DETECTION OF MINIMAL RESIDUAL DISEASE OF ACUTE CHILDHOOD LEUKEMIA BY FOLLOWING WT1 GENE EXPRESSION IN THE PERIPHERAL BLOOD

Cytomorphology and Southern blot technique are not sensitive enough to detect minimal residual disease and to diagnose relapse, and the different DNA markers, which are detected by other PCR techniques are present only in 20-30% of childhood leukemias. Several authors are of the opinion that monitoring WT gene expression in the peripheral blood can be used to monitor the progression of the disease, to detect minimal residual disease and to diagnose relapse early. The WT1 gene has two splice regions and four different isoforms, which may play different roles in the disrupted expression of all WT1 isoforms. WT1 gene expression in the bone marrow and in the peripheral blood in leukemia patients is well known in the literature, but the expression of WT1 isoforms has not been investigated yet. The aim of our study was to investigate if monitoring WT1 gene expression in the peripheral blood was an appropriate method to monitor the progression of acute childhood leukemias. In the course of the study, the peripheral blood of 27 newly diagnosed, 17 previously diagnosed and 21 nonleukemic children was tested for WT1 gene expression. Twenty consecutive pediatric patients were included in this study for the analysis of the peripheral blood samples and the initial diagnosis of ALL for WT1 isoforms expression. In agreement with the literature, we found that all ALL cases except one expressed the WT1 gene (23/24, 96%). The level of WT1 expression did not correlate to the ratio of the blast cells in the peripheral blood. The initial high rate of WT1 positivity (23/24) became low (621%) at the end of the induction phase of the therapy (day 15: 7/24, day 33: 5/24), although remission occurred in all the patients under treatment except one. Twenty patients were followed for 12 months following induction therapy and 16 of them were further monitored for the second year (14-21 month). Clinical relapse occurred in two cases during the first year where the WT1 expression at the periphery was maintained for 11-15 months and both patients died. On the other hand, there was no WT1 gene expression found in the peripheral blood of non-leukemic hematological diseases, except myelodysplasia. We were the first to examine the expression of different WT1 isoforms in the peripheral blood of children and we observed that the WT1 pattern is constant. We found that the 5 patients in the low-risk group expressed the 17AA(+) WT1 isoform, but 2 patients had the 17AA(-) WT1 isoform. We found the