Fluorescent 5 '-exonuclease assay for the absolute quantification of Wilms' tumour gene (WT1) mRNA: implications for monitoring human leukaemias

The Wilms' tumour gene (WT1) has been suggested as a powerful parameter for molecular monitoring of minimal residual disease (MRD) in leukaemias. Howe ver, molecular monitoring via WT1 RNA levels is far from being routinely pe rformed, which is possibly owing to the complex and inaccurate quantitative reverse transcription polymerase chain reaction (PT-PCP,) procedures. Usin g a newly-developed quantitative real time RT-PCR, we measured WT1 transcri pts in peripheral blood leucocytes of patients with acute myeloid (AM), acu te lymphoid (ALL) and chronic myeloid leukaemia (CAM). While healthy blood donors did not show measurable amounts of WT1 transcripts, WT1 RNA levels w ere detectable in all types of leukaemia. Furthermore, intraindividual WT1 transcript kinetics were exclusively dependent on disease progression, trea tment and subsequent disease outcome. Using this approach, we could disting uish between treatment response and failure within the first days of therap eutic intervention. Moreover, gradually rising WT1 levels over a period of weeks and months paralleled long-term disease progression and appeared to b e a prognostic indicator for subsequent clinical relapse. A linear correlat ion between quantities of WT1 and bcr/abl fusion transcripts could be seen in CML. We conclude that quantitative assessment of WT1 transcripts using r eal-time PCR is an appropriate method for molecular monitoring of AML, ALL and CML, and can be used independently for both short- and long-term monito ring of leukaemia patients.