The Presence of Foxp3 Expressing T Cells Within Grafts of Tolerant Human Liver Transplant Recipients

Background. Some experimental transplant-tolerance models have shown that the presence of regulatory T cells within grafts is important for the development of tolerance (Tol). Methods. To determine if the presence of regulatory T cells correlates with graft acceptance in living-donor liver-transplantation tolerance, the expression of Foxp3 mRNA and the presence of CD4(+), CD8(+), and Foxp3(+) cells were quantified in biopsies from tolerant recipients by real-time polymerase chain reaction and by immunohistochemistry and immunofluorescent staining (Gr-Tol). The results were compared with biopsies from the recipients oil maintenance immunosuppression (Gr-IS), grafts removed because of chronic rejection (Gr-CR), or normal liver (Gr-NL). Results. The expression of Foxp3 mRNA in Gr-Tol was higher than that in Gr-IS (P=0.07) and Gr-NL (P<0.0001), but equivalent to that in Gr-CR. In Gr-Tol, Foxp3(+) cells were detectable within the clustered CD4(+) and CD8(+) cells in the portal areas. Ninety-two percent of those Foxp3(+) cells were CD4(+), whereas 8% were CD8(+). The number of Foxp3(+) cells was significantly increased in Gr-Tol, compared with that in Gr-IS (P<0.05), although the number of CD4(+) or CD8(+) cells did not differ between the two. Foxp3(+) cells were hardly detectable in Gr-CR or -NL. Conclusions. This is the first report showing that CD4(+) Foxp3(+) cells are present within grafts in a subset of tolerant patients after human liver transplantation. A prospective study is needed to elucidate whether the assessment of intragraft expression of Foxp3 protein, but not Foxp3 mRNA, can aid the identification of living-donor liver-transplantation recipients who can successfully withdraw IS.