Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($)	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Operating activities
Net loss	$ (26,337,000)	$ (27,820,000)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation	2,679,000	2,782,000
Depreciation expense	242,000	236,000
Non-cash lease expense	57,000	51,000
Amortization of premiums and accretion of discounts on available-for-sale securities, net	(266,000)	(331,000)
Loss on disposal of equipment	7,000
Changes in operating assets and liabilities:
Unbilled grant receivable		1,227,000
Prepaid expenses and other current and long-term assets, net	1,155,000	(970,000)
Accounts payable and accrued liabilities	(3,254,000)	(1,292,000)
Operating lease liability	(87,000)	(77,000)
Net cash used in operating activities	(25,804,000)	(26,194,000)
Investing activities
Purchases of available-for-sale securities	(5,911,000)	(9,712,000)
Maturities of available-for-sale securities	18,957,000	45,475,000
Purchases of property and equipment	(5,000)	(241,000)
Net cash provided by investing activities	13,041,000	35,522,000
Financing activities
Proceeds from exercise of common stock options and issuance of common stock under employee stock purchase plan		99,000
Net cash provided by financing activities		99,000
Net (decrease) increase in cash, cash equivalents and restricted cash	(12,763,000)	9,427,000
Cash, cash equivalents and restricted cash, beginning of period	91,215,000	96,386,000
Cash, cash equivalents and restricted cash, end of period	$ 78,452,000	$ 105,813,000