Stockholders' Equity and Stock-Based Compensation Expense (Tables)

3 Months Ended

Mar. 31, 2020

Stockholders' Equity and Stock-Based Compensation Expense

Summary of Stock option activity under the 2015 and 2018 Plan

				Weighted-
		Weighted-		Average
		Average		Remaining	Aggregate
	Number of	Exercise		Contractual	Intrinsic
	Options	Price		Term (Years)	Value (in thousands)
Outstanding as of December 31, 2019	2,388,400	$	6.20	8.44	$	906
Granted	839,200		4.87
Exercised	—		—
Forfeited	(11,100)		5.01
Outstanding as of March 31, 2020	3,216,500	$	5.86	8.58	$	—
Exercisable as of March 31, 2020	1,110,613	$	5.66	7.50	$	—

Schedule of stock-based compensation expense

Stock‑based compensation expense was classified in the consolidated statement of operations as follows (in thousands):

	Three Months Ended March 31,
	2020		2019
Research and development	$	349	$	232
General and administrative		436		346
Total stock-based compensation expense	$	785	$	578