Abstract 3294: PD-L1 status and versican proteolysis predict CD8+ T cell infiltration in esophageal cancer

Abstract

Abstract Background: Esophageal cancer is a highly lethal cancer with a 20% 5-year overall survival despite standard of care treatment.. Pembrolizumab (anti-PD1, Merck) is FDA-approved for PD-L1 positive esophageal cancer, which comprises roughly 40% of all patients. PD-L1 positive (+) esophageal cancers have previously been shown to demonstrate elevated CD8+ T cell infiltration (CD8+ TILs). Versican (VCAN) is an immunosuppressive extracellular matrix proteoglycan which produces an immunostimulatory fragment, versikine (Vkine), upon proteolytic cleavage by ADAMTS proteases. Previously, VCAN proteolysis has been shown to correlate with enhanced CD8+ TILs in colorectal cancer (CRC), indicating potential for use as an immune biomarker. Methods: A human esophageal cancer tissue microarray (TMA) was developed consisting of multiple samples across 106 representative esophageal cancer patients. Immunohistochemistry (IHC) was used to evaluate VCAN and Vkine expression, and a binning system was used to quantify these stains based on stromal intensity (0: 0-10%, 1: 10-25%, 2:25-50%, 3: 50-100%). IHC was also conducted for CD8, and the number of CD8+ tumor-infiltrating cells per 400x field of view was counted. PD-L1 IHC 22C3 pharmDx was performed and quantified per CPS guidelines for GEJ cancers to quantify PD-L1 status. The VCAN proteolytic predominant (VPP) phenotype was defined as both low VCAN (0 or 1) and high Vkine (2 or 3), and VCAN proteolytic weak phenotype (VPW) was defined as either high VCAN (2 or 3) or low Vkine (0 or 1). Results: Overall, 42.7% of all samples were scored as PD-L1+ (CPS≥1). PD-L1+ samples demonstrated greater CD8+ TILs than PD-L1- samples (44.5±71 vs 14±22; p<0.001). The presence of immunosuppressive VCAN negatively correlated with CD8+ TILs (16.8±27 in VCAN+ samples vs 39.4±67 in VCAN- samples; p<0.01). The VPP phenotype was observed in 47.8% of the cancer samples. VPP samples also demonstrated a trend towards greater CD8+ TILs compared to VPW samples (35.9±63 vs 22.7±46; p=0.09); however, this was not statistically significant. Of all samples, 33.9% were both PD-L1+ and VCAN-. These dual PD-L1+ and VCAN- samples demonstrated even greater CD8+ TILs compared to either PD-L1- or VCAN+ samples (49.5±79 vs 18.1±29; p<0.001). Discussion: Our TMA demonstrates enhanced CD8+ TILs in PD-L1+ samples, as previously reported. Additionally, we discovered the presence of VCAN and its proteolysis are independent predictors of enhanced CD8+ TILs in esophageal cancers. These data indicate the potential importance of the tumor matrix in establishing a permissive tumor microenvironment. These data support the potential for combining VCAN testing with PD-L1 testing to further select appropriate patients for immunotherapeutic trials in esophageal cancer. Citation Format: Phillip B. Emmerich, Jacob Witt, Darya Buehler, Mitchell Depke, Nathaniel Verhagen, Linda Clipson, Kristina Matkowskyj, Nataliya Uboha, Andrew Baschnagel, Dustin Deming. PD-L1 status and versican proteolysis predict CD8+ T cell infiltration in esophageal cancer [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 3294.