CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Revenues:
Grant revenue	$ 3,911	$ 1,153
Collaboration revenue	$ 3,807
Type of Revenue [Extensible List]	us-gaap:LicenseMember	us-gaap:LicenseMember
Total revenues	$ 7,718	$ 1,153
Operating expenses:
Research and development	9,526	8,925
General and administrative	3,888	3,044
Total operating expenses	13,414	11,969
Loss from operations	(5,696)	(10,816)
Other income (expense):
Interest income and other income (expense), net	624	172
Total other income (expense), net	624	172
Net loss	$ (5,072)	$ (10,644)
Net loss per share attributable to common stockholders, basic and diluted	$ (0.29)	$ (0.74)
Weighted average common shares outstanding, basic and diluted:	17,221,120	14,369,182
Comprehensive loss:
Net loss	$ (5,072)	$ (10,644)
Other comprehensive gain (loss):
Unrealized gain (loss) on marketable securities	23	(29)
Reclassification adjustment for gains included in net loss	6
Net unrealized gains (losses) on securities	29	(29)
Total comprehensive loss	$ (5,043)	$ (10,673)