Table of Contents
 
Filed Pursuant to Rule 424(b)(5)
Registration No. 333-178480

			
PROSPECTUS SUPPLEMENT	  		
(To the Prospectus dated January 10, 2012)	  		

8,333,333 Shares

Common Stock
We are offering 8,333,333 shares of our common stock pursuant to this prospectus supplement and the accompanying prospectus.
Our common stock is listed on The NASDAQ Global Market under the symbol “CERS.” The last reported sale price of our common stock on March 13, 2013 was $4.20 per share.
Our business and an investment in our common stock include significant risks. See “ Risk Factors ” on page S-4 of this prospectus supplement and in our Annual Report on Form 10-K for the year ended December 31, 2012, which has been filed with the Securities and Exchange Commission and is incorporated by reference in this prospectus supplement.
Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or determined if this prospectus supplement or the accompanying prospectus is truthful or complete. Any representation to the contrary is a criminal offense.

 
									
 	  	Per Share	 	  	Total	 	
Public offering price	  	$	4.200	  	  	$	34,999,999	  	
			
Underwriting discount from 3,833,333 shares offered to the public	  	 	0.084	  	  	 	322,000	  	
			
Proceeds, before expenses, to us from 3,833,333 shares offered to the public	  	 	4.116	  	  	 	15,777,999	  	
			
Underwriting discount from remaining 4,500,000 shares offered to the public	  	 	0.252	  	  	 	1,134,000	  	
			
Proceeds, before expenses, to us from remaining 4,500,000 shares offered to the public	  	 	3.948	  	  	 	17,766,000	  	
			
Total proceeds, before expenses, to us from all shares offered to the public	  				  	 	33,543,999	  	
The underwriters may also purchase up to an additional 1,250,000 shares from us at the public offering price, less an underwriting discount of $0.252 per share, within 30 days from the date of this prospectus supplement to cover overallotments, if any. If the underwriters exercise the option in full, the total discount will be $1,771,000 and the total net proceeds, before expenses, to us will be $38,478,999.
The underwriters expect to deliver the shares against payment on or about March 19, 2013.

Cowen and Company
Sole Book-Running Manager

Baird	 	Wedbush PacGrow Life Sciences	 	Lazard Capital Markets	
Co-Managers
March 14, 2013.

Table of Contents
 TABLE OF CONTENTS
Prospectus Supplement

 	  	Page	 	
About this Prospectus Supplement	  	 	ii	  	
Prospectus Supplement Summary	  	 	S-1	  	
Risk Factors	  	 	S-4	  	
Forward-Looking Statements	  	 	S-5	  	
Use of Proceeds	  	 	S-6	  	
Dividend Policy	  	 	S-6	  	
Dilution	  	 	S-7	  	
Certain U.S. Federal Income Tax Considerations for Non-U.S. Holders of Common Stock	  	 	S-8	  	
Underwriting	  	 	S-12	  	
Legal Matters	  	 	S-17	  	
Experts	  	 	S-17	  	
Where You Can Find More Information	  	 	S-17	  	
Incorporation of Certain Information by Reference	  	 	S-17	  	
Prospectus

 	  	Page	 	
About this Prospectus	  	 	i	  	
Prospectus Summary	  	 	1	  	
Risk Factors	  	 	6	  	
Forward-Looking Statements	  	 	6	  	
Financial Ratios	  	 	7	  	
Use of Proceeds	  	 	7	  	
Description of Capital Stock	  	 	8	  	
Description of Debt Securities	  	 	13	  	
Description of Warrants	  	 	20	  	
Legal Ownership of Securities	  	 	22	  	
Plan of Distribution	  	 	25	  	
Legal Matters	  	 	27	  	
Experts	  	 	27	  	
Where You Can Find Additional Information	  	 	27	  	
Incorporation of Certain Information by Reference	  	 	28	  	
 
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 ABOUT THIS PROSPECTUS SUPPLEMENT
This document is in two parts. The first part is this prospectus supplement, which describes the terms of this offering of common stock and also adds to and updates information contained in the accompanying prospectus and the documents incorporated by reference into this prospectus supplement and the accompanying prospectus. The second part, the accompanying prospectus dated January 10, 2012, including the documents incorporated by reference therein, provides more general information. Generally, when we refer to this prospectus, we are referring to both parts of this document combined. To the extent there is a conflict between the information contained in this prospectus supplement, on the one hand, and the information contained in the accompanying prospectus or in any document incorporated by reference that was filed with the Securities and Exchange Commission, or SEC, before the date of this prospectus supplement, on the other hand, you should rely on the information in this prospectus supplement. If any statement in one of these documents is inconsistent with a statement in another document having a later date—for example, a document incorporated by reference in the accompanying prospectus—the statement in the document having the later date modifies or supersedes the earlier statement.
We have not, and the underwriters have not, authorized anyone to provide you with different information than that contained in or incorporated by reference in this prospectus supplement, the accompanying prospectus or in any free writing prospectus that we have authorized for use in connection with this offering. If anyone provides you with different or inconsistent information, you should not rely on it. We are not, and the underwriters are not, making an offer to sell these securities in any jurisdiction where the offer or sale is not permitted. You should assume that the information appearing in this prospectus supplement, the accompanying prospectus, the documents incorporated by reference in this prospectus supplement and the accompanying prospectus, and in any free writing prospectus that we have authorized for use in connection with this offering, is accurate only as of the date of those respective documents. Our business, financial condition, results of operations and prospects may have changed since those dates. You should read this prospectus supplement, the accompanying prospectus, the documents incorporated by reference in this prospectus supplement and the accompanying prospectus, and any free writing prospectus that we have authorized for use in connection with this offering, in their entirety before making an investment decision. You should also read and consider the information in the documents to which we have referred you in the sections of this prospectus supplement entitled “Where You Can Find More Information” and “Incorporation of Certain Information by Reference.”
Unless otherwise mentioned or unless the context requires otherwise, all references in this prospectus supplement to “Cerus,” “Cerus Corporation,” “we,” “us” and “our” refer to Cerus Corporation, a Delaware corporation, and its wholly-owned subsidiary, Cerus Europe B.V.
This prospectus supplement, the accompanying prospectus and the information incorporated herein and therein by reference include trademarks, service marks and trade names owned by us or other companies. All trademarks, service marks and trade names included or incorporated by reference into this prospectus supplement or the accompanying prospectus are the property of their respective owners.
 
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 PROSPECTUS SUPPLEMENT SUMMARY
This summary highlights certain information about us, this offering and selected information contained elsewhere in or incorporated by reference into this prospectus supplement and the accompanying prospectus. This summary is not complete and does not contain all of the information that you should consider before deciding whether to invest in our common stock. For a more complete understanding of our company and this offering, we encourage you to read and consider carefully the more detailed information in this prospectus supplement and the accompanying prospectus, including the information incorporated by reference in this prospectus supplement and the accompanying prospectus, and the information included in any free writing prospectus that we have authorized for use in connection with this offering, including the information under the heading “Risk Factors” in this prospectus supplement on page S-4.
Cerus Corporation
Our Business
We are a biomedical products company focused on developing and commercializing the INTERCEPT Blood System to enhance blood safety. The INTERCEPT Blood System, which is based on our proprietary technology for controlling biological replication, is designed to inactivate blood-borne pathogens in donated blood components intended for transfusion.
We have worldwide rights for our INTERCEPT Blood System for three blood components: platelets, plasma and red blood cells. The INTERCEPT Blood System for platelets, or platelet system, and the INTERCEPT Blood System for plasma, or plasma system, have received CE marks and are being marketed and sold in a number of countries around the world including those in Europe, The Commonwealth of Independent States, or CIS, and the Middle East. We sell both the platelet and plasma systems using our direct sales force and through distributors.
We are developing the INTERCEPT Blood System for red blood cells, or red blood cell system, and plan to perform in vitro studies and clinical trials. Subject to the availability of adequate funding from partners and/or capital markets, we intend to complete development activities for the red blood cell system necessary for potential regulatory approval in Europe. We are currently enrolling patients in a Phase II recovery and lifespan study and plan to complete that trial and certain other prerequisites before proposing a Phase III clinical trial protocol for the red blood cell system in support of approval in the United States. These development activities will result in increased research and development expenses in future periods, and our ability to conduct and complete any future clinical trials of the red blood cell system to support approval in the United States is subject to our ability to generate sufficient cash flows from our operations or obtain adequate funding from external sources. In any event, we will be required to obtain additional capital in order to complete the development of and obtain any regulatory approvals for the red blood cell system.
The United States Food and Drug Administration, or FDA, accepted our proposed modular Premarket Approval Application, or PMA, shell for review of our plasma system. We will proceed with a modular PMA approach, in which we will submit sections, or modules, of the PMA at different times and the compilation of these sections or modules will become a complete PMA. We believe that the modular approach increases the likelihood that we will be able to resolve any deficiencies identified by FDA earlier in the review process. Based on our recent discussions with the FDA, we believe that our existing clinical data is sufficient for the clinical requirements of the PMA submission process for the plasma system. In February 2013, we also reached agreement with the FDA regarding our platelet system. The FDA indicated that our existing clinical trial and European haemovigilance data will be sufficient to submit a proposal for a modular PMA submission for the platelet system without the need to complete additional Phase III clinical trials at this time. The submission of the PMA modules for our plasma system, and potentially for our platelet system, will result in increased research and development expenses in future periods. Should the FDA require us to complete any additional clinical trials, our ability to conduct and complete any additional clinical trials to support approval in the United States would be subject to our ability to generate sufficient cash flows from our operations or obtain adequate funding from external sources before we initiate any additional trials.

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We recognize product revenues from the sale of our platelet and plasma systems in a number of countries around the world including those in Europe, the CIS and the Middle East. Although our revenues have grown over time, if we are unable to gain widespread commercial adoption in markets where our blood safety products are approved for commercialization, we will have difficulties achieving profitability. In order to commercialize all of our products and product candidates, we will be required to conduct significant research, development, preclinical and clinical evaluation, commercialization and regulatory compliance activities for our product candidates, which, together with anticipated selling, general and administrative expenses, are expected to result in substantial losses. Accordingly, we may never achieve a profitable level of operations in the future.
Corporate Information
We were incorporated in California in 1991 and reincorporated in Delaware in 1996. Our corporate address is 2550 Stanwell Drive, Concord, California 94520, and our telephone number is (925) 288-6000. Our website address is www.cerus.com . Information found on, or accessible through, our website is not a part of, and is not incorporated into, this prospectus supplement, and you should not consider it part of this prospectus supplement or the accompanying prospectus. Our website address is included in this document as an inactive textual reference only.

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The Offering
 
Common stock offered by us	8,333,333 shares	
 
Overallotment option	1,250,000 shares	
Common stock to be outstanding
immediately after this offering	64,585,603 shares	
 
Use of proceeds	We intend to use the net proceeds from this offering for clinical development and other research and development activities related to the INTERCEPT Blood System, preparatory activities for the potential commercialization of the INTERCEPT Blood System in the United States and elsewhere, and for other general corporate purposes, including regulatory activity, selling, general and administrative expenses and working capital. In addition, we may use a portion of the net proceeds from this offering to prepay the remaining outstanding indebtedness under our growth capital loan with Comerica Bank. See “Use of Proceeds” on page S-6 of this prospectus supplement.	
 
Risk factors	Investing in our common stock involves significant risks. See “Risk Factors” on page S-4 of this prospectus supplement.	
 
NASDAQ Global Market symbol	CERS	
The number of shares of our common stock to be outstanding immediately after this offering as shown above is based on 56,252,270 shares outstanding as of December 31, 2012, and excludes, as of that date:
 
 	•	 	8,504,110 shares of common stock issuable upon the exercise of outstanding stock options with a weighted-average exercise price of $3.40 per share;	
 
 	•	 	2,400,000 shares of common stock issuable upon the exercise of outstanding warrants with an exercise price of $2.90 per share;	
 
 	•	 	3,679,127 shares of common stock issuable upon the exercise of outstanding warrants with an exercise price of $3.20 per share;	
 
 	•	 	53,973 shares of common stock issuable upon the vesting of outstanding restricted stock units; and	
 
 	•	 	up to an aggregate of 4,903,352 shares of common stock remaining available for future issuance under our 2008 Equity Incentive Plan and 1996 Employee Stock Purchase Plan.	
In addition, the number of shares of our common stock to be outstanding immediately after this offering as shown above does not include the up to approximately $25.6 million of shares of our common stock that remained available for sale at December 31, 2012 under our At-The-Market Issuance Sales Agreement, dated as of June 3, 2011, as amended January 4, 2012 and August 31, 2012, or the MLV Agreement, by and between us and MLV & Co. LLC, and our Controlled Equity Offering SM Sales Agreement, dated as of August 31, 2012, or the Cantor Agreement, by and between us and Cantor Fitzgerald & Co. Between December 31, 2012 and the date of this prospectus supplement, we sold an aggregate of 3,755,423 shares of our common stock for gross proceeds of approximately $13.3 million under the MLV Agreement and the Cantor Agreement, which we refer to collectively as the Sales Agreements in this prospectus supplement.
Except as otherwise indicated, all information in the prospectus supplement assumes no exercise by the underwriters of their overallotment option.

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 RISK FACTORS
An investment in our common stock involves a high degree of risk. Before deciding whether to invest in our common stock, you should consider carefully the risks described below and discussed under the section captioned “Risk Factors” contained in our Annual Report on Form 10-K for the year ended December 31, 2012, which is incorporated by reference in this prospectus supplement and the accompanying prospectus in its entirety, together with the other information in this prospectus supplement, the accompanying prospectus, the information and documents incorporated by reference and any free writing prospectus that we have authorized for use in connection with this offering. If any of these risks actually occurs, our business, financial condition, results of operations or cash flows could be seriously harmed. This could cause the trading price of our common stock to decline, resulting in a loss of all or part of your investment.
Risks Related to This Offering
Management will have broad discretion as to the use of the proceeds from this offering, and we may not use the proceeds effectively.
Our management will have broad discretion in the application of the net proceeds from this offering and could spend the proceeds in ways that do not improve our results of operations or enhance the value of our common stock. Our failure to apply these funds effectively could have a material adverse effect on our business, delay the development of our product candidates and cause the price of our common stock to decline.
If you purchase the common stock sold in this offering, you will experience immediate and substantial dilution in your investment. You will experience further dilution if we issue additional equity securities in future fundraising transactions.
Since the price per share of our common stock being offered is substantially higher than the net tangible book value per share of our common stock, you will suffer substantial dilution with respect to the net tangible book value of the common stock you purchase in this offering. Based on the public offering price of $4.20 per share and our net tangible book value as of December 31, 2012, if you purchase shares of common stock in this offering, you will suffer immediate and substantial dilution of $3.44 per share with respect to the net tangible book value of the common stock. See the section entitled “Dilution” below for a more detailed discussion of the dilution you will incur if you purchase common stock in this offering.
If we issue additional common stock, or securities convertible into or exchangeable or exercisable for common stock following the expiration or earlier waiver of the lock-up agreement we entered into with the underwriters as described in the section entitled “Underwriting,” including pursuant to the Sales Agreements, our stockholders, including investors who purchase shares of common stock in this offering, could experience additional dilution, and any such issuances may result in downward pressure on the price of our common stock.
 
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 FORWARD-LOOKING STATEMENTS
This prospectus supplement, the accompanying prospectus, the documents we have filed with the SEC that are incorporated by reference and any free writing prospectus that we have authorized for use in connection with this offering contain “forward-looking statements” within the meaning of Section 27A of the Securities Act of 1933, as amended, or the Securities Act, and Section 21E of the Securities Exchange Act of 1934, as amended, or the Exchange Act. These statements relate to future events or to our future operating or financial performance and involve known and unknown risks, uncertainties and other factors that may cause our actual results, performance or achievements to be materially different from any future results, performances or achievements expressed or implied by the forward-looking statements. Forward-looking statements may include, but are not limited to, statements about:
 
 	•	 	our ability to commercialize and achieve market acceptance of the INTERCEPT Blood System;	
 
 	•	 	the anticipated progress and successful completion of our research, development and clinical programs, and our ability to manage cost increases associated with pre-clinical and clinical development of the INTERCEPT Blood System;	
 
 	•	 	our ability to obtain and maintain regulatory approvals of the INTERCEPT Blood System;	
 
 	•	 	the ability of our products to inactivate pathogens that may emerge in the future;	
 
 	•	 	our ability to protect our intellectual property and operate our business without infringing upon the intellectual property rights of others;	
 
 	•	 	the use of proceeds from this offering; and	
 
 	•	 	our estimates regarding the sufficiency of our cash resources and our need for additional funding.	
In some cases, you can identify forward-looking statements by terms such as “may,” “will,” “should,” “could,” “would,” “expects,” “plans,” “anticipates,” “believes,” “estimates,” “projects,” “predicts,” “potential” and similar expressions intended to identify forward-looking statements. These statements reflect our current views with respect to future events, are based on assumptions and are subject to risks and uncertainties. Given these uncertainties, you should not place undue reliance on these forward-looking statements. We discuss many of these risks in greater detail under the heading “Risk Factors” on page S-4 of this prospectus supplement and in our Annual Report on Form 10-K for the year ended December 31, 2012, which is incorporated by reference in this prospectus supplement and the accompanying prospectus. Also, these forward-looking statements represent our estimates and assumptions only as of the date of the document containing the applicable statement.
You should read this prospectus supplement, the accompanying prospectus, the documents we have filed with the SEC that are incorporated by reference and any free writing prospectus that we have authorized for use in connection with this offering completely and with the understanding that our actual future results may be materially different from what we expect. We qualify all of the forward-looking statements in the foregoing documents by these cautionary statements.
Unless required by law, we undertake no obligation to update or revise any forward-looking statements to reflect new information or future events or developments. Thus, you should not assume that our silence over time means that actual events are bearing out as expressed or implied in such forward-looking statements.
 
