The Company maintains two equity compensation plans, the 2017 Stock Incentive Plan (as amended, the “2017 Plan”) and the 2019 Inducement Equity Incentive Plan (as amended, the “2019 Inducement Plan”), which provide for the grant of stock-based awards to its directors, officers and employees. The equity plans provide for the grant of non-qualified and incentive stock options, as well as restricted stock units (“RSUs”), restricted stock and other stock-based awards.

As of March 31, 2024, a total of 15,345,127 shares of common stock have been authorized and reserved for issuance under all of the Company's equity plans and 2,749,693 shares of common stock were available for future issuance under such plans.

The weighted-average grant date fair value of options, estimated as of the grant date using the Black-Scholes option pricing model, was $1.12 and $1.29 per option for those options granted during the three months ended March 31, 2024 and 2023, respectively.

The following table summarizes stock option activity under all equity plans (excluding RSUs) during the three months ended March 31, 2024:


	Number of Shares			Weighted Average Exercise Price		Weighted Average Contractual Term		Aggregate Intrinsic Value
						(in years)		(in thousands)
Outstanding as of December 31, 2023		2,865,594		$	10.89		5.76	$	1
Granted		35,604			1.52
Exercised		—			—
Forfeited or cancelled		(20,135	)		13.66
Outstanding as of March 31, 2024		2,881,063		$	10.75		5.51	$	8
Outstanding as of March 31, 2024 - vested and expected to vest		2,881,063		$	10.75		5.51	$	8
Exercisable at March 31, 2024		2,488,009		$	10.37		5.22	$	2

As of March 31, 2024, there was approximately $3.6 million of total unrecognized compensation expense related to stock options, which is expected to be recognized over a weighted-average period of approximately 1.37 years.

The Company granted 3,123,496 RSUs to employees during the three months ended March 31, 2024.

The following table summarizes RSU activity under all equity plans during the three months ended March 31, 2024:


	Number of RSU Shares			Weighted Average Grant Date Fair Value
Outstanding as of December 31, 2023		5,368,807		$	2.45
Granted		3,123,496			1.57
Vested and released		(869,459	)		2.73
Forfeited or cancelled		(149,600	)		1.93
Outstanding as of March 31, 2024		7,473,244		$	2.06

As of March 31, 2024, there was approximately $13.7 million of total unrecognized compensation expense related to RSUs, which is expected to be recognized over a weighted-average period of approximately 3.22 years.

The fair value of the RSUs is determined on the date of grant based on the market price of the Company’s common stock on that date. Each RSU represents the right to receive one share of the Company’s common stock upon vesting. Other than RSUs granted as retention awards, the RSUs vest in four equal annual installments, subject to the individual’s continued service to the Company through the applicable vesting date, and are subject to the terms and conditions of the Company’s form of RSU agreement under the 2017 Plan and 2019 Inducement Plan, as applicable.

In September 2022, the Company approved an award of 140,000 performance-based stock units as part of an executive inducement grant ("Inducement PSUs"). The Inducement PSUs were awarded based on certain performance criteria relating to pipeline execution, business development, and financial stewardship. As these performance criteria were deemed to be achieved by May 31, 2023, 70,001 of the Inducement PSUs vested in September 2023 and the remaining 69,999 of the Inducement PSUs will vest in September 2024 upon fulfilment of the service condition. The Company recognized less than $0.1 million of expense associated with the Inducement PSUs during the three months ended March 31, 2024.

The following table summarizes Inducement PSU activity under all equity plans during the three months ended March 31, 2024:


	Number of Inducement PSU Shares		Weighted Average Grant Date Fair Value
Outstanding as of December 31, 2023		69,999	$	1.08
Granted		—		—
Vested and released		—		—
Forfeited or cancelled		—		—
Outstanding as of March 31, 2024		69,999	$	1.08

The Company recorded share-based compensation expense related to incentive stock options, nonqualified stock options, stock grants, and stock-based awards in the following expense categories of its consolidated statements of operations and comprehensive loss (in thousands):


	Three Months Ended March 31,
	2024		2023

Research and development expenses	$	690	$	798
General and administrative expenses		1,333		1,372
Total	$	2,023	$	2,170