Genome-wide copy number profiling reveals molecular evolution from diagnosis to relapse in childhood acute lymphoblastic leukemia

CREBBP is a Major Prognostic Biomarker for Relapse in Childhood B-cell Acute Lymphoblastic Leukemia: A National Study of Unselected Cohort

Although the identification of disease subtypes conveying prognostic significance along with minimal residual disease (MRD) assessment represent cornerstones for stratification in childhood acute lymphoblastic leukemia (ALL), approximately half of the relapses occur in patients from standard-risk groups. Identification of the drivers of treatment failure is crucial for detection of high-risk clones at diagnosis. We evaluated clinical variables and the most common genetic alterations in an unselected cohort of 55 patients with B-ALL treated according to the ALL-IC-BFM 2002 protocol, with a median follow-up of 46 months. Matched diagnosis-relapse samples underwent screening for additional alterations using whole-exome sequencing. Mutations in the CREBBP gene were found in 80% (4/5) of the patients with relapse, either present from the disease onset or acquired at relapse, while none of the examined patients in remission presented alterations in this gene. Deletions in TP53 and EBF1 (present in 2/5 and 1/5 of the patients with relapse, respectively) were infrequent or absent in the patients in remission, respectively. Screening for alterations in the CREBBP gene at diagnosis and/or at multiple time-points during chemotherapy could be incorporated into treatment protocols, as it may contribute to the identification of significant number of patients with predefined or acquired chemoresistant clones.

Molecular and cellular mechanisms of chemoresistance in paediatric pre-B cell acute lymphoblastic leukaemia

Paediatric patients with relapsed B cell acute lymphoblastic leukaemia (B-ALL) have poor prognosis, as relapse-causing clones are often refractory to common chemotherapeutics. While the molecular mechanisms leading to chemoresistance are varied, significant evidence suggests interactions between B-ALL blasts and cells within the bone marrow microenvironment modulate chemotherapy sensitivity. Importantly, bone marrow mesenchymal stem cells (BM-MSCs) and BM adipocytes are known to support B-ALL cells through multiple distinct molecular mechanisms. This review discusses the contribution of integrin-mediated B-ALL/BM-MSC signalling and asparagine supplementation in B-ALL chemoresistance. In addition, the role of adipocytes in sequestering anthracyclines and generating a BM niche favourable for B-ALL survival is explored. Furthermore, this review discusses the role of BM-MSCs and adipocytes in promoting a quiescent and chemoresistant B-ALL phenotype. Novel treatments which target these mechanisms are discussed herein, and are needed to improve dismal outcomes in patients with relapsed/refractory disease.

Clonal evolution of the 3D chromatin landscape in patients with relapsed pediatric B-cell acute lymphoblastic leukemia

Relapsed pediatric B-cell acute lymphoblastic leukemia (B-ALL) remains one of the leading causes of cancer mortality in children. We performed Hi-C, ATAC-seq, and RNA-seq on 12 matched diagnosis/relapse pediatric leukemia specimens to uncover dynamic structural variants (SVs) and 3D chromatin rewiring that may contribute to relapse. While translocations are assumed to occur early in leukemogenesis and be maintained throughout progression, we discovered novel, dynamic translocations and confirmed several fusion transcripts, suggesting functional and therapeutic relevance. Genome-wide chromatin remodeling was observed at all organizational levels: A/B compartments, TAD interactivity, and chromatin loops, including some loci shared by 25% of patients. Shared changes were found to drive the expression of genes/pathways previously implicated in resistance as well as novel therapeutic candidates, two of which (ATXN1 and MN1) we functionally validated. Overall, these results demonstrate chromatin reorganization under the selective pressure of therapy and offer the potential for discovery of novel therapeutic interventions.

SETD2 mutations do not contribute to clonal fitness in response to chemotherapy in childhood B cell acute lymphoblastic leukemia

Mutations in genes encoding epigenetic regulators are commonly observed at relapse in B cell acute lymphoblastic leukemia (B-ALL). Loss-of-function mutations in SETD2, an H3K36 methyltransferase, have been observed in B-ALL and other cancers. Previous studies on mutated SETD2 in solid tumors and acute myelogenous leukemia support a role in promoting resistance to DNA damaging agents. We did not observe chemoresistance, an impaired DNA damage response, nor increased mutation frequency in response to thiopurines using CRISPR-mediated knockout in wild-type B-ALL cell lines. Likewise, restoration of SETD2 in cell lines with hemizygous mutations did not increase sensitivity. SETD2 mutations affected the chromatin landscape and transcriptional output that was unique to each cell line. Collectively our data does not support a role for SETD2 mutations in driving clonal evolution and relapse in B-ALL, which is consistent with the lack of enrichment of SETD2 mutations at relapse in most studies.

Early B-Cell Factor 1: An Archetype for a Lineage-Restricted Transcription Factor Linking Development to Disease

The development of highly specialized blood cells from hematopoietic stem cells (HSCs) in the bone marrow (BM) is dependent upon a stringently orchestrated network of stage- and lineage-restricted transcription factors (TFs). Thus, the same stem cell can give rise to various types of differentiated blood cells. One of the key regulators of B-lymphocyte development is early B-cell factor 1 (EBF1). This TF belongs to a small, but evolutionary conserved, family of proteins that harbor a Zn-coordinating motif and an IPT/TIG (immunoglobulin-like, plexins, transcription factors/transcription factor immunoglobulin) domain, creating a unique DNA-binding domain (DBD). EBF proteins play critical roles in diverse developmental processes, including body segmentation in the Drosophila melanogaster embryo, and retina formation in mice. While several EBF family members are expressed in neuronal cells, adipocytes, and BM stroma cells, only B-lymphoid cells express EBF1. In the absence of EBF1, hematopoietic progenitor cells (HPCs) fail to activate the B-lineage program. This has been attributed to the ability of EBF1 to act as a pioneering factor with the ability to remodel chromatin, thereby creating a B-lymphoid-specific epigenetic landscape. Conditional inactivation of the Ebf1 gene in B-lineage cells has revealed additional functions of this protein in relation to the control of proliferation and apoptosis. This may explain why EBF1 is frequently targeted by mutations in human leukemia cases. This chapter provides an overview of the biochemical and functional properties of the EBF family proteins, with a focus on the roles of EBF1 in normal and malignant B-lymphocyte development.

Prognostic Impact of Copy Number Alterations' Profile and AID/RAG Signatures in Acute Lymphoblastic Leukemia (ALL) with BCR::ABL and without Recurrent Genetic Aberrations (NEG ALL) Treated with Intensive Chemotherapy

Adult acute lymphoblastic leukemia (ALL) is associated with poor outcomes. ALL is initiated by primary aberrations, but secondary genetic lesions are necessary for overt ALL. In this study, we reassessed the value of primary and secondary aberrations in intensively treated ALL patients in relation to mutator enzyme expression. RT-PCR, genomic PCR, and sequencing were applied to evaluate primary aberrations, while qPCR was used to measure the expression of RAG and AID mutator enzymes in 166 adult ALL patients. Secondary copy number alterations (CNA) were studied in 94 cases by MLPA assay. Primary aberrations alone stratified 30% of the patients (27% high-risk, 3% low-risk cases). The remaining 70% intermediate-risk patients included BCR::ABL1pos subgroup and ALL lacking identified genetic markers (NEG ALL). We identified three CNA profiles: high-risk bad-CNA (CNAhigh/IKZF1pos), low-risk good-CNA (all other CNAs), and intermediate-risk CNAneg. Furthermore, based on RAG/AID expression, we report possible mechanisms underlying the CNA profiles associated with poor outcome: AID stratified outcome in CNAneg, which accompanied most likely a particular profile of single nucleotide variations, while RAG in CNApos increased the odds for CNAhigh/IKZF1pos development. Finally, we integrated primary genetic aberrations with CNA to propose a revised risk stratification code, which allowed us to stratify 75% of BCR::ABL1pos and NEG patients.

