted children), father, mother, brother or sister of the transferor. [add to ▇▇▇▇▇ ▇▇▇▇▇ lockup: Notwithstanding the foregoing, the foregoing restrictions shall not apply to any transactions with the Company or in which the undersigned exercises investment discretion as a fiduciary for any other legal person.] In addition, notwithstanding the lock-up restrictions described herein, the undersigned may at any time after the date hereof (x) exercise any stock options granted by the Company, provided that any Common Stock acquired upon any such exercise shall be subject to the restrictions imposed by this Letter Agreement and (y) establish any new 10b5-1 Plan, provided that no sales of Common Stock shall be made pursuant to such new 10b5-1 Plan prior to the expiration of the 45-day restricted period; provided further, that the Company is not required to report the establishment of such new 10b5-1 Plan in any public report or filing with the Securities and Exchange Commission under the Exchange Act during the 45-day restricted period and does not otherwise voluntarily effect any such public filing or report regarding such new 10b5-1 Plan.

If (1) during the last 17 days of the 45-day restricted period, the Company issues an earnings release or material news or a material event relating to the Company occurs; or (2) prior to the expiration of the 45-day restricted period, the Company announces that it will release

Ex A-2

earnings results during the 16-day period beginning on the last day of the 45-day period, the restrictions imposed by this Letter Agreement shall continue to apply until the expiration of the 18-day period beginning on the issuance of the earnings release or the occurrence of the material news or material event; provided that, such extension will not apply if (a) shares of Common Stock are “actively traded securities” (as defined in Regulation M of the Exchange Act), (b) the Company meets the applicable requirements of paragraph (a)(1) of Rule 139 under the Securities Act of 1933, as amended, (the “Securities Act”), in the manner contemplated by NASD Conduct Rule 2711(f)(4), and (c) the provisions of NASD Conduct Rule 2711(f)(4) do not restrict the publishing or distribution of any research reports relating to the Company by any of the Underwriters during the 15 days before or after the last day of the 45-day period (before giving effect to such extension).

In furtherance of the foregoing, the Company, and any duly appointed transfer agent for the registration or transfer of the securities described herein, are hereby authorized to decline to make any transfer of securities if such transfer would constitute a violation or breach of this Letter Agreement.

The undersigned hereby represents and warrants that the undersigned has full power and authority to enter into this Letter Agreement. All authority herein conferred or agreed to be conferred and any obligations of the undersigned shall be binding upon the successors, assigns, heirs or personal representatives of the undersigned.

The undersigned understands that, if the Company notifies the Representatives that it does not intend to proceed with the Public Offering, if the Underwriting Agreement does not become effective prior to February 28, 2011, or if the Underwriting Agreement (other than the provisions thereof which survive termination) shall terminate or be terminated prior to payment for and delivery of the Common Stock to be sold thereunder, the undersigned shall be released from all obligations under this Letter Agreement. The undersigned understands that the Company and the Underwriters are entering into the Underwriting Agreement and proceeding with the Public Offering in reliance upon this Letter Agreement.

[signature page follows]

Ex A-3

This Letter Agreement shall be governed by and construed in accordance with the laws of the State of New York, without regard to the conflict of laws principles thereof.


Very truly yours,

By:
		Name:
		Title:

Ex A-4

10,000,000 Shares SEATTLE GENETICS, INC. Common Stock ($0.001 par value per Share) UNDERWRITING AGREEMENT February 2, 2011

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