THE COMBI‐EFFECT—REDUCED REJECTION OF THE HEART BY COMBINED TRANSPLANTATION WITH THE LUNG OR SPLEEN

The term combi-effect was introduced to describe the phenomenon of a reduction in rejection of heart grafts after combined transplantation with the lung. In this study in rats we investigated whether the combi-effect was an immunological process and whether it could also be induced by combined transplantation of the heart with the spleen or with a lymphocyte-depleted spleen. Heart and spleen grafts were transplanted into the abdomen; left lungs were transplanted into the thorax of recipient rats. To deplete spleens of their lymphocytes, prospective donor rats were irradiated. Cyclosporine was injected once, on day 2 after transplantation. All heart allografts transplanted alone and treated with cyclosporine were rejected acutely (median survival time [MST] of 14.5 days). In contrast, after combined transplantation of a donor lung or spleen with the heart, almost all heart grafts survived indefinitely. Transplantation of a syngeneic lung or third-party spleen had little effect on heart graft survival (MST of