Effect of in vitroexpanded CD4(+)CD25(+)Foxp3(+) regulatory T cell therapy combined with lymphodepletion in murine skin allotransplantation.

A promising approach for preventing allograft rejection involves shifting the balance between cytopathic and regulatory T cells to dominance of the latter cell type. Nonspecific lymphodepletion was conducted by administration of depleting anti-CD4 and anti-CD8 antibodies to reduce effector T cells and adoptive transfer of ex vivo-expanded host Treg cells by stimulation with donor dendritic cells to augment the Treg cell compartment. Evaluation of an MHC-mismatched skin allograft model revealed that combined therapy with these two protocols consistently induced modest prolongation of allograft survival, although all skin grafts were eventually rejected. The administration of IL-2/anti-IL-2 complexes significantly improved the efficacy of combination therapy via promoting the expansion of adoptively transferred Treg cells as well as endogenous recipient Treg cells. We conclude that Treg cell therapy combined with lymphodepletion is of practical benefit for the control of allograft rejection, but requires supplementary measures to promote immune tolerance.

Effect of immunosuppressants on the expansion and function of naturally occurring regulatory T cells.

The induction of immune tolerance is one of the final therapeutic goals in clinical transplantation. Regulatory T lymphocytes are important for the induction and maintenance of immune tolerance to grafts. If immunosuppressive drugs used clinically to prevent immune rejection also inhibit regulatory T lymphocytes, tolerance would not be achieved. We therefore tested the effect of several immunosuppressants with different mechanisms of action on the proliferation and suppressive activity of CD4(+)CD25(+) regulatory T cells. Highly purified CD4(+)CD25h(+) T cells from C57BL/6 (H-2(b)) mice were stimulated with allogeneic T-depleted splenocytes (BALB/c; H-2(d)) in the presence of various immunosuppressants. After one week in culture, viable T cells were recovered, their regulatory capacity was assessed by their ability to inhibit responder T cell proliferation in MLR, and their cytokine production profile was measured by ELISA. The immunosuppressants rapamycin, cyclosporine A, and methylprednisolone significantly inhibited the expansion of regulatory T cells upon stimulation with alloantigen, whereas mycophenolic acid and the costimulatory blockers, anti-CD40L and CTLA4Ig, did not. None of these immunosuppressants, however, reduced the suppressive capacity of regulatory T cells. Pretreatment with immunosuppressants did not induce significant changes in the cytokine production profile of regulatory T cells. Our results suggest that costimulatory blockers and mycophenolate mofetil can be utilized therapeutically in the induction of immune tolerance. In contrast, the use of rapamycin, cyclosporine A, and methylprednisolone should be reconsidered, due to their deleterious effects on the expansion of naturally occurring regulatory T cells.