Targeted Lipid Nanoparticle Delivery of FAP-CAR mRNA Enables Potent In Vivo T-cell Engineering against Pancreatic Tumors

Fibroblast activation protein (FAP), which is highly expressed on cancer-associated fibroblasts (CAF), is a promising therapeutic target to achieve normalization of the tumor microenvironment. We previously established an ex vivo retroviral-transduced FAP-specific chimeric antigen receptor (FAP-CAR) T-cell approach to deplete FAP+ CAFs that resulted in delayed tumor growth associated with disruption of desmoplastic matrix and enhanced immune cell infiltration and reversed immune exclusion and immunosuppression. In this study, we describe an in vivo strategy for generating FAP-CAR T cells using anti-CD5-conjugated targeted lipid nanoparticles (tLNP) encapsulating FAP-CAR mRNA and assessed the efficacy of this approach compared with adoptive transfer of retrovirus-transduced CAR T cells in a preclinical model of pancreatic ductal adenocarcinoma. With transient CAR expression in >45% of splenic, >69% of circulating, and >35% of tumor-infiltrating T cells, the abundance of peripheral and intratumoral FAP-CAR+ T cells detected following a single intravenous dose of FAP-CAR mRNA tLNPs was greater than that detected following administration of 1 × 107ex vivo retrovirally transduced FAP-CAR T cells. Furthermore, in vivo mRNA CAR T-cell engineering resulted in as good or greater inhibition of tumor growth as compared with adoptive transfer of ex vivo retroviral-engineered T cells. Given that in vivo generation of CAR T cells resulted in transient CAR expression and circumvented the need for autologous T-cell isolation, viral vectors, and lymphodepletion, this platform represents a potentially safer, more accessible, and cost-effective method for targeting stromal cells to normalize the tumor microenvironment in desmoplastic tumors and has potential implications for tumor antigen-targeted CAR T cells.