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 USE OF PROCEEDS
We estimate that the net proceeds from the sale of the 8,333,333 shares of common stock that we are offering will be approximately $33.1 million, or approximately $38.0 million if the underwriters exercise in full their option to purchase up to 1,250,000 additional shares of common stock, after deducting the underwriting discount and estimated offering expenses payable by us.
We intend to use the net proceeds from this offering for clinical development and other research and development activities related to the INTERCEPT Blood System, preparatory activities for potential commercialization of the INTERCEPT Blood System in the United States and elsewhere, and for other general corporate purposes, including regulatory activity, selling, general and administrative expenses and working capital. In addition, we may use a portion of the net proceeds from this offering to prepay the remaining outstanding indebtedness under our growth capital loan with Comerica Bank, with any such repayment, and the timing thereof, at our discretion. Our loan and security agreement that we entered into with Comerica Bank on September 30, 2011, as amended on December 13, 2011 and June 30, 2012, provides for an aggregate borrowing of up to $12.0 million, comprised of a growth capital loan of $5.0 million and a formula based revolving line of credit of up to $7.0 million. In September 2011, we borrowed $5.0 million of the growth capital loan, of which $4.2 million principal amount remains outstanding as of the date of this prospectus supplement. Borrowings under the loan and security agreement are secured by all of our assets, except intellectual property, with the growth capital loan carrying a fixed interest rate of 6.37% with equal principal and interest payments under the growth capital loan scheduled until August 2015. Substantially all of the proceeds from the growth capital loan were used to repay our prior debt with Oxford Finance Corporation, with the reminder used for general corporate purposes. The amounts and timing of our use of the net proceeds from this offering will depend on a number of factors, such as the timing and progress of our research and development efforts, the timing and progress of any partnering and commercialization efforts, technological advances and the competitive environment for our products. As of the date of this prospectus supplement, we cannot specify with certainty all of the particular uses for the net proceeds to us from this offering. Accordingly, our management will have broad discretion in the application of these proceeds. Pending application of the net proceeds as described above, we intend to temporarily invest the proceeds in short-term, interest-bearing instruments.
 DIVIDEND POLICY
We have not declared or paid dividends on our common stock and do not intend to pay cash dividends on our common stock in the foreseeable future. Additionally, any cash dividends declared or paid would require prior written consent under the terms of our loan and security agreement with Comerica Bank.
 
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 DILUTION
Our net tangible book value as of December 31, 2012 was approximately $16.2 million, or $0.29 per share. Net tangible book value per share is determined by dividing our total tangible assets, less total liabilities, by the number of shares of our common stock outstanding as of December 31, 2012. Dilution with respect to net tangible book value per share represents the difference between the amount per share paid by purchasers of shares of common stock in this public offering and the net tangible book value per share of our common stock immediately after this public offering.
After giving effect to the sale of 8,333,333 shares of our common stock in this offering at the public offering price of $4.20 per share and after deducting the underwriting discount and estimated offering expenses payable by us, our as adjusted net tangible book value as of December 31, 2012 would have been approximately $49.3 million, or $0.76 per share. This represents an immediate increase in net tangible book value of $0.47 per share to existing stockholders and immediate dilution of $3.44 per share to investors purchasing our common stock in this offering at the public offering price. The following table illustrates this dilution on a per share basis:

Public offering price per share	  				  	$	4.20	  	
Net tangible book value per share of as December 31, 2012	  	$	  0.29	  	  				
Increase in net tangible book value per share attributable to investors purchasing our common stock in this offering	  	 	0.47	  	  				
	  	 	 	 	  				
As adjusted net tangible book value per share after this offering	  				  	 	0.76	  	
	  				  	 	 	 	
Dilution per share to investors purchasing our common stock in this offering	  				  	$	3.44	  	
	  				  	 	 	 	
If the underwriters exercise in full their option to purchase up to 1,250,000 additional shares of common stock, the as adjusted net tangible book value after this offering would be $0.82 per share, representing an increase in net tangible book value of $0.53 per share to existing stockholders and immediate dilution of $3.38 per share to investors purchasing our common stock in this offering at the public offering price.
The above discussion and table are based on 56,252,270 shares outstanding as of December 31, 2012, and exclude as of that date:
 
 	•	 	8,504,110 shares of common stock issuable upon the exercise of outstanding stock options with a weighted-average exercise price of $3.40 per share;	
 
 	•	 	2,400,000 shares of common stock issuable upon the exercise of outstanding warrants with an exercise price of $2.90 per share;	
 
 	•	 	3,679,127 shares of common stock issuable upon the exercise of outstanding warrants with an exercise price of $3.20 per share;	
 
 	•	 	53,973 shares of common stock issuable upon the vesting of outstanding restricted stock units; and	
 
 	•	 	up to an aggregate of 4,903,352 shares of common stock remaining available for future issuance under our 2008 Equity Incentive Plan and 1996 Employee Stock Purchase Plan.	
In addition, the discussion and table above exclude the up to approximately $25.6 million of shares of our common stock that remained available for sale at December 31, 2012 under the Sales Agreements. Between December 31, 2012 and the date of this prospectus supplement, we sold an aggregate of 3,755,423 shares of our common stock for gross proceeds of approximately $13.3 million under the Sales Agreements.
To the extent that outstanding options or warrants are exercised or other shares issued, including sales of our common stock pursuant to the Sales Agreements following the expiration or waiver of the lock-up agreement we entered into with the underwriters as described in the section entitled “Underwriting,” investors purchasing our common stock in this offering may experience further dilution. In addition, we may choose to raise additional capital due to market conditions or strategic considerations even if we believe we have sufficient funds for our current or future operating plans. To the extent that additional capital is raised through the sale of equity or convertible debt securities, the issuance of these securities could result in further dilution to our stockholders.
 
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 CERTAIN U.S. FEDERAL INCOME TAX CONSIDERATIONS FOR
NON-U.S. HOLDERS OF COMMON STOCK
The following is a discussion of certain U.S. federal income tax considerations to non-U.S. holders with respect to their ownership and disposition of our common stock issued pursuant to this offering (as defined below).
This discussion is based on current provisions of the Internal Revenue Code, U.S. Treasury Regulations promulgated under the Internal Revenue Code, judicial opinions, published positions of the Internal Revenue Service, or IRS, and all other applicable authorities, all of which are subject to change, possibly with retroactive effect. No ruling has been or will be sought from the IRS with respect to the matters discussed below, and there can be no assurance that the IRS will not take a contrary position or that any such contrary position would not be sustained by a court. This discussion assumes that the non-U.S. holder will hold our common stock as a capital asset (generally property held for investment).
This discussion does not address all aspects of U.S. federal income taxation or any aspects of alternative minimum, medicare contribution, estate, state, local, or non-U.S, taxation. It also does not consider any specific facts or circumstances that may apply to particular non-U.S. holders that may be subject to special treatment under the U.S. federal income tax laws, including, but not limited to:
 
 	•	 	insurance companies;	
 
 	•	 	tax-exempt organizations;	
 
 	•	 	financial institutions;	
 
 	•	 	regulated investment companies;	
 
 	•	 	tax-qualified retirement plans;	
 
 	•	 	brokers or dealers in securities;	
 
 	•	 	investors that hold our common stock as part of a straddle, hedge, conversion transaction, synthetic security or other integrated investment;	
 
 	•	 	controlled foreign corporations;	
 
 	•	 	passive foreign investment companies; and	
 
 	•	 	U.S. expatriates.	
For purposes of this discussion, the term “non-U.S. Holder” means a beneficial owner of our shares that is not a partnership (or entity or arrangement treated as a partnership for U.S. federal income tax purposes) and is not:
 
 	•	 	an individual who is a citizen or resident of the United States;	
 
 	•	 	a corporation created or organized in the United States or under the laws of the United States or of any state thereof or the District of Columbia;	
 
 	•	 	an estate, the income of which is subject to U.S. federal income tax regardless of its source; or	
 
 	•	 	a trust if (1) a U.S. court can exercise primary supervision over the trust’s administration and one or more U.S. persons have the authority to control all of the trust’s substantial decisions or (2) the trust has a valid election in effect under applicable U.S. Treasury Regulations to be treated as a U.S. person.	
If a partnership or any other entity or arrangement taxed as a partnership for U.S. federal income tax purposes is a beneficial owner of our common stock, the treatment of a partner in the partnership will generally depend upon the status of the equity owner of such partnership and the activities of the partnership. Accordingly, partnerships (and entities and arrangements taxed as partnerships) that hold our common stock and owners in such partnerships (or other entities or arrangements taxed as partnerships) are urged to consult their tax advisors regarding the specific U.S. federal income tax consequences to them of acquiring, owning or disposing of our common stock.
 
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PROSPECTIVE INVESTORS ARE URGED TO CONSULT THEIR TAX ADVISORS REGARDING THE PARTICULAR U.S. FEDERAL INCOME TAX CONSEQUENCES TO THEM OF ACQUIRING, OWNING AND DISPOSING OF SHARES OF OUR COMMON STOCK, AS WELL AS THE U.S. FEDERAL, STATE, LOCAL AND NON-U.S. INCOME AND OTHER TAX CONSIDERATIONS OF ACQUIRING, OWNING AND DISPOSING OF SHARES OF COMMON STOCK.
Distributions
We do not anticipate declaring or paying any cash distributions on our common stock in the foreseeable future. However, if we do make distributions on our common stock, those payments will constitute dividends for U.S. tax purposes to the extent paid from our current or accumulated earnings and profits, as determined under U.S. federal income tax principles. To the extent those distributions exceed our current and accumulated earnings and profits, they will constitute a return of capital and will first reduce the recipient’s adjusted tax basis in our common stock, but not below zero, and then will be treated as gain from the sale of stock as described below under the heading “Gain on Sale or Other Disposition of Common Stock.”
Dividends paid to a non-U.S. holder will be subject to U.S. federal withholding tax at a rate equal to 30 percent of the gross amount of the dividend, or a lower rate prescribed by an applicable income tax treaty, unless the dividends are effectively connected with a trade or business carried on by the non-U.S. holder within the United States (and, if required by an applicable income tax treaty, are attributable to a U.S. permanent establishment maintained by the non-U.S. holder). Under applicable Treasury Regulations, a non-U.S. holder will be required to satisfy certain certification requirements, generally on IRS Form W-8BEN (or applicable successor form), directly or through an intermediary, in order to claim a reduced rate of withholding under an applicable income tax treaty. If tax is withheld in an amount in excess of the amount prescribed by an applicable income tax treaty, a refund of the excess amount may be obtained by the non-U.S. holder by timely filing an appropriate claim for refund with the IRS.
Dividends that are effectively connected with such a U.S. trade or business (and, if required by an applicable income tax treaty, are attributable to a U.S. permanent establishment maintained by the recipient) will not be subject to U.S. withholding tax if the non-U.S. holder files the required forms, generally an IRS Form W-8ECI (or applicable successor form), with the payor of the dividend, but instead will be subject to U.S. federal income tax on a net income basis in the same manner as if the non-U.S. holder were a resident of the United States. A foreign corporation that receives dividends constituting effectively connected income may, under certain circumstances, be subject to an additional branch profits tax at a rate of 30 percent, or a lower rate prescribed by an applicable income tax treaty, with respect to such effectively connected income.
Gain on Sale or Other Disposition of Common Stock
A non-U.S. holder will not be subject to U.S. federal income tax on any gain realized upon the sale or other taxable disposition of the non-U.S. holder’s shares of common stock unless:
 
 	•	 	the gain is effectively connected with a trade or business carried on by the non-U.S. holder within the United States (and, if required by an applicable tax treaty, is attributable to a U.S. permanent establishment or a fixed base maintained by the non-U.S. holder), in which case the non-U.S. holder generally will be required to pay tax on the net gain derived from the sale under regular graduated U.S. federal income tax rates and, if the non-U.S. holder is a corporation, the branch profits tax may apply, at a 30 percent rate or such lower rate as may be specified by an applicable income tax treaty;	
 
 	•	 	the non-U.S. holder is a nonresident alien individual who is present in the United States for 183 days or more in the taxable year of disposition (and is not otherwise treated as a U.S. resident alien for U.S. federal income tax purposes) and certain other conditions are met, in which case the non-U.S. holder will be required to pay a flat 30 percent tax (or such lower rate as may be specified by an applicable income tax treaty between the United States and such non-U.S. holder’s country of residence) on the	
 
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 	net gain derived from the disposition, which tax may be offset by U.S. source capital losses, if any, provided that the non-U.S. holder has timely filed U.S. federal income tax returns with respect to such losses; or	
 
 	•	 	our common stock constitutes a U.S. real property interest by reason of our status as a “United States real property holding corporation,” or USRPHC, for U.S. federal income tax purposes at any time within the shorter of the five-year period preceding the disposition or the non-U.S. holder’s holding period for our common stock.	
We believe that we are not currently and will not become a USRPHC. However, because the determination of whether we are a USRPHC depends on the fair market value of our U.S. real property relative to the fair market value of our other business assets, there can be no assurance that we will not become a USRPHC in the future. Even if we become a USRPHC, however, as long as our common stock is regularly traded on an established securities market, such common stock will be treated as U.S. real property interests only if the non-U.S. holder actually or constructively held more than five percent of our common stock at any time during the shorter of the five-year period preceding the disposition or the non-U.S. holder’s holding period for our common stock.
Information Reporting and Backup Withholding
We must report annually to the IRS and to each non-U.S. holder the amount of dividends on our common stock, the name and address of the recipient and the amount, if any, of tax withheld. These information reporting requirements apply even if withholding was not required because the dividends were effectively connected dividends or withholding was reduced by an applicable income tax treaty. Under tax treaties or other agreements, the IRS may make its reports available to tax authorities in the country in which the non-U.S. holder resides or is established.
Dividend payments made to a non-U.S. holder that is not an exempt recipient generally will be subject to backup withholding at the then applicable rate (currently 28 percent) unless the non-U.S. holder certifies as to its foreign status, which certification may be made by providing the Company with an IRS Form W-8BEN or IRS Form W-8ECI, as applicable, and certain other requirements are met. Notwithstanding the foregoing, backup withholding may apply if either we or our paying agent has actual knowledge, or reason to know, that the holder is a U.S. person that is not an exempt recipient.
Proceeds from the sale or other disposition of common stock by a non-U.S. Holder effected by or through a U.S. office of a broker will generally be subject to information reporting and backup withholding, currently at a rate of 28 percent unless the non-U.S. Holder certifies to the payor under penalties of perjury as to, among other things, its name, address and status as a non-U.S. Holder or otherwise esablishes an exemption. Payment of disposition proceeds effected outside the United States by or through a non-U.S. office of a non-U.S. broker generally will not be subject to information reporting or backup withholding if the payment is not received in the United States. Information reporting, but generally not backup withholding, will apply to such a payment if the broker has certain connections with the United States unless the broker has documentary evidence in its records that the beneficial owner thereof is a non-U.S. Holder and specified conditions are met or an exemption is otherwise established.
Backup withholding is not an additional tax. Rather, the amount of tax withheld is applied to the U.S. federal income tax liability of persons subject to backup withholding. If backup withholding results in an overpayment of U.S. federal income taxes, a refund may be obtained, provided the required documents are timely filed with the IRS.
Foreign Accounts
The Internal Revenue Code generally will impose a U.S. federal withholding tax of 30 percent on dividends and the gross proceeds of a disposition of our common stock paid to a “foreign financial institution” (as
 
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specifically defined for this purpose) unless such institution enters into an agreement with the U.S. government to, among other things, withhold on certain payments and to collect and provide to the U.S. tax authorities substantial information regarding U.S. account holders of such institution (which includes certain equity and debt holders of such institution, as well as certain account holders that are foreign entities with U.S. owners). A U.S. federal withholding tax of 30 percent also applies to dividends and the gross proceeds of a disposition of our common stock to a non-financial foreign entity unless such entity provides the withholding agent with either a certification that it does not have any substantial direct or indirect U.S. owners or provides information regarding direct and indirect U.S. owners of the entity. The withholding provisions described above will generally apply to dividends on our common stock paid on or after January 1, 2014 and with respect to gross proceeds of a sale or other disposition of our common stock on or after January 1, 2017. Under certain circumstances, a non-U.S. holder might be eligible for refunds or credits of such taxes.
 
