[Ex vivo expansion of megakaryocyte progenitors from human umbilical cord blood CD34(+) cells].

This study was purposed to investigate the biological characteristics and immunogenicity changes of ex vivo expanded megakaryocyte progenitors from human umbilical cord blood CD34(+) cells in order to provide experimental basis for clinical application of ex vivo expanded umbilical cord blood megakaryocyte progenitor cells. Mononuclear cells (MNCs) were obtained from umbilical cord blood by Ficoll-Hyapaque density gradient separation. CD34(+) cells were enriched by magnetic cell sorting (MACS). The selected CD34(+) cells were seeded in serum-free medium stimulated with thrombopoietin (TPO, 50 ng/ml), interleukin 11 (IL-11, 50 ng/ml), and heparin (25 U/ml) for 14 days. The immunophenotyping (CD34(+), CD41a(+), CD61(+), CD34(+) CD41a(+) and CD34(+) CD61(+) cells) of amplificated products, matured megakaryocyte apoptosis, and expression of human leukocyte antigen (HLA) class I and class II molecules were measured by fluorescence-activated cell sorter (FACS). The number of colony-forming units-megakaryocyte (CFU-Mk) was also evaluated by CFU-Mk assay. The results showed that the umbilical cord blood CD34(+) mononuclear cells could be effectively differentiated into megakaryocytes. The peak expression ratios of CD41a(+) and CD61(+) cells were all at 14th days, while that of CD34(+) CD41(+) and CD34(+) CD61(+) cells were at 7th day [(3.41 +/- 2.80)% and (1.89 +/- 1.43)%, respectively]. The expansion times of large and small CFU-Mk reached peak at 7th day (20.66 +/- 32.79) and 10th day (435.62 +/- 482.65), respectively. The apoptotic rates of megakaryocytes at 7th, 10th, 14th day were (19.48 +/- 9.64)%, (26.87 +/- 9.03)%, and (52.46 +/- 11.74)%, respectively. The apoptotic rate of megakaryocytes had no significant difference in 7 and 10 days culture (p > 0.05), while that significantly increased in culture for 14 day culture, compared with culture for 7 and 10 days (p < 0.05, respectively). The expression of HLA class I and class II molecules on megakaryocytes decreased along with the prolongation of expansion time and sharply decreased in 0 to 10 days. It is concluded that the cytokines of TPO, IL-11, and heparin can promote the expansion of megakaryocyte progenitors from umbilical cord blood CD34(+) mononuclear cells effectively in vitro. The peaked expansion times of large CFU-Mk, the peaked expression ratios of CD34(+) CD41(+) and CD34(+) CD61(+) cells were all at 7th day. So the culture for 7 days appeared to be the optimal duration of expanding megakaryocyte progenitors.