Cytokine effects on proliferation and hemoglobin expression. CD34⁺ cells were cultured for 14 days in EPO (E), EPO + TGF-B (ET), EPO + SCF (ES), and EPO + SCF + TGF-B (EST). (A) Cell counts and (B) hemoglobin expression levels calculated from HPLC analyses on day 14 are shown. The cell counts represent the number of cells enumerated per 10⁵ CD34⁺ cells placed in culture on day 0. The mean values ± standard deviation bars are from separate experiments with cells from 4 donors. ^*Significant (P ≤ .001) changes relative to cells cultured in EPO alone. (C) HPLC tracings from cells achieving HbF dominance in EST. Controls were used to identify the hemoglobin peaks as HbF (F), HbA (A), or HbA2 (A2). The percentages above the HbF peaks represent HbF/HbF + HbA ratios. (mV indicates millivolts; elution time is represented on the x-axis.)