Single Fraction Stereotactic Body Radiation Therapy Induces Dynamic Changes to the Peripheral Blood T Cell Repertoire in Renal Cell Carcinoma Patients

Abstract

Clinical studies combining radiation and immunotherapy have shown promising response rates, strengthening efforts to sensitize tumors to immune-mediated attack. Thus, there is an ongoing surge in trials using preconditioning regimens with immunotherapy. Yet, due to scarcity of resected tumors treated in situ with radiotherapy, there has been little investigation of radiation’s sole contributions towards local and systemic anti-tumor immunity in patients. Without this access, translational studies have been limited to evaluating circulating immune subsets and systemic remodeling of peripheral T cell receptor repertoires. This constraint has left gaps in how radiation impacts intratumoral responses and whether tumor-resident T cell clones are amplified following treatment. Therefore, to interrogate the immune impact of radiation on the tumor microenvironment and test the hypothesis that radiation initiates local and systemic expansion of tumor-resident clones, we analyzed renal cell carcinoma from patients treated with stereotactic body radiation therapy. Blood and tumor samples were collected from patients prior to nephrectomy for renal cell carcinoma. These samples were compared to samples from patients treated on a 15 patient clinical trial of single fraction stereotactic body radiation therapy delivered 4 weeks prior to nephrectomy. Transcriptomic comparisons were evaluated by bulk RNA sequencing. T cell receptor sequencing monitored repertoires during the 4-week period between SBRT and nephrectomy. Pathway analysis from tumor transcriptomic data showed radiation-specific enrichment of immune-related processes. T cell receptor sequencing revealed increased clonality in radiation-treated tumors. The frequency of identified, tumor-enriched clonotypes was tracked across serial blood samples. Compared to pre-treatment, we observed increased abundance of tumor-enriched clonotypes 2 weeks post-radiation. However, this expansion was not sustained and contracted towards baseline levels 4 weeks after treatment. Altogether, these results indicate robust intratumoral immune remodeling and a window of tumor-resident T cell expansion following radiation that may be leveraged for rational design of combinatorial strategies. Samples from renal cell carcinoma (RCC) patients underwent high-throughput analysis to reveal transcriptional immune activation and increased clonality in irradiated tumors. Analysis across longitudinal blood samples showed tumor-enriched clonotypes undergo phases of peripheral expansion and contraction following radiation. Collectively, these findings demonstrate radiotherapy remodels intratumoral T cell responses and have significant implications for refined sequencing of combination strategies in RCC.