Application of irradiation as an immunosuppressive agent.

The concept of using total lymphoid irradiation (TLI) for immunosuppression is based on the prolonged and profound immunosuppressive effects observed after TLI in the treatment of patients with Hodgkin's disease. Pre-operative TLI of allograft recipients has been shown to be immunosuppressive when used alone or together with chemical immunosuppression. Fractionated TLI and allogeneic bone marrow injections produce stable chimaerism without graft-versus-host disease in inbred mice, rats and mongrel dogs and transplantation tolerance of skin and cardiac grafts in rats. In the primate, TLI and bone marrow injection result in significant tolerance of liver and kidney allografts. In 1959 sublethal whole-body irradiation was used as an immunosuppressive agent for the first successful related-human renal allografts between non-identical twins. Despite the dangers of myelosuppression, recent clinical experience has shown TLI to be a useful immunosuppressant for organ transplantation, allowing decreased dosage of concomitant immunosuppressive drugs.