Stock-based Compensation

12 Months Ended

Dec. 31, 2021

Share-based Payment Arrangement [Abstract]

7. Stock-based Compensation

The 2015 Stock Plan, as amended, is our primary plan through

which

equity based grants are awarded. We ceased making new awards under the 2006 Stock Plan upon adoption of the 2015 Stock Plan. The 2015 Stock Plan provides for the grant of incentive stock options,

non-statutory

stock options, restricted stock and other stock-based compensation awards to employees, officers, directors, and consultants of the Company. The administration of the 2015 Stock Plan is under the general supervision of the Compensation Committee of the Board of Directors. The terms of stock options awarded under the 2015 Stock Plan, in general, are determined by the Compensation Committee, provided the exercise price per share generally shall not be set at less than the fair market value of a share of the common stock on the date of grant and the term shall not be greater than ten years from the date the option is granted. As of December 31, 2021, the Company had options outstanding to purchase 2,301,574 shares of its common stock. As of December 31, 2021, 1,661,293 shares were available for future issuance.

The following table summarizes stock option activity during the twelve months ended December 31, 2021:


	Shares			Weighted average exercise price		Weighted average remaining contractual life (years)		Aggregate intrinsic value (in thousands)
Outstanding at January 1, 2021		1,837,540		$	71.80
Options granted		687,059			109.03
Options exercised		(11,080	)		92.96
Options cancelled		(211,945	)		114.34

Outstanding at December 31, 2021		2,301,574		$	78.89		6.51	$	62,566

Exercisable at December 31, 2021		1,432,144		$	62.66		5.38	$	60,932

The total cash received by the Company as a result of stock option exercises was $1.0 million, $0.7 million and $0.2 million for the years ended December 31, 2021, 2020, and 2019. The total intrinsic value of options exercised was $0.1 million $4.1 million and $2.2 million for the years ended December 31, 2021, 2020, and 2019. The weighted-average grant date fair values, based on the Black-Scholes option model, of options granted during the year ended December 31, 2021, 2020 and 2019 was $ 73.29, $68.07, and $91.19, respectively.

Restricted Common Stock

The Company’s share-based compensation plan provides for awards of restricted shares of common stock to employees, officers, directors and consultants to the Company. Restricted stock awards are subject to forfeiture if employment or service terminates during the prescribed retention period. Restricted shares vest over the service period. There were no outstanding restricted shares or activity in 2021.

Stock-Based Compensation Expense

Stock-based compensation expense during the years ended December 31, 2021, 2020 and 2019 was as follows (in thousands):


	Years Ended December 31,
	2021		2020		2019
Stock-based compensation expense by type of award:
Stock options	$	26,873	$	20,730	$	22,487
Restricted stock		—		—		272

Total stock-based compensation expense	$	26,873	$	20,730	$	22,759

Effect of stock-based compensation expense by line item:
Research and development	$	10,698	$	8,833	$	8,277
General and administrative		16,175		11,897		14,482

Total stock-based compensation expense included in net loss	$	26,873	$	20,730	$	22,759

Unrecognized stock-based compensation expense on stock options as of December 31, 2021 was $48.9 million with a weighted average remaining period of 2.79 years.