Stock Based Compensation (Tables)

9 Months Ended

Sep. 30, 2022

Stock Based Compensation [Abstract]

Weighted-Average Assumptions for Stock Options

The weighted average assumptions that the Company used in the Black-Scholes pricing model to determine the fair value of the stock options granted to employees, non-employees and directors were as follows:

	Nine Months Ended September 30,
	2022			2021
Risk-free interest rate		2.40	%		0.78	%
Expected term (in years)		5.82			5.84
Expected volatility		73.21	%		69.31	%
Expected dividend yield		0.00	%		0.00	%
Exercise price	$	15.79		$	53.98
Fair value of common stock	$	15.79		$	53.98

Stock Option Activity

The following table summarizes stock option activity for the nine months ended September 30, 2022, under the Second Amended and Restated 2014 Stock Option and Incentive Plan:

				Weighted		Weighted
				Average		Average		Aggregate
	Number of			Exercise		Contractual		Intrinsic
	Shares			Price		Term (Years)		Value
Outstanding as of December 31, 2021		11,143,761		$	14.51		5.95	$	128,817
Granted		2,192,166			15.79		6.30
Exercised		(30,824	)		9.99				167
Cancelled		(574,109	)		33.07
Outstanding as of September 30, 2022		12,730,994		$	13.91		5.68	$	88,457
Options vested and exercisable as of September 30, 2022		9,715,600		$	10.92		4.60	$	85,081
Options unvested as of September 30, 2022		3,015,394		$	23.48		9.15	$	3,376

RSU Activity

The following table summarizes the Company’s RSU activity for the nine months ended September 30, 2022:

				Weighted
				Average
	Number of			Grant Date
	Shares			Fair Value
Unvested as of December 31, 2021		23,500		$	30.61
Granted		939,122			16.10
Vested		(10,168	)		62.32
Forfeited		(56,585	)		16.10
Unvested as of September 30, 2022		895,869		$	16.23

Stock-Based Compensation Expense by Award Type

Stock-based compensation expense recognized by award type was as follows:

	Three Months Ended September 30,				Nine Months Ended September 30,
	2022		2021		2022		2021
Stock options	$	6,694	$	6,831	$	19,332	$	21,872
Restricted stock units		983		158		1,984		328
Total share based compensation expense	$	7,677	$	6,989	$	21,316	$	22,200

Stock-Based Compensation Expense

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

	Three Months Ended September 30,				Nine Months Ended September 30,
	2022		2021		2022		2021
Research and development	$	3,040	$	3,084	$	8,247	$	9,148
General and administrative		4,637		3,905		13,069		13,052
Total share based compensation expense	$	7,677	$	6,989	$	21,316	$	22,200

Warrants Outstanding and Changes in Warrants to Purchase Common Stock

A summary of the warrants outstanding as of September 30, 2022 is as follows:

Exercise Price		Outstanding		Grant Date	Expiration Date
24.42			7,051	June 28, 2013	June 28, 2023
57.11			603,386	December 21, 2020	December 21, 2030
33.63			301,291	August 9, 2021	August 9, 2031
22.51			153,155	December 17, 2021	December 17, 2031
22.51			153,155	December 17, 2021	December 17, 2031
	Total		1,218,038

The following table below is a summary of changes in warrants to purchase common stock for the nine months ended September 30, 2022:

	Number of Warrant Shares Outstanding and Exercisable		Exercise Price per Share
Balance as of December 31, 2021		1,218,038
Granted		-	$	-
Exercised		-	$	-
Balance as of September 30, 2022		1,218,038