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Stock-Based Compensation (Tables)

9 Months Ended

Sep. 30, 2024

Share-Based Payment Arrangement [Abstract]

Schedule of Total Share Based Compensation Expense

Total stock-based compensation expense related to share-based awards was comprised of the following (in thousands):

		Three months ended								Nine months ended
		September 30,								September 30,
		2024				2023				2024				2023
Research and development		$	2,648			$	4,112			$	8,082			$	11,443
General and administrative			2,803				3,896				9,683				11,000
Total stock-based compensation expense		$	5,451			$	8,008			$	17,765			$	22,443

Stock-based compensation expense by type of share-based award (in thousands):

		Three months ended								Nine months ended
		September 30,								September 30,
		2024				2023				2024				2023
Stock options		$	4,619			$	6,864			$	14,981			$	19,103
Restricted stock awards			—				27				37				82
Restricted stock units			792				1,051				2,655				3,097
Employee Stock Purchase Plan			40				66				92				161
Total stock-based compensation expense		$	5,451			$	8,008			$	17,765			$	22,443

Summary of Stock Option Activity

The following table summarizes stock option activity for the nine months ended September 30, 2024:

										Weighted
						Weighted				Average
						Average				Remaining				Aggregate
		Number				Exercise				Contractual				Intrinsic
		of Shares				Price				Term				Value
										(in years)				(in thousands)
Outstanding as of December 31, 2023			10,338,724			$	14.42				8.24			$	1,737
Granted			2,739,250				2.88
Exercised			(133,571	)			0.97
Forfeited and cancelled			(2,460,634	)			15.28
Outstanding as of September 30, 2024			10,483,769			$	11.37				7.75			$	920
Vested and expected to vest as of September 30, 2024			10,483,769			$	11.37				7.75			$	920
Exercisable as of September 30, 2024			4,921,703			$	12.92				6.55			$	747

Summary of Assumptions Used in Black-Scholes Option Pricing Model

The fair value of each option award is estimated on the date of grant using the Black-Scholes option pricing model. The following assumptions were used in the Black-Scholes option pricing model to estimate the fair value of stock options granted to employees under the Company’s Plans during the periods presented:

		Nine months ended
		September 30,
		2024				2023
Risk-free interest rate		3.5% - 5.2%				3.4% - 4.8%
Expected volatility		99.7% - 102.6%				68.4% - 73.5%
Expected term (in years)		0.3 - 10.0				0.4 - 10.0
Expected dividend yield			—				—

Summary of Restricted Stock Award Activity

The following table summarizes restricted stock award activity for the nine months ended September 30, 2024:

						Weighted
						Average
						Grant Date
		Number				Fair Value
		of Shares				Per Share
Unvested balance as of December 31, 2023			13,236			$	3.45
Vested			(13,236	)			3.45
Unvested balance as of September 30, 2024			—			$	—

Summary of Restricted Stock Unit Activity

The following table summarizes restricted stock unit activity for the nine months ended September 30, 2024:

						Weighted
						Average
						Grant Date
		Number				Fair Value
		of Shares				Per Share
Unvested Balance as of December 31, 2023			530,726			$	21.11
Granted			—			$	—
Vested			(52,308	)		$	31.42
Forfeited			(49,376	)		$	29.71
Unvested balance as of September 30, 2024			429,042			$	18.86

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Tabular disclosure of the changes in outstanding nonvested restricted stock shares.

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