High endothelial venules are associated with microsatellite instability, hereditary background and immune evasion in colorectal cancer

Pauline L. Pfuderer1,2,3, Alexej Ballhausen1,2,3, Florian Seidler1,2,3, Hans-Jürgen Stark1,2,3, Niels Grabe4,5, Ian M. Frayling 6, Ann Ager7, Magnus von Knebel Doeberitz 1,2,3, Matthias Kloor1,2,3, Aysel Ahadova1,2,3

1Department of Applied Tumor Biology, Institute of Pathology, University Hospital Heidelberg, Heidelberg, Germany. 2Clinical Cooperation Unit Applied Tumor Biology, DKFZ, Heidelberg, Germany. 3Molecular Medicine Partnership Unit (MMPU), University Hospital Heidelberg, Heidelberg, Germany. 4Hamamatsu Tissue Imaging and Analysis (TIGA) Center, Heidelberg, Germany. 5Department of Medical Oncology, National Center for Tumor Diseases (NCT), Heidelberg, Germany. 6Inherited Tumour Syndromes Research Group, Institute of Cancer & Genetics, Cardiff University School of Medicine, Cardiff, United Kingdom. 7Division of Infection and Immunity, School of Medicine and Systems Immunity Research Institute, Cardiff University, Cardiff, United Kingdom

Abstract

Objective Microsatellite instability (MSI) can occur sporadically or in the context of Lynch syndrome. Due to accumulation of frameshift mutations giving rise to neoantigens, MSI tumors are highly immunogenic. This is evidenced by the dense immune infiltration and frequent development of immune escape mechanisms, such as B2M mutations. However, it is unknown whether improved lymphocyte recruitment contributes to the active immune microenvironment of MSI tumors. To answer this, we analyzed the density of high endothelial venules (HEV), postcapillary blood vessels specialized for lymphocyte trafficking, in MSI colorectal cancers (CRC).

Methods HEV density was analyzed in FFPE tissue sections from MSI (n=48) and microsatellite-stable (MSS, n=35) CRCs using immunohistochemistry. Associations with additional histopathology parameters (CD3, PD1, PD-L1 density) and clinical status were analyzed.

Results HEV densities were remarkably elevated in MSI compared to MSS CRCs (p=0.0002, Wilcoxon Rank Sum Test). Notably, HEV density was highest in MSI CRCs from Lynch syndrome patients. B2M-mutant Lynch syndrome CRCs presented with higher HEV densities compared to their B2M-wild type counterparts, suggesting a link between lymphocyte recruitment and immune evasion (B2M-mutant vs B2M-wild type, p=0.0237, Wilcoxon Rank Sum Test).

Conclusions This work for the first time suggests a significant contribution of lymphocyte trafficking via HEVs to the active immune milieu in MSI CRCs. Highly elevated HEV counts in Lynch syndrome-associated MSI CRCs indicate fundamental differences regarding the immune biology of hereditary and sporadic MSI tumors. High HEV densities in B2M-mutant tumors emphasize the importance of immunoediting during MSI CRC evolution.

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