BACKGROUND: Donor lymphocytes infused after organ transplantation can have strong immunoregulatory effects. Application of such protocols for transplant tolerance induction in a clinical setting will, however, require combination of specific immunomodulatory strategies with nonspecific immunosuppressive medication for safety reasons. The aim of this study was to analyze the effects of immunosuppressive treatment on tolerance induction protocols by posttransplantation donor lymphocyte infusion. METHODS: The interaction of postoperative donor leukocyte infusion with different types, dosage, and timing of immunosuppressive drugs were studied in a rat model of heart transplantation. RESULTS: Tolerance could be achieved if donor cell infusion was combined with delayed, but not immediate, low-dose cyclosporine treatment, and this was associated with activation and apoptosis of host lymphocytes. In contrast, combinations with an antibody against the interleukin 2 receptor led to long-term graft survival but severe chronic rejection, and combinations with high-dose cyclosporine or sirolimus led to acute rejection. CONCLUSIONS: Postoperative donor leukocyte infusion is a potential way for tolerance induction, but the type, dose, and timing of medication are highly critical for its efficacy.
