Stock-based Compensation (Tables)

9 Months Ended

Sep. 30, 2020

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Stock-based Compensation Expense Recognized

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

	Three Months Ended September 30,				Nine Months Ended September 30,
	2020		2019		2020		2019
Research and development	$	43	$	13	$	62	$	42
General and administrative		68		56		156		147
Total stock-based compensation expense	$	111	$	69	$	218	$	189

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:

	Nine Months Ended September 30,
	2020			2019
Risk-free interest rate		0.49	%		1.58	%
Expected volatility		80.11	%		74.59	%
Expected term (in years)		6.93			6.59
Expected dividend yield		—			—

Summary of Option Activity

A summary of option activity for the nine months ended September 30, 2020 was as follows:

	Available for Grant			Shares			Weighted- Average Exercise price per Share		Weighted- Average Remaining Contractual Term (in years)		Aggregate Intrinsic Value (in thousands)
Balance at December 31, 2019		399,737			1,514,770		$	1.03	7.16		$	500
Authorized		4,343,534			—
Granted		(994,293	)		994,293			16.20
Exercised		—			(540,334	)		1.00
Forfeited/expired		41,301			(41,301	)		1.35
Balance at September 30, 2020		3,790,279			1,927,428		$	8.85		8.18	$	18,521
Expected to vest					1,298,059		$	12.71		9.52	$	7,460
Options exercisable					629,373		$	0.89		5.43	$	11,061

Summary of Stock Options Outstanding and Exercisable

Stock options outstanding and exercisable consisted of the following at September 30, 2020:

	Employees and Directors				Non-employees
Exercise Price ($)	Shares Outstanding		Shares Exercisable		Shares Outstanding		Shares Exercisable
0.16		75,660		75,660		12,611		12,611
0.48		162,353		162,353		—		—
1.00		—		—		37,830		37,830
1.04		70,933		70,933		31,525		31,525
1.19		52,645		38,878		34,677		34,677
1.31		63,050		63,050		—		—
1.35		294,754		27,529		116,642		63,049
1.49		31,525		10,508		—		—
17.00		747,770		770		195,453		—
Total		1,498,690		449,681		428,738		179,692

Summary of RSA Activity

A summary of RSA activity for the nine months ended September 30, 2020 was as follows:

	Share Equivalent			Weighted- Average Grant Date Fair Value
Non-vested at December 31, 2019		8,407			1.35
Granted		—			—
Vested		(4,203	)		1.35
Non-vested at September 30, 2020		4,204		$	1.35