Suppression of alloimmunity in mice by regulatory T cells converted with conditioned media.

BACKGROUND: Compared with rare CD4+CD25+ regulatory T cells (Tregs), CD4+CD25- T cells are abundant in peripheral blood. Studies have demonstrated that tumors can convert naive CD4+CD25- T cells into CD4+CD25+Foxp3+ Tregs; however, the potential application of the converted Tregs in transplant medicine has not well demonstrated.

MATERIALS AND METHODS: CD4+CD25- T cells isolated cultured for 5 d in various combinations of cell culture medium and conditioned medium from RenCa cells. Foxp3 levels were determined by flow cytometry and real-time polymerase chain reaction. BALB/c mouse mononuclear cells (responder) combined with different ratios of the converted CD4+CD25+ Tregs were co-cultured with inactivated C57BL/6 mononuclear cells (stimulator) in one-way mixed lymphocyte reaction (MLR). In addition, the converted Tregs were transferred into a mouse skin transplant model, and graft histology, survival time, and delayed-type hypersensitivity were assessed.

RESULTS: CD4+CD25- T cells cultured in media supplemented with increasing concentrations of RenCa conditioned medium were partially converted into CD4+CD25+ Tregs; conversion increased as the percentage of conditioned medium increased. Moreover, the converted CD4+CD25+ Tregs possessed characteristics similar to those of naturally occurring Tregs, including Foxp3 expression and the ability to suppress T cell proliferation in one-way MLR in a concentration-dependent manner. Immunosuppressive effects of the converted CD4+CD25+ Tregs were also similar to those of naturally occurring Tregs in vivo, suppressing allograft rejection and prolonging survival time of allogeneic skin grafts following adoptive transfer in mice (P<0.05).

CONCLUSION: Our findings indicate that CD4+CD25- T cells cultured with conditioned media from tumor cells may be useful for obtaining sufficient numbers of Tregs, which may help suppress acute rejection and prolong graft survival.