Stock Based Compensation (Tables)

9 Months Ended

Sep. 30, 2019

Schedule of stock based compensation expense

The Company recorded stock‑based compensation expense in the following expense categories of its accompanying consolidated statements of operations and comprehensive loss for the three months ended September 30, 2019 and 2018 and nine months ended September 30, 2019 and 2018, respectively (in thousands):


	Three Months				Nine Months
	Ended				Ended
	September 30,				September 30,
	2019		2018		2019		2018
Research and development	$	180	$	177	$	981	$	315
General and administrative		1,016		246		2,149		444
Total	$	1,196	$	423	$	3,130	$	759

Summary of the activity related to stock option grants to employees and nonemployees

The following table summarizes the activity related to stock option grants to employees and nonemployees for the nine months ended September 30, 2019:


		Weighted		Weighted-average
		average		remaining
		exercise price		contractual
	Shares	per share		life (years)
Outstanding at December 31, 2018	1,764,287	$	26.81	8.0
Granted	1,190,501		9.82
Exercised	(97,225)		3.71
Forfeited	(269,328)		41.50
Outstanding at September 30, 2019	2,588,235	$	18.34	7.7
Vested and exercisable at September 30, 2019	992,969	$	29.61	5.2
Vested and expected to vest at September 30, 2019	2,588,235	$	18.34	7.7

Summary of grant date fair value assumptions

The grant date fair value of each option grant was estimated during the three and nine months ended September 30, 2019 and 2018 using the following assumptions within the Black‑Scholes option‑pricing model:


	Three Months Ended			Three Months Ended			Nine Months Ended			Nine Months Ended
	September 30,			September 30,			September 30,			September 30,
	2019			2018			2019			2018
Expected term (in years)		6.08			6.08			6.02			6.08
Expected volatility		81	%		65	%		80	%		65	%
Risk-free interest rate		1.51	%		2.78	%		2.23	%		2.78	%
Expected dividend yield		0	%		0	%		0	%		0	%