DISTINCTION OF EOSINOPHILIC LEUKEMIA FROM IDIOPATHIC HYPEREOSINOPHILIC SYNDROME BY ANALYSIS OF WILMS-TUMOR GENE-EXPRESSION

In patients presenting with immature eosinophilic precursors it is not oriously difficult to distinguish acute eosinophilic leukaemia (EoL) f rom the benign idiopathic hypereosinophilic syndrome (HES), based on m orphological, cytochemical and immunophenotyping criteria, alone. Cyto genetic analysis or fluorescence in situ hybridization (FISH) can help in discriminating between these rare haematological disorders, but of ten treatment decisions cannot wait for the results of these time-cons uming techniques. Recently we and others found Wilms' tumour (WT1) gen e expression to be increased in virtually all patients with acute leuk aemias, whereas normal haemopoietic progenitors express the WT1 gene a t much lower levels or not at all. To determine whether detection of W T1 gene expression is useful to distinguish EoL from HES patients, we analysed, by RT-PCR, bone marrow or blood mononuclear cells from EoL ( n=3), HES (n=3) and reactive eosinophilia patients (n=4) for WT1 gene expression. Using our WT1-RT-PCR protocol, we found WT1 gene expressio n to be restricted to EoL patients. By detecting WT1 mRNA transcripts in the cerebrospinal fluid using RT-PCR, we were also able to diagnose isolated CNS-relapsed leukaemia, initially confused with bacterial me ningitis, in an EoL patient. In conclusion, we show that WT1-RT-PCR is a powerful complementary diagnostic tool to distinguish acute eosinop hilic leukaemia from the hypereosinophilic syndromes, This observation needs confirmation in a larger series of EoL and HES patients.