Prognostic significance of quantitative analysis of WT1 gene transcripts by competitive reverse transcription polymerase chain reaction in acute leukaemia.

We have developed a sensitive, competitive, nested reverse transcription polymerase chain reaction (RT-PCR) titration assay that quantifies the number of Wilm's tumour (WT1) gene transcripts in bone marrow (BM) and peripheral blood (PB), coupled with a competitive RT-PCR protocol for the ABL gene as control. We studied BM/PB samples from 107 acute myeloid leukaemia (AML) patients and 22 acute lymphoblastic leukaemia (ALL) patients at presentation and detected the WT1 gene in > 90% of patients by a qualitative assay. Quantitative analysis of WT1 transcript at presentation in 66 patients (52 AML, 14 ALL) correlated significantly with remission rate, disease-free survival (DFS) and overall survival (OS) (P = 0.003). WT1 levels were normalized to 105ABL transcripts. Within good and standard cytogenetic risk groups, high WT1 levels correlated with poorer outcome. Serial quantification was performed in 35 patients (28 AML, seven ALL); those with less than 103 copies of WT1 after induction and second consolidation chemotherapy had significantly better DFS and OS. Fourteen patients have relapsed with a median complete remission duration of 12 (range 4-49) months. We detected a rise in WT1 levels in nine out of 14 patients, 2-4 months before the onset of haematological relapse, whereas in the remaining five patients, WT1 levels remained persistently high during the disease course. WT1 levels were lower in PB than in BM, but mirrored changes in the BM samples and were equally informative. We suggest that WT1 is a useful molecular target to monitor minimal residual disease in acute leukaemia, especially in cases without a specific fusion gene.