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 UNDERWRITING
We and the underwriters for the offering named below have entered into an underwriting agreement with respect to the common stock being offered. Subject to the terms and conditions of the underwriting agreement, each underwriter has severally agreed to purchase from us the number of shares of our common stock set forth opposite its name below. Cowen and Company, LLC is the representative of the underwriters.

Underwriter	  	Number
of Shares	 	
Cowen and Company, LLC	  	 	5,000,000	  	
Robert W. Baird & Co. Incorporated	  	 	1,458,333	  	
Wedbush Securities Inc	  	 	1,041,667	  	
Lazard Capital Markets LLC	  	 	833,333	  	
	  	 	 	 	
Total	  	 	8,333,333	  	
	  	 	 	 	
The underwriting agreement provides that the obligations of the underwriters are subject to certain conditions precedent and that the underwriters have agreed, severally and not jointly, to purchase all of the shares sold under the underwriting agreement if any of these shares are purchased, other than those shares covered by the overallotment option described below. If an underwriter defaults, the underwriting agreement provides that the purchase commitments of the non-defaulting underwriters may be increased or the underwriting agreement may be terminated.
We have agreed to indemnify the underwriters against specified liabilities, including liabilities under the Securities Act, and to contribute to payments the underwriters may be required to make in respect thereof.
The underwriters are offering the shares, subject to prior sale, when, as and if issued to and accepted by them, subject to approval of legal matters by their counsel and other conditions specified in the underwriting agreement. The underwriters reserve the right to withdraw, cancel or modify offers to the public and to reject orders in whole or in part.
Overallotment option to purchase additional shares.  We have granted to the underwriters an option to purchase up to 1,250,000 additional shares of common stock at the public offering price, less the underwriting discount. This option is exercisable for a period of 30 days. The underwriters may exercise this option solely for the purpose of covering overallotments, if any, made in connection with the sale of common stock offered hereby. To the extent that the underwriters exercise this option, the underwriters will purchase additional shares from us in approximately the same proportion as shown in the table above.
Discounts and commissions.  The following table shows the public offering price, underwriting discount and proceeds, before expenses, to us. These amounts are shown assuming both no exercise and full exercise of the underwriters’ option to purchase additional shares.
We estimate that the total expenses of the offering, excluding the underwriting discount, will be approximately $455,000 and are payable by us.

 	  	Per Share	 	  	Total	 	
 	  			  	Without
Overallotment	 	  	With
Overallotment	 	
Public offering price	  	$	4.200	 	  	$	34,999,999	 	  	$	40,249,999	 	
Underwriting discount from 3,833,333 shares offered to the public	  	 	0.084	  	  	 	322,000	  	  	 	322,000	  	
Proceeds, before expenses, to us from 3,833,333 shares offered to the public	  	 	4.116	  	  	 	15,777,999	  	  	 	15,777,999	  	
Underwriting discount from remaining shares offered to the public	  	 	0.252	  	  	 	1,134,000	  	  	 	1,449,000	  	
Proceeds, before expenses, to us from remaining shares offered to the public	  	 	3.948	  	  	 	17,766,000	  	  	 	22,701,000	  	
Total proceeds, before expenses, to us from all shares offered to the public	  				  	 	33,543,999	  	  	 	38,478,999	  	
 
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The underwriters propose to offer the shares of common stock to the public at the public offering price set forth on the cover of this prospectus supplement. The underwriters may offer the shares of common stock referenced in the table above to securities dealers at the public offering price less, in the case of the 3,833,333 shares purchased from us and referenced in the table above, a concession not in excess of $0.0504 per share, and in the case of the remaining shares of common stock purchased from us, a concession not in excess of 0.1512 per share. If all of the shares are not sold at the public offering price, the underwriters may change the offering price and other selling terms.
Blueprint Life Science Group, LLC and MLV & Co. LLC acted as our financial advisors in connection with the offering. The estimated expenses of this offering include the fees for services rendered as our financial advisor in connection with this offering. Lazard Frères & Co. LLC referred this transaction to Lazard Capital Markets LLC and will receive a referral fee from Lazard Capital Markets LLC in connection therewith.
Discretionary accounts.  The underwriters do not intend to confirm sales of the shares to any accounts over which they have discretionary authority.
Stabilization.  In connection with this offering, the underwriters may engage in stabilizing transactions, overallotment transactions, syndicate covering transactions, penalty bids and purchases to cover positions created by short sales.
 
 	•	 	Stabilizing transactions permit bids to purchase shares of common stock so long as the stabilizing bids do not exceed a specified maximum, and are engaged in for the purpose of preventing or retarding a decline in the market price of the common stock while the offering is in progress.	
 
 	•	 	Overallotment transactions involve sales by the underwriters of shares of common stock in excess of the number of shares the underwriters are obligated to purchase. This creates a syndicate short position which may be either a covered short position or a naked short position. In a covered short position, the number of shares over-allotted by the underwriters is not greater than the number of shares that they may purchase in the overallotment option. In a naked short position, the number of shares involved is greater than the number of shares in the overallotment option. The underwriters may close out any short position by exercising their overallotment option and/or purchasing shares in the open market.	
 
 	•	 	Syndicate covering transactions involve purchases of common stock in the open market after the distribution has been completed in order to cover syndicate short positions. In determining the source of shares to close out the short position, the underwriters will consider, among other things, the price of shares available for purchase in the open market as compared with the price at which they may purchase shares through exercise of the overallotment option. If the underwriters sell more shares than could be covered by exercise of the overallotment option and, therefore, have a naked short position, the position can be closed out only by buying shares in the open market. A naked short position is more likely to be created if the underwriters are concerned that after pricing there could be downward pressure on the price of the shares in the open market that could adversely affect investors who purchase in the offering.	
Penalty bids permit the representative to reclaim a selling concession from a syndicate member when the common stock originally sold by that syndicate member is purchased in stabilizing or syndicate covering transactions to cover syndicate short positions.
These stabilizing transactions, syndicate covering transactions and penalty bids may have the effect of raising or maintaining the market price of our common stock or preventing or retarding a decline in the market price of our common stock. As a result, the price of our common stock in the open market may be higher than it would otherwise be in the absence of these transactions. Neither we nor the underwriters make any representation or prediction as to the effect that the transactions described above may have on the price of our common stock. These transactions may be effected on The NASDAQ Global Market, in the over-the-counter market or otherwise and, if commenced, may be discontinued at any time.
 
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Passive market making.  In connection with this offering, underwriters and selling group members may engage in passive market making transactions in our common stock on The NASDAQ Global Market in accordance with Rule 103 of Regulation M under the Exchange Act during a period before the commencement of offers or sales of common stock and extending through the completion of the distribution. A passive market maker must display its bid at a price not in excess of the highest independent bid of that security. However, if all independent bids are lowered below the passive market maker’s bid, that bid must then be lowered when specified purchase limits are exceeded.
Lock-up agreements.  Pursuant to certain “lock-up” agreements, we and our executive officers and directors, have agreed, subject to certain exceptions, not to offer, sell, assign, transfer, pledge, contract to sell, or otherwise dispose of or announce the intention to otherwise dispose of, or enter into any swap, hedge or similar agreement or arrangement that transfers, in whole or in part, the economic consequence of ownership of, directly or indirectly, or make any demand or request or exercise any right with respect to the registration of, or file with the SEC a registration statement under the Securities Act relating to, any common stock or securities convertible into or exchangeable or exercisable for any common stock without the prior written consent of Cowen and Company, LLC for a period of 90 days after the date of the pricing of the offering. Notwithstanding the foregoing, if either (i) during the last 17 days of the 90-day restricted period we issue an earnings release or material news or a material event relating to us occurs or (ii) prior to the expiration of the 90-day restricted period, we announce that we will release earnings results during the 16-day period beginning on the last day of the 90-day restricted period, the restrictions described above will continue to apply until the expiration of the 18-day period beginning on the issuance of the earnings release or the public announcement of the material news or the occurrence of the material event, as applicable, unless (i) we meet certain requirements of NASD Rule 2711(f)(4) and the applicable rules under the Securities Act or (ii) Cowen and Company, LLC waives, in writing, such extension.
This lock-up provision applies to common stock and to securities convertible into or exchangeable or exercisable for common stock. It also applies to common stock owned now or acquired later by the person executing the agreement or for which the person executing the agreement later acquires the power of disposition. The exceptions to the lock-up for executive officers and directors are: (a) transactions relating to shares of common stock or other securities acquired in open market transactions after the date of the underwriting agreement related to this offering; (b) the transfer of shares of common stock or any securities convertible into or exercisable or exchangeable for common stock (i) as a bona fide gift to the spouse, domestic partner, parent, sibling, child, grandchild or other lineal descendant of the executive officer or director or to a trust formed for the benefit of any such immediate family member, (ii) by will or intestate succession or (iii) by bona fide gift to a charity or educational institution; (c) the transfer of shares of common stock to us to cover tax withholding obligations or to effect a net exercise or cashless exercise of equity awards; (d) the establishment of a trading plan pursuant to Rule 10b5-1 under the Exchange Act for the transfer of shares of common stock, provided that the shares subject to such plan shall be subject to the lock-up restrictions; and (e) the transfer of shares of common stock or any securities convertible into or exercisable or exchangeable for common stock pursuant to the conversion or sale of, or an offer to purchase, all or substantially all of our outstanding common stock; each of which is subject to certain conditions set forth in the lock-up agreements with the executive officers and directors. The exceptions to the lock-up for us are: (a) our sale of shares in this offering; (b) the issuance of common stock or any securities convertible into or exercisable or exchangeable for common stock pursuant to our equity compensation plans currently in existence; (c) the issuance of common stock pursuant to the exercise or conversion of outstanding securities or other rights; or (d) the issuance of common stock in connection with a strategic partnership, joint venture, collaboration or acquisition or license of any business products or technology; in each case subject to certain conditions as set forth in the underwriting agreement. In addition the lock-up for us does not prevent us from filing any registration statement on Form S-8 in respect of any equity compensation plans or arrangements maintained by us or that we may be required to file pursuant to our stockholder rights agreement, or rights agreement, or under applicable law with respect to the rights issuable under the rights agreement and the securities issuable upon exercise or exchange of these rights. Finally, the lock-up for us does not prohibit us from keeping in effect the Sales Agreements, provided that no sales of our common stock under the Sales Agreements may be made during the 90-day restricted period.
 
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United Kingdom.  Each of the underwriters has represented and agreed that:
 
 	•	 	it has not made or will not make an offer of the securities to the public in the United Kingdom within the meaning of section 102B of the Financial Services and Markets Act 2000 (as amended), or the FSMA, except to legal entities which are authorized or regulated to operate in the financial markets or, if not so authorized or regulated, whose corporate purpose is solely to invest in securities or otherwise in circumstances which do not require the publication by us of a prospectus pursuant to the Prospectus Rules of the Financial Services Authority, or FSA;	
 
 	•	 	it has only communicated or caused to be communicated and will only communicate or cause to be communicated an invitation or inducement to engage in investment activity (within the meaning of section 21 of FSMA) to persons who have professional experience in matters relating to investments falling within Article 19(5) of the Financial Services and Markets Act 2000 (Financial Promotion) Order 2005 or in circumstances in which section 21 of FSMA does not apply to us; and	
 
 	•	 	it has complied with and will comply with all applicable provisions of FSMA with respect to anything done by it in relation to the securities in, from or otherwise involving the United Kingdom.	
Switzerland.  The securities will not be offered, directly or indirectly, to the public in Switzerland and this prospectus does not constitute a public offering prospectus as that term is understood pursuant to article 652a or 1156 of the Swiss Federal Code of Obligations.
European Economic Area.  In relation to each Member State of the European Economic Area (Iceland, Norway and Lichtenstein in addition to the member states of the European Union) that has implemented the Prospectus Directive (each, a Relevant Member State), each underwriter has represented and agreed that with effect from and including the date on which the Prospectus Directive is implemented in that Relevant Member State, or the Relevant Implementation Date, it has not made and will not make an offer of the securities to the public in that Relevant Member State prior to the publication of a prospectus in relation to the securities that has been approved by the competent authority in that Relevant Member State or, where appropriate, approved in another Relevant Member State and notified to the competent authority in that Relevant Member State, all in accordance with the Prospectus Directive, except that it may, with effect from and including the Relevant Implementation Date, make an offer of the securities to the public in that Relevant Member State at any time:
 
 	•	 	to legal entities which are authorized or regulated to operate in the financial markets or, if not so authorized or regulated, whose corporate purpose is solely to invest in securities;	
 
 	•	 	to any legal entity which has two or more of (1) an average of at least 250 employees during the last financial year; (2) a total balance sheet of more than €43,000,000 and (3) an annual net turnover of more than €50,000,000, as shown in its last annual or consolidated accounts; and	
 
 	•	 	in any other circumstances which do not require the publication by the issuer of a prospectus pursuant to Article 3 of the Prospectus Directive.	
Each person in a Relevant Member State who receives any communication in respect of, or who acquires any securities under, the offer contemplated in this prospectus will be deemed to have represented, warranted and agreed to and with us and each underwriter that:
 
 	•	 	it is a qualified investor within the meaning of the law in that Relevant Member State implementing Article 2(1)(e) of the Prospectus Directive; and	
 
 	•	 	in the case of any securities acquired by it as a financial intermediary, as that term is used in Article 3(2) of the Prospectus Directive, (1) the securities acquired by it in the offer have not been acquired on behalf of, nor have they been acquired with a view to their offer or resale to, persons in any Relevant Member State other than qualified investors, as that term is defined in the Prospectus Directive, or in circumstances in which the prior consent of the representative of the underwriters has been given to the offer or resale; or (2) where securities have been acquired by it on behalf of persons in any Relevant Member State other than qualified investors, the offer of those securities to it is not treated under the Prospectus Directive as having been made to such persons.	
 
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For the purposes of the provisions in the two immediately preceding paragraphs, the expression an “offer of the securities to the public” in relation to the securities in any Relevant Member State means the communication in any form and by any means of sufficient information on the terms of the offer and the securities to be offered so as to enable an investor to decide to purchase or subscribe for the securities, as the same may be varied in that Relevant Member State by any measure implementing the Prospectus Directive in that Relevant Member State, and the expression “Prospectus Directive” means Directive 2003/71/EC and includes any relevant implementing measure in each Relevant Member State.
Electronic offer, sale and distribution of shares.  A prospectus in electronic format may be made available on the websites maintained by one or more of the underwriters or selling group members, if any, participating in this offering and one or more of the underwriters participating in this offering may distribute prospectuses electronically. The representative may agree to allocate a number of shares to underwriters and selling group members for sale to their online brokerage account holders. Internet distributions will be allocated by the underwriters and selling group members that will make internet distributions on the same basis as other allocations. Other than the prospectus in electronic format, the information on these websites is not part of this prospectus supplement, the accompanying prospectus or the registration statement of which this prospectus supplement and the accompanying prospectus forms a part, has not been approved or endorsed by us or any underwriter in its capacity as underwriter, and should not be relied upon by investors.
Other relationships.  Certain of the underwriters and their affiliates have provided, and may in the future provide, various investment banking, commercial banking and other financial services for us and our affiliates for which they have received, and may in the future receive, customary fees.
 
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 LEGAL MATTERS
The validity of the common stock offered by this prospectus supplement and the accompanying prospectus will be passed upon for us by Cooley LLP, Palo Alto and San Diego, California. Goodwin Procter LLP, New York, New York, is counsel for the underwriters in connection with this offering.
 EXPERTS
Ernst & Young LLP, independent registered public accounting firm, has audited our consolidated financial statements included in our Annual Report on Form 10-K for the year ended December 31, 2012, and the effectiveness of our internal control over financial reporting as of December 31, 2012, as set forth in their reports, which are incorporated by reference in this prospectus and elsewhere in the registration statement. Our financial statements are incorporated by reference in reliance on Ernst  & Young LLP’s report, given on their authority as experts in accounting and auditing.
 WHERE YOU CAN FIND MORE INFORMATION
This prospectus supplement and the accompanying prospectus are part of the registration statement on Form S-3 we filed with the SEC under the Securities Act and do not contain all the information set forth or incorporated by reference in the registration statement. Whenever a reference is made in this prospectus supplement or the accompanying prospectus to any of our contracts, agreements or other documents, the reference may not be complete and you should refer to the exhibits that are a part of the registration statement or the exhibits to the reports or other documents incorporated by reference in this prospectus supplement and the accompanying prospectus for a copy of such contract, agreement or other document. Because we are subject to the information and reporting requirements of the Exchange Act, we file annual, quarterly and current reports, proxy statements and other information with the SEC. Our SEC filings are available to the public over the Internet at the SEC’s website at http://www.sec.gov. You may also read and copy any document we file at the SEC’s Public Reference Room at 100 F Street, N.E., Washington, D.C. 20549. Please call the SEC at 1-800-SEC-0330 for further information on the operation of the Public Reference Room.
 INCORPORATION OF CERTAIN INFORMATION BY REFERENCE
The SEC allows us to “incorporate by reference” information from other documents that we file with them, which means that we can disclose important information to you by referring you to those documents. The information incorporated by reference is considered to be part of this prospectus supplement and the accompanying prospectus. Information contained in this prospectus supplement and the accompanying prospectus and information that we file with the SEC in the future and incorporate by reference in this prospectus supplement and the accompanying prospectus will automatically update and supersede this information. We incorporate by reference the documents listed below and any future filings (other than Current Reports on Form 8-K furnished under Item 2.02 or Item 7.01 and exhibits filed on such form that are related to such items) we make with the SEC under Sections 13(a), 13(c), 14 or 15(d) of the Exchange Act after the date of the prospectus supplement and before the sale of all the securities covered by this prospectus supplement (SEC File No. 000-21937):
 
 	•	 	our Annual Report on Form 10-K for the year ended December 31, 2012 filed with the SEC on March 12, 2013;	
 
 	•	 	our Current Report on Form 8-K filed with the SEC on January 17, 2013;	
 
 	•	 	the description of our common stock in our registration statement on Form 8-A filed with the SEC on January 8, 1997, including all amendments and reports filed for the purpose of updating such description; and	
 
 	•	 	the description of our preferred share purchase rights in our registration statement on Form 8-A filed with the SEC on October 30, 2009, including all amendments and reports filed for the purpose of updating such description.	
 
