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Equity Plans (Tables)

3 Months Ended

Mar. 31, 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		1,122,100	​	​	28.85		​		​
Options exercised		(165,488)	​	​	11.68		​		​	​
Options forfeited	​	(37,542)	​	​	39.04	​	​	​	​	​
Balances at March 31, 2022		6,809,610		$	19.53		7.37	​	$	46.0
Options exercisable – March 31, 2022	​	3,349,241		$	13.59		6.05	​	$	34.5
Options vested and expected to vest – March 31, 2022	​	6,809,610	​	$	19.53		7.37	​	$	46.0

(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 March 31, 2022. The calculation excludes options with an exercise price higher than the closing price of the Company’s common stock on March 31, 2022.

Schedule of stock-based compensation expense

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

​

​	​	​	​	​	​	​
​	​	Three Months Ended March 31,
​		2022			2021
Research and development	​	$	3,326	​	$	1,475
General and administrative	​		2,609	​		1,185
Total stock-based compensation expense	​	$	5,935	​	$	2,660

Options to Purchase Common Stock

Black-Scholes option-pricing model assumptions

​

​	​	​	​	​
​	​	Three Months Ended March 31,
​	​	2022	​	2021
Expected term (in years)		5.27- 6.08		5.27- 6.08
Expected volatility		97.1% - 98.2%	​	89.8% - 90.2%
Risk-free interest rate		1.64% - 2.13%	​	0.11% - 0.97%
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	​	312,550	​	​	28.73
Vested	​	(104,712)	​	​	14.73
Forfeited	​	(7,000)	​	​	28.73
Unvested RSUs at March 31, 2022	​	606,810	​	$	24.61

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		—	​	​	—
Vested	​	—	​	​	—
Forfeited	​	—	​	​	—
Unvested PSUs at March 31, 2022	​	105,500	​	$	23.57

X

- Definition

Tabular disclosure of allocation of amount expensed and capitalized for award under share-based payment arrangement to statement of income or comprehensive income and statement of financial position. Includes, but is not limited to, corresponding line item in financial statement.

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