On March 11, 2022, upon the recommendation of the compensation committee of the Company’s board of directors, and subject to stockholder approval, the Company’s board of directors adopted the 2022 Equity Incentive Plan. At the Company’s 2022 Annual Meeting of Stockholders on May 17, 2022, the stockholders of the Company approved the 2022 Equity Incentive Plan, which replaces the Company’s 2013 Stock Incentive Plan. Following approval of the 2022 Equity Incentive Plan, no additional awards may be made under the 2013 Stock Incentive Plan.

The Company also maintains the 2013 Employee Stock Purchase Plan. At the Company’s 2022 Annual Meeting of Stockholders on May 17, 2022, the stockholders of the Company also approved an amendment to the 2013 Employee Stock Purchase Plan to eliminate the annual “evergreen” provision and authorize an aggregate of 2,500,000 shares of the Company’s common stock for issuance under such plan. Such amendment will become effective as of September 1, 2022.

In addition, during the year ended December 31, 2021, the Company granted options to purchase an aggregate of 248,366 shares of the Company's common stock and 106,955 restricted stock units (RSUs) to four new employees as equity inducement awards outside of the Company's 2013 Stock Incentive Plan and material to the employees’ acceptance of employment with the Company. These options have a weighted average exercise price of $5.12 per share, and the RSUs have a weighted average grant date fair value of $5.08 per unit. On April 1, 2022, the Company granted options to purchase an aggregate of 800,000 shares of the Company's common stock to a new employee as equity inducement awards outside of the Company's 2013 Stock Incentive Plan and material to the employee’s acceptance of employment with the Company. These options have an exercise price of $1.14 per share, which is equal to the closing price of the Company's common stock on April 1, 2022, the grant date of these options. These equity inducement awards were approved in accordance with Nasdaq Listing Rule 5635(c)(4), and these equity inducement awards remained outstanding as of June 30, 2022. These equity inducement awards are included in stock-based compensation expense and the following tables.

Total stock-based compensation expense related to stock options, restricted stock units, shares issued under the 2013 Employee Stock Purchase Plan, and shares of common stock issued to non-employee directors in lieu of board and board committee fees was $4.5 million and $6.7 million for the three months ended June 30, 2022 and 2021, respectively, and $9.7 million and $13.7 million for the six months ended June 30, 2022 and June 30, 2021, respectively.

Stock-based compensation expense is classified in the condensed consolidated statements of operations and comprehensive loss as follows:


	Three Months Ended June 30,				Six Months Ended June 30,
	2022		2021		2022		2021
	(In thousands)				(In thousands)
Research and development	$	1,417	$	2,023	$	3,209	$	4,253
General and administrative		3,034		4,695		6,531		9,480
Total	$	4,451	$	6,718	$	9,740	$	13,733

The weighted-average grant date fair value of options, estimated as of the grant date using the Black-Scholes option pricing model, was $0.84 and $5.10 per option for those options granted during the six months ended June 30, 2022 and June 30, 2021, respectively.

Key assumptions used to apply this pricing model were as follows:


	Three Months Ended June 30,						Six Months Ended June 30,
	2022			2021			2022			2021
Risk-free interest rate		2.7	%		0.8	%		2.2	%		0.5	%
Expected life of options	5.87 years			5.71 years			5.94 years			5.94 years
Expected volatility of underlying stock		74.2	%		70.7	%		73.1	%		70.5	%
Expected dividend yield		0.0	%		0.0	%		0.0	%		0.0	%

The following is a summary of stock option activity for the six months ended June 30, 2022:


	Number of Options			Weighted Average Exercise Price per Share		Weighted Average Remaining Contractual Term		Aggregate Intrinsic Value
	(In thousands)					(In years)		(In thousands)
Outstanding at December 31, 2021		12,946		$	11.61
Granted		5,681			1.29
Exercised		—			—
Forfeited		(3,204	)		11.26
Outstanding at June 30, 2022		15,423		$	7.87		8.06	$	1,073
Exercisable at June 30, 2022		5,525		$	13.85		5.95	$	—

As of June 30, 2022, there was $23.8 million of unrecognized compensation cost related to stock options that are expected to vest. These costs are expected to be recognized over a weighted average remaining vesting period of 2.71 years.

During the six months ended June 30, 2022, 87,500 RSUs were granted to an executive (the “executive RSUs”) and 80,946 RSUs were granted to non-employee directors (the “non-employee RSUs”). RSUs vest based on continuing service to the Company. Assuming all service conditions are achieved, the executive RSUs will vest in three equal installments with the first installment vesting approximately six and a half months following the grant date and the second and third installments vesting annually thereafter, and the non-employee director RSUs will vest as to 100% of the RSUs on the earlier of the first anniversary of the grant date and the date of the succeeding annual meeting of stockholders.


	Number of Service Based RSU Shares (in thousands)			Weighted Average Grant Date Fair Value
Outstanding at December 31, 2021		2,222		$	8.70
Granted		169			1.00
Vested		(361	)		12.57
Forfeited		(537	)		7.62
Outstanding at June 30, 2022		1,493		$	7.28

Compensation expense totaling $1.1 million and $2.3 million was recognized for the RSUs for the three and six months ended June 30, 2022, respectively. Compensation expense totaling $1.2 million and $2.2 million was recognized for the RSUs for the three and six months ended June 30, 2021, respectively.

As of June 30, 2022, there was $8.0 million of unrecognized compensation cost related to RSUs that are expected to vest. These costs are expected to be recognized over a weighted average remaining vesting period of 1.72 years.