The Company has four plans that provide for equity-based compensation. Two are legacy plans for which no further grants are to be made. As of April 30, 2022, 787,918 stock options remain available for grant under the 2017 Equity Incentive Plan (“2017 Plan”). There are 4,904,939 shares of the Company’s common stock that are reserved for issuance upon exercise or settlement of stock options or other awards under these four plans. Initial awards generally vest 25% after one year and then ratably on a monthly basis over the next three years. Recurring grants typically vest on a monthly basis over four years. Stock option grants expire after ten years.

In July 2021, the Company approved the 2021 Equity Inducement Plan to reserve 350,000 shares of its common stock to be used exclusively for grants of awards as a material inducement to such individuals' entry into employment with the Company within the meaning of Rule 5635(c)(4) of the Nasdaq Listing Rules. As of April 30, 2022, there were 164,000 shares remaining available to be issued under the 2021 Inducement Plan.

The Company also has in place the 2017 Employee Stock Purchase Plan (“ESPP”), under which employees have the option to purchase the Company’s common stock at a discount of 15% from the market price during predetermined offering periods each year. There are 678,976 shares available for future issuance under the ESPP as of April 30, 2022. Activity under the ESPP was not significant in the periods presented.

The Company recognizes stock-based compensation expense over the requisite service period based on the grant date fair value of the award. The Company has elected to use the Black-Scholes option pricing model to determine the fair value of awards granted. The determination of the fair value of stock-based awards utilizing the Black-Scholes model is affected by the share price and a number of assumptions, including expected volatility, expected life, risk-free interest rate and expected dividends. The Company determined the expected volatility by using available historical price information. The expected life of the awards is estimated based on the simplified method. The risk-free interest rate assumption is based on observed interest rates appropriate for the terms of the awards. The dividend yield assumption is based on history and expectation of paying no dividends. Forfeitures have not been material in the periods presented.

The fair value of the share-based awards was measured with the following weighted-average assumptions for the fiscal years ended April 30:


	2022	2021	2020
Risk-free interest rate	1.08%	0.47%	2.06%
Expected life of the options	6.25 years	6.25 years	6.25 years
Expected volatility of the underlying stock	85.4%	81.7%	81.1%
Expected dividend rate	0%	0%	0%

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


	Year ended April 30,
	2022		2021		2020
Research and development	$	5,189	$	3,174	$	1,944
General and administrative		5,897		3,944		2,504
Total stock-based compensation expense	$	11,086	$	7,118	$	4,448

A summary of option activity for the year ended April 30, 2022 is presented below:


	Shares			Weighted Average Exercise Price		Weighted Average Remaining Contractual Life		Aggregate Intrinsic Value
Outstanding at May 1, 2021		2,836,598		$	13.22		7.60	$	33,514
Options Exercised		(114,199	)		8.49
Options Granted		1,007,000			23.73
Options Cancelled		(136,378	)		18.86
Outstanding at April 30, 2022		3,593,021		$	16.10		7.26	$	6,430
Exercisable at April 30, 2022		2,067,684		$	13.61		6.51	$	5,454
Vested and expected to vest at April 30, 2022		3,593,021		$	16.10		7.26	$	6,430

The weighted-average grant date fair value of stock options granted during the years ended April 30, 2022, 2021 and 2020 was $16.98, $8.24, and $15.76, respectively. The total intrinsic value (the amount by which the fair market value exceeded the exercise price) of stock options exercised during the years ended April 30, 2022, 2021 and 2020 was $0.8 million, $4.2 million and $0.4 million, respectively. The total cash received by the Company as a result of employee stock option exercises during the years ended April 30, 2022, 2021 and 2020 was $1.4 million, $1.5 million, and $0.2 million, respectively.

As of April 30, 2022, there was $17.6 million of unrecognized compensation expense related to unvested awards, which is expected to be recognized over a weighted-average period of 2.6 years.

In March 2022, the Company granted 360,000 performance-based restricted stock units (“PSUs”) to five executives under the 2017 Equity Incentive Plan with a grant date fair value of $15.39. The performance-based metric for the awards is the success of the Company’s Phase 3 trial of the sebetralstat program. Upon successful completion of the performance metric, 100% of the PSUs will be eligible to vest. As of April 30, 2022 the Company has not recognized any compensation expense related to these awards as the achievement of the Performance Metric is not yet deemed to be probable.