On July 1, 2022, the Company’s board of directors approved the 2022 Equity Inducement Plan (the “2022 Plan”), which became effective on that date. The 2022 Plan allows the Company to make equity-based incentive awards to its officers and employees without stockholder approval pursuant to Rule 5635(c)(4) of the NASDAQ Listing Rules, or any successor rule relating to inducement awards. Unless earlier terminated by the Board, 2022 Plan will terminate on the tenth anniversary of the effective date. The Company has initially reserved 1,400,000 shares of its common stock for the issuance of awards under the 2022 Plan. As of December 31, 2022, options to purchase 400,692 shares of common stock and 320,550 restricted stock units were outstanding under the 2022 Plan and 678,758 shares remained available for future issuance under the 2022 Plan.

On September 27, 2021, the Company’s board of directors and stockholders approved the 2021 Equity Incentive Plan (the “2021 Plan”), which became effective on October 7, 2021, when the Company’s registration statement was declared effective by the SEC. The 2021 Plan allows the Company to make equity-based and cash-based incentive awards to its officers, employees, directors and consultants. The Company has initially reserved 3,852,807 shares of its common stock for the issuance of awards under the 2021 Plan. The number of shares of common stock reserved for issuance under the 2021 Plan will automatically increase annually on the first day of each fiscal year, beginning with the fiscal year ending December 31, 2022, and continuing until (and including) the fiscal year ending December 31, 2031 by the lesser of (i) 5% of the total number of shares of common stock outstanding on December 31st of the immediately preceding fiscal year and (ii) the number of shares as may be determined by the board of directors. As a result of the evergreen provision of the 2021 Plan, the Company added an additional 1,639,643 shares of common stock to the 2021 Plan as of January 1, 2022. The maximum number of shares of common stock that may be issued pursuant to the exercise of incentive options under the 2021 Plan is 7,705,614. Unless earlier terminated by the Board, 2021 Plan will terminate on the tenth anniversary of the effective date. As of December 31, 2022, options to purchase 2,668,700 shares of common stock and 2,449,172 restricted stock units were outstanding under the 2021 plan and 360,924 shares remained available for future issuance under the 2021 plan.

In 2019, the Company established the 2019 Equity Incentive Plan (the "2019 Plan"), under which the Company is allowed to grant options and restricted stock to its employees and non-employees. The maximum number of shares of common stock reserved for issuance under the 2019 Plan is 4,042,408 shares. Options granted under the 2019 Plan include incentive stock options that can be granted only to the Company’s employees and non-statutory stock options that can be granted to the Company’s employees, consultants, advisors and directors. The 2019 Plan also permits the Company to issue restricted stock awards. Unless earlier terminated by the Board, the 2019 Plan will terminate on the tenth anniversary of the effective date.

Prior to the IPO, the exercise prices, vesting and other restrictions of the awards granted under the 2019 Plan were determined by the board of directors, except that no stock option may be issued with an exercise price less than the fair market value of the common stock at the date of the grant or have a term in excess of ten years. Options granted under the 2019 Plan are exercisable in whole or in part at any time subsequent to vesting. As of December 31, 2022, options to purchase 2,651,023 shares of common stock and 94,379 restricted stock units were outstanding under the 2019 Plan and 657,484 shares remained available for future issuance under the 2019 Plan.

On September 27, 2021, the Company’s board of directors and stockholders approved the 2021 Employee Stock Purchase Plan (the “2021 ESPP”), which became effective on October 7, 2021, when the Company’s registration statement was declared effective by the SEC. The 2021 ESPP initially reserved and authorized the issuance of up to a total of 424,595 shares of common stock to participating employees. The number of shares of common stock reserved for issuance under the ESPP will automatically increase annually on the first day of each fiscal year, beginning with the fiscal year ending December 31, 2022, and continuing until (and including) the fiscal year ending December 31, 2031 by the lesser of (1) 1% of the total number of shares of common stock outstanding on December 31st of the immediately preceding fiscal year and (ii) the number of shares as may be determined by the board of directors. As a result of the evergreen provision of the 2021 ESPP, the Company added an additional 327,929 shares of common stock to the 2021 ESPP as of January 1, 2022. No shares are issued under 2021 ESPP plan as of the date of issuance of these consolidated financial statements. As of December 31, 2022, the authorized number of shares and shares available for issuance under the 2021 ESPP is 752,524.