Transcription factor networks link B-lymphocyte development and malignant transformation in leukemia

Rapid advances in genomics have opened unprecedented possibilities to explore the mutational landscapes in malignant diseases, such as B-cell acute lymphoblastic leukemia (B-ALL). This disease is manifested as a severe defect in the production of normal blood cells due to the uncontrolled expansion of transformed B-lymphocyte progenitors in the bone marrow. Even though classical genetics identified translocations of transcription factor-coding genes in B-ALL, the extent of the targeting of regulatory networks in malignant transformation was not evident until the emergence of large-scale genomic analyses. There is now evidence that many B-ALL cases present with mutations in genes that encode transcription factors with critical roles in normal B-lymphocyte development. These include PAX5, IKZF1, EBF1, and TCF3, all of which are targeted by translocations or, more commonly, partial inactivation in cases of B-ALL. Even though there is support for the notion that germline polymorphisms in the PAX5 and IKZF1 genes predispose for B-ALL, the majority of leukemias present with somatic mutations in transcription factor-encoding genes. These genetic aberrations are often found in combination with mutations in genes that encode components of the pre-B-cell receptor or the IL-7/TSLP signaling pathways, all of which are important for early B-cell development. This review provides an overview of our current understanding of the molecular interplay that occurs between transcription factors and signaling events during normal and malignant B-lymphocyte development.

Therapy-Acquired Clonal Mutations in Thiopurine Drug-Response Genes Drive Majority of Early Relapses in Pediatric B-Cell Precursor Acute Lymphoblastic Leukemia

METHODS

Forty pediatric (0-12 years) B-ALL DNA samples (20 paired Diagnosis-Relapse) and an additional six B-ALL DNA samples (without relapse at 3 years post treatment), as the non-relapse arm, were retrieved from the biobank for advanced genomic analysis. Deep sequencing (1050-5000X; mean 1600X) was performed using a custom NGS panel of 74 genes incorporating unique molecular barcodes.

RESULTS

A total 47 major clones (>25% VAF) and 188 minor clones were noted in 40 cases after bioinformatic data filtering. Of the forty-seven major clones, eight (17%) were diagnosis-specific, seventeen (36%) were relapse-specific and 11 (23%) were shared. In the control arm, no pathogenic major clone was noted in any of the six samples. The most common clonal evolution pattern observed was therapy-acquired (TA), with 9/20 (45%), followed by M-M, with 5/20 (25%), m-M, with 4/20 (20%) and unclassified (UNC) 2/20 (10%). The TA clonal pattern was predominant in early relapses 7/12 (58%), with 71% (5/7) having major clonal mutations in the NT5C2 or PMS2 gene related to thiopurine-dose response. In addition, 60% (3/5) of these cases were preceded by an initial hit in the epigenetic regulator, KMT2D. Mutations in common relapse-enriched genes comprised 33% of the very early relapses, 50% of the early and 40% of the late relapses. Overall, 14/46 (30%) of the samples showed the hypermutation phenotype, of which the majority (50%) had a TA pattern of relapse.

CONCLUSIONS

Our study highlights the high frequency of early relapses driven by TA clones, demonstrating the need to identify their early rise during chemotherapy by digital PCR.

Maintenance of Lineage Identity: Lessons from a B Cell

The maintenance of B cell identity requires active transcriptional control that enforces a B cell-specific program and suppresses alternative lineage genes. Accordingly, disrupting the B cell identity regulatory network compromises B cell function and induces cell fate plasticity by allowing derepression of alternative lineage-specific transcriptional programs. Although the B lineage is incredibly resistant to most differentiating factors, loss of just a single B lineage-specific transcription factor or the forced expression of individual non-B cell lineage transcription factors can radically disrupt B cell maintenance and allow dedifferentiation or transdifferentiation into entirely distinct lineages. B lymphocytes thereby offer an insightful and useful case study of how a specific cell lineage can maintain a stable identity throughout life and how perturbations of a single master regulator can induce cellular plasticity. In this article, we review the regulatory mechanisms that safeguard B cell identity, and we discuss how dysregulation of the B cell maintenance program can drive malignant transformation and enable therapeutic resistance.

Pharmacologic Inhibition of NT5C2 Reverses Genetic and Nongenetic Drivers of 6-MP Resistance in Acute Lymphoblastic Leukemia

Low-intensity maintenance therapy with 6-mercaptopurine (6-MP) limits the occurrence of acute lymphoblastic leukemia (ALL) relapse and is central to the success of multiagent chemotherapy protocols. Activating mutations in the 5'-nucleotidase cytosolic II (NT5C2) gene drive resistance to 6-MP in over 35% of early relapse ALL cases. Here we identify CRCD2 as a first-in-class small-molecule NT5C2 nucleotidase inhibitor broadly active against leukemias bearing highly prevalent relapse-associated mutant forms of NT5C2 in vitro and in vivo. Importantly, CRCD2 treatment also enhanced the cytotoxic activity of 6-MP in NT5C2 wild-type leukemias, leading to the identification of NT5C2 Ser502 phosphorylation as a novel NT5C2-mediated mechanism of 6-MP resistance in this disease. These results uncover an unanticipated role of nongenetic NT5C2 activation as a driver of 6-MP resistance in ALL and demonstrate the potential of NT5C2 inhibitor therapy for enhancing the efficacy of thiopurine maintenance therapy and overcoming resistance at relapse.

SIGNIFICANCE

Relapse-associated NT5C2 mutations directly contribute to relapse in ALL by driving resistance to chemotherapy with 6-MP. Pharmacologic inhibition of NT5C2 with CRCD2, a first-in-class nucleotidase inhibitor, enhances the cytotoxic effects of 6-MP and effectively reverses thiopurine resistance mediated by genetic and nongenetic mechanisms of NT5C2 activation in ALL. This article is highlighted in the In This Issue feature, p. 2483.

The Promise of Single-cell Technology in Providing New Insights Into the Molecular Heterogeneity and Management of Acute Lymphoblastic Leukemia

Drug resistance and treatment failure in pediatric acute lymphoblastic leukemia (ALL) are in part driven by tumor heterogeneity and clonal evolution. Although bulk tumor genomic analyses have provided some insight into these processes, single-cell sequencing has emerged as a powerful technique to profile individual cells in unprecedented detail. Since the introduction of single-cell RNA sequencing, we now have the capability to capture not only transcriptomic, but also genomic, epigenetic, and proteomic variation between single cells separately and in combination. This rapidly evolving field has the potential to transform our understanding of the fundamental biology of pediatric ALL and guide the management of ALL patients to improve their clinical outcome. Here, we discuss the impact single-cell sequencing has had on our understanding of tumor heterogeneity and clonal evolution in ALL and provide examples of how single-cell technology can be integrated into the clinic to inform treatment decisions for children with high-risk disease.

Oncogene-Induced Reprogramming in Acute Lymphoblastic Leukemia: Towards Targeted Therapy of Leukemia-Initiating Cells

Simple Summary

Acute lymphoblastic leukemia is a heterogeneous disease characterized by a diversity of genetic alterations, following a sophisticated and controversial organization. In this review, we present and discuss the concepts exploring the cellular, molecular and functional heterogeneity of leukemic cells. We also review the emerging evidence indicating that cell plasticity and oncogene-induced reprogramming should be considered at the biological and clinical levels as critical mechanisms for identifying and targeting leukemia-initiating cells.

