Incentive Stock Options and Employee Stock Purchase Plan (Tables)

6 Months Ended

Jun. 30, 2021

Summary of Stock Option Activity

The following table summarizes the Company’s stock option activity since December 31, 2020 (in thousands, except share and per share amounts):

	Number of Shares			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term		Intrinsic Value
						(in years)
Outstanding as of December 31, 2020		9,557,391		$	8.79		7.92	$	93,256
Granted		3,126,560		$	21.81
Exercised		(286,899	)	$	8.25
Forfeited		(154,303	)	$	14.68
Outstanding as of June 30, 2021		12,242,749		$	12.06		8.07	$	189,483
Exercisable as of June 30, 2021		5,953,908		$	8.14		7.07	$	115,421
Vested and expected to vest as of June 30, 2021		12,242,749		$	12.06		8.07	$	189,483

Summary of Assumptions Used in Black-Scholes Option-Pricing Model to Determine Grant-Date Fair Value of Stock Option Granted

The following table presents, on a weighted average basis, the assumptions used in the Black-Scholes option-pricing model to determine the grant-date fair value of stock options granted to employees and directors:

	Six Months Ended June 30,
	2021			2020
Risk-free interest rate		1.03	%		0.79	%
Expected term (in years)		6.1			6.1
Expected volatility		69.7	%		68.6	%
Expected dividend yield		0	%		0	%

Summary of Stock-Based Compensation Expense

Stock-based compensation expense was classified in the condensed consolidated statements of operations as follows (in thousands):

	Three Months Ended June 30,				Six Months Ended June 30,
	2021		2020		2021		2020
Research and development expenses	$	2,841	$	4,091	$	4,921	$	5,545
General and administrative expenses		2,495		1,923		4,399		3,641
	$	5,336	$	6,014	$	9,320	$	9,186