To elucidate the cellular and molecular mechanisms underlying normal and malignant hematopoiesis, it is critical to isolate the stem cell compartment as well as downstream lineage-restricted ...progenitor populations. Recent advances in the fluorescence-activated cell sorting (FACS) technology have greatly contributed to the progress of stem/progenitor isolation, providing the multicolor platform for simultaneous analyses of cell-surface antigens and/or specific gene expression profiles. In murine system, the almost ultimate purification of hematopoietic stem cell (HSC) has been achieved, demonstrating a long-term hematopoietic reconstitution by the single HSC transplantation. A variety of lineage-committed progenitors are also isolatable at the diverse checkpoints in the hierarchy of normal murine hematopoiesis. In human system, the emergence of xenotransplant models utilizing immunodeficient mice helped the identification of hematopoietic stem and progenitor populations, demonstrating that the expression patterns of surface antigens as well as the developmental pathways are considerably different between human and mouse. Furthermore, the verification of the concept of cancer stem cell is in progress. In this review, we summarize the phenotypic and functional properties of murine and human hematopoietic stem/progenitor cells and also discuss the recent topics of leukemic stem cells.
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