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This article presents data demonstrating frequent BAALC hyperexpression, also in combination with WT1 hyperexpression, in children and adults with acute myeloid leukemia (AML). Treatment included allogeneic hematopoietic stem cell transplantation. The analysis of serial measurements of BAALC and WT1 expression level in 50 AML patients (37 adults and 13 children) showed that the increased BAALC expression is more common in patients with M1, M2, M4, and M5 FAB variants of AML with equal frequency in adults and children. Furthermore, the increased BAALC expression was rather common in combination with the increased WT1 expression, which predicted poorer prognosis. Since BAALC expression level in AML patients is closely related to AMLproducing progenitor cells of leukemia hemato poiesis, a serial study of this phenomenon off ers insights into the role of these cells in emergence and development of post-transplantation relapses, which is of both theoretical and practical importance.

Aim. To estimate the efficacy of chemotherapy in acute leukemia patients resistant to previous standard treatment according to the series measurement of WT1 expression. Materials & Methods. The series measurement of WT1 expression formed the basis of the efficacy estimation of induction chemotherapy in 31 patients (15 men and 16 women aged from 3 months to 68 years; the median age was 28 years) with prognostically unfavourable variants of acute myeloid (AML) and lymphoblastic leukemia (ALL) (23 AML and 8 ALL patients). The WT1 gene expression was measured at baseline and 2-3 weeks after the treatment by the quantitative real-time PCR. The threshold level for detection was 250 copies of WT1/10⁴ copies of ABL. The cytogenetic profile of leukemia cells was assessed by standard cytogenetics and FISH. Results. The baseline expression level of WT1 varied from 305 to 58,569 copies/10⁴ copies of ABL. The expected reduction of WT1 expression after the first induction chemotherapy treatment was reported in 22/23 (96 %) AML patients and in 6/8 (75 %) ALL patients. According to our results WT1 expression reached the threshold in 13/31 (42 %) patients, including 9 AML patients and 4 ALL patients. After 11/31 (35 %) patients received the second course of treatment, WT1 expression level became normal in 8 cases (5 ALL and 3 AML patients). Despite high dose chemotherapy, HSCT and such agents as blinatumomab and gemtuzumab, an unfavourable outcome was observed in 18/31 (58 %) patients including 6 patients with complex karyotype (CK+) and 2 patients with monosomal karyotype (MK+). Once the MK+ and CK+ combination was observed, in another case the MK+ was combined with the prognostically unfavourable inv(3)(q21q26) inversion. Conclusion. Our results show that the molecular monitoring should be included as part of treatment of the prognostically unfavourable acute leukemia. The WT1 gene was shown to be the most appropriate marker. WT1 expression was shown to correlate with the common fusion genes allowing to estimate the blast cell count at the molecular level.