Mixed chimerism of cardiomyocytes and vessels after allogeneic bone marrow and stem-cell transplantation in comparison with cardiac allografts.

Controversy persists about mixed chimerism (mCh) occurring in the hearts of patients after orthotopic cardiac transplantation in comparison with allogeneic bone marrow (BM) and peripheral blood stem-cell (PBSC) transplants. Cadaver hearts were examined after sex-mismatched transplantation by immunophenotyping combined with dual color fluorescence in situ hybridization (X and Y chromosome-specific probes). A striking disparity in the extent of mCh depending on the different transplantation procedures was recognizable. After allografting with PBSCs, 1.7% chimeric cardiomyocytes were detectable contrasting 5.4% of donor cells after full BM transplantation. In cardiac transplants, host-type endothelial cells (16.2%) and myocytes (14.3%) of the vessel walls were more often encountered than after BM and PBSC allografting. A sprouting of vascular structures into the donor heart after orthotopic cardiac transplantation has to be assumed, as does a pivotal role of the mesenchymal stem cells of the BM in the development of mCh.