Abstract

Our understanding of the hierarchical structure of acute leukemia has yet to be fully translated into therapeutic approaches. Indeed, chemotherapy still has to take into account the possibility that leukemia-initiating cells may have a distinct chemosensitivity profile compared to the bulk of the tumor, and therefore are spared by the current treatment, causing the relapse of the disease. Therefore, the identification of the cell-of-origin of leukemia remains a longstanding question and an exciting challenge in cancer research of the last few decades. With a particular focus on acute lymphoblastic leukemia, we present in this review the previous and current concepts exploring the phenotypic, genetic and functional heterogeneity in patients. We also discuss the benefits of using engineered mouse models to explore the early steps of leukemia development and to identify the biological mechanisms driving the emergence of leukemia-initiating cells. Finally, we describe the major prospects for the discovery of new therapeutic strategies that specifically target their aberrant stem cell-like functions.

Sister chromatid cohesion defects are associated with chromosomal copy number heterogeneity in high hyperdiploid childhood acute lymphoblastic leukemia

High hyperdiploid acute lymphoblastic leukemia (ALL) is one of the most common malignancies in children. The main driver event of this disease is a nonrandom aneuploidy consisting of gains of whole chromosomes but without overt evidence of chromosomal instability (CIN). Here, we investigated the frequency and severity of defective sister chromatid cohesion-a phenomenon related to CIN-in primary pediatric ALL. We found that a large proportion (86%) of hyperdiploid cases displayed aberrant cohesion, frequently severe, to compare with 49% of ETV6/RUNX1-positive ALL, which mostly displayed mild defects. In hyperdiploid ALL, cohesion defects were associated with increased chromosomal copy number heterogeneity, which could indicate increased CIN. Furthermore, cohesion defects correlated with RAD21 and NCAPG mRNA expression, suggesting a link to reduced cohesin and condensin levels in hyperdiploid ALL. Knockdown of RAD21 in an ALL cell line led to sister chromatid cohesion defects, aberrant mitoses, and increased heterogeneity in chromosomal copy numbers, similar to what was seen in primary hyperdiploid ALL. In summary, our study shows that aberrant sister chromatid cohesion is frequent but heterogeneous in pediatric high hyperdiploid ALL, ranging from mild to very severe defects, and possibly due to low cohesin or condensin levels. Cases with high levels of aberrant chromosome cohesion displayed increased chromosomal copy number heterogeneity, possibly indicative of increased CIN. These abnormalities may play a role in the clonal evolution of hyperdiploid pediatric ALL.

Frequency and Correlation of Common Genes Copy Number Alterations in Childhood Acute Lymphoblastic Leukemia with Prognosis

Objective:

It was shown by genomic profiling that despite no detectable chromosomal abnormalities a proportion of children with pre-B acute lymphoblastic leukemia harbors copy number alterations (CNA) of genes playing role in B-cell development and function. The aim of the study was to determine the frequency of CNA in pediatric acute lymphoblastic leukemia and correlate these findings with clinical outcome.

Methods:

DNA extracted from peripheral blood or bone marrow at diagnosis/relapse of fifty newly diagnosed children with precursor B-cell acute lymphoblastic leukemia was analyzed for CNA with multiplex ligation-dependent probe amplification.

Results:

The analysis revealed 76 CNA in 24 patients most frequently found in PAR1 (17%), CDKN2A/B (15.7%) and PAX5 (14.4%) genes. There were significant CNA co-occurrences between PAX5, CDKN2A/B, BTG1, ETV6, PAR1 or XP22 genes, (p<0.020) and the high-risk group. There was a significant correlation between EBF1, RB1, and IKZF1 alterations and bone marrow relapse. Patients with CNA in screened genes are more likely to succumb to their disease except for those with PAR1 or XP22 genes (p<0.050).

Conclusion:

The multiplex ligation-dependent probe amplification could be considered as an independent diagnostic tool allowing prompt identification of patients at high risk of treatment failure and, subsequently, a more adequate treatment approach.

The evolution of relapse of adult T cell acute lymphoblastic leukemia

BACKGROUND

Adult T cell acute lymphoblastic leukemia (T-ALL) is a rare disease that affects less than 10 individuals in one million. It has been less studied than its cognate pediatric malignancy, which is more prevalent. A higher percentage of the adult patients relapse, compared to children. It is thus essential to study the mechanisms of relapse of adult T-ALL cases.

RESULTS

We profile whole-genome somatic mutations of 19 primary T-ALLs from adult patients and the corresponding relapse malignancies and analyze their evolution upon treatment in comparison with 238 pediatric and young adult ALL cases. We compare the mutational processes and driver mutations active in primary and relapse adult T-ALLs with those of pediatric patients. A precise estimation of clock-like mutations in leukemic cells shows that the emergence of the relapse clone occurs several months before the diagnosis of the primary T-ALL. Specifically, through the doubling time of the leukemic population, we find that in at least 14 out of the 19 patients, the population of relapse leukemia present at the moment of diagnosis comprises more than one but fewer than 108 blasts. Using simulations, we show that in all patients the relapse appears to be driven by genetic mutations.

CONCLUSIONS

The early appearance of a population of leukemic cells with genetic mechanisms of resistance across adult T-ALL cases constitutes a challenge for treatment. Improving early detection of the malignancy is thus key to prevent its relapse.

Prognostic Impact of Somatic Copy Number Alterations in Childhood B-Lineage Acute Lymphoblastic Leukemia

PURPOSE OF REVIEW

The high prevalence of relapse in pediatric B-lineage acute lymphoblastic leukemia (B-ALL) despite the improvements achieved using current risk stratification schemes, demands more accurate methods for outcome prediction. Here, we provide a concise overview about the key advances that have expanded our knowledge regarding the somatic defects across B-ALL genomes, particularly focusing on copy number alterations (CNAs) and their prognostic impact.

RECENT FINDINGS

The identification of commonly altered genes in B-ALL has inspired the development of risk classifiers based on copy number states such as the IKZF1^plus and the United Kingdom (UK) ALL-CNA classifiers to improve outcome prediction in B-ALL. CNA-risk classifiers have emerged as effective tools to predict disease relapse; though, their clinical applications are yet to be transferred to routine practice.

Combined analysis of IKZF1 deletions and CRLF2 expression on prognostic impact in pediatric B-cell precursor acute lymphoblastic leukemia

This study aimed to investigate the combined impact of IKZF1 deletions/high expression of CRLF2 on the prognosis of pediatric B-cell precursor acute lymphoblastic leukemia (BCP-ALL). IKZF1 deletions and CRLF2 expression were assessed in bone marrow samples from 117 children with newly diagnosed BCP-ALL. Sixteen (13.7%) patients were found to harbor IKZF1 deletions, which was associated with inferior outcomes. The event-free survival (EFS) for patients with high -CRLF2 expression was significantly worse than that for low -CRLF2 expression. Moreover, combined modeling of IKZF1⁺ /CRLF2 ^high identified 7.8% of cases as the highest risk subgroup (7-year EFS 33.3 ± 15.7%). In a multivariate analysis, IKZF1⁺ /CRLF2 ^high remained a strong independent prognostic factor for EFS (HR: 14.263, p = 0.019). IKZF1 deletions and high -CRLF2 expression were associated with inferior outcomes, and the coexistence of IKZF1⁺ /CRLF2 ^high had a significant impact on an integrated prognostic model for high-risk BCP-ALL.

