Equity Plans (Tables)

6 Months Ended

Jun. 30, 2022

Schedule of activity under equity incentive plans

		Weighted-		Weighted-
		Average		Average
		Exercise		Remaining	Aggregate
	Options	Price Per		Contractual	Intrinsic
	Outstanding	Share		Life (years)	Value (1)
					(in millions)
Balances at December 31, 2021	5,890,540	$	17.66	7.47	$	102.7
Options granted	1,444,600		25.47
Options exercised	(297,317)		8.71
Options forfeited	(212,702)		23.42
Balances at June 30, 2022	6,825,121	$	19.53	7.31	$	1.7
Options exercisable – June 30, 2022	3,660,098	$	15.36	6.05	$	1.6
Options vested and expected to vest – June 30, 2022	6,825,121	$	19.53	7.31	$	1.7

(1) The aggregate intrinsic values were calculated as the difference between the exercise price of the options and the closing price of the Company’s common stock on June 30, 2022. The calculation excludes options with an exercise price higher than the closing price of the Company’s common stock on June 30, 2022.

Schedule of stock-based compensation expense

Total stock-based compensation expense was as follows (in thousands):

	Three Months Ended				Six Months Ended
	June 30,				June 30,
	2022		2021		2022		2021
Research and development	$	4,106	$	2,155	$	7,432	$	3,630
General and administrative		2,699		1,781		5,308		2,966
Total stock-based compensation expense	$	6,805	$	3,936	$	12,740	$	6,596

Options to Purchase Common Stock

Black-Scholes option-pricing model assumptions

	Three Months Ended		Six Months Ended
	June 30,		June 30,
	2022	2021	2022	2021
Expected term (in years)	5.50 - 6.08	5.27 - 6.08	5.27 - 6.08	5.27- 6.08
Expected volatility	96.3% - 99.9%	88.0% - 88.8%	96.3% - 99.9%	88.0% - 90.2%
Risk-free interest rate	2.71% - 2.93%	0.85% - 1.11%	1.64% - 2.93%	0.11% - 1.11%
Dividend yield	—	—	—	—

Restricted stock units

Schedule of activity under equity incentive plans

		Weighted
		Average
	Number of	Grant Date
	Shares	Fair Value
Unvested RSUs at December 31, 2021	405,972	$	20.13
Granted	495,250		21.65
Vested	(104,712)		14.73
Forfeited	(30,420)		25.17
Unvested RSUs at June 30, 2022	766,090	$	19.88

Performance Stock Units

Schedule of performance stock unit activity

		Weighted
		Average
	Number of	Grant Date
	Shares	Fair Value
Unvested PSUs at December 31, 2021	105,500	$	23.57
Granted	121,000		8.76
Vested	—		—
Forfeited	(7,500)		23.57
Unvested PSUs at June 30, 2022	219,000	$	15.39