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ABSTRACT
Background: Presence of hematopoietic stem-cell-derived hepatocytes after clinical liver transplantation was demonstrated repeatedly. The relevance of this controversial mechanism of regeneration was discussed. Regarding frequency, the demonstrated results were divergent. In the present study, we propose to investigate the influence of growth and regeneration on the frequency of hematopoietic stem-cell-derived hepatocytes in transplanted organs. Material and Method: Paraffin-embedded liver specimens, obtained as clinically indicated, from female grafts transplanted into male recipients were investigated. The presence of Y-chromosome in hepatocytes, detected by fluorescence in situ hybridization (FISH), was the indicator for recipient origin. Slides were evaluated by assessing the relative number of Y-chromosome containing hepatocytes within 50 images representing an average of 775 hepatocytes. Results: In only 9 out of 81 specimens, single Y-chromosome positive hepatocytes were detected, resulting in a maximal frequency of 0.64%. Six positive specimens were obtained from full-size liver grafts and one from a partial liver graft. In the pediatric group, two positive samples were found. By staining additional sections from the nine positive specimens, no additional positive hepatocytes were detected suggesting an even lower frequency within the whole sample. We did not find any accumulation of Y-chromosome positive cells in any of the individually analyzed patient groups. Conclusion: Transdifferentiation of hematopoietic stem cells is an extremely rare event in liver growth and regeneration after transplantation. Due to the low number of positive events, the biological relevance seems questionable.