On May 21, 2021, the Company entered into a Sales Agreement (the “Sales Agreement”) with Cowen and Company, LLC (“Cowen”) to sell shares of the Company’s common stock, with aggregate gross sales proceeds of up to $150,000, from time to time, through an “at the market” equity offering program under which Cowen acts as sales agent. During the three months ended March 31, 2023, the Company sold 787,170 shares of common stock under the Sales Agreement, at an average price of approximately $5.67 per share, raising aggregate net proceeds of approximately $4,238 after deducting an aggregate commission of approximately 3% and other issuance costs. During the three months ended March 31, 2022, the Company did not sell any shares of common stock under the Sales Agreement.

The following table summarizes the Company’s stock option activity since December 31, 2022:


	Number of Shares			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term		Aggregate Intrinsic Value
						(in years)
Outstanding as of December 31, 2022		14,940,034		$	10.03		7.25	$	11,608
Granted		2,118,845		$	5.50
Exercised		(56,523	)	$	3.32
Forfeited		(176,212	)	$	10.46
Outstanding as of March 31, 2023		16,826,144		$	9.48		7.31	$	12,188
Options exercisable as of March 31, 2023		8,676,217		$	10.16		5.98	$	8,764

The weighted average grant-date fair value of stock options granted during the three months ended March 31, 2023 and 2022 was $4.56 and $5.90 per share, respectively.

During the year ended December 31, 2021, the Company granted performance-based stock options to employees for the purchase of an aggregate of approximately 562,000 shares of common stock with a grant date fair value of $5.53 per share. These stock options are exercisable only upon achievement of specified performance targets. As of March 31, 2023, none of these options were exercisable because none of the specified performance targets had been achieved. Because achievement of the specified performance targets was not deemed probable as of March 31, 2023, the Company did not record any expense for these stock options from the dates of issuance through March 31, 2023.

The following table summarizes the Company’s restricted stock unit activity since December 31, 2022:


	Number of Shares			Weighted Average Grant Date Fair Value
Unvested restricted stock units as of December 31, 2022		1,549,540		$	9.37
Granted		3,014,810		$	5.50
Vested		(259,023	)	$	8.91
Forfeited		(89,493	)	$	9.50
Unvested restricted stock units as of March 31, 2023		4,215,834		$	6.63

The Company has granted restricted stock units with service-based vesting conditions ("RSUs") and performance-based vesting conditions ("PSUs"). RSUs and PSUs represent the right to receive shares of common stock upon meeting specified vesting requirements. RSUs and PSUs may not be sold or transferred by the holder and vest according to the service-based or performance-based vesting conditions of the award. During the three months ended March 31, 2023 and 2022, the Company granted 1,692,095 and 989,544 RSUs and 1,322,715 and 0 PSUs, respectively. RSUs generally vest over four years, with 25% vesting after one year, and the remaining 75% vesting quarterly over the next 3 years, subject to continued service to the Company through the applicable vesting date. PSUs vest according to the performance requirements of the awards, generally when the Company has determined that the specified performance targets have been achieved.

During the year ended December 31, 2021, the Company granted PSUs to two employees for the purchase of an aggregate of 85,000 shares of common stock with a grant date fair value of $9.59 per share and 40,000 shares of common stock with a grant date fair value of $20.35 per share. These PSUs vest only upon achievement of specified performance targets. In October 2022, 42,500 of the PSUs with a grant date fair value of $9.59, and 20,000 of the PSUs with a grant date fair value of $20.35, vested fully, as the associated performance targets were achieved. Accordingly, the Company recorded $815 in compensation expense during the year ended December 31, 2022, with respect to these PSUs. As of March 31, 2023, the remaining PSUs underlying these awards were not vested because the associated targets had not been achieved. In addition, the performance targets were not deemed probable of achievement. Accordingly, the Company did not record any expense for these PSUs from the dates of issuance through March 31, 2023.

During the three months ended March 31, 2023, the Company granted PSUs to employees for the purchase of an aggregate of 1,322,715 shares of common stock with a grant date fair value of $5.50. These PSUs begin to vest ratably only upon achievement of

specified performance targets. As of March 31, 2023, none of these PSUs had started to vest because the associated targets had not been achieved and were not deemed probable of achievement. Accordingly, the Company did not record any expense for these PSUs from the date of issuance through March 31, 2023.

The Company recorded stock-based compensation expense in the following expense categories of its condensed consolidated statements of operations and comprehensive loss (in thousands):


	Three Months Ended March 31,
	2023		2022
Research and development expenses	$	3,731	$	2,483
General and administrative expenses		3,119		2,596
	$	6,850	$	5,079