The Company adopted the 2017 Stock Option and Incentive Plan (“2017 Plan”) on October 31, 2017. Upon adoption of the 2017 Plan, no further grants were made under the 2011 Stock Incentive Plan (“2011 Plan”). The 2017 Plan initially provided for the grant of awards for 2,038,021 shares of common stock. In addition to the shares available for grant under the 2017 Plan, any awards outstanding under the 2011 Plan as of the October 31, 2017 that are cancelled, forfeited or otherwise terminated without being exercised, the number of shares underlying such awards are available for future grant under the 2017 Plan. The 2017 Plan also provides that an additional number of shares will automatically be added to the shares authorized for issuance under the 2017 Plan on January 1 of each year. The number of shares added each year will be equal to the lesser of: (i) 4% of the outstanding shares on the immediately preceding December 31 or (ii) such amount as determined by the Compensation Committee of the registrant’s Board of Directors. On January 1, 2020, 2021 and 2022, the shares available for grant under the 2017 Plan were automatically increased by 989,400, 2,032,854 and 3,318,776 shares, respectively.

All of the Company’s employees, officers, directors, consultants and advisors are eligible to be granted options, restricted stock units (“RSUs”), and other stock-based awards under the terms of the 2017 Plan. As of December 31, 2021, 798,476 shares of common stock were available for future grant under the 2017 Plan.

On January 22, 2021, the Company adopted the 2021 Inducement Equity Plan (“2021 Plan”). The 2021 Plan provides for the grant of awards for 1,600,000 shares of common stock. The purpose of the 2021 plan is to enable the Company to grant equity awards to induce highly qualified prospective officers and employees who are not

currently employed by the Company to accept employment and provide them with an equity interest in the Company. The Company is utilizing the 2021 Plan for awards the Company may make without stockholder approval as an inducement pursuant to Rule 5635(c)(4) of the Marketplace Rules of the Nasdaq Stock Market, Inc. As of December 31, 2021, 808,000 shares of common stock were available for future grant under the 2021 Plan.

All stock option grants are nonstatutory stock options except option grants to employees (including officers and directors) intended to qualify as incentive stock options under the Internal Revenue Code of 1986, as amended. Incentive stock options may not be granted at less than the fair market value of the Company’s common stock on the date of grant. Nonqualified stock options may be granted at an exercise price established by the Board of Directors at its sole discretion (which has not been less than fair market value on the date of grant) and the vesting periods may vary. Vesting periods are generally four years and are determined by the Board of Directors or a delegated subcommittee. Stock options become exercisable as they vest. Stock options granted under the 2021, 2017 and 2011 Plans expire no more than 10 years from the date of grant.

Stock-based compensation expense included in the Company’s statements of operations and comprehensive loss is as follows (in thousands):


	Years Ended December 31,
	2021		2020		2019
Research and development	$	1,128	$	1,286	$	1,175
General and administrative		2,543		2,765		1,814
Total	$	3,671	$	4,051	$	2,989

The fair value of each stock option granted to employees and directors was estimated on the date of grant using the Black-Scholes option-pricing model, with the following range of assumptions for the years ended December 31, 2021, 2020 and 2019:


	Years Ended December 31,
	2021	2020	2019
Risk-free interest rate	0.4% – 1.4%	0.4% – 0.5%	1.4% – 2.6%
Expected dividend yield	—%	—%	—%
Expected term (in years)	5.0 – 7.0	5.5 – 6.1	5.5 – 6.8
Expected volatility	92% – 95%	94% – 95%	80% – 83%

The expense related to stock options granted to employees and directors for their service on the Board of Directors was $2.9 million, $2.6 million, and $2.9 million for the years ended December 31, 2021, 2020 and 2019, respectively.

The Company did not grant any stock options to non-employees during the years ended December 31, 2021, 2020 or 2019. The expense related to awards granted to non-employees was not material to the consolidated financial statements for the years ended December 31, 2021, 2020 and 2019.

A summary of the stock option activity under the 2021, 2017 and 2011 Plans is as follows:


	Shares			Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Life (in years)		Aggregate Intrinsic Value (in thousands)
Outstanding at December 31, 2020		4,110,691		$	3.89		7.3	$	124
Granted		3,341,350			1.87
Exercised		—			—
Cancelled		(686,204	)		4.72
Outstanding at December 31, 2021		6,765,837		$	2.81		7.6	$	3
Exercisable at December 31, 2021		3,282,830		$	3.52		6.2	$	3

The weighted-average fair value of options granted to employees and directors for their service on the Board of Directors during the years ended December 31, 2021, 2020 and 2019 was $1.41, $1.01 and $3.29 per share, 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 total intrinsic value of options exercised during the years ended December 31, 2020 and 2019 was $8,000 and $58,000, respectively. There were no options exercised during the year ended December 31, 2021.

As of December 31, 2021, total unrecognized stock-based compensation expense relating to unvested stock options was $5.1 million. This amount is expected to be recognized over a weighted-average period of 2.5 years.

During the years ended December 31, 2021, 2020 and 2019, the Company made awards of time-based RSUs to certain employees of the Company. The RSUs are generally forfeited if the employment relationship terminates with the Company prior to vesting. The weighted average fair value of RSUs granted to employees during the years ended December 31, 2021, 2020 and 2019 was $1.29, $1.39 and $2.42 per share, respectively. For the years ended December 31, 2021, 2020 and 2019, the Company recognized $0.8 million, $1.5 million and $0.1 million, respectively of stock-based compensation expense related to these awards. As of December 31, 2021, the Company did not have any unrecognized compensation cost related to nonvested remaining to be recognized.

A summary of the status of nonvested RSUs as of December 31, 2021 and the changes during the year then ended are presented below (in thousands, except fair values):


	Shares			Weighted-Average Grant Date Fair Value
Nonvested at December 31, 2020		620,277		$	1.29
Granted		—			—
Vested		(620,277	)		1.29
Forfeited		—			—
Nonvested at December 31, 2021		—			—

The Company adopted the 2017 Employee Stock Purchase Plan (“ESPP”) on October 31, 2017. The ESPP permits eligible employees to enroll in six-month offering periods. Participants may purchase shares of the Company’s common stock, through payroll deductions, at a price equal to 85% of the fair market value of the common stock on the first or last day of the applicable six-month offering period, whichever is lower. Purchase dates under the ESPP occur on or about January 1 and July 1 each year. The ESPP initially reserved 206,284 shares of common stock for issuance. The ESPP also provides that an additional number of shares will automatically be added to the shares authorized for issuance under the ESPP on January 1 of each year. The number of shares added each year will be equal to the lesser of: (i) 1% of the outstanding shares on the immediately preceding December 31 or (ii) such amount as determined by the Compensation Committee of the registrant’s Board of Directors. On January 1, 2018, the shares available for grant under the ESPP was automatically increased by 206,946 shares. No shares were added to the ESPP on January 1, 2019, 2020 and 2021.

During the years ended December 31, 2021 and 2020, $18,000 and $52,000, respectively, were withheld from employees, on an after-tax basis, in order to purchase 30,383 and 43,095 shares of the Company’s common stock, respectively. As of December 31, 2021, 306,527 shares of Company’s common stock remained available for issuance under the ESPP.