Stock-based Compensation (Tables)

12 Months Ended

Dec. 31, 2021

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Schedule of Stock-based Compensation Expense

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

	Years Ended December 31,
	2021		2020		2019
Stock-based compensation expense:
Research and development	$	7,526	$	972	$	395
General and administrative		13,986		2,460		1,247
Total stock-based compensation expense	$	21,512	$	3,432	$	1,642

Summary of Stock Option Activity

The following table summarizes the stock option activity under the Company’s equity awards plans for the year ended December 31, 2021:

	Number of Options			Weighted-Average Exercise Price		Weighted-Average Remaining Contractual Term (in years)		Aggregate Intrinsic Value (in thousands)
Outstanding as of December 31, 2020		5,029,364		$	12.72		9.25	$	102,635
Granted		1,926,579			41.71
Exercised		(474,850	)		4.91
Forfeited/expired		(497,668	)		16.91
Outstanding as of December 31, 2021		5,983,425		$	22.33		8.64	$	75,538
Exercisable as of December 31, 2021		1,362,477		$	16.86		8.10	$	22,699
Vested and expected to vest as of December 31, 2021		5,983,425		$	22.33		8.64	$	75,538

Other information related to the option activity of the Company was as follows:

	Years Ended December 31,
	2021		2020		2019
Weighted-average fair value of options granted	$	29.54	$	9.24	$	4.13
Intrinsic value of options exercised (in thousands)	$	17,321	$	2,587	$	337

Summary of Significant Assumptions Used in the Black-scholes Pricing Model to Determine the Fair Value of Stock Options Granted

The following table summarizes assumptions used in the Black-Scholes option pricing model to determine the fair value of stock options granted to employees:

	Years Ended December 31,
	2021	2020	2019
Expected option life (years)	5.50 - 6.11	5.23 - 6.35		6.35
Risk-free interest rate	0.59% - 1.34%	0.32% - 0.57%	1.71% - 2.36%
Expected volatility	80.45% - 86.20%	69.54% - 83.76%	65.50% - 76.80%
Expected dividend yield	0.00%	0.00%	0.00%