TWIST and p53 expression and apoptosis in primary CD34⁺ cells. (A) Apoptosis in CD34⁺ marrow cells from healthy normal bone marrow donors (NBM) and patients with MDS cocultured with either unmodified HS5 stroma or HS5 with suppression of TWIST by siRNA (KD TWIST). Apoptosis was determined by flow cytometry. Error bars indicate SEM. (B) Levels of TWIST and p53 mRNA in CD34⁺ cells from healthy donors (NBM) and patients with MDS cocultured with either unmodified HS5 stroma (WT) or HS5 stroma with inhibition of TWIST (KD TWIST).