Seq-ing the source of radiation-induced anti-tumor immunogenicity in patient tumors

Abstract Translational studies in a small number of patients have demonstrated a clinical benefit when combining radiation and immunotherapy. These findings are supported by correlative data showing that transcriptional changes to the tumor microenvironment following radiotherapy are associated with responses. Yet, given limited access to patient specimens following treatment, few studies have addressed how radiation primes anti-tumor immunity at single cell resolution, thus limiting our understanding of the source of radiation-induced changes within tumors. Here, we acquired renal cell carcinoma (RCC) tumors from patients treated with stereotactic body radiation therapy (SBRT) followed by nephrectomy in a pilot study (NCT01892930), to evaluate radiation-induced transcriptional changes to immune and RCC cells by single-cell RNA sequencing. We hypothesized that SBRT-induced interferon (IFN) and immune-activating signals, previously detected by bulk sequencing and array platforms, would localize to the dense lymphocyte infiltrate characterized in RCC and that the transcriptional signatures in SBRT-treated RCC would reflect increased immune recognition. Single-cell transcriptomics uncovered increased frequency of mature T cells in irradiated tumors, including increased expression of IFN-gamma and granzymes, as well as PD1 and other exhaustion markers. Additionally, irradiated-RCC cells expressed more IFN-gamma receptor and were enriched for IFN signaling and antigen processing pathways. Collectively, these results indicate radiation may improve anti-tumor immunity by increasing both T cell activity and tumor cell sensitivity to pro-inflammatory cytokines and cytolysis in human malignancies.