Stock-based Compensation

6 Months Ended

Jun. 30, 2022

Share-based Payment Arrangement [Abstract]

Stock-based Compensation

9. 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 six months ended June 30, 2022:

	Number of shares			Weighted average exercise		Weighted average remaining contractual term		Aggregate intrinsic
	in Plans			price		(in years)		value
Outstanding as of December 31, 2021		6,830,037		$	14.72		7.76	$	6,987
Granted		172,176			2.19		8.91		—
Exercised		(9,997	)		1.24		—	$	37
Forfeited		(924,065	)		19.72		—		—
Outstanding as of June 30, 2022		6,068,151		$	13.63		6.86	$	789
Options exercisable as of June 30, 2022		4,390,918		$	10.59		6.39	$	759
Options unvested as of June 30, 2022		1,677,233		$	21.58		8.07	$	30

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:

	June 30,
	2022
Risk-free interest rate		2.9	%
Expected term (in years)		6.0
Expected volatility		80.0	%
Expected dividend yield		0.0	%

The weighted-average grant date fair value of options granted during the three and six months ended June 30, 2022 and 2021 was $0.92 and $1.57 and $7.20 and $23.89, respectively.

The total grant date fair value of options vested during the three and six months ended June 30, 2022 and 2021 was $3,620 and $8,036 and $4,614 and $8,898, respectively.

Restricted common stock

The Company issued common stock to founders, employees and advisors which was subject to vesting over four years. If any of these individuals ceased to be employed or to provide services to the Company prior to vesting, the Company had the right to repurchase any unvested Common Stock at the price paid by the holder.

There was no unvested restricted common stock as of June 30, 2022.

The total value of restricted stock awards that vested during the three and six months ended June 30, 2022 and 2021, based on estimated fair values of the stock underlying the restricted stock awards was $0 and $0 and $1 and $2, respectively.

Restricted stock units

The below summary includes restricted stock unit activity within the Company's 2019 Incentive Award Plan for the six months ended June 30, 2022:

	Number of shares			Weighted average fair value
Unvested, December 31, 2021		626,300		$	9.54
Awarded		2,426,650			3.77
Vested		(310,600	)		9.54
Forfeited		(436,850	)		5.40
Unvested as of June 30, 2022		2,305,500		$	4.25

Stock-based compensation

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

	Three Months Ended June 30,				Six Months Ended June 30,
	2022		2021		2022		2021
Research and development	$	1,598	$	3,090	$	3,899	$	4,619
General and administrative		2,966		2,999		5,931		6,081
Total	$	4,564	$	6,089	$	9,830	$	10,700

As of June 30, 2022, total unrecognized stock-based compensation expense relating to unvested stock options and restricted stock units was $28,179. This amount is expected to be recognized over a weighted-average period of 1.91 years.