CONDENSED CONSOLIDATED BALANCE SHEETS (Unaudited) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 63,999	$ 76,793
Grant and incentive receivables	1,926	1,608
Restricted cash	51
Prepaid expenses and other current assets	2,549	1,129
Total current assets	68,525	79,530
Property and equipment, net	384	421
Restricted cash	312	355
Other assets		948
Total assets	69,221	81,254
Current liabilities:
Accounts payable	1,108	1,893
Accrued expenses	5,141	5,779
Unearned income	730	694
Loans payable, net of discount	2,318	2,314
Total current liabilities	9,297	10,680
Loan payable, net of discount and current portion	9,698	9,922
Unearned income	1,796	1,936
Other long-term liabilities	7	9
Total liabilities	20,798	22,547
Stockholders’ equity:
Common stock, $0.001 par value; 200,000,000 shares authorized as of March 31, 2018 and December 31, 2017; 14,294,421 and 14,294,383 shares issued and outstanding as of March 31, 2018 and December 31, 2017, respectively	15	15
Additional paid-in capital	151,396	150,830
Accumulated other comprehensive income (loss)	(93)	127
Accumulated deficit	(102,895)	(92,265)
Total stockholders' equity	48,423	58,707
Total liabilities and stockholders’ equity	$ 69,221	$ 81,254