The MLL recombinome of adult CD10-negative B-cell precursor acute lymphoblastic leukemia: results from the GMALL study group

Abstract

IntroductionMolecular aberrations involving the mixed lineage leukemia (MLL) gene on 11q23 are found in 5% to 10% of acute leukemia cases. 1 In B-cell precursor (BCP) acute lymphoblastic leukemia (ALL), these aberrations are largely restricted to the immature CD10 Ϫ immunophenotypes (pro-B and CD10 Ϫ pre-B). The translocation t(4;11)(q22;q23) with MLL-AF4 (MLL-AFF1) fusion is known to be the most prevalent MLL fusion gene in ALL, but precise and reliable data regarding the prevalence of the different MLL fusion partner genes, that is, the MLL "recombinome" in adult ALL are lacking. Knowledge of the MLL recombinome is warranted, since MLL fusions are of interest in detecting minimal residual disease in affected patients 2,3 and also because controversy exists over whether adult ALL patients with pro-B ALL immunophenotype with or without MLL aberration might have a different prognosis. [4][5][6] We report our experience within the framework of the German Multicenter Therapy Trials for Adult ALL (GMALL) between January 2001 and October 2007 at the central diagnostic laboratory of the GMALL study group.We investigated 184 patients with a CD10 Ϫ BCP immunophenotype by reverse transcription polymerase chain reactions (RT-PCRs) for different MLL fusion genes. Since the chromosomal breakpoints in the MLL gene cluster in a relatively restricted region between exons 8 and 13 (numbering according to Nilsson et al 7 ), encompassing approximately 8.2 kb, we additionally investigated all samples by a recently published long-distance inverse polymerase chain reaction (LDI-PCR) method that also allowed the identification of unknown MLL translocation partners at the DNA level. Methods Patient materialBone marrow (n ϭ 136) and peripheral blood (n ϭ 45) samples (n ϭ 3 samples unspecified) were obtained for diagnostic purposes within the framework of the GMALL therapy studies 6/99 and 7/03 between January 2001 and October 2007. A list of GMALL study participants appears in the Supplemental Materials and Methods (available on the Blood website; see the Supplemental Materials link at the top of the online article). All samples were taken at the time of primary diagnosis and had a high blast count, as revealed by flow cytometry. The genetic investigations were done retrospectively and prospectively on archived residual material. Preparation of samples, immunophenotyping, and all RT-PCR investigations were performed at the central diagnostic laboratory of the GMALL study group in Berlin. The samples were obtained within clinical studies that were approved by the institutional ethics committees of all participating institutions. The study design and our investigations were conducted in accordance with the Declaration of Helsinki. Nucleic acid isolation and reverse transcriptionTotal RNA was isolated using the TRIZOL method (Invitrogen, Carlsbad, CA) or the RNEasy kit (QIAGEN, Hilden, Germany). Genomic DNA was For personal use only. on May 12, 2018. by guest www.bloodjournal.org From isolated using the PureGene Kit (Gentra Systems, Mi...

TET2 gene mutation is a frequent and adverse event in chronic myelomonocytic leukemia

“…21,22 The MLL-TET1 fusion gene was also detected in two adults with CD10-negative Bcell precursor acute lymphoblastic leukemia 23 and a single nucleotide polymorphism in the TET1 gene coding region has been associated with late-onset Alzheimer's disease. 24 Recent evidence indicates that TET1, and possibly other proteins of the family, encodes an enzyme responsible for the conversion of 5-methylcytosine to 5-hydroxymethylcytosine, 19 thus having potential roles in CpG methylation pattern and epigenetic regulation.…”

The molecular biology of mixed lineage leukemia

“…Secondly, proteins joined to MLL clearly fall into two classes. Only 6 frequent partner proteins (AF4, AF9, ENL, AF10, ELL, AF6) constitute the bulk (> 85%) of all clinical cases of mixed lineage leukemia 65,66 (Table 1) whereas the remaining fusions were cloned each from a few isolated, mostly adult patients. This distinction is mirrored by the biology of the respective proteins.…”

Biochemistry of the Mixed Lineage Leukemia 1 (MLL1) Protein and Targeted Therapies for Associated Leukemia

“…Chromosomal translocations fuse the N-terminal part (~1400 amino acids) of the MLL1 protein in-frame to one of more than 60 partner proteins that range from nuclear factors to cytoplasmic proteins (Daser and Rabbitts, 2005;Huret et al, 2001;Schoch et al, 2003). The five most common MLL1 translocations include: MLL1-AF4 or t(4;11)(q21;q23); MLL1-ENL or t(11;19)(q23;p13.3); MLL1-AF9 or t(9;11)(p23;q23), MLL1-AF10 or t(10;11)(p12;q23), and MLL1-AF6 or t(6;11)(q27;q23) and account for greater than 80% of MLL1-rearranged leukemias (Burmeister et al, 2009;Meyer et al, 2009;Meyer et al, 2006;Slany, 2009). In addition, chimeric MLL1-fusions involving ELL, EEN, GAS7, AF1p, AFx, Septins, and histone acetyltransferases CBP/p300 have also been reported (Bernard et al, 1994;Dobson et al, 2000;Hall and Russell, 2004;Ida et al, 1997;Krivtsov and Armstrong, www.intechopen.com 2007; Meyer et al, 2009;Schichman et al, 1995;So et al, 2003;Taki et al, 1997;Tkachuk et al, 1992;Wang et al, 2005).…”

“…Furthermore, the endogenous ENL protein was purified as a part of a macromolecular complex (ENL associated protein complex or EAP) that also contains p-TEFb, DOT1 and AF4 and plays a putative role in transcriptional elongation (Bitoun et al, 2007;Mueller et al, 2007). Despite the fact that MLL1-AF4 translocations and MLL1-AF9/ENL fusions account for more than 50% of MLL1 11q23 associated leukemias (Burmeister et al, 2009;Meyer et al, 2009;Meyer et al, 2006), there exists no functional similarity between these MLL1 fusion partners. It is tempting to hypothesize that MLL1 fusion proteins might hijack the p-TEFb/DOT1 mediated transcriptional elongation activity or the SWI/SNF dependent nucleosome remodeling activity through the fusion partner and result in constitutive target gene expression leading to leukemia.…”