6-Methylprednisolone does not impair anti-thymocyte globulin (ATG) immunosuppressive activity in non-human primates

Background: Induction treatments with anti-thymocyte globulin (ATG) in solid organ transplantation may enhance the efficacy of maintenance immunosuppressive therapy. Since ATG can trigger Fas (CD95) mediated T cell apoptosis, a process antagonized in vitro by corticosteroids, an important issue is whether corticosteroids could interfere with T cell depleting and immunosuppressive activities of ATG. Methods: MHC mismatched skin allografts were performed on cynomolgus and rhesus monkeys treated with ATG (20 mg/kg) associated or not with 6-methylprednisolone (10 mg/kg). Results: There was no difference between the two immunosuppressive regimens as regards the intensity and duration of peripheral T lymphocyte depletion and the appearance of anti-ATG antibodies. Skin graft survival was increased in monkeys treated with 6-methylprednisolone as compared with ATG alone. Conclusions: In vivo, corticosteroids do not interfere with ATG ability to induce massive T cell depletion and to delay skin allograft rejection in non-human primates.