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You can request a copy of these filings, at no cost, by writing or telephoning us at the following address or telephone number:
Cerus Corporation
2550 Stanwell Drive
Concord, CA 94520
(925) 288-6000
Attention: Investor Relations
 
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Prospectus

$150,000,000
Common Stock
Preferred Stock
Debt Securities
Warrants

From time to time, we may offer and sell up to $150,000,000 of any combination of the securities described in this prospectus, either individually or in combination with other securities. We may also offer common stock or preferred stock upon conversion of debt securities, common stock upon conversion of preferred stock, or common stock, preferred stock or debt securities upon the exercise of warrants.
We will provide the specific terms of these offerings and securities in one or more supplements to this prospectus. We may also authorize one or more free writing prospectuses to be provided to you in connection with these offerings. The prospectus supplement and any related free writing prospectus may also add, update or change information contained in this prospectus. You should carefully read this prospectus, the applicable prospectus supplement and any related free writing prospectus, as well as any documents incorporated by reference, before buying any of the securities being offered.
Our common stock is listed on The NASDAQ Global Market under the trading symbol “CERS.” On January 9, 2012, the last reported sale price of our common stock was $2.87 per share. The applicable prospectus supplement will contain information, where applicable, as to other listings, if any, on The NASDAQ Global Market or other securities exchange of the securities covered by the prospectus supplement.
Investing in our securities involves a high degree of risk. You should review carefully the risks and uncertainties described under the heading “ Risk Factors ” contained in the applicable prospectus supplement and in any free writing prospectuses we have authorized for use in connection with a specific offering, and under similar headings in the documents that are incorporated by reference into this prospectus.
This prospectus may not be used to consummate a sale of securities unless accompanied by a prospectus supplement.
The securities may be sold directly by us to investors, through agents designated from time to time or to or through underwriters or dealers, on a continuous or delayed basis. For additional information on the methods of sale, you should refer to the section entitled “Plan of Distribution” in this prospectus. If any agents or underwriters are involved in the sale of any securities with respect to which this prospectus is being delivered, the names of such agents or underwriters and any applicable fees, commissions, discounts and over-allotment options will be set forth in a prospectus supplement. The price to the public of such securities and the net proceeds we expect to receive from such sale will also be set forth in a prospectus supplement.
Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or determined if this prospectus is truthful or complete. Any representation to the contrary is a criminal offense.

The date of this prospectus is January 10, 2012.

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 TABLE OF CONTENTS

ABOUT THIS PROSPECTUS	  	 	i	  	
PROSPECTUS SUMMARY	  	 	1	  	
RISK FACTORS	  	 	6	  	
FORWARD-LOOKING STATEMENTS	  	 	6	  	
FINANCIAL RATIOS	  	 	7	  	
USE OF PROCEEDS	  	 	7	  	
DESCRIPTION OF CAPITAL STOCK	  	 	8	  	
DESCRIPTION OF DEBT SECURITIES	  	 	13	  	
DESCRIPTION OF WARRANTS	  	 	20	  	
LEGAL OWNERSHIP OF SECURITIES	  	 	22	  	
PLAN OF DISTRIBUTION	  	 	25	  	
LEGAL MATTERS	  	 	27	  	
EXPERTS	  	 	27	  	
WHERE YOU CAN FIND MORE INFORMATION	  	 	27	  	
INCORPORATION BY CERTAIN INFORMATION BY REFERENCE	  	 	28	  	

 ABOUT THIS PROSPECTUS
This prospectus is part of a registration statement on Form S-3 that we filed with the Securities and Exchange Commission, or SEC, utilizing a “shelf” registration process. Under this shelf registration process, we may offer and sell shares of our common stock and preferred stock, various series of debt securities and/or warrants to purchase any of such securities, either individually or in combination with other securities, in one or more offerings, up to a total dollar amount of $150,000,000. This prospectus provides you with a general description of the securities we may offer.
Each time we offer securities under this prospectus, we will provide a prospectus supplement that will contain more specific information about the terms of that offering. We may also authorize one or more free writing prospectuses to be provided to you that may contain material information relating to these offerings. The prospectus supplement and any related free writing prospectus that we may authorize to be provided to you may also add, update or change any of the information contained in this prospectus or in the documents that we have incorporated by reference into this prospectus. We urge you to read carefully this prospectus, any applicable prospectus supplement and any free writing prospectuses we have authorized for use in connection with a specific offering, together with the information incorporated herein by reference as described under the heading “Incorporation of Certain Information by Reference,” before buying any of the securities being offered.
This prospectus may not be used to consummate a sale of securities unless it is accompanied by a prospectus supplement.
You should rely only on the information contained in, or incorporated by reference into, this prospectus and any applicable prospectus supplement, along with the information contained in any free writing prospectuses we have authorized for use in connection with a specific offering. We have not authorized anyone to provide you with different or additional information. This prospectus is an offer to sell only the securities offered hereby, but only under circumstances and in jurisdictions where it is lawful to do so.
 
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The information appearing in this prospectus, any applicable prospectus supplement or any related free writing prospectus is accurate only as of the date on the front of the document and that any information we have incorporated by reference is accurate only as of the date of the document incorporated by reference, regardless of the time of delivery of this prospectus, any applicable prospectus supplement or any related free writing prospectus, or any sale of a security. Our business, financial condition, results of operations and prospects may have changed since those dates.
This prospectus contains summaries of certain provisions contained in some of the documents described herein, but reference is made to the actual documents for complete information. All of the summaries are qualified in their entirety by the actual documents. Copies of some of the documents referred to herein have been filed, will be filed or will be incorporated by reference as exhibits to the registration statement of which this prospectus is a part, and you may obtain copies of those documents as described below under the section entitled “Where You Can Find More Information.”
 
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 PROSPECTUS SUMMARY
This summary highlights selected information contained elsewhere in this prospectus or incorporated by reference in this prospectus, and does not contain all of the information that you need to consider in making your investment decision. You should carefully read the entire prospectus, the applicable prospectus supplement and any related free writing prospectus, including the risks of investing in our securities discussed under the heading “Risk Factors” contained in the applicable prospectus supplement and any related free writing prospectus, and under similar headings in the other documents that are incorporated by reference into this prospectus. You should also carefully read the information incorporated by reference into this prospectus, including our financial statements, and the exhibits to the registration statement of which this prospectus is a part.
Cerus Corporation
Overview
We are a biomedical products company focused on commercializing the INTERCEPT Blood System, or INTERCEPT system, to enhance blood safety. The INTERCEPT system is designed to inactivate blood-borne pathogens in donated blood components intended for transfusion.
We have worldwide commercial rights for the INTERCEPT Blood System for platelets, plasma and red blood cells. We currently market and sell the INTERCEPT system for both platelets and plasma in a number of countries in Europe, the Commonwealth of Independent States, the Middle East and selected countries in other regions outside of the United States using our direct sales force or through distributors. The INTERCEPT platelet and plasma systems have both received CE mark approval. We are prioritizing the commercialization of the INTERCEPT Blood System for platelets and plasma in these countries and regions. Subject to the availability of adequate funding from partners, government grants and/or capital markets, we intend to complete development activities for the red blood cell system necessary for regulatory approval in Europe and we may seek regulatory approval of our products in the United States.
To date, the product revenues that we recognize from the sale of our platelet and plasma systems have been less than our combined product and operating costs. We expect to continue to generate substantial losses, at least until our platelet and plasma systems gain broader commercial acceptance than they currently have. Our ability to achieve a profitable level of operations in the future will depend on our ability to successfully commercialize and achieve market acceptance of our blood safety products. We may never achieve a profitable level of operations.
Risks Associated with our Business
Our business is subject to numerous risks, as described under the heading “Risk Factors” contained in the applicable prospectus supplement and in any free writing prospectuses we have authorized for use in connection with a specific offering, and under similar headings in the documents that are incorporated by reference into this prospectus. These risks include the following, among others:
 
 	•	 	The INTERCEPT Blood System may not achieve broad market acceptance.	
 
 	•	 	Our products, blood products treated with the INTERCEPT Blood System and we are subject to extensive regulation by domestic and foreign authorities. If our preclinical and clinical data are not considered sufficient by a country’s regulatory authorities to grant marketing approval, we will be unable to commercialize our products and generate revenue in that country. Our red blood cell system requires extensive additional testing and development.	
 
 	•	 	We have limited experience operating a global commercial organization. We rely on third parties to market, sell, distribute and maintain our products and to maintain customer relationships in certain countries.	

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 	•	 	Our product design and manufacturing supply chain is highly technical and exposes us to significant risks.	
 
 	•	 	The INTERCEPT platelet system is not compatible with some commercial platelet collection methods.	
 
 	•	 	We have used prototype components in our preclinical studies and clinical trials of the INTERCEPT red blood cell system and have not completed the components’ commercial design. We will be required to identify and enter into agreements with third parties to manufacture the red blood cell system.	
 
 	•	 	If our competitors develop superior products to ours or market their products more effectively than we market our products, our commercial opportunities could be reduced or eliminated.	
 
 	•	 	We may be liable and we may need to withdraw our products from the market if our products harm people. We may be liable if an accident occurs in our controlled use of hazardous materials. Our insurance coverage may be inadequate to offset losses we may incur.	
 
 	•	 	If we fail to obtain the capital necessary to fund our future operations or if we are unable to generate positive cash flows from our operations, we will need to curtail planned development or sales and commercialization activities.	
 
 	•	 	We have only a limited operating history, and we expect to continue to generate losses.	
 
 	•	 	Virtually all of our research and development activities and the significant majority of our general and administrative activities are performed in or managed from a single site that may be subject to lengthy business interruption in the event of a severe earthquake. We also may suffer loss of computerized information and may be unable to make timely filings with regulatory agencies in the event of catastrophic failure of our data storage and backup systems.	
 
 	•	 	We may not be able to protect our intellectual property or operate our business without infringing the intellectual property rights of others.	
 
 	•	 	As our international operations grow, we may be subject to adverse fluctuations in exchange rates between the United States dollar and foreign currencies. Consequently, we may suffer losses.	
Company Information
We were incorporated in California in 1991 and reincorporated in Delaware in 1996. Our corporate address is 2550 Stanwell Drive, Concord, California 94520, and our telephone number is (925) 288-6000. Our website address is www.cerus.com . Information found on, or accessible through, our website is not a part of, and is not incorporated into, this prospectus, and you should not consider it part of this prospectus or part of any prospectus supplement. Our website address is included in this document as an inactive textual reference only.
Unless the context indicates otherwise, as used in this prospectus, the terms “Cerus,” “Cerus Corporation,” “we,” “us” and “our” refer to Cerus Corporation, a Delaware corporation, and its wholly-owned subsidiary, Cerus Europe B.V. Cerus, INTERCEPT and INTERCEPT Blood System are U.S. registered trademarks of Cerus Corporation. All other trademarks or trade names referred to in this prospectus and any prospectus supplement are the property of their respective owners.
The Securities We May Offer
We may offer shares of our common stock and preferred stock, various series of debt securities and/or warrants to purchase any of such securities, either individually or in combination with other securities, with

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a total value of up to $150,000,000 from time to time under this prospectus, together with any applicable prospectus supplement and any related free writing prospectus, at prices and on terms to be determined by market conditions at the time of any offering. This prospectus provides you with a general description of the securities we may offer. Each time we offer a type or series of securities under this prospectus, we will provide a prospectus supplement that will describe the specific amounts, prices and other important terms of the securities, including, to the extent applicable:
 
 	•	 	designation or classification;	
 
 	•	 	aggregate principal amount or aggregate offering price;	
 
 	•	 	maturity date, if applicable;	
 
 	•	 	original issue discount, if any;	
 
 	•	 	rates and times of payment of interest or dividends, if any;	
 
 	•	 	redemption, conversion, exercise, exchange or sinking fund terms, if any;	
 
 	•	 	ranking;	
 
 	•	 	restrictive covenants, if any;	
 
 	•	 	voting or other rights, if any;	
 
 	•	 	conversion or exchange prices or rates, if any, and, if applicable, any provisions for changes to or adjustments in the conversion or exchange prices or rates and in the securities or other property receivable upon conversion or exchange; and	
 
 	•	 	material or special U.S. federal income tax considerations, if any.	
The applicable prospectus supplement and any related free writing prospectus that we may authorize to be provided to you may also add, update or change any of the information contained in this prospectus or in the documents we have incorporated by reference. However, no prospectus supplement or free writing prospectus will offer a security that is not registered and described in this prospectus at the time of the effectiveness of the registration statement of which this prospectus is a part.
THIS PROSPECTUS MAY NOT BE USED TO CONSUMMATE A SALE OF SECURITIES UNLESS IT IS ACCOMPANIED BY A PROSPECTUS SUPPLEMENT.
We may sell the securities directly to investors or to or through agents, underwriters or dealers. We, and our agents or underwriters, reserve the right to accept or reject all or part of any proposed purchase of securities. If we do offer securities to or through agents or underwriters, we will include in the applicable prospectus supplement:
 
 	•	 	the names of those agents or underwriters;	
 
 	•	 	applicable fees, discounts and commissions to be paid to them;	
 
 	•	 	details regarding over-allotment options, if any; and	
 
 	•	 	the net proceeds to us.	
Common Stock . We may issue shares of our common stock from time to time. The holders of our common stock are entitled to one vote for each share held of record on all matters submitted to a vote of stockholders. Subject to preferences that may be applicable to any outstanding shares of preferred stock, the holders of common stock are entitled to receive ratably such dividends as may be declared by our board of directors out of legally available funds. Upon our liquidation, dissolution or winding up, holders of our

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common stock are entitled to share ratably in all assets remaining after payment of liabilities and the liquidation preferences of any outstanding shares of preferred stock. Holders of common stock have no preemptive rights and no right to convert their common stock into any other securities. There are no redemption or sinking fund provisions applicable to our common stock. In this prospectus, we have summarized certain general features of the common stock under “Description of Capital Stock — Common Stock.” We urge you, however, to read the applicable prospectus supplement (and any related free writing prospectus that we may authorize to be provided to you) related to any common stock being offered.
Preferred Stock. We may issue shares of our preferred stock from time to time, in one or more series. Under our certificate of incorporation, our board of directors has the authority to designate up to 5,000,000 shares of preferred stock in one or more series and to fix the privileges, preferences and rights of each series of preferred stock, any or all of which may be greater than the rights of the common stock. Our board of directors has previously designated (a) 5,000 of the authorized shares of preferred stock as Series A Preferred Stock, all of which shares converted to common stock in July 2002, (b) 3,327 of the 5,000,000 authorized shares of preferred stock as Series B Preferred Stock, and (c) 250,000 of the 5,000,000 authorized shares of preferred stock as Series C Junior Participating Preferred Stock. We are not offering any of the previously designated series of preferred stock under this prospectus. If we sell any new series of preferred stock under this prospectus and any applicable prospectus supplement, our board of directors will determine the designations, voting powers, preferences and rights of the preferred stock being offered, as well as the qualifications, limitations or restrictions thereof, including dividend rights, conversion rights, preemptive rights, terms of redemption or repurchase, liquidation preferences, sinking fund terms and the number of shares constituting any series or the designation of any series. Convertible preferred stock will be convertible into our common stock or exchangeable for our other securities. Conversion may be mandatory or at the holder’s option and would be at prescribed conversion rates. We will file as an exhibit to the registration statement of which this prospectus is a part, or will incorporate by reference from reports that we file with the SEC, the form of any certificate of designation that describes the terms of the series of preferred stock that we are offering before the issuance of the related series of preferred stock. In this prospectus, we have summarized certain general features of the preferred stock under “Description of Capital Stock — Preferred Stock.” We urge you, however, to read the applicable prospectus supplement (and any related free writing prospectus that we may authorize to be provided to you) related to the series of preferred stock being offered, as well as the complete certificate of designation that contains the terms of the applicable series of preferred stock.
Debt Securities. We may issue debt securities from time to time, in one or more series, as either senior or subordinated debt or as senior or subordinated convertible debt. The senior debt securities will rank equally with any other unsecured and unsubordinated debt. The subordinated debt securities will be subordinate and junior in right of payment, to the extent and in the manner described in the instrument governing the debt, to all of our senior indebtedness. Convertible debt securities will be convertible into or exchangeable for our common stock or our other securities. Conversion may be mandatory or at the holder’s option and would be at prescribed conversion rates.
The debt securities will be issued under an indenture that we will enter into with a national banking association or other eligible party, as trustee. In this prospectus, we have summarized certain general features of the debt securities under “Description of Debt Securities.” We urge you, however, to read the applicable prospectus supplement (and any related free writing prospectus that we may authorize to be provided to you) related to the series of debt securities being offered, as well as the complete indenture and any supplemental indentures that contain the terms of the debt securities. We have filed a form of indenture as an exhibit to the registration statement of which this prospectus is a part, and supplemental indentures and forms of debt securities containing the terms of the debt securities being offered will be filed as exhibits to the registration statement of which this prospectus is a part or will be incorporated by reference from reports that we file with the SEC.

