CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Cash flows from operating activities:
Net loss	$ (29,808)	$ (24,873)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization expense	110	125
Stock-based compensation expense	1,748	806
Amortization and accretion of investments	(596)
Changes in operating assets and liabilities:
Accounts receivable	(7,000)
Grants receivable	386	(2,208)
Prepaid expenses and other assets	(3,731)	(1,896)
Accounts payable	(385)	536
Accrued expenses and other current liabilities	2,750	(386)
Deferred rent	(175)	109
Net cash used in operating activities	(36,701)	(27,787)
Cash flows from investing activities:
Purchase of property and equipment	(98)	(322)
Proceeds from maturities of short-term investments	37,820
Purchases of short-term investments	(34,970)
Net cash provided by (used in) investing activities	2,752	(322)
Cash flows from financing activities:
Proceeds from exercise of stock options	40	3
Proceeds from initial public offering, net of issuance costs paid in the period		67,026
Payments of initial public offering costs	(150)	(9,376)
Net cash (used in) provided by financing activities	(110)	67,029
Net (decrease) increase in cash and cash equivalents	(34,059)	38,920
Cash and cash equivalents at beginning of the period	49,360	55,101
Cash and cash equivalents at end of the period	$ 15,301	94,021
Supplemental disclosure of non-cash investing and financing activities:
Deferred offering costs included in accounts payable and accrued expenses		1,105
Conversion of preferred stock to common stock upon initial public offering		$ 104,713