A novel co-culture system using human brain endothelial cells (HUBEC) which promotes the expansion of human CD34+CD38- cells consistent with the PMVEC system is disclosed. HUBEC were isolated from cadaveric donors, passed in primary culture, cloned and found to be Von Willebrand Factor positive. Cultivation of purified bone marrow CD34+ cells on HUBEC monolayers supplemented with GM-CSF+IL-3+IL-6+SCF+flt-3 ligand caused a 14.5-fold increase in total cells, an 6.6-fold increase in CD34+ cells, and, most remarkably, a 440-fold increase in CD34+CD38- cells after 7 days. Further, CFU-GM production increased 15.1-fold, BFU-E increased 8-fold, and CFU-Mix increased 5.2-fold. Optimal generation was dependent upon the continued presence of exogenous supplied cytokines. Moreover, we found that non-brain human endothelial cells isolated from the same donors supported neither the expansion nor the maintenance of human CD34+CD38- cells.
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