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Warrants. We may issue warrants for the purchase of common stock, preferred stock and/or debt securities in one or more series. We may issue warrants independently or in combination with common stock, preferred stock and/or debt securities. In this prospectus, we have summarized certain general features of the warrants under “Description of Warrants.” We urge you, however, to read the applicable prospectus supplement (and any related free writing prospectus that we may authorize to be provided to you) related to the particular series of warrants being offered, as well as the form of warrant and/or the warrant agreement and warrant certificate, as applicable, that contain the terms of the warrants. We have filed the forms of the warrant agreements and forms of warrant certificates containing the terms of the warrants that we may offer as exhibits to the registration statement of which this prospectus is a part. We will file as exhibits to the registration statement of which this prospectus is a part, or will incorporate by reference from reports that we file with the SEC, the form of warrant and/or the warrant agreement and warrant certificate, as applicable, that describe the terms of the particular series of warrants we are offering, and any supplemental agreements, before the issuance of such warrants.
Warrants may be issued under a warrant agreement that we enter into with a warrant agent. We will indicate the name and address of the warrant agent, if any, in the applicable prospectus supplement relating to a particular series of warrants.
Use of Proceeds
Except as described in any applicable prospectus supplement or in any free writing prospectuses we have authorized for use in connection with a specific offering, we currently intend to use the net proceeds from this offering, if any, for working capital and general corporate purposes, including research and development expenses, selling, general and administrative expenses and manufacturing expenses. See “Use of Proceeds” on page 7 of this prospectus.
NASDAQ Global Market Listing
Our common stock is listed on The NASDAQ Global Market under the symbol “CERS.”

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 RISK FACTORS
Investing in our securities involves a high degree of risk. Before deciding whether to invest in our securities, you should consider carefully the risks and uncertainties described under the heading “Risk Factors” contained in the applicable prospectus supplement and any related free writing prospectus, and discussed under the section entitled “Risk Factors” contained in our most recent Annual Report on Form 10-K and in our most recent Quarterly Report on Form 10-Q, as well as any amendments thereto reflected in subsequent filings with the SEC, which are incorporated by reference into this prospectus in their entirety, together with other information in this prospectus, the documents incorporated by reference and any free writing prospectus that we may authorize for use in connection with this offering. The risks described in these documents are not the only ones we face, but those that we consider to be material. There may be other unknown or unpredictable economic, business, competitive, regulatory or other factors that could have material adverse effects on our future results. Past financial performance may not be a reliable indicator of future performance, and historical trends should not be used to anticipate results or trends in future periods. If any of these risks actually occurs, our business, financial condition, results of operations or cash flow could be seriously harmed. This could cause the trading price of our common stock to decline, resulting in a loss of all or part of your investment. Please also read carefully the section below entitled “Forward-Looking Statements.”
 FORWARD-LOOKING STATEMENTS
This prospectus and the documents we have filed with the SEC that are incorporated by reference contain “forward-looking statements” within the meaning of Section 27A of the Securities Act and Section 21E of the Exchange Act. These statements relate to future events or to our future operating or financial performance and involve known and unknown risks, uncertainties and other factors which may cause our actual results, performance or achievements to be materially different from any future results, performances or achievements expressed or implied by the forward-looking statements. Forward-looking statements may include, but are not limited to, statements about:
 
 	•	 	our ability to commercialize and achieve market acceptance of the INTERCEPT Blood Systems;	
 
 	•	 	the successful completion of our research, development and clinical programs and our ability to manage cost increases associated with pre-clinical and clinical development for the INTERCEPT Blood Systems;	
 
 	•	 	our ability to obtain and maintain regulatory approvals of the INTERCEPT Blood Systems;	
 
 	•	 	our ability to protect our intellectual property and operate our business without infringing upon the intellectual property rights of others; and	
 
 	•	 	our ability to protect our intellectual property and operate our business without infringing upon the intellectual property rights of others; and	
 
 	•	 	our estimates regarding the sufficiency of our cash resources and our need for additional funding.	
In some cases, you can identify forward-looking statements by terms such as “may,” “will,” “should,” “could,” “would,” “expects,” “plans,” “anticipates,” “believes,” “estimates,” “projects,” “predicts,” “potential” and similar expressions intended to identify forward-looking statements. These statements reflect our current views with respect to future events and are based on assumptions and are subject to risks and uncertainties. Given these uncertainties, you should not place undue reliance on these forward-looking statements. We discuss in greater detail, and incorporate by reference into this prospectus in their entirety, many of these risks under the heading “Risk Factors” contained in any applicable prospectus supplement, in any free writing prospectuses we may authorize for use in connection with a specific offering, and in our most recent annual report on Form 10-K and in our most recent quarterly report on Form 10-Q, as well as any amendments thereto reflected in subsequent
 
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filings with the SEC. Also, these forward-looking statements represent our estimates and assumptions only as of the date of the document containing the applicable statement. Unless required by law, we undertake no obligation to update or revise any forward-looking statements to reflect new information or future events or developments. Thus, you should not assume that our silence over time means that actual events are bearing out as expressed or implied in such forward-looking statements. You should read this prospectus, any applicable prospectus supplement, together with the documents we have filed with the SEC that are incorporated by reference and any free writing prospectus that we may authorize for use in connection with this offering completely and with the understanding that our actual future results may be materially different from what we expect. We qualify all of the forward-looking statements in the foregoing documents by these cautionary statements.
 FINANCIAL RATIOS
The following table sets forth our ratio of earnings to fixed charges and the ratio of our earnings to combined fixed charges and preferred stock dividends to earnings for each of the periods presented. Our net losses were insufficient to cover fixed charges and combined fixed charges and preferred stock dividends in each of the years ended December 31, 2007, 2008, 2009 and 2010 and in the nine months ended September 30, 2011. Because of these deficiencies, the ratio information is not applicable for those periods. The extent to which earnings were insufficient to cover fixed charges and combined fixed charges and preferred stock dividends for those periods is shown below. Amounts shown are in thousands, except for ratios.

 	  	Year Ended December 31,	 	 	Nine Months Ended
September 30,	 	
 	  	2006	 	  	2007	 	 	2008	 	 	2009	 	 	2010	 	 	2011	 	
Ratio of earnings to fixed charges	  	 	7.32	 	  	 	—  	  	 	 	—  	  	 	 	—  	  	 	 	—  	  	 	 	—  	  	
Ratio of earnings to combined fixed charges and preferred stock dividends	  	 	7.32	 	  	 	—  	  	 	 	—  	  	 	 	—  	  	 	 	—  	  	 	 	—  	  	
Deficiency of earnings available to cover fixed charges	  	 	—  	  	  	$	(38,527	) 	 	$	(28,671	) 	 	$	(23,777	)	 	$	(16,656	) 	 	$	(8,204	) 	
Deficiency of earnings available to cover combined fixed charges and preferred stock dividends	  	 	—  	  	  	$	(38,527	) 	 	$	(28,671	) 	 	$	(23,777	)	 	$	(16,656	) 	 	$	(8,204	) 	
 USE OF PROCEEDS
Except as described in any applicable prospectus supplement or in any free writing prospectuses we have authorized for use in connection with a specific offering, we currently intend to use the net proceeds from this offering, if any, for working capital and general corporate purposes, including research and development expenses, selling, general and administrative expenses and manufacturing expenses.
The amounts and timing of our use of the net proceeds from this offering will depend on a number of factors, such as the timing and progress of our research and development efforts, the timing and progress of any partnering and commercialization efforts, technological advances and the competitive environment for our products. As of the date of this prospectus, we cannot specify with certainty all of the particular uses for the net proceeds to us from this offering. Accordingly, our management will have broad discretion in the timing and application of these proceeds. Pending application of the net proceeds as described above, we intend to temporarily invest the proceeds in short-term, interest-bearing instruments.
 
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 DESCRIPTION OF CAPITAL STOCK
As of the date of this prospectus, our certificate of incorporation authorizes us to issue 112,500,000 shares of common stock, par value $0.001 per share, and 5,000,000 shares of preferred stock, par value $0.001 per share. As of September 30, 2011, 47,744,285 shares of common stock were outstanding. As of the date of this prospectus, our board of directors has also designated 5,000 of the 5,000,000 authorized shares of preferred stock as Series A Preferred Stock, 3,327 of the 5,000,000 authorized shares of preferred stock as Series B Preferred Stock, and 250,000 of the 5,000,000 authorized shares of preferred stock as Series C Junior Participating Preferred Stock. As of the date of this prospectus, no shares of our Series A Preferred Stock are outstanding, 3,327 shares of our Series B Preferred Stock are outstanding, and no shares of our Series C Junior Participating Preferred Stock are outstanding.
The following summary describes the material terms of our capital stock and stockholder rights agreement. The description of our capital stock and stockholder rights plan is qualified by reference to our amended and restated certificate of incorporation, as amended, our bylaws, as amended, the certificate of designation for our Series B Preferred Stock, the certificate of designation for our Series C Junior Participating Preferred Stock, and our stockholder rights agreement, as amended, which are incorporated by reference as exhibits into the registration statement of which this prospectus is a part.
Common Stock
The holders of common stock are entitled to one vote for each share held of record on all matters submitted to a vote of the stockholders. Subject to preferences that may be applicable to any outstanding shares of the preferred stock, the holders of common stock are entitled to receive ratably such dividends as may be declared by the board of directors out of funds legally available therefor. In the event of a liquidation, dissolution or winding up of our company, holders of the common stock are entitled to share ratably in all assets remaining after payment of liabilities and the liquidation preferences of any outstanding shares of preferred stock. Holders of common stock have no preemptive rights and no right to convert their common stock into any other securities. There are no redemption or sinking fund provisions applicable to the common stock. All outstanding shares of common stock are, and all shares of common stock to be outstanding upon the closing of this offering will be, fully paid and nonassessable.
Additional shares of authorized common stock may be issued, as authorized by our board of directors from time to time, without stockholder approval, except as may be required by applicable stock exchange requirements.
Preferred Stock
Pursuant to our Amended and Restated Certificate of Incorporation, or the Restated Certificate, our board of directors has the authority, without further action by the stockholders, to issue up to 5,000,000 shares of preferred stock in one or more series and to fix the designations, powers, preferences, privileges and relative participating, optional or special rights and the qualifications, limitations or restrictions thereof, including dividend rights, conversion rights, voting rights, terms of redemption and liquidation preferences, any or all of which may be greater than the rights of the common stock. The board of directors, without stockholder approval, can issue preferred stock with voting, conversion or other rights that could adversely affect the voting power and other rights of the holders of common stock. Preferred stock could thus be issued quickly with terms calculated to delay or prevent a change in control of our company or make removal of management more difficult. Additionally, the issuance of preferred stock may have the effect of decreasing the market price of the common stock and may adversely affect the voting power of holders of common stock and reduce the likelihood that common stockholders will receive dividend payments and payments upon liquidation.
Series A Preferred Stock.  All 5,000 shares of our Series A Preferred Stock were previously issued and outstanding and were subsequently converted to shares of common stock in July 2002. Pursuant to the terms of the Series A Preferred Stock, these shares may not be reissued.
 
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Series B Preferred Stock.  There are currently 3,327 shares of Series B Preferred Stock outstanding. The holders of Series B Preferred Stock have no voting rights, except as required under the General Corporation Law of Delaware, and except as follows: (i) without first obtaining the affirmative vote or written consent of the holders of at least a majority of the outstanding shares of Series B Preferred Stock, voting together as a separate class, we may not authorize or issue shares of any class or series of stock, or reclassify any class or series of stock, into shares having preference or priority over the Series B Preferred Stock as to voting, liquidation preference or conversion rights; and (ii) to determine the fair market value of any securities delivered to the holders of the Series B Preferred Stock pursuant to a transaction treated as a liquidation of Cerus, the fair market value must be mutually determined by the board of directors and the holders of not less than a majority of the outstanding Series B Preferred, voting together as a single class. Upon any liquidation, dissolution, or winding up of our company, before any payment or distribution of assets shall be made to the holders of common stock or any other class or series of stock ranking junior to the Series B Preferred Stock with respect to liquidation preference, the holders of Series B Preferred Stock shall be entitled to be paid out of the assets of the company an amount per share of Series B Preferred Stock equal to $2,854.793, the original issue price.
We have the right to redeem, at the original issue price, all, but not less than all, of the Series B Preferred Stock at any time. At any time, each share of Series B Preferred Stock, at the option of the holder, may be converted at any time into that number of shares of common stock equal to the original issue price divided by 100. However, in the event that the approval of our stockholders is required by NASDAQ rules prior to the issuance of any of the shares of common stock issuable upon conversion of the Series B Preferred Stock, we must obtain such approval by the conversion date, or, if such approval is not obtained, we must redeem any shares of Series B Preferred Stock that would be convertible into shares of common stock in excess of the limitation specified under NASDAQ rules.
Neither the Series B Preferred Stock nor any right to receive redemption payments may be assigned, transferred, hypothecated or otherwise alienated by a Series B Preferred Stock holder without our prior written consent, except (i) in connection with, and to the transferee of, all or substantially all of the business and assets of such holder, or (ii) to a direct or indirect wholly owned subsidiary of Baxter International, Inc.
Series C Junior Participating Preferred Stock.  The Series C Junior Participating Preferred Stock, or Series C Preferred, is reserved for issuance in connection with the rights outstanding under our Rights Agreement as described below. The Series C Preferred will not be redeemable. Each share of Series C Preferred will be entitled to a minimum preferential quarterly dividend payment of $1.00 per share but will be entitled to an aggregate dividend of 100 times the dividend declared per share of common stock. In the event of liquidation, the holders of the Series C Preferred will be entitled to a minimum preferential liquidation payment of $100 per share but will be entitled to an aggregate payment of 100 times the payment made per share of common stock. Each Series C Preferred share will have 100 votes, voting together with the shares of common stock. Finally, in the event of any merger, consolidation or other transaction in which share of common stock are exchanged, each Series C Preferred share will be entitled to receive 100 times the amount of consideration received per share of common stock. These rights are protected by customary anti-dilution provisions. Because of the nature of the Series C Preferred dividend, liquidation and voting rights, the value of the one one-hundredth interest in a Series C Preferred share purchasable upon exercise of each Right should approximate the value of one share of common stock. The Series C Preferred would rank junior to any other series of our preferred stock.
Future Preferred Stock. Our board of directors will fix the rights, preferences, privileges, qualifications and restrictions of the preferred stock of each series that we sell under this prospectus and applicable prospectus supplements in the certificate of designation relating to that series. We will incorporate by reference into the registration statements of which this prospectus is a part the form of any certificate of designation that describes the terms of the series of preferred stock we are offering before the issuance of the related series of preferred stock. This description will include:
 
 	•	 	the title and stated value;	
 
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 	•	 	the number of shares we are offering;	
 
 	•	 	the liquidation preference per share;	
 
 	•	 	the purchase price per share;	
 
 	•	 	the dividend rate per share, dividend period and payment dates and method of calculation for dividends;	
 
 	•	 	whether dividends will be cumulative or non-cumulative and, if cumulative, the date from which dividends will accumulate;	
 
 	•	 	our right, if any, to defer payment of dividends and the maximum length of any such deferral period;	
 
 	•	 	the procedures for any auction and remarketing, if any;	
 
 	•	 	the provisions for a sinking fund, if any;	
 
 	•	 	the provisions for redemption or repurchase, if applicable, and any restrictions on our ability to exercise those redemption and repurchase rights;	
 
 	•	 	any listing of the preferred stock on any securities exchange or market;	
 
 	•	 	whether the preferred stock will be convertible into our common stock or other securities of ours, including warrants, and, if applicable, the conversion period, the conversion price, or how it will be calculated, and under what circumstances it may be adjusted;	
 
 	•	 	whether the preferred stock will be exchangeable into debt securities, and, if applicable, the exchange period, the exchange price, or how it will be calculated, and under what circumstances it may be adjusted;	
 
 	•	 	voting rights, if any, of the preferred stock;	
 
 	•	 	preemption rights, if any;	
 
 	•	 	restrictions on transfer, sale or other assignment, if any;	
 
 	•	 	a discussion of any material or special United States federal income tax considerations applicable to the preferred stock;	
 
 	•	 	the relative ranking and preferences of the preferred stock as to dividend rights and rights if we liquidate, dissolve or wind up our affairs;	
 
 	•	 	any limitations on issuances of any class or series of preferred stock ranking senior to or on a parity with the series of preferred stock being issued as to dividend rights and rights if we liquidate, dissolve or wind up our affairs; and	
 
 	•	 	any other specific terms, rights, preferences, privileges, qualifications or restrictions of the preferred stock.	
When we issue shares of preferred stock under this prospectus, the shares will be fully paid and nonassessable and will not have, or be subject to, any preemptive or similar rights.
The General Corporation Law of the State of Delaware, the state of our incorporation, provides that the holders of preferred stock will have the right to vote separately as a class on any proposal involving fundamental changes in the rights of holders of that preferred stock. This right is in addition to any voting rights that may be provided for in the applicable certificate of designation.
 
