The MLL recombinome of acute leukemias in 2017.

Chromosomal rearrangements of the human MLL/KMT2A gene are associated with infant, pediatric, adult and therapy-induced acute leukemias. Here we present the data obtained from 2345 acute leukemia patients. Genomic breakpoints within the MLL gene and the involved translocation partner genes (TPGs) were determined and 11 novel TPGs were identified. Thus, a total of 135 different MLL rearrangements have been identified so far, of which 94 TPGs are now characterized at the molecular level. In all, 35 out of these 94 TPGs occur recurrently, but only 9 specific gene fusions account for more than 90% of all illegitimate recombinations of the MLL gene. We observed an age-dependent breakpoint shift with breakpoints localizing within MLL intron 11 associated with acute lymphoblastic leukemia and younger patients, while breakpoints in MLL intron 9 predominate in AML or older patients. The molecular characterization of MLL breakpoints suggests different etiologies in the different age groups and allows the correlation of functional domains of the MLL gene with clinical outcome. This study provides a comprehensive analysis of the MLL recombinome in acute leukemia and demonstrates that the establishment of patient-specific chromosomal fusion sites allows the design of specific PCR primers for minimal residual disease analyses for all patients.

[THE COMPARISON OF RESULTS OF DETECTION OF MINIMAL RESIDUAL DISEASE IN PERIPHERAL BLOOD AND MARROW IN CHILDREN OF THE FIRST YEAR OF LIFE WITH ACUTE LYMPHOBLASTIC LEUCOSIS].

The occurrence of minimal residual disease is an important prognostic factor under acute lymphoblastic leucosis in children and adults. In overwhelming majority of research studies bone marrow is used to detect minimal residual disease. The comparative characteristic of detection of minimal residual disease in peripheral blood and bone marrow was carried out. The prognostic role of occurrence of minimal residual disease in peripheral blood and bone marrow under therapy according protocol MLL-Baby was evaluated. The analysis embraced 142 pair samples from 53 patients with acute lymphoblastic leucosis and various displacements of gene MLL younger than 365 days. The minimal residual disease was detected by force of identification of chimeric transcripts using polymerase chain reaction in real-time mode in 7 sequential points of observation established by protocol of therapy. The comparability of results of qualitative detection of minimal residual disease in bone marrow and peripheral blood amounted to 84.5%. At that, in all 22 (15.5%) discordant samples minimal residual disease was detected only in bone marrow. Despite of high level of comparability of results of detection of minimal residual disease in peripheral blood and bone marrow the occurrence of minimal residual disease in peripheral blood at various stages of therapy demonstrated no independent prognostic significance. The established differences had no relationship with sensitivity of method determined by value of absolute expression of gene ABL. Most likely, these differences reflected real distribution of tumor cells. The results of study demonstrated that application of peripheral blood instead of bone marrow for monitoring of minimal residual disease under acute lymphoblastic leucosis in children of first year of life is inappropriate. At the same time, retention of minimal residual disease in TH4 in bone marrow was an independent and prognostic unfavorable factor under therapy of acute lymphoblastic leucosis of children of first year of life according protocol MLL-Baby (OO=7.326, confidence interval 2.378-22.565).

The MLL recombinome of acute leukemias in 2013.

Chromosomal rearrangements of the human MLL (mixed lineage leukemia) gene are associated with high-risk infant, pediatric, adult and therapy-induced acute leukemias. We used long-distance inverse-polymerase chain reaction to characterize the chromosomal rearrangement of individual acute leukemia patients. We present data of the molecular characterization of 1590 MLL-rearranged biopsy samples obtained from acute leukemia patients. The precise localization of genomic breakpoints within the MLL gene and the involved translocation partner genes (TPGs) were determined and novel TPGs identified. All patients were classified according to their gender (852 females and 745 males), age at diagnosis (558 infant, 416 pediatric and 616 adult leukemia patients) and other clinical criteria. Combined data of our study and recently published data revealed a total of 121 different MLL rearrangements, of which 79 TPGs are now characterized at the molecular level. However, only seven rearrangements seem to be predominantly associated with illegitimate recombinations of the MLL gene (≈ 90%): AFF1/AF4, MLLT3/AF9, MLLT1/ENL, MLLT10/AF10, ELL, partial tandem duplications (MLL PTDs) and MLLT4/AF6, respectively. The MLL breakpoint distributions for all clinical relevant subtypes (gender, disease type, age at diagnosis, reciprocal, complex and therapy-induced translocations) are presented. Finally, we present the extending network of reciprocal MLL fusions deriving from complex rearrangements.

Drug resistance associated properties of blasts subpopulations with different CD34 expression in childhood acute lymphoblastic leukemia (ALL).

