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o(BM) and umbilical cord blood (CB). Materials and Methods. BM and CB CD34-enriched cells were cultured in serum-free medium supplemented with SCF, bFGF, LIF, and Flt-3, in the presence or absence of stroma, and analyzed for proliferation, phenotype, and clonogenic potential. Results. Significant expansion of BM and CB CD34 and CD34CD38 cells were achieved in the presence of hu-ST. The differentiative potential of both BM and CB CD34-enriched cells cocultured with hu-ST was primarily shifted toward the myeloid lineage, while maintaining/ expanding a CD7 population. Clonogenic analysis of the expanded cells showed increases in progenitors of the myeloid lineage, including colony-forming unit-granulocyte, macrophage (CFU-GM) and colony-forming unit-granulocyte, erythroid, macrophage, megakaryocyte (CFU-Mix) for both BM (stroma and stroma-free conditions) and CB cells in the presence of stroma. Conclusions. These results indicate that adult hu-ST in the presence of appropriate cytokines can be used to efficiently expand/maintain myeloid and lymphoid cell populations from human BM and CB HSC. 2005 International Society for Experimental Hematology. Publishe