Intratumoral B cells as predictive biomarkers for response to immune check point blockade in patients with recurrent ovarian cancer

Abstract

<h3>Objectives:</h3> Single agent immune check point inhibitors are largely ineffective in recurrent OC patients. A recently completed phase 2 clinical trial (NCT02853318) on recurrent ovarian cancer patients at Roswell Park combined pembrolizumab with bevacizumab and oral cyclophosphamide and showed an overall response rate of 47.5%, a median progression-free survival (PFS) of 10.0 months and disease control over 12 months in 25% of the patients. Our objective was to evaluate the transcriptomic and proteomic signatures in the tumor microenvironment (TME) to understand the factors that drive durable clinical responses. <h3>Methods:</h3> RNASeq analysis was performed on 28 patients on the clinical trial using paired baseline and on-therapy tumor biopsies. Celltype expression was deconvoluted using CIBERSORT from RNASeq results. In parallel, NanoString Digital Spatial Imaging was used to evaluate the TME in 13 of these patients for 50 immuno-oncology proteins to compare their mean expression and the changes in expression levels between responder (PFS > 12 months) and non-responder (PFS < 6 months) patients throughout the treatment. <h3>Results:</h3> RNASeq pathway enrichment analysis of baseline and on-treatment tumor biopsies revealed significant enrichment of immune-related pathways in responder patients, including B-cell signaling pathways, and a strong correlation of B-cell presence with T-cells in responding patients (p<0.001). CIBERSORT analysis showed higher levels of naïve and memory B-cells in baseline tumor samples of responders compared to non-responders, which further increased on treatment. High expression of B cell markers strongly correlated with increased PFS (CD19+ p=0.0029, CD20+ p=0.0030). Digital spatial imaging data revealed higher T-cell expression (CD4+ p=0.025, CD8+ p=0.05) and B-cell expression (CD20+ p=0.019) in baseline and on treatment tumor biopsies in responding patients. No significant changes were observed in CD20 expression during the clinical trial in non-responders. <h3>Conclusions:</h3> More recently the outcome of immune checkpoint inhibitor therapy in cancer patients has been linked to the quality and magnitude of both T cell and B cell responses within the tumor microenvironment. Similarly, we demonstrate here that B cells as crucial supportive regulators in immune tumor control.