Condensed Consolidated Balance Sheets (Current Period Unaudited) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Current Assets
Cash and cash equivalents	$ 35,924	$ 53,689
Prepaid expenses and other current assets	3,139	4,281
Total current assets	39,063	57,970
Restricted cash	2,458	2,445
Property and equipment, net	240	270
Operating lease right-of-use assets	1,277	1,462
Other assets	6	6
Total assets	43,044	62,153
Current liabilities
Accounts payable	9,794	8,765
Accrued liabilities	4,646	6,738
Operating lease obligation, current portion	2,170	2,195
Current portion of deferred revenue	3,582	4,414
Total current liabilities	20,192	22,112
Deferred revenue, net of current portion	28	621
Operating lease obligation, net of current portion	1,347	1,882
Warrant liability	60,088	26,881
Total liabilities	81,655	51,496
Commitments and contingencies (Note 6)
Stockholders' (deficit) equity
Common stock, $0.0001 par value, 250,000,000 shares authorized at March 31, 2023 and 100,000,000 shares authorized at December 31, 2022; 59,844,850 shares issued and outstanding at March 31, 2023 and December 31, 2022	6	6
Additional paid-in capital	627,466	626,778
Accumulated deficit	(666,083)	(616,127)
Total stockholders' (deficit) equity	(38,611)	10,657
Total liabilities and stockholders’ (deficit) equity	$ 43,044	$ 62,153