Immunotherapy in Pediatric B-Cell Acute Lymphoblastic Leukemia: Advances and Ongoing Challenges

Leukemia, most commonly B-cell acute lymphoblastic leukemia (B-ALL), accounts for about 30% of childhood cancer diagnoses. While there have been dramatic improvements in childhood ALL outcomes, certain subgroups-particularly those who relapse-fare poorly. In addition, cure is associated with significant short- and long-term side effects. Given these challenges, there is great interest in novel, targeted approaches to therapy. A number of new immunotherapeutic agents have proven to be efficacious in relapsed or refractory disease and are now being investigated in frontline treatment regimens. Blinatumomab (a bispecific T-cell engager that targets cluster of differentiation [CD]-19) and inotuzumab ozogamicin (a humanized antibody-drug conjugate to CD22) have shown the most promise. Chimeric antigen receptor T (CAR-T) cells, a form of adoptive immunotherapy, rely on the transfer of genetically modified effector T cells that have the potential to persist in vivo for years, providing ongoing long-term disease control. In this article, we discuss the clinical biology and treatment of B-ALL with an emphasis on the role of immunotherapy in overcoming the challenges of conventional cytotoxic therapy. As immunotherapy continues to move into the frontline of pediatric B-ALL therapy, we also discuss strategies to address unique side effects associated with these agents and efforts to overcome mechanisms of resistance to immunotherapy.

Integrated Genomic Analysis of Chromosomal Alterations and Mutations in B-Cell Acute Lymphoblastic Leukemia Reveals Distinct Genetic Profiles at Relapse

The clonal basis of relapse in B-cell precursor acute lymphoblastic leukemia (BCP-ALL) is complex and not fully understood. Next-generation sequencing (NGS), array comparative genomic hybridization (aCGH), and multiplex ligation-dependent probe amplification (MLPA) were carried out in matched diagnosis–relapse samples from 13 BCP-ALL patients to identify patterns of genetic evolution that could account for the phenotypic changes associated with disease relapse. The integrative genomic analysis of aCGH, MLPA and NGS revealed that 100% of the BCP-ALL patients showed at least one genetic alteration at diagnosis and relapse. In addition, there was a significant increase in the frequency of chromosomal lesions at the time of relapse (p = 0.019). MLPA and aCGH techniques showed that IKZF1 was the most frequently deleted gene. TP53 was the most frequently mutated gene at relapse. Two TP53 mutations were detected only at relapse, whereas the three others showed an increase in their mutational burden at relapse. Clonal evolution patterns were heterogeneous, involving the acquisition, loss and maintenance of lesions at relapse. Therefore, this study provides additional evidence that BCP-ALL is a genetically dynamic disease with distinct genetic profiles at diagnosis and relapse. Integrative NGS, aCGH and MLPA analysis enables better molecular characterization of the genetic profile in BCP-ALL patients during the evolution from diagnosis to relapse.

Extensive Remodeling of the Immune Microenvironment in B Cell Acute Lymphoblastic Leukemia

A subset of B cell acute lymphoblastic leukemia (B-ALL) patients will relapse and succumb to therapy-resistant disease. The bone marrow microenvironment may support B-ALL progression and treatment evasion. Utilizing single-cell approaches, we demonstrate B-ALL bone marrow immune microenvironment remodeling upon disease initiation and subsequent re-emergence during conventional chemotherapy. We uncover a role for non-classical monocytes in B-ALL survival, and demonstrate monocyte abundance at B-ALL diagnosis is predictive of pediatric and adult B-ALL patient survival. We show that human B-ALL blasts alter a vascularized microenvironment promoting monocytic differentiation, while depleting leukemia-associated monocytes in B-ALL animal models prolongs disease remission in vivo. Our profiling of the B-ALL immune microenvironment identifies extrinsic regulators of B-ALL survival supporting new immune-based therapeutic approaches for high-risk B-ALL treatment.

Comprehensive profiling of disease-relevant copy number aberrations for advanced clinical diagnostics of pediatric acute lymphoblastic leukemia

Acute lymphoblastic leukemia is the most common pediatric cancer characterized by a heterogeneous genomic landscape with copy number aberrations occurring at various stages of pathogenesis, disease progression, and treatment resistance. In this study, disease-relevant copy number aberrations were profiled in bone marrow samples of 91 children with B- or T-cell precursor acute lymphoblastic leukemia using digital multiplex ligation-dependent probe amplification (digitalMLPA^TM). Whole chromosome gains and losses, subchromosomal copy number aberrations, as well as unbalanced alterations conferring intrachromosomal gene fusions were simultaneously identified with results available within 36 hours. Aberrations were observed in 96% of diagnostic patient samples, and increased numbers of copy number aberrations were detected at the time of relapse as compared with diagnosis. Comparative scrutiny of 24 matching diagnostic and relapse samples from 11 patients revealed three different patterns of clonal relationships with (i) one patient displaying identical copy number aberration profiles at diagnosis and relapse, (ii) six patients showing clonal evolution with all lesions detected at diagnosis being present at relapse, and (iii) four patients displaying conserved as well as lost or gained copy number aberrations at the time of relapse, suggestive of the presence of a common ancestral cell compartment giving rise to clinically manifest leukemia at different time points during the disease course. A newly introduced risk classifier combining cytogenetic data with digitalMLPA^TM-based copy number aberration profiles allowed for the determination of four genetic subgroups of B-cell precursor acute lymphoblastic leukemia with distinct event-free survival rates. DigitalMLPA^TM provides fast, robust, and highly optimized copy number aberration profiling for the genomic characterization of acute lymphoblastic leukemia samples, facilitates the decipherment of the clonal origin of relapse and provides highly relevant information for clinical prognosis assessment.

The NSD2 p.E1099K Mutation Is Enriched at Relapse and Confers Drug Resistance in a Cell Context-Dependent Manner in Pediatric Acute Lymphoblastic Leukemia

The NSD2 p.E1099K (EK) mutation is observed in 10% of acute lymphoblastic leukemia (ALL) samples with enrichment at relapse indicating a role in clonal evolution and drug resistance. To discover mechanisms that mediate clonal expansion, we engineered B-precursor ALL (B-ALL) cell lines (Reh, 697) to overexpress wildtype (WT) and EK NSD2, but observed no differences in proliferation, clonal growth, or chemosensitivity. To address whether NSD2 EK acts collaboratively with other pathways, we used short hairpin RNAs to knockdown expression of NSD2 in B-ALL cell lines heterozygous for NSD2 EK (RS4;11, RCH-ACV, SEM). Knockdown resulted in decreased proliferation in all lines, decreased clonal growth in RCH-ACV, and increased sensitivity to cytotoxic chemotherapeutic agents, although the pattern of drug sensitivity varied among cell lines implying that the oncogenic properties of NSD2 mutations are likely cell context specific and rely on cooperative pathways. Knockdown of both Type II and REIIBP EK isoforms had a greater impact than knockdown of Type II alone, suggesting that both SET containing EK isoforms contribute to phenotypic changes driving relapse. Furthermore, in vivo models using both cell lines and patient samples revealed dramatically enhanced proliferation of NSD2 EK compared with WT and reduced sensitivity to 6-mercaptopurine in the relapse sample relative to diagnosis. Finally, EK-mediated changes in chromatin state and transcriptional output differed dramatically among cell lines further supporting a cell context-specific role of NSD2 EK. These results demonstrate a unique role of NSD2 EK in mediating clonal fitness through pleiotropic mechanisms dependent on the genetic and epigenetic landscape. IMPLICATIONS: NSD2 EK mutation leads to drug resistance and a clonal advantage in childhood B-ALL.

