IGH@ translocations co-exist with other primary rearrangements in B-cell precursor acute lymphoblastic leukemia

Cytogenetics in the management of B-cell acute lymphoblastic leukemia: Guidelines from the Groupe Francophone de Cytogénétique Hématologique (GFCH)

Cytogenetic analysis is mandatory at initial assessment of B-cell acute lymphoblastic leukemia (B-ALL) due to its diagnostic and prognostic value. Results from chromosome banding analysis and complementary FISH are taken into account in therapeutic protocols and further completed by other techniques (RT-PCR, SNP-array, MLPA, NGS, OGM). Indeed, new genomic entities have been identified by NGS, mostly RNA sequencing, such as Ph-like ALL that can benefit from targeted therapy. Here, we have attempted to establish cytogenetic guidelines by reviewing the most recent published data including the novel 5th World Health Organization and International Consensus Classifications. We also focused on newly described cytogenomic entities and indicate alternative diagnostic tools such as NGS technology, as its importance is vastly increasing in the diagnostic setting.

Genomic landscape of Down syndrome-associated acute lymphoblastic leukemia

Trisomy 21, the genetic cause of Down syndrome (DS), is the most common congenital chromosomal anomaly. It is associated with a 20-fold increased risk of acute lymphoblastic leukemia (ALL) during childhood and results in distinctive leukemia biology. To comprehensively define the genomic landscape of DS-ALL, we performed whole-genome sequencing and whole-transcriptome sequencing (RNA-Seq) on 295 cases. Our integrated genomic analyses identified 15 molecular subtypes of DS-ALL, with marked enrichment of CRLF2-r, IGH::IGF2BP1, and C/EBP altered (C/EBPalt) subtypes compared with 2257 non-DS-ALL cases. We observed abnormal activation of the CEBPD, CEBPA, and CEBPE genes in 10.5% of DS-ALL cases via a variety of genomic mechanisms, including chromosomal rearrangements and noncoding mutations leading to enhancer hijacking. A total of 42.3% of C/EBP-activated DS-ALL also have concomitant FLT3 point mutations or insertions/deletions, compared with 4.1% in other subtypes. CEBPD overexpression enhanced the differentiation of mouse hematopoietic progenitor cells into pro-B cells in vitro, particularly in a DS genetic background. Notably, recombination-activating gene-mediated somatic genomic abnormalities were common in DS-ALL, accounting for a median of 27.5% of structural alterations, compared with 7.7% in non-DS-ALL. Unsupervised hierarchical clustering analyses of CRLF2-rearranged DS-ALL identified substantial heterogeneity within this group, with the BCR::ABL1-like subset linked to an inferior event-free survival, even after adjusting for known clinical risk factors. These results provide important insights into the biology of DS-ALL and point to opportunities for targeted therapy and treatment individualization.

C/EBPβ induces B-cell acute lymphoblastic leukemia and cooperates with BLNK mutations

BLNK (BASH/SLP‐65) encodes an adaptor protein that plays an important role in B‐cell receptor (BCR) signaling. Loss‐of‐function mutations in this gene are observed in human pre‐B acute lymphoblastic leukemia (ALL), and a subset of Blnk knock‐out (KO) mice develop pre‐B‐ALL. To understand the molecular mechanism of the Blnk mutation‐associated pre‐B‐ALL development, retroviral tagging was applied to KO mice using the Moloney murine leukemia virus (MoMLV). The Blnk mutation that significantly accelerated the onset of MoMLV‐induced leukemia and increased the incidence of pre‐B‐ALL Cebpb was identified as a frequent site of retroviral integration, suggesting that its upregulation cooperates with Blnk mutations. Transgenic expression of the liver‐enriched activator protein (LAP) isoform of Cebpb reduced the number of mature B‐lymphocytes in the bone marrow and inhibited differentiation at the pre‐BI stage. Furthermore, LAP expression significantly accelerated leukemogenesis in Blnk KO mice and alone acted as a B‐cell oncogene. Furthermore, an inverse relationship between BLNK and C/EBPβ expression was also noted in human pre‐B‐ALL cases, and the high level of CEBPB expression was associated with short survival periods in patients with BLNK‐downregulated pre‐B‐ALL. These results indicate the association between the C/EBPβ transcriptional network and BCR signaling in pre‐B‐ALL development and leukemogenesis. This study gives insight into ALL progression and suggests that the BCR/C/EBPβ pathway can be a therapeutic target.