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Antitakeover Effects of Provisions of Charter Documents and Delaware Law
Charter Documents.  Our Restated Certificate and Amended and Restated Bylaws, or Bylaws, include a number of provisions that may have the effect of deterring hostile takeovers or delaying or preventing changes in control or management of our company. First, our board of directors is classified into three classes of directors. Under Delaware law, directors of a corporation with a classified board may be removed only for cause unless the corporation’s certificate of incorporation provides otherwise. Our Restated Certificate does not provide otherwise. In addition, the Restated Certificate provides that all stockholder action must be effected at a duly called meeting of stockholders and not by a consent in writing. Further, our Bylaws limit who may call special meetings of the stockholders. Our Restated Certificate does not include a provision for cumulative voting for directors. Under cumulative voting, a minority stockholder holding a sufficient percentage of a class of shares may be able to ensure the election of one or more directors. Finally, our Bylaws establish procedures, including advance notice procedures, with regard to the nomination of candidates for election as directors and stockholder proposals. These and other provisions of our Restated Certificate and Bylaws and Delaware law could discourage potential acquisition proposals and could delay or prevent a change in control or management of our company.
Delaware Takeover Statute. We are subject to Section 203 of the General Corporation Law of the State of Delaware, or DGCL, which regulates acquisitions of some Delaware corporations. In general, Section 203 prohibits, with some exceptions, a publicly held Delaware corporation such as us from engaging in a “business combination” with an “interested stockholder” for a period of three years following the time that the stockholder became an interested stockholder, unless:
 
 	•	 	prior to the time the stockholder became an interested stockholder, the board of directors of the corporation approved either the business combination or the transaction which resulted in the stockholder becoming an interested stockholder;	
 
 	•	 	upon consummation of the transaction which resulted in the stockholder becoming an interested stockholder, the interested stockholder owned at least 85% of the voting stock of the corporation outstanding at the time the transaction commenced, excluding for purposes of determining the number of shares outstanding (a) shares owned by persons who are directors and also officers and (b) employee stock plans in which employee participants do not have the right to determine confidentially whether shares held subject to the plan will be tendered in a tender or exchange offer; or	
 
 	•	 	at or subsequent to the time the stockholder became an interested stockholder, the business combination is approved by the board and authorized at an annual or special meeting of stockholders, and not by written consent, by the affirmative vote of at least 66-2/3% of the outstanding voting stock which is not owned by the interested stockholder.	
 
 	Section	203 of the DGCL generally defines a “business combination” to include any of the following:	
 
 	•	 	any merger or consolidation involving the corporation and the interested stockholder;	
 
 	•	 	any sale, lease, exchange, mortgage, pledge, transfer or other disposition (in one transaction or a series of transactions) involving the interested stockholder of 10% or more of the assets of the corporation (or its majority-owned subsidiary);	
 
 	•	 	subject to exceptions, any transaction that results in the issuance or transfer by the corporation of any stock of the corporation to the interested stockholder;	
 
 	•	 	subject to exceptions, any transaction involving the corporation that has the effect, directly or indirectly, of increasing the proportionate share of the stock or any class or series of the corporation beneficially owned by the interested stockholder; and	
 
 	•	 	the receipt by the interested stockholder of the benefit, directly or indirectly (except proportionately as a stockholder of such corporation), of any loans, advances, guarantees, pledges or other financial benefits, other than certain benefits set forth in Section 203, provided by or through the corporation.	
 
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In general, Section 203 defines an “interested stockholder” as any entity or person beneficially owning 15% or more of the outstanding voting stock of the corporation and any entity or person that is an affiliate or associate of such entity or person.
Section 203 of the DGCL could depress our stock price and delay, discourage or prohibit transactions not approved in advance by our board of directors, such as takeover attempts that might otherwise involve the payment to our stockholders of a premium over the market price of our common stock.
Rights Agreement
We have entered into a stockholder rights agreement, dated as of November 3, 1999, and amended as of October 28, 2009, or the Rights Agreement, pursuant to which each share of our common stock outstanding has attached to it a right, or Right. The Rights trade with our common stock until the earlier to occur of (i) 10 days after a public announcement that a person (or a group of affiliated or associated persons) has acquired beneficial ownership of 15% or more of the outstanding common stock, which we refer to as an Acquiring Person, or (ii) 10 business days (or such later date as may be determined by action of the board of directors prior to such time as any person or entity becomes an Acquiring Person) following the commencement of, or announcement of an intention to make, a tender offer or exchange offer the consummation of which would result in the beneficial ownership by an Acquiring Person of 15% or more of the outstanding common stock. The earlier of these dates is called the Distribution Date.
Following the Distribution Date, the Rights will be evidenced by separate certificates. The Rights are not exerciseable until after the Distribution Date. Each Right entitles the holder to purchase, for $30 per Right, one one-hundredth of a share of Series C Preferred, subject to adjustment. Each one one-hundredth of a share of Series C Preferred has designations and powers, preferences and rights, and the qualifications, limitations and restrictions designed to make it the economic equivalent of a share of common stock. The expiration date of the Rights is October 27, 2019.
In the event that any person (or a group of affiliated or associated persons) becomes an Acquiring Person, proper provision shall be made so that each holder of a Right, other than Rights beneficially owned by the Acquiring Person or any affiliate or associate thereof (which will thereafter be void), will thereafter have the right to receive upon exercise that number of shares of common stock having a market value of two times the exercise price of the Right. This right will commence on the date 10 days following public announcement that a person has become an Acquiring Person (or the effective date of a registration statement relating to distribution of the rights, if later) and terminate 60 days later (subject to adjustment in the event exercise of the rights is enjoined). At the time the rights flip in, they no longer represent the right to purchase shares of Series C Preferred.
In the event that Cerus is acquired in a merger or other business combination transaction or 50% or more of its consolidated assets or earning power are sold to an Acquiring Person, its affiliates or associates or certain other persons in which such persons have an interest, proper provision will be made so that each holder of a Right will thereafter have the right to receive, upon the exercise thereof at the then current exercise price of the Right, that number of shares of common stock of the acquiring company which at the time of such transaction will have a market value of two times the exercise price of the Right.
At any time prior to the earliest of (i) the close of business on the day of the first public announcement that a person has become an Acquiring Person, or (ii) October 27, 2019, the board of directors may redeem the Rights in whole, but not in part, at a price of $.001 per Right, or the Redemption Price. In general, the redemption of the Rights may be made effective at such time, on such basis and with such conditions as the board of directors in its sole discretion may establish. Immediately upon any redemption of the Rights, the right to exercise the Rights will terminate and the only right of the holders of Rights will be to receive the Redemption Price.
 
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At any time after the acquisition by a person (or a group of affiliated or associated persons) of beneficial ownership of 15% or more of the outstanding shares of common stock and prior to the acquisition by such person or group of 50% or more of the outstanding shares of common stock, the board of directors may exchange the Rights (other than Rights owned by such person or group which have become void), in whole or in part, at an exchange ratio of one share of common stock, or, under circumstances set forth in the Rights Agreement, cash, property or other securities of Cerus, including fractions of a Series C Preferred (or of a share of a class or series of Cerus’s preferred stock having equivalent designations and the powers, preferences and rights, and the qualifications, limitations and restrictions), per Right (with value equal to such shares of common stock).
The terms of the Rights may be amended by the board of directors without the consent of the holders of the Rights, except that from and after such time as the Rights are distributed no such amendment may adversely affect the interests of the holders of the Rights (excluding the interest of any Acquiring Person).
The Rights have certain anti-takeover effects. The Rights will cause substantial dilution to a person or group that attempts to acquire us on terms not approved by our board of directors. The Rights should not interfere with any merger or other business combination approved by our board of directors since the Rights may be amended to permit such acquisition or redeemed by us at $.001 per Right prior to the earliest of (a) the time that a person or group has acquired beneficial ownership of 15% or more of the common stock or (b) the final expiration date of the rights, October 27, 2019.
Transfer Agent And Registrar
The transfer agent and registrar for our common stock is Wells Fargo Shareowner Services.
Listing on The NASDAQ Global Market
Our common stock is listed on The NASDAQ Global Market under the symbol “CERS.”
 DESCRIPTION OF DEBT SECURITIES
We may issue debt securities from time to time, in one or more series, as either senior or subordinated debt or as senior or subordinated convertible debt. While the terms we have summarized below will apply generally to any debt securities that we may offer under this prospectus, we will describe the particular terms of any debt securities that we may offer in more detail in the applicable prospectus supplement or any related free writing prospectuses. The terms of any debt securities offered under a prospectus supplement may differ from the terms described below.
Unless the context requires otherwise, whenever we refer to the indenture, we also are referring to any supplemental indentures that specify the terms of a particular series of debt securities.
We will issue the debt securities under an indenture that we will enter into with the trustee named in the indenture. The indenture will be qualified under the Trust Indenture Act of 1939. We have filed a form of the indenture as an exhibit to the registration statement of which this prospectus is a part, and supplemental indentures and forms of debt securities containing the terms of the debt securities being offered will be filed as exhibits to the registration statement of which this prospectus is a part or will be incorporated by reference from reports that we file with the SEC.
The following summaries of material provisions of the debt securities and the indenture are subject to, and qualified in their entirety by reference to, all of the provisions of the indenture, including any supplemental indentures applicable to a particular series of debt securities. We urge you to read the applicable prospectus supplements and any related free writing prospectuses related to the debt securities that we may offer under this prospectus, as well as the complete indenture that contains the terms of the debt securities.
 
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General
The indenture does not limit the amount of debt securities that we may issue. It provides that we may issue debt securities up to the principal amount that we may authorize and may be in any currency or currency unit that we may designate. Except for the limitations on consolidation, merger and sale of all or substantially all of our assets contained in the indenture, the terms of the indenture do not contain any covenants or other provisions designed to give holders of any debt securities protection against changes in our operations, financial condition or transactions involving us.
We may issue the debt securities issued under an indenture as “discount securities,” which means they may be sold at a discount below their stated principal amount. These debt securities, as well as other debt securities that are not issued at a discount, may be issued with “original issue discount,” or OID, for U.S. federal income tax purposes because of interest payment and other characteristics or terms of the debt securities. Certain U.S. federal income tax considerations applicable to debt securities issued with OID will be described in more detail in any applicable prospectus supplement.
We will describe in the applicable prospectus supplement the terms of the series of debt securities being offered, including:
 
 	•	 	the title;	
 
 	•	 	any limit on the amount that may be issued;	
 
 	•	 	whether or not we will issue the series of debt securities in whole or in part in the form of a global security or securities; the terms and conditions, if any, upon which such global security or securities may be exchanged in whole or in part for other individual securities; and the depositary for such global security or securities;	
 
 	•	 	the maturity date or dates;	
 
 	•	 	the form of debt securities of the series;	
 
 	•	 	the applicability of any guarantees;	
 
 	•	 	whether and under what circumstances, if any, we will pay additional amounts on any debt securities held by a person who is not a United States person for tax purposes, and whether we can redeem the debt securities if we have to pay such additional amounts;	
 
 	•	 	if the price (expressed as a percentage of the aggregate principal amount thereof) at which such debt securities will be issued is a price other than the principal amount thereof, the portion of the principal amount thereof payable upon declaration of acceleration of the maturity thereof, or if applicable, the portion of the principal amount of such debt securities that is convertible into another security or the method by which any such portion shall be determined;	
 
 	•	 	any and all other terms (including terms, to the extent applicable, relating to any auction or remarketing of the debt securities of that series and any security for our obligations with respect to such debt securities) with respect to such series, including any terms which may be required by or advisable under United States laws or regulations or advisable in connection with the marketing of debt securities of that series;	
 
 	•	 	the interest rate or rates, which may be fixed or variable, or the method for determining the rate and the date interest will begin to accrue, the dates interest will be payable and the regular record dates for interest payment dates or the method for determining such dates;	
 
 	•	 	whether or not the debt securities will be secured or unsecured, and the terms of any secured debt;	
 
 	•	 	whether the debt securities rank as senior debt, senior subordinated debt, subordinated debt or any combination thereof, and the terms of any subordination;	
 
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 	•	 	whether the debt securities will be convertible into or exchangeable for, or based upon the price of, shares of common stock, preferred stock or other securities of ours or any other person and, if so, the terms and conditions upon which such debt securities will be so convertible or exchangeable, including the conversion or exchange price, as applicable, or how it will be calculated and may be adjusted, any mandatory or optional (at our option or the holders’ option) conversion or exchange features, the applicable conversion or exchange period and the manner of settlement for any conversion or exchange, which may, without limitation, include the delivery of cash as well as the delivery of securities;	
 
 	•	 	if other than the full principal amount thereof, the portion of the principal amount of debt securities of the series which shall be payable upon declaration of acceleration of the maturity thereof;	
 
 	•	 	any changes in or additions to the covenants applicable to the particular debt securities being issued, including, among others, the consolidation, merger or sale covenant;	
 
 	•	 	additions to or changes in the events of default with respect to the debt securities and any change in the right of the trustee or the holders to declare the principal, premium, if any, and interest, if any, with respect to such debt securities to be due and payable;	
 
 	•	 	additions to or changes in or deletions of the provisions relating to covenant defeasance and legal defeasance;	
 
 	•	 	additions to or changes in the provisions relating to satisfaction and discharge of an indenture;	
 
 	•	 	additions to or changes in the provisions relating to the modification of an indenture both with and without the consent of holders of debt securities issued under an indenture;	
 
 	•	 	whether interest will be payable in cash or additional debt securities at our or the holders’ option and the terms and conditions upon which the election may be made;	
 
 	•	 	additional or alternative provisions, if any, related to defeasance and discharge of the offered debt securities;	
 
 	•	 	the place where payments will be payable;	
 
 	•	 	restrictions on transfer, sale or other assignment, if any;	
 
 	•	 	our right, if any, to defer payment of interest and the maximum length of any such deferral period;	
 
 	•	 	the date, if any, after which, and the price at which, we may, at our option, redeem the series of debt securities pursuant to any optional or provisional redemption provisions and the terms of those redemption provisions;	
 
 	•	 	the date, if any, on which, and the price at which we are obligated, pursuant to any mandatory sinking fund or analogous fund provisions or otherwise, to redeem, or at the holder’s option to purchase, the series of debt securities and the currency or currency unit in which the debt securities are payable;	
 
 	•	 	a discussion of material United States federal income tax considerations, if any, applicable to the debt securities;	
 
 	•	 	information describing any book-entry features;	
 
 	•	 	whether the debt securities are to be offered at a price such that they will be deemed to be offered at an “original issue discount” as defined in paragraph (a) of Section 1273 of the Internal Revenue Code;	
 
 	•	 	the denominations in which we will issue the series of debt securities, if other than denominations of $1,000 and any integral multiple thereof;	
 
 	•	 	the currency of payment of debt securities if other than U.S. dollars and the manner of determining the equivalent amount in U.S. dollars; and	
 
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 	•	 	any other specific terms, preferences, rights or limitations of, or restrictions on, the debt securities, including any additional events of default or covenants provided with respect to the debt securities, and any terms that may be required by us or advisable under applicable laws or regulations.	
Conversion or Exchange Rights
We will set forth in the prospectus supplement the terms on which a series of debt securities may be convertible into or exchangeable for our common stock or our other securities. We will include provisions as to whether conversion or exchange is mandatory, at the option of the holder or at our option. We may include provisions pursuant to which the number of shares of our common stock or our other securities that the holders of the series of debt securities receive would be subject to adjustment.
Consolidation, Merger or Sale
Unless we provide otherwise in the prospectus supplement applicable to a particular series of debt securities, the indenture will not contain any covenant that restricts our ability to merge or consolidate, or sell, convey, transfer or otherwise dispose of all or substantially all of our assets. However, any successor to or acquirer of such assets must assume all of our obligations under the indenture or the debt securities, as appropriate. If the debt securities are convertible into or exchangeable for our other securities or securities of other entities, the person with whom we consolidate or merge or to whom we sell all of our property must make provisions for the conversion of the debt securities into securities that the holders of the debt securities would have received if they had converted the debt securities before the consolidation, merger or sale.
Events of Default Under the Indenture
Unless we provide otherwise in the prospectus supplement applicable to a particular series of debt securities, the following are events of default under the indenture with respect to any series of debt securities that we may issue:
 
