Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($)	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022
Operating activities
Net loss	$ (90,387,000)	$ (65,504,000)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation	8,395,000	8,246,000
Depreciation expense	724,000	606,000
Non-cash lease expense	158,000	154,000
Amortization of premiums and accretion of discounts on available-for-sale securities, net	(1,131,000)	(67,000)
Changes in operating assets and liabilities:
Unbilled grant receivable	1,227,000	636,000
Prepaid expenses and other current and long-term assets, net	(366,000)	(1,605,000)
Accounts payable and accrued liabilities	7,159,000	944,000
Operating lease liability	(239,000)	(212,000)
Net cash used in operating activities	(74,460,000)	(56,802,000)
Investing activities
Purchases of available-for-sale securities	(27,671,000)	(85,117,000)
Maturities of available-for-sale securities	116,673,000	119,274,000
Purchases of property and equipment	(304,000)	(1,140,000)
Net cash provided by investing activities	88,698,000	33,017,000
Financing activities
Proceeds from exercise of common stock options and issuance of common stock under employee stock purchase plan	341,000	507,000
Net cash provided by financing activities	341,000	507,000
Net increase (decrease) in cash, cash equivalents and restricted cash	14,579,000	(23,278,000)
Cash, cash equivalents and restricted cash, beginning of period	96,386,000	110,537,000
Cash, cash equivalents and restricted cash, end of period	$ 110,965,000	$ 87,259,000