AIM: The objective of this study was to investigate expression of drug resistance associated genes in CD34+ and CD34- leukemic subpopulations in childhood acute lymphoblastic leukemia (ALL). METHODS: ALL samples with heterogeneous CD34 expression were separated into CD34-positive and CD34-negative subpopulations and mRNA levels of MDR1, LRP, BCRP and BCL-2 genes were compared. RESULTS: BCL-2 gene expression levels did not differ significantly between CD34+ vs CD34- subpopulations in most analyzed ALL cases. Oppositely, MDR1 gene had >two-fold differences in expression levels between subpopulations in the majority of ALL cases. In T-lineage ALL CD34- fractions had increased level of BCRP and LRP genes in comparison with CD34+ ones whereas in most of B-lineage ALL expression of these genes did not differ. CONCLUSION: It was not found the unique pattern of resistance related genes expression in CD34+ vs CD34- subpopulations. However, in majority of studied pediatric ALL cases with CD34 heterogeneous expression one of subpopulations (positive or negative) could have an advantage for survival through elevated expression of drug resistance related genes.

DNA-PK, ATM and MDR proteins inhibitors in overcoming fludarabine resistance in CLL cells.

AIM: To perform the comparative study of the effects of DNA-dependent protein kinase (DNA-PK) inhibitors vanillin and NU7026, ataxia telangiectasia mutated kinase (ATM)/ ATM and Rad3 related (ATR) kinase inhibitor caffeine and multidrug resistance (MDR) protein modulator cyclosporine A (CsA) on fludarabine resistant and sensitive lymphocytes from chronic lymphocytic leukemia (CLL) patients. METHODS: Cells sensitivity in vitro was determined with 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT). DNA-PKs and ATM expression in CLL cells was evaluated using Western blotting. Multidrug tansporter protein expression and function was assessed by flow cytometry. Pro- or anti-apoptotic genes (BAX, LICE BCL-2, BCL-XS FLICE, FAS, TRAIL) expression on mRNA level was evaluated. RESULTS: Caffeine, vanillin, NU7026 and CsA increased fludarabine cytotoxicity against fludarabine-resistant CLL cells samples in comparison with sensitive cell samples. However, fludarabine-sensitive CLL samples were sensitized with inhibitors to a greater extent compared with resistant CLL samples. ATM expression increased in fludarabine-resistant CLL samples, but no apparent correlation between DNA-PKs level and fludarabine sensitivity in vitro or sensitization effect of DNA-PK inhibitors were observed. Fludarabine-resistant CLL lymphocytes showed tendency for depressed MDR efflux and decreased level of mRNA of pro-apoptotic gene BCL-XS. CONCLUSION: Absence of any definite conformity between fludarabine-resistant cell susceptibility to combined action of fludarabine and inhibitors, and molecular pathways that might be involved in this process does not exclude drugs synergy in fludarabine-resistant cells that could be used for overcoming resistance to nucleoside analogs in CLL.

Growth kinetics and self-renewal of human mesenchymal stem cells derived from bone marrow of children with oncohematological diseases during expansion in vitro.

AIM: We investigated the ability of mesenchymal stem cells (MSCs) derived from bone marrow (BM) of children with oncohematological diseases after chemotherapy and radiation therapy to the self-renewal and proliferation for further expansion and their implementation as co-transplant, together with autologous hemopoietic stem cells (HSCs). MATERIALS AND METHODS: BM samples from 20 patients with tumors and BM samples from healthy children-donors (for allogenic HSCs transplantation) were under study. The colony forming unit-fibroblast (CFU-F) assay and the colony forming unit-granulocytes and macrophages (CFU-GM) assay were used for the evaluation of MSCs and HSCs proliferative capacity. Mononuclear cells (MNCs) were plated 1 x 10(6). Following 14 days cells subcultured in primary culture (I passage) to study MSCs ability to self-renewal in culture. 6 passages were performed. The population doubling (PD) in each passage and the cumulative population doubling were calculated. RESULTS: Data revealed 3-4-fold reduction of the mean incidence of CFU-F in patients after treatment compared to donors. The number of CFU-GM in patients was lower than in donors as well (39.0, 9.0-130.0 vs 95.0, 31-205). Correlation between numbers of CFU-F and CFU-GM was revealed in patients BM (r = 0.63, p < 0.003) as well as in healthy children. MSCs from BM possessed high potential to self-renewal. Their number increased 900-fold in primary cultures in the first 14 days and 17-fold in subculture in 60 days. The analysis of cumulative PD in patients and donors demonstrated the slowing of cell proliferation and telomere length decrease from passage to passage. CONCLUSION: Despite the low content MSCs from BM of children with oncohematological diseases possessed high potential to self-renewal. The total number of MSCs can be increased 1.5 x 10(4) fold in 2 months period in vitro.