FACS analysis showing the costaining of CD34 and cyclin A1 in myeloid progenitors. (A) Dot plot shows that CD34 and cyclin A1 are costained in the population of the upper right square. Lower left square: cyclin A1⁻/CD34⁻; lower right square: cyclin A1⁻/ CD34⁺; upper left square: cyclin A1⁺/ CD34⁻. (B and D) Histograms show the specificity of cyclin A1 staining. The staining for cyclin A1 (shaded curve) is significantly stronger than the staining for the control rabbit antibody (solid curve) in the CD34⁺ cell population (shown in [B]), but no difference was observed between the cyclin A1 (shaded) and control (solid) staining in the CD4⁺ T-lymphocyte population (D). (C) Dot plot shows that the control CD4-stained cells are negatively stained for cyclin A1 (lower right square). CD34⁺, peripheral blood progenitor cells were partially purified for use in these experiments, as described in the Materials and Methods.