Commitments and Contingencies - Additional Information (Detail) - USD ($)					1 Months Ended		12 Months Ended
	Sep. 01, 2020	Oct. 22, 2019	May 28, 2019	Jan. 13, 2015	Sep. 30, 2020	Jan. 31, 2020	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2017	Nov. 28, 2020	May 10, 2019	Feb. 19, 2019	May 10, 2018	Aug. 24, 2004
Accrued Payments
Incurred expenses							$ 500,000	$ 0
Research and development expense							49,643,000	52,696,000
Cash balance							76,054,000	115,069,000
Agreement commencement date										2015-05
Expected Cash Payment Payable											$ 1,500,000
Royalties amount payable thereafter											$ 100,000
Collaboration revenue							$ 398,000	0
MD Anderson Warrant [Member]
Accrued Payments
Number of Warrants							3,333,333
Warrant exercise per share							$ 0.00
Warrant Expiry date							Dec. 31, 2026
MD Anderson License and the Research and Development Agreement Member [Member]
Accrued Payments
Reimbursement of historical costs		$ 20,000,000
Accrued Payments		3,000,000.0
Aggregate potential benchmark payments		36,500,000
CRADA Agreement [Member]
Accrued Payments
Obligations due under contract													$ 5,000,000.0
Quarterly payments under contract							$ 1,250,000	2,500,000
C A R Products Member
Accrued Payments
Amount of royalties receivable							100,000,000.0
The University of Texas MD Anderson Cancer Center and The Texas A & M University System
Accrued Payments
Milestone maximum payment															$ 4,500,000
Payment under license agreement								0
Collaboration Agreement with Solasia Pharma K.K.
Accrued Payments
Collaboration revenue							400,000	0
MD Anderson License
Accrued Payments
Accrued expenses							8,100,000	12,200,000
Development costs paid							100,000	0
License Agreement with the National Cancer Institute [Member] | One Time Benchmark Payments [Member]
Accrued Payments
Accrued payments or receipts							100,000
Ziop License Agreement With The National Cancer Institute [Member]
Accrued Payments
Annual Licensing fee paid									$ 1,000,000.0
Reimbursement of historical costs			$ 46,000
Expected Cash Payment Payable			1,500,000
Expected cash payment payable per installments			500,000
Maximum royalties amount payable			$ 300,000
Description Of First Benchmark Payable			The first benchmark payment of $0.1 million will be due upon the initiation of our first sponsored Phase 1 clinical trial of a licensed product or licensed process in the field of use licensed under the Patent License
Description Of option To terminate Agreement			The NCI may terminate or modify the Patent License in the event of a material breach, including if we do not meet certain milestones by certain dates, or upon certain insolvency events that remain uncured following the date that is 90 days following written notice of such breach or insolvency event.
Agreement termination, notice period			60 days		60 days
payments under the Patent License	$ 411,000					$ 600,000
Ziop License Agreement With The National Cancer Institute [Member] | Performance Based Payments Member [Member]
Accrued Payments
Aggregate Benchmark Payments Payable			$ 4,300,000
Ziop License Agreement With The National Cancer Institute [Member] | One Time Benchmark Payments [Member]
Accrued Payments
Potential Benchmark Payments Payable			12,000,000.0
Ziop License Agreement With The National Cancer Institute [Member] | Post Marketing Approval [Member] | Performance Based Payments Member [Member]
Accrued Payments
Aggregate Benchmark Payments Payable			3,000,000.0
Ziop License Agreement With The National Cancer Institute [Member] | licensed products [Member] | One Time Benchmark Payments [Member]
Accrued Payments
Maximum Sales Revenue On Which Benchmark Payments Payable			1,000,000,000.0
Minimum sales revenue on which benchmark payments payable			$ 250,000,000.0
Patent And Technology License Agreement [Member] | The University of Texas MD Anderson Cancer Center and The Texas A & M University System
Accrued Payments
Accrued Payments							100,000
Prepaid Expenses and Other Current Assets | MD Anderson License
Accrued Payments
Cash balance							0	8,100,000
Intrexon Corporation
Accrued Payments
Annual Licensing fee									$ 100,000
Expected additional milestones payable												$ 52,500,000
Intrexon Corporation | T-cell receptor
Accrued Payments
Maximum royalty amount														$ 100,000,000.0
Portion of income payable to related party														20.00%
Maximum [Member] | MD Anderson License and the Research and Development Agreement Member [Member]
Accrued Payments
Research and development expense				$ 20,000,000.0
Minimum [Member] | MD Anderson License and the Research and Development Agreement Member [Member]
Accrued Payments
Research and development expense		$ 15,000,000.0
Minimum [Member] | License Agreement with the National Cancer Institute [Member]
Accrued Payments
Royalty fee							$ 500,000
Minimum [Member] | Ziop License Agreement With The National Cancer Institute [Member]
Accrued Payments
Royalty fee								$ 1,500,000