The RIG-I Agonist 3pRNA Synergizes with Checkpoint Blockade in Cancer Immunotherapy

Antibody-mediated targeting of regulatory T cell receptors such as CTLA-4 has been shown to enhance anti-tumor immune responses against several cancer entities including malignant melanoma. Yet, therapeutic success in patients remains variable underscoring the need for novel combinatorial approaches. Here we established a vaccination protocol that combines selective engagement of the nucleic acid-sensing pattern recognition receptor RIG-I, antigen and CTLA-4-blockade. We found that vaccination together with RIG-I ligation strongly synergized with CTLA-4 blockade to induce expansion and activation of antigen-specific CD8⁺ T cells and potent anti-tumor immunity. Cross-priming of cytotoxic T cells as well as anti-tumor immunity required the adapter protein MAVS and type I interferon (IFN) signaling and were mediated by dendritic cells. In addition, the benefit of the combined immunization with anti-CTLA-4 was reduced by systemic antibiotics pointing to the requisite of an intact commensal microbiota in this context. Together, our findings describe a novel combinatorial strategy that may form the basis for the design of new type I IFN-based regimens that enhance antigen-specific T cell reactivity against cancer.