CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Cash flows from operating activities:
Net loss	$ (28,662)	$ (26,323)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization expense	76	77
Stock-based compensation expense	1,535	1,177
Amortization and accretion of investments	(38)	(431)
Changes in operating assets and liabilities:
Grants receivable	991	492
Prepaid expenses	1,949	(1,420)
Other assets	1,347	(1,983)
Accounts payable	230	(632)
Accrued expenses and other liabilities	(1,992)	3,252
Deferred rent		(175)
Net cash used in operating activities	(24,564)	(25,966)
Cash flows from investing activities:
Purchases of property and equipment		(37)
Proceeds from maturities of short-term investments	25,000	7,000
Purchases of short-term investments		(25,050)
Net cash provided by (used in) investing activities	25,000	(18,087)
Cash flows from financing activities:
Proceeds from the issuance of common stock in Private Placement, net	34,301
Proceeds from exercise of stock options		40
Payments of initial public offering costs		(150)
Net cash provided by (used in) financing activities	34,301	(110)
Net increase (decrease) in cash and cash equivalents	34,737	(44,163)
Cash and cash equivalents at beginning of the period	16,034	49,360
Cash and cash equivalents at end of the period	50,771	$ 5,197
Supplemental disclosure of non-cash investing and financing activities:
Financing costs included in accrued expenses and other current liabilities	$ 61