Liver repopulation for the treatment of metabolic diseases.

Orthotopic liver transplantation is the treatment of choice for several inborn errors of metabolism. Unfortunately, the supply of donor organs is limiting and therefore many patients cannot benefit from this therapy. In contrast, hepatocyte transplantation could potentially overcome the shortage in donor livers by use of cells from a single donor for multiple recipients. In classic hepatocyte transplantation, however, only 1% of the liver mass or less can be replaced by donor cells. Recently, though, it has been shown in animal models that >90% of host hepatocytes can be replaced by a small number of transplanted donor cells in a process we term 'therapeutic liver repopulation'. This phenomenon is analogous to repopulation of the haematopoietic system after bone marrow transplantation. Liver repopulation occurs when transplanted cells have a growth advantage in the setting of damage to recipient liver cells. It has been discovered that transplanted cells from extrahepatic sources such as the adult pancreas or bone marrow can also be used for liver repopulation. Because bone marrow donors are widely available, this finding raises the hope of therapeutic application of these cells in the future. Here, the current knowledge regarding therapeutic liver repopulation and the hopeful implications for treatment of liver diseases will be discussed.