Acute lymphoblastic leukaemia

Acute lymphoblastic leukaemia develops in both children and adults, with a peak incidence between 1 year and 4 years. Most acute lymphoblastic leukaemia arises in healthy individuals, and predisposing factors such as inherited genetic susceptibility or environmental exposure have been identified in only a few patients. It is characterised by chromosomal abnormalities and genetic alterations involved in differentiation and proliferation of lymphoid precursor cells. Along with response to treatment, these abnormalities are important prognostic factors. Disease-risk stratification and the development of intensified chemotherapy protocols substantially improves the outcome of patients with acute lymphoblastic leukaemia, particularly in children (1-14 years), but also in adolescents and young adults (15-39 years). However, the outcome of older adults (≥40 years) and patients with relapsed or refractory acute lymphoblastic leukaemia remains poor. New immunotherapeutic strategies, such as monoclonal antibodies and chimeric antigen receptor (CAR) T cells, are being developed and over the next few years could change the options for acute lymphoblastic leukaemia treatment.

Upfront Treatment Influences the Composition of Genetic Alterations in Relapsed Pediatric B-Cell Precursor Acute Lymphoblastic Leukemia

Supplemental Digital Content is available in the text

Genomic alterations in relapsed B-cell precursor acute lymphoblastic leukemia (BCP-ALL) may provide insight into the role of specific genomic events in relapse development. Along this line, comparisons between the spectrum of alterations in relapses that arise in different upfront treatment protocols may provide valuable information on the association between the tumor genome, protocol components and outcome. Here, we performed a comprehensive characterization of relapsed BCP-ALL cases that developed in the context of 3 completed Dutch upfront studies, ALL8, ALL9, and ALL10. In total, 123 pediatric BCP-ALL relapses and 77 paired samples from primary diagnosis were analyzed for alterations in 22 recurrently affected genes. We found pronounced differences in relapse alterations between the 3 studies. Specifically, CREBBP mutations were observed predominantly in relapses after treatment with ALL8 and ALL10 which, in the latter group, were all detected in medium risk-treated patients. IKZF1 alterations were enriched 2.2-fold (p = 0.01) and 2.9-fold (p < 0.001) in ALL8 and ALL9 relapses compared to diagnosis, respectively, whereas no significant enrichment was found for relapses that were observed after treatment with ALL10. Furthermore, IKZF1 deletions were more frequently preserved from a major clone at diagnosis in relapses after ALL9 compared to relapses after ALL8 and ALL10 (p = 0.03). These data are in line with previous studies showing that the prognostic value of IKZF1 deletions differs between upfront protocols and is particularly strong in the ALL9 regimen. In conclusion, our data reveal a correlation between upfront treatment and the genetic composition of relapsed BCP-ALL.

Immune-Based Therapies in Acute Leukemia

Treatment resistance remains a leading cause of acute leukemia-related deaths. Thus, there is an unmet need to develop novel approaches to improve outcome. New immune-based therapies with chimeric antigen receptor (CAR) T cells, bi-specific T cell engagers (BiTEs), and immune checkpoint blockers (ICBs) have emerged as effective treatment options for chemoresistant B cell acute lymphoblastic leukemia (B-ALL) and acute myeloid leukemia (AML). However, many patients show resistance to these immune-based approaches. This review describes crucial lessons learned from immune-based approaches targeting high-risk B-ALL and AML, such as the leukemia-intrinsic (e.g., target antigen loss, tumor heterogeneity) and -extrinsic (e.g., immunosuppressive microenvironment) mechanisms that drive treatment resistance, and discusses alternative approaches to enhance the effectiveness of these immune-based treatment regimens.

Omics-based insights into therapy failure of pediatric B-lineage acute lymphoblastic leukemia

B-lineage acute lymphoblastic leukemia (B-ALL) is the most common type of cancer seen in children and is characterized by a variable clinical course. Although there have been remarkable improvements in the therapy outcomes of pediatric B-ALL, treatment failure remains the leading-cause of death in 18% of the afflicted patients during the first 5 years after diagnosis. Molecular heterogeneities of pediatric B-ALL play important roles as determinants of the therapy response. Therefore, many of these molecular abnormalities have an established prognostic value in the disease. The present review discusses the omics-based revelations from epigenomics, genomics, transcriptomics and proteomics about treatment failure in pediatric B-ALL. Next it highlights the promise of the molecular aberration-targeted therapy to improve the treatment outcomes.

Mechanisms of NT5C2-Mediated Thiopurine Resistance in Acute Lymphoblastic Leukemia

Relapse remains a formidable challenge for acute lymphoblastic leukemia (ALL). Recently, recurrent mutations in NT5C2 were identified as a common genomic lesion unique in relapsed ALL and were linked to acquired thiopurine resistance. However, molecular mechanisms by which NT5C2 regulates thiopurine cytotoxicity were incompletely understood. To this end, we sought to comprehensively characterize the biochemical and cellular effects of NT5C2 mutations. Compared with wild-type NT5C2, mutant proteins showed elevated 5'-nucleotidase activity with a stark preference of thiopurine metabolites over endogenous purine nucleotides, suggesting neomorphic effects specific to thiopurine metabolism. Expression of mutant NT5C2 mutations also significantly reduced thiopurine uptake in vitro with concomitant increase in efflux of 6-mercaptopurine (MP) metabolites, plausibly via indirect effects on drug transporter pathways. Finally, intracellular metabolomic profiling revealed significant shifts in nucleotide homeostasis induced by mutant NT5C2 at baseline; MP treatment also resulted in global changes in metabolomic profiles with completely divergent effects in cells with mutant versus wild-type NT5C2. Collectively, our data indicated that NT5C2 mutations alter thiopurine metabolism and cellular disposition, but also influence endogenous nucleotide homeostasis and thiopurine-induced metabolomic response. These complex mechanisms contributed to NT5C2-mediated drug resistance in ALL and pointed to potential opportunities for therapeutic targeting in relapsed ALL.

Mechanisms of extramedullary relapse in acute lymphoblastic leukemia: Reconciling biological concepts and clinical issues

Long-term survival rates in childhood acute lymphoblastic leukemia (ALL) are currently above 85% due to huge improvements in treatment. However, 15-20% of children still experience relapses. Relapses can either occur in the bone marrow or at extramedullary sites, such as gonads or the central nervous system (CNS), formerly referred to as ALL-blast sanctuaries. The reason why ALL cells migrate to and stay in these sites is still unclear. In this review, we have attempted to assemble the evidence concerning the microenvironmental factors that could explain why ALL cells reside in such sites. We present criteria that make extramedullary leukemia niches and solid tumor metastatic niches comparable. Indeed, considering extramedullary leukemias as metastases could be a useful approach for proposing more effective treatments. In this context, we conclude with several examples of potential niche-based therapies which could be successfully added to current treatments of ALL.

Genetics and mechanisms of NT5C2-driven chemotherapy resistance in relapsed ALL

Mutations in the cytosolic 5' nucleotidase II (NT5C2) gene drive resistance to thiopurine chemotherapy in relapsed acute lymphoblastic leukemia (ALL). Mechanistically, NT5C2 mutant proteins have increased nucleotidase activity as a result of altered activating and autoregulatory switch-off mechanisms. Leukemias with NT5C2 mutations are chemoresistant to 6-mercaptopurine yet show impaired proliferation and self-renewal. Direct targeting of NT5C2 or inhibition of compensatory pathways active in NT5C2 mutant cells may antagonize the emergence of NT5C2 mutant clones driving resistance and relapse in ALL.

