Regulatory T cells reduce endothelial neutral sphingomyelinase 2 to prevent T-cell migration into tumors.

Endothelial cells are key regulators of trans-endothelial migration and their secretion of chemokines and expression of adhesion molecules facilitates lymphocyte entry into tissues. Previously, we demonstrated that regulatory T-cells (Tregs) can reduce trans-endothelial migration of T-cells into tumors by decreasing endothelial CXCL10 secretion, but the mechanism by which this occurs is still not known. In this study, we aimed to define how Tregs decrease trans-endothelial migration into tumors. mRNA sequencing of intestinal tumor endothelial cells from Treg depleted mice identified neutral sphingomyelinase 2 (nSMase2) as a gene down-regulated in the presence of Tregs. nSMase2 is expressed in human umbilical vein endothelial cells (HUVECs) and was decreased after co-culture with Tregs. Furthermore, blocking of nSMase2 activity in vitro decreased VCAM1, CX3CL1 and CXCL10 expression in HUVECs, mirroring the same decrease found in Treg co-cultures. In the APCmin/+ mouse model of intestinal cancer, nSMase2 is lower in tumor endothelial cells than in unaffected small intestine and chronic treatment with a nSMase2 inhibitor suppressed the increased migration that is otherwise seen in the absence of Tregs. We conclude that nSMase2 is an important mediator in endothelial cells supporting trans-endothelial migration, which may be targeted by Tregs to reduce T cell migration into tumors. This article is protected by copyright. All rights reserved.