Stem cells are found in all multi-cellular organism. They retain the ability to renew themselves and can differentiate into a diverse range of specialised cell types.
As stem cells can be grown and transformed into specialized cells with characteristics consistent with cells of various tissues such as muscles or nerves through cell culture, their use in medical therapies has been proposed. In particular, embryonic cell lines, autologous embryonic stem cells generated through therapeutic cloning, and highly plastic adult stem cells from the umbilical cord blood or bone marrow are touted as promising candidates.
Human umbilical cord blood cells have many advantages as grafts for cell transplantation because of the immaturity of newborn cells compared with adult cells. In contrast to their hematopoietic and mesenchymal potential, it remains unclear whether umbilical cord blood cells have endodermal competences. Here, with a view to utilize umbilical cord blood cells for cell transplantation into injured liver, we investigated the hepatic potential of umbilical cord blood cells both in vitro and in vivo. We determined the most efficient conditions leading umbilical cord blood cells to produce albumin. In a novel primary culture system supplemented with a combination of growth/differentiation factors, about 50% of umbilical cord blood cells in 21-day cultures expressed albumin, and the albumin cells coexpressed hepatocyte lineage markers. The albumin expressing cells were able to proliferate in the culture system. Moreover, in the cell-transplantation model into liver-injured severe combined immunodeficient mice, inoculated umbilical cord blood cells developed into functional hepatocytes in the liver, which released human albumin into the sera of the recipient mice. In conclusion, this study demonstrates that human umbilical cord blood is a source of transplantable hepatic progenitor cells. Our finding may have relevance to clinical application of umbilical cord blood derived cell transplantation as a novel therapeutic option for liver failure.

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