7. Equity-Based Compensation

The Company recorded equity-based compensation expense related to all equity-based awards for employees and nonemployees, which was allocated as follows in the consolidated statements of operations (in thousands):


	Three Months Ended				Six Months Ended
	June 30,				June 30,
	2019		2018		2019		2018
Research and development expense	$	638	$	542	$	1,217	$	786
General and administrative expense		1,176		548		2,215		785
	$	1,814	$	1,090	$	3,432	$	1,571

Restricted Stock

The following table summarizes restricted common stock activity as of June 30, 2019:


		Weighted
		Average Fair
		Value per Share
	Number of Shares	at Issuance
Restricted common stock as of December 31, 2018	664,174	$	5.77
Granted	—	$	—
Vested	(181,274)	$	5.77
Forfeited	(2,237)	$	5.77
Restricted common stock as of June 30, 2019	480,663	$	5.77

As of June 30, 2019, the Company had unrecognized equity-based compensation expense of $2.1 million related to restricted stock issued to employees and directors, which is expected to be recognized over a period of 1.6 years.

Stock Options

The following table summarizes stock option activity as of June 30, 2019:


				Weighted
		Weighted		Average
	Number of	Average		Remaining	Aggregate
	Shares	Exercise Price		Contractual Term	Intrinsic Value
				(in years)	(in thousands)
Outstanding as of December 31, 2018	1,627,947	$	10.86	9.26	$	19,831
Granted	843,235		16.11
Exercised	(14,866)		6.23
Cancelled	(32,755)		13.91
Outstanding as of June 30, 2019	2,423,561		12.68	9.08	$	10,568
Options exercisable as of June 30, 2019	489,347	$	10.40	8.74	$	2,994

Using the Black-Scholes option pricing model, the weighted average fair value of options granted to employees and directors during the six months ended June 30, 2019 was $11.33.

The following assumptions were used in determining the fair value of options granted in the six months ended June 30, 2019:


Risk-free interest rate	2.46	%
Expected dividend yield	0.0	%
Expected term (years to liquidity)	6.19
Expected volatility	80.40	%

As of June 30, 2019, the Company has unrecognized equity-based compensation expense related to its employee stock options of $17.1 million which the Company expects to recognize over the remaining weighted average vesting period of 2.9 years.