Abstract 3129: Fibroblast activation protein directed CAR T cells engineered <i>in situ</i> using targeted lipid nanoparticles inhibit progression of pancreatic ductal adenocarcinoma

The growth of solid tumors is greatly influenced by stromal components including cancer-associated fibroblasts (CAFs) and desmoplastic matrix through both immune-dependent and immune-independent mechanisms. Fibroblast activation protein (FAP) is a stromal cell target that is selectively expressed at high levels on the cell surface of CAFs. We previously established an ex vivo retroviral-transduced CAR T cell approach to target FAP+ CAFs that resulted in depletion of FAP+ stromal cells, disruption of desmoplastic matrix, enhanced immune infiltration, and inhibition of tumor growth. In this study, we generated FAP-CAR T cells in situ using a novel platform to deliver modified FAP-CAR mRNA encased in anti-CD5 conjugated targeted lipid nanoparticles (tLNPs) and assessed the efficacy of this approach in a preclinical model of pancreatic ductal adenocarcinoma utilizing a cell line derived from a spontaneous pancreatic tumor isolated from a genetically engineered KPC mouse. We found that a single intravenous dose of anti-CD5 tLNP loaded with 30 μg of FAP-CAR mRNA resulted in transient FAP-CAR expression on &amp;gt;45%, &amp;gt;69% and &amp;gt;35% of CD3 T cells in spleen, blood and tumor tissues, respectively. Although CAR expression was more transient, the percentage of FAP-CAR+ T cells generated using this approach was significantly greater than the percentage of FAP-CAR+ cells detected following administration of 1X107 ex vivo retrovirally transduced FAP-CAR T cells. Notably, this in situ mRNA CAR T-cell engineering resulted in significantly increased inhibition of tumor growth, as compared to adoptive transfer of ex vivo retroviral-engineered T cells (74% vs 48%) respectively. Given that this approach circumvents the need for autologous T cell isolation, ex vivo viral transduction and expansion (thereby reducing the potential risk of insertional mutagenesis, while also eliminating the need for pre-conditioning by lymphodepletion), our data indicate a promising therapeutic delivery platform for treating desmoplastic solid tumors using a more accessible and cost-efficient technology. Citation Format: Khuloud Bajbouj, Zebin Xiao, Leslie A. Hopper, Li Huang, Tyler E. Papp, Jayalakshmi Ramani, Adrian Bot, Yanjie Bao, Matthew Butcher, Haig Aghajanian, Carl H. June, Drew Weissman, Hamideh Parhiz, Steven M. Albelda, Ellen Puré. Fibroblast activation protein directed CAR T cells engineered in situ using targeted lipid nanoparticles inhibit progression of pancreatic ductal adenocarcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 3129.