The Company has two equity incentive plans that provide for the granting of stock options, restricted stock, stock appreciation rights, stock units, and performance cash awards to certain employees, members of the board of directors, and consultants of the Company with a generally prescribed contractual term of ten years. As of June 30, 2022, there were 5,050,230 shares of common stock available for grant under the Company’s equity incentive plans.

In 2019, 2020, and 2022 the Company granted performance cash awards under its Management Cash Incentive Plan, as amended. The performance cash awards vest in four annual installments from the date of grant and entitle the employees to receive a cash payment, on the earlier of (i) four years from the date of grant or (ii) a change of control, equal in value to the amount by which the then value of the Company’s common stock exceeds the base value. As of June 30, 2022, $0.6 million was accrued as compensation expense for vested performance cash awards.

The Company recognizes stock-based compensation expense over the requisite service period. The Company's share-based awards are accounted for as equity instruments. The amounts included in the consolidated statements of operations relating to stock-based compensation associated with the two equity incentive plans, performance cash awards, and Helio founders’ shares are as follows:


	Three Months Ended June 30,				Six Months Ended June 30,
	2022		2021		2022		2021
Research and development expenses	$	640,017	$	1,180,305	$	1,485,683	$	2,373,172
General and administrative expenses		654,318		1,143,256	$	1,745,230	$	2,332,046
Total stock-based compensation expense	$	1,294,335	$	2,323,561	$	3,230,913	$	4,705,218

The table below summarizes activity relating to stock options under the incentive plans for the six months ended June 30, 2022:


	Number of Shares			Weighted Average Exercise Price		Weighted Average Contractual Term		Aggregate Intrinsic Value(a)
Outstanding at December 31, 2021		4,622,870		$	6.73
Granted		1,721,297		$	4.04
Forfeitures		(479,829	)	$	6.19
Outstanding at June 30, 2022		5,864,338		$	5.99		7.06	$	1,600,420
Exercisable at June 30, 2022		3,661,884		$	6.18		5.75	$	1,190,252

As of June 30, 2022, unamortized stock-based compensation for stock options outstanding was $8.0 million and is expected to be recognized over a weighted average period of 2.58 years. Total unrecognized compensation cost will be adjusted for future forfeitures, if necessary.

The table below summarizes activity relating to restricted stock units (RSUs) for the six months ended June 30, 2022:


	Number of Shares
Outstanding at December 31, 2021		501,255
Granted		407,717
Cancelled / Forfeited		(169,586	)
Vested / Settled		(202,526	)
Outstanding at June 30, 2022		536,860

The weighted-average grant date fair value of RSUs granted was $4.52 per share for the six months ended June 30, 2022. As of June 30, 2022, the outstanding RSUs had unamortized stock-based compensation of $2.2 million with a weighted-average remaining recognition period of 2.68 years and an aggregate intrinsic value of $2.1 million.

At June 30, 2022, the Company had 1,807,619 shares available for issuance under the 2016 Employee Stock Purchase Plan (2016 ESPP). A summary of the weighted-average grant-date fair value, and total stock-based compensation expense recognized related to the 2016 ESPP are as follows:


	Six Months Ended June 30,
	2022		2021
Weighted-average grant-date fair value per share	$	1.65	$	2.49
Total stock-based compensation expense	$	33,342	$	23,127