[Underwriting Agreement] 29,669,154 Shares Warrants to purchase 14,834,577 Shares XOMA Corporation Common Stock ($0.0075 Par Value) EQUITY UNDERWRITING AGREEMENT

Exhibit 1.1

[Underwriting Agreement]

29,669,154 Shares

Warrants to purchase 14,834,577 Shares

XOMA Corporation

Common Stock

($0.0075 Par Value)

March 6, 2012

RBC CAPITAL MARKETS, LLC

COWEN AND COMPANY, LLC

As the Representatives of the

several underwriters named in Schedule I hereto

c/o RBC Capital Markets, LLC

Three World Financial Center

200 Vesey Street

New York, NY 10281-8098

Ladies and Gentlemen:

XOMA Corporation, a Delaware corporation (the “Issuer”), proposes to sell to the several underwriters (the “Underwriters”) named in Schedule I hereto for whom you are acting as representatives (the “Representatives”) (i) an aggregate of 29,669,154 shares (the “Shares”) of the Issuer's Common Stock, $0.0075 par value, and (ii) warrants to purchase an aggregate of 14,834,577 shares of the Issuer’s Common Stock (the “Warrants” and together with the Shares, the “Securities”) in the form attached hereto as Exhibit A.  The shares of Common Stock underlying the Warrants are hereinafter referred to as the “Warrant Shares.”  The respective amounts of the Shares and Warrants to be so purchased by the several Underwriters are set forth opposite their names in Schedule I hereto.  The Securities will be sold to the Underwriters in a combination consisting of (i) one share of Common Stock and (ii) a Warrant to purchase 0.5 of a share of Common Stock.

As the Representatives, you have advised the Issuer (a) that you are authorized to enter into this Agreement on behalf of the several Underwriters, and (b) that the several Underwriters are willing, acting severally and not jointly, to purchase the numbers of Securities set forth opposite their respective names in Schedule I.

In consideration of the mutual agreements contained herein and of the interests of the parties in the transactions contemplated hereby, the parties hereto agree as follows:

1.           Representations and Warranties of the Issuer.

The Issuer represents and warrants to each of the Underwriters as follows:

(a)           The Issuer has prepared and filed in conformity with the requirements of the Securities Act of 1933, as amended (the “Securities Act”), and published rules and regulations thereunder (the “Rules and Regulations”) adopted by the Securities and Exchange Commission (the “Commission”) a “shelf” Registration Statement (as hereinafter defined) on Form S-3 (File No. 333-172197), including a base prospectus relating to the Securities (the “Base Prospectus”), and such amendments and supplements thereto as may have been required to the date of this Agreement.  The term “Registration Statement” as used in this Agreement means the registration statement described in the foregoing sentence (including all exhibits, financial schedules and all documents and information deemed to be a part of such registration statement pursuant to Rules 430A, 430B and 430C of the Rules and Regulations), as amended and/or supplemented to the date of this Agreement, including the Base Prospectus.  As used in this Agreement, “Effective Time” means the date and the time as of which such registration statement, or the most recent post-effective amendment thereto, if any, was declared effective by the Commission and “Effective Date” means the date of the Effective Time.  The Registration Statement is effective under the Securities Act and no stop order preventing or suspending the effectiveness of the Registration Statement or suspending or preventing the use of the Prospectus (as defined below) has been issued by the Commission and no proceedings for that purpose have been instituted or, to the knowledge of the Issuer, are threatened by the Commission. The Issuer, if required by the Rules and Regulations, will file the Prospectus with the Commission pursuant to Rule 424(b) of the Rules and Regulations.  The term “Prospectus” as used in this Agreement means the prospectus, in the form in which it is to be filed with the Commission pursuant to Rule 424(b) of the Rules and Regulations, or, if the prospectus is not to be filed with the Commission pursuant to Rule 424(b), the prospectus in the form included as part of the Registration Statement as of the Effective Date, except that if any revised prospectus or prospectus supplement shall be provided to the Underwriters by the Issuer for use in connection with the offering and sale of the Securities which differs from the Prospectus (whether or not such revised prospectus or prospectus supplement is required to be filed by the Issuer pursuant to Rule 424(b) of the Rules and Regulations), the term “Prospectus” shall refer to such revised prospectus or prospectus supplement, as the case may be, from and after the time it is first provided to the Underwriters for such use. Any preliminary prospectus or prospectus subject to completion included in the Registration Statement or filed with the Commission pursuant to Rule 424 of the Rules and Regulations is hereafter called a “Preliminary Prospectus.” Any reference herein 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 which were filed under the Securities Exchange Act of 1934, as amended (the “Exchange Act”), on or before the last to occur of the Effective Date, the date of the Preliminary Prospectus, if any, or the date of the Prospectus, and any reference herein to the terms “amend,” “amendment,” or “supplement” with respect to the Registration Statement, any Preliminary Prospectus or the Prospectus shall be deemed to refer to and include (i) the filing of any document under the

Exchange Act after the Effective Date, the date of such Preliminary Prospectus or the date of the Prospectus, as the case may be, which is incorporated by reference therein, and (ii) any such document so filed. If the Issuer has filed an abbreviated registration statement to register additional securities pursuant to Rule 462(b) under the Rules and Regulations (the “462(b) Registration Statement”), then any reference herein to the Registration Statement shall also be deemed to include such 462(b) Registration Statement.

                      (b)           As of the Applicable Time (as defined below) and as of the Closing Date, neither (i) any General Use Free Writing Prospectus (as defined below) issued at or prior to the Applicable Time, and the Pricing Prospectus (as defined below) and the information included on Schedule III hereto, all considered together (collectively, the “Disclosure Package”), (ii) any individual Limited Use Free Writing Prospectus (as defined below) nor (iii) the bona fide electronic road show (as defined in Rule 433(h)(5) of the Rules and Regulations), if any, that has been made available without restriction to any person, when considered together with the Disclosure Package, included or as of the Closing Date will include, any untrue statement of a material fact or omitted or as of the Closing Date will 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, however, that the Issuer makes no representations or warranties as to information contained in or omitted from any Issuer Free Writing Prospectus, in reliance upon and in conformity with written information furnished to the Issuer by any Underwriter through the Representatives expressly for use therein, such information being listed in Section 13 below.  As used in this paragraph (b) and elsewhere in this Agreement:

“Applicable Time” means 8:00 a.m., New York time, on the date of this Agreement.

“General Use Free Writing Prospectus” means any Issuer Free Writing Prospectus that is identified on Schedule II to this Agreement.

“Issuer Free Writing Prospectus” means any “issuer free writing prospectus,” as defined in Rule 433 of the Rules and Regulations relating to the Securities in the form filed or required to be filed with the Commission or, if not required to be filed, in the form retained in the Issuer’s records pursuant to Rule 433(g) of the Rules and Regulations.

“Limited Use Free Writing Prospectuses” means any Issuer Free Writing Prospectus that is not a General Use Free Writing Prospectus.

“Pricing Prospectus” means the Preliminary Prospectus, if any, and the Base Prospectus, each as amended and supplemented immediately prior to the Applicable Time, including any document incorporated by reference therein and any prospectus supplement deemed to be a part thereof.

                      (c)           No order preventing or suspending the use of any Preliminary Prospectus, any Issuer Free Writing Prospectus or the Prospectus relating to the offering of the Securities has been issued by the Commission, and no proceeding for that purpose or pursuant to Section 8A of the Securities Act has been instituted or, to the knowledge of the Issuer, threatened by the Commission, and each Preliminary Prospectus (if any), at the time of filing thereof, conformed in all material respects to the requirements of the Securities Act and the Rules and Regulations, and did not contain an 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; provided, however, that the Issuer makes no representations or warranties as to information contained in or omitted from any Preliminary Prospectus, in reliance upon and in conformity with written information furnished to the Issuer by any Underwriter through the Representatives expressly for use therein, such information being listed in Section 13 below.

                      (d)           At the time the Registration Statement became effective, at the date of this Agreement and at the Closing Date, the Registration Statement conformed and will conform in all material respects to the requirements of the Securities Act and the Rules and Regulations and did not and will not contain any untrue statement of a material fact or omit to state any material fact required to be stated therein or necessary to make the statements therein not misleading; the Prospectus, at the time the Prospectus was issued and at the Closing Date, conformed and will conform in all material respects to the requirements of the Securities Act and the Rules and Regulations and did not and will not contain an untrue statement of a material fact or omit to state a material fact necessary in order to make the statements therein, in light of the circumstances under which they were made, not misleading; provided, however, that the foregoing representations and warranties in this paragraph (d) shall not apply to information contained in or omitted from the Registration Statement or the Prospectus in reliance upon and in conformity with written information furnished to the Issuer by any Underwriter through the Representatives expressly for use therein, such information being listed in Section 13 below.  At the time the Registration Statement was filed with and declared effective by the Commission, the Issuer was eligible to register the Securities on Form S-3 promulgated under the Securities Act, and as of the date hereof, remains eligible to use the Registration Statement pursuant to General Instruction I.B.1 of Form S-3.

