On September 17, 2018, the Board of Directors and stockholders approved the 2018 Plan. The 2018 Plan allows for the issuance of up to 7,033,971 incentive or non-qualified stock options, restricted stock or restricted stock units, or unrestricted stock to employees, consultants or advisors of the Company which vest in accordance with the specific terms of each individual grant (generally over four-year periods). The number of stock options, restricted stock, or restricted stock units and unrestricted stock is subject to adjustment as a result of a reorganization, recapitalization, stock dividend, stock split, reverse stock split or other similar change in the Company’s capital stock. At June 30, 2020, the Company had 3,856,978 shares of unvested restricted stock units and stock options outstanding and 375,093 shares available for grant under the 2018 Plan.

The Company granted 64,016 and 2,141,445 shares of restricted stock to employees during the six months ended June 30, 2020 and 2019, respectively. Stock-based compensation expense recognized for the restricted stock granted was $0.5 million and $1.4 million for the three months ended June 30, 2020 and June 30, 2019, respectively, and $1.1 million and $1.7 million for the six months ended June 30, 2020 and 2019, respectively.

The following table summarizes restricted stock activity for the six months ended June 30, 2020:

	Restricted Stock
	Shares			Weighted Average Grant Date Fair Value
Unvested as of January 1, 2020		4,403,148		$	1.87
Granted		64,016			3.19
Forfeited		(6,710	)		3.01
Vested		(702,119	)		1.88
Unvested as of June 30, 2020		3,758,335		$	1.89

The weighted average grant-date fair value of restricted stock granted during the six months ended June 30, 2020 was $3.19 per share. At June 30, 2020, there was $5.1 million of unrecognized stock-based compensation cost related to the restricted stock, which is expected to be recognized over a weighted average period of 2.8 years.

The Company granted 53,683 incentive stock options during the six months ended June 30, 2020. They vest over a four-year period and have a 10-year contractual term. There were no stock options granted during the six months ended June 30, 2019.

	Stock Options
	Shares		Weighted Average Exercise Price		Weighted Average Contractual Life (in years)		Aggregate Intrinsic Value
Options outstanding as of January 1, 2020		44,960	$	3.01		9.5
Granted		53,683		4.50		9.9
Exercised		—		—		—
Forfeited		—		—		—
Options outstanding as of June 30, 2020		98,643	$	3.82		9.6		—
Options vested and exercisable at June 30, 2020		11,238		3.01		9.3		—

The aggregate intrinsic value of 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 common stock as of the end of the period.

The weighted average grant-date fair value of stock options granted during the three and six months ended June 30, 2020 was $3.38 and $3.30 per share.

The fair value was estimated on the date of grant using the Black Scholes option-pricing model, with the following assumptions:

	Three Months Ended June 30, 2020
Expected term (in years)		6.11
Expected volatility		89.5	%
Risk-free interest rate		0.48	%
Expected dividend yield		—
Fair value of common stock	$	4.60

	Three Months Ended June 30,				Six Months Ended June 30,
(in thousands)	2020		2019		2020		2019
Research and development	$	94	$	168	$	308	$	182
General and administrative		398		1,273		830		1,490
Total stock-based compensation expense	$	492	$	1,441	$	1,138	$	1,672