Chemoradiation-induced alteration of programmed death-ligand 1 and CD8+ tumor-infiltrating lymphocytes in rectal cancer.

Abstract

570Background: DNA damage and subsequent neoantigen formation has been hypothesized as a mechanismfor radiotherapy and PD-1/PD-L1 pathway inhibition to synergize in an antitumor immune response. We investigated neoadjuvant chemoradiotherapy (nCRT)-induced changes in CD8+ tumor infiltrating lymphocyte, PD-L1 and mucin expression in rectal cancer patients as compared to patients who did not receive nCRT. Methods: Tumor samples were collected from rectal adenocarcinoma patients who had undergone resection between 2008-2014 with (n = 62) or without (n = 17) nCRT treatment. Tissue sections were stained with CD8 and PD-L1 antibodies for immunohistochemistry. Whole slides images were acquired at 20x magnification. The prevalence of positive CD8 stained cells was recorded in tumor, interface tumor side, interface background rectal side. Image analysis (HALO Indica Labs) was used to determine the density (# of cells/surface area analyzed) of CD8 expressing lymphocytes. The percentage of PD-L1 membranous expression...