                      (e)           Each Issuer Free Writing Prospectus, if any, as of its issue date and at all subsequent times through the completion of the public offer and sale of the Securities or until any earlier date that the Issuer notified or notifies the Representatives, did not, does not and will not include any information that conflicted, conflicts or will conflict with the information contained in the Registration Statement, the Pricing Prospectus, if any, or the Prospectus, including any document incorporated by reference therein and any prospectus supplement deemed to be a part thereof that has not been superseded or modified, or includes an untrue statement of a material fact or omitted or would 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. The foregoing sentence does not apply to statements in or omissions from any Issuer Free Writing Prospectus in reliance upon and in conformity with written information furnished to the Issuer by any Underwriter through the Representatives expressly for use therein, such information being listed in Section 13 below.

                      (f)           The documents incorporated by reference in the Prospectus, 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 the rules and regulations of the Commission thereunder and none of such documents contained any untrue statement of a material fact or omitted to state any material fact required to be stated therein or necessary to make the statements therein, in light of the circumstances under which they were made, not misleading; and any further documents so filed and incorporated by reference in the Prospectus, 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 the rules and regulations of the Commission thereunder and will not contain any untrue statement of a material fact or omit to state any material fact required to be stated therein or necessary to make the statements therein, in light of the circumstances under which they were made, not misleading.

                      (g)           The Issuer has not, directly or indirectly, distributed and will not distribute any offering material in connection with the offering of the Securities other than any Preliminary Prospectus, the Prospectus and other materials, if any, permitted under the Securities Act. The Issuer is not an “ineligible issuer” in connection with the offering pursuant to Rules 164, 405 and 433 under the Securities Act. The Issuer will file with the Commission all Issuer Free Writing Prospectuses (other than a “road show,” as defined in Rule 433(h)(4) of the Rules and Regulations), if any, in the time and manner required under Rules 163(b)(2) and 433(d) of the Rules and Regulations.

(h)           This Agreement has been duly authorized, executed and delivered by the Issuer; the Warrants, when executed and delivered pursuant to the terms of this Agreement, will be duly authorized, executed and delivered by the Issuer; and the Agreement constitutes, and the Warrants, when executed and delivered, will constitute, a valid, legal, and binding obligation of the Issuer, enforceable in accordance with its terms, except as rights to indemnity hereunder may be limited by federal or state securities laws and except as such enforceability may be limited by bankruptcy, insolvency, reorganization or similar laws affecting the rights of creditors generally, and subject to general principles of equity.  The Issuer has full power and authority to enter into this Agreement and to authorize, issue and sell the Securities as contemplated by this Agreement.

(i)           The Issuer has been duly organized and is validly existing as a corporation in good standing under the laws of the State of Delaware, with corporate power and authority to own or lease its properties and conduct its business as described in the Prospectus and the Disclosure Package.  Each of the subsidiaries of the Issuer, as listed in Schedule IV hereto (collectively, the “Subsidiaries”), has been duly incorporated or organized and is validly existing as a corporation or other legal entity in good standing under the laws of the jurisdiction of its incorporation or organization, with all power and authority to own or lease its properties and conduct its business as described in the Prospectus and the Disclosure Package.  The Subsidiaries are the only subsidiaries, direct or indirect, of the Issuer.  The Issuer and each of the Subsidiaries are duly qualified to transact business and are in good standing in all jurisdictions in which the conduct of their business requires such qualification; except where the failure to be so qualified or to be in good standing would not have a material adverse effect on the condition (financial or otherwise), properties, assets, liabilities, rights, operations, earnings, business, management or prospects of the Issuer and its Subsidiaries taken as a whole, whether or not arising from transactions in the ordinary course of business (a “Material Adverse Effect”).  The outstanding shares of capital stock or equity interests of each of the Subsidiaries have been duly authorized and validly issued, are fully paid and non-assessable and are wholly owned by the Issuer or another Subsidiary free and clear of all liens, encumbrances and equities and claims; and no options, warrants or other rights to purchase, agreements or other obligations to issue or other rights to convert any obligations into shares of capital stock or ownership interests in the Subsidiaries are outstanding.

(j)           The outstanding shares of Common Stock of the Issuer have been duly authorized and validly issued and are fully paid and non-assessable; the Shares to be issued and sold by the Issuer have been duly authorized and when issued and paid for as contemplated herein will be validly issued, fully paid and non-assessable; and no preemptive rights of shareholders exist with respect to any of the Shares or the issue and sale thereof.  The Warrant Shares have been duly authorized and reserved for issuance pursuant to the terms of the Warrants, and when issued by the Issuer upon valid exercise of the Warrants and payment of the exercise price, will be duly and validly issued, fully paid and nonassessable, free and clear of all liens and free of any preemptive or similar rights and will conform to the description thereof contained in the Registration Statement, Disclosure Package and the Prospectus.  Neither the filing of the Registration Statement nor the offering or sale of the Securities as contemplated by this Agreement gives rise to any rights, other than those which have been waived or satisfied, for or relating to the registration of any shares of Common Stock.

(k)           The information set forth under the caption “Capitalization” in the Prospectus and the Disclosure Package is true and correct in all material respects.  All of the Securities conform in all material respects to the description thereof contained in the Prospectus and the Disclosure Package.  The form of certificates for the Securities conforms to the corporate law of the jurisdiction of the Issuer's incorporation.  No holders of securities of the Issuer have rights to the registration of such securities under the Registration Statement that have not been waived.

(l)           The consolidated financial statements of the Issuer and the Subsidiaries, together with related notes and schedules as set forth in, or incorporated by reference into, the Registration Statement, the Prospectus and the Disclosure Package, present fairly in all material respects the financial position and the results of operations and cash flows of the Issuer and the consolidated Subsidiaries, at the indicated dates and for the indicated periods.  Such financial statements and related schedules have been prepared in accordance with U.S. generally accepted principles of accounting, consistently applied throughout the periods involved, except as disclosed therein, and all adjustments necessary for a fair presentation of results for such periods have been made. The summary financial and statistical data included in, or incorporated by reference into, the Registration Statement, the Prospectus and the Disclosure Package presents fairly in all material respects the information shown therein and such data has been compiled on a basis consistent with the financial statements presented therein and the books and records of the Issuer.  The statistical, industry−related and market−related data included in, or incorporated by reference into, the Registration Statement, the Prospectus and the Disclosure Package are based on or derived from sources which the Issuer reasonably and in good faith believes are reliable and accurate.

(m)           The Issuer maintains a system of internal accounting controls sufficient to provide reasonable assurances that (i) transactions are executed in accordance with management's general or specific authorization; (ii) transactions are recorded as necessary to permit preparation of financial statements in conformity with generally accepted accounting principles and to maintain accountability for assets; (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 existing assets at reasonable intervals and appropriate action is taken with respect to any differences.

(n)           Ernst & Young LLP, which has certified certain financial statements of the Issuer and delivered its opinion with respect to the audited financial statements and schedules included in, or incorporated by reference into, the Registration Statement and the Prospectus, is an independent registered public accounting firm with respect to the Issuer within the meaning of the Securities Act and the Rules and Regulations.

(o)           There is no action, suit, claim or proceeding pending or, to the knowledge of the Issuer, threatened against the Issuer or any of the Subsidiaries before any court or administrative agency or otherwise (1) that is required to be described in the Registration Statement, the Prospectus or the Disclosure Package and is not so described or (2) which, if determined adversely to the Issuer or any of its Subsidiaries, could reasonably be expected to have a Material Adverse Effect or prevent the consummation of the transactions contemplated hereby, except as set forth in the Registration Statement, the Prospectus and the Disclosure Package.

(p)           No labor problem or dispute with the employees of the Issuer or the Subsidiaries exists or, to the Issuer’s knowledge, is threatened or imminent that could reasonably be expected to have a Material Adverse Effect.

(q)           The Issuer and the Subsidiaries have good and marketable title to all of the properties and assets reflected in the financial statements (or as described in the Prospectus and the Disclosure Package) hereinabove described, subject to no lien, mortgage, pledge, charge or encumbrance of any kind except those reflected in such financial statements (or as described in the Prospectus and the Disclosure Package) or which are not material in amount.  The Issuer and the Subsidiaries occupy their material leased properties under valid and binding leases conforming in all material respects to the descriptions thereof set forth in the Prospectus and the Disclosure Package.

(r)           The Issuer and the Subsidiaries have filed all Federal, state, local and foreign tax returns which have been required to be filed and have paid all taxes indicated by said returns and all assessments received by them or any of them to the extent that such taxes have become due and are not being contested in good faith and for which an adequate reserve for accrual has been established in accordance with U.S. generally accepted accounting principles.  All tax liabilities have been adequately provided for in the financial statements of the Issuer, and the Issuer does not know of any actual or proposed additional material tax assessments.  There are no transfer taxes or other similar fees or charges under Federal law or the laws of any state, or any political subdivision thereof, required to be paid in connection with the execution and delivery of this Agreement or the issuance by the Issuer or sale by the Issuer of the Securities.

(s)           Since the respective dates as of which information is given in the Registration Statement and the Prospectus, as it may be amended or supplemented, there has not been any material adverse change which has had or is reasonably likely to have a Material Adverse Effect, and there has not been any material transaction entered into or any material transaction that is probable of being entered into by the Issuer or the Subsidiaries, other than transactions in the ordinary course of business and changes and transactions described in the Prospectus and the Disclosure Package.  The Issuer and the Subsidiaries have no material contingent obligations that are not disclosed in the Issuer's financial statements in, or incorporated by reference into, the Registration Statement and the Prospectus.

