Stock-based Compensation Expense (Tables)

3 Months Ended

Mar. 31, 2022

Summary of Stock Option Activity

Shares issued upon the exercise of stock options are issued from the Company’s pool of authorized but unissued common stock. In addition to stock options granted under the 2019 Plan and 2016 Plan, the Company has granted stock options as material inducements to employment in accordance with Nasdaq Listing Rule 5635(c)(4), which were granted outside of the 2019 Plan and 2016 Plan. The following table summarizes the Company’s stock option activity during the three months ended March 31, 2022:

	Number of Shares			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term (in years)		Aggregate Intrinsic Value
Outstanding at December 31, 2021		5,188,354		$	13.91		8.57	$	27,082,052
Granted		1,607,401			13.33
Exercised		(47,627	)		8.29
Cancelled		(221,155	)		12.60
Outstanding at March 31, 2022		6,526,973		$	13.85		8.11	$	67,305,741
Exercisable at March 31, 2022		1,668,499		$	11.66		6.52	$	20,009,494

Weighted Average Assumptions Used to Calculate Fair Value of Stock Option

The fair value of stock options granted during the three months ended March 31, 2022 and 2021 has been calculated on the date of grant using the following weighted average assumptions:

	Three Months Ended March 31, 2022			Three Months Ended March 31, 2021
Risk-free interest rate		1.7	%		0.7	%
Expected dividend yield		0.0	%		0.0	%
Expected term (years)		6.0			6.0
Expected stock price volatility		88.6	%		85.6	%

Summary of Stock-Based Compensation Expense Recognized

The total compensation cost recognized in the statements of operations and comprehensive loss associated with all stock-based compensation awards granted by the Company is as follows (in thousands):

	Three Months Ended March 31,
	2022		2021
General and administrative	$	2,465	$	1,284
Research and development		1,382		789
Total stock-based compensation expense	$	3,847	$	2,073

2019 Plan and 2016 Plan

Summary of Restricted Stock Activity

The following table summarizes the Company’s restricted stock award activity during the three months ended March 31, 2022:

	Number of Shares			Weighted Average Grant Date Fair Value
Unvested at December 31, 2021		10,174		$	3.35
Granted		—			—
Vested		(9,754	)		3.29
Repurchased		—			—
Unvested at March 31, 2022		420		$	4.76

Grants Outside of 2016 Stock Incentive Plan and 2019 Stock Incentive Plan

Summary of Restricted Stock Activity

The Company has also granted restricted stock units. The shares of common stock underlying restricted stock units typically vest over a four-year period. The shares of common stock are recorded in stockholders’ equity as they vest.

The following table summarizes the Company’s restricted stock unit activity during the three months ended March 31, 2022:

	Number of Shares			Weighted Average Grant Date Fair Value
Unvested at December 31, 2021		—		$	—
Granted		48,421			12.46
Vested		—			—
Cancelled		(3,994	)		12.46
Unvested at March 31, 2022		44,427		$	12.46