In the present study we investigated the proliferative response of megakaryocyte progenitor cells (CFU-MK) derived from peripheral blood stem cell (PBSC) collections of patients with haematological malignancies and normal donors. Highly purified CD34+ cells and mononuclear cell fractions were assayed in the presence of recombinant interleukin-3 (IL-3) and pegylated-recombinant human megakaryocyte growth and development factor (PEG-rHuMGDF), alone or in combination, and megakaryocyte colony formation was evaluated in the plasma clot. In comparison, steady-state bone marrow samples from normal donors were highly enriched in CD34+ cells and tested with the cytokines studied. Our results showed that IL-3 was able to stimulate CFU-MK colony formation from bone marrow and peripheral blood CD34+ cells. Similarly, PEG-rHuMGDF stimulated, in a dose-response manner, CD34+ cells from the bone marrow. However, normal mobilized peripheral blood CD34+ cells were not induced to generate CFU-MK colonies by PEG-rHuMGDE The same lack of response was observed when patients peripheral blood CD34+ cells primed with chemotherapy plus G-CSF or with G-CSF alone were assessed. In contrast, PEG-rHuMGDF stimulated CFU-MK growth when mononuclear cells, either from the bone marrow or from mobilized peripheral blood, were grown in plasma clot. Moreover, we analysed by flow cytometry the expression of Mpl receptor on the cell membrane of normal mobilized peripheral blood and normal steady-state bone marrow CD34+ cells. Our results showed a reduced expression of Mpl receptor on mobilized peripheral blood progenitor cells in comparison with bone marrow cells.
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