Condensed Consolidated Balance Sheets (Current Period Unaudited) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Current Assets
Cash and cash equivalents	$ 65,825	$ 59,424
Prepaid expenses and other current assets	3,227	3,321
Total current assets	69,052	62,745
Restricted cash	2,431	2,431
Property and equipment, net	365	400
Operating lease right-of-use assets	2,020	2,207
Other assets	3	4
Total assets	73,871	67,787
Current liabilities
Accounts payable	4,246	2,657
Accrued liabilities	8,840	8,416
Operating lease obligation, current portion	2,271	2,297
Current portion of deferred revenue	4,423	4,571
Total current liabilities	19,780	17,941
Deferred revenue, net of current portion	2,604	3,548
Operating lease obligation, net of current portion	3,516	4,076
Warrant liability	8,772	0
Total liabilities	34,672	25,565
Commitments and contingencies (Note 6)
Stockholders' equity
Common stock, $0.0001 par value, 100,000,000 shares authorized at March 31, 2022 and December 31, 2021; 24,279,573 and 21,039,594 shares issued and outstanding at March 31, 2022 and December 31, 2021, respectively	2	2
Additional paid-in capital	592,059	582,025
Accumulated deficit	(552,862)	(539,805)
Total stockholders' equity	39,199	42,222
Total liabilities and stockholders’ equity	$ 73,871	$ 67,787