The combined use of antilymphocyte serum and cyclophosphamide to suppress renal allograft rejection in the rat.

Cyclophosphamide and antilymphocyte serum (ALS) were compared for their ability to suppress renal allograft rejection in the rat. These two agents were chosen since they are generally considered to act on different arms of the immune response, and might therefore complement each other's action. Dose response studies showed that both agents could suppress rejection completely. There were no differences in their ability to suppress the lymphocytotoxic antibody response to the graft and the histological patterns of rejection were similar. There was no evidence that cyclo-phosphamide was more effective in suppressing vascular lesions. The doses of both agents which suppressed the lymphocytotoxic antibody response were substantially lower than those required to suppress graft rejection. When suboptimal doses of the two agents were administered together, the combinations were found to be additive and not synergistic.