Progenitor cell characterization and location in the developing human liver.

Tissue-derived stem cells may offer future liver disease therapies. The developing human liver provides an excellent model to examine normal hepatic progenitor cell maturation, but candidate populations are poorly characterized. We sought to identify putative progenitor phenotypes in first-trimester human liver, by characterizing the architectural relationship between developing epithelial, mesenchymal, and hematopoietic lineages. Bipotential hepatoblasts were identified by co-expression of hepatocytic (cytokeratin 18, albumin) and biliary(cytokeratin 19) specific markers and epithelial-specific E-cadherin. Restriction of dlk/pref-1 expression to hepatoblasts identifies this as a novel human marker allowing for hepatoblast sorting for in vitro analysis. Furthermore, the liver stem cell and haematopoietic marker Thy-1 was co-expressed with markers of hematopoietic (CD34) and mesenchymal (vimentin) lineage restriction on portal vein endothelium. Therefore, this structure may constitute a novel progenitor compartment with hemangioblast-like properties.