Stock option activity under the 2019 Equity Incentive Plan (the “2019 Plan”) is set forth below for the six months ended June 30, 2022:


				Weighted		Average
				Average		Remaining		Aggregate
	Number of			Exercise		Contractual		Intrinsic
	Shares			Price Per		Term		Value
	Outstanding			Share		(Years)		(in thousands)
Balances at December 31, 2021		2,024,681		$	18.33		8.0	$	38,417
Stock options authorized		—
Stock options granted		1,005,432			19.39
Stock options exercised		(44,910	)		8.24
Stock options forfeited		(77,607	)		24.96
Balances at June 30, 2022		2,907,596		$	18.67		8.3	$	8,158

As of June 30, 2022, 2,942,751 shares remained available for issuance under the 2019 Plan.

Restricted stock unit (“RSU”) activity under the 2019 Plan is set forth below for the six months ended June 30, 2022:


				Weighted
				Average
	Number of			Grant Date
	Shares			Fair Value
	Outstanding			Per Share
Balances at December 31, 2021		40,500		$	44.66
RSUs granted		—			—
RSUs vested and settled		(13,500	)		44.66
RSUs forfeited		—			—
Balances at June 30, 2022		27,000		$	44.66

Total stock-based compensation expense recognized for options and RSUs granted to both employees and non-employees and for the 2019 Employee Stock Purchase Plan (the “2019 ESPP”) was as follows (in thousands):


	For the Three Months Ended June 30,				For the Six Months Ended June 30,
	2022		2021		2022		2021
Research and development	$	1,269	$	1,627	$	2,448	$	3,101
General and administrative		1,403		1,261		2,926		2,474
Total stock-based compensation expense	$	2,672	$	2,888	$	5,374	$	5,575

As of June 30, 2022, unrecognized stock-based compensation expense related to outstanding unvested stock options and RSUs that are expected to vest was $24.2 million. This unrecognized stock-based compensation expense is expected to be recognized over 2.8 years.

The Company recorded stock-based compensation expense related to the 2019 ESPP of $0.2 million and $0.3 million for the three and six months ended June 30, 2022, respectively, and $1.0 million and $1.8 million for the three and six months ended June 30, 2021, respectively.