Hepatic properties and transplantation of Thy-1+ cells isolated from ED14 rat fetal liver

Thy–1, a phenotypic marker of hematopoietic progenitor cells, is also expressed in activated oval cells of the adult rat liver. Thy1⁺ cells have also been observed in the rat fetal liver and these cells exhibit properties of bipotent hepatic epithelial progenitor cells in vitro. However, the stem-like properties of Thy–1⁺ fetal liver cells have not yet been fully established and there is no information available concerning the liver repopulation capacity of Thy1⁺ fetal liver cells. We therefore isolated Thy–1⁺ cells from ED14 fetal liver and examined their hepatic gene expression profile and characteristics in vitro and proliferative and differentiation potential after transplantation into the adult rat liver in comparison to Thy–1^- fetal liver cells.

Fetal liver cells were selected for Thy–1 expression using immunomagnetic microbeads (MACS) and were enriched from 5.2% Thy–1⁺ in unfractionated cells to 87.2% Thy–1⁺. In multiple preparations of Thy–1⁺ cells, only rare cells were positive for AFP (0.1%); however, 4.3% AFP positive hepatoblasts were detected in Thy–1^- cell fractions. Analysis for albumin expression showed similar results, i.e., substantially greater albumin expression in Thy1^- vs. Thy–1⁺ cells. In addition, analysis for CK–19 showed 0.8% of the Thy–1⁺ cells to be positive. In Thy–1⁺ cell cultures, the majority of attached cells were scattered and exhibited a fibroblastoid morphology. A minority of the cells formed small cell clusters and exhibited typical characteristics of epithelial cells expressing AFP and albumin.

In the normal rat liver, transplanted Thy–1⁺ cells produced only rare, small DPPIV⁺ cell clusters and very few of these clusters exhibited an hepatocytic phenotype. In contrast, Thy–1^- fetal liver cells substantially repopulated the normal adult liver and differentiated into both hepatocytes and bile duct cells. However, by transplanting Thy–1⁺ fetal liver cells into the retrorsine-treated rat liver, we achieved up to 31.4% repopulation after two months. Transplanted Thy–1⁺ cells differentiated primarily into hepatocytes but only rarely into bile duct cells. Therefore, highly enriched Thy–1⁺ ED14 fetal liver cells proliferate and repopulate the liver only after extensive liver injury. This cell population shows characteristics of oval cells in the adult liver but is distinct from Thy1^- fetal liver stem/progenitor cells that repopulate the normal adult liver.

Fetal liver stem/progenitor cells - Thy-1 - cell transplantation - liver repopulation