Early chimerism of macrophages and lymphocytes in lung transplant recipients is predictive of graft tolerance

Background The persistence of donor cells derived from the graft (chimerism ) has been documented in various tissues after organ transplantation. It wa s suggested that stable chimerism might reflect a state of donor-specific t olerance. Chimerism of macrophages and lymphocytes were studied over time a fter lung transplantation as well as its impact on graft tolerance. Material and Methods. Macrophages and lymphocytes were purified from bronch oalveolar lavage sequentially obtained from 24 patients between 1 and 41 mo nths posttransplantation (20, 22, 24, and 17 patients at, respectively, 1, 3, 6, and 12 months). DNA was extracted from these cells and their recipien t-donor origin was evaluated by PCR amplification of highly polymorphic DNA regions (minisatellites). Results. We show that the remaining donor cells over the first month vary f rom 10 up to 50% and 5 up to 55% for lymphocytes and macrophages respective ly (+/-2 SD). All patients presented some chimerism up to the 6th postopera tive month. Good correlation was observed between the residual amount of do nor lymphocytes and macrophages during the first 3 months (P <0.001), Patie nts with at least 30% donor lymphocytes at 1 month after transplantation ha d less rejections (greater than or equal to stage II) in the follow up (P=0 .0007), The same observation is true for donor macrophages although to lowe r extend (P=0,02), The chimerism lost its predictive value beyond 3 months. Conclusions. These data demonstrate that a level of chimerism above 30% of either donor lymphocytes or macrophages at 1 month is related to a better s tate of graft tolerance. However, chimerism decreases markedly beyond 3 mon ths and has then no predictive value.