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Stock-based Compensation Plans (Tables)

12 Months Ended

Dec. 31, 2023

Share-Based Payment Arrangement [Abstract]

Schedule of Stock Option Activity

The following table summarizes stock option activity for the twelve months ended December 31, 2023 and 2022 under the 2019 Plan:

			Options						Weighted- Average Exercise Price						Weighted- Average Remaining Contractual Term (Years)						Aggregate Intrinsic Value
Outstanding as of January 1, 2023			3,791,688						$	11.33
Granted			2,810,564						$	1.70
Exercised			—						$	—
Forfeited or expired			(406,112)						$	8.52
Outstanding as of December 31, 2023			6,196,140						$	7.15					8.14						$	185,169
Options vested and expected to vest as of December 31, 2023			6,196,140						$	7.15					8.14						$	185,169
Options exercisable as of December 31, 2023			2,534,017						$	11.33					7.19						$	12,381
			Options						Weighted- Average Exercise Price						Weighted- Average Remaining Contractual Term (Years)						Aggregate Intrinsic Value
Outstanding as of January 1, 2022			2,157,460						$	13.54
Granted			1,886,263						$	8.73
Exercised			(852)						$	5.67
Forfeited or expired			(251,183)						$	10.79
Outstanding as of December 31, 2022			3,791,688						$	11.33					8.35						$	375
Options vested and expected to vest as of December 31, 2022			3,791,688						$	11.33					8.35						$	375
Options exercisable as of December 31, 2022			1,398,490						$	13.33					7.50						$	—

Schedule of Valuation Assumptions Used

The following are the underlying assumptions used in the Black-Scholes-Merton option pricing model to determine the fair value of stock options granted to employees and to non-employees under this stock plan:

			2023			2022
Risk-free interest rate			3.98%			2.09%
Expected dividend yield			0%			0%
Expected volatility			96.1%			97.8%
Expected term of options (years)			6.0			6.0

Schedule of Stock-based Compensation Expense for Stock Awards Recognized

Total stock-based compensation expense for all stock awards recognized in the accompanying audited consolidated statements of operations is as follows (in thousands):

			Year  Ended December 31,
			2023						2022
Research and development			$	3,398					$	3,219
General and administrative			3,704						4,710
Total			$	7,102					$	7,929

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Tabular disclosure of allocation of amount expensed and capitalized for award under share-based payment arrangement to statement of income or comprehensive income and statement of financial position. Includes, but is not limited to, corresponding line item in financial statement.

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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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