Suppression of Tissue Immunity by Cyclophosphamide

Cyclophosphamide, like other alkylating agents, has been shown to have marked inhibitory effects on humoral antibody formation. Reports have varied as to its action on suppression of cellular immunity. The present experiments were designed to assess the effectiveness of cyclophosphamide in prolonging skin homograft survival in mice, to determine action in relation to dosage, frequency of administration, and time of commencement of treatment. Maximal prolongation was obtained by repeated i.p. administration, started on the day of, or 3 days.before, grafting. Graft survival was increased from 10.5 days in controls to 16 days in injected animals (across the H-2 histocompatibility barrier). Cyclophosphamide was employed in 4 cases of human cadaveric renal homotransplantation. One patient is surviving 12 months and another 5 months after grafting. These findings suggest that cyclophosphamide has an effect in suppressing cellular immunity, in the human being.