An inherent T cell-activating mRNA delivery platform for in vivo CAR T generation

The clinical success of CAR T cell therapy has underscored the need for scalable, non-invasive strategies for in vivo T cell engineering. Although mRNA delivery offers a promising alternative, current lipid-based vectors lack intrinsic T cell tropism and often rely on antibody conjugation, complicating manufacturing and raising safety concerns. Here we present an inherent T cell-activating polymer-lipid nanoparticle (ERTLNPs) that enable ligand-free, efficient mRNA transfection and activation of T cells in vivo. ERTLNPs, composed of p-toluenesulfonyl arginine (RT)-functionalized polyethylenimine (denoted as PEI-RT) and helper lipids, preferentially accumulate in the spleen following systemic administration. Without exogenous stimulation, ERTLNPs intrinsically activate T cells, triggering robust mRNA expression and proliferation. Mechanistically, ERTLNPs engage the PI3K/AKT/mTOR signaling axis to reprogram T cell metabolism, promoting expansion while restraining exhaustion. Systemic delivery of mRNA encoding fibroblast activation protein chimeric antigen receptor (mFAP CAR) via ERTLNPs leads to in situ generation of functional CAR T cells, which efficiently eliminate pathological fibroblasts in models of cancer and fibrosis, with minimal off-target effects. This ligand-free, metabolically reprogramming mRNA delivery platform provides a clinically translatable approach for in vivo CAR T cell generation and broadens the landscape of non-viral immunotherapeutic engineering.