OBJECTIVETo evaluate the significance of quantification of WT1 mRNA for monitoring minimal residual disease (MRD) in patients with acute myeloid leukemia (AML).

METHODSWT1 mRNA level was detected with real-time quantitative RT-PCR (RQ-PCR) technique in bone marrow samples from 15 normal subjects (NBM) and 123 AML patients. Sixty-two AML samples were also detected AML1-ETO mRNA expression by RQ-PCR. Simultaneously follow-up of WT1 and AML1-ETO levels were carried out in 50 samples from 8 AML patients. WT1 and AML1-ETO levels were normalized by internal control ABL gene.

RESULTSAll correlation co-efficiencies were over 0.99 for WT1, AML1-ETO and ABL standard curves. Co-efficiencies of both interassay and intraassay variation were below 4%. The WT1 expression levels in NBM were 0.001 to 0.019 with a median level of 0.008. Higher levels of WT1 expression were found in 61 of 67 (91%) newly diagnosed AML patients compared with NBMs and 37 of the 67 (55.2%) showed 100-fold higher WT1 levels than that in NBMs. WT1 mRNA levels were highest in M(4EO) and M(3) and lowest in M(1) and M(5) patients. There was an excellent correlation between WT1 and AML1-ETO gene expression levels (r = 0.88, P < 0.001). WT1 expression levels in three patients who were in continuous complete hematological remission (CHR) were within normal range. In three of four relapsing patients, WT1 expression levels increased 31.4, 11.4 and 4.0 fold respectively one month before hematological relapse.

CONCLUSIONSQuantification of WT1 expression level by RQ-PCR may be used to monitor MRD for most AML patients, but it is less sensitive than fusion gene. Continuous or significant increase of WT1 expression in CHR patients predicts an impending relapse.