Microchimerism in bone marrow-derived CD34(+) cells of patients after liver transplantation

Lymphoid and dendritic cells of donor origin can be detected in the recipie nt several years after a solid organ transplantation. This phenomenon Is te rmed micro-chimerism and could play a role in the induction of tolerance. T he fate of other hematopoietic cells transferred by liver transplantation, in particular of stem and progenitor cells, is unknown. For this reason, we studied peripheral blood and bone marrow samples of 12 patients who had re ceived a liver transplant from an HLA-DR mismatched donor. Eight patients w ere long-term survivors between 2.8 and 10.1 years after allografting. CD34 (+) cells from bone marrow were highly enriched with the use of a P-step me thod, and a nested polymerase chain reaction was applied to detect donor ce lls on the basis of allelic differences of the HLA-DRB1 gene. Rigorous cont rols with DRB1 specificities equal to the donor and host were included. In 5 of 8 long-term liver recipients, donor-specific CD34(+) cells could be de tected in bone marrow. Microchimerism in the CD34(+) cell fraction did not correlate to the chimeric status in peripheral blood. In conclusion, our re sults demonstrate a frequent microchimerism among bone marrow-derived CD34( +) cells after liver transplantation. The functional role of this phenomeno n still needs to be defined.