Stockholders' Equity (Tables)

6 Months Ended

Jun. 30, 2022

Summary of Unvested Shares

A summary of the Company’s unvested shares is as follows:

Balance at December 31, 2021	1,144,809
Share vesting	(445,185	)
Balance at June 30, 2022	699,624

Summary of Common Stock Reserved for Future Issuance

Common stock reserved for future issuance consists of the following:

	June 30, 2022
Common stock warrants		91,228
Stock options, PSUs and RSUs outstanding		6,624,915
Shares available for issuance under the 2019 Incentive Plan		1,311,660
Shares available for issuance under the ESPP Plan		802,085
Balance at June 30, 2022		8,829,888

Summary of PSU Activity Under the 2019 Incentive Award Plan

The following table summarizes PSU activity under the 2019 Incentive Award Plan during the six months ended June 30, 2022.

	Number of Stock Units			Weighted- Average Grant Date Fair Value Per Share
Unvested balance at December 31, 2021		394,300		$	32.23
Granted		37,500			20.06
Vested	-			-
Forfeited		(11,250	)		38.14
Unvested balance at June 30, 2022		420,550		$	30.99

Summary of Weighted-Average Assumptions Used to Estimate Fair Value of Stock Options Granted and ESPP Awards

The weighted-average assumptions used to estimate the fair value of ESPP awards using the Black-Scholes option valuation model were as follows:

	Six Months Ended June 30,
	2022			2021
Assumptions:
Expected term (in years)		0.49			0.75
Expected volatility		72.41	%		81.83	%
Risk free interest rate		0.37	%		0.10	%
Dividend yield	-			-

Summary of Stock Option Activity

A summary of the Company’s stock option activity and related information is as follows:

	Options Outstanding			Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Term		Aggregate Intrinsic Value (in thousands)
Balance at December 31, 2021		4,186,729		$	27.53		8.43	$	13,973
Options granted		1,520,297			14.76
Options exercised and shares vested		—			—
Options forfeited, expired or cancelled		(89,548	)		32.99
Balance at June 30, 2022		5,617,478		$	23.99		8.34	$	1,435
Options exercisable as of June 30, 2022		2,013,657		$	24.74		7.57	$	838

Summary of Weighted-Average Assumptions Used to Estimate Fair Value of Stock Options

The weighted-average assumptions used to estimate the fair value of stock options using the Black-Scholes option valuation model were as follows:

	Six Months Ended June 30,
	2022			2021
Assumptions:
Expected term (in years)		6.05			6.04
Expected volatility		66.04	%		67.38	%
Risk free interest rate		1.89	%		0.64	%
Dividend yield		—			—

Summary of Stock-Based Compensation Expense

Stock-based compensation expense recognized for all equity awards, including founder stock, has been reported in the statements of operations and comprehensive loss as follows (in thousands):

	Three Months Ended June 30,				Six Months Ended June 30,
	2022		2021		2022		2021
Research and development expense	$	1,319	$	1,027	$	2,458	$	1,886
General and administrative expense		4,566		3,210		9,202		6,169
Total	$	5,885	$	4,237	$	11,660	$	8,055

Restricted Stock Units (RSUs)

Summary of Unvested Shares

The following table summarizes RSU activity under the 2019 Incentive Award Plan during the six months ended June 30, 2022.

	Number of Stock Units			Weighted- Average Grant Date Fair Value Per Share
Unvested balance at December 31, 2021		-		$	-
Granted		590,937			11.66
Vested		-			-
Forfeited		(4,050	)		15.21
Unvested balance at June 30, 2022		586,887		$	11.64