Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (267,892)	$ (134,231)	$ (99,533)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	6,891	6,311	5,587
Equity-based compensation	47,009	19,903	15,091
Amortization/(accretion) of investment premiums/(discounts)	7,604	538	3,725
Loss from equity method investments	1,325	0	0
Deferral of equity method investment intra-entity profit on sales	2,937	0	0
Loss on disposal of property and equipment	0	35	1
Changes in operating assets and liabilities:
Accounts receivable	99	2,490	2,927
Prepaid expenses and other current assets	(9,798)	(9,206)	(1,763)
Operating lease right-of-use assets	9,349	6,457	5,728
Other assets	117	83	153
Accounts payable	529	5,060	1,880
Accrued expenses	17,260	13,031	2,310
Deferred revenue	(31,355)	45,121	(27,122)
Operating lease liabilities	(9,105)	(5,504)	(4,774)
Net cash used in operating activities	(225,030)	(49,912)	(103,240)
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of property and equipment	(12,756)	(3,585)	(6,794)
Purchases of marketable securities	(1,020,620)	(473,702)	(297,030)
Maturities of marketable securities	485,598	262,800	329,000
Investment in Kyverna Therapeutics, Inc.	(3,000)	0	0
Net cash (used in) provided by investing activities	(550,778)	(214,487)	25,176
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of common stock	1,817,900
Proceeds from options exercised	41,094	11,574	3,086
Issuance of shares through employee stock purchase plan	2,024	1,557	1,092
Net cash provided by financing activities	736,688	371,779	76,434
Net (decrease) increase in cash and cash equivalents and restricted cash equivalents	(39,120)	107,380	(1,630)
Cash and cash equivalents and restricted cash equivalents, beginning of period	164,606	57,226	58,856
Cash and cash equivalents and restricted cash equivalents, end of period	125,486	164,606	57,226
Reconciliation of cash, cash equivalents and restricted cash equivalents to consolidated balance sheet:
Cash and cash equivalents	123,406	160,020	57,226
Restricted cash equivalents, included in investments and other assets	2,080	4,586	0
Cash and cash equivalents and restricted cash equivalents, end of period	125,486	164,606	57,226
SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION:
Purchases of property and equipment unpaid at period end	667	1,508	800
Right-of-use assets acquired under operating leases	49,378	26,432	2,554
Regeneron Pharmaceuticals Inc. [Member]
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of common stock	0	12,580	0
AvenCell Therapeutics, Inc [Member]
Adjustments to reconcile net loss to net cash used in operating activities:
Loss from equity method investments	2,900
SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION:
Non-cash contribution of intellectual property	62,900	0	0
Sparing Vision SAS [Member]
SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION:
Non-cash contribution of intellectual property	14,759	0	0
Kyverna Therapeutics, Inc. [Member]
SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION:
Non-cash contribution of intellectual property	7,000	0	0
Follow On Public Offering
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of common stock	648,315	296,607	0
At The Market Offerings
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of common stock	$ 45,255	$ 49,461	$ 72,256