CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Cash flows from operating activities:
Net loss	$ (15,266)	$ (12,941)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization expense	37	40
Stock-based compensation expense	785	578
Amortization and accretion of investments	(27)	(195)
Changes in operating assets and liabilities:
Grants receivable	331	(22)
Prepaid expenses	1,628	(340)
Other assets	1,032	(2,208)
Accounts payable	(154)	2,747
Accrued expenses and other liabilities	(1,934)	1,917
Deferred rent		(175)
Net cash used in operating activities	(13,568)	(10,599)
Cash flows from investing activities:
Purchases of property and equipment		(37)
Proceeds from maturities of short-term investments	15,000
Purchases of short-term investments		(25,050)
Net cash provided by (used in) investing activities	15,000	(25,087)
Cash flows from financing activities:
Proceeds from exercise of stock options		11
Payments of initial public offering costs		(150)
Payments of financing costs	(16)
Net cash used in financing activities	(16)	(139)
Net increase (decrease) in cash and cash equivalents	1,416	(35,825)
Cash and cash equivalents at beginning of the period	16,034	49,360
Cash and cash equivalents at end of the period	17,450	$ 13,535
Supplemental disclosure of non-cash investing and financing activities:
Deferred financing costs included in accrued expenses and other current liabilities	$ 166