CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Cash flows from operating activities:
Net loss	$ (43,850)	$ (32,952)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization expense	142	164
Stock-based compensation expense	2,421	1,201
Loss on disposal of property and equipment		282
Amortization and accretion of investments	(686)	(21)
Changes in operating assets and liabilities:
Grants receivable	474	(984)
Prepaid expenses	(3,206)	(860)
Other current assets	(2,711)	(637)
Accounts payable	(30)	133
Accrued expenses and other current liabilities	2,878	(2,280)
Deferred rent	(175)	137
Net cash used in operating activities	(44,743)	(35,817)
Cash flows from investing activities:
Purchase of property and equipment	(105)	(370)
Proceeds from maturities of short-term investments	56,415
Purchases of short-term investments	(44,950)	(35,721)
Net cash provided by (used in) investing activities	11,360	(36,091)
Cash flows from financing activities:
Proceeds from the sale of shares under common stock purchase agreement, net of issuance costs	155
Proceeds from exercise of stock options	52	96
Proceeds from initial public offering, net of issuance costs paid in the period		66,071
Payments of initial public offering costs	(150)
Net cash provided by financing activities	57	66,167
Net decrease in cash and cash equivalents	(33,326)	(5,741)
Cash and cash equivalents at beginning of the year	49,360	55,101
Cash and cash equivalents at end of the year	16,034	49,360
Supplemental disclosure of non-cash investing and financing activities:
Purchases of property and equipment included in accounts payable		37
Commitment shares issued in connection with common stock purchase agreement	642
Initial public offering costs included in accounts payable and accrued expenses		150
Conversion of preferred stock into common stock upon initial public offering		104,713
Supplemental disclosure of cash flow information:
Cash paid for taxes	$ 677	$ 472