CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Cash flows from operating activities:
Net loss	$ (23,388,507)	$ (12,551,350)	$ (5,669,577)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	75,301	26,027	27,063
Forgiveness of accounts payable			(180,782)
Common stock issued for services			2,063,565
Stock-based compensation	3,269,366	1,600,625
Loss on disposal of equipment	99,147		22,550
Changes in operating assets and liabilities:
Incentive and tax receivable	(3,257,225)	(356,718)
Grant receivables			34,514
Prepaid expenses and other assets	(285,041)	(359,968)	437,691
Deferred grant revenue	(7,250)	(278,900)	(641,321)
Accounts payable	1,044,127	536,354	140,105
Accrued expenses	2,011,916	1,597,131	225,537
Net cash used in operating activities	(20,438,166)	(9,786,799)	(3,540,655)
Cash flows from investing activities:
Purchases of property and equipment	(109,628)	(216,335)	(19,717)
Net cash used in investing activities	(109,628)	(216,335)	(19,717)
Cash flows from financing activities:
Proceeds from issuance of Series B redeemable convertible preferred stock, net			309,911
Proceeds from issuance of Series 1 convertible preferred stock, net			12,925,034
Proceeds from issuance of common stock, net of offering costs	10,000,525	42,122,004	1,409
Proceeds from the exercise of stock options		63,509
Repayment of borrowings			(499,996)
Net cash provided by financing activities	10,000,525	42,185,513	12,736,358
Net (decrease) increase in cash and cash equivalents	(10,547,269)	32,182,379	9,175,986
Cash and cash equivalents at beginning of period	41,513,060	9,330,681	154,695
Cash and cash equivalents at end of period	30,965,791	41,513,060	9,330,681
Supplemental disclosures of cash flow information:
Accrued dividends on redeemable convertible preferred stock			48,078
Accretion of redeemable convertible preferred stock			39,876
Deferred offering costs included in accounts payable			1,080,199
Change in property and equipment acquired but not yet paid	$ (19,444)	$ 17,696	1,748
Cash paid for interest			$ 1,920