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. As of March 31, 2022, the Company had not sold any shares of common stock under the Sales Agreement.

The following table summarizes the Company’s stock option activity since December 31, 2021:


	Number of Shares			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term		Aggregate Intrinsic Value
						(in years)
Outstanding as of December 31, 2021		11,517,189		$	11.10		7.42	$	28,006,768
Granted		3,638,997			7.41
Exercised		(92,478	)		2.78
Forfeited		(243,395	)		10.19
Outstanding as of March 31, 2022		14,820,313		$	10.26		7.78	$	19,851,760
Options exercisable as of March 31, 2022		6,183,983		$	9.53		6.01	$	12,878,550

The weighted average grant-date fair value of stock options granted during the three months ended March 31, 2022 and 2021 was $5.90 and $19.33 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 562 thousand 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, 2022, 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, 2022, the Company did not record any expense for these stock options from the dates of issuance through March 31, 2022.

The Company has granted restricted stock units ("RSUs") with time-based vesting conditions. The table below summarizes the Company’s restricted stock unit activity since December 31, 2021:


	Number of Shares			Weighted Average Grant Date Fair Value
Unvested restricted stock units as of December 31, 2021		734,755		$	17.68
Granted		989,544		$	7.43
Vested		(69,195	)	$	24.32
Forfeited		(72,463	)	$	13.11
Unvested restricted stock units as of March 31, 2022		1,582,641		$	11.19

The Company has granted RSUs with service-based vesting conditions. RSUs represent the right to receive shares of common stock upon meeting specified vesting requirements. Unvested shares of restricted common stock may not be sold or transferred by the holder. These restrictions lapse according to the service-based vesting conditions of each award. During the three months ended March 31, 2022, the Company granted 989,544 RSUs. RSU’s 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.

During the year ended December 31, 2021, the Company granted performance-based restricted stock awards to two employees for the purchase of an aggregate of 85 thousand shares of common stock with a grant date fair value of $9.59 per share and 40 thousand shares with a grant date fair value of $20.35 per share. These restricted stock awards vest only upon achievement of specified performance targets. As of March 31, 2022, none of these awards were vested 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, 2022, the Company did not record any expense for these awards from the dates of issuance through March 31, 2022.

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


	Three Months Ended March 31,
	2022		2021
Research and development expenses	$	2,483	$	2,137
General and administrative expenses		2,596		1,487
	$	5,079	$	3,624