(t)           Neither the Issuer nor any of the Subsidiaries is or with the giving of notice or lapse of time or both, will be, in violation of or in default under its Certificate of Incorporation (“Charter”) or By-Laws (or other governing documents), or under any agreement, lease, contract, indenture or other instrument or obligation to which it is a party or by which it, or any of its properties, is bound and which default has had or is reasonably expected to have a Material Adverse Effect.  The execution and delivery of this Agreement and the consummation of the transactions herein contemplated and the fulfillment of the terms hereof will not conflict with or result in a breach of any of the terms or provisions of, or constitute a default under, any contract, indenture, mortgage, deed of trust or other agreement or instrument to which the Issuer or any of the Subsidiaries is a party, or of the Charter or By-Laws of the Issuer or any order, rule or regulation applicable to the Issuer or any of the Subsidiaries of any court or of any regulatory body or administrative agency or other governmental body having jurisdiction.

(u)           Each approval, consent, order, authorization, designation, declaration or filing by or with any regulatory, administrative or other governmental body necessary in connection with the execution and delivery by the Issuer of this Agreement and the consummation of the transactions herein contemplated (except such additional steps as may be required by the Commission, the Financial Industry Regulatory Authority, Inc. (“FINRA”) or such additional steps as may be necessary to qualify the Securities for public offering by the Underwriters under state securities or Blue Sky laws) has been obtained or made and is in full force and effect.

(v)           The Issuer and each of the Subsidiaries has all material licenses, certifications, permits, franchises, approvals, clearances and other regulatory authorizations (“Permits”) from governmental authorities as are necessary to conduct its businesses as currently conducted and to own, lease and operate its properties in the manner described in the Prospectus and the Disclosure Package.  There is no claim, proceeding or controversy, pending or, to the knowledge of the Issuer or any of the Subsidiaries, threatened, involving the status of or sanctions under any of the Permits which could reasonably be expected to have a Material Adverse Effect.  The Issuer and each of the Subsidiaries has fulfilled and performed all of its material obligations with respect to the Permits, and no event has occurred which allows, or after notice or lapse of time would allow, the revocation, termination, modification or other impairment of the rights of the Issuer or any of the Subsidiaries under such Permit which could reasonably be expected to have a Material Adverse Effect.

(w)           To the Issuer’s knowledge, there are no affiliations or associations between any member of FINRA and any of the Issuer’s officers, directors or 5% or greater security holders, except as set forth in the Registration Statement.

(x)           Neither the Issuer, nor to the Issuer's knowledge, any of its affiliates, has taken or may take, directly or indirectly, any action designed to cause or result in, or which has constituted or which might reasonably be expected to constitute, the stabilization or manipulation of the price of the shares of Common Stock to facilitate the sale or resale of the Securities.  The Issuer acknowledges that the Underwriters may engage in passive market making transactions in the Shares on The NASDAQ Global Market in accordance with Regulation M under Exchange Act.

(y)           Neither the Issuer nor any of the Subsidiaries is an “investment company” within the meaning of such term under the Investment Issuer Act of 1940, and the rules and regulations of the Commission thereunder (collectively, the “1940 Act”).

(z)           The Issuer and each of the Subsidiaries carry, or are covered by, insurance in such amounts and covering such risks as are prudent for the conduct of their respective businesses and the value of their respective properties and customary for companies engaged in similar industries.  All policies of insurance insuring the Issuer or any Subsidiary or any of their respective businesses, assets, employees, officers and directors are in full force and effect, and the Issuer and the Subsidiaries are in compliance with the terms of such policies in all material respects. There are no claims by the Issuer or any Subsidiary under any such policy or instrument as to which an insurance company is denying liability or defending under a reservation of rights clause.

(aa)           The Issuer is in compliance in all material respects with all presently applicable provisions of the Employee Retirement Income Security Act of 1974, as amended, including the regulations and published interpretations thereunder (“ERISA”); no “reportable event” (as defined in ERISA) has occurred with respect to any “pension plan” (as defined in ERISA) subject to Title IV of ERISA for which the Issuer would have any liability; the Issuer has not incurred and does not expect to incur liability under (i) Title IV of ERISA with respect to termination of, or withdrawal from, any “pension plan” or (ii) Sections 412 or 4971 of the Internal Revenue Code of 1986, as amended, including the regulations and published interpretations thereunder (the “Code”); and each “pension plan” for which the Issuer would have any liability that is intended to be qualified under Section 401(a) of the Code is so qualified in all material respects and, to the Issuer’s knowledge, nothing has occurred, whether by action or by failure to act, which would cause the loss of such qualification.

(bb)           The Issuer's change in jurisdiction of incorporation from Bermuda to Delaware (the “Domestication”) is effective.  The Domestication (i) was approved by the Board of Directors of the Issuer in accordance with applicable law and (ii) complied in all respects with all applicable laws of Bermuda and Delaware and the U.S. federal securities laws and there are no material liabilities of the Issuer's predecessor Bermuda entity that have not been discharged or otherwise accounted for in connection with such Domestication.  The Issuer has received all necessary consents, authorizations and approvals of third parties necessary to effect the Domestication, except for any such consents, authorizations or approvals the absence of which could not reasonably be expected to have a Material Adverse Effect.  The Domestication did not require the approval of the Issuer’s shareholders, and such shareholders do not have statutory dissenters’ rights of appraisal as a result of the Domestication.

(cc)           Other than as contemplated by this Agreement, the Issuer has not incurred any liability for any finder's or broker's fee, or agent's commission in connection with the execution and delivery of this Agreement or the consummation of the transactions contemplated hereby.

(dd)           Other than the Subsidiaries, the Issuer does not own, directly or indirectly, any shares of capital stock and does not have any other equity or ownership or proprietary interest in any corporation, partnership, association, trust, limited liability company, joint venture or other entity.

(ee)            There are no statutes, regulations, contracts or other documents (including, without limitation, any voting agreement) that are required to be described in the Registration Statement, the Prospectus or the Disclosure Package or to be filed as exhibits to the Registration Statement that are not described or filed as required.  Neither the Issuer nor any of the Subsidiaries has sent or received any notice indicating the termination of or intention to terminate any of the contracts or agreements referred to or described in the Registration Statement, Prospectus or the Disclosure Package, or filed as an exhibit to the Registration Statement, and no such termination has been threatened by the Issuer, any Subsidiary or any other party to any such contract or agreement.

(ff)           Neither the Issuer nor any Subsidiary is in violation of any statute, any rule, regulation, decision or order of any governmental agency or body or any court, domestic or foreign, relating to the use, disposal or release of hazardous chemicals, toxic substances or radioactive and biological materials or relating to the protection or restoration of the environment or human exposure to hazardous chemicals, toxic substances or radioactive and biological materials (collectively, “Environmental Laws”) except for any such violation which could not reasonably be expected to have a Material Adverse Effect.  To the knowledge of the Issuer, neither the Issuer nor the Subsidiaries own or operate any real property contaminated with any substance that is subject to any Environmental Laws, is liable for any off-site disposal or contamination pursuant to any Environmental Laws, or is subject to any claim relating to any Environmental Laws, which violation, contamination, liability or claim would individually or in the aggregate have a Material Adverse Effect; and the Issuer is not aware of any pending investigation which might lead to such a claim.

(gg)           No payments or inducements have been made or given, directly or indirectly, to any federal or local official or candidate for, any federal or state office in the United States or foreign offices by the Issuer or any Subsidiary, or, to the knowledge of the Issuer, by any of their officers, directors, employees or agents, by any other person in connection with any opportunity, contract, permit, certificate, consent, order, approval, waiver or other authorization relating to the business of the Issuer or any Subsidiary, except for such payments or inducements as were lawful under applicable laws, rules and regulations.  Neither the Issuer nor any Subsidiary, nor, to the knowledge of the Issuer, any director, officer, agent, employee or other person associated with or acting on behalf of the Issuer or any Subsidiary, (i) has 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 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, unlawful rebate, payoff, influence payment, kickback or other unlawful payment in connection with the business of the Issuer or any Subsidiary.

(hh)           The Issuer and each of the Subsidiaries owns, licenses, or otherwise has rights in all United States and foreign patents, trademarks, service marks, tradenames, copyrights, trade secrets and other proprietary rights currently necessary for the conduct of all material aspects of its respective business as currently carried on and as proposed to be carried on as described in the Prospectus and the Disclosure Package (collectively and together with any applications or registrations for the foregoing, the “Intellectual Property”). Except as specifically described in the Prospectus and the Disclosure Package, (i) no third parties have obtained rights to any such Intellectual Property from the Issuer, other than licenses granted in the ordinary course and those that would not have a Material Adverse Effect; (ii) to the Issuer's knowledge, there is no infringement or misappropriation by third parties of any such Intellectual Property which could reasonably be expected to have a Material Adverse Effect; (iii) there is no pending or, to the Issuer's knowledge, threatened action, suit, proceeding or claim by others challenging the Issuer's or any Subsidiary's rights in or to any such Intellectual Property, and the Issuer is unaware of any facts which would form a basis for any such claim, except for any such action, suit, proceeding or claim which could not reasonably be expected to have a Material Adverse Effect; (iv) there is no pending or, to the Issuer's knowledge, threatened action, suit, proceeding or claim by others challenging the validity, enforceability, or scope of any such Intellectual Property, and the Issuer is unaware of any facts which would form a basis for any such claim, except for any such action, suit, proceeding or claim which could not reasonably be expected to have a Material Adverse Effect; and (v) there is no pending or, to the Issuer's knowledge, threatened action, suit, proceeding or claim by others that the Issuer’s, or any of its Subsidiaries’, products, product candidates, or services as described in the Prospectus and the Disclosure Package infringes, misappropriates, or otherwise violates, or would infringe upon, misappropriate or otherwise violate, any patent, trademark, copyright, trade secret or other proprietary right of others, and the Issuer is unaware of any facts which would form a basis for any such claim, except for any such action, suit, proceeding or claim which could not reasonably be expected to have a Material Adverse Effect.  None of the technology employed by the Issuer has been obtained or, to the knowledge of any of the officers of the Issuer, is being used by the Issuer in violation of the rights of any person or third party.

