Abstract 147: A multipronged approach to improve gene delivery efficiency for <i>in vivo</i> CAR-T using CD3 and CD7 retargeted LVVs.

Abstract Chimeric antigen receptor (CAR)-T therapies have advanced cancer treatment; however, for conventional ex vivo CAR-T therapies, patient access is often hindered by high costs, long manufacturing times, lymphodepleting chemotherapy needed to precondition the patient, and the inconvenience to travel to specialized treatment centers. To address these limitations, strategies have recently emerged to generate CAR-T cells in situ. These approaches, comprising the field of in vivo CAR-T, are based on delivering the CAR construct to T cells in situ typically using either lentiviral vectors (LVV) or lipid nanoparticles (LNP) decorated with T cell-specific antibodies. In vivo CAR-T approaches have demonstrated encouraging efficacy in preclinical and early clinical studies, but still face challenges in terms of efficiency, specificity, durability, and scalability. CD3 and CD7 are well-established T cell targets used in current in vivo CAR-T delivery vehicles, and such LVV and LNP-based approaches are showing encouraging efficacy in CAR gene delivery to T cells in situ; however, the efficiency of current approaches based on monospecific CD3 or CD7 antibodies for in vivo gene delivery still remains low, thereby limiting their therapeutic potency. By using internally developed CD3 and CD7 VHH antibodies, we implemented a multipronged approach to improve the gene delivery efficiency in vivo, including 1) incorporation of a CD3+CD7 bispecific antibody in the LVV particle; 2) inclusion of a HIV component in the LVV particles that counteracts host antiviral defense mechanisms to enhance transgene expression; 3) co-administration of an approved cardiovascular drug that enhances CD7 expression in T cells. In vitro assays in a T cell line and primary T cells and in vivo studies with mice and non-human primates demonstrated that these novel approaches and their combinations substantially improved CAR gene expression compared with CD3 or CD7 monospecific-targeted LVVs. Citation Format: Longshan Liu, Cheng Luo, Yangyang Tang, Lianqu Li, Hai Huang, Mangmang Li, Yu Liang. A multipronged approach to improve gene delivery efficiency for in vivo CAR-T using CD3 and CD7 retargeted LVVs [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 147.