CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Statement of Comprehensive Income [Abstract]
Grant and collaboration revenue	$ 2,017	$ 1,236	$ 4,105	$ 2,270
Operating expenses:
Research and development	6,000	5,314	12,648	10,286
General and administrative	2,418	2,238	4,799	4,110
Total operating expenses	8,418	7,552	17,447	14,396
Operating Income (Loss), Total	(6,401)	(6,316)	(13,342)	(12,126)
Investment income	10	62	23	124
Foreign currency transaction gain (loss), net	(158)	(246)	(378)	(52)
Interest expense	(310)	(330)	(620)	(509)
Other expense, net	(64)	(37)	(82)	(37)
Net loss	(6,923)	(6,867)	(14,399)	(12,600)
Other Comprehensive Income (Loss), Tax [Abstract]
Foreign currency translation adjustment	170	245	401	37
Comprehensive loss	(6,753)	(6,622)	(13,998)	(12,563)
Net loss	(6,923)	(6,867)	(14,399)	(12,600)
Accretion of redeemable convertible preferred stock	(2,210)	(1,562)	(4,566)	(3,123)
Net loss attributable to common stockholders	$ (9,133)	$ (8,429)	$ (18,965)	$ (15,723)
Net loss per share attributable to common Basic and diluted	$ (2.75)	$ (3.93)	$ (6.90)	$ (7.36)
Weighted average common shares outstanding Basic an diluted	3,322,546	2,147,184	2,749,105	2,137,144