Stock-based Compensation Expense (Tables)

9 Months Ended

Sep. 30, 2019

Summary of Stock Option Activity

The following table summarizes the Company’s stock option activity under the 2019 Plan and 2016 Plan since December 31, 2018:

	Number of Shares			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term (in years)		Aggregate Intrinsic Value
Outstanding at December 31, 2018		507,891		$	7.12		9.84	$	367,427
Granted		1,516,294			9.95
Exercised		(33,561	)		7.50
Cancelled		(9,167	)		10.09
Outstanding at September 30, 2019		1,981,457		$	9.27		9.38	$	202,742
Exercisable at September 30, 2019		193,292		$	7.96		9.23	$	72,559

Weighted Average Assumptions Used to Calculate Fair Value of Stock Option

The fair value of stock options granted during the three and nine months ended September 30, 2019 and 2018 under the 2019 Plan and the 2016 Plan has been calculated on the date of grant using the following weighted average assumptions:

	Three Months Ended September 30, 2019			Three Months Ended September 30, 2018			Nine Months Ended September 30, 2019			Nine Months Ended September 30, 2018
Risk-free interest rate		1.7	%		2.8	%		2.4	%		2.8	%
Expected dividend yield		0.0	%		0.0	%		0.0	%		0.0	%
Expected term (years)		6.0			6.0			6.0			5.9
Expected stock price volatility		80.1	%		84.3	%		81.0	%		83.9	%

Summary of Stock-Based Compensation Expense Recognized

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

	Three Months Ended September 30,				Nine Months Ended September 30,
	2019		2018		2019		2018
Research and development	$	533	$	282	$	1,398	$	808
General and administrative		646		224		1,552		589
Total stock-based compensation expense	$	1,179	$	506	$	2,950	$	1,397

2019 Plan and 2016 Plan

Summary of Restricted Stock Activity

The following table summarizes the Company’s restricted stock activity under the 2019 Plan and 2016 Plan since December 31, 2018:

	Number of Shares			Weighted Average Grant Date Fair Value
Unvested at December 31, 2018		757,022		$	3.07
Granted		—			—
Vested		(280,833	)		3.04
Repurchased		(56,324	)		3.07
Unvested at September 30, 2019		419,865		$	3.09

Grants Outside of Stock Incentive Plans

Summary of Restricted Stock Activity

The following table summarizes the Company’s restricted stock activity outside of the 2019 Plan and 2016 Plan since December 31, 2018:

	Number of Shares			Weighted Average Grant Date Fair Value
Unvested at December 31, 2018		446,789		$	2.94
Granted		—			—
Vested		(84,106	)		2.94
Repurchased		—			—
Unvested at September 30, 2019		362,683		$	2.94