We use equity-based compensation programs to provide long-term performance incentives for our employees. These incentives consist primarily of stock options and RSUs. In December 2008, we adopted the MEI Pharma, Inc. 2008 Stock Omnibus Equity Compensation Plan (the “Omnibus Plan”), as amended and restated from time to time, under which 29,014,794 shares of common stock are authorized for issuance. The Omnibus Plan provides for the grant of options and/or other stock-based or stock-denominated awards to our non-employee directors, officers, employees and advisors. As of June 30, 2022, there were 9,154,665 shares available for future grant under the Omnibus Plan.

In May 2021, we adopted the 2021 Inducement Plan ("Inducement Plan"), under which 2,500,000 shares of common stock are authorized for issuance. The Inducement Plan is intended to assist us in attracting and retaining selected individuals to serve as employees who are expected to contribute to our success, by providing an inducement for such individuals to enter into employment with us, and to achieve long-term objectives that will benefit stockholders of the Company. As of June 30, 2022, there were 143,000 shares available for future grant under the Inducement Plan.

Total share-based compensation expense for all stock awards consists of the following, in thousands:


	Years Ended June 30,
	2022		2021		2020
Research and development	$	2,610	$	4,144	$	2,777
General and administrative		5,740		6,101		4,024
Total share-based compensation	$	8,350	$	10,245	$	6,801

Stock options granted to employees vest 25% one year from the date of grant and ratably each month thereafter for a period of 36 months and expire ten years from the date of grant. Stock options granted to directors vest ratably each month for a period of 12 months from the date of grant and expire ten years from the date of grant. As of June 30, 2022, there were a total of 19,934,007 options outstanding. Of the total outstanding options, 17,577,007 were granted under the Omnibus Plan and 2,357,000 were granted under the Inducement Plan.

A summary of our stock option activity and related data follows:


	Number of Options	Weighted-Average Exercise Price	Weighted-Average Remaining Contractual Term (in years)	Aggregate Intrinsic Value
Outstanding at June 30, 2021	16,668,542	$3.01
Granted	7,124,734	$2.57
Exercised	(348,547)	$1.64
Forfeited	(3,510,722)	$3.15
Outstanding at June 30, 2022	19,934,007	$2.85	7.4	$50,600
Vested and exercisable at June 30, 2022	10,844,635	$2.95	6.2	$—

As of June 30, 2022, the aggregate intrinsic value of outstanding options is calculated as the difference between the exercise price of the underlying options and the closing price of our common stock of $0.61 on that date. The total fair value of options that vested during the years ended June 30, 2022, 2021 and 2020 was $9.0 million, $6.4 million and $5.4 million, respectively.

Unrecognized compensation expense related to non-vested stock options totaled $6.6 million as of June 30, 2022. Such compensation expense is expected to be recognized over a weighted-average period of 1.7 years. As of June 30, 2022, we expect all outstanding options to vest.

We use a Black-Scholes valuation model to estimate the grant date fair value of stock options. To calculate these fair values, the following weighted-average assumptions were used:


	Years Ended June 30,
	2022			2021			2020
Risk-free interest rate		1.3	%		0.5	%		1.7	%
Expected life (years)		6.0			6.0			6.0
Expected volatility		69.6	%		80.1	%		74.1	%
Dividend yield		0.0	%		0.0	%		0.0	%
Weighted-average grant date fair value	$	1.57		$	2.30		$	1.64

A summary of our RSU activity and related data follows:


	Number of RSUs	Weighted-Average Grant Date Fair Value
Non-vested at June 30, 2021	400,650	$3.49
Vested	(130,000)	$3.49
Forfeited	(86,250)	$3.49
Non-vested at June 30, 2022	184,400	$3.49

Each RSU represents the contingent right to receive one share of our common stock. Under the terms of the Omnibus Plan, each of the RSUs is calculated as 1.25 shares of common stock for purposes of determining the number of shares available for future grant. As of June 30, 2022, unrecognized compensation expense related to the unvested portion of our RSUs was de minimis.