Stock Incentive Plans (Tables)

3 Months Ended

Mar. 31, 2022

Share-based Payment Arrangement [Abstract]

Stock-based compensation expense by classification included within the consolidated statements of operations and comprehensive income (loss) was as follows (in thousands):


	Three Months Ended March 31,
	2022		2021
Research and development	$	1,018	$	754
General and administrative	1,735		1,026
Total stock-based compensation expense	$	2,753	$	1,780

Schedule of Weighted Average Assumptions Used

The estimated grant date fair values of employee stock option awards granted under the 2016 Plan and the 2018 Inducement Incentive Award Plan were calculated using the Black-Scholes option pricing model, based on the following weighted-average assumptions:


	Three Months Ended March 31,
	2022			2021
Risk-free interest rate	1.48		%	0.44		%
Dividend yield	—			—
Expected term	6.03			5.28
Expected volatility	91.84		%	83.26		%
Weighted-average fair value of common stock	$	3.26		$	3.13

Summary of Options Activity

The following table summarizes the stock option activity under the 2008 Plan, 2016 Plan, and 2018 Inducement Incentive Award Plan:


				Weighted-average
				remaining	Aggregate
	Number of	Weighted-average		contractual term	intrinsic value
	options	exercise price ($)		(in years)	(in thousands)
Employees








Outstanding at December 31, 2021	10,616,800	$	3.99	8.19	$	4,982
Granted	4,476,500	$	3.26
Exercised	(10,000)	$	2.10

Outstanding at March 31, 2022	15,083,300	$	3.78	8.49	$	—

Vested at March 31, 2022	5,602,046	$	4.46	7.30	$	—
Vested and expected to vest at March 31, 2022	13,738,523	$	3.82	8.40	$	—

Non-employee consultants








Outstanding at December 31, 2021	423,073	$	6.34	3.85	$	42


Forfeited	(156,834)	$	3.44
Outstanding at March 31, 2022	266,239	$	8.05	5.83	$	—

Vested at March 31, 2022	266,239	$	8.05	5.83	$	—
Vested and expected to vest at March 31, 2022	266,239	$	8.05	5.83	$	—

Disclosure of Share-based Compensation Arrangements by Share-based Payment Award

The following table summarizes the Company’s restricted stock units under the 2016 Plan and 2018 Inducement Incentive Award Plan:


	Number of shares	Weighted average grant date fair value ($)
Unvested at December 31, 2021	394,450	$	3.45
Granted	813,200	3.31
Vested	(89,142)	3.36


Unvested at March 31, 2022	1,118,508	$	3.36