Experimental modulation and suppression of anti-allograft immune response

Abstract The objective of this investigation was to characterise the immunomodulatory or immunosuppressive effects of single drug treatment and the potential synergistic or additive effects of combined treatment with the focus on ciprofloxacin, thalidomide, mycophenolate mofetil, azathioprine, cyclophosphamide or leflunomide added to cyclosporin A (CyA). A rat cardiac transplant model was used to study graft survival and the influence on lymphocytes was evaluated by in vitro tests. Ciprofloxacin stimulated rat lymphocyte proliferation and IL-2 production in vitro and reduced the inhibitory effect of CyA at low concentrations. In the transplant model, however, graft survival was enhanced and further prolonged by combined treatment with ciprofloxacin and CyA. Addition of thalidomide to cultures of human or rat lymphocytes was not associated with any inhibitory effects. On the contrary, after incubation with metabolised thalidomide, the IL-2 production was significantly increased. However, thalidomide reduced the rat CD4 /CD8 T cell ratio and was demonstrated to prolong graft survival. The immunomodulatory drug linomide may induce rejection in the transplant model despite CyA treatment and this was used to test additive or synergistic effects of combined therapy with CyA and another drug. Thalidomide and CyA, as dual treatment, overcame the challenge of linomide. Mycophenolate mofetil and cyclophosphamide prolonged graft survival as sole treatment but azathioprine did not. However, all three drugs were demonstrated to enhance the immunosuppressive effect of CyA when studied in the linomide model. Leflunomide was found to induce graft unresponsiveness as sole treatment in a low responder rat strain combination. The criteria for the linomide model were fulfilled only in a high responder rat strain combination and now the effect of leflunomide was reduced only when given in a low dose regimen. An additive effect was demonstrated after combined leflunomide and CyA treatment in this model.