Liver stem cells: prospects for treatment of inherited and acquired liver diseases.

It is now understood that there are three cell compartments which physiologically contribute to vertebrate liver parenchymal maintenance and regeneration after injury: mature liver cells (hepatocytes, cholangiocytes), intraorgan stem/progenitor cells (cells of the proximal biliary tree, periductal cells) and extraorgan stem cells (from the circulation and the bone marrow). All of these cell populations, as well as other, non-physiologic stem cells (e.g., mesenchymal stromal cells from the bone marrow, fetal hepatoblasts, embryonic stem [ES] cells), may be used therapeutically for treatment of inherited and acquired liver diseases. This article will summarise our current understanding of these various cell populations, and review possible approaches to their therapeutic use, including cell transplantation, bioartificial liver devices (BLDs), gene therapy and administration of exogenous factors to stimulate normal physiological responses to repair.