 	•	 	if we fail to pay any installment of interest on any series of debt securities as and when the same becomes due and payable, and such default continues uncured for 90 consecutive days; provided, however, that a valid extension of an interest payment period by us in accordance with the terms of any indenture supplemental thereto shall not constitute a default in the payment of interest for this purpose;	
 
 	•	 	if we fail to pay the principal of, or premium, if any, on any series of debt securities as and when the same becomes due and payable whether at maturity, upon redemption, by declaration or otherwise, or in any payment required by any sinking or analogous fund established with respect to such series; provided, however, that a valid extension of the maturity of such debt securities in accordance with the terms of any indenture supplemental thereto shall not constitute a default in the payment of principal or premium, if any;	
 
 	•	 	if we fail to observe or perform any other covenant or agreement contained in the debt securities or the indenture, other than a covenant specifically relating to another series of debt securities, and our failure continues for 90 consecutive days after we receive written notice of such failure, requiring the same to be remedied and stating that such is a notice of default thereunder, from the trustee or holders of at least 25% in aggregate principal amount of the outstanding debt securities of the applicable series; and	
 
 	•	 	if specified events of bankruptcy, insolvency or reorganization occur.	
If an event of default with respect to debt securities of any series occurs and is continuing, other than an event of default specified in the last bullet point above, the trustee or the holders of at least 25% in aggregate principal amount of the outstanding debt securities of that series, by notice to us in writing, and to the trustee if notice is given by such holders, may declare the unpaid principal of, premium, if any, and accrued interest, if any, due and payable immediately. If an event of default specified in the last bullet point above occurs with
 
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respect to us, the principal amount of and accrued interest, if any, of each issue of debt securities then outstanding shall be due and payable without any notice or other action on the part of the trustee or any holder.
The holders of a majority in principal amount of the outstanding debt securities of an affected series may waive any default or event of default with respect to the series and its consequences, except defaults or events of default regarding payment of principal, premium, if any, or interest, unless we have cured the default or event of default in accordance with an indenture. Any waiver shall cure the default or event of default.
Subject to the terms of the indenture, if an event of default under an indenture shall occur and be continuing, the trustee will be under no obligation to exercise any of its rights or powers under such indenture at the request or direction of any of the holders of the applicable series of debt securities, unless such holders have offered the trustee reasonable indemnity. The holders of a majority in principal amount of the outstanding debt securities of any series will have the right to direct the time, method and place of conducting any proceeding for any remedy available to the trustee, or exercising any trust or power conferred on the trustee, with respect to the debt securities of that series, provided that:
 
 	•	 	the direction so given by the holder is not in conflict with any law or the applicable indenture; and	
 
 	•	 	subject to its duties under the Trust Indenture Act of 1939, the trustee need not take any action that might involve it in personal liability or might be unduly prejudicial to the holders not involved in the proceeding.	
A holder of the debt securities of any series will have the right to institute a proceeding under the indenture or to appoint a receiver or trustee, or to seek other remedies only if:
 
 	•	 	the holder has given written notice to the trustee of a continuing event of default with respect to that series;	
 
 	•	 	the holders of at least 25% in aggregate principal amount of the outstanding debt securities of that series have made written request, and such holders have offered reasonable indemnity to the trustee to institute the proceeding as trustee; and	
 
 	•	 	the trustee does not institute the proceeding, and does not receive from the holders of a majority in aggregate principal amount of the outstanding debt securities of that series other conflicting directions within 90 days after the notice, request and offer.	
These limitations do not apply to a suit instituted by a holder of debt securities if we default in the payment of the principal, premium, if any, or interest on, the debt securities.
Modification of Indenture; Waiver
We and the trustee may change an indenture without the consent of any holders with respect to specific matters:
 
 	•	 	to fix any ambiguity, defect or inconsistency in an indenture or in the debt securities of any series;	
 
 	•	 	to comply with the provisions described above under “Description of Debt Securities—Consolidation, Merger or Sale;”	
 
 	•	 	to comply with any requirements of the SEC in connection with the qualification of any indenture under the Trust Indenture Act of 1939;	
 
 	•	 	to add to, delete from or revise the conditions, limitations, and restrictions on the authorized amount, terms, or purposes of issue, authentication and delivery of debt securities, as set forth in an indenture;	
 
 	•	 	to provide for the issuance of and establish the form and terms and conditions of the debt securities of any series as provided above under “Description of Debt Securities—General” to establish the form of	
 
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 	any certifications required to be furnished pursuant to the terms of an indenture or any series of debt securities, or to add to the rights of the holders of any series of debt securities;	
 
 	•	 	to evidence and provide for the acceptance of appointment under any indenture by a successor trustee;	
 
 	•	 	to provide for uncertificated debt securities in addition to or in place of certificated debt securities and to make all appropriate changes for such purpose;	
 
 	•	 	to add to our covenants such new covenants, restrictions, conditions or provisions for the protection of the holders, and to make the occurrence, or the occurrence and the continuance, of a default in any such additional covenants, restrictions, conditions or provisions an event of default or to surrender any right or power conferred upon us in an indenture; or	
 
 	•	 	to make any change that does not materially adversely affect the interests of any holder of debt securities of any series.	
In addition, under the indenture, the rights of holders of a series of debt securities may be changed by us and the trustee with the written consent of the holders of at least a majority in aggregate principal amount of the outstanding debt securities of each series that is affected. However, unless we provide otherwise in the prospectus supplement applicable to a particular series of debt securities, we and the trustee may make the following changes only with the consent of each holder of any outstanding debt securities affected:
 
 	•	 	extending the fixed maturity of any series of debt securities;	
 
 	•	 	reducing the principal amount, reducing the rate of or extending the time of payment of interest, or reducing any premium payable upon the redemption of any series of debt securities; or	
 
 	•	 	reducing the percentage of debt securities, the holders of which are required to consent to any amendment, supplement, modification or waiver.	
Discharge
The indenture provides that we can elect to be discharged from our obligations with respect to one or more series of debt securities, except for specified obligations, including obligations to:
 
 	•	 	provide for payment;	
 
 	•	 	register the transfer or exchange of debt securities of the series;	
 
 	•	 	replace stolen, lost or mutilated debt securities of the series;	
 
 	•	 	pay principal of and premium and interest on any debt securities of the series;	
 
 	•	 	maintain paying agencies;	
 
 	•	 	hold monies for payment in trust;	
 
 	•	 	recover excess money held by the trustee;	
 
 	•	 	compensate and indemnify the trustee; and	
 
 	•	 	appoint any successor trustee.	
In order to exercise our rights to be discharged, we must deposit with the trustee money or government obligations sufficient to pay all the principal of, any premium, if any, and interest on, the debt securities of the series on the dates payments are due.
 
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Form, Exchange and Transfer
We will issue the debt securities of each series only in fully registered form without coupons and, unless we provide otherwise in the applicable prospectus supplement, in denominations of $1,000 and any integral multiple thereof. The indenture provides that we may issue debt securities of a series in temporary or permanent global form and as book-entry securities that will be deposited with, or on behalf of, The Depository Trust & Clearing Corporation or another depositary named by us and identified in a prospectus supplement with respect to that series. See “Legal Ownership of Securities” below for a further description of the terms relating to any book-entry securities.
At the option of the holder, subject to the terms of the indenture and the limitations applicable to global securities described in the applicable prospectus supplement, the holder of the debt securities of any series can exchange the debt securities for other debt securities of the same series, in any authorized denomination and of like tenor and aggregate principal amount.
Subject to the terms of the indenture and the limitations applicable to global securities set forth in the applicable prospectus supplement, holders of the debt securities may present the debt securities for exchange or for registration of transfer, duly endorsed or with the form of transfer endorsed thereon duly executed if so required by us or the security registrar, at the office of the security registrar or at the office of any transfer agent designated by us for this purpose. Unless otherwise provided in the debt securities that the holder presents for transfer or exchange, we will impose no service charge for any registration of transfer or exchange, but we may require payment of any taxes or other governmental charges.
We will name in the applicable prospectus supplement the security registrar, and any transfer agent in addition to the security registrar, that we initially designate for any debt securities. We may at any time designate additional transfer agents or rescind the designation of any transfer agent or approve a change in the office through which any transfer agent acts, except that we will be required to maintain a transfer agent in each place of payment for the debt securities of each series.
If we elect to redeem the debt securities of any series, we will not be required to:
 
 	•	 	issue, register the transfer of, or exchange any debt securities of that series during a period beginning at the opening of business 15 days before the day of mailing of a notice of redemption of any debt securities that may be selected for redemption and ending at the close of business on the day of the mailing; or	
 
 	•	 	register the transfer of or exchange any debt securities so selected for redemption, in whole or in part, except the unredeemed portion of any debt securities we are redeeming in part.	
Information Concerning the Trustee
The trustee, other than during the occurrence and continuance of an event of default under an indenture, undertakes to perform only those duties as are specifically set forth in the applicable indenture. Upon an event of default under an indenture, the trustee must use the same degree of care as a prudent person would exercise or use in the conduct of his or her own affairs. Subject to this provision, the trustee is under no obligation to exercise any of the powers given it by the indenture at the request of any holder of debt securities unless it is offered reasonable security and indemnity against the costs, expenses and liabilities that it might incur.
Payment and Paying Agents
Unless we otherwise indicate in the applicable prospectus supplement, we will make payment of the interest on any debt securities on any interest payment date to the person in whose name the debt securities, or one or more predecessor securities, are registered at the close of business on the regular record date for the interest.
 
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We will pay principal of and any premium and interest on the debt securities of a particular series at the office of the paying agents designated by us, except that unless we otherwise indicate in the applicable prospectus supplement, we will make interest payments by check that we will mail to the holder or by wire transfer to certain holders. Unless we otherwise indicate in the applicable prospectus supplement, we will designate the corporate trust office of the trustee as our sole paying agent for payments with respect to debt securities of each series. We will name in the applicable prospectus supplement any other paying agents that we initially designate for the debt securities of a particular series. We will maintain a paying agent in each place of payment for the debt securities of a particular series.
All money we pay to a paying agent or the trustee for the payment of the principal of or any premium or interest on any debt securities that remains unclaimed at the end of two years after such principal, premium or interest has become due and payable will be repaid to us, and the holder of the debt security thereafter may look only to us for payment thereof.
Governing Law
The indenture and the debt securities will be governed by and construed in accordance with the laws of the State of New York, except to the extent that the Trust Indenture Act of 1939 is applicable.
 DESCRIPTION OF WARRANTS
The following description, together with the additional information we may include in any applicable prospectus supplements and free writing prospectuses, summarizes the material terms and provisions of the warrants that we may offer under this prospectus, which may consist of warrants to purchase common stock, preferred stock or debt securities and may be issued in one or more series. Warrants may be offered independently or in combination with common stock, preferred stock or debt securities offered by any prospectus supplement. While the terms we have summarized below will apply generally to any warrants that we may offer under this prospectus, we will describe the particular terms of any series of warrants in more detail in the applicable prospectus supplement. The following description of warrants will apply to the warrants offered by this prospectus unless we provide otherwise in the applicable prospectus supplement. The applicable prospectus supplement for a particular series of warrants may specify different or additional terms.
We have filed forms of the warrant agreements and forms of warrant certificates containing the terms of the warrants that may be offered as exhibits to the registration statement of which this prospectus is a part. We will file as exhibits to the registration statement of which this prospectus is a part, or will incorporate by reference from reports that we file with the SEC, the form of warrant and/or the warrant agreement and warrant certificate, as applicable, that describe the terms of the particular series of warrants we are offering, and any supplemental agreements, before the issuance of such warrants. The following summaries of material terms and provisions of the warrants are subject to, and qualified in their entirety by reference to, all the provisions of the form of warrant and/or the warrant agreement and warrant certificate, as applicable, and any supplemental agreements applicable to a particular series of warrants that we may offer under this prospectus. We urge you to read the applicable prospectus supplement related to the particular series of warrants that we may offer under this prospectus, as well as any related free writing prospectuses, and the complete form of warrant and/or the warrant agreement and warrant certificate, as applicable, and any supplemental agreements, that contain the terms of the warrants.
General
We will describe in the applicable prospectus supplement the terms of the series of warrants being offered, including:
 
 	•	 	the offering price and aggregate number of warrants offered;	
 
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 	•	 	the currency for which the warrants may be purchased;	
 
 	•	 	if applicable, the designation and terms of the securities with which the warrants are issued and the number of warrants issued with each such security or each principal amount of such security;	
 
 	•	 	in the case of warrants to purchase debt securities, the principal amount of debt securities purchasable upon exercise of one warrant and the price at, and currency in which, this principal amount of debt securities may be purchased upon such exercise;	
 
 	•	 	in the case of warrants to purchase common stock or preferred stock, the number of shares of common stock or preferred stock, as the case may be, purchasable upon the exercise of one warrant and the price at which these shares may be purchased upon such exercise;	
 
 	•	 	the effect of any merger, consolidation, sale or other disposition of our business on the warrant agreements and the warrants;	
 
 	•	 	the terms of any rights to redeem or call the warrants;	
 
 	•	 	any provisions for changes to or adjustments in the exercise price or number of securities issuable upon exercise of the warrants;	
 
 	•	 	the dates on which the right to exercise the warrants will commence and expire;	
 
 	•	 	the manner in which the warrant agreements and warrants may be modified;	
 
 	•	 	a discussion of material or special U.S. federal income tax considerations, if any, of holding or exercising the warrants;	
 
 	•	 	the terms of the securities issuable upon exercise of the warrants; and	
 
 	•	 	any other specific terms, preferences, rights or limitations of or restrictions on the warrants.	
Before exercising their warrants, holders of warrants will not have any of the rights of holders of the securities purchasable upon such exercise, including:
 
 	•	 	in the case of warrants to purchase debt securities, the right to receive payments of principal of, or premium, if any, or interest on, the debt securities purchasable upon exercise or to enforce covenants in the applicable indenture; or	
 
 	•	 	in the case of warrants to purchase common stock or preferred stock, the right to receive dividends, if any, or payments upon our liquidation, dissolution or winding up or to exercise voting rights, if any.	
Exercise of Warrants
Each warrant will entitle the holder to purchase the securities that we specify in the applicable prospectus supplement at the exercise price that we describe in the applicable prospectus supplement. The warrants may be exercised as set forth in the prospectus supplement relating to the warrants offered. Unless we otherwise specify in the applicable prospectus supplement, warrants may be exercised at any time up to the close of business on the expiration date set forth in the prospectus supplement relating to the warrants offered thereby. After the close of business on the expiration date, unexercised warrants will become void.
Upon receipt of payment and the warrant or warrant certificate, as applicable, properly completed and duly executed at the corporate trust office of the warrant agent, if any, or any other office, including ours, indicated in the prospectus supplement, we will, as soon as practicable, issue and deliver the securities purchasable upon such exercise. If less than all of the warrants (or the warrants represented by such warrant certificate) are exercised, a new warrant or a new warrant certificate, as applicable, will be issued for the remaining warrants.
 
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Governing Law
Unless we provide otherwise in the applicable prospectus supplement, the warrants and any warrant agreements will be governed by and construed in accordance with the laws of the State of New York.
Enforceability of Rights by Holders of Warrants
Each warrant agent, if any, will act solely as our agent under the applicable warrant agreement and will not assume any obligation or relationship of agency or trust with any holder of any warrant. A single bank or trust company may act as warrant agent for more than one issue of warrants. A warrant agent will have no duty or responsibility in case of any default by us under the applicable warrant agreement or warrant, including any duty or responsibility to initiate any proceedings at law or otherwise, or to make any demand upon us. Any holder of a warrant may, without the consent of the related warrant agent or the holder of any other warrant, enforce by appropriate legal action its right to exercise, and receive the securities purchasable upon exercise of, its warrants.
Outstanding Warrants
As of September 30, 2011, there were outstanding warrants to purchase 6,084,211 shares of our common stock, of which warrants to purchase 2,400,000 shares of our common stock were outstanding with an exercise price of $2.90 per share, and warrants to purchase 3,684,211 shares of our common stock were outstanding at an exercise price of $3.20 per share. The warrants may be exercised for cash or, under certain circumstances, on a cashless basis, in which case we will deliver, upon exercise, the number of shares with respect to which the warrant is being exercised reduced by a number of shares having a value (as determined in accordance with the terms of the applicable warrant) equal to the aggregate exercise price of the shares with respect to which the warrant is being exercised.
 LEGAL OWNERSHIP OF SECURITIES
We can issue securities in registered form or in the form of one or more global securities. We describe global securities in greater detail below. We refer to those persons who have securities registered in their own names on the books that we or any applicable trustee, depositary or warrant agent maintain for this purpose as the “holders” of those securities. These persons are the legal holders of the securities. We refer to those persons who, indirectly through others, own beneficial interests in securities that are not registered in their own names, as “indirect holders” of those securities. As we discuss below, indirect holders are not legal holders, and investors in securities issued in book-entry form or in street name will be indirect holders.
Book-Entry Holders
We may issue securities in book-entry form only, as we will specify in the applicable prospectus supplement. This means securities may be represented by one or more global securities registered in the name of a financial institution that holds them as depositary on behalf of other financial institutions that participate in the depositary’s book-entry system. These participating institutions, which are referred to as participants, in turn, hold beneficial interests in the securities on behalf of themselves or their customers.
Only the person in whose name a security is registered is recognized as the holder of that security. Securities issued in global form will be registered in the name of the depositary or its participants. Consequently, for securities issued in global form, we will recognize only the depositary as the holder of the securities, and we will make all payments on the securities to the depositary. The depositary passes along the payments it receives to its participants, which in turn pass the payments along to their customers who are the beneficial owners. The depositary and its participants do so under agreements they have made with one another or with their customers; they are not obligated to do so under the terms of the securities.
 
