Use of antithymocyte serum in clinical and experimental marrow transplantation.

Pre-sensitization was investigated in the dog marrow transplant model with donor and recipient mismatching at the canine major histocompatibility complex (MHC). Various prophylactic immunosuppressive regimes were used and it was concluded from these regimes that sensitization to histocompatibility antigens could be abrogated by a combination of procarbazine and antithymocyte serum (ATS) together, before total body irradiation. Subsequent work in humans showed that rejection of a bone marrow graft can be successfully treated by using the procarbazine-antithymocyte clobulin regime and a second transplant. Based upon animal studies, attempts were made to prevent graft-versus-host disease in humans by the use of methotrexate following grafting. Despite matching at the MHC and the use of methotrexate some recipients developed graft-versus-host disease with a fatal outcome. Further work using ATS in the immediate pre- and post-grafting period was inconclusive. Accordingly ATS was used in animals once graft-versus-host disease became manifest with drmatic improvement in clinical status. As a result it was decided to treat all patients who developed graft-versus-host disease with antithymocyte globulin (ATG). Under ATG therpy twelve out of nineteen patients showed complete resolution, and five showed improvement. Six patients became long term survivors. Of the remaining 13, 11 died on interstitial pneumonitis, and two of fungal and bacterial infections. ATG in estblished graft-versus-host disease appears capable of modigying an otherwise fatal disease in a therpeutically beneficial manner.