CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Cash flows from operating activities
Net loss	$ (50,964)	$ (34,347)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	171	169
Amortization of debt issuance costs	111
Stock-based compensation expense	8,026	3,672
Noncash lease expense	152	127
Noncash lease liability	162	187
Changes in operating assets and liabilities:
Prepaid expenses and other current and non-current assets and federal contract revenue receivables	(1,017)	(680)
Accounts payable, accrued expenses and other long term-liabilities	4,229	827
Net cash used in operating activities	(39,130)	(30,045)
Cash flows from investing activities
Maturities of short-term investments	1,474	2,729
Purchases of short-term investments		(8,931)
Deposit on property and equipment	(1,124)
Purchases of property and equipment	(172)
Net cash provided by (used in) investing activities	178	(6,202)
Cash flows from financing activities
Proceeds from exercise of stock options	801	512
Proceeds from notes payable, net of issuance costs	12,283
Financing costs, paid	(148)
Proceeds from equity offerings, net of offering costs		43,722
Net cash provided by financing activities	12,936	44,234
Net (decrease) increase in cash and cash equivalents	(26,016)	7,987
Cash and cash equivalents-beginning of period	138,509	90,943
Cash and cash equivalents-end of period	112,493	98,930
Supplemental disclosure of cash flow information
Accrued financing costs associated with notes payable	1,423
Contractual exit fee included in notes payable	300
Property and equipment in accounts payable and accrued expenses	$ 27
Conversion of preferred stock to common stock		4
Accrued equity offering costs		$ 210