The Company’s 2021 Stock Incentive Plan (the “2021 Plan”) was approved by the Company’s stockholders on June 15, 2021 and became effective on June 16, 2021. Under the 2021 Plan, the Company may grant incentive stock options, nonstatutory stock options, stock appreciation rights, restricted stock awards, awards of restricted stock units and other stock-based awards. The Company’s employees, officers, directors, consultants and advisors are eligible to receive awards under the 2021 Plan; however, incentive stock options may only be granted to employees. The 2021 Plan is administered by the board of directors or, at the discretion of the board of directors, by a committee of the board. The number of shares of common stock covered by options and the date those options become exercisable, type of options to be granted, exercise prices, vesting and other restrictions are determined at the discretion of the board of directors, or its committee if so delegated.

Stock options granted under the 2021 Plan with service-based vesting conditions generally vest over four years and may not have a duration in excess of ten years, although options have been granted with vesting terms of less than four years.

The total number of shares of common stock that may be issued under the 2021 Plan was 14,185,751 as of June 30, 2022, of which 5,937,751 shares remained available for grant. The Company initially reserved 12,500,000 shares of common stock, plus the number of shares of common stock subject to then outstanding awards under the Company’s 2017 Stock Incentive Plan (the “2017 Plan”), the Company’s 2016 Stock Incentive Plan (“the 2016 Plan”), and the Company’s 2006 Stock Incentive Plan, as amended (the

“2006 Plan”) that expire, terminate or are otherwise surrendered, canceled, forfeited or repurchased by the Company at their original issuance price pursuant to a contractual repurchase right up to 6,280,135 shares.

Shares that are expired, terminated, surrendered or canceled without having been fully exercised will be available for future awards. In addition, shares of common stock that are tendered to the Company by a participant to exercise an award are added to the number of shares of common stock available for the grant of awards.

The exercise price for stock options granted may not be less than the fair market value of the common stock as of the date of grant.

The 2017 Plan was approved by the Company’s stockholders on June 16, 2017, and became effective on June 28, 2017. Under the 2017 Plan, the Company could grant incentive stock options, nonstatutory stock options, stock appreciation rights, restricted stock awards, awards of restricted stock units and other stock-based awards. The Company’s employees, officers, directors, consultants and advisors were eligible to receive awards under the 2017 Plan; however, incentive stock options could only be granted to employees. The 2017 Plan is administered by the board of directors or, at the discretion of the board of directors, by a committee of the board. The number of shares of common stock covered by options and the date those options become exercisable, type of options granted, exercise prices, vesting and other restrictions were determined at the discretion of the board of directors, or its committee if so delegated.

Stock options granted under the 2017 Plan with service-based vesting conditions generally vest over four years and may not have a duration in excess of ten years, although options have been granted with vesting terms of less than four years. The exercise price for stock options granted may not be less than the fair market value of the common stock as of the date of grant.

As of the effective date of the 2021 Plan, the board of directors determined to grant no further awards under the 2017 Plan.

Shares that are expired, terminated, surrendered or canceled without having been fully exercised will be available for future awards under the 2021 Plan. In addition, shares of common stock that are tendered to the Company by a participant to exercise an award are added to the number of shares of common stock available for the grant of awards under the 2021 Plan.

On June 16, 2017, the Company’s stockholders approved the 2017 Employee Stock Purchase Plan (the “2017 ESPP”), which became effective on June 28, 2017. A total of 150,000 shares of common stock were initially reserved for issuance under this plan. Under the 2017 ESPP, the number of shares of common stock that may be issued under the 2017 ESPP will automatically increase on each January 1, beginning with the fiscal year ending December 31, 2018 and continuing for each fiscal year until, and including, the fiscal year ending December 31, 2027, equal to the least of (i) 622,408 shares, (ii) 1% of the outstanding shares of common stock on such date and (iii) an amount determined by the Company’s board of directors. The compensation committee of the board of directors has determined that the number of shares of common stock that may be issued under the 2017 ESPP would not be increased on January 1, 2021 or January 1, 2022. The Company has not issued any shares under the 2017 ESPP.

The assumptions that the Company used to determine the grant-date fair value of the stock options granted to employees and directors during the six months ended June 30, 2022 and 2021 were as follows, presented on a weighted average basis:


	Six Months Ended June 30, 2022		Six Months Ended June 30, 2021
Risk-free interest rate	2.46%		0.96%
Expected term (in years)		5.9		6.2
Expected volatility	94.2%		91.0%
Expected dividend yield	0%		0%

The following table summarizes the Company’s stock option activity since January 1, 2022:


	Number of Options			Weighted Average Exercise Price		Weighted Average Remaining Term in Years		Aggregate Intrinsic Value
Outstanding at December 31, 2021		9,375,497		$	1.79		8.5	$	4
Granted		3,148,500			0.46
Exercised		—			0.00
Canceled, forfeited or expired		(1,401,565	)		1.02
Outstanding at June 30, 2022		11,122,432		$	1.51		8.2	$	—

Options exercisable at June 30, 2022		5,099,852		$	2.21		7.0	$	—
Options vested and expected to vest at June 30, 2022		10,902,956		$	2.21		8.1	$	—

The weighted average grant-date fair value of stock options granted during the six months ended June 30, 2022 and 2021 was $0.35 and $0.97, respectively.

The aggregate fair value of stock options that vested during the six months ended June 30, 2022 and 2021 was $2,003 and $708, respectively.

The aggregate intrinsic value of stock options is calculated as the difference between the exercise price of the stock options and the fair value of the Company’s common stock for those stock options that had exercise prices lower than the fair value of the Company’s common stock. The aggregate intrinsic value of stock options exercised during the six months ended June 30, 2022 and 2021 was $0.

The following table summarizes the Company’s restricted stock activity since January 1, 2022:


				Weighted-Average
	Number of			Grant Date Fair Value
	Units			per Unit
Outstanding, non-vested at December 31, 2021		—		$	—
Issued		250,000			0.39
Vested		(250,000	)		0.39
Canceled/forfeited		—			—
Outstanding, non-vested at June 30, 2022		—			—

The Company recorded stock-based compensation expense related to stock options and restricted stock units in the following expense categories of its statements of operations and comprehensive loss:


	Three Months Ended June 30,				Six Months Ended June 30,
	2022		2021		2022		2021
Research and development expenses	$	178	$	103	$	321	$	202
General and administrative expenses		350		258		896		791
Total Stock Based Compensation	$	528	$	361	$	1,217	$	993

As of June 30, 2022, the Company had an aggregate of $4,050 of unrecognized stock-based compensation expense, which it expects to recognize over a weighted average period of 2.86 years.