Condensed Consolidated Statements of Operations (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Revenue
Grant revenue	$ 1,699
Type of Revenue [Extensible List]	us-gaap:GrantMember	us-gaap:GrantMember
Operating expenses
Research and development	$ 2,848	$ 3,600
General and administrative	4,590	4,917
Total operating expenses	7,438	8,517
Loss from operations	(5,739)	(8,517)
Interest income	346	193
Other income (expense), net	689	(657)
Net loss	$ (4,704)	$ (8,981)
Net loss per share - basic and diluted	$ (0.42)	$ (1.50)
Weighted-average common shares used to compute basic and diluted net loss per share	11,273	6,003

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