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Equity Plans (Tables)

9 Months Ended

Sep. 30, 2021

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, 2020		4,648,120		$	11.87		7.61		$	40.0
Options granted		1,920,540	​	​	29.93		​		​
Options exercised		(308,125)	​	​	9.87		​		​	​
Options forfeited	​	(176,580)	​	​	16.60	​	​	​	​	​
Balances at September 30, 2021		6,083,955		$	17.54		7.58	​	$	27.6
Options exercisable – September 30, 2021	​	3,121,045		$	12.89		6.29	​	$	18.7
Options vested and expected to vest – September 30, 2021	​	6,083,955	​	$	17.54		7.58	​	$	27.6

(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, 2021. The calculation excludes options with an exercise price higher than the closing price of the Company’s common stock on September 30, 2021.

Schedule of stock-based compensation expense

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

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Three Months Ended

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Nine Months Ended

​

​

September 30,

​

September 30,

​

2021

2020

2021

2020

Research and development

​

$

2,611

​

$

1,006

​

$

6,241

​

$

3,098

General and administrative

​

2,164

​

882

​

5,130

​

2,834

Total stock-based compensation expense

​

$

4,775

​

$

1,888

​

$

11,371

​

$

5,932

Options to purchase common stock

Black-Scholes option-pricing model assumptions

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​	​	​	​	​	​	​	​	​
​	​	Three Months Ended			​	Nine Months Ended
​	​	September 30,			​	September 30,
​	​	2021	​	2020	​	2021	​	2020
Expected term (in years)		6.02 - 6.08		5.27 - 6.08	​	5.27 - 6.08		5.27- 6.08
Expected volatility		87.4% - 88.4%	​	84.5% - 85.1%	​	87.4% - 90.2%	​	72.1% - 85.1%
Risk-free interest rate		0.85% - 1.16%	​	0.23% - 0.40%	​	0.11% - 1.16%	​	0.23% - 1.44%
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, 2020	​	244,545	​	$	9.31
Granted	​	302,250		​	24.40
Vested	​	(78,165)	​		10.13
Forfeited	​	(49,970)	​	​	18.86
Unvested RSUs at September 30, 2021	​	418,660	​	$	20.07

Performance Stock Units

Schedule of performance stock unit activity

​

​	​	​	​	​	​
​	​	​	​	Weighted
​	​	​	​	Average
​	​	Number of	​	Grant Date
​		Shares		Fair Value
Unvested PSUs at December 31, 2020	​	—	​	​	—
Granted		110,500	​	$	23.57
Vested	​	—	​	​	—
Forfeited	​	(5,000)	​	​	—
Unvested PSUs at September 30, 2021	​	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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