Abstract LB105: In vivo CAR T therapy: targeted in vivo gene delivery of a CAR using a CD8-specific fusogen results in tumor eradication (2021)

Abstract CAR T cells are highly effective at inducing remissions in patients with refractory B cell malignancies. The ex vivo process used to manufacture these therapies limits patient access and exposes T cells to non-physiologic conditions in culture. Viral vectors are efficient at genetically modifying T cells and are used in the ex vivo manufacture of most CAR T cell products but lack target-cell specificity. Here we describe how viral envelope glycoproteins, termed fusogens, engineered to target the CD8 co-receptor can efficiently and specifically deliver a chimeric antigen receptor (CAR) to human T cells in vivo that support target cell killing and tumor eradication. Modification of viral envelope proteins to include antibody-based binding domains (CD8 binders) can produce fusogen-viral vector compositions that deliver genetic payloads to CD8 T cells with therapeutic effect (1, 2). Screening CD8-targeted binders identified fusogens with a range of on-target cell transduction efficiencies and off-target cell line specificities. CD8-targeted fusogens with the highest efficiency were comparable to VSVg-pseudotyped lentiviruses at transducing CD8 T cells, but unlike VSVg showed CD8 T cell specific transduction. Interestingly, CD8-targeted fusogens were superior to VSVg-pseudotyped lentivirus at transducing non-activated human T cells. In vivo fusogen-mediated delivery showed efficient and specific CD8 T cell transduction and expression of a GFP reporter gene. Second-generation CARs containing a CD19 binding domain and a 41BB costimulatory domain delivered by targeted fusogen demonstrated CD8 specific expression and functional activity against non-malignant B cells and CD19+ Nalm6 leukemia cells. To demonstrate targeted fusogen-mediated in vivo CAR delivery and activity, we established Nalm6 xenografts in mice into which unmodified activated human PBMCs were infused. Activated human PBMCs alone were unable to control tumor growth. A single intravenous delivery of a CD8 fusogen containing a second-generation CD19 CAR transgene across a range of functional titer doses resulted in the generation of CD8 CAR Ts that eradicated the CD19+ tumor xenografts. A high percentage of T cells demonstrated CAR expression after fusogen delivery with clear specificity for the CD8+ cells. Importantly, the fusogen was able to generate a functional CAR response regardless of prior activation status of the T cells. Targeted in vivo delivery of CAR into T cell subsets may represent a novel therapeutic approach for human B cell malignancies. The ability to specifically deliver a CAR gene to a T cell in vivo would be transformative in terms of patient access and is likely to generate a qualitatively superior therapeutic T cell. References: 1) Bender, R. R. et al. PLOS Pathogens 12, e1005641 (2016). 2) Agarwal, S. et al. OncoImmunology 8, 1-8 (2019). Citation Format: Akinola Emmanuel, Patty Cruite, Hanane Ennajdaoui, Carmela Passaro, Paige Baldwin, Victoria Duback, Anna Liang, Jess Elman, Samantha Crocker, Shirisha Amatya, Caspian Harding, Allyse Mazarelli, Sergey Lyubinetsky, Vidur Patel, Avani Parikh, Kelan Hlavaty, Jason Rodriguez, Lauren Pepper, Albert Ruzo, Salvatore Iovino, Kutlu Elpek, Michael Laska, Trevor McGill, Donna Dambach, Terry Fry, Jagesh Shah. In vivo CAR T therapy: targeted in vivo gene delivery of a CAR using a CD8-specific fusogen results in tumor eradication [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr LB105.