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Stock-Based Compensation (Tables)

9 Months Ended

Sep. 30, 2021

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Summary of Stock-Based Compensation Expense

Total stock-based compensation expense recognized was as follows (in thousands):

		Three Months Ended September 30,								Nine Months Ended September 30,
		2021				2020				2021				2020
Research and development		$	796			$	951			$	3,209			$	1,125
General and administrative			1,733				2,015				5,022				2,491
Total stock-based compensation		$	2,529			$	2,966			$	8,231			$	3,616

Summary of Stock Option Activity

A summary of stock option activity for the nine months ended September 30, 2021 is set forth below:

		Number of Shares Available for Grant				Number of Shares Underlying Outstanding Options				Weighted- Average Exercise Price				Weighted- Average Remaining Contractual Term (in years)				Aggregate Intrinsic Value (in thousands)
Outstanding, December 31, 2020			1,739,621				3,706,945			$	10.90				7.98			$	15,126
Options authorized			2,287,089				—
Options granted			(2,171,632	)			1,954,472			$	14.89
Options exercised			—				(546,642	)		$	2.98
Options forfeited or cancelled			838,419				(838,419	)		$	14.15
Outstanding, September 30, 2021			2,693,497				4,276,356			$	13.10				7.96			$	2,101
Options exercisable, September 30, 2021							1,329,752			$	9.77				5.33			$	1,907
Vested and expected to vest, September 30, 2021							4,276,356			$	13.10				7.96			$	2,101

Schedule of Assumptions to Estimate Fair Value of Stock Options Using Black-Scholes Option Pricing Model

The assumptions used in the Black Scholes Model to calculate stock-based compensation are as follows:

		Three Months Ended September 30,				Nine Months Ended September 30,
		2021		2020		2021		2020
Fair value of common stock		$7.84 - $8.35		$5.96 - $10.66		$7.84 - $16.82		$4.85 - $10.66
Expected term (years)		5.6 - 6.1		1.0 - 6.1		0.9 - 6.1		1.0 - 6.1
Volatility		78.0% - 78.2%		77.1% - 96.4%		77.9% - 79.8%		72.6% - 96.3%
Risk free rates		0.9% - 1.2%		0.1% - 0.4%		0.1% - 1.2%		0.1% - 1.7%
Dividend rate		0.0%		0.0%		0.0%		0.0%

Summary of Restricted Stock Unit Activity

The summary of RSU activity and related information follows:

		Number of Units Outstanding				Weighted- Average Grant Date Fair Value
Outstanding, December 31, 2020			—
RSUs granted			217,160			$	7.37
RSUs Vested			—
RSUs forfeited			—
Outstanding, September 30, 2021			217,160			$	7.37

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Tabular disclosure of cost recognized for award under share-based payment arrangement by plan. Includes, but is not limited to, related tax benefit.

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Tabular disclosure of the number and weighted-average grant date fair value for restricted stock units that were outstanding at the beginning and end of the year, and the number of restricted stock units that were granted, vested, or forfeited during the year.

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Tabular disclosure for stock option plans. Includes, but is not limited to, outstanding awards at beginning and end of year, grants, exercises, forfeitures, and weighted-average grant date fair value.

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Tabular disclosure of the significant assumptions used during the year to estimate the fair value of stock options, including, but not limited to: (a) expected term of share options and similar instruments, (b) expected volatility of the entity's shares, (c) expected dividends, (d) risk-free rate(s), and (e) discount for post-vesting restrictions.

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