In 2017, the Company adopted the 2017 Stock Incentive Plan (the “2017 Plan”). Under the 2017 Plan, a total of 537,914 shares of the Company’s common stock were reserved for the issuance of stock options to employees, directors, and consultants under terms and provisions established by the Board of Directors (the “Board”). Under the terms of the 2017 Plan, options were granted at an exercise price not less than fair market value. The terms of options granted under the 2017 Plan may not exceed ten years. The Board determined the terms and conditions of a Restricted Stock Award, including the conditions for vesting and repurchase (or forfeiture) and the issue price, if any. On October 11, 2017, the Company increased

the number of shares of common stock available for issuance under the 2017 Plan from 537,914 shares to 630,662 shares. On November 29, 2017, the Company increased the number of shares of common stock available for issuance under the 2017 Plan from 630,662 shares to 1,866,009 shares.

In connection with the Company’s initial public offering completed in January 2018, the Board adopted and the Company’s stockholders approved the 2018 Stock Incentive Plan (“2018 Plan”), which became effective on the date immediately preceding the date on which the Company’s registration statement became effective. The 2018 Plan provides for the grant of incentive stock options, nonstatutory stock options, restricted stock awards, restricted stock units, stock appreciation rights, and other stock-based awards. The Company’s employees, officers, directors, consultants and advisors are eligible to receive awards under the 2018 Plan. The number of shares of common stock that were reserved for issuance under the 2018 Plan were 2,200,260 shares. The 2018 Plan provides that the number of shares reserved and available for issuance under the plan will automatically increase each January 1, beginning on January 1, 2019, by 4% of the outstanding number of shares of the Company’s common stock on the immediately preceding December 31 or such lesser number of shares as determined by the Board. On January 1, 2019, as a result of the foregoing evergreen provision, the number of shares of common stock available for issuance under the 2018 Plan automatically increased from 2,200,260 to 3,322,473 shares. On January 1, 2020, as a result of the foregoing evergreen provision, the number of shares of common stock available for issuance under the 2018 Plan automatically increased from 3,322,473 to 4,780,262 shares.

Since the date of effectiveness of the 2018 Plan, the Company has not and will not grant any further awards under the 2017 Plan. However, any shares of common stock subject to awards under the 2017 Plan that expire, terminate, or otherwise are surrendered, canceled, forfeited or repurchased without having been fully exercised or resulting in any common stock being issued will become available for issuance under the 2018 Plan.

Total stock-based compensation expense is recognized for stock options granted to employees and non-employees and has been reported in the Company’s condensed consolidated condensed statements of operations and comprehensive loss as follows:

	Three Months Ended June 30,				Six Months Ended June 30,
	2020		2019		2020		2019
Research and development	$	289	$	499	$	689	$	776
General and administrative		470		444		1,045		831
Total stock-based compensation expense	$	759	$	943	$	1,734	$	1,607

	Shares Available for Grant			Number of Options Outstanding			Weighted- Average Exercise Price per Option		Weighted- Average Remaining Contract Term		Aggregate Intrinsic Value
											(In thousands)
Outstanding, December 31, 2019		215,043			2,562,800		$	7.85		8.84
Shares reserved for issuance		1,457,789
Options granted		(86,484	)		86,484			2.23
Options cancelled		509,272			(509,272	)		7.44
Restricted stock units cancelled		165,036
Outstanding, June 30, 2020		2,260,656			2,140,012			7.54		8.59	$	567
Exercisable, June 30, 2020					771,444			10.02		8.04		91
Vested and expected to vest, June 30, 2020					2,140,012			7.54		8.59		567

The aggregate intrinsic values of options outstanding, exercisable, vested and expected to vest were calculated as the difference between the exercise price of the in-the-money options and the fair value of the Company’s common stock as of June 30, 2020. No options were exercised during the six months ended June 30, 2020.

