Human Endothelial-Like Cells Transdifferentiated from CD14 + Monocytes Shows Suppressive Activity to Allo-Reactive T Cells

Abstract

Although it is well known that liver allografts are often accepted by recipients, leading to donor-specific tolerance of further organ transplants, the underlying mechanisms remain unclear. We had previously showed that mouse liver sinusoidal endothelial cells (LSECs) had been proven capable of suppressing T-cells with cognate specificity for LSECs through programmed death (PD) 1/PD-L1 pathway in both of in vitro and in vivo models. Such immune-regulatory functions of LSECs have not been extensively investigated in human because of the limited availability of appropriate human samples. In this study, we have determined immune-regulatory properties of human LSECs on allogeneic T cells. We have also proven that endothelial-like cells, phenotypically and functionally resembling LSECs, can be transdifferentiated from human peripheral blood monocytes. Human LSECs were isolated from the disaggregated liver tissues obtained from patients undergoing surgical resection of colorectal liver metastasis. Human CD14+ cells were isolated from peripheral blood by using magnetic sorting and cultured in EGM2 medium supplemented with GM-CSF, IL-4, VEGF, hFGF-B, R3-IGF-1, and LPS for 14 days. Naïve human LSECs constitutively express molecules necessary for antigen presentation, i.e., freshly isolated CD105+ LSECs express MHC-class II, CD40, CD80, and CD86 together with PD-L1. The transdifferentiated cells morphologically appeared endothelial-like cells and phenotypically resembled LSECs, i.e., they were MHC-class II+, CD40low, CD80low, CD86low, CD105+, PDL-1+. The suppressive activity of those cells on allogeneic T cells was analyzed by a MLR assay using CFSE labeling technique. Allo-immune responses of both of CD4+ and CD8+ T cells in the MLR assays were significantly suppressed by subsequently adding the stimulator-type transdifferentiated endothelial-like cells, whereas there were not suppressed in response to anti-third party stimuli. The PD-1 expression on allo-reactive T cells among the final products of the MLR assays was elevated over time during culture. We have proven that human endothelial-like cells transdifferentiated from monocytes phenotypically resemble LSECs and suppress alloreactive T cells probably through PD-1/PD-L1 pathway. These findings raise a novel concept to induce hyporesponsiveness of alloreactive T cells by inoculating donor-derived those cells even in transplantation of organs other than liver.