Serial Biopsies of Sex-Mismatched Liver Transplants Show No Evidence for Recipient-Derived Hepatocytes

Abstract

Background: Bone marrow-derived hematopoietic stem cells (BMHSCs) are able to develop into multiple tissue-types during growth and regeneration. Moreover, BM-HSCs have been shown to act as source for hepatic regeneration in rodent models, however their ability to participate in human liver regeneration remains controversial. The aim of this study was to investigate the origin of hepatocytes in sex mismatched cases of orthotopic liver transplantation in longitudinally performed liver biopsies. Methods: Paraffin-embedded liver biopsy samples of 14 patients after sex-mismatched liver transplantation were investigated. Biopsies were taken for clinical reasons and subjected to histologic examination for recurrence of hepatitis C or rejection episodes. All consecutive biopsies were included into analysis. Immunohistochemical staining with hepatocyte specific Ab and fluorescent in-situ hybridisation (FISH) for visualization of Y chromosomes were performed to analyse presence of recipient-derived hepatocytes. Ki-67 specific mAb was used to demonstrate proliferative activity in the transplanted liver parenchyma. Results: We analysed 30 liver biopsy samples ranging from one week to more than 3 years after transplantation. Multiple biopsies were available in 10 out of 14 patients. There was no evidence for recipient derived hepatocytes in liver transplants at any time point. We were able to detect recipient specific chromosomal status in inflammatory cells within the liver but not within hepatocytes. Chromosomal status was independent of liver injury at the time of biopsy, caused by hepatitis C recurrence or rejection episodes. Moreover, there was no correlation between rejection episodes and proliferative capacity in post-transplant biopsies. Conclusions: Our results show no evidence for involvement of BMHSCs in liver regeneration after orthotopic liver transplantation. Results were independent of both, biopsy time post-transplantation and degree of tissue injury due to rejection episodes or viral re-infection. We conclude that BM-HSCs are not the primary source for hepatocytes in liver regeneration and suggest that recipient BM-HSC derived hepatocyte repopulation is a very rare event and may not be considered to be of clinical relevance.