QUANTITATIVE ASSESSMENT OF WT1 EXPRESSION FOR MONITORING MINIMAL RESIDUAL DISEASE IN ACUTE LEUKEMIA PATIENTS
I Shmunk,1 E Koneva,1 M Lyubchenko,2 M Rusakov,2 M Kiseleva,2
Y Markova,2 M Zakharova,2 O Korobitsina,2 A Korobkin,2
Wilms’ tumor 1 (WT1) gene encodes a transcriptional factor involved in normal cellular development and is abnormally expressed in many types of haematological malignancies. It is over-expressed in most cases of acute myeloid leukemia (AML). Aims. Our study aims to estimate the usefulness of WT1 expression quantitative assessment for monitoring MRD and for relapse prediction in acute myeloid leukemia and in acute lymphoblastic leukemia (ALL). Methods. Real time quantitative RT-PCR was made according to the Europe Against Cancer Protocol. WT1 transcript level was determined in BM samples of adult patients with AML (except acute promyelocytic leukemia) and ALL. We examined the samples of 65 patients with AML and 33 patients with ALL at diagnosis. We also analyzed 106 specimens of AML patients and 100 specimens of ALL patients during follow-up. The obtained WT1 values were normalized with respect to the βGUS transcripts. Results. The median value of WT1 levels at diagnosis was 649 (range 1,6-8462) in AML patients and 1188 (range 1,5-14879) in ALL patients (no statistical difference in Student’s t-test). The median value of WT1 levels of patients in complete remission was 4,3 (range 1,1-9,7) for AML and 7,5 (range 1,0-36,5) for ALL (P=0,05) . At diagnosis 91% of AML patients and 61% of ALL patients showed the expression of WT1 one log higher than the median values in complete remission. There were 2 patients (10%) with BCR-ABL (one p190 and one p210) within the ALL subgroup with high WT1 expression at diagnosis whereas within the ALL patients with low WT1 expression at diagnosis were 7 ones (54%) with BCR-ABL (6 patients with p190 and 1 with p210) (10% versus 54%, P=0,02 in chi-sguare test with Yate’s correction). We had 6 patients with T-ALL, all of them showed the over-expression of WT1 at diagnosis. In the patients bearing a fusion gene transcript we performed a simultaneous analysis of WT1 and fusion-gene transcript expression: in 15 patients with AML (7 AML1-ETO, 1 CBFβ-MYH11, 2 BCR-ABL, 1 DEK-CAN, 4 MLL duplications) and in 15 patients with ALL (9 BCR-ABL, 3 MLL-AF4, 1 MLL-ENL, 2 E2A-PBX1). It was found the parallelism between the dynamics of WT1 level and fusion-gene transcript level during follow-up. The haematological relapse was correlated with the increase of WT1 expression: 8 AML patients had a median of 1545 (range 140-2578) and for 7 ALL patients a median value was 263 (range 8,0-2665) in relapse (no statistical difference in Mann-Whitney U test). We observed that the increase of WT1 level was occurred earlier than the relapse was stated for AML patients and also for ALL patients with high WT1 expression at diagnosis. Except one AML patient with BCR-ABL (p190): the increase of fusion gene expression was occurred in haematological remission without the increase of WT1 level. Conclusion. Quantitative assessment of WT1 expression may be useful for detection of MRD and can predict imminent relapse during follow-up in patients without additional molecular markers in AML and in ALL with high WT1 expression at diagnosis.