CHARACTERIZATION OF CD34(+)HLA-DR(-)CD38(+) AND CD34(+)HLA-DR(-)CD38(-) PROGENITOR CELLS FROM HUMAN UMBILICAL-CORD BLOOD

In this study we show that depletion of cells expressing mature cell markers, including HLA-DR, followed by positive cell sorting for cells expressing CD34 and CD38, can be used to define functionally distinct hematopoietic cells from human umbilical cord blood (HUCB). The CD34(+)HLA-DR(-)CD38(+) population contained the majority of directly clonogenic cells, while the optimal ability to maintain long term co-culture with bone marrow stromal cells was present within the CD34(+)HLA-DR(-)CD38(-) population. 1.2 +/- 0.4% of the CD34(+)HLA-DR(-)CD38(-) cells plated at 1 cell/well and grown in the presence of hematopoietic growth factors (HGF) formed hemopoietic colonies. Mesenchymal elements were observed in 20% of these cultures. No cell growth, however, was observed when the CD34(+)HLA-DR(-)CD38(-) cells were cultured in the absence of HGF. This is in contrast with the findings in fetal bone marrow which demonstrated the presence of stem cells that were independent of HGF. Thus, while it is possible to isolate very immature hemopoietic progenitor cells from HUCB defined by the phenotype Lin-CD34(+)HLA-DR(-)CD38(-), these cells do not appear to exhibit the pluripotentiality of the analogous population reported in fetal bone marrow. We conclude that these cells are absent or at a very small frequency in HUCB.