(ii)           The conduct of business by the Issuer and each of the Subsidiaries complies, and at all times has complied, in all material respects with federal, state, local and foreign laws, statutes, ordinances, rules, regulations, decrees, orders, Permits and other similar items (“Laws”) applicable to its business, including, without limitation, (a) the U.S. Food, Drug and Cosmetic Act and similar federal, state, local and foreign Laws, (b) the Occupational Safety and Health Act, the Environmental Protection Act, the Toxic Substance Control Act and similar federal, state, local and foreign Laws applicable to hazardous or regulated substances and radioactive or biologic materials and (c) licensing and certification Laws covering any aspect of the business of the Issuer or any of the Subsidiaries.  Neither the Issuer nor any of the Subsidiaries has received any notification asserting, or has knowledge of, any present or past failure to comply with or violation of any such Laws.

(jj)           Except to the extent disclosed in the Prospectus and the Disclosure Package (or any amendment or supplement thereto), the pending and completed clinical, pre-clinical and other studies, tests and research conducted by the Issuer or any of its Subsidiaries that are disclosed in the Prospectus and the General Disclosure Package, if still pending, are and, if completed, were conducted in compliance, in all material respects, with, to the extent applicable, the U.S. Food, Drug and Cosmetic Act and the regulations and guidelines promulgated thereunder, including Title 21 of the Code of Federal Regulations, and other U.S. Food and Drug Administration (“FDA”) regulations and guidelines governing clinical studies, current good laboratory practices and good clinical practices, the International Conference on Harmonisation Guidelines and applicable institutional review board and independent ethics committee requirements.

(kk)           The information contained in the Registration Statement and the Prospectus regarding the Issuer’s expectations, plans and intentions, and any other information that constitutes “forward-looking” information within the meaning of the Securities Act and the Exchange Act were made by the Issuer on a reasonable basis and reflect the Issuer’s good faith belief and/or estimate of the matters described therein.

(ll)           The Issuer is in compliance with all applicable provisions of the Sarbanes−Oxley Act of 2002 (the “Sarbanes−Oxley Act”).

(mm)           The Issuer has established and maintains “disclosure controls and procedures” (as defined in Rules 13a−15(e) and 15d−15(e) of the Exchange Act; the Issuer’s “disclosure controls and procedures” are reasonably designed to ensure that all information (both financial and non−financial) required to be disclosed by the Issuer in the reports that it files or furnishes under the Exchange Act is recorded, processed, summarized and reported within the time periods specified in the rules and regulations of the Commission, and that all such information is accumulated and communicated to the Issuer’s management as appropriate to allow timely decisions regarding required disclosure and to make the certifications of the Chief Executive Officer and Chief Financial Officer of the Issuer required under the Exchange Act with respect to such reports.

(nn)           There are no outstanding loans, advances (except normal advances for business expenses in the ordinary course of business) or guarantees of indebtedness by the Issuer to or for the benefit of any of the executive officers or directors of the Issuer or any of their respective family members, except as disclosed in the Prospectus and the Disclosure Package. The Issuer has not directly or indirectly extended or maintained credit, arranged for the extension of credit, or renewed an extension of credit, in the form of a personal loan to or for any director or executive officer of the Issuer.

(oo)           The Issuer is subject to and in compliance in all material respects with the reporting requirements of Section 13 or Section 15(d) of the Exchange Act.  The Common Stock is registered pursuant to Section 12(b) of the Exchange Act and is listed on The NASDAQ Global Market, and the Issuer has taken no action designed to, or reasonably likely to have the effect of, terminating the registration of the Common Stock under the Exchange Act or delisting the Common Stock from The NASDAQ Global Market, nor has the Issuer received any notification that the Commission or FINRA is contemplating terminating such registration or listing. No consent, approval, authorization or order of, or filing, notification or registration with, The NASDAQ Global Market is required for the listing and trading of the Shares and Warrant Shares on The NASDAQ Global Market that will not have been obtained or filed as of the Closing Date.

(pp)           No approval of the stockholders of the Issuer under the rules and regulations of The NASDAQ Global Market is required for the Issuer to issue and deliver the Securities.

(qq)           The Issuer and its Board of Directors have taken all necessary action, if any, to render inapplicable any control share acquisition, business combination, poison pill (including any distribution under a rights agreement) or other similar anti-takeover provision under the Issuer’s Charter or the laws of the State of Delaware that is or could become applicable as of result of the Issuer’s issuance of the Securities hereunder.

(rr)           Any certificate signed by any officer of the Issuer and delivered to the Representatives or counsel for the Underwriters in connection with the offering of the Securities contemplated hereby shall be deemed a representation and warranty by the Issuer to each Underwriter and shall be deemed to be a part of this Section 1 and incorporated herein by this reference.

2.           Purchase, Sale and Delivery of the Securities.

(a)           On the basis of the representations, warranties and covenants herein contained, and subject to the conditions herein set forth, the Issuer agrees to sell to the Underwriters and each Underwriter agrees, severally and not jointly, to purchase, at a price of $1.2408 per Share and accompany Warrant, the number of Shares and Warrants set forth opposite the name of each Underwriter in Schedule I hereof, subject to adjustments in accordance with Section 9 hereof.

(b)           Payment for the Securities to be sold hereunder is to be made in New York Clearing House funds by Federal (same day) against delivery of certificates therefor to the Representatives for the several accounts of the Underwriters.  Such payment and delivery are to be made (i) through the facilities of the Depository Trust Company, New York, New York, with respect to the Shares, and (ii) by physical delivery in certificated form with respect to the Warrants, at 10:00 a.m., New York time, on the third business day after the date of this Agreement or at such other time and date not later than five business days thereafter as you and the Issuer shall agree upon, such time and date being herein referred to as the “Closing Date.”  As used herein, “business day” means a day on which The NASDAQ Global Market is open for trading and on which banks in New York are open for business and are not permitted by law or executive order to be closed.

3.           Offering by the Underwriters.

It is understood that the several Underwriters are to make a public offering of the Securities as soon as the Representatives deem it advisable to do so.  The Securities are to be initially offered to the public at the initial public offering price set forth in the Prospectus.  The Representatives may from time to time thereafter change the public offering price and other selling terms.

It is further understood that you will act as the Representatives for the Underwriters in the offering and sale of the Securities in accordance with a Master Agreement Among Underwriters entered into by you and the several other Underwriters.

4.           Covenants.

(a)           The Issuer covenants and agrees with the several Underwriters that it will prepare and timely file with the Commission under Rule 424(b) of the Rules and Regulations a Prospectus in a form approved by the Representatives containing information previously omitted at the time of effectiveness of the Registration Statement in reliance on Rule 430A, Rule 430B and Rule 430C of the Rules and Regulations; (ii) not file any amendment to the Registration Statement or supplement to the Prospectus, any Preliminary Prospectus or any Issuer Free Writing Prospectus of which the Representatives shall not previously have been advised and furnished with a copy or to which the Representatives shall have reasonably objected in writing or which is not in compliance with the Rules and Regulations; and (iii) file on a timely basis all reports and any definitive proxy or information statements required to be filed by the Issuer with the Commission subsequent to the date of the Prospectus and prior to the termination of the offering of the Securities by the Underwriters.

(b)           The Issuer has not distributed and without the prior consent of the Representatives, it will not distribute any prospectus or other offering material (including, without limitation, any offer relating to the Securities that would constitute a “free writing prospectus” and content on the Issuer’s website that may be deemed to be a prospectus or other offering material) in connection with the offering and sale of the Securities, other than the materials referred to in Sections 1(a) and 1(b).   Each Underwriter represents and agrees that it has not made and, without the prior consent of the Issuer and the Representatives, it will not make, any offer relating to the Securities that would constitute an Issuer Free Writing Prospectus.  Any such Issuer Free Writing prospectus the use of which has been consented to by the Issuer and the Representatives is listed on Schedule II hereto.  The Issuer has complied and will comply with the requirements of Rule 433 under the Securities Act applicable to any Issuer Free Writing Prospectus, including timely filing with the Commission or retention where required and legending.  The Issuer represents that it has satisfied and agrees that it will satisfy the conditions under Rule 433 under the Securities Act to avoid a requirement to file with the Commission any electronic road show.  The Issuer agrees that if at any time following issuance of an Issuer Free

Writing Prospectus any event occurred or occurs as a result of which such Issuer Free Writing Prospectus would conflict with the information in the Registration Statement, the Pricing Prospectus or the Prospectus or would include an untrue statement of a material fact or omit to state any material fact necessary in order to make the statements therein, in light of the circumstances then prevailing, not misleading, the Issuer will give prompt notice thereof the Representatives and, if requested by Representatives, will prepare and furnish without charge to each Underwriter an Issuer Free Writing Prospectus or other document which will correct such conflict, statement or omission; provided, however, that this representation and warranty shall not apply to any statements or omissions in an Issuer Free Writing Prospectus made in reliance upon and in conformity with written information furnished to the Issuer by any Underwriter through the Representatives expressly for use therein, such information being listed in Section 13 below.

