Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021
Cash flows from operating activities
Net loss	$ (21,645)	$ (13,630)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation	3,655	2,674
Non-cash lease expense	109	82
Changes in operating assets and liabilities:
Prepaid and other	276	(2,562)
Accounts payable	560	(134)
Accrued liabilities	1,207	(544)
Change in lease liability	(109)	(82)
Deferred grant revenue	211	603
Net cash used in operating activities	(15,736)	(13,593)
Cash flows from financing activities
Proceeds from issuance of common stock in public offerings, net	3,871	0
Proceeds from exercise of stock options	0	414
Proceeds from exercise of common stock warrants	0	105
Net cash provided by financing activities	3,871	519
Net increase (decrease) in cash and cash equivalents	(11,865)	(13,074)
Cash and cash equivalents at beginning of period	90,765	116,737
Cash and cash equivalents at end of period	78,900	103,663
Supplemental disclosure of non-cash financing activities:
Cashless exercise of warrants	0	1,836
Right-of-use assets obtained in exchange for operating lease liabilities	$ 191	$ 0