Abstract PO-038: Hide and Seq: Radiation-induced immunogenicity of patient tumors revealed by single cell analysis

Abstract Robust preclinical investigations into radiation-induced immunogenicity has led to increased enthusiasm for combining radiation with immunotherapy. Promising results in a limited number of patients treated with radiotherapy and immune-activating strategies has supported the initiation of over 150 ongoing clinical trials. Yet, due to reduced availability of patient samples following treatment, tumor tissue in particular, there has been sparse investigation of the impact of radiation on immunogenicity in human malignancies. While murine models have revealed important insights into understanding radiation-induced immunogenic mechanisms, inherent differences in radiation sensitivity between mice and humans limit translation to patients. To determine the impact of radiation on patient tumor cells we analyzed samples from renal cell carcinoma (RCC) patients treated with stereotactic body radiation therapy (SBRT) in a pilot study (NCT01892930). Previous data showed radiation induced surface presentation of tumor-associated antigens in resected irradiated tumors. Bulk transcriptomic data of in situ-irradiated tumors showed evidence of immune activation, including increased interferon-gamma (IFNG) signaling, as well as increased T cell clonality and higher abundance of T cells clones with similar binding affinities predicted by dominant motif analysis. We hypothesized that the tumor response to in situ irradiation included increased transcript abundance for tumor antigen genes and antigen-presentation machinery, as well as a response to IFNG signaling. Tumor cell comparisons following single-cell RNA sequencing uncovered RCC cell-specific responses to in situ irradiation. Irradiated RCC tumor cells expressed higher levels of genes encoding MUC-1 and carbonic anhydrase 9, as well as higher expression of calreticulin and genes encoding MHC class 1 molecules: HLA-A, HLA-B, and HLA-C; furthermore, gene set enrichment identified enhancement of antigen processing and presentation pathways. Additionally, irradiated tumor cells expressed higher levels of the IFNG receptor, its downstream targets, and the enrichment of several interferon response gene sets. Collectively, these results indicate radiation may improve tumor recognition through both increased antigen expression and surface presentation as well as sensitize tumor cells to immunogenic cytokines and T cell-mediated cytolysis in human malignancies, such as RCC. Citation Format: Jacky L. Chow, Nicholas Hoffend, Madeline Gaudieri, Scott Abrams, Thomas Schwaab, Anurag Singh, Jason Muhitch. Hide and Seq: Radiation-induced immunogenicity of patient tumors revealed by single cell analysis [abstract]. In: Proceedings of the AACR Virtual Special Conference on Radiation Science and Medicine; 2021 Mar 2-3. Philadelphia (PA): AACR; Clin Cancer Res 2021;27(8_Suppl):Abstract nr PO-038.