Flow cytometry and immunoselection of human stem cells

Human hematopoietic stem cells (HSCs) can be obtained from a variety of hematopoietic tissues, including bone marrow, blood, cord blood, and fetal liver. Various techniques have been used to fractionate hematopoietic cell populations based on differences in size and density, expression of cell-surface antigens, differential dye uptake, and sensitivity to cytotoxic drugs. The very low frequency of HSCs in hematopoietic tissues presents an enormous challenge to purification strategies aimed at isolation of sufficient cells of suitablpurity for further study. The most effective approaches invariably involve several cell-separation steps which differ in capacity and degree of selectivity.