(c)           The Issuer will not take, directly or indirectly, any action designed to cause or result in, or that has constituted or might reasonably be expected to constitute, the stabilization or manipulation of the price of any securities of the Issuer.

(d)           The Issuer will advise the Representatives promptly (i) when the Registration Statement or any post-effective amendment thereto shall have become effective; (ii) of receipt of any comments from the Commission; (iii) of any request of the Commission for amendment of the Registration Statement or for supplement to the Prospectus or for any additional information; and (iv) of the issuance by the Commission of any stop order suspending the effectiveness of the Registration Statement or the use of the Prospectus or of the institution of any proceedings for that purpose.  The Issuer will use its best efforts to prevent the issuance of any such stop order preventing or suspending the use of the Prospectus and to obtain as soon as possible the lifting thereof, if issued.

(e)           The Issuer will cooperate with the Representatives in endeavoring to qualify the Securities for sale under the securities laws of such jurisdictions as the Representatives may reasonably have designated in writing and will make such applications, file such documents, and furnish such information as may be reasonably required for that purpose, provided the Issuer shall not be required to qualify as a foreign corporation or to file a general consent to service of process in any jurisdiction where it is not now so qualified or required to file such a consent.

(f)           The Issuer will deliver to, or upon the order of, the Representatives, from time to time, as many copies of any Preliminary Prospectus as the Representatives may reasonably request.  The Issuer will deliver to, or upon the order of, the Representatives during the period when delivery of a Prospectus is required under the Securities Act, as many copies of the Prospectus in final form, or as thereafter amended or supplemented, as the Representatives may reasonably request.  The Issuer will deliver to the Representatives at or before the Closing Date, such number of copies of the Registration Statement (including such number of copies of the exhibits filed therewith that may reasonably be requested) and of all amendments thereto, as the Representatives may reasonably request.

(g)           The Issuer will comply with the Securities Act and the Rules and Regulations, and the Exchange Act, and the rules and regulations of the Commission thereunder, so as to permit the completion of the distribution of the Securities as contemplated in this Agreement and the Prospectus.  If during the period in which a prospectus is required by law to be delivered by an Underwriter or dealer, any event shall occur as a result of which, in the judgment of the Issuer or in the reasonable opinion of the Representatives, it becomes necessary to amend or supplement the Prospectus in order to make the statements therein, in the light of the circumstances existing at the time the Prospectus is delivered to a purchaser, not misleading, or, if it is necessary at any time to amend or supplement the Prospectus to comply with any law, the Issuer promptly will prepare and file with the Commission an appropriate amendment to the Registration Statement or supplement to the Prospectus so that the Prospectus as so amended or supplemented will not, in the light of the circumstances when it is so delivered, be misleading, or so that the Prospectus will comply with the law.

(h)           The Issuer will make generally available to its security holders, as soon as it is practicable to do so, but in any event not later than 15 months after the effective date of the Registration Statement, an earning statement (which need not be audited) in reasonable detail, covering a period of at least 12 consecutive months beginning after the effective date of the Registration Statement, which earning statement shall satisfy the requirements of Section 11(a) of the Securities Act and Rule 158 of the Rules and Regulations.

(i)           Prior to the Closing Date, the Issuer will furnish to the Underwriters, as soon as they have been prepared by or are available to the Issuer, a copy of any unaudited interim financial statements of the Issuer for any period subsequent to the period covered by the most recent financial statements appearing in, or incorporated by reference into, the Registration Statement and the Prospectus.

(j)           The Issuer covenants and agrees that no offering, sale, short sale or other disposition of any shares of Common Stock of the Issuer or other securities convertible into or exchangeable or exercisable for shares of Common Stock or derivative of Common Stock (or agreement for such) will be made for a period of 90 days after the date of this Agreement, directly or indirectly, by the Issuer otherwise than hereunder or with the prior written consent of the Representatives; provided, that this provision will not restrict the Issuer from (i) making awards to purchase its Common Stock, or issuing Common Stock, pursuant to employee benefit plans as described in the Prospectus and the Disclosure Package or (ii) issuing Common Stock upon the exercise, conversion or exchange of convertible or exchangeable securities outstanding as of the date of this Agreement; provided further, that this provision will not restrict the Issuer from issuing shares of Common Stock or other securities convertible into or exchangeable or exercisable for shares of Common Stock or derivative of Common Stock, which in the aggregate shall not exceed 5% of the outstanding shares of Common Stock as of the date of this Agreement, as consideration in connection with collaborations, acquisitions or strategic transactions approved by a majority of the disinterested directors of the Issuer, provided that any such issuance shall only be to a person or entity (or to the equityholders of such entity) which is, itself or through its subsidiaries, an operating company or an owner of an asset in a business synergistic with the business of the Issuer or any of its Subsidiaries and shall provide to the Issuer additional benefits in addition to the investment of funds, but shall not include a transaction in which the Issuer is issuing securities primarily for the purpose of raising capital or to an entity whose primary business is investing in securities.

(k)           The Issuer will use its best efforts to list, subject to notice of issuance, the Shares and Warrant Shares on The NASDAQ Global Market.

(l)           The Issuer has caused each officer and director and specific shareholders of the Issuer to furnish to you, on or prior to the date of this Agreement, a letter or letters, in form and substance satisfactory to the Representatives, pursuant to which each such person shall agree not to offer, sell, sell short or otherwise dispose of any shares of Common Stock of the Issuer or other capital stock of the Issuer, or any other securities convertible, exchangeable or exercisable for Common Stock or derivative of Common Stock owned by such person or request the registration for the offer or sale of any of the foregoing  (or as to which such person has the right to direct the disposition of) for a period of 90 days after the date of this Agreement, directly or indirectly, except with the prior written consent of the Representatives  (the “Lockup Agreements”).

(m)           The Issuer shall apply the net proceeds of its sale of the Securities as described under the heading “Use of Proceeds” in the Prospectus and the Disclosure Package and shall report with the Commission with respect to the sale of the Securities and the application of the proceeds therefrom as may be required in accordance with Rule 463 under the Securities Act.

(n)           The Issuer shall not invest, or otherwise use the proceeds received by the Issuer from its sale of the Securities in such a manner as would require the Issuer or any of the Subsidiaries to register as an investment company under the 1940 Act.

(o)           The Issuer will maintain a transfer agent and, if necessary under the jurisdiction of incorporation of the Issuer, a registrar for the Common Stock.

5.           Costs and Expenses.

The Issuer will pay all costs, expenses and fees incident to the performance of the obligations of the Issuer under this Agreement, including, without limiting the generality of the foregoing, the following:  accounting fees of the Issuer; the fees and disbursements of counsel for the Issuer; the cost of printing and delivering to, or as requested by, the Underwriters copies of the Registration Statement, Preliminary Prospectuses, the Pricing Prospectus, any Issuer Free Writing Prospectus, the Prospectus, any Blue Sky surveys and any supplements or amendments thereto; the filing fees of the Commission; the filing fees and expenses (including legal fees and disbursements) incident to securing any required review by FINRA of the terms of the sale of the Securities; the listing fee of The NASDAQ Global Market; and the expenses, including the fees and disbursements of counsel for the Underwriters incurred in connection with the qualification of the Securities under state securities or Blue Sky laws.  The Issuer shall reimburse the several Underwriters for (i) the costs and expenses incurred by the Underwriters in connection with the marketing of the offering and the sale of the Securities to prospective investors including, but not limited to, those related to any presentations or meetings undertaken in connection therewith including, without limitation, expenses associated with the production of road show slides and graphics, fees and expenses of any consultants engaged with the written consent of the Issuer in connection with the road show presentations, travel, lodging and other expenses incurred by the officers of the Issuer and any such consultants, and the cost of any aircraft or other transportation chartered in connection with the road show and (i) the fees, disbursements and other charges of counsel to the Underwriters.  Notwithstanding the foregoing, in no event shall the Issuer be obligated to reimburse the Underwriters pursuant to this paragraph in an amount in excess of $100,000 for any third party legal costs, and $50,000 for any reasonably documented non-legal out-of-pocket expenses.

In addition, if this Agreement shall not be consummated because the conditions in Section 6 hereof are not satisfied, or because this Agreement is terminated by the Representatives pursuant to Section 11 hereof, or by reason of any failure, refusal or inability on the part of the Issuer to perform any undertaking or satisfy any condition of this Agreement or to comply with any of the terms hereof on its part to be performed, unless such failure to satisfy said condition or to comply with said terms be due to the default or omission of any Underwriter, then the Issuer shall reimburse the several Underwriters for reasonable out-of-pocket expenses, including all fees and disbursements of counsel, reasonably incurred in connection with investigating, marketing and proposing to market the Securities or in contemplation of performing their obligations hereunder; but the Issuer shall not in any event be liable to any of the several Underwriters for damages on account of loss of anticipated profits from the sale by them of the Securities.

