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Umbilical cord blood (UCB) has emerged as a promising source of haemopoietic stem/progenitor cells (HSPC) for human bone marrow reconstitution, the limitation being the low harvestable number of HSPC from a single UCB sample.

In developing our UCB ex vivo expansion strategies, our group designed ‘negative’ immunomagnetic selection systems to deplete developing haemopoietic cells from HSPC. The resulting highly purified non-committed ‘lineage negative’ (LinNeg) cell population represents 0·12% (± 0·02 SEM, n = 9) of original UCB mononuclear cells. In liquid culture (Iscove's modified Dulbecco's medium – 10% fetal calf serum, supplemented with thrombopoietin, Flt-3 ligand and c-Kit-ligand), LinNeg cells proliferated and maintained haemopoietic colonies for at least 5 weeks. In three independent experiments, LinNeg cells also produced a distinct adherent cell population showing neuroglial cell morphology. Further analysis with laser-scanning confocal microscopy revealed (i) active cell–cell communication through extensive membrane projections from these adherent cells (top image) and (ii) positivity for Glial Fibrillary Acidic Protein, a neuroglial marker (immuno-fluorescence bottom image). These results support the existence of a cell population with multi-tissue differentiation ability within UCB. Our findings widen the potential of UCB as an accessible and ethically sound stem cell source for treatment of haematological diseases, and possibly for certain neurological disorders.