Purification and functional assay of pluripotent hematopoietic stem cells.

Hematolymphopoietic stem cells (HSC) have the capacity for extensive self-renewal and pluripotent myelolymphoid differentiation. Recent studies have emphasized the heterogeneity of human HSC subsets in terms of proliferative and self-renewal capacity. In the NOD-SCID (nonobese diabetic-severe combined immunodeficient) mouse xenograft assay, most CD34+38- stem cell clones proliferate at early times, but then disappear, whereas only few clones persist: possibly, the latter ones consist of long-term engrafting CD34+38- HSC expressing the KDR receptor (i.e. the vascular endothelial growth factor receptor II). In this regard, isolation of the small KDR+ subset from the CD34+ hematopoietic progenitors (and possibly from the CD34-lin- population) may provide a novel and effective approach for the purification of long-term proliferating HSC. More importantly, KDR+ HSC isolation will pave the way to cellular/molecular characterization and improved functional manipulation of HSC/HSC subsets, as well as to innovative approaches for HSC clinical utilization, specifically transplantation, transfusion medicine and gene therapy.