Consolidated Statements of Cash Flows - USD ($)	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Cash flows from operating activities
Net loss	$ (166,014,000)	$ (174,523,000)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation expense	1,172,000	492,000
Research and development license expense	1,250,000	9,750,000
Stock-based compensation	18,043,000	18,184,000
Impairment of long-lived assets	36,420,000	0
Non-cash lease expense	1,315,000
Other	906,000	388,000
Changes in operating assets and liabilities:
Prepaid expenses and other assets	2,088,000	(3,361,000)
Accounts payable	(7,804,000)	14,494,000
Accrued expenses and other liabilities	(9,323,000)	17,542,000
Deferred revenue	33,557,000
Due to related party		(8,000)
Net cash used in operating activities	(88,390,000)	(117,042,000)
Cash flows from investing activities
Purchase of research and development license	(4,250,000)	(6,250,000)
Purchase of property, plant and equipment	(20,619,000)	(15,304,000)
Other	(61,000)
Net cash used in investing activities	(24,930,000)	(21,554,000)
Cash flows from financing activities
Proceeds from Term Loan, net		39,957,000
Payment of shelf registration costs	(358,000)	(360,000)
Proceeds from common stock issuances under ESPP	253,000
Other	(1,042,000)	(514,000)
Net cash provided by financing activities	52,097,000	39,083,000
Net decrease in cash, cash equivalents and restricted cash	(61,223,000)	(99,513,000)
Cash, cash equivalents and restricted cash at the beginning of the period	151,740,000	251,253,000
Cash, cash equivalents and restricted cash at the end of the period	90,517,000	151,740,000
Cash and cash equivalents	87,880,000	149,103,000
Restricted cash	2,637,000	2,637,000
Supplemental disclosure of cash flow information:
Cash paid for interest	2,775,000	641,000
Supplemental disclosure of noncash investing and financing activities:
Property, plant and equipment in accounts payable and accrued expenses	4,002,000	8,282,000
Acquisition of property, plant and equipment funded by landlord		606,000
Right-of-use assets obtained in exchange for lease liabilities	23,432,000
Offering costs not yet paid	387,000	141,000
Purchase of research and development license not yet paid		3,500,000
Build-to-suit lease liability		$ 26,250,000
Public Offering
Cash flows from financing activities
Net proceeds from issuance of common stock	27,717,000
Offering to Astellas
Cash flows from financing activities
Net proceeds from issuance of common stock	13,887,000
At-the-Market Offering
Cash flows from financing activities
Net proceeds from issuance of common stock	$ 11,640,000