Equity Plans (Tables)

9 Months Ended

Sep. 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	1,596,600		23.87
Options exercised	(378,272)		8.05
Options forfeited	(667,453)		22.25
Balances at September 30, 2022	6,441,415	$	19.29	7.23	$	2.3
Options exercisable – September 30, 2022	3,784,700	$	16.28	6.12	$	2.1
Options vested and expected to vest – September 30, 2022	6,441,415	$	19.29	7.17	$	2.3

(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 September 30, 2022. The calculation excludes options with an exercise price higher than the closing price of the Company’s common stock on September 30, 2022.

Schedule of stock-based compensation expense

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

	Three Months Ended				Nine Months Ended
	September 30,				September 30,
	2022		2021		2022		2021
Research and development	$	3,858	$	2,611	$	11,290	$	6,241
General and administrative		2,092		2,164		7,400		5,130
Total stock-based compensation expense	$	5,950	$	4,775	$	18,690	$	11,371

Options to Purchase Common Stock

Black-Scholes option-pricing model assumptions

	Three Months Ended		Nine Months Ended
	September 30,		September 30,
	2022	2021	2022	2021
Expected term (in years)	5.27 - 6.08	6.02 - 6.08	5.27 - 6.08	5.27- 6.08
Expected volatility	97.7% - 101.7%	87.4% - 88.4%	96.3% - 101.7%	87.4% - 90.2%
Risk-free interest rate	2.70% - 4.01%	0.85% - 1.16%	1.64% - 4.01%	0.11% - 1.16%
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	506,450		21.36
Vested	(108,462)		15.83
Forfeited	(109,546)		21.85
Unvested RSUs at September 30, 2022	694,414	$	19.55

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	(27,000)		23.57
Unvested PSUs at September 30, 2022	199,500	$	14.59