During the three months ended March 31, 2022, the Company’s stock option compensation expense was approximately $3.4 million, and during the three months ended March 31, 2021, the Company’s stock option compensation expense was approximately $2.7 million. There was no recognized tax benefit in either of the periods. As of March 31, 2022, unamortized expense balance was $37.8 million, to be amortized over a weighted average period of 2.76 years.

Stock option activity during the three months ended March 31, 2022 is as follows:


	Shares subject to options			Weighted- average exercise price		Weighted- average remaining contractual term (years)		Aggregate Intrinsic Value (in thousands)
Outstanding as of January 1, 2022		5,692,514		$	12.07	8.63		$	16,763
Granted		3,642,824		$	3.06
Exercised		(4,966	)	$	2.00
Cancelled		(90,298	)	$	10.94
Outstanding as of March 31, 2022		9,240,074		$	8.53		8.97	$	115

Options vested and expected to vest as of March 31, 2022		9,205,154		$	8.55		8.97	$	115
Options vested and exercisable as of March 31, 2022		2,186,541		$	9.65		8.19	$	83

The weighted-average grant date fair value of options granted was $2.12 per share during the three months ended March 31, 2022, and $17.33 during the three months ended March 31, 2021.

During the three months ended March 31, 2022, the Company recorded a total stock-based compensation expense related to the restricted stock awards of $76,000. During the three months ended March 31, 2021, the Company recorded a total stock-based compensation expense related to the restricted stock awards of $90,000. As of March 31, 2022, unrecognized stock-based compensation expense related to outstanding unvested shares of restricted stock was de minimis.

The following table summarizes the Company’s restricted common stock activity for the three months ended March 31, 2022:


	Number of Awards			Weighted- Average Grant Date Fair Value		Aggregate Fair Value (in thousands)
Issued and unvested as of January 1, 2022		89,054		$	1.30	$	117
Restricted stock awards granted		—
Restricted stock awards vested		(67,816	)	$	1.30	$	(88	)
Issued and unvested as of March 31, 2022		21,238		$	1.30	$	29

During the three months ended March 31, 2022 and 2021, the Company did not issue shares of common stock, upon exercise of unvested stock options or purchases for unvested restricted stock awards. As of March 31, 2022 and December 31, 2021, there were 105,692 and 163,855 shares of Common Stock held by employees subject to repurchase at an aggregate price of approximately $192,000 and $276,000, respectively. A corresponding liability was recorded and included in accrued expenses on the condensed consolidated balance sheet as of March 31, 2022 and December 31, 2021, respectively.

During the three months ended March 31, 2022, the Company recorded total stock-based compensation expense of $306,000 related to the employee stock purchase plan. The employee stock purchase plan began in the second quarter of 2021, therefore there was no compensation expense as of the three months ended March 31, 2021. No purchases of common stock were made as of the three months ended March 31, 2022.

Stock-based compensation expense was allocated as follows for the three months ended March 31, 2022 and 2021 (in thousands):


	Three Months Ended
	March 31,
	2022		2021
Research and development	$	2,001	$	1,709
General and administrative		1,785		1,047
Total	$	3,786	$	2,756