Human umbilical cord blood cells have many advantages as grafts for cell transplantation mainly because of the immaturity of the newborn cells in comparison with adult cells.

In contrast to their hematopoietic and mesenchymal potential, it remains unclear whether umbilical cord blood cells have endodermal competence.

Umbilical cord blood contains circulating stem/progenitor cells, and the cellular contents of umbilical cord blood are known to be quite distinct from those of bone marrow and adult peripheral blood. Over the past two decades, the presence and characteristics of hematopoietic stem cells in umbilical cord blood have been clarified. The frequency of umbilical cord blood hematopoietic stem/progenitor cells equals or exceeds that of bone marrow and greatly surpasses that of adult peripheral blood. Compared with adult cells, umbilical cord blood hematopoietic stem cells produce larger hematopoietic colonies in vitro, have different growth factor requirements, are able to expand in long-term culture in vitro, and have longer telomeres. Umbilical cord blood transplantation for various hematopoietic reconstitutions and a lower incidence of graft-versus-host disease than expected with conventional therapies. Recently, it has been reported that umbilical cord blood contains mesenchymal progenitor cells capable of differentiating into marrow stroma, bone, cartilage, muscle, and connective tissues.

Furthermore, umbilical cord blood provides no ethical problems for basic suties and clinical applications. Umbilical cord blood cells can be collected without any harm to the newborn infant, and umbilical cord blood hematopoietic stem cell grafts can be cryopreserved and transplanted to a host after thawing without losing their repopulating ability. For these reasons, umbilical cord blood could be a prominent source of cells for transplantation in various diseases. It remains obscure, however, whether umbilical cord blood contains stem/progenitor cells leading to endodermal cells, including hepatocytes.

Human umbilical cord blood cells can proliferate hepatocyte lineage cells in the original primary culture system in vitro, and differentiate into functionally mature hepatocytes in vivo. To our knowledge, this is the first evidence that human umbilical cord blood contains cells that produce endoderm-proliferating cells.