Representative result of two-color flow cytometric analysis of enriched CD34⁺ PB cells after 60 hours of infection with the Ax1w (mock vector) or Ax/hEGFR virus at an MOI of 250 or 1,000 pfu/cell. Enriched CD34⁺ PB cells (purity, 86.2%) were cultured with each adenovirus vector in a serum-free medium in the presence of cytokines. After 60 hours of infection, cells were double-stained simultaneously and analyzed as described in the Materials and Methods.