In patients with acute leukemia, Wilms' tumor gene 1 (WT1) has been used as a target for the detection of minimal residual disease (MRD) by PCR techniques. The expression of WT1 protein, however, has not been extensively studied. To determine the relation between expression of WT1 transcripts and of the encoded protein, we examined leukemic cell lines and primary childhood leukemia samples using both real-time quantitative PCR (RQ-PCR) and flow cytometry. WT1 protein was highly expressed in the leukemic cell lines K562, HL-60, PLB 985, KG-1a and CEM. By contrast, 40 primary samples of acute lymphoblastic leukemia (ALL; B-ALL, n = 15 and T-ALL, n = 10) and acute myeloid leukemia (n = 15) expressed low levels of WT1 protein. RQ-PCR detected WT1 transcript levels in the same range as reported in earlier studies in childhood acute leukemia. The results of this study indicate the following: (i) there are considerable discrepancies between WT1 transcripts and protein expression; (ii) WT1 is not a suitable marker for flow cytometric MRD detection in childhood acute leukemia.
