Condensed Consolidated Statements of Operations (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Revenue
Grant revenue	$ 3,054		$ 4,753
Type of Revenue [Extensible List]	us-gaap:GrantMember	us-gaap:GrantMember	us-gaap:GrantMember	us-gaap:GrantMember
Operating expenses
Research and development	$ 3,637	$ 3,438	$ 6,485	$ 7,038
General and administrative	3,291	6,003	7,881	10,920
Total operating expenses	6,928	9,441	14,366	17,958
Loss from operations	(3,874)	(9,441)	(9,613)	(17,958)
Interest income	233	249	579	442
Other income (expense), net	597	(656)	1,286	(1,313)
Net loss	$ (3,044)	$ (9,848)	$ (7,748)	$ (18,829)
Net loss per share - basic and diluted	$ (0.27)	$ (1.64)	$ (0.69)	$ (3.14)
Weighted-average common shares used to compute basic and diluted net loss per share	11,280	6,023	11,277	6,002

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