Stock-Based Compensation (Tables)

6 Months Ended

Jun. 30, 2023

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Stock-Based Compensation Expense on All Employee and Non-Employee Awards

The Company recognized stock-based compensation expense on all employee and non-employee awards as follows:

	For the Three Months Ended June 30,				For the Six Months Ended June 30,
(in thousands)	2023		2022		2023		2022
Research and development		180		214		356		528
General and administrative		734		776		1,468		1,315
Stock-based compensation expense	$	914	$	990	$	1,824	$	1,843

Fair Value of Stock Options Assumptions Using Black-Scholes Option Valuation Model

For the three and six months ended June 30, 2023 and 2022, the fair value of stock options was estimated on the date of grant using a Black-Scholes option valuation model with the following assumptions:

	For the Three Months Ended June 30,		For the Six Months Ended June 30,
	2023	2022	2023	2022
Risk-free interest rate	3.51 – 3.84%	2.83 – 3.54%	3.51 – 3.87%	1.63 – 3.54%
Expected life in years	5.27 – 6.25	5.27 – 6.25	5.06 – 6.25	5.27 – 6.25
Expected volatility	90.04 – 95.36%	78.58 – 82.97%	89.69 – 95.63%	74.49 – 82.97%
Expected dividend yield	—%	—%	—%	—%

Stock Option Activity under Stock Option Plan

Stock option activity under the Company’s stock option plans for the six months ended June 30, 2023 was as follows:

(in thousands, except share and per share data)	Number of Shares			Weighted- Average Exercise Price		Weighted- Average Contractual Term (Years)		Aggregate Intrinsic Value
Outstanding, December 31, 2022		10,408,622		$	1.84
Granted		3,685,167			0.51
Cancelled		(484,903	)		1.62
Outstanding, June 30, 2023		13,608,886		$	1.49		8.36	$	45
Options exercisable, June 30, 2023		5,308,410		$	2.14		6.64	$	2
Options exercisable, December 31, 2022		3,891,598		$	2.46		8.08	$	—
Options available for future grant, June 30, 2023		12,259,824

Summary of Unvested Restricted Stock

A summary of the status of unvested restricted stock for the six months ended June 30, 2023 was as follows:

	Number of Shares			Weighted-Average Grant Date Fair Value
Unvested, December 31, 2022		939,062		$	1.40
Vested		(281,875	)		0.84
Unvested, June 30, 2023		657,187		$	1.64