Summary
Stem cells can be derived either from growing embryos or from certain somatic tissues with continuous proliferative activity and high turnover, such as bone marrow hematopoietic cells and epithelial cells of the intestinal mucosa and skin. Whether such cells exist in other tissues and organs has been controversial for many years, but recent studies have clearly identified cells with stem-cell properties in muscle, brain, liver, and pancreas. This Chapter will review the general characteristics of stem cells, the evidence for progenitor or stem cells in the liver, the liver-cell transplantation models in which such cells have been studied, the differentiation of cells of hematopoietic and other origin into hepatocytes after transplantation into the liver, and liver repopulation by transplanted cells.