Stock-based Compensation (Tables)

3 Months Ended

Mar. 31, 2021

Stock-based Compensation Expense Recognized

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

	Three Months Ended March 31,
	2021		2020
Research and development	$	260	$	10
General and administrative		714		48
Total stock-based compensation expense	$	974	$	58

Weighted-Average Assumptions used in Estimating Fair Value of each Stock Options using Black-Scholes Option-Pricing Model

The fair value of each stock option was estimated using the Black‑Scholes option‑pricing model with the following weighted-average assumptions:

	Three Months Ended March 31,
	2021			2020
Risk-free interest rate		0.79	%		1.34	%
Expected volatility		89.13	%		78.17	%
Expected term (in years)		6.17			6.87
Expected dividend yield		—			—

Summary of Option Activity Changes in Shares Available for Grant

Changes in shares available for grant during the three months ended March 31, 2021 were as follows:

	Shares Available for Grant
Shares available for grant at December 31, 2020		3,742,235
2020 Plan reserve increase on January 1, 2021		1,624,259
Options and restricted stock units granted		(601,044	)
Shares available for grant at March 31, 2021		4,765,450

Summary of Option Activity

A summary of stock option activity for the three months ended March 31, 2021 was as follows:

	Shares			Weighted- Average Exercise price per Share		Weighted- Average Remaining Contractual Term (in years)		Aggregate Intrinsic Value (in thousands)
Balance at December 31, 2020		1,974,870		$	9.31	7.98		$	49,275
Granted		597,892			21.07
Exercised		(62,951	)		1.11
Forfeited/expired		—			—
Balance at March 31, 2021		2,509,811		$	12.32		8.27	$	17,291
Expected to vest		1,840,595		$	16.26		9.39	$	5,933
Options exercisable		669,216		$	1.46		5.19	$	11,359

Summary of Stock Options Outstanding and Exercisable

Stock options outstanding and exercisable consisted of the following at March 31, 2021:

	Employees and Directors				Non-employees
Exercise Price ($)	Shares Outstanding		Shares Exercisable		Shares Outstanding		Shares Exercisable
0.16		75,660		75,660		12,610		12,610
0.48		151,320		151,320		—		—
1.00		—		—		37,830		37,830
1.04		66,931		66,931		31,525		31,525
1.19		26,825		21,465		34,677		34,677
1.31		63,050		63,050		—		—
1.35		290,974		68,509		97,727		63,049
1.49		31,525		21,016		—		—
17.00		737,052		19,263		195,453		—
19.29		27,742		—		—		—
21.15		558,150		—		—		—
21.40		9,600		—		—		—
21.62		2,400		—		—		—
22.22		29,618		—		—		—
23.79		1,400		—		—		—
29.41		27,742		2,311		—		—
Total		2,099,989		489,525		409,822		179,691

Restricted Stock Award (RSA)

Summary of Restricted Stock Activity

A summary of RSA activity for the three months ended March 31, 2021 was as follows:

	Share Equivalent		Weighted- Average Grant Date Fair Value
Non-vested at December 31, 2020		4,204	$	1.35
Granted		—		—
Vested		—		—
Non-vested at March 31, 2021		4,204	$	1.35

Restricted Stock Unit (RSUs)

Summary of Restricted Stock Activity

A summary of RSU activity for the three months ended March 31, 2021 was as follows:

	Share Equivalent			Weighted- Average Grant Date Fair Value
Non-vested at December 31, 2020		—		$	—
Granted		3,152			21.15
Vested		(1,576	)		21.15
Non-vested at March 31, 2021		1,576		$	21.15