STABLE LUNG ALLOGRAFT OUTCOME CORRELATES WITH THE PRESENCE OF INTRAGRAFT DONOR-DERIVED LEUKOCYTES

Background. The role of bone marrow-derived ''passenger'' leukocytes i n the outcome of solid organ transplantation remains controversial. Th is study tested the relationship between high levels of donor-derived leukocytes within the transplanted organ and clinical outcome after lu ng transplantation. Methods. Sequential bronchoalveolar lavage samples were obtained from human lung allograft recipients. Leukocytes of don or origin in the bronchoalveolar lavage fluid were detected using two- color immunofluorescence, and the results were correlated with multipl e clinical parameters. Results. Mean donor leukocyte levels for the fi rst 200 days after transplantation were higher in patients with a good transplantation outcome compared with those patients who lost their g rafts due to acute rejection (AR) or developed bronchiolitis obliteran s syndrome. The presence of low numbers of donor-derived leukocytes fo r the first 200 days after transplantation was found to be a significa nt risk factor for graft loss clue to either acute or chronic rejectio n (P=0.032). Nearly all patients (85%) experienced AR episodes. Howeve r, the time to onset of severe AR episodes was significantly longer (P =0.049), and the incidence of these episodes reduced, in patients who maintained high numbers of donor-derived leukocytes for the first 200 days after transplantation. Conclusions. The presence of high numbers of donor-derived leukocytes, particularly macrophages, in the transpla nted lung in the first 200 days after transplantation was associated w ith stable graft function. Donor-derived leukocytes were reduced or ab sent in patients with a poor transplantation outcome. These findings r ule out a negative influence of persisting donor leukocytes and are co nsistent with the emerging two-way models of transplant tolerance.