Characterization of multiple CD34+ cell populations in cord blood

Unlike granulocyte colony-stimulating factor (G-CSF)-mobilized peripheral blood, which show a single homogeneous population of CD34(+) cells, umbilical cord blood ( CB) CD34(+) cells are present as multiple populations, CD34(regular) and CD34(bright) (the latter comprising 7.0 - 58.2% of the total CD34(+) cells), using the ProCOUNT(TM) procedure or with anti-CD34 labeling of immunoselected cells. The CD34regular population contains cells with high forward scatter (CD34(regular)FSC(high)) and with low forward scatter (CD34(regular) FSClow). Immunomagnetically selected CD34(+) cells, sorted into CD34(regular), CD34(regular) FSChigh, CD34(regular)FSC(low), and CD34(bright) cell populations, were used in in vitro assays: only the CD34(regular)FSC(high) population transmigrated and showed growth of colony-forming unit (CFU) and long-term culture initiating cells ( LTC-IC) colonies. The absolute number of CD34(+) cells in CB samples was determined by ProCOUNT(TM) and Stem Kit(TM) enumeration protocols. In liquid stored CB units, ProCOUNT(TM) and Stem Kit(TM) count differences are accounted for by the enumeration of CD34(bright) cells. Differences between ProCOUNT(TM) and Stem Kit(TM) counts using cryopreserved/thawed samples are accounted for by increased CD34(regular) FS-C-low cell numbers (2.0 +/- 1.4% in liquid stored and 27.8 +/- 14.6% in cryopreserved/thawed samples). The ProCOUNT(TM) assay includes the nonfunctional CD34(bright) and CD34(regular)FSC(low) cells as part of the CD34(+) cell count, thereby elevating the absolute number of CD34(+) cells. Using the Stem Kit(TM) assay method of gating, CD34(bright) and CD34(regular)FSC(low) cells are not counted. Our data indicate that the CD34(regular)FSC(high) cell population has functional characteristics based on the in vitro assays and a more accurate count of these cells can be achieved using the Stem Kit T assay.