Successful treatment of acute, ongoing rat lung allograft rejection with the novel immunosuppressant SDZ-RAD

Background. Recent experimental data have shown that coadministration of microemulsion cyclosporine and the novel immunosuppressant SDZ-RAD potentiates the immunosuppressive efficacies of both drugs to suppress allograft rejection. Our study was designed to assess the potential of delayed SDZ-RAD administration, in addition to cyclosporine maintenance therapy, to reverse acute rejection in an allogeneic rat lung transplant model. Methods. Unilateral left lung transplantation was performed using Brown-Norway donors implanted into Lewis recipients. An untreated control group and a cyclosporine monotherapy group (7.5 mg/kg) were followed for 7 days. An additional cyclosporine monotherapy group (7.5 mg/kg), and a combined therapy group treated with cyclosporine (7.5 mg/kg) plus SDZ-RAD (2.5 mg/kg), were followed for 21 days. For treatment of ongoing rejection, 7.5 mg/kg cyclosporine was given as maintenance therapy, and SDZ-RAD (2.5 mg/kg) was added on postoperative day 7. Drugs were given orally, and in the combined therapy regimens, administered 6 hours apart. Outcome variables included daily weight, radiographs, and histology. Results. Radiographs on postoperative day 7 showed mad and moderate opacification of the left chest in the cyclosporine monotherapy groups and the untreated control group. Addition of SDZ-RAD to cyclosporine treatment on postoperative day 7 reversed opacification by postoperative days 14 and 21. Monotherapy with micro-emulsion CsA resulted in mild histological rejection by day 7, which progressed to moderate rejection by day 21 Addition of SDZ-RAD on postoperative day 7 reversed acute rejection, resulting in none or minimal rejection at day 21. Conclusions. SDZ RAD reverses acute rejection under cyclosporine maintenance therapy in a stringent lung allotransplant model.