Proliferation and viability of normal hematopoietic progenitor cells. (A) CD34⁺ cells enriched from cord blood samples (n = 7) were cultured in the presence of BIBR1532 in serum-free medium supplemented with cytokines (SCF, Flt, IL-3, IL-6, and G-CSF). At the indicated time intervals, viable cells were counted using trypan blue exclusion assay. Note that cell expansion was moderately reduced only at drug concentrations of 160 μM. Experiments were performed in duplicates. (B) Viability was measured using FSC/SSC pattern and DiOC₆/PI staining at the indicated time points. FACS diagrams represent the nontreated control cells, the DMSO-treated cells (not shown), and the cells cultured with 80 μM BIBR1532. There was no decrease in cell viability of cells cultured under presence of 80 μM BIBR1532 compared with negative and DMSO controls at any time point of culture. (C) The mean telomere length was measured in peripheral blood stem cells (CD34⁺ leukapheresis sample) following treatment with BIBR1532. Representative telomere fluorescence histograms analyzed at indicated time points are shown, which illustrate no substantial difference in the mean telomere length of treated compared with untreated cells.