Stock options granted under the 2022 Plan, 2021 Plan and 2019 Plan (together, the “Plans”) to employees generally vest over four years and expire after 10 years.

The following table summarizes stock option activity for the year ended December 31, 2022 (in thousands, except share and per share amounts):


	Number of Options			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term (Years)		Aggregate Intrinsic Value

Outstanding at January 1, 2022		5,926,969		$	10.03		9.5	$	16,414
Granted		1,178,280			4.06
Exercised		(73,841	)		2.48
Forfeited		(834,095	)		7.24
Expired		(476,898	)		5.51
Outstanding at December 31, 2022		5,720,415		$	9.68		8.8	$	72
Options exercisable at December 31, 2022		2,037,934		$	9.34		8.5	$	59

The weighted-average grant-date fair value of options granted during the years ended December 31, 2022 and 2021, was $3.06 and $7.57 per share, respectively. The aggregate intrinsic value is calculated as the difference between the exercise price of all outstanding and exercisable stock options and the fair value of the Company’s common stock of $1.34 per share as of December 31, 2022. The aggregate intrinsic value of stock options exercised during the years ended December 31, 2022 and 2021 was less than $0.1 million and $0.6 million, respectively.

The Company estimated the fair value of each option on the date of grant using the Black-Scholes option-pricing model applying the range of assumptions in the following table:


	Year Ended December 31,
	2022	2021
Expected volatility	96.09% - 101.66%	72.88% - 103.41%
Risk-free interest rate	1.60% - 4.02%	0.81% - 1.36%
Expected dividend yield	0.00%	0.00%
Expected term (in years)	6.00 - 6.11	5.25 - 7.00

Stock-based compensation expense related to stock options recorded in the statements of operations is as follows (in thousands):


	Year Ended December 31,
	2022		2021
Research and development	$	4,330	$	2,396
General and administrative		7,617		3,976
Total	$	11,947	$	6,372

The Company has an aggregate $25.2 million of gross unrecognized stock-based compensation expense as of December 31, 2022, remaining to be amortized over a weighted average period of 2.29 years. The Company has not recognized and does not expect to recognize in the near future, any tax benefit related to employee stock-based compensation expense as a result of the full valuation allowance related to its net deferred tax assets.

Under the 2019 Plan, 2021 Plan and 2022 Inducement Plan, the Company issued 3,174,656 restricted stock units ("RSU") to employees and non-employees. Compensation costs related to these RSUs were recorded based on the Company's stock price on the date of issuance and amortized over the service period.

Additionally, the Company issued certain shares of restricted common stock ("RSA") to the employee co-founders and certain non-employee consultants in 2019. The shares of restricted common stock were issued pursuant to standalone restricted stock purchase agreements that are independent of the 2019 Plan, 2021 Plan and 2022 Inducement Plan. The shares of restricted common stock pursuant to standalone restricted stock purchase agreements carried a purchase price equivalent of $0.01 per share. As of December 31, 2022, 151,286 RSAs were unvested and outstanding.

Under the terms of the restricted stock purchase agreements, the Company has a repurchase option whereby it has the right to repurchase any unvested shares upon termination at a price per share equal to the lesser of (i) the fair market value of the Company’s common stock on the date of repurchase and (ii) the original purchase price. The shares of restricted common stock issued to the Company’s co-founders and non-employee consultants vest based on a predefined number of shares.

The Company recognized an associated deposit liability for restricted stock awards issued pursuant to standalone restricted stock purchase agreements upon issuance based on the purchase price of the awards as the unvested shares are subject to repurchase upon termination. As the awards of restricted stock vest, the Company reclassifies the deposit liability to additional paid-in capital. The compensation cost was measured based on the fair value of the underlying common stock less the purchase price of the restricted common stock and the Company recognizes compensation costs over the requisite service period.

The following table summarizes restricted stock activity for the year ended December 31, 2022:


	Number of Shares			Weighted Average Grant Date Fair Value
Non-vested at December 31, 2021		618,494		$	3.04
Granted		3,174,656			3.69
Vested and settled		(432,354	)		0.55
Forfeited		(345,409	)		3.74
Non-vested and unsettled at December 31, 2022		3,015,387		$	3.64

The Company has recorded stock-based compensation expense related to the restricted stock of $3.8 million and $0.1 million for the years ended December 31, 2022, and 2021, respectively. The Company has an aggregate $7.4 million of gross unrecognized restricted stock-based compensation expense as of December 31, 2022, remaining to be amortized over a weighted average period of 2.26 years.