Stock-Based Compensation (Tables)

3 Months Ended

Mar. 31, 2021

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Stock-Based Compensation Expense on All Employee and Non-Employee Awards

The Company recognized stock-based compensation expense on all employee and non-employee awards as follows:

	For the three months ended March 31,
(in thousands)	2021		2020
Research and development	$	733	$	530
General and administrative		1,464		1,410
Stock-based compensation expense	$	2,197	$	1,940

Fair Value of Stock Options Assumptions Using Black-Scholes Option Valuation Model

For the three months ended March 31, 2021 and 2020, the fair value of stock options was estimated on the date of grant using a Black-Scholes option valuation model with the following assumptions:

	For the three months ended March 31,
	2021	2020
Risk-free interest rate	0.09 - 1.05%	0.36 - 0.39%
Expected life in years	5.50 - 6.25	5.75 - 6.25
Expected volatility	72.92 - 74.20%	73.59 - 74.18%
Expected dividend yield	0%	0%

Stock Option Activity under Stock Option Plan

Stock option activity under the Company’s stock option plans for the three months ended March 31, 2021 is as follows:

(in thousands, except share and per share data)	Number of Shares			Weighted- Average Exercise Price		Weighted- Average Contractual Term (Years)		Aggregate Intrinsic Value
Outstanding, December 31, 2020		6,840,719		$	3.81
Granted		4,314,438			3.79
Exercised		(352,442	)		2.89
Cancelled		(84,337	)		3.53
Outstanding, March 31, 2021		10,718,378		$	3.83		13.40	$	4,926
Options exercisable, March 31, 2021		3,562,744		$	4.23		6.68	$	2,176
Options exercisable, December 31, 2020		3,596,315		$	4.17		6.90	$	598
Options available for future grant		1,267,888

Summary of Unvested Restricted Stock

A summary of the status of unvested restricted stock for the three months ended March 31, 2021 is as follows:

	Number of Shares		Weighted-Average Grant Date Fair Value
Unvested, December 31, 2020		786,280	$	3.08
Granted		313,326		4.31
Vested		—		—
Cancelled		—		—
Unvested, March 31, 2021		1,099,606	$	3.43