Hes1 expression was elevated in approximately 40% of patients with CML in blast crisis. (A) Real-time RT-PCR for Hes1 in bone marrow or peripheral blood cells from healthy subjects, patients with CML in chronic phase, or patients with CML in blast crisis. Expression levels were normalized by GAPDH mRNA. RNA from normal bone marrow cells served as a control (mean of 10 RNA levels of normal bone marrow was defined as 1). Hes1 mRNA levels exceeded 4 (solid bar) in 8 of 20 samples from CML in blast crisis patients. The correlation coefficient determined by the Wilcoxon signed-rank test between blast ratio and Hes1-expression level was −0.395. PB indicates peripheral blood; BM, bone marrow; CSF, cerebrospinal fluid. The solid bar represents CML in blast crisis exceeding 4; the hatched bar represents CML in blast crisis less than 4. (B) Hes1 expression in 5 human CML blast crisis cell lines. Expression levels of HES1 in K-562, JK-1, KCL-22, TS9:22, and JURL-MK1 were evaluated by real-time RT-PCR and were normalized by GAPDH mRNA. (C) Growth repression by transduction of dnHes1 (a dominant-negative Hes1) retrovirus vector into 3 human cell lines (K-562, TS9:22, and JURL-MK1). Six days after retrovirus transduction, cell numbers were counted. Growth is shown as a percentage of the control cells that were transduced with control vector. A representative result from 2 independent and reproducible experiments is shown. Error bars represent the SD from duplicate cultures. (D) Real-time RT-PCR for C/EBP-α in Hes1-transduced KSLs, CMPs, and GMPs compared with control vector-transduced KSLs, CMPs and GMPs. Total RNA was extracted at 60 hours from the initiation of Hes1-transduction. Error bars represent the SD from 2 independent experiments in (A-B,D).