Quantitation of β- and γ-globin by amplification of mRNA from human hematopoietic progenitor cells. CD34⁺ cells grown in EPO for 6 days were stimulated by SCF and RNA extracted from cells harvested on days 6, 8, 10, 12, and 14 were amplified by quantitative PCR. (A) Average number of γ-globin molecules per cell. (B) Average number of β-globin molecules per cell. (C) Average γ/γ+β percentages in SCF-stimulated cells (solid bars) were compared with matched controls cultured in EPO alone (open bars). The panels show values averaged from 3 donors performed in separate experiments. Standard deviation bars are shown by vertical lines. The significant P values are shown and represent a comparison between EPO+SCF versus EPO.