Stock-based Compensation Expense (Tables)

6 Months Ended

Jun. 30, 2022

Summary of Stock Option Activity

The following table summarizes the Company’s stock option activity during the six months ended June 30, 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		2,253,030			12.77
Exercised		(349,871	)		8.59
Cancelled		(953,773	)		16.35
Outstanding at June 30, 2022		6,137,740		$	13.42		8.09	$	3,971
Exercisable at June 30, 2022		1,786,579		$	11.92		6.72	$	3,967

Weighted Average Assumptions Used to Calculate Fair Value of Stock Option

The fair value of stock options granted during the three and six months ended June 30, 2022 and 2021 has been calculated on the date of grant using the following weighted average assumptions:

	Three Months Ended June 30, 2022			Three Months Ended June 30, 2021			Six Months Ended June 30, 2022			Six Months Ended June 30, 2021
Risk-free interest rate		3.0	%		1.0	%		2.0	%		0.9	%
Expected dividend yield		0.0	%		0.0	%		0.0	%		0.0	%
Expected term (years)		6.0			6.0			6.0			6.0
Expected stock price volatility		88.0	%		86.9	%		88.4	%		86.2	%

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 June 30,				Six Months Ended June 30,
	2022		2021		2022		2021
General and administrative	$	2,076	$	1,562	$	4,541	$	2,846
Research and development		803		984		2,185		1,773
Total stock-based compensation expense	$	2,879	$	2,546	$	6,726	$	4,619

2019 Plan and 2016 Plan

Summary of Restricted Stock Activity

The following table summarizes the Company’s restricted stock award activity during the six months ended June 30, 2022:

	Number of Shares			Weighted Average Grant Date Fair Value
Unvested at December 31, 2021		10,174		$	3.35
Granted		—			—
Vested		(10,174	)		3.35
Repurchased		—			—
Unvested at June 30, 2022		—		$	—

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 six months ended June 30, 2022:

	Number of Shares			Weighted Average Grant Date Fair Value
Unvested at December 31, 2021		—		$	—
Granted		126,803			10.09
Vested		—			—
Cancelled		(11,614	)		11.72
Unvested at June 30, 2022		115,189		$	9.93