STOCKHOLDERS' EQUITY (Tables)

12 Months Ended

Dec. 31, 2021

STOCKHOLDERS' EQUITY

Schedule of status of stock options

				Weighted
		Weighted		Average	Aggregate
	Number	Average		Remaining	Intrinsic
	of	Exercise		Contract	Value
	Options	Price		Life	(in thousands)
Outstanding at January 1, 2019	6,889,287	$	10.25
Issued	4,166,600		14.73
Exercised	(727,492)		8.85
Expired/Cancelled	(833,683)		13.87
Outstanding at December 31, 2019	9,494,712	$	12.00
Issued	4,981,001		28.17
Exercised	(973,854)		9.92
Expired/Cancelled	(886,221)		18.67
Outstanding at December 31, 2020	12,615,638	$	18.08
Issued	5,528,724		38.05
Exercised	(2,822,617)		11.88
Expired/Cancelled	(2,800,880)		32.58
Outstanding at December 31, 2021	12,520,865	$	25.05	7.64	$	35,047
Ending vested and expected to vest at December 31, 2021	12,520,865	$	25.05	7.64	$	35,047
Options exercisable at December 31, 2021	6,466,673	$	16.67	6.40	$	34,112

Schedule of summary of RSU activity

		Weighted
	Number	Average
	of	Grant Date
	RSUs	Fair Value
Outstanding, non-vested as of December 31, 2020	—	$	—
Granted	1,253,540		23.87
Vested	—		—
Canceled/Forfeited	(143,530)		23.87
Outstanding, non-vested as of December 31, 2021	1,110,010	$	23.87

Schedule of stock-based compensation

	Years Ended December 31,
	2021		2020		2019
Research and development	$	40,833	$	19,727	$	11,396
General and administrative		28,932		21,160		12,881
Total stock-based compensation expense	$	69,765	$	40,887	$	24,277

Schedule of compensation cost for share-based payment arrangements, allocation of share-based compensation costs by plan

	Years Ended December 31,
	2021		2020		2019
Stock option expense	$	56,305	$	40,714	$	23,964
Restricted stock unit expense		12,247		112		313
ESPP expense		1,213		61		—
Total stock-based compensation expense	$	69,765	$	40,887	$	24,277

Schedule of share-based payment award, stock options, valuation assumptions

	Stock Option			ESPP
	Years Ended December 31,			Years Ended December 31,
Assumptions:	2021	2020	2019	2021	2020
Expected term (years)	4.94 - 5.28	5.18 - 6.19	6.14 - 6.06	0.50	0.50
Expected volatility	70.35% - 73.88%	69.99% - 70.99%	71.62% - 70.63%	52.04% - 94.56%	54.90%
Risk-free interest rate	0.36% - 0.97%	0.28% - 1.83%	2.59% - 1.62%	0.06% - 0.13%	0.09%
Expected dividend yield	0%	0%	0%	0%	0%