RNA methylation in hematological malignancies and its interactions with other epigenetic modifications

Hematological malignancies are a class of malignant neoplasms attributed to abnormal differentiation of hematopoietic stem cells (HSCs). The systemic involvement, poor prognosis, chemotherapy resistance, and recurrence common in hematological malignancies urge researchers to look for novel treatment targets and mechanisms. In recent years, epigenetic abnormalities have been shown to play a vital role in tumorigenesis and progression in hematological malignancies. In addition to DNA methylation and histone modifications, which are most studied, RNA methylation has become increasingly significant. In this review, we elaborate recent advances in the understanding of RNA modification in the pathogenesis, diagnosis and molecular targeted therapies of hematological malignancies and discuss its intricate interactions with other epigenetic modifications, including DNA methylation, histone modifications and noncoding RNAs.

Therapy-induced Deletion in 11q23 Leading to Fusion of KMT2A With ARHGEF12 and Development of B Lineage Acute Lymphoplastic Leukemia in a Child Treated for Acute Myeloid Leukemia Caused by t(9;11)(p21;q23)/KMT2A-MLLT3

BACKGROUND/AIM

Fusion of histone-lysine N-methyltransferase 2A gene (KMT2A) with the Rho guanine nucleotide exchange factor 12 gene (ARHGEF12), both located in 11q23, was reported in some leukemic patients. We report a KMT2A-ARHGEF12 fusion occurring during treatment of a pediatric acute myeloid leukemia (AML) with topoisomerase II inhibitors leading to a secondary acute lymphoblastic leukemia (ALL).

MATERIALS AND METHODS

Multiple genetic analyses were performed on bone marrow cells of a girl initially diagnosed with AML.

RESULTS

At the time of diagnosis with AML, the t(9;11)(p21;q23)/KMT2A-MLLT3 genetic abnormality was found. After chemotherapy resulting in AML clinical remission, a 2 Mb deletion in 11q23 was found generating a KMT2A-ARHGEF12 fusion gene. When the patient later developed B lineage ALL, a t(14;19)(q32;q13), loss of one chromosome 9, and KMT2A-ARHGEF12 were detected.

CONCLUSION

The patient sequentially developed AML and ALL with three leukemia-specific genomic abnormalities in her bone marrow cells, two of which were KMT2A-rearrangements.

Recurrent genetic abnormalities detected by FISH in adult B ALL and association with hematological parameters

Background

Recurrent genetic abnormalities influence prognosis in B lymphoblastic leukemia. BCR‐ABL rearrangement is associated with higher leukocyte counts and older age at presentation. Among adults, BCR ‐ABL ‐ is the commonest recurrent abnormality whereas, IgH rearrangements are rare.

Aim

Aim of this study was to identify common recurrent genetic abnormalities in adult B ALL and study their association with hematological findings.

Methods

Bone marrow and peripheral blood from patients with B acute lymphoblastic leukemia were analyzed for complete blood counts, bone marrow morphology and cytogenetic abnormalities. The study group was divided into smaller groups based on cytogenetic abnormalities. Hematological parameters and presence of recurrent genetic abnormalities was compared across age groups and gender by non parametric tests.

Results

BCR‐ABL positive group had a higher leukocyte count than BCR‐ABL negative group. Among groups 1 to 5, group 1 with gains of chromosomes was associated with leucopenia and higher age at presentation. BCR‐ABL is commonest recurrent abnormality followed by IgH rearrangements.

Conclusion

Patients with gains of chromosomes alone have low total leukocyte counts at presentation.

Proteogenomics and Hi-C reveal transcriptional dysregulation in high hyperdiploid childhood acute lymphoblastic leukemia

Hyperdiploidy, i.e. gain of whole chromosomes, is one of the most common genetic features of childhood acute lymphoblastic leukemia (ALL), but its pathogenetic impact is poorly understood. Here, we report a proteogenomic analysis on matched datasets from genomic profiling, RNA-sequencing, and mass spectrometry-based analysis of >8,000 genes and proteins as well as Hi-C of primary patient samples from hyperdiploid and ETV6/RUNX1-positive pediatric ALL. We show that CTCF and cohesin, which are master regulators of chromatin architecture, display low expression in hyperdiploid ALL. In line with this, a general genome-wide dysregulation of gene expression in relation to topologically associating domain (TAD) borders were seen in the hyperdiploid group. Furthermore, Hi-C of a limited number of hyperdiploid childhood ALL cases revealed that 2/4 cases displayed a clear loss of TAD boundary strength and 3/4 showed reduced insulation at TAD borders, with putative leukemogenic effects.

