Stereotactic body radiation therapy enriches mediators of humoral immune activity in metastatic renal cell carcinoma

Background Stereotactic body radiation therapy (SBRT) has recently been shown to be effective against renal cell carcinoma (RCC); ongoing clinical trials seek to assess the impact of SBRT on immune checkpoint blockade (ICB) efficacy in patients with RCC. Previous analysis of SBRT-treated RCC tumors has elucidated a phenotypic maturation of tumor-infiltrating T cells and increased tumor-associated antigen expression compared with non-irradiated tumors. However, the impacts of SBRT on humoral immunity, which has consistently been linked to ICB responsiveness in RCC, remain unknown.Methods Analysis of bulk RNA sequencing of SBRT-treated tumors obtained from a prospective clinical trial ( NCT01892930) compared with non-irradiated tumors was performed. A subset of samples was further profiled with single-cell RNA sequencing (scRNA-seq) to investigate the impacts of SBRT on B cell populations. Full spectrum flow cytometry was also employed to phenotype B cell subsets. The impact of findings on ICB response in RCC patients was validated in two clinical cohorts—IMmotion151 and HCRN-GU16-260—using immune deconvolution of tumor transcriptomic data.Results Bulk transcriptomic analysis of SBRT-treated RCC tumor samples revealed a significant increase in the predicted abundance of B cells and class-switched memory B cells relative to controls, along with consistent upregulation of B cell-, tertiary lymphoid structure-, and phagocytosis-associated gene sets. SBRT was associated with a transition to mature, effector plasma cells by scRNA-seq, with significantly increased expression of immunoglobulin-encoding genes. This was validated by flow cytometry, with heightened IgG and CD38 expression in SBRT-enriched clusters compared with overexpression of non-class switched immunoglobulins (IgD/IgM) in control-enriched clusters. Antibody-secreting B cells were significantly increased in SBRT while control tumors demonstrated a significant increase in naïve B cells. In IMmotion151 and HCRN-GU16-260, mature B cell populations (memory and class switched memory) were significantly enriched in ICB responders compared with non-responders, whereas naïve B cell scores were heightened in ICB non-responders.Conclusions SBRT is associated with maturation of the humoral immune compartment within the RCC microenvironment, which ultimately correlates with ICB response among RCC patients. Together, these findings support ongoing investigations into the impact of SBRT as an immune adjuvant to improve ICB sensitivity.