Abstract 4581: High endothelial venules are associated with immune evasion and hereditary background in mismatch repair-deficient colorectal cancers

Abstract

Abstract DNA mismatch repair (MMR)-deficient cancers can develop in the context of Lynch syndrome or sporadically. MMR-deficient cancers accumulate a high load of immunogenic frameshift peptide neoantigens as a consequence of insertion/deletion mutations at coding microsatellites (microsatellite instability, MSI). Whether enhanced lymphocyte recruitment contributes to the high immune infiltration and the pronounced local immune response typically observed in MSI colorectal cancers (CRCs) is not known. Here we analyzed the density of high endothelial venules (HEVs), postcapillary blood vessels specialized for lymphocyte trafficking, in MSI CRC of sporadic and hereditary origin. Immunohistochemical staining with rat monoclonal MECA-79 antibody was used to detect HEVs in tumor specimens from MSI (hereditary, n=20 and sporadic, n=28) and MSS CRCs (n=35). Lymph follicle-associated HEVs were normalized per mm2 of tumor and peritumoral area. Mutations of the B2M gene were determined by Sanger sequencing. Significantly elevated HEV densities were detected in MSI (n=48) compared to MSS CRCs (n=35) (0.09 vs 0.02 counts per mm2, p=0.0002). Lynch syndrome-associated MSI CRCs presented with significantly higher HEV densities compared to sporadic counterparts (0.15 vs 0.05 counts per mm2, p=0.025). This difference remained significant when age-matched groups of hereditary and sporadic MSI CRCs were compared. MSI CRCs with B2M mutations (n=12) presented with significantly higher HEV densities than their B2M-wild type counterparts (n=14, p=0.016). Our results demonstrate that a high density of HEVs correlates with the MSI phenotype in CRC, underlining the elevated local immune activation in these tumors. Within MSI CRC, Lynch syndrome was a predictor of high HEV counts, suggesting a likely role of lymphocyte recruitment in immune surveillance of Lynch syndrome CRCs. The observation of high HEV counts particularly in MSI CRCs harboring B2M mutations supports the model that immune evasion occurs particularly in an activated local immune environment. The prognostic value of HEVs in MSI CRCs should be addressed in the future studies. Citation Format: Aysel Ahadova, Pauline Pfuderer, Alexej Ballhausen, Ian Frayling, Ann Ager, Magnus von Knebel Doeberitz, Matthias Kloor. High endothelial venules are associated with immune evasion and hereditary background in mismatch repair-deficient colorectal cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4581.