Circulating and intratumoral immune determinants of response to atezolizumab plus bevacizumab in patients with variant histology or sarcomatoid renal cell carcinoma

BACKGROUND: Renal cell carcinoma of variant histology (vRCC) encompasses approximately 20% of RCC diagnoses. Due to a poor understanding of the different biologies of vRCCs, there is currently no standard of care for this type of tumor and guidelines are extrapolated from clear-cell RCC trials. A phase II trial of atezolizumab plus bevacizumab in patients with vRCC or sarcomatoid differentiation had an acceptable safety profile and evidence of clinical activity, particularly in tumors with positive PD-L1 expression or sarcomatoid differentiation. To better understand the determinants of immunotherapy response in this population, we characterized blood- and tissue-based immune markers for patients with vRCC, or any RCC histology with sarcomatoid differentiation, enrolled in this phase II trial of atezolizumab and bevacizumab. METHODS: We used patient data and biospecimens (blood and tumor) from a prospective phase-II clinical trial of the anti-PD-L1 antibody atezolizumab and the anti-VEGF-A antibody bevacizumab in patients with metastatic RCC with variant histology and/or sarcomatoid differentiation (NCT02724878). Blood samples were collected at baseline, prior to therapy (C1D1: cycle one day one), and on-treatment, following two cycles of therapy (C3D1: cycle three day one). Plasma was assayed for the levels of soluble factors (e.g., cytokines and growth factors), and peripheral blood mononuclear cells (PBMCs) were immunophenotyped using flow cytometry. In addition, formalin-fixed, paraffin-embedded (FFPE) archival or pre-treatment study tumor biopsies were analyzed by immunohistochemistry and immunofluorescence for enrolled subjects with available biospecimen. Baseline demographics, clinical characteristics, and treatment outcomes, including progression-free survival (PFS), overall survival (OS), and clinical benefit, were collected, and analyzed from the trial database. This study was approved by each participating institution's institutional review board, and all patients provided written informed consent. We used R (version 4.1.1) to carry out our analyses. We assessed the relationships between biomarker variables were analyzed using Pearson correlations and hierarchical clustering using Euclidean distance. All biomarker variables were Z-score normalized. We calculated an inflammatory module, the systemic inflammation score (SIS), which corresponds to the average score of the five highly correlated inflammatory cytokines: MIP-1b, IL-1, MCP-1, IL-6, and IL-13. We applied pair-wise Wilcoxon tests to evaluate the association of biomarkers with clinical benefit groups and log-rank-tests and univariate Cox regression models to evaluate the relationship of biomarkers with PFS and OS. RESULTS: With the exception of two angiogenic cytokines (VEGF-A and Angiopoietin 2) that were more abundant in patients with non-sarcomatoid tumors, baseline circulating cytokines (plasma) had similar distributions between sarcomatoid and non-sarcomatoid subgroups. Baseline circulating inflammatory cytokines were highly correlated with one another, forming an “inflammatory module” that was increased in IMDC-poor risk patients and was associated with worse PFS (p=0.028) and with resistance to therapy (p=0.033). At baseline, an elevated circulating VEGF-A level was associated with a lack of response (p=0.03) and worse PFS (p=0.021). However, a larger increase in on-treatment levels of circulating VEGF-A was associated with clinical benefit (p=0.01) and improved overall survival (p=0.0058). Among peripheral immune cell populations, an on-treatment decrease in circulating PD-L1+ T cells was associated with improved outcomes, with a reduction in CD4+ PD-L1+ (HR:0.62[0.49-0.91], p=0.016) and CD8+ PD-L1+ T cells (HR:0.59[0.39-0.87], p=0.009) correlated with improved PFS. Within the tumor itself, a higher percentage of terminally exhausted (PD-1+ and either TIM-3+ or LAG-3+) CD8+ T cells was associated with worse PFS (p=0.028). We observed similar trends for all of these results in different subgroups according to sarcomatoid status and histology. CONCLUSIONS: Overall, these findings support the value of tumor and blood-based immune assessments in determining therapeutic benefit for patients with RCC receiving atezolizumab plus bevacizumab. Furthermore, they provide a foundation for future biomarker studies for patients with variant histology RCC receiving immunotherapy-based combinations.