Single-cell analysis identifies CRLF2 rearrangements as both early and late events in Down syndrome and non-Down syndrome acute lymphoblastic leukaemia

Deregulated expression of the type I cytokine receptor, CRLF2, is observed in 5-15% of precursor B-cell acute lymphoblastic leukaemia (B-ALL). We have previously reported the genomic landscape of patients with CRLF2 rearrangements (CRLF2-r) using both whole genome and exome sequencing, which identified a number of potential clonal and sub-clonal genomic alterations. In this study, we aimed to assess when the CRLF2-r; IGH-CRLF2 or P2RY8-CRLF2, arose during the evolution of both Down syndrome-ALL (DS-ALL) and non-DS-ALL. Using fluorescence in situ hybridisation, we were able to track up to four structural variants in single cells from 47 CRLF2-r B-ALL patients, which in association with our multiplex single cell analysis of a further four patients, permitted simultaneous tracking of copy number alterations, structural and single nucleotide variants within individual cells. We observed CRLF2-r arising as both early and late events in DS and non-DS-ALL patients. Parallel evolution of discrete clones was observed in the development of CRLF2-r B-ALL, either involving the CRLF2-r or one of the other tracked abnormalities. In depth single cell analysis identified both linear and branching evolution with early clones harbouring a multitude of abnormalities, including the CRLF2-r in DS-ALL patients.

Impact of cytogenetic abnormalities in adults with Ph-negative B-cell precursor acute lymphoblastic leukemia

Multiple cytogenetic subgroups have been described in adult Philadelphia chromosome (Ph)-negative B-cell precursor (BCP) acute lymphoblastic leukemia (ALL), often comprising small numbers of patients. In this study, we aimed to reassess the prognostic value of cytogenetic abnormalities in a large series of 617 adult patients with Ph-negative BCP-ALL (median age, 38 years), treated in the intensified Group for Research on Adult Acute Lymphoblastic Leukemia (GRAALL)-2003/2005 trials. Combined data from karyotype, DNA index, fluorescence in situ hybridization, and polymerase chain reaction screening for relevant abnormalities were centrally reviewed and were informative in 542 cases (88%), allowing classification in 10 exclusive primary cytogenetic subgroups and in secondary subgroups, including complex and monosomal karyotypes. Prognostic analyses focused on cumulative incidence of failure (including primary refractoriness and relapse), event-free survival, and overall survival. Only 2 subgroups, namely t(4;11)/KMT2A-AFF1 and 14q32/IGH translocations, displayed a significantly worse outcome in this context, still observed after adjustment for age and after censoring patients who received allogeneic stem cell transplantation (SCT) in first remission at SCT time. A worse outcome was also observed in patients with low hypodiploidy/near triploidy, but this was likely related to their higher age and worse tolerance to therapy. The other cytogenetic abnormalities, including complex and monosomal karyotypes, had no prognostic value in these intensive protocols designed for adult patients up to the age of 60 years.

Characterisation of the genomic landscape of CRLF2-rearranged acute lymphoblastic leukemia

