Inducing Neoepitopes in Cancer Cells Unmasks Tumors to the Immune System

Immunotherapy with immune checkpoint inhibitors (ICIs) is limited to a subset of cancer types. The treatment of immunologically cold tumors that lack T cell infiltration remains a challenge. Since tumor mutational burden correlates with ICI efficacy, here our objective is to artificially induce “mutations” in cancer cells at the level of RNA to unmask cold tumors to the immune system and render them susceptible to ICI. To accomplish this, we engineered human Adenosine Deaminase that Acts on RNA 2 (ADAR2) to create abundant, genome-wide editing events. We hypothesized that these edits would induce neoepitopes and unmask tumors to the immune system. We tested this hypothesis in immunologically cold murine melanoma (B16F10). Mice received one injection of adeno-associated viruses (AAVs) encoding ADAR2 in combination with αPD1. Tumor growth was suppressed upon treatment, resulting in a significant improvement in overall survival compared to αPD1 monotherapy. Flow cytometry analysis of the tumor revealed significantly increased CD8⁺ T cell infiltration and tumor-specific T cells as well as a reduction of regulatory T cells and myeloid-derived suppressor cells. In an immune excluded model of breast cancer (EMT6), we achieve complete remission of established tumors in a quarter of treated mice. Thus, inducing neoepitopes through RNA editing may be a novel method of enhancing immunotherapy by unmasking a variety of cold tumors to the immune system.