6.           Conditions of Obligations of the Underwriters.

The several obligations of the Underwriters to purchase the Securities on the Closing Date are subject to the accuracy, as of the Closing Date, of the representations and warranties of the Issuer contained herein, and to the performance by the Issuer of its covenants and obligations hereunder and to the following additional conditions:

(a)           The Registration Statement and all post-effective amendments thereto shall have become effective and any and all filings required by Rule 424 and Rule 430A, 430B and 430C of the Rules and Regulations shall have been made, and any request of the Commission for additional information (to be included in the Registration Statement or otherwise) shall have been disclosed to the Representatives and complied with to their reasonable satisfaction.  All material required to be filed by the Issuer pursuant to Rule 433(d) under the Securities Act shall have been filed with the Commission within the applicable time period prescribed for such filing by Rule 433 under the Securities Act; if the Issuer has elected to rely upon Rule 462(b) under the Securities Act, the Rule 462(b) Registration Statement shall have become effective by 10:00 p.m., Washington, D.C. time, on the date of this Agreement.  No stop order suspending the effectiveness of the Registration Statement, as amended from time to time, shall have been issued and no proceedings for that purpose shall have been taken or, to the knowledge of the Issuer, shall be contemplated by the Commission; no stop order suspending or preventing the use of the Pricing Prospectus, Prospectus or any Issuer Free Writing Prospectus shall have been initiated or, to the knowledge of the Issuer, shall be contemplated by the Commission; all requests for additional information on the part of the Commission shall have been complied with to your reasonable satisfaction; and no injunction, restraining order, or order of any nature by a Federal or state court of competent jurisdiction shall have been issued as of the Closing Date which would prevent the issuance of the Securities.

(b)           The Representatives shall have received on the Closing Date the written opinion of Cooley LLP, counsel for the Issuer, dated the Closing Date addressed to the Underwriters, in form and substance reasonably satisfactory to the Representatives as set forth in Exhibit B hereto.

(c)           The Representatives shall have received on the Closing Date the written opinion of Cahill Gordon & Reindel LLP, counsel for the Issuer, dated the Closing Date addressed to the Underwriters, in form and substance reasonably satisfactory to the Representatives as set forth in Exhibit C hereto.

(d)           The Representatives shall have received on the Closing Date the written opinion of Christopher Margolin, General Counsel to the Issuer, dated the Closing Date addressed to the Underwriters, in form and substance reasonably satisfactory to the Representatives as set forth in Exhibit D hereto.

(e)           The Representatives shall have received on the Closing Date the written opinion of Goodwin Procter LLP, counsel for the Underwriters, dated the Closing Date addressed to the Underwriters, with respect to such matters as the Representatives reasonably may request, and such counsel shall have received such papers and information as they request to enable them to pass upon such matters.

(f)           The Representatives shall have received on each of the date hereof and the Closing Date a letter dated the date hereof and the Closing Date in form and substance satisfactory to the representatives, of Ernst & Young LLP confirming that they are independent public accountants within the meaning of the Securities Act and the applicable published Rules and Regulations thereunder and stating that in their opinion the financial statements and schedules examined by them and included in, or incorporated by reference into, the Registration Statement comply in form in all material respects with the applicable accounting requirements of the Securities Act and the related published Rules and Regulations; and containing such other statements and information as is ordinarily included in accountants' “comfort letters” to Underwriters with respect to the financial statements and certain financial and statistical information contained in, or incorporated by reference into, the Registration Statement and the Prospectus.

(g)           The Representatives shall have received on the Closing Date a certificate or certificates of the Issuer’s Chief Executive Officer and Chief Financial Officer to the effect that, as of the Closing Date each of them severally represents as follows:

(i)           The Registration Statement has become effective under the Securities Act and no stop order suspending the effectiveness of the Registrations Statement has been issued, and no proceedings for such purpose have been taken or are, to his knowledge, contemplated by the Commission;

(ii)           The representations and warranties of the Issuer contained in Section 1 hereof are true and correct as of the Closing Date;

(iii)           All filings required to have been made pursuant to Rules 424 or 430A, 430B and 430C under the Securities Act have been made;

(iv)           They have carefully examined the Registration Statement and the Prospectus and, in their opinion, as of the effective date of the Registration Statement, the statements contained in the Registration Statement were true and correct, and such Registration Statement and Prospectus did not omit to state a material fact required to be stated therein or necessary in order to make the statements therein not misleading, and since the effective date of the Registration Statement, no event has occurred which should have been set forth in a supplement to or an amendment of the Prospectus which has not been so set forth in such supplement or amendment; and

(v)           Since the respective dates as of which information is given in the Disclosure Package, (1) there has not been any material adverse change or any development involving a prospective change, which has had or is reasonably likely to have a Material Adverse Effect, whether or not arising in the ordinary course of business; (2) neither the Issuer nor any of its Subsidiaries shall have sustained any loss or interference with its business from fire, explosion, flood or other calamity, whether or not covered by insurance, or from any labor dispute or court or governmental action, order or decree, otherwise than as set forth or contemplated in the  Disclosure Package, and (3) there shall not have been any change in the capital stock (other than issuances of capital stock in the ordinary course of business pursuant to the Issuer’s employee benefit plans) or long-term debt of the Issuer or any of the Subsidiaries.

(h)           The Issuer shall have filed a Notification: Listing of Additional Shares with The NASDAQ Global Market with respect to the Shares and Warrant Shares, if any, and shall have received no objection thereto from The NASDAQ Global Market.

(i)           The Lockup Agreements described in Section 4(l) shall be in full force and effect.

(j)           The Representatives shall have received on the Closing Date a certificate of the Secretary of the Issuer certifying as to (i) the Issuer’s Charter, (ii) the Issuer’s By-Laws and (iii) the resolutions of the Board of Directors of the Issuer authorizing the filing of the Registration Statement, the execution and delivery of this Agreement and all other matters related thereto.

(k)           The Representatives shall have received on the Closing Date a certificate of the Chief Financial Officer of the Issuer in the form agreed to by the Issuer and the Representatives.

(l)           The Underwriters shall not have received any unresolved objection from FINRA as to the fairness and reasonableness of the amount of compensation allowable or payable to the Underwriters in connection with the issuance and sale of the Securities.

(m)           The Issuer shall have furnished to the Representatives such further certificates and documents confirming the representations and warranties, covenants and conditions contained herein and related matters as the Representatives may reasonably have requested.

If any of the conditions hereinabove provided for in this Section 6 shall not have been fulfilled when and as required by this Agreement to be fulfilled, the obligations of the Underwriters hereunder may be terminated by the Representatives.

In such event, the Issuer and the Underwriters shall not be under any obligation to each other (except to the extent provided in Sections 5 and 8 hereof).

7.           Conditions of the Obligations of the Issuer.

The obligations of the Issuer to sell and deliver the portion of the Securities required to be delivered as and when specified in this Agreement are subject to the conditions that at the Closing Date no stop order suspending the effectiveness of the Registration Statement shall have been issued and in effect or proceedings therefor initiated or threatened.

8.           Indemnification.

(a)           The Issuer agrees:

(i)           to indemnify and hold harmless each Underwriter and each person, if any, who controls such Underwriter within the meaning of Section 15 of the Securities Act, against any losses, claims, damages or liabilities to which such Underwriter or any such controlling person may become subject under the Securities Act or otherwise, insofar as such losses, claims, damages or liabilities (or actions or proceedings in respect thereof) arise out of or are based upon  (i) any untrue statement or alleged untrue statement of any material fact contained in (A) the Registration Statement, any Preliminary Prospectus, the Pricing Prospectus, the Prospectus or any amendment or supplement thereto, (B) any Issuer Free Writing Prospectus or any “issuer information” filed or required to be filed pursuant to Rule 433(d) under the Securities Act,  (ii) the omission or alleged omission to state therein a material fact required to be stated therein or necessary to make the statements therein not misleading, or (iii) any alleged act or failure to act by any Underwriter in connection with, or relating in any manner to, the Securities or the offering contemplated hereby, and which is included as part of or referred to in any loss, claim, damage, liability or action arising out of or based upon matters covered by clause (i) or (ii) above (provided, however, that the Issuer shall not be liable under this clause (iii) to the extent that it is determined in a final judgment by a court of competent jurisdiction that such loss, claim, damage, liability or action resulted directly from any such acts or failures to act undertaken or omitted to be taken by such Underwriter through its gross negligence or willful misconduct); provided, however, that the Issuer will not be liable in any such case to the extent that any such loss, claim, damage or liability arises out of or is based upon an untrue statement or alleged untrue statement, or omission or alleged omission made in the Registration Statement, any Preliminary Prospectus, Pricing Prospectus, the Prospectus, or such amendment or supplement, or any Issuer Free Writing Prospectus or any “issuer information” filed or required to be filed pursuant to Rule 433(d) under the Securities Act in reliance upon and in conformity with written information furnished to the Issuer by any Underwriter through the Representatives expressly for use therein, such information being listed in Section 13 below.