Deregulated expression of the type I cytokine receptor, CRLF2, is observed in 5-15% of precursor B-cell acute lymphoblastic leukaemia (B-ALL). We aimed to determine the clinical and genetic landscape of those with IGH-CRLF2 or P2RY8-CRLF2 (CRLF2-r) using multiple genomic approaches. Clinical and demographic features of CRLF2-r patients were characteristic of B-ALL. Patients with IGH-CRLF2 were older (14 y vs. 4 y, P < .001), while the incidence of CRLF2-r among Down syndrome patients was high (50/161, 31%). CRLF2-r co-occurred with primary chromosomal rearrangements but the majority (111/161, 69%) had B-other ALL. Copy number alteration (CNA) profiles were similar to B-other ALL, although CRLF2-r patients harbored higher frequencies of IKZF1 (60/138, 43% vs. 77/1351, 24%) and BTG1 deletions (20/138, 15% vs. 3/1351, 1%). There were significant differences in CNA profiles between IGH-CRLF2 and P2RY8-CRLF2 patients: IKZF1 (25/35, 71% vs. 36/108, 33%, P < .001), BTG1 (11/35, 31% vs. 10/108, 9%, P =.004), and ADD3 deletions (9/19, 47% vs. 5/38, 13%, P =.008). A novel gene fusion, USP9X-DDX3X, was discovered in 10/54 (19%) of patients. Pathway analysis of the mutational profile revealed novel involvement for focal adhesion. Although the functional relevance of many of these abnormalities are unknown, they likely activate additional pathways, which may represent novel therapeutic targets.

Recurrent Cytogenetic Abnormalities in Acute Lymphoblastic Leukemia

Both B-cell and T-cell acute lymphoblastic leukemia (ALL) exhibit recurrent cytogenetic alterations, many with prognostic implications. This chapter overviews the major recurrent categories of cytogenetic abnormalities associated with ALL, with an emphasis on the detection and characterization of these cases by G-band and FISH analyses.

ETV6/RUNX1 transcript is a target of RNA-binding protein IGF2BP1 in t(12;21)(p13;q22)-positive acute lymphoblastic leukemia

The oncofetal RNA-binding protein IGF2BP1 (IGF2 mRNA binding protein 1) is overexpressed in a subset of cancers and promotes cell cycle, migration and aggressive phenotype by regulating post-transcriptionally a number of key mRNAs (e. g, ACTB, CD44, CTNNB1, KRAS, MAPK4, MYC, PTEN and others). IGF2BP1 is also overexpressed in t(12;21)(p13;q22)-positive acute lymphoblastic leukemia (ALL), but the biological significance of this phenomenon has not been addressed so far. We have identified leukemia fusion gene ETV6/RUNX1 mRNA to be highly enriched in immunoprecipitated fraction of endogenous IGF2BP1 from a model cell line REH and t(12;21)(p13;q22)-positive ALL samples. Furthermore, downregulation of IGF2BP1 by two-fold has resulted in a corresponding decrease of ETV6/RUNX1 mRNA validating this transcript as a target of IGF2BP1 protein in t(12;21)(p13;q22)-positive ALL. These data infer that IGF2BP1 is a potent regulator of ETV6/RUNX1 mRNA stability and potentially link this evolutionary-highly conserved protein to cell transformation events in ETV6/RUNX1-mediated leukemogenesis of t(12;21)(p13;q22)-positive ALL.

Cytogenetic and Molecular Findings in Children with Acute Lymphoblastic Leukemia: Experience of a Single Institution in Argentina

The purpose of the current study was to evaluate the cytogenetic findings in 1,057 children with acute lymphoblastic leukemia (ALL) referred to the cytogenetics laboratory at the Hospital de Pediatría Dr. Juan P. Garrahan, between 1991 and 2014. Chromosomal abnormalities were evaluated by G-banding and FISH. Since December 2002, RT-PCR determinations were systematically carried out for BCR-ABL1, KMT2A-AFF1, ETV6-RUNX1, and TCF3-PBX1 rearrangements in children, adding KMT2A-MLLT3 and KMT2A-MLLT1 in infants. The percentage of abnormalities detected by cytogenetics was 70.1%. Four novel abnormalities, t(2;8)(p11.2;p22), inv(4)(p16q25), t(1;7)(q25;q32), and t(5;6)(q21;q21), were found in this cohort. We compared cytogenetic and RT-PCR results for BCR-ABL1, KMT2A-AFF1 and TCF3-PBX1 rearrangements in 497 children evaluated by both methods. The results were highly concordant (p < 0.7), and interestingly, FISH was relevant to confirm G-banding findings that were discordant with RT-PCR studies. This study showed the importance of performing G-banding, FISH and RT-PCR simultaneously to improve the detection of chromosomal abnormalities considering their important value in the diagnosis and prognosis of childhood ALL patients. Finally, to the best of our knowledge, this is the first series of cytogenetic findings in children with ALL reported in Argentina.