During the six months ended June 30, 2020, the Company granted options to directors to purchase an aggregate of 86,484 common shares with a grant date fair value of $1.80 per share. During the six months ended June 30, 2020, the Company did not grant any options to employees and nonemployees to purchase common shares. The expense related to options granted to employees and directors for the three and six months ended June 30, 2020 was $0.7 million and $1.6 million, respectively. The expense related to options granted to non-employees for the three and six months ended June 30, 2020 was $7,000 and $ 8,000, respectively. The expense related to options granted to employees and directors was $0.9 million and $1.5 million for the three and six months ended June 30, 2019, respectively. The expense related to options granted to non-employees was $40,000 and $48,000 for the three and six months ended June 30, 2019, respectively.

As of June 30, 2020, the total unrecognized compensation expense related to unvested options granted to employees and directors was $5.9 million, which the Company expects to recognize over an estimated weighted-average period of 2.36 years. As of June 30, 2020, the total unrecognized compensation expense related to unvested non-employee options was $28,000, which the Company expects to recognize over an estimated weighted-average period of 1.74 years.

The fair value of stock options for employees and non-employees was estimated using a Black-Scholes option pricing model with the following assumptions:

	Three Months Ended June 30,			Six Months Ended June 30,
	2020		2019	2020		2019
Employees:
Fair value of common stock		$2.23	$6.97 - $8.08		$2.23	$6.97 - $8.90
Expected term (in years)		5.5	5.5 - 6.1		5.5	5.5 - 6.1
Expected volatility	110.2%		94.5% - 104.8%	110.2%		93.7% - 104.8%
Risk-free interest rate	0.4%		1.9% - 2.4%	0.4%		1.9% - 2.6%
Expected dividend yield	0.0%		0.0%	0.0%		0.0%
Non-employees:
Fair value of common stock	$2.09 - $2.18		$8.90 - $10.20	$0.96 - $2.18		$6.82 - $10.20
Expected term (in years)	7.0 - 8.8		8.0 - 9.7	7.0 - 9.0		8.0 - 10.0
Expected volatility	100.8% - 103.5%		93.4% - 94.2%	99.6% - 103.5%		90.0% - 94.9%
Risk-free interest rate	0.5% - 0.6%		1.9% - 2.1%	0.5% - 0.9%		1.9% - 2.6%
Expected dividend yield	0.0%		0.0%	0.0%		0.0%

In May 2018, the Company granted 24,960 restricted stock units to an employee with a grant date fair value of $9.03 per share. In December 2019, the Company granted 813,335 restricted stock units to employees with a grant date fair value of $1.27 per share.

The summary of restricted stock unit activity and related information is as follows:

The Company recognized $52,000 and $0.1 million of stock-based compensation expense related to restricted stock units during the three and six months ended June 30, 2020, respectively. As of June 30, 2020, there was $0.7 million of unrecognized stock-based compensation expense related to unvested restricted stock units. This amount is expected to be recognized over a remaining weighted-average period of 3.44 years. There were no restricted stock units granted to employees or non-employees during the three and six months ended June 30, 2020 and 2019.

The Board adopted and the Company’s stockholders approved the 2018 Employee Stock Purchase Plan (“2018 ESPP”), which became effective on the date immediately preceding the date on which the Company’s registration statement became effective. The 2018 ESPP enables eligible employees to purchase shares of the Company’s Common Stock at a discount. The number of shares of common stock originally reserved for issuance under the 2018 ESPP were 275,030 shares. The 2018 ESPP provides that the number of shares reserved and available for issuance will automatically increase each January 1, beginning on January 1, 2019 and increasing each January 1 thereafter through January 1, 2028, by the least of (i) 1% of the outstanding number of shares of the Company’s common stock on the immediately preceding December 31; (ii) 543,926 shares or (iii) such number of shares as determined by the ESPP administrator. On January 1, 2019, as a result of the foregoing evergreen provision, the number of shares of common stock available for issuance under the 2018 ESPP automatically increased from 275,030 to 555,583 shares. On January 1, 2020, as a result of the foregoing evergreen provision, the number of shares of common stock available for issuance under the 2018 ESPP automatically increased from 555,583 to 920,030 shares. No shares have been issued under the 2018 ESPP during the three and six months ended June 30, 2020.