Analysis of Wilms tumor gene (WT1) expression in acute leukemia patients with special reference to the differential diagnosis between eosinophilic leukemia and idiopathic hypereosinophilic syndromes

Continuous Wilms' tumor gene (WT1) expression is a typical feature of leuke mic blasts in AML, ALL, and blast crisis CML patients. It is easily detecta ble by a variety of RT-PCR protocols, which differ mainly in their sensitiv ity. The nuclear WT1 protein can be found in blasts of approximately 50-60% of acute leukemia patients at diagnosis. Conversely, WTI is only transient ly expressed in normal hemopoiesis. Early CD34(+) hemopoietic progenitors e xpress WT1, whereas no WT1 mRNA transcripts can be found in mature blood ce lls and differentiation-induced committed CD34(-) progenitors. As a powerfu l complementary diagnostic tool, testing for WT1 expression can be helpful to discriminate between eosinophilic leukemia (EoL) patients and patients w ith idiopathic hypereosinophilic syndromes. Conflicting data about the usef ulness of testing for WT1 expression to monitor minimal residual disease (M RD) in treated leukemia patients will be discussed. Finally, research strat egies to circumvent shortcomings in detecting leukemia-associated WT1 expre ssion will be outlined.