Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
CASH FLOWS FROM OPERATING ACTIVITIES
Net loss	$ (99,404)	$ (57,892)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	279	87
Stock-based compensation	7,799	3,180
Non-cash expense in connection with equity issuance to MSK/MIT	1,331
Non-cash expense in connection with equity issuance to inventors	7,376
Foreign currency transactions	(62)	123
Changes in assets and liabilities:
Other current assets	1,939	2,262
Other assets	2	(131)
Accounts payable	1,800	1,031
Accrued liabilities and other	5,404	2,422
NET CASH USED IN OPERATING ACTIVITIES	(73,536)	(48,918)
CASH FLOWS FROM INVESTING ACTIVITIES
Purchase of property and equipment	(131)	(818)
Loans to inventors	(2,610)
NET CASH USED IN INVESTING ACTIVITIES	(2,741)	(818)
CASH FLOWS FROM FINANCING ACTIVITIES
Proceeds from exercised stock options	585
NET CASH PROVIDED BY FINANCING ACTIVITIES	585
Effect of exchange rates on cash and cash equivalents	(177)	57
NET DECREASE IN CASH AND CASH EQUIVALENTS	(75,869)	(49,679)
Cash and cash equivalents at the beginning of period	207,136	147,871
Cash and cash equivalents at the end of period	131,267	98,192
SUPPLEMENTAL DISCLOSURE OF NON-CASH ACTIVITIES
Property and equipment purchases in accounts payable		752
Right-of-use assets obtained in exchange for lease obligations	$ 2,679	$ 901