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As a result, investors in a book-entry security will not own securities directly. Instead, they will own beneficial interests in a global security, through a bank, broker or other financial institution that participates in the depositary’s book-entry system or holds an interest through a participant. As long as the securities are issued in global form, investors will be indirect holders, and not holders, of the securities.
Street Name Holders
We may terminate a global security or issue securities in non-global form. In these cases, investors may choose to hold their securities in their own names or in “street name.” Securities held by an investor in street name would be registered in the name of a bank, broker or other financial institution that the investor chooses, and the investor would hold only a beneficial interest in those securities through an account he or she maintains at that institution.
For securities held in street name, we will recognize only the intermediary banks, brokers and other financial institutions in whose names the securities are registered as the holders of those securities, and we will make all payments on those securities to them. These institutions pass along the payments they receive to their customers who are the beneficial owners, but only because they agree to do so in their customer agreements or because they are legally required to do so. Investors who hold securities in street name will be indirect holders, not holders, of those securities.
Legal Holders
Our obligations, as well as the obligations of any applicable trustee and of any third parties employed by us or a trustee, run only to the legal holders of the securities. We do not have obligations to investors who hold beneficial interests in global securities, in street name or by any other indirect means. This will be the case whether an investor chooses to be an indirect holder of a security or has no choice because we are issuing the securities only in global form.
For example, once we make a payment or give a notice to the holder, we have no further responsibility for the payment or notice even if that holder is required, under agreements with depositary participants or customers or by law, to pass it along to the indirect holders but does not do so. Similarly, we may want to obtain the approval of the holders to amend an indenture, to relieve us of the consequences of a default or of our obligation to comply with a particular provision of an indenture or for other purposes. In such an event, we would seek approval only from the holders, and not the indirect holders, of the securities. Whether and how the holders contact the indirect holders is up to the holders.
Special Considerations For Indirect Holders
If you hold securities through a bank, broker or other financial institution, either in book-entry form or in street name, you should check with your own institution to find out:
 
 	•	 	how it handles securities payments and notices;	
 
 	•	 	whether it imposes fees or charges;	
 
 	•	 	how it would handle a request for the holders’ consent, if ever required;	
 
 	•	 	whether and how you can instruct it to send you securities registered in your own name so you can be a holder, if that is permitted in the future;	
 
 	•	 	how it would exercise rights under the securities if there were a default or other event triggering the need for holders to act to protect their interests; and	
 
 	•	 	if the securities are in book-entry form, how the depositary’s rules and procedures will affect these matters.	
 
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Global Securities
A global security is a security that represents one or any other number of individual securities held by a depositary. Generally, all securities represented by the same global securities will have the same terms.
Each security issued in book-entry form will be represented by a global security that we deposit with and register in the name of a financial institution or its nominee that we select. The financial institution that we select for this purpose is called the depositary. Unless we specify otherwise in the applicable prospectus supplement, The Depository Trust & Clearing Corporation, known as DTC, will be the depositary for all securities issued in book-entry form.
A global security may not be transferred to or registered in the name of anyone other than the depositary, its nominee or a successor depositary, unless special termination situations arise. We describe those situations below under “Special Situations When a Global Security Will Be Terminated.” As a result of these arrangements, the depositary, or its nominee, will be the sole registered owner and holder of all securities represented by a global security, and investors will be permitted to own only beneficial interests in a global security. Beneficial interests must be held by means of an account with a broker, bank or other financial institution that in turn has an account with the depositary or with another institution that does. Thus, an investor whose security is represented by a global security will not be a holder of the security, but only an indirect holder of a beneficial interest in the global security.
If the prospectus supplement for a particular security indicates that the security will be issued in global form only, then the security will be represented by a global security at all times unless and until the global security is terminated. If termination occurs, we may issue the securities through another book-entry clearing system or decide that the securities may no longer be held through any book-entry clearing system.
Special Considerations For Global Securities
The rights of an indirect holder relating to a global security will be governed by the account rules of the investor’s financial institution and of the depositary, as well as general laws relating to securities transfers. We do not recognize an indirect holder as a holder of securities and instead deal only with the depositary that holds the global security.
If securities are issued only in the form of a global security, an investor should be aware of the following:
 
 	•	 	an investor cannot cause the securities to be registered in his or her name, and cannot obtain non-global certificates for his or her interest in the securities, except in the special situations we describe below;	
 
 	•	 	an investor will be an indirect holder and must look to his or her own bank or broker for payments on the securities and protection of his or her legal rights relating to the securities, as we describe above;	
 
 	•	 	an investor may not be able to sell interests in the securities to some insurance companies and to other institutions that are required by law to own their securities in non-book-entry form;	
 
 	•	 	an investor may not be able to pledge his or her interest in a global security in circumstances where certificates representing the securities must be delivered to the lender or other beneficiary of the pledge in order for the pledge to be effective;	
 
 	•	 	the depositary’s policies, which may change from time to time, will govern payments, transfers, exchanges and other matters relating to an investor’s interest in a global security;	
 
 	•	 	we and any applicable trustee have no responsibility for any aspect of the depositary’s actions or for its records of ownership interests in a global security, nor do we or any applicable trustee supervise the depositary in any way;	
 
 	•	 	the depositary may, and we understand that DTC will, require that those who purchase and sell interests in a global security within its book-entry system use immediately available funds, and your broker or bank may require you to do so as well; and	
 
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 	•	 	financial institutions that participate in the depositary’s book-entry system, and through which an investor holds its interest in a global security, may also have their own policies affecting payments, notices and other matters relating to the securities.	
There may be more than one financial intermediary in the chain of ownership for an investor. We do not monitor and are not responsible for the actions of any of those intermediaries.
Special Situations When a Global Security Will Be Terminated
In a few special situations described below, the global security will terminate and interests in it will be exchanged for physical certificates representing those interests. After that exchange, the choice of whether to hold securities directly or in street name will be up to the investor. Investors must consult their own banks or brokers to find out how to have their interests in securities transferred to their own name, so that they will be direct holders. We have described the rights of holders and street name investors above.
Unless we provide otherwise in the applicable prospectus supplement, the global security will terminate when the following special situations occur:
 
 	•	 	if the depositary notifies us that it is unwilling, unable or no longer qualified to continue as depositary for that global security and we do not appoint another institution to act as depositary within 90 days;	
 
 	•	 	if we notify any applicable trustee that we wish to terminate that global security; or	
 
 	•	 	if an event of default has occurred with regard to securities represented by that global security and has not been cured or waived.	
The applicable prospectus supplement may also list additional situations for terminating a global security that would apply only to the particular series of securities covered by the applicable prospectus supplement. When a global security terminates, the depositary, and not we or any applicable trustee, is responsible for deciding the names of the institutions that will be the initial direct holders.
 PLAN OF DISTRIBUTION
We may sell the securities from time to time pursuant to underwritten public offerings, negotiated transactions, block trades or a combination of these methods. We may sell the securities to or through underwriters or dealers, through agents, or directly to one or more purchasers. We may distribute securities from time to time in one or more transactions:
 
 	•	 	at a fixed price or prices, which may be changed;	
 
 	•	 	at market prices prevailing at the time of sale;	
 
 	•	 	at prices related to such prevailing market prices; or	
 
 	•	 	at negotiated prices.	
A prospectus supplement or supplements (and any related free writing prospectus that we may authorize to be provided to you) will describe the terms of the offering of the securities, including, to the extent applicable:
 
 	•	 	the name or names of the underwriters, if any;	
 
 	•	 	the purchase price of the securities or other consideration therefor, and the proceeds, if any, we will receive from the sale;	
 
 	•	 	any over-allotment options under which underwriters may purchase additional securities from us;	
 
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 	•	 	any agency fees or underwriting discounts and other items constituting agents’ or underwriters’ compensation;	
 
 	•	 	any public offering price;	
 
 	•	 	any discounts or concessions allowed or reallowed or paid to dealers; and	
 
 	•	 	any securities exchange or market on which the securities may be listed.	
Only underwriters named in the prospectus supplement will be underwriters of the securities offered by the prospectus supplement.
If underwriters are used in the sale, they will acquire the securities for their own account and may resell the securities from time to time in one or more transactions at a fixed public offering price or at varying prices determined at the time of sale. The obligations of the underwriters to purchase the securities will be subject to the conditions set forth in the applicable underwriting agreement. We may offer the securities to the public through underwriting syndicates represented by managing underwriters or by underwriters without a syndicate. Subject to certain conditions, the underwriters will be obligated to purchase all of the securities offered by the prospectus supplement, other than securities covered by any over-allotment option. Any public offering price and any discounts or concessions allowed or reallowed or paid to dealers may change from time to time. We may use underwriters with whom we have a material relationship. We will describe in the prospectus supplement, naming the underwriter, the nature of any such relationship.
We may sell securities directly or through agents we designate from time to time. We will name any agent involved in the offering and sale of securities and we will describe any commissions we will pay the agent in the prospectus supplement. Unless the prospectus supplement states otherwise, our agent will act on a best-efforts basis for the period of its appointment.
We may authorize agents or underwriters to solicit offers by certain types of institutional investors to purchase securities from us at the public offering price set forth in the prospectus supplement pursuant to delayed delivery contracts providing for payment and delivery on a specified date in the future. We will describe the conditions to these contracts and the commissions we must pay for solicitation of these contracts in the prospectus supplement.
We may provide agents and underwriters with indemnification against civil liabilities, including liabilities under the Securities Act, or contribution with respect to payments that the agents or underwriters may make with respect to these liabilities. Agents and underwriters may engage in transactions with, or perform services for, us in the ordinary course of business.
All securities we may offer, other than common stock, will be new issues of securities with no established trading market. Any underwriters may make a market in these securities, but will not be obligated to do so and may discontinue any market making at any time without notice. We cannot guarantee the liquidity of the trading markets for any securities.
Any underwriter may engage in over-allotment, stabilizing transactions, short-covering transactions and penalty bids in accordance with Regulation M under the Exchange Act. Over-allotment involves sales in excess of the offering size, which create a short position. Stabilizing transactions permit bids to purchase the underlying security so long as the stabilizing bids do not exceed a specified maximum price. Syndicate-covering or other short-covering transactions involve purchases of the securities, either through exercise of the over-allotment option or in the open market after the distribution is completed, to cover short positions. Penalty bids permit the underwriters to reclaim a selling concession from a dealer when the securities originally sold by the dealer are purchased in a stabilizing or covering transaction to cover short positions. Those activities may cause the price of the securities to be higher than it would otherwise be. If commenced, the underwriters may discontinue any of the activities at any time.
 
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Any underwriters that are qualified market makers on The NASDAQ Global Market may engage in passive market making transactions in the common stock on The NASDAQ Global Market in accordance with Regulation M under the Exchange Act, during the business day prior to the pricing of the offering, before the commencement of offers or sales of the common stock. Passive market makers must comply with applicable volume and price limitations and must be identified as passive market makers. In general, a passive market maker must display its bid at a price not in excess of the highest independent bid for such security; if all independent bids are lowered below the passive market maker’s bid, however, the passive market maker’s bid must then be lowered when certain purchase limits are exceeded. Passive market making may stabilize the market price of the securities at a level above that which might otherwise prevail in the open market and, if commenced, may be discontinued at any time.
In compliance with guidelines of the Financial Industry Regulatory Authority, or FINRA, the maximum consideration or discount to be received by any FINRA member or independent broker dealer may not exceed 8% of the aggregate amount of the securities offered pursuant to this prospectus and any applicable prospectus supplement.
 LEGAL MATTERS
Unless otherwise indicated in the applicable prospectus supplement, the validity of the securities offered by this prospectus, and any supplement thereto, will be passed upon for us by Cooley LLP, Palo Alto, California.
 EXPERTS
Ernst & Young LLP, independent registered public accounting firm, has audited our consolidated financial statements included in our Annual Report on Form 10-K for the year ended December 31, 2010, and the effectiveness of our internal control over financial reporting as of December 31, 2010, as set forth in their reports, which are incorporated by reference in this prospectus and elsewhere in the registration statement. Our financial statements are incorporated by reference in reliance on Ernst & Young LLP’s report, given on their authority as experts in accounting and auditing.
 WHERE YOU CAN FIND MORE INFORMATION
This prospectus is part of the registration statement on Form S-3 we filed with the SEC under the Securities Act and does not contain all the information set forth in the registration statement. Whenever a reference is made in this prospectus to any of our contracts, agreements or other documents, the reference may not be complete and you should refer to the exhibits that are a part of the registration statement or the exhibits to the reports or other documents incorporated by reference into this prospectus for a copy of such contract, agreement or other document. Because we are subject to the information and reporting requirements of the Exchange Act, we file annual, quarterly and current reports, proxy statements and other information with the SEC. Our SEC filings are available to the public over the Internet at the SEC’s website at http://www.sec.gov. You may also read and copy any document we file at the SEC’s Public Reference Room at 100 F Street, N.E., Washington, D.C. 20549. Please call the SEC at 1-800-SEC-0330 for further information on the operation of the Public Reference Room.
 
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 INCORPORATION OF CERTAIN INFORMATION BY REFERENCE
The SEC allows us to “incorporate by reference” information from other documents that we file with it, which means that we can disclose important information to you by referring you to those documents. The information incorporated by reference is considered to be part of this prospectus. Information in this prospectus supersedes information incorporated by reference that we filed with the SEC prior to the date of this prospectus, while information that we file later with the SEC will automatically update and supersede the information in this prospectus. We incorporate by reference into this prospectus and the registration statement of which this prospectus is a part the information or documents listed below that we have filed with the SEC (Commission File No. 000-21937):
 
 	•	 	our Annual Report on Form 10-K for the year ended December 31, 2010, which was filed on March 16, 2011;	
 
 	•	 	our Quarterly Report on Form 10-Q for the quarter ended March 31, 2011, which was filed on May 6, 2011;	
 
 	•	 	our Quarterly Report on Form 10-Q for the quarter ended June 30, 2011, which was filed on August 8, 2011, as amended by our Quarterly Report on Form 10-Q/A, Amendment No. 1, for the quarter ended June 30, 2011, which was filed on August 30, 2011;	
 
 	•	 	our Quarterly Report on Form 10-Q for the quarter ended September 30, 2011, which was filed on November 3, 2011;	
 
 	•	 	our Current Reports on Form 8-K which were filed on January 21, 2011, March 2, 2011, March 3, 2011 (reporting under Items 1.01 and 2.03), April 20, 2011 (as amended on May 18, 2011), May 18, 2011, June 6, 2011, June 8, 2011, June 29, 2011, September 8, 2011, October 5, 2011 and November 10, 2011;	
 
 	•	 	the information specifically incorporated by reference into our 2010 Annual Report on Form 10-K referred to above from our definitive proxy statement relating to our 2011 annual meeting of stockholders, which was filed on April 22, 2011;	
 
 	•	 	the description of our common stock in our registration statement on Form 8-A filed with the SEC on January 8, 1997, including all amendments and reports filed for the purpose of updating such description; and	
 
 	•	 	the description of our preferred share purchase rights in our registration statement on Form 8-A filed with the SEC on October 30, 2009, including all amendments and reports filed for the purpose of updating such description.	
We also incorporate by reference any future filings (other than current reports furnished under Item 2.02 or Item 7.01 of Form 8-K and exhibits filed on such form that are related to such items unless such Form 8-K expressly provides to the contrary) made with the SEC pursuant to Sections 13(a), 13(c), 14 or 15(d) of the Exchange Act between the date of this prospectus and the termination of the offering. Information in such future filings updates and supplements the information provided in this prospectus. Any statements in any such future filings will automatically be deemed to modify and supersede any information in any document we previously filed with the SEC that is incorporated or deemed to be incorporated herein by reference to the extent that statements in the later filed document modify or replace such earlier statements.
You can request a copy of these filings, at no cost, by writing or telephoning us at the following address or telephone number:
Cerus Corporation
2550 Stanwell Drive
Concord, CA. 94520
(925) 288-6000
Attention: Investor Relations
 
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8,333,333 Shares

Common Stock

PROSPECTUS SUPPLEMENT

Cowen and Company
Sole Book-Running Manager

Baird	 	Wedbush PacGrow Life Sciences	 	Lazard Capital Markets	
Co-Managers
March 14, 2013