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Published on: February 17, 2022
PET Reporter Gene Imaging and Ganciclovir-Mediated Ablation of Chimeric Antigen Receptor T Cells in Solid Tumors
Surya Murty1,2, Louai Labanieh1, Tara Murty3
1Department of Bioengineering, Stanford University School of Medicine, Stanford, California.
Abstract:
Imaging strategies to monitor chimeric antigen receptor (CAR) T-cell biodistribution and proliferation harbor the potential to facilitate clinical translation for the treatment of both liquid and solid tumors. In addition, the potential adverse effects of CAR T cells highlight the need for mechanisms to modulate CAR T-cell activity. The herpes simplex virus type 1 thymidine kinase (HSV1-tk) gene has previously been translated as a PET reporter gene for imaging of T-cell trafficking in patients with brain tumor. The HSV1-TK enzyme can act as a suicide gene of transduced cells through treatment with the prodrug ganciclovir. Here we report the molecular engineering, imaging, and ganciclovir-mediated destruction of B7H3 CAR T cells incorporating a mutated version of the HSV1-tk gene (sr39tk) with improved enzymatic activity for ganciclovir. The sr39tk gene did not affect B7H3 CAR T-cell functionality and in vitro and in vivo studies in osteosarcoma models showed no significant effect on B7H3 CAR T-cell antitumor activity. PET/CT imaging with 9-(4-[18F]-fluoro-3-[hydroxymethyl]butyl)guanine ([18F]FHBG) of B7H3-sr39tk CAR T cells in an orthotopic model of osteosarcoma revealed tumor homing and systemic immune expansion. Bioluminescence and PET imaging of B7H3-sr39tk CAR T cells confirmed complete tumor ablation with intraperitoneal ganciclovir administration. This imaging and suicide ablation system can provide insight into CAR T-cell migration and proliferation during clinical trials while serving as a suicide switch to limit potential toxicities. SIGNIFICANCE: This study showcases the only genetically engineered system capable of serving the dual role both as an effective PET imaging reporter and as a suicide switch for CAR T cells.
Insights
This study engineered B7H3 chimeric antigen receptor (CAR) T cells with a dual-function gene for PET imaging and ganciclovir-induced suicide. The system enables tracking CAR T-cell activity and controlling potential toxicities in cancer treatment.
Area of Science:
- Immunology
- Molecular Biology
- Oncology
Background:
- Chimeric antigen receptor (CAR) T-cell therapy shows promise for treating liquid and solid tumors.
- Effective CAR T-cell therapy requires monitoring biodistribution and proliferation, alongside mechanisms for controlling potential adverse effects.
- The herpes simplex virus type 1 thymidine kinase (HSV1-tk) gene has been used for T-cell imaging and as a suicide gene.
Purpose of the Study:
- To molecularly engineer B7H3 CAR T cells with a mutated HSV1-tk gene (sr39tk) for enhanced PET imaging and ganciclovir-mediated suicide.
- To evaluate the functionality, antitumor activity, and imaging capabilities of the engineered CAR T cells in osteosarcoma models.
- To demonstrate the dual role of the sr39tk gene as a PET reporter and a suicide switch for CAR T cells.
Main Methods:
- Genetically engineered B7H3 CAR T cells incorporating the sr39tk gene.
- In vitro and in vivo studies using osteosarcoma models.
- PET/CT imaging with [18F]FHBG to track T-cell migration and expansion.
- Ganciclovir administration for CAR T-cell ablation and tumor destruction assessment.
- Bioluminescence imaging for tumor ablation confirmation.
Main Results:
- The sr39tk gene did not compromise B7H3 CAR T-cell functionality or antitumor activity in vitro and in vivo.
- PET/CT imaging successfully visualized tumor homing and systemic immune expansion of B7H3-sr39tk CAR T cells.
- Complete tumor ablation was achieved with ganciclovir treatment, confirmed by bioluminescence and PET imaging.
- The sr39tk gene demonstrated improved enzymatic activity for ganciclovir.
Conclusions:
- The sr39tk gene can be effectively integrated into CAR T cells for dual PET imaging and suicide ablation.
- This engineered system allows for real-time monitoring of CAR T-cell biodistribution and therapeutic response.
- The system provides a crucial safety mechanism to control CAR T-cell activity and mitigate potential toxicities during clinical application.
