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Stock-Based Compensation (Tables)

6 Months Ended

Jun. 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								Six months ended
		June 30,								June 30,
		2024				2023				2024				2023
Research and development		$	2,574			$	4,117			$	5,434			$	7,331
General and administrative			3,197				3,751				6,880				7,104
Total stock-based compensation expense		$	5,771			$	7,868			$	12,314			$	14,435

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

		Three months ended								Six months ended
		June 30,								June 30,
		2024				2023				2024				2023
Stock options		$	4,885			$	6,735			$	10,362			$	12,239
Restricted stock awards			10				28				37				55
Restricted stock units			850				1,047				1,863				2,046
Employee Stock Purchase Plan			26				58				52				95
Total stock-based compensation expense		$	5,771			$	7,868			$	12,314			$	14,435

Summary of Stock Option Activity

The following table summarizes stock option activity for the six months ended June 30, 2024:

										Weighted
						Weighted				Average
						Average				Remaining				Aggregate
		Number				Exercise				Contractual				Intrinsic
		of Shares				Price				Term				Value
Outstanding as of December 31, 2023			10,338,724			$	14.42				8.24			$	1,737
Granted			2,044,500				3.08
Exercised			(127,996	)			0.92
Forfeited and cancelled			(1,462,027	)			17.18
Outstanding as of June 30, 2024			10,793,201			$	12.05				7.88			$	1,142
Vested and expected to vest as of June 30, 2024			10,793,201			$	12.05				7.88			$	1,142
Exercisable as of June 30, 2024			4,962,290			$	12.86				6.60			$	821

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:

		Six months ended
		June 30,
		2024				2023
Risk-free interest rate		3.9% - 4.7%				3.4% - 4.8%
Expected volatility		99.7% - 102.6%				68.4% - 73.5%
Expected term (in years)		5.5 - 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 six months ended June 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 June 30, 2024			—			$	—

Summary of Restricted Stock Unit Activity

The following table summarizes restricted stock unit activity for the six months ended June 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			(51,558	)		$	31.46
Forfeited			(34,450	)		$	28.65
Unvested balance as of June 30, 2024			444,718			$	19.33

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

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