Versican proteolysis as a key regulator of CD8+ T-cell infiltration in colorectal cancer.

Abstract

e15082 Background: Colorectal cancer (CRC) originates within immunologically complex microenvironments. To date the benefits of immunotherapy have been modest except in neoantigen-laden mismatch repair (MMR)-deficient tumors. Approaches to enhance tumor-infiltrating lymphocytes (TILS) in the tumor bed may substantially augment clinical immunotherapy responses. Proteolysis of the tolerogenic matrix proteoglycan versican (VCAN) generates a bioactive fragment, versikine, with putative immunostimulatory activities. Methods: Matched normal and CRC tissue samples were collected from 122 patients with cancers across all stages and locations throughout the colon and rectum. These samples were stained for VCAN, αDPEAAE (neoepitope generated in cleaving VCAN to versikine), and CD8 and scored by a pathologist. Tumors were classified as VCAN proteolysis-predominant (VPP) if their staining for total VCAN staining intensity was < 1+ and staining for VCAN proteolysis (αDPEAAE antibody) was > 2. Conversely, tumors were classified as VCAN proteolysis-weak (VPW) if intact VCAN staining intensity was > 1+ or αDPEAAE intensity was < 2+. IHC for mismatch repair (MMR) proteins was also performed. Results: Overall increased VCAN staining was observed in cancer versus (vs) normal tissue. VPP tumors had a 10 fold greater infiltration of CD8+ T-cells vs VPW cancers (p < 0.001). The correlation between VCAN proteolysis and CD8+ T-cell infiltration was maintained in both cancers with proficient (p) MMR and deficient (d) MMR. In both pMMR and dMMR, the VPP tumors had the greatest degree of CD8+ T-cell infiltration (Wilcoxon rank sum tests: pMMR p = 0.006; dMMR p = 0.03). Among the VPP tumors there was a greater degree of CD8+ T cell infiltration in the dMMR cancers vs pMMR cancers (35 versus 14.8 TILs per high power filed, p = 0.04). Nuclear CTNNB1, a marker for activation of WNT signaling, negatively correlated with CD8+ T cell infiltration( p = 0.014). In addition, VCAN accumulation correlated with the presence of nuclear CTNNB1 (p < 0.001) Conclusions: This is the first description indicating that VCAN proteolysis may shape CRC immune contexture and provide a rationale for testing VCAN proteolysis as a predictive and/or prognostic immune biomarker.