Stem cells are interesting candidates as a new source for cell/organ culture or cell transplantation concepts. So far it is believed that the hepatoblast is the common progenitor cell during fetal liver development. In previous studies two distinct fractions of liver cells were found during development: cells co-expressing Thy1 and CK-18 (cytokeratin-18) and cells expressing CK-18 only. In this study we cultured Thy1-positive and Thy1-negative hepatic progenitors isolated from collagenase digested fetal rat livers after depletion of OX43/OX44-positive hematopoietic cells. The cells were cultured on a collagen-I matrix in a medium containing epidermal growth factor, insulin, and fetal calf serum. Thy1-positive cells isolated from ED16, ED18, or ED20 livers showed significantly enhanced cell growth compared with Thy1-negative cells during the culture period. Both cell types showed expression of the liver-specific genes CK-18, albumin and alpha-feto-protein at the beginning of the culture period, as assessed by reverse-transcription polymerase chain reaction and immunocytochemistry. The growth of Thy1-positive cells was significantly higher when compared with Thy1-negative cells and declined with maturation of the liver. The data suggest a stem cell-like growth potential of Thy1-positive fetal hepatic cells. Thus, these cells might be useful for concepts of cell-based therapies. However, further efforts must be undertaken to define the biological, ethical, and legal aspects of using fetal cells.
