Ultrastructural features of CD34+ hematopoietic progenitor cells from bonemarrow, peripheral blood and umbilical cord blood

Hematopoietic progenitor cells from different sources have been widely char acterized, but their ultrastructural morphology has never been described in detail. In this study, imunomagnetically separated CD34(+) cells from norm al bone marrow (BM), mobilized peripheral blood (PBSC) and human umbilical cord blood (CB) were studied by transmission electron microscopy (TEM) usin g a cytochemical method which reveals endogenous myelo-peroxidase (MPO) act ivity. This technique is particularly suited for detecting early signs of t he myeloid commitment. The CD34(+) cells from PBSC were morphologically ver y homogeneous and 94.7 +/- 4.5% of these cells were MPO-: these ultrastruct ural features are generally considered typical of immature cells. The CD34( +) BM cells were instead more heterogeneous, with 24.6 +/- 7.4% showing int ense MPO activity. The ultrastructural characteristics of CB cells fell bet ween those observed in PBSC and BM, but there was a high percentage of morp hologically immature cells with no evidence of MPO activity (about 83%). Th e number of apoptotic cells within samples from different sources was also examined both by TEM and flow cytometry. The percentage of apoptotic cells was 0.7% in PBSC. 2.3% in BM, 2.9% in CB from vaginal delivery and 11.6% in CB from cesarean section. These observations confirm the relative phenotyp ic immaturity of CB in comparison with BM cells; they also suggest that CB collected after cesarean section may be associated with reduced stem cells viability.