Pharmacogenomic and Pharmacotranscriptomic Profiling of Childhood Acute Lymphoblastic Leukemia: Paving the Way to Personalized Treatment

Personalized medicine is focused on research disciplines which contribute to the individualization of therapy, like pharmacogenomics and pharmacotranscriptomics. Acute lymphoblastic leukemia (ALL) is the most common malignancy of childhood. It is one of the pediatric malignancies with the highest cure rate, but still a lethal outcome due to therapy accounts for 1%⁻3% of deaths. Further improvement of treatment protocols is needed through the implementation of pharmacogenomics and pharmacotranscriptomics. Emerging high-throughput technologies, including microarrays and next-generation sequencing, have provided an enormous amount of molecular data with the potential to be implemented in childhood ALL treatment protocols. In the current review, we summarized the contribution of these novel technologies to the pharmacogenomics and pharmacotranscriptomics of childhood ALL. We have presented data on molecular markers responsible for the efficacy, side effects, and toxicity of the drugs commonly used for childhood ALL treatment, i.e., glucocorticoids, vincristine, asparaginase, anthracyclines, thiopurines, and methotrexate. Big data was generated using high-throughput technologies, but their implementation in clinical practice is poor. Research efforts should be focused on data analysis and designing prediction models using machine learning algorithms. Bioinformatics tools and the implementation of artificial i Lack of association of the CEP72 rs924607 TT genotype with intelligence are expected to open the door wide for personalized medicine in the clinical practice of childhood ALL.

Metabolite-Centric Reporter Pathway and Tripartite Network Analysis of Arabidopsis Under Cold Stress

The study of plant resistance to cold stress and the metabolic processes underlying its molecular mechanisms benefit crop improvement programs. Here we investigate the effects of cold stress on the metabolic pathways of Arabidopsis when directly inferred at system level from transcriptome data. A metabolite-centric reporter pathway analysis approach enabled the computation of metabolites associated with transcripts at four time points of cold treatment. Tripartite networks of gene-metabolite-pathway connectivity outlined the response of metabolites and pathways to cold stress. Our metabolome-independent analysis revealed stress-associated metabolites in pathway routes of the cold stress response, including amino acid, carbohydrate, lipid, hormone, energy, photosynthesis, and signaling pathways. Cold stress first triggered the mobilization of energy from glycolysis and ethanol degradation to enhance TCA cycle activity via acetyl-CoA. Interestingly, tripartite networks lacked power law behavior and scale free connectivity, favoring modularity. Network rewiring explicitly involved energetics, signal, carbon and redox metabolisms and membrane remodeling.

Genetics and epigenetics of pediatric leukemia in the era of precision medicine

Pediatric leukemia represents a heterogeneous group of diseases characterized by germline and somatic mutations that manifest within the context of disturbances in the epigenetic machinery and genetic regulation. Advances in genomic medicine have allowed finer resolution of genetic and epigenetic strategies that can be effectively used to risk-stratify patients and identify novel targets for therapy. This review discusses the genetic and epigenetic mechanisms of leukemogenesis, particularly as it relates to acute lymphocytic leukemias, the mechanisms of epigenetic control of leukemogenesis, namely DNA methylation, histone modifications, microRNAs, and LINE-1 retroelements, and highlights opportunities for precision medicine therapeutics in further guiding disease management. Future efforts to broaden the integration of advances in genomic and epigenomic science into the practice of pediatric oncology will not only identify novel therapeutic strategies to improve clinical outcomes but also improve the quality of life for this unique patient population. Recent findings in precision therapeutics of acute lymphocytic leukemias over the past three years, along with some provocative areas of epigenetics research, are reviewed here.

Deletion of CDKN2A/B is associated with inferior relapse free survival in pediatric B cell acute lymphoblastic leukemia

Considering conflicting data on CDKN2A/B deletion in ALL, this study to assess its prognostic significance as an independent marker in a total of 96 pediatric B and T-ALL cases was planned. The overall frequency of CDKN2A/B deletion was 44% (n = 43) with 36% (30/83) in B-ALL and 100% (13/13) in T-ALL. CDKN2A/B deletion was significantly associated with high WBC count (p = .002) and National Cancer Institute risk (p = .01) in B-ALL. Importantly, CDKN2A/B deletion cases had poor EFS of 42% at 28 months compared to EFS of 90% in rest (p = .0004). Further, relapse free survival was only 56% for cases with CDKN2A/B deletions (n = 25), compared to 100% in control group (p = .001). Moreover, CDKN2A/B deletion was the only risk factor associated with early relapse (p = .01) compared to IKZF1 deletion (p = .73) or occurrence of BCR-ABL1 fusion transcript (p = .26). Thus our study data highlights potential prognostic role of CDKN2A/B deletions in early disease stratification in pediatric B-ALL.

Association of the independent polymorphisms in CDKN2A with susceptibility of acute lymphoblastic leukemia

Acute lymphoblastic leukemia (ALL) is the most common cancer in children, and alterations in CDKN2A were considered to play an important role on leukemogenesis. Two single nucleotide polymorphisms (SNPs) at CDKN2A locus were identified to impact on ALL susceptibility via genome wide association studies, and followed by multiple subsequent replication studies at the specific hits. Here, we conducted a systematic review and meta-analysis to re-evaluate the association of both SNPs (rs3731217 and rs3731249) with ALL susceptibility by gathering the data from 24 independent studies, totally containing 7922 cases/21503 controls for rs3731217 and 6295 cases/24191 controls for rs3731249. Both SNPs were significantly associated with ALL risk (odds ratio [OR] = 0.72 and 2.26 respectively), however, exhibit race-specific pattern. In summary, our meta-analysis indicated that two SNPs at CDKN2A locus are associated with ALL susceptibility independently mainly in Caucasians. Future large-scale studies are required to validate the associations in other ethnicities.

Single-cell sequencing reveals the origin and the order of mutation acquisition in T-cell acute lymphoblastic leukemia

Next-generation sequencing has provided a detailed overview of the various genomic lesions implicated in the pathogenesis of T-cell acute lymphoblastic leukemia (T-ALL). Typically, 10–20 protein-altering lesions are found in T-ALL cells at diagnosis. However, it is currently unclear in which order these mutations are acquired and in which progenitor cells this is initiated. To address these questions, we used targeted single-cell sequencing of total bone marrow cells and CD34⁺CD38⁻ multipotent progenitor cells for four T-ALL cases. Hierarchical clustering detected a dominant leukemia cluster at diagnosis, accompanied by a few smaller clusters harboring only a fraction of the mutations. We developed a graph-based algorithm to determine the order of mutation acquisition. Two of the four patients had an early event in a known oncogene (MED12, STAT5B) among various pre-leukemic events. Intermediate events included loss of 9p21 (CDKN2A/B) and acquisition of fusion genes, while NOTCH1 mutations were typically late events. Analysis of CD34⁺CD38⁻ cells and myeloid progenitors revealed that in half of the cases somatic mutations were detectable in multipotent progenitor cells. We demonstrate that targeted single-cell sequencing can elucidate the order of mutation acquisition in T-ALL and that T-ALL development can start in a multipotent progenitor cell.

