The 2013 Equity Incentive Plan (2013 Plan) provides the Board of Directors the discretion to grant stock options and other equity-based awards to employees, directors, and consultants of the Company. The Board of Directors administers the 2013 Plan and has discretion to delegate some or all of the administration of the 2013 Plan to a committee or committees or an officer. To date, the Company has only granted Incentive Stock Options (ISOs) and Non-statutory Stock Options (NSOs) to employees, consultants, and directors. Following the completion of the Company’s IPO no additional shares have been granted under the 2013 Plan. However, the 2013 Plan will continue to govern outstanding equity awards granted thereunder. To the extent outstanding options granted under the 2013 Plan are cancelled, forfeited or otherwise terminated without being exercised and would otherwise have been returned to the share reserve under the 2013 Plan, the number of shares underlying such awards will be available for future grant under the 2021 Equity Incentive Plan.

In February 2021, the Board of Directors adopted the 2021 Equity Incentive Plan (2021 Plan), and our stockholders approved the 2021 Plan. The 2021 Plan is a successor to and continuation of the 2013 Plan. To date, the Company has only granted ISOs, NSOs and Restricted Stock Units (RSUs) to employees and directors. Therefore, the below discussion is limited to the terms applicable to ISOs and NSOs (collectively, stock options or options), and RSUs.

In February 2021, the Company’s Board of Directors adopted the ESPP, and our stockholders approved the ESPP. The price at which stock is purchased under the ESPP is equal to 85% of the fair market value of the Company's common stock on the first or the last day of the offering period, whichever is lower. Generally, each offering under the ESPP will be for a period of six months as determined by the Company's Board of Directors. Employees may invest up to 15% of their qualifying gross compensation through payroll deductions. In no event may an employee purchase more than 4,750 shares of common stock during any six-month offering period.

As of June 30, 2022, there were 212,147 shares issued under the ESPP. The ESPP is a compensatory plan as defined by the authoritative guidance for stock compensation. Stock-based compensation expense of $0.2 million and $0.3 million related to the ESPP has been recorded for the six months ended June 30, 2022 and 2021, respectively.

In November 2021, the Company's Board of Directors adopted the 2021 Inducement Plan (Inducement Plan). The Inducement Plan was adopted without stockholder approval pursuant to Nasdaq Listing Rule 5635(c)(4). Under the Inducement Plan, the Company may grant nonstatutory stock options, stock appreciation rights, restricted stock awards, restricted stock unit awards, performance awards and other awards to individuals not previously employees or non-employee directors of the Company, as an inducement toward entering into employment with the Company. The maximum number of shares of common stock that may be issued under the Inducement Plan is 3,000,000 shares.

A summary of stock option activity during the six months ended June 30, 2022 is as follows:


	Number of Units Outstanding			Weighted Average Strike Price per Unit		Weighted Average Remaining Contractual Term (in years)		Aggregate Intrinsic Value (in thousands)
Outstanding at December 31, 2021		8,590,411		$	5.48		8.8	$	6,196
Granted		4,347,646		$	1.08
Exercised		(65,862	)	$	1.50
Forfeited		(2,200,917	)	$	5.30
Expired		(422,657	)	$	4.51
Outstanding at June 30, 2022		10,248,621		$	3.72		9.0	$	—
Exercisable at June 30, 2022		2,804,018		$	5.33		8.1	$	—
Nonvested at June 30, 2022		7,444,603		$	3.11		9.4	$	—

As of June 30, 2022, the total unrecognized stock-based compensation related to stock options was $14.2 million, which is expected be recognized over a weighted-average period of approximately 3 years.

As of June 30, 2022, the Company has granted service-based stock option awards which may accelerate vesting upon performance-based or market-based conditions. For awards that vest based on multiple conditions, the Company estimates the fair value on its grant date using the Black-Scholes option valuation model or the Monte Carlo Simulation valuation model, depending on the terms and conditions of the particular award. For awards where vesting occurs based on a service condition only, the Company recognizes compensation expense using the straight line method over the requisite service period. For awards where vesting occurs based on either a service condition or a performance condition, the Company recognizes stock-based compensation over the requisite service period using the accelerated attribution method for awards with a performance condition if the performance condition is deemed probable of being met. For awards where vesting occurs based on either a service condition or a market condition, compensation expense is recognized over the requisite service period. If the market condition is satisfied prior to the completion of the requisite service period, any remaining unrecognized compensation expense will be accelerated at that time.

A summary of RSU activity during the six months ended June 30, 2022 is as follows:


	Number of Units Outstanding			Weighted Average Grant Date Fair Value (per RSU)
Outstanding at December 31, 2021		407,720		$	5.72
Granted		324,300		$	1.24
Vested		—		$	—
Forfeited		(132,105	)	$	5.51
Outstanding at June 30, 2022		599,915		$	3.35

As of June 30, 2022, the total unrecognized stock-based compensation related to RSUs was $1.7 million, which is expected to be recognized over a weighted average period of approximately 3 years.

The following table summarizes the components of stock-based compensation expense recorded in the Company’s statement of operations and comprehensive loss (in thousands):


	Three Months Ended June 30,				Six Months Ended June 30,
	2022		2021		2022		2021
Research and development	$	234	$	558	$	809	$	1,181
Selling, general and administrative		1,011		1,233		1,981		2,382
Total stock-based compensation	$	1,245	$	1,791	$	2,790	$	3,563