Description of Operations and Summary of Significant Accounting Policies (Policies)

3 Months Ended

Mar. 31, 2012

Description of Operations and Summary of Significant Accounting Policies

Principles of Consolidation

The consolidated financial statements include the accounts of the Company and its wholly owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation.

Use of Management's Estimates

The preparation of consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the consolidated financial statements and accompanying notes. Actual results could differ materially from those estimates.

Segment Reporting

The Company has determined that it operates in a single segment which is the research and development of human therapeutics. Revenues are generated primarily from the Company’s collaborations with GlaxoSmithKline plc (GSK), located in the United Kingdom and, through January 6, 2012, Astellas Pharma Inc. (Astellas), located in Japan. All long-lived assets are maintained in the United States.

Marketable Securities

The Company determines the appropriate classification of its marketable securities, which consist of debt securities, at the time of purchase and reevaluates such designation at each balance sheet date. All of the marketable securities are classified as available-for-sale and carried at estimated fair values and reported in either cash equivalents or marketable securities. Unrealized gains and losses on available-for-sale securities are reported in accumulated other comprehensive income (loss) as a separate component of stockholders’ equity (net capital deficiency). Interest, amortization of purchase premiums and discounts, and realized gains and losses on sales of securities are included in interest. The cost of securities sold is based on the specific identification method.

The Company regularly reviews all of its investments for other-than-temporary declines in fair value. The Company’s review includes the consideration of the cause of the impairment, including the creditworthiness of the security issuers, the number of securities in an unrealized loss position, the severity and duration of the unrealized losses, whether the Company has the intent to sell the securities and whether it is more likely than not that the Company will be required to sell the securities before the recovery of their amortized cost basis. When the Company determines that the decline in fair value of an investment is below the amortized cost basis and the decline is other-than-temporary, the Company reduces the carrying value of the security and records a loss for the amount of such decline.

Research and Development Costs

Research and development costs are expensed in the period that services are rendered or goods are received. Research and development costs consist of salaries and benefits, laboratory supplies and facility costs, as well as fees paid to third parties that conduct certain research and development activities on behalf of the Company, net of certain external research costs reimbursed by GSK and, through 2011, Astellas.

Fair Value of Stock-Based Compensation Awards

Stock-based compensation arrangements currently include the following awards granted under the 2004 Equity Incentive Plan (2004 Plan) and the 2008 New Employee Equity Incentive Plan (2008 Plan): stock options, restricted stock unit awards (RSUs), performance-contingent RSUs, restricted stock awards (RSAs), and performance-contingent RSAs. In addition, stock-based compensation arrangements include purchases of common stock by the Company’s employees at a discount to the market price during offering periods under the Company’s Employee Stock Purchase Plan (ESPP). Under the 2004 Plan and 2008 Plan, stock options are to be granted at an exercise price not less than the fair market value per share on the grant date for incentive options and are generally granted with terms of up to ten years and vest over a period of four years. Following the approval by stockholders of the amendment and restatement of the 2004 Plan on April 27, 2010, no additional awards have been made or will be made in the future under the 2008 Plan.

The Company uses the Black Scholes option pricing model to estimate the fair value of options granted under its equity incentive plans and rights to acquire stock granted under its employee stock purchase plan. The Black Scholes option valuation model requires the use of assumptions, including the expected term of the award and the expected stock price volatility. The Company used the “simplified” method as described in Staff Accounting Bulletin No. 107 for the expected option term because the usage of its historical exercise data is limited due to post-IPO exercise restrictions. Beginning April 1, 2011, the Company used its historical volatility to estimate expected stock price volatility. Prior to April 1, 2011, the Company used peer company price volatility to estimate expected stock price volatility due to the Company’s limited historical common stock price volatility since its initial public offering in 2004. RSUs and RSAs are measured based on the fair market values of the underlying stock on the dates of grant.

Stock-based compensation expense was calculated based on awards ultimately expected to vest and has been reduced for estimated forfeitures at the time of grant and revised, if necessary, in subsequent periods if actual forfeitures differ from those estimates. The Company’s estimated annual forfeiture rates for stock options, RSUs and RSAs are based on its historical forfeiture experience.

The estimated fair value of stock options, RSUs and RSAs is expensed on a straight-line basis over the expected term of the grant and the fair value of performance-contingent RSUs and RSAs is expensed during the term of the award when the Company determines that it is probable that certain performance milestones will be achieved. Compensation expense for purchases under the ESPP is recognized based on the estimated fair value of the common stock during each offering period and purchase discount percentage.

The Company has not recognized, and does not expect to recognize in the near future, any tax benefit related to employee stock-based compensation costs as a result of the full valuation allowance on the Company’s deferred tax assets including deferred tax assets related to its net operating loss carryforwards.

Recently Adopted Accounting Updates

On January 1, 2012, the Company adopted Accounting Standards Update (ASU) No. 2011-05, “Presentation of Comprehensive Income” an update to Accounting Standards Codification (ASC) Topic 220, “Comprehensive Income”. This update requires that all nonowner changes in stockholders’ equity be presented either in a single continuous statement of comprehensive income or in two separate but consecutive statements. This update is to be applied retrospectively and is effective for financial statements issued for fiscal years, and interim periods within those years, beginning after December 15, 2011, and interim and annual periods thereafter. This update was effective for the Company January 1, 2012. The Company elected the two separate but consecutive statements approach.