Outcome of children with multiply relapsed B-cell acute lymphoblastic leukemia: a therapeutic advances in childhood leukemia & lymphoma study

The survival of pediatric patients with multiply relapsed and/or refractory (R/R) B-cell acute lymphoblastic leukemia has historically been very poor; however, data are limited in the current era. We conducted a retrospective study to determine the outcome of multiply R/R childhood B-ALL treated at 24 TACL institutions between 2005 and 2013. Patient information, treatment, and response were collected. Prognostic factors influencing the complete remission (CR) rate and event-free survival (EFS) were analyzed. The analytic set included 578 salvage treatment attempts among 325 patients. CR rates (mean ± SE) were 51 ± 4% for patients with bone marrow R/R B-ALL who underwent a second salvage attempt, 37 ± 6% for a third attempt, and 31 ± 6% for the fourth through eighth attempts combined. For patients achieving a CR after their second, third, and fourth through eighth attempts, the 2 year EFS was 41 ± 6%, 13 ± 7%, and 27 ± 13% respectively. Our results showed slight improvement when compared to previous studies. This is the largest and most recent study to date that evaluates the outcome of this patient population. Our data will provide detailed reference for the evaluation of new agents being developed for childhood B-ALL.

Pathogenesis of ETV6/RUNX1-positive childhood acute lymphoblastic leukemia and mechanisms underlying its relapse

ETV6/RUNX1 (E/R) is the most common fusion gene in childhood acute lymphoblastic leukemia (ALL). Multiple lines of evidence imply a “two-hit” model for the molecular pathogenesis of E/R-positive ALL, whereby E/R rearrangement is followed by a series of secondary mutations that trigger overt leukemia. The cellular framework in which E/R arises and the maintenance of a pre-leukemic condition by E/R are fundamental to the mechanism that underlies leukemogenesis. Accordingly, a variety of studies have focused on the relationship between the clones giving rise to the primary and recurrent E/R-positive ALL. We review here the most recent insights into the pathogenic mechanisms underlying E/R-positive ALL, as well as the molecular abnormalities prevailing at relapse.

MSH6 haploinsufficiency at relapse contributes to the development of thiopurine resistance in pediatric B-lymphoblastic leukemia

Survival of children with relapsed acute lymphoblastic leukemia is poor, and understanding mechanisms underlying resistance is essential to developing new therapy. Relapse-specific heterozygous deletions in MSH6, a crucial part of DNA mismatch repair, are frequently detected. Our aim was to determine whether MSH6 deletion results in a hypermutator phenotype associated with generation of secondary mutations involved in drug resistance, or if it leads to a failure to initiate apoptosis directly in response to chemotherapeutic agents. We knocked down MSH6 in mismatch repair proficient cell lines (697 and UOCB1) and showed significant increases in IC50s to 6-thioguanine and 6-mercaptopurine (697: 26- and 9-fold; UOCB1: 5- and 8-fold) in vitro, as well as increased resistance to 6-mercaptopurine treatment in vivo. No shift in IC50 was observed in deficient cells (Reh and RS4;11). 697 MSH6 knockdown resulted in increased DNA thioguanine nucleotide levels compared to non-targeted cells (3070 vs. 1722 fmol/μg DNA) with no difference observed in mismatch repair deficient cells. Loss of MSH6 did not give rise to microsatellite instability in cell lines or clinical samples, nor did it significantly increase mutation rate, but rather resulted in a defect in cell cycle arrest upon thiopurine exposure. MSH6 knockdown cells showed minimal activation of checkpoint regulator CHK1, γH2AX (DNA damage marker) and p53 levels upon treatment with thiopurines, consistent with intrinsic chemoresistance due to failure to recognize thioguanine nucleotide mismatching and initiate mismatch repair. Aberrant MSH6 adds to the list of alterations/mutations associated with acquired resistance to purine analogs emphasizing the importance of thiopurine therapy.

Anti-leukemic activity of bortezomib and carfilzomib on B-cell precursor ALL cell lines

Prognosis of childhood acute lymphoblastic leukemia (ALL) has been dramatically improved. However, prognosis of the cases refractory to primary therapy is still poor. Recent phase 2 study on the efficacy of combination chemotherapy with bortezomib (BTZ), a proteasome inhibitor, for refractory childhood ALL demonstrated favorable clinical outcomes. However, septic death was observed in over 10% of patients, indicating the necessity of biomarkers that could predict BTZ sensitivity. We investigated in vitro BTZ sensitivity in a large panel of ALL cell lines that acted as a model system for refractory ALL, and found that Philadelphia chromosome-positive (Ph+) ALL, IKZF1 deletion, and biallelic loss of CDKN2A were associated with favorable response. Even in Ph-negative ALL cell lines, IKZF1 deletion and bilallelic loss of CDKN2A were independently associated with higher BTZ sensitivity. BTZ showed only marginal cross-resistance to four representative chemotherapeutic agents (vincristine, dexamethasone, l-asparaginase, and daunorubicin) in B-cell precursor-ALL cell lines. To improve the efficacy and safety of proteasome inhibitor combination chemotherapy, we also analyzed the anti-leukemic activity of carfilzomib (CFZ), a second-generation proteasome inhibitor, as a substitute for BTZ. CFZ showed significantly higher activity than BTZ in the majority of ALL cell lines except for the P-glycoprotein-positive t(17;19) ALL cell lines, and IKZF1 deletion was also associated with a favorable response to CFZ treatment. P-glycoprotein inhibitors effectively restored the sensitivity to CFZ, but not BTZ, in P-glycoprotein-positive t(17;19) ALL cell lines. P-glycoprotein overexpressing ALL cell line showed a CFZ-specific resistance, while knockout of P-glycoprotein by genome editing with a CRISPR/Cas9 system sensitized P-glycoprotein-positive t(17;19) ALL cell line to CFZ. These observations suggested that IKZF1 deletion could be a useful biomarker to predict good sensitivity to CFZ and BTZ, and that CFZ combination chemotherapy may be a new therapeutic option with higher anti-leukemic activity for refractory ALL that contain P-glycoprotein-negative leukemia cells.

Copy number profiling of adult relapsed B-cell precursor acute lymphoblastic leukemia reveals potential leukemia progression mechanisms

The outcome of relapsed adult acute lymphoblastic leukemia (ALL) remains dismal despite new therapeutic approaches. Previous studies analyzing relapse samples have shown a high degree of heterogeneity regarding gene alterations without an evident relapse signature. Bone marrow or peripheral blood samples from 31 adult B-cell precursor ALL patients at first relapse, and 21 paired diagnostic samples were analyzed by multiplex ligation probe-dependent amplification (MLPA). Nineteen paired diagnostic and relapse samples of these 21 patients were also analyzed by SNP arrays. A trend to acquire homozygous CDKN2A/B deletions and a significant increase in the number of copy number alterations (CNA) was observed from diagnosis to first relapse. Evolution from an ancestral clone was the main pattern of clonal evolution. Relapse samples were extremely heterogeneous regarding CNA frequencies. However, CDKN2A/B, PAX5, ETV6, ATM, IKZF1, VPREB1, and TP53 deletions and duplications of 1q, 8q, 17q, 21, X/Y PAR1, and Xp were frequently detected at relapse. Duplications of genes involved in cell proliferation, drug resistance and stem cell homeostasis regulation, as well as deletions of KDM6A and STAG2 genes emerged as specific alterations at relapse. Genomics of relapsed adult B-cell precursor ALL is highly heterogeneous, although some recurrent lesions involved in essential pathways deregulation were frequently observed. Selective and simultaneous targeting of these deregulated pathways may improve the results of current salvage therapies.

