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.

The results of allogeneic hematopoietic stem cell transplantation (alloHSCT) in 10 pediatric patients (4 boys, 6 girls at the age of 4 to 17 years, mean age is 9.8 years) with relapses of acute lymphoblastic leukemia (ALL) with TEL-AMLI fusion gene are presented. The first remission duration ranged from 20 to 70 months (mean duration 39.9 months). Transplantation was performed in 6 patients during the second (and further) remission, whereas 4 patients underwent transplantation during the relapse. Six patients received a graft from matched related (n = 3) or unrelated (n = 3) donors, haploidentical HSCT was performed in four other patients because there was no donor. Conditioning regimens were myeloablative in 8 cases and RIC (Reduced Intensity Conditioning) in 2 cases. Successful engrafting took place in 9 (90 %) of 10 patients. Additional haploidentical transplantation was performed in 1 case, when the transplant was rejected. Monitoring of treatment was performed by means of serial testing of TEL-AMLI fusion gene expression level, of serial donor chimerism and the blast cell count in bone marrow and peripheral blood. The study demonstrated that four patients younger than 4 years had TEL-AML1 gene expression at all stages of their disease, including preand post-transplantation period. Due to it, even the donor chimerism and blast cell count in bone marrow and/or peripheral blood changed. On the contrary, in 3 more patients, TEL-AML1 gene expression levels were low before alloHSCT, being absent after HSCT. In general, seven patients have been monitored for 178-2627 days (at the average of 870 days) including two patients with post-transplant relapses. At the same time, 3 patients died on days 20-263 after transplantation. The observed difference in response to chemotherapy might be supposedly explained by involvement of not only hematopoietic, but also mesenchymal cells into the leukemic process (this fact was demonstrated for this group of patients by S. Shalapour et al., 2010). But this fact should be confirmed in further studies.

We present the case of successful treatment of posttransplantation relapse of prognostically unfavorable AML with inv(3)(q21q26), -7 and EVI1 oncogene overexpression, when stable donor hematopoiesis reconstitution was achieved due to one high-dose cytarabine course, DLI, and hypomethylating agents (decitabine, 5-azacitidine). Possible molecular mechanisms of this effect are discussed with respect to the new approaches to management of such patients.