Total stock-based compensation expense under the 2019 Plan was $6.9 million and $6.8 million for the three months ended June 30, 2022 and 2021, respectively, and $13.8 million and $15.4 million for the six months ended June 30, 2022 and 2021, respectively. The total unrecognized compensation expense related to unvested stock option grants as of June 30, 2022 was $45.2 million, with a weighted average remaining vesting period of 2.5 years. Total unrecognized compensation expense related to unvested restricted stock unit (“RSU”) grants as of June 30, 2022 was $23.5 million, with a weighted average remaining vesting period of 3.4 years.

A summary of stock option activity under the 2019 Plan for the six months ended June 30, 2022 is as follows:


	Options Outstanding			Weighted- Average Exercise Price		Aggregate Intrinsic Value (in thousands)
Outstanding at December 31, 2021		22,515,513		$	6.19	$	—
Options Granted		550,000			1.61
Options Canceled		(1,453,020	)		6.56
Options Exercised		(15,499	)		2.37
Outstanding at June 30, 2022		21,596,994		$	6.05	$	539

A summary of RSU activity under the 2019 Plan for the six months ended June 30, 2022 is as follows:


	Number of Shares			Weighted- Average Grant Date Fair Value Per Share
Outstanding at December 31, 2021		3,433,896		$	9.50
RSUs Granted		2,355,500			1.41
RSUs Released		(471,999	)		10.02
RSUs Canceled		(460,069	)		9.44
Outstanding at June 30, 2022		4,857,328		$	5.53

Under the Scilex Holding Company 2019 Stock Option Plan, total stock-based compensation expense was $1.4 million and $1.0 million for the three months ended June 30, 2022 and 2021, respectively, and $2.8 million and $2.9 million for the six months ended June 30, 2022 and 2021, respectively. The total unrecognized compensation expense related to unvested stock option grants as of June 30, 2022 was $5.6 million, with a weighted average vesting period of 1.4 years.

Total stock-based compensation recorded as operating expense for the Company’s 2020 Employee Stock Purchase Plan was $0.2 million for the six months ended June 30, 2022 and was not material for the three months ended June 30, 2022.

Total stock-based compensation recorded as operating expense for the 10-year CEO performance award that was granted to the Company’s chief executive officer in 2020 and tied solely to the Company achieving market capitalization milestones (the “CEO Performance Award”) was $10.2 million and $22.4 million during the three and six months ended June 30, 2022, respectively. As of June 30, 2022, the Company had approximately $65.3 million of total unrecognized stock-based compensation expense remaining under the CEO Performance Award.