Stock-Based Compensation

9 Months Ended

Sep. 30, 2024

Share-Based Payment Arrangement [Abstract]

6. Stock-Based Compensation

In January 2024 and 2023, the number of shares of common stock available for issuance under the 2018 Equity Incentive Plan (the "2018 Plan") was increased by approximately 2.1 million shares in each period, as a result of the automatic increase provision in the 2018 Plan.

Stock Options

Stock option activity, including stock options and performance-based stock options under the 2021 Long-Term Performance Incentive Plan (“2021 LTPIP”), 2018 Plan and 2015 Plan is summarized as follows:


	Number of Options			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term (in years)		Aggregate Intrinsic Value (in thousands)
Outstanding at December 31, 2023		17,601,466		$	43.86		7.29	$	933
Granted		4,173,150		$	2.56
Exercised		(8,333	)	$	4.54
Forfeited or canceled		(1,105,760	)	$	31.29
Outstanding at September 30, 2024		20,660,523		$	36.21		7.10	$	1,190

Restricted Shares

Restricted share activity, including restricted stock awards, restricted stock units, and performance-based restricted stock units, under the 2018 Plan is summarized as follows:


	Number of Restricted Shares			Weighted Average Grant Date Fair Value
Unvested at December 31, 2023		164,817		$	49.87
Granted		64,200		$	3.02
Vested		(79,346	)	$	60.15
Canceled		(27,322	)	$	44.73
Unvested at September 30, 2024		122,349		$	19.77

Stock-Based Compensation Expense

Stock-based compensation is classified in the condensed consolidated statements of operations and comprehensive loss as follows (in thousands):


	Three Months Ended September 30,				Nine Months Ended September 30,
	2024		2023		2024		2023
Research and development	$	6,295	$	2,733	$	23,936	$	32,093
General and administrative		8,515		11,213		27,658		33,634
Total stock-based compensation	$	14,810	$	13,946	$	51,594	$	65,727