Commitments and Contingencies - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands					3 Months Ended		6 Months Ended
	Aug. 14, 2023	May 28, 2019	Aug. 17, 2015	Jan. 13, 2015	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022	Apr. 03, 2023	Oct. 22, 2019	Feb. 19, 2019	Oct. 05, 2018	Aug. 24, 2004
Accrued Payments
Research and development expense					$ 5,186	$ 5,937	$ 11,689	$ 11,518
Royalty amount					0	0	0	0
Maximum Royalty Amount												$ 100,000
Collaboration revenue					4	0	4	0
MD Anderson Warrant [Member]
Accrued Payments
Number of Warrants										3,333,333
Warrant exercise per share										$ 0.001
Warrant Expiry date										Dec. 31, 2026
MD Anderson Agreement and Worldwide License [Member]
Accrued Payments
License agreement commencing date				Jan. 13, 2015
MD Anderson License and the Research and Development Agreement [Member]
Accrued Payments
Reimbursement of historical costs										$ 20,000
Quarterly expense incurred					200	200	400	300
Aggregate potential benchmark payments										36,500
Payments due prior to the first marketing approval										$ 3,000
CRADA Agreement [Member]
Accrued Payments
Quarterly expense incurred					300	0	500	0
Contribution payable on per annum basis							1,000
Obligations due under contract											$ 5,000
CRADA Agreement [Member] | Subsequent Event [Member]
Accrued Payments
Agreement termination date	Oct. 13, 2023
The University of Texas MD Anderson Cancer Center and The Texas A & M University System
Accrued Payments
Milestone maximum payment													$ 4,500
The University of Texas MD Anderson Cancer Center and The Texas A & M University System | Royalty [Member]
Accrued Payments
Payment under license agreement					0	0	0	0
License Agreement with the National Cancer Institute [Member]
Accrued Payments
License Expense					100	200	400	500
License Agreement with the National Cancer Institute [Member] | One Time Benchmark Payments [Member]
Accrued Payments
First benchmark payment		$ 100
Ziop License Agreement With The National Cancer Institute [Member]
Accrued Payments
Minimum royalties amount payable		300
Royalties amount payable thereafter		100
Aggregate minimum annual royalties paid		$ 1,500
Description Of First Benchmark Payable		The first benchmark payment of $0.1 million was paid during the year ended December 31, 2022 upon the initiation of the Company's TCR-T Library Phase 1/2 Trial, which was a qualifying Phase 1 clinical trial under the terms of 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 the Company does 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
Ziop License Agreement With The National Cancer Institute [Member] | Performance Based Payments Member [Member]
Accrued Payments
Aggregate Benchmark Payments Payable		$ 4,300
Ziop License Agreement With The National Cancer Institute [Member] | One Time Benchmark Payments [Member]
Accrued Payments
Potential Benchmark Payments Payable		12,000
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
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
Minimum sales revenue on which benchmark payments payable		$ 250,000
Collaboration Agreement With Solasia Pharma KK [Member]
Accrued Payments
Collaboration revenue					4	4	4	4
Collaboration Agreement With Solasia Pharma KK [Member] | Royalty [Member]
Accrued Payments
Collaboration revenue					$ 0	$ 0	$ 0	$ 0
Intrexon Corporation
Accrued Payments
Annual License Fees									$ 75			100
Expected additional milestones payable												52,500
Intrexon Corporation | T-cell receptor
Accrued Payments
Maximum royalty amount												$ 100,000
Portion of income payable to related party												20.00%
Minimum | MD Anderson License and the Research and Development Agreement [Member]
Accrued Payments
Research and development expense			$ 15,000
Maximum | MD Anderson License and the Research and Development Agreement [Member]
Accrued Payments
Research and development expense			$ 20,000