Use of cyclophosphamide and enhancing serum to suppress renal allograft rejection in the rat.

Cyclophosphamide was tested for its interaction with passive enhancement in suppressing the rejection of kidney allografts in the (DA x Lewis)F1 to Lewis rat strain. Dose response studies with cyclophosphamide showed that 10 mg/kg/day for 14 days was necessary for complete suppression of rejection and indefinite graft survival. Doses of 5 and 3.5 mg/kg/day had only a marginal effect on graft function and survival, although the lymphocytotoxin response to the graft was completely or very substantially suppressed by these smaller doses. The use of passive enhancement with cyclophosphamide at the 5- and 3.5-mg/kg/day doses resulted in a favourable interaction with improved graft function and survival. Interestingly, passive enhancement in combination with 5 mg/kg/day of cyclophosphamide resulted in indefinite graft survival only if cyclophosphamide was given for 28 days. If cyclophosphamide was given for 14 days, rejection was suppressed only during the period of cyclophosphamide treatment.