Condensed Consolidated Balance Sheets (Current Period Unaudited) - USD ($) $ in Thousands	Jun. 30, 2023	Dec. 31, 2022
Current Assets
Cash and cash equivalents	$ 18,359	$ 53,689
Prepaid expenses and other current assets	3,686	4,281
Total current assets	22,045	57,970
Restricted cash	2,392	2,445
Property and equipment, net	204	270
Operating lease right-of-use assets	1,092	1,462
Other assets	4	6
Total assets	25,737	62,153
Current liabilities
Accounts payable	3,893	8,765
Accrued liabilities	5,553	6,738
Operating lease obligation, current portion	2,145	2,195
Current portion of deferred revenue	2,630	4,414
Total current liabilities	14,221	22,112
Deferred revenue, net of current portion	16	621
Operating lease obligation, net of current portion	821	1,882
Warrant liability	30,496	26,881
Total liabilities	45,554	51,496
Commitments and contingencies (Note 6)
Stockholders' (deficit) equity
Common stock, $0.0001 par value, 250,000,000 shares authorized at June 30, 2023 and 100,000,000 shares authorized at December 31, 2022; 59,868,553 shares issued and outstanding at June 30, 2023 and 59,844,850 shares issued and outstanding at December 31, 2022	6	6
Additional paid-in capital	628,252	626,778
Accumulated deficit	(648,075)	(616,127)
Total stockholders' (deficit) equity	(19,817)	10,657
Total liabilities and stockholders’ (deficit) equity	$ 25,737	$ 62,153