Stock-Based Compensation

6 Months Ended

Jun. 30, 2021

Stock-Based Compensation

Stock-Based Compensation

(8)  Stock-Based Compensation

A summary of stock option activity for the six months ended June 30, 2021 is as follows:

		Weighted		Weighted
		Average		Average
		Exercise		Remaining
		Price		Contractual
	Shares	Per Share		Term (In Years)
Options outstanding at December 31, 2020	3,042,229	$	28.93	8.2
Granted	1,340,010	$	27.97
Exercised	(2,058)	$	4.74
Canceled	(35,559)	$	9.78
Options outstanding at June 30, 2021	4,344,622	$	28.80	8.4
Options vested and expected to vest at June 30, 2021	4,174,361	$	29.17	8.4
Options exercisable at June 30, 2021	1,445,834	$	51.46	6.7
Shares available for grant under the 2021 Plan	3,294,526

The weighted average grant-date fair value of stock options granted during the three and six months ended June 30, 2021 was $21.73 and $21.71, respectively.

The aggregate intrinsic value of stock options vested and expected to vest at June 30, 2021 was $69.9 million. The aggregate intrinsic value of stock options exercisable at June 30, 2021 was $26.0 million. As of June 30, 2021, total compensation cost related to non-vested employee and non-employee director stock options not yet recognized was approximately $36.0 million, net of estimated forfeitures, which is expected to be recognized as expense over a weighted average period of 3.1 years.

Stock-based compensation expense for the three and six months ended June 30, 2021 and 2020 was recorded as follows:

	Three months ended June 30,				Six months ended June 30,
	2021		2020		2021		2020
	(In thousands)				(In thousands)
Research and development	$	762	$	342	$	1,423	$	652
General and administrative		747		380		1,361		756
Total stock-based compensation expense	$	1,509	$	722	$	2,784	$	1,408

The fair values of employee and director stock options granted during the three and six months ended June 30, 2021 and 2020 were valued using the Black-Scholes option pricing model with the following assumptions:

	Three months ended June 30,		Six months ended June 30,
	2021	2020	2021	2020
Expected stock price volatility	97 – 98%	97%	97 – 98%	91 – 97%
Expected option term	6.0 Years	6.0 Years	6.0 Years	6.0 Years
Risk-free interest rate	1.2 – 1.3%	0.5%	0.8 – 1.3%	0.5 – 0.6%
Expected dividend yield	None	None	None	None