Abstract
Transplant tolerance allowing the elimination of lifelong immunosuppression has been the goal of research for 60 years. The induction of mixed chimerism has shown promise and has been extended successfully to large animals and to the clinic; however, it remains cumbersome and requires heavy early immunosuppression. In this study, we reported that four injections of AMD3100, a CXCR4 antagonist, plus eight injections of low-dose FK506 (0.05 mg/kg per day) in the first week after kidney transplantation extended survival, but death from renal failure occurred at 30-90 days. Repeating the same course of AMD3100 and FK506 at 1, 2 and 3 mo after transplant resulted in 92% allograft acceptance (n = 12) at 7 mo, normal kidney function and histology with no further treatment. Transplant acceptance was associated with the influx of host stem cells, resulting in a hybrid kidney and a modulated host immune response. Confirmation of these results could initiate a paradigm shift in posttransplant therapy.