Human biliary tree stem/progenitor cells (hBTSCs) from peribiliary glands (PBGs) of adult liver display immunomodulatory properties through Fas/Fas ligand induced T-cell lymphocyte apoptosis

Background and aim: hBTSCs have been retrieved in peribiliary glands (PBGs) of adult and fetal biliary tree, and have the potential for regenerative medicine in liver, biliary tree, and pancreas diseases. The ability of stem cells to control T-cells’ immune responses was recently demonstrated by human mesenchymal stem cells. The aims of the present study were to evaluate Fas-L expression within the stem cell niches of adult biliary tree, and to study the in vitro interaction between hBTSCs and human lymphocytes. Material and methods: HLA antigens, Fas and Fas-L expression were evaluated in situ and in vitro by immunofluorescence and Western blots in cells of the human biliary tree in comparison with fibroblast cells, dental pulp stem cells and bone marrow mesechymal stem cells. Co-cultures of hBTSCs with human leucocytes were used to analyze the influence of hBTSCs on lymphocytes’ activation and apoptosis. Results: Adult hBTSCs expressed both class I and class II HLA antigens, whereas fetal hBTSCs had class I HLA antigens only. In PBG niche 10-30% BTSCs were positive for Fas-L. Fas-L positive cells were mostly located at the bottom of PBGs and co-expressed EpCAM (epithelial cell adhesion molecule) and a marker of proliferation (PCNA: Proliferating Cell Nuclear Antigen). Conversely, mature cells at the surface epithelium and cholangiocytes of large intrahepatic ducts were almost all negative for Fas-L. In culture experiments confocal microscopy demonstrated that Fas-L expression was restricted to EpCAM+/LGR5+(a marker associated with endodermal stem cells) cells. Western blot data confirmed that hBTSCs constitutively expressed high level of Fas-L that increased after co-culture with T-cells. FACS analysis of T-cells co-cultured with hBTSCs indicated that hBTSCs were able to induce apoptosis in activated CD4+ and CD8+ T-cell populations. Moreover, Fas receptor appears to be more expressed in T-cells co-cultured with hBTSCs than in resting T-cells. Conclusions: In conclusion our data suggest that hBTSCs could modulate the T-cells response through the production of Fas-L, which influences the lymphocyte Fas/Fas-L pathway by inducing “premature” apoptosis in CD4+ and CD8+ T-cells.