Quantification of WT1 mRNA by competitive NASBA in AML patients

The measurement of Wilms' tumor gene (WT1) mRNA levels by reverse transcriptase-polymerase chain reaction (RT-PCR) is useful in detecting minimal residual disease (MRD) in leukemia patients. In the present study, we quantified the level of WT1 mRNA in the peripheral blood and bone marrow of patients with acute myelocytic leukemia (AML) at initial onset, remission and recurrence by the use of nucleic acid sequence based amplification (NASBA), and then ascertained the clinical usefulness of this method. At initial onset, the level of WT1 mRNA in the peripheral blood was above 10(3) copies/microgram and that in the bone marrow was above 10(4) copies/microgram. The level of WT1 mRNA was decreased in cases where therapy resulted in complete remission, but it was abnormally high in recurring cases. In AML (M3) patients, the relationship between the level of WT1 mRNA and the expression of the PML-retinoic acid alpha receptor (RAR alpha) gene, assessed by fluorescence in situ hybridization (FISH), was investigated. When leukemia was in remission hematologically, the PML-RAR alpha gene was negative and the level of WT1 mRNA decreased. These findings suggest that the quantification of WT1 gene expression by competitive NASBA is useful in assessing therapeutic effects and detecting MRD.