Study on Clinical and Biological Characteristics of Childhood Acute Leukemia with MLL Gene Rearrangements.

The rearrangement of MLL gene is reported in 70%~80% of infant and in 5%~10% of older children (under the age of 15) with acute leukemia (AL). The biological features associated with alterations in MLL gene are hyperleukocytosis, CD10⁻/CD19⁺ phenotype and very poor prognosis. To explore the MLL rearrangement in details in our AL children patients and obtain more information on the relationship between the MLL gene abnormality and clinical outcomes. The following study has been conducted. A total of 298 patients with AL attended The Affiliated Children’s Hospital of Soochow University, including 16 cases with MLL rearrangements, were recruited in this study. Of the cohort, 11 were diagnosed as ALL, 5 were AML. 9 of 16 patients were in infant age (up to 2 year) and the rest were between the age of 2 to 13 years. Fluorescence in situ hybridization (FISH) analysis using LSI MLL dual color probe. Multiplex reverse transcriptase- polymerase chain reaction (multiplex RT-PCR) were used to discriminate 13 different fusion transcripts. These results were analyzed together with R banding karyotyping and immunolphenotyping determined by flow cytometry. We have found MLL rearrangements in 16 cases of childhood AL which were accounted for 5.4% of 298 AL patients, and 56.3% of infant AL. Among 106 cases analyzed by multiplex RT-PCR, MLL gene rearrangement was found in 11 cases, including MLL/AF4 fusion gene in 2, MLL/AF6 fusion gene in 1, MLL/AF6, MLL/ELL combined with MLL/AFX or HOX11 in one of each, MLL/AF9 in 2, MLL/AF10 in 1, MLL/ELL in 2. MLL partial tandem duplication in 1. In addition an activated HOX11 gene was found in 1 case.. In 27 cases assayed by FISH, MLL gene rearrangements have been detected in 9 cases (36.0%). In 16 patients with MLL gene rearrangements, 14 (87.5%) exhibited clonal chromosome abnormalities involved chromosome 11 in 11 cases, presenting as t(4;11) in 2, t(6;11), t(8;11), t(7;8;11), and t(9;11) in one of each, respectively, trisomy 11 in 2 and 11q- in 3 cases. Among these 16 patients, 11 were B-ALL, including Pro-B and Pre-B ALL; 5 of AML-M5, 3 of these 5 M5 patients were CD7⁺ and CD2⁺. Of these 16 patients 8 received chemotherapy and 7 of them achieved complete remission, while the other 8 patients eventually gave up treatment. Our results demonstrated that multiplex RT-PCR combined with FISH provided a more accurate and sensitive method for detection of MLL gene rearrangements, including chromosome translocation, deletion and duplication. Our findings lead to the detection of novel rearrangements at molecular genetic level. These findings regarding the MLL rearrangement provide most important information in guiding therapy and predicting prognosis in childhood AL. Besides our results also provide evidence in support of the value of 11q23/MLL in WHO classification categories.