RIG-I agonists promote antigen-spreading and facilitate durable CAR-T responses in pancreatic ductal adenocarcinoma

Background: Pancreatic ductal adenocarcinoma (PDAC) remains largely refractory to chimeric antigen receptor (CAR)-T cell therapy. Insufficient T cell infiltration, a highly immunosuppressive microenvironment, and antigen loss pose major challenges for CAR-T cell therapy. Methods: We investigated therapeutic synergies of synthetic 5'-triphosphate RNA (3p-RNA), an agonist of the cytoplasmic double-stranded RNA sensor Retinoic Acid Inducible Gene I (RIG-I), and CAR-T cell therapy using syngeneic and human xenograft PDAC models. Tumor growth, chemokine secretion, immune-cell composition, CAR-T persistence, and endogenous T cell responses were assessed by flow cytometry, multiplex cytokine arrays, Enzyme-linked Immunospot (ELISpot), and vaccination-challenge. Results: 3p-RNA provoked rapid type I interferon accompanied with chemokine ligand CCL5 and CXCL9/10/11 secretion, creating chemokine gradients that recruited chemokine receptor CCR5+/CXCR3+ CAR-T cells into tumors. RIG-I activation enhanced CAR-T cell proliferation, activity, and CAR-T persistence. Combination therapy eradicated established tumors in 60%-70% of mice, whereas either monotherapy was largely ineffective. Cured animals rejected CAR antigen-negative tumor cell rechallenge, demonstrating antigen-spreading and endogenous T cell responses. Conclusions: Intratumoral RIG-I priming reprograms the PDAC microenvironment, transforming a non-responsive cancer into a CAR-T-permissive one, supporting durable, poly-antigenic immunity. These findings position 3p-RNA as a rapid, clinically tractable co-therapy to extend CAR-T efficacy to solid tumors.