Abstract 146: <i>In vivo</i> lentiviral CAR-T gene delivery demonstrates high specificity and potent anti-tumor activity in a humanized B cell lymphoma model.

Abstract Introduction: Chimeric Antigen Receptor T (CAR-T) cell therapies have revolutionized treatment for hematologic malignancies, particularly B cell cancers, and show promise in autoimmune diseases and solid tumors. Despite this success, the conventional approach to CAR-T manufacturing presents several limitations: it requires leukapheresis, PBMC isolation, ex vivo genetic modification and expansion, and reinfusion back into the patient. These steps are time-consuming, costly, and logistically complex, limiting scalability and patient accessibility. Furthermore, current CAR-T therapies have shown limited efficacy against solid tumors due to poor trafficking, immunosuppressive microenvironments, and antigen heterogeneity. Methods: To improve the cost-inefficient and time-consuming challenges of the standard CAR-T therapy, Syenex developed Vivo-T, a novel T cell-specific lentiviral vector (LVV) platform enabling in vivo delivery of CAR constructs, eliminating the need for ex vivo manipulation and personalized CAR-T manufacturing. This system was evaluated in JAX PBMC-humanized B cell lymphoma mouse model. NSG-MHC I/II double knockout mice were irradiated and injected intravenously with 2.5×105 Raji-Luc cells. Five days later, mice were engrafted with 1×107 human PBMCs. Between 4-24 hours post-engraftment, mice received intravenous doses of T cell-targeted LVVs encoding anti-CD19 CARs. Tumor burden was monitored via IVIS imaging for 3 weeks. Toxicity was assessed through body weight, clinical observations, and serum cytokine analysis. CAR-T engraftment and expansion were evaluated by flow cytometry of peripheral blood. Results: In vivo delivery of the CAR construct resulted in efficient T cell transduction, with rapid and robust CAR-T expansion surpassing that of ex vivo-engineered CAR-T control. Notably, significant anti-tumor activity was observed as early as 7 days post-LVV administration. Initial signs of toxicity were primarily attributed to high viral titers; however, these effects were mitigated by reducing the viral load, without compromising the antitumor efficacy of the treatment. These findings validate the efficacy of the in vivo CAR-T system and support its potential for clinical translation. Conclusion: The Vivo-T system represents a transformative approach to CAR-T therapy by simplifying manufacturing, reducing costs, and enabling scalable, off-the-shelf immunotherapy. Citation Format: Ilian Radichev, Devin Stranford, Hailey Edelstein, Oanh Pham, Destanie Rose, Jiwon Yang, Mahdy Yassine, Henry Schirmer, Teresa Nikolich, Joshua Leonard, James Keck, Matteo Stoppato. In vivo lentiviral CAR-T gene delivery demonstrates high specificity and potent anti-tumor activity in a humanized B cell lymphoma model [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 146.