OBJECTIVETo investigate whether WT1 gene overexpressed in leukemic stem cells (LSCs) and its significance.

METHODSExpression of WT1(+17AA) and WT1(+KTS) gene isoforms in CD34(+)CD38(-)CD123(+) cells (LSCs) of 47 AML patients were determined by fluorescence quantitative RT-PCR. The ratio of the four splicing isoforms WT1(+/+), WT1(+/-), WT1(-/+) and WT1(-/-) in LSCs were calculated and compared with that in normal CD34(+)CD38(-)CD123(-) cells (HSCs). The relationship in AML patients between LSCs WT1 expression and remission rate, survival time and relapse rate was analyzed.

RESULTSThe expression of WT1 gene was highest (0.034 +/- 0.034) in LSCs, and higher in CD34(+)CD38(-)CD123(-) AML cells as compared with that in HSCs (P < 0.05). The proportion of +17AA isoform was predominant over -17AA in all the three cell subsets with no difference. The proportion of +KTS isoform was the highest in HSCs (0.57 +/- 0.04), while the lowest in CD34(+)CD38(-)CD123(-)AML cells (0.50 +/- 0.12) (P < 0.05). No significant difference in the four isoforms expression ratio was observed among the three groups. WT1 expression in LSCs was not correlated with sex, age, FAB subtype and blast cell ratio, while the ratio of CD34(+) cells in blast cell was significantly higher in the WT1 high expression group than in the low expression group (P < 0.01). The CR rate was significantly lower in WT1 high expression group (21.1%) than in the WT1 low expression group (59.1%) (P < 0.05). The follow-up data were available in 41 patients with a median follow-up duration of 118 (3 - 290) days. The median overall survival (OS) for WT1 high and low expression group were 77\[95% confident interval (CI) 45 - 108\], 158 (95%CI 100 - 215) days respectively (P = 0.041).

CONCLUSIONWT1 gene overexpressed in AML LSCs and the ratios of four WT1 isoforms have no difference in LSC compared with HSC. Patients with higher LSC WT1 expression have lower CR rate and shorter survival time.