Differentiation of Non-Adherent Hematopoietic Stem Cells from Umbilical Cord Blood Cells into Adherent Hepatocytic Lineage.

The liver consists of a variety of different cell types, the vast majority of which are hepatocytes. It has been shown that adult, as well as umbilical cord blood (UCB) mesenchymal stem cells (MSC) are capable of differentiation into mesenchymal and non-mesenchymal tissues including hepatocytes. Only a limited number of UCB units (20%) such as frozen, unfractionated and concentrate leukocytes induced by hydroxyethyl starch volume reduced UCB units can generate MSC. In light of this, we have developed the technology to generate potent MSC from all frozen UCB samples tested (3/3). In the present study, the incubation of thawed out UCB mononuclear cells (MNC) and non-selected CD34+ cells in the presence of SCF (25ng/ml), FLt-3 (25ng/ml), MGDF (10ng/ml) & IL-6 (20ng/ml) and 10% human serum in stroma-free liquid culture not only generated long term expansion of transplantable UCB hematopoietic stem cells (non-adherent) (Peters et al., 2004), but also long-term expansion of MSC (adherent cells). Adherent cells were enriched by medium changes followed by trypsinization and subsequent culture and passing on fibronectin in the presence of 10% human serum and 30ng/ml bFGF. The stroma-free liquid cultures were tested for the production of hematopoietic stem cells (HSC), as well as MSC over a period of 15 weeks; MSC increased throughout expansion of HSC. We used the CFU-Fibroblast assay to demonstrate MSC activity in stromal cell formation in vitro. Expanded MSC between passages 3–5 were plated using MesenCult™ (Stem Cell Technologies). After 14 days incubation at 37^oC, 5% CO₂, very large and small CFU-fibroblast colonies generated from 10⁵ MNC/ml (initiated on Day 0 in stroma-free liquid culture) were continuously detected throughout expansion. In order to test the capacity of MSC to differentiate into hepatocytes, cells were cultured in DMEM supplemented with dexamethasone and 25ng/ml HGF, the latter of which was replaced with 50ng/ml oncostatin M after incubation day 14. The cells were able to expand to cell lines and took on the common hexagonal shape characteristic of hepatocytes; this parameter was used as a primary screening criterion. In addition, the hepatocyte-like cells were further assessed by reverse transcription-polymerase chain reaction and found to express mRNA for albumin, as well as two hepatocyte-specific bile salt transport proteins, basolateral bile transport system NTCP and the canalicular bile salt export pump BSEP. These data demonstrate the presence of pluripotent stem cells in UCB with the capacity to differentiate into a hepatocytic lineage.The research in this area has great potential, both with respect to future application in patients with end-stage liver disease, as well as for learning more about the role of MSC in new clinical cellular therapies.