A summary of the restricted stock unit activity under the Plans for the three months ended March 31, 2023 was as follows:


	Shares			Weighted- Average Grant Date Fair Value
Restricted stock units outstanding as of December 31, 2022		28,212		$	4.78
Granted		270,716		$	2.85
Vested		(7,041	)	$	4.78
Forfeited		(31,271	)	$	2.85
Restricted stock units outstanding as of March 31, 2023		260,616		$	3.01

A summary of the stock option activity under the Plans for the three months ended March 31, 2023 was as follows:


	Shares			Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Life (in years)		Aggregate Intrinsic Value (in thousands)
Outstanding at December 31, 2022		4,311,333		$	7.07		8.2	$	378
Granted		1,424,630			2.75
Exercised		(2,115	)		2.10
Cancelled		(238,022	)		7.02
Outstanding at March 31, 2023		5,495,826		$	5.95		8.5	$	57

The fair value of each stock option granted to employees, directors and non-employees was estimated on the date of grant using the Black-Scholes option-pricing model in the case of the options granted to executive officers, with the following weighted-average assumptions for the three months ended March 31:


	Three Months Ended March 31,
	2023			2022
Risk-free interest rate		3.7	%		2.0	%
Expected dividend yield		—	%		—	%
Expected term (in years)		6.0			4.2
Expected volatility		83.3	%		80.8	%

The weighted-average fair value of options granted to employees, directors and non-employees during the three months ended March 31, 2023 and 2022 was $2.00 and $2.84, respectively.

Stock-based compensation expense included in the Company’s consolidated statements of operations and comprehensive loss was as follows (in thousands):


	Three Months Ended March 31,
	2023		2022
Research and development	$	284	$	227
General and administrative		1,326		617
Total	$	1,610	$	844

Unrecognized share-based compensation related to stock-based options amounted to $10.1 million at March 31, 2023 and is expected to be recognized over a weighted average period of approximately 2.55 years. Unrecognized share-based compensation related to restricted stock units amounted to $0.7 million at March 31, 2023 and is expected to be recognized over a weighted average period of approximately 3.72 years.

At March 31, 2023, there were 1,486,622 shares available for grant under the Company’s 2020 Incentive Award Plan and 280,000 shares available for grant under the Company’s 2022 Inducement Award Plan.