Stock-based Compensation

9 Months Ended

Sep. 30, 2023

Share-Based Payment Arrangement [Abstract]

10. Stock-based compensation

Stock options

The below summary includes stock option activity within the Company’s 2014 Stock Incentive Plan and 2019 Incentive Award Plan for the nine months ended September 30, 2023:


	Number of shares			Weighted average exercise		Weighted average remaining contractual term		Aggregate intrinsic
	in Plans			price		(in years)		value
Outstanding as of December 31, 2022		5,742,053		$	2.35		6.69	$	9,114
Granted		27,350			4.66		4.66		—
Exercised		(2,969	)		0.07		—	$	1
Forfeited		(1,103,713	)		2.45		—		—
Outstanding as of September 30, 2023		4,662,721		$	2.34		6.20	$	3
Options exercisable as of September 30, 2023		4,324,933		$	2.35		5.92	$	3
Options unvested as of September 30, 2023		337,788		$	2.23		7.28	$	—

The aggregate intrinsic value of stock options is calculated as the difference between the exercise price of the stock options and the fair value of the Company’s common stock for those stock options that had exercise prices lower than the fair value of the Company’s common stock.

Stock option valuation

The assumptions that the Company used to determine the grant-date fair value of stock options granted to employees and directors were as follows, presented on a weighted average basis:


	September 30,
	2023
Risk-free interest rate		3.6	%
Expected term (in years)		6.0
Expected volatility		92.0	%
Expected dividend yield		0.0	%

The weighted-average grant date fair value of options granted during the three and nine months ended September 30, 2023 was $0 and $3.58, respectively. The weighted-average grant date fair value of options granted during the three and nine months ended September 30, 2022 was $1.40 and $1.60, respectively.

The total grant date fair value of options vested during the three and nine months ended September 30, 2023 was $2,171 and $6,672, respectively. The total grant date fair value of options vested during the three and nine months ended September 30, 2022 was $3,100 and $11,390, respectively.

Repricing of stock options

On August 17, 2022, the Board of Directors approved the repricing of all options granted under the 2019 Incentive Award Plan that were held by then current employees, executives, directors, and consultants for which the exercise price per share was greater than the closing price per share of the Company's common stock on August 17, 2022 (Underwater Options) by reducing the exercise price of each Underwater Option to $2.14, the closing price per share of the Company's common stock on August 17, 2022. Except for the modification of the exercise price, all other terms and conditions of the Underwater Options remain in effect.

The option repricing resulted in incremental stock-based compensation of $2,505, of which $179 and $518 was recorded as expense in the three and nine months ended September 30, 2023, respectively. At September 30, 2023, $357 incremental expense remains which will be recognized as expense over the requisite service period in which the options vest.

Restricted stock units

The below summary includes restricted stock unit activity within the Company's 2019 Incentive Award Plan for the nine months ended September 30, 2023:


	Number of shares			Weighted average fair value
Unvested, December 31, 2022		3,101,650		$	2.51
Awarded		1,666,340			4.78
Vested		(1,630,150	)		2.91
Forfeited		(1,207,690	)		3.58
Unvested as of September 30, 2023		1,930,150		$	3.47

Stock-based compensation

The Company recognized stock-based compensation within the accompanying consolidated statements of operations as follows:


	Three Months Ended September 30,				Nine Months Ended September 30,
	2023		2022		2023		2022
Research and development	$	750	$	2,095	$	1,760	$	5,994
General and administrative		2,175		3,500		7,493		9,431
Total	$	2,925	$	5,595	$	9,253	$	15,425

As of September 30, 2023, total unrecognized stock-based compensation expense relating to unvested stock options and restricted stock units was $9,454. This amount is expected to be recognized over a weighted-average period of 1.52 years.