(ii)           to reimburse each Underwriter and each such controlling person upon demand for any legal or other out-of-pocket expenses reasonably incurred by such Underwriter or such controlling person in connection with investigating or defending any such loss, claim, damage or liability, action or proceeding or in responding to a subpoena or governmental inquiry related to the offering of the Securities, whether or not such Underwriter or controlling person is a party to any action or proceeding.  In the event that it is finally judicially determined that the Underwriters were not entitled to receive payments for legal and other expenses pursuant to this subparagraph, the Underwriters will promptly return all sums that had been advanced pursuant hereto.

(b)           Each Underwriter severally and not jointly will indemnify and hold harmless the Issuer, each of its directors, each of its officers who have signed the Registration Statement, and each person, if any, who controls the Issuer within the meaning of Section 15 of the Securities Act, against any losses, claims, damages or liabilities to which the Issuer or any such director, officer, or controlling person may become subject under the Securities Act or otherwise, insofar as such losses, claims, damages or liabilities (or actions or proceedings in respect thereof) arise out of or are based upon (i)  any untrue statement or alleged  untrue statement of any material fact contained in the Registration Statement, any Preliminary Prospectus, the Pricing Prospectus, the Prospectus or any amendment or supplement thereto, or in any Issuer Free Writing Prospectus (ii) the omission or the alleged omission to state therein a material fact required to be stated therein or necessary to make the statements therein not misleading in the light of the circumstances under which they were made; and will reimburse any legal or other expenses reasonably incurred by the Issuer or any such director, officer, or controlling person in connection with investigating or defending any such loss, claim, damage, liability, action or proceeding; provided, however, that each Underwriter will be liable in each case to the extent, but only to the extent, that such untrue statement or alleged untrue statement or omission or alleged omission has been made in the Registration Statement, any Preliminary Prospectus, the Pricing Prospectus, the Prospectus or any amendment or supplement thereto, or in any Issuer Free Writing Prospectus in reliance upon and in conformity with written information furnished to the Issuer by any Underwriter through the Representatives expressly for use therein, such information being listed in Section 13 below.

(c)           In case any proceeding (including any governmental investigation) shall be instituted involving any person in respect of which indemnity may be sought pursuant to this Section, such person (the “indemnified party”) shall promptly notify the person against whom such indemnity may be sought (the “indemnifying party”) in writing.  No indemnification provided for in Section 8(a) or (b) shall be available to any party who shall fail to give notice as provided in this Subsection if the party to whom notice was not given was unaware of the proceeding to which such notice would have related and was materially prejudiced by the failure to give such notice, but the failure to give such notice shall not relieve the indemnifying party or parties from any liability which it or they may have to the indemnified party for contribution or otherwise than on account of the provisions of Section 8(a) or (b).  In case any such proceeding shall be brought against any indemnified party and it shall notify the indemnifying party of the commencement thereof, the indemnifying party shall be entitled to participate therein and, to the extent that it shall wish, jointly with any other indemnifying party similarly notified, to assume the defense thereof, with counsel

satisfactory to such indemnified party and shall pay as incurred the fees and disbursements of such counsel related to such proceeding.  In any such proceeding, any indemnified party shall have the right to retain its own counsel at its own expense.  Notwithstanding the foregoing, the indemnifying party shall pay as incurred (or within 30 days of presentation) the fees and expenses of the counsel retained by the indemnified party in the event  (i) the indemnifying party and the indemnified party shall have mutually agreed to the retention of such counsel,  (ii) the named parties to any such proceeding (including any impleaded parties) include both the indemnifying party and the indemnified party and representation of both parties by the same counsel would be inappropriate due to actual or potential differing interests between them or (iii) the indemnifying party shall have failed to assume the defense and employ counsel acceptable to the indemnified party within a reasonable period of time after notice of commencement of the action.

It is understood that the indemnifying party shall not, in connection with any proceeding or related proceedings in the same jurisdiction, be liable for the reasonable fees and expenses of more than one separate firm for all such indemnified parties.  Such firm shall be designated in writing by you in the case of parties indemnified pursuant to Section 8(a) and by the Issuer in the case of parties indemnified pursuant to Section 8(b).  The indemnifying party 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, the indemnifying party agrees to indemnify the indemnified party from and against any loss or liability by reason of such settlement or judgment.  In addition, the indemnifying party will not, without the prior written consent of the indemnified party, settle or compromise or consent to the entry of any judgment in any pending or threatened claim, action or proceeding of which indemnification may be sought hereunder (whether or not any indemnified party is an actual or potential party to such claim, action or proceeding) unless such settlement, compromise or consent includes an unconditional release of each indemnified party from all liability arising out of such claim, action or proceeding.

(d)           If the indemnification provided for in this Section is unavailable to or insufficient to hold harmless an indemnified party under Section 8(a) or (b) above in respect of any losses, claims, damages or liabilities (or actions or proceedings in respect thereof) referred to therein, then each indemnifying party shall contribute to the amount paid or payable by such indemnified party as a result of such losses, claims, damages or liabilities (or actions or proceedings in respect thereof) in such proportion as is appropriate to reflect the relative benefits received by the Issuer on the one hand and the Underwriters on the other from the offering of the Securities.  If, however, the allocation provided by the immediately preceding sentence is not permitted by applicable law then each indemnifying party shall contribute to such amount paid or payable by such indemnified party in such proportion as is appropriate to reflect  not only such relative benefits but also the relative fault of the Issuer on the one hand and the Underwriters on the other in connection with the statements or omissions which resulted in such losses, claims, damages or liabilities, (or actions or proceedings in respect thereof), as well as any other relevant equitable considerations.  The relative benefits received by the Issuer on the one hand and the Underwriters on the other shall be deemed to be in the same proportion as the total net proceeds from the offering (before deducting expenses) received by the Issuer bear to the total underwriting discounts and commissions received by the Underwriters, in each case as set forth in the table on the cover page of the Prospectus.  The relative fault 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 Issuer on the one hand or the Underwriters on the other and the parties' relative intent, knowledge, access to information and opportunity to correct or prevent such statement or omission.

The Issuer and the Underwriters agree that it would not be just and equitable if contributions pursuant to this Section 8(d) 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 which does not take account of the equitable considerations referred to above in this Section 8(d).  The amount paid or payable by an indemnified party as a result of the losses, claims, damages or liabilities (or actions or proceedings in respect thereof) referred to above in this Section 8(d) shall be deemed to include any legal or other expenses reasonably incurred by such indemnified party in connection with investigating or defending any such action or claim.  Notwithstanding the provisions of this Section 8(d), (i) no Underwriter shall be required to contribute any amount in excess of the underwriting discounts and commissions applicable to the Securities purchased by such Underwriter and (ii) 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 in this Section 8(d) to contribute are several in proportion to their respective underwriting obligations and not joint.

(e)           In any proceeding relating to the Registration Statement, any Preliminary Prospectus, the Pricing Prospectus, the Prospectus or any supplement or amendment thereto, or any Issuer Free Writing Prospectus, each party against whom contribution may be sought under this Section hereby consents to the jurisdiction of any court having jurisdiction over any other contributing party, agrees that process issuing from such court may be served upon him or it by any other contributing party and consents to the service of such process and agrees that any other contributing party may join him or it as an additional defendant in any such proceeding in which such other contributing party is a party.

(f)           Any losses, claims, damages, liabilities or expenses for which an indemnified party is entitled to indemnification or contribution under this Section shall be paid by the indemnifying party to the indemnified party as such losses, claims, damages, liabilities or expenses are incurred.  The indemnity and contribution agreements contained in this Section and the representations and warranties of the Issuer set forth in this Agreement shall remain operative and in full force and effect, regardless of (i) any investigation made by or on behalf of any Underwriter or any person controlling any Underwriter, the Issuer, its directors or officers or any persons controlling the Issuer, (ii) acceptance of any Securities and payment therefor hereunder, and (iii) any termination of this Agreement.  A successor to any Underwriter, or to the Issuer, its directors or officers, or any person controlling the Issuer, shall be entitled to the benefits of the indemnity, contribution and reimbursement agreements contained in this Section.

9.           Default by Underwriters.

If on the Closing Date any Underwriter shall fail to purchase and pay for the portion of the Securities which such Underwriter has agreed to purchase and pay for on such date (otherwise than by reason of any default on the part of the Issuer), you, as the Representatives of the Underwriters, shall use your reasonable efforts to procure within 36 hours thereafter one or more of the other Underwriters, or any others, to purchase from the Issuer such amounts as may be agreed upon and upon the terms set forth herein, the Securities which the defaulting Underwriter or Underwriters failed to purchase.  If during such 36 hours you, as such Representatives, shall not have procured such other Underwriters, or any others, to purchase the Securities agreed to be purchased by the defaulting Underwriter or Underwriters, then (a) if the aggregate number of shares with respect to which such default shall occur does not exceed 10% of the Securities covered hereby, the other Underwriters shall be obligated, severally, in proportion to the respective numbers of Securities which they are obligated to purchase hereunder, to purchase the Securities which such defaulting Underwriter or Underwriters failed to purchase, or (b) if the aggregate number of Securities with respect to which such default shall occur exceeds 10% of the Securities covered hereby, the Issuer or you as the Representatives of the Underwriters will have the right to terminate this Agreement without liability on the part of the non-defaulting Underwriters or of the Issuer except to the extent provided in Section 8 hereof.  In the event of a default by any Underwriter or Underwriters, as set forth in this Section 9, the Closing Date may be postponed for such period, not exceeding seven days, as you, as Representatives, may determine in order that the required changes in the Registration Statement or in the Prospectus or in any other documents or arrangements may be effected.  The term “Underwriter” includes any person substituted for a defaulting Underwriter.  Any action taken under this Section 9 shall not relieve any defaulting Underwriter from liability in respect of any default of such Underwriter under this Agreement.

10.           Notices.

All communications hereunder shall be in writing and, except as otherwise provided herein, will be mailed, delivered, or faxed and confirmed as follows:

if to the Underwriters, to	RBC Capital Markets, LLC Three World Financial Center, 8th Floor 200 Vesey Street, New York, New York 10281-8098 Attention:  Joe Morea, Syndicate Director Fax:   ###-###-####
if to the Issuer, to	XOMA Corporation 2910 Seventh Street Berkeley, CA 94710 Attention:  Christopher J. Margolin, General Counsel Fax:   ###-###-####

11.           Termination.

(a)           This Agreement may be terminated by you at any time prior to the Closing Date if any of the following has occurred: (i) since the respective dates as of which information is given in the Registration Statement and the Prospectus, any material adverse change or any development involving a prospective change, which (A) in the absolute discretion of any group of Underwriters (which may include the Representatives) that has agreed to purchase in the aggregate at least 50% of the Securities, as long as the Representatives do not affirmatively assert that termination should not occur, or (B) in the absolute discretion of the Representatives (whether or not the condition of clause (A) is satisfied) has had or is reasonably likely to have a Material Adverse Effect, (ii) any outbreak, attack, or escalation of hostilities or declaration of war, national emergency, act of terrorism or other national or international calamity or crisis or change in economic, financial or political conditions if the effect of such outbreak, escalation, declaration, emergency, calamity, crisis or change on the financial markets of the United States would, in (A) the absolute discretion of any group of Underwriters (which may include the Representatives) that has agreed to purchase in the aggregate at least 50% of the Securities, as long as the Representatives do not affirmatively assert that termination should not occur, or (B) in the absolute discretion of the Representatives (whether or not the condition of clause (A) is satisfied), make it impracticable or inadvisable to market the Securities or to enforce contracts for the sale of the Securities, or (iii) suspension of trading in securities generally on the New York Stock Exchange, The NASDAQ Global Select Market, The NASDAQ Global Market, The NASDAQ Capital Market or the NYSE Amex or limitation on prices (other than limitations on hours or numbers of days of trading) for securities on any such trading market, (iv) the enactment, publication, decree or other promulgation of any statute, regulation, rule or order of any court or other governmental authority which in your opinion materially and adversely affects or may materially and adversely affect the business or operations of the Issuer, (v) declaration of a banking moratorium by United States or New York State authorities, (vi) the suspension of trading of the Issuer's common stock by The NASDAQ Global Market, the Commission, or any other governmental authority, or (vii) the taking of any action by any governmental body or agency in respect of its monetary or fiscal affairs which in your reasonable opinion has a material adverse effect on the securities markets in the United States; or

(b)           as provided in Sections 6 and 9 of this Agreement.

12.           Successors.

This Agreement has been and is made solely for the benefit of the Issuer and Underwriters and their respective successors, executors, administrators, heirs and assigns, and the officers, directors and controlling persons referred to herein, and no other person will have any right or obligation hereunder.  No purchaser of any of the Securities from any Underwriter shall be deemed a successor or assign merely because of such purchase.

13.           Information Provided by Underwriters.

The Issuer and the Underwriters acknowledge and agree that the only information furnished or to be furnished by any Underwriter to the Issuer for inclusion in any Preliminary Prospectus, Prospectus, Issuer Free Writing Prospectus or the Registration Statement consists of the information contained in (i) the last paragraph under the heading “Commissions and Discounts,” and (ii) the paragraph under the heading “Price Stabilization, Short Positions and Penalty Bids” under the caption “Underwriting” in the Prospectus.

14.            Research Independence

In addition, the Issuer acknowledges that the Underwriters’ research analysts and research departments are required to be independent from their respective investment banking divisions and are subject to certain regulations and internal policies, and that such Underwriters’ research analysts may hold and make statements or investment recommendations and/or publish research reports with respect to the Issuer and/or the offering that differ from the views of its investment bankers.  The Issuer hereby waives and releases, to the fullest extent permitted by law, any claims that the Issuer may have against the Underwriters with respect to any conflict of interest that may arise from the fact that the views expressed by their independent research analysts and research departments may be different from or inconsistent with the views or advice communicated to the Issuer by such Underwriters’ investment banking divisions.  The Issuer acknowledges that each of the Underwriters is a full service securities firm and as such from time to time, subject to applicable securities laws, may effect transactions for its own account or the account of its customers and hold long or short position in debt or equity securities of the companies which may be the subject to the transactions contemplated by this Agreement.

15.           No fiduciary duty

Notwithstanding any preexisting relationship, advisory or otherwise, between the parties or any oral representations or assurances previously or subsequently made by the underwriters, the Issuer acknowledges and agrees that:

(a)           nothing herein shall create a fiduciary or agency relationship between the Issuer and the Underwriters;

(b)           the Underwriters are not acting as advisors, expert or otherwise, to the Issuer in connection with this offering, sale of the Securities or any other services the Underwriters may be deemed to be providing hereunder, including, without limitation, with respect to the public offering price of the Securities;

(c)           the relationship between the Issuer and the Underwriters is entirely and solely commercial, based on arms-length negotiations;

(d)           any duties and obligations that the Underwriters may have to the Issuer shall be limited to those duties and obligations specifically stated herein; and

(e)            notwithstanding anything in this Underwriting Agreement to the contrary, the Issuer acknowledges that the Underwriters may have financial interests in the success of the Offering that are not limited to the difference between the price to the public and the purchase price paid to the Issuer by the Underwriters for the Securities and the Underwriters have no obligation to disclose, or account to the Issuer for, any of such additional financial interests.

The Issuer hereby waives and releases, to the fullest extent permitted by law, any claims that the Issuer may have against the Underwriters with respect to any breach or alleged breach of fiduciary duty.

16.           Miscellaneous.

The reimbursement, indemnification and contribution agreements contained in this Agreement and the representations, warranties and covenants in this Agreement shall remain in full force and effect regardless of  (a) any termination of this Agreement,  (b) any investigation made by or on behalf of any Underwriter or controlling person thereof, or by or on behalf of the Issuer or its directors or officers and  (c) delivery of and payment for the Securities under this Agreement.

This Agreement may be executed in counterparts, each of which shall be deemed an original, but all of which together shall constitute one and the same instrument.

This Agreement shall be governed by, and construed in accordance with, the laws of the State of New York.

This Agreement constitutes the entire agreement of the parties to this Agreement and supersedes all prior written or oral and all contemporaneous oral agreements, understandings and negotiations with respect to the subject matter hereof.

This Agreement may only be amended or modified in writing, signed by all of the parties hereto, and no condition herein (express or implied) may be waived unless waived in writing by each party whom the condition is meant to benefit.

[remainder of page intentionally blank]

If the foregoing is in accordance with your understanding of our agreement, please sign and return to us the enclosed duplicates hereof, whereupon it will become a binding agreement among the Issuer and the several Underwriters in accordance with its terms.

Very truly yours,

XOMA CORPORATION

By  /s/  Fred Kurland

Name:  Fred Kurland

Title:    Vice President, Finance and Chief Financial Officer

The foregoing Underwriting Agreement is hereby confirmed

and accepted as of the date first above written.

RBC CAPITAL MARKETS, LLC

COWEN AND COMPANY, LLC

As the Representatives of the several

Underwriters listed on Schedule I

By:  RBC CAPITAL MARKETS, LLC

By:  /s/  Andrew Singer                                                     

       Name:  Andrew Singer

       Title:    Managing Director

By:  COWEN AND COMPANY, LLC

By:  /s/  Grant Miller                                                     

       Name:  Grant Miller

       Title:    Managing Director

SCHEDULE I

Schedule of Underwriters

Underwriter	Number of Shares and Accompanying Warrants to be Purchased
RBC Capital Markets, LLC	11,867,662
Cowen and Company, LLC	11,867,662
Roth Capital Partners, LLC	5,933,830
Total	29,669,154

Schedule II

Issuer Free Writing Prospectuses

None.

Schedule III

Pricing Information

Public Offering Price: $1.32 per Share and accompanying Warrant

Number of Shares Offered: 29,669,154

Number of Warrants Offered:  14,834,577

Exercise Price of the Warrant:  $1.76 per Warrant Share

Underwriting Discount: 6.0%

Time of Delivery:  March 9, 2012

Schedule IV

List of Subsidiaries

Name	Jurisdiction
XOMA Ireland Limited	Ireland
XOMA LS Limited	Ireland
XOMA Technology Ltd.	Bermuda
XOMA (Bermuda) Ltd.	Bermuda
XOMA (US) LLC	United States
XOMA CDRA LLC	United States

Exhibit A

Form of Warrant

Exhibit B

Form of Legal Opinion of Cooley LLP

Exhibit C

Form of Legal Opinion of Cahill Gordon & Reindel LLP

Exhibit D

Form of Opinion of Christopher Margolin, General Counsel