A p53-regulated apoptotic gene signature predicts treatment response and outcome in pediatric acute lymphoblastic leukemia

Gene signatures have been associated with outcome in pediatric acute lymphoblastic leukemia (ALL) and other malignancies. However, determining the molecular drivers of these expression changes remains challenging. In ALL blasts, the p53 tumor suppressor is the primary regulator of the apoptotic response to genotoxic chemotherapy, which is predictive of outcome. Consequently, we hypothesized that the normal p53-regulated apoptotic response to DNA damage would be altered in ALL and that this alteration would influence drug response and treatment outcome. To test this, we first used global expression profiling in related human B-lineage lymphoblastoid cell lines with either wild type or mutant TP53 to characterize the normal p53-mediated transcriptional response to ionizing radiation (IR) and identified 747 p53-regulated apoptotic target genes. We then sorted these genes into six temporal expression clusters (TECs) based upon differences over time in their IR-induced p53-regulated gene expression patterns, and found that one cluster (TEC1) was associated with multidrug resistance in leukemic blasts in one cohort of children with ALL and was an independent predictor of survival in two others. Therefore, by investigating p53-mediated apoptosis in vitro, we identified a gene signature significantly associated with drug resistance and treatment outcome in ALL. These results suggest that intersecting pathway-derived and clinically derived expression data may be a powerful method to discover driver gene signatures with functional and clinical implications in pediatric ALL and perhaps other cancers as well.

Spontaneous loss of B lineage transcription factors leads to pre-B leukemia in Ebf1+/-Bcl-xLTg mice

Early B-cell factor 1 (EBF1) plays a central role in B-cell lineage specification and commitment. Loss of this critical transcription factor is strongly associated with high-risk, relapsed and therapy-resistant B–cell-acute lymphoblastic leukemia, especially in children. However, Ebf1 haploinsufficient mice exhibit a normal lifespan. To determine whether prolonged survival of B cells would enable tumorigenesis in Ebf1 haploinsufficient animals, we generated Ebf1^+/–Bcl-x_L^Tg mice, which express the anti-apoptotic factor Bcl-x_L in B cells. Approximately half of Ebf1^+/–Bcl-x_L^Tg mice develop aggressive oligoclonal leukemia as they age, which engrafts in congenic wild-type recipients without prior conditioning. The neoplastic cells display a pre-B phenotype and express early developmental- and natural killer cell/myeloid-markers inappropriately. In addition, we found tumor cell-specific loss of several transcription factors critical for maintaining differentiation: EBF1, TCF3 and RUNX1. However, in the majority of tumors, loss of Ebf1 expression was not due to loss of heterozygosity. This is the first spontaneous mouse model of pre-B leukemia to demonstrate inappropriate expression of non-B-cell-specific genes associated with loss of Ebf1, Tcf3 and Runx1 expression.

New targeted therapies for relapsed pediatric acute lymphoblastic leukemia

INTRODUCTION

The improvement in outcomes for children with acute lymphoblastic leukemia (ALL) is one of the greatest success stories of modern oncology however the prognosis for patients who relapse remains dismal. Recent discoveries by high resolution genomic technologies have characterized the biology of relapsed leukemia, most notably pathways leading to the drug resistant phenotype. These observations open the possibility of targeting such pathways to prevent and/or treat relapse. Likewise, early experiences with new immunotherapeutic approaches have shown great promise. Areas covered: We performed a literature search on PubMed and recent meeting abstracts using the keywords below. We focused on the biology and clonal evolution of relapsed disease highlighting potential new targets of therapy. We further summarized the results of early trials of the three most prominent immunotherapy agents currently under investigation. Expert commentary: Discovery of targetable pathways that lead to drug resistance and recent breakthroughs in immunotherapy show great promise towards treating this aggressive disease. The best way to treat relapse, however, is to prevent it which makes incorporation of these new approaches into frontline therapy the best approach. Challenges remain to balance efficacy with toxicity and to prevent the emergence of resistant subclones which is why combining these newer agents with conventional chemotherapy will likely become standard of care.

Genomic characterization of pediatric B-lymphoblastic lymphoma and B-lymphoblastic leukemia using formalin-fixed tissues

BACKGROUND

Recurrent genomic changes in B-lymphoblastic leukemia (B-ALL) identified by genome-wide single-nucleotide polymorphism (SNP) microarray analysis provide important prognostic information, but gene copy number analysis of its rare lymphoma counterpart, B-lymphoblastic lymphoma (B-LBL), is limited by the low incidence and lack of fresh tissue for genomic testing.

PROCEDURE

We used molecular inversion probe (MIP) technology to analyze and compare copy number alterations (CNAs) in archival formalin-fixed paraffin-embedded pediatric B-LBL (n = 23) and B-ALL (n = 55).

RESULTS

Similar to B-ALL, CDKN2A/B deletions were the most common alteration identified in 6/23 (26%) B-LBL cases. Eleven of 23 (48%) B-LBL patients were hyperdiploid, but none showed triple trisomies (chromosomes 4, 10, and 17) characteristic of B-ALL. IKZF1 and PAX5 deletions were observed in 13 and 17% of B-LBL, respectively, which was similar to the reported frequency in B-ALL. Immunoglobulin light chain lambda (IGL) locus deletions consistent with normal light chain rearrangement were observed in 5/23 (22%) B-LBL cases, compared with only 1% in B-ALL samples. None of the B-LBL cases showed abnormal, isolated VPREB1 deletion adjacent to IGL locus, which we identified in 25% of B-ALL.

CONCLUSIONS

Our study demonstrates that the copy number profile of B-LBL is distinct from B-ALL, suggesting possible differences in pathogenesis between these closely related diseases.

Deregulation of kinase signaling and lymphoid development in EBF1-PDGFRB ALL leukemogenesis

The chimeric fusion oncogene early B-cell factor 1-platelet-derived growth factor receptor-β (EBF1-PDGFRB) is a recurrent lesion observed in Philadelphia-like B-acute lymphoblastic leukemia (B-ALL) and is associated with particularly poor prognosis. While it is understood that this fusion activates tyrosine kinase signaling, the mechanisms of transformation and importance of perturbation of EBF1 activity remain unknown. EBF1 is a nuclear transcription factor required for normal B-lineage specification, commitment and development. Conversely, PDGFRB is a receptor tyrosine kinase that is normally repressed in lymphocytes, yet PDGFRB remains a common fusion partner in leukemias. Here, we demonstrate that the EBF1-PDGFRB fusion results in loss of EBF1 function, multimerization and autophosphorylation of the fusion protein, activation of signal transducer and activator of transcription 5 (STAT5) signaling and gain of interleukin-7 (IL-7)-independent cell proliferation. Deregulation and loss of EBF1 function is critically dependent on the nuclear export activity of the transmembrane (TM) domain of PDGFRB. Deletion of the TM domain partially rescues EBF1 function and restores IL-7 dependence, without requiring kinase inhibition. Moreover, we demonstrate that EBF1-PDGFRB synergizes with loss of IKAROS function in a fully penetrant B-ALL in vivo. Thus, we establish that EBF1-PDGFRB is sufficient to drive leukemogenesis through TM-dependent loss of transcription factor function, increased proliferation and synergy with additional genetic insults including loss of IKAROS function.

Molecular profiling of gene copy number abnormalities in key regulatory genes in high-risk B-lineage acute lymphoblastic leukemia: frequency and their association with clinicopathological findings in Indian patients

Genes related to key cellular pathways are frequently altered in B cell ALL and are associated with poor survival especially in high-risk (HR) subgroups. We examined gene copy number abnormalities (CNA) in 101 Indian HR B cell ALL patients and their correlation with clinicopathological features by multiplex ligation-dependent probe amplification. Overall, CNA were detected in 59 (59%) cases, with 26, 10 and 23% of cases harboring 1, 2 or +3 CNA. CNA were more prevalent in BCR-ABL1 (60%), pediatric (64%) and high WCC (WBC count) (63%) patients. Frequent genes deletions included CDNK2A/B (26%), IKZF1 (25%), PAX5 (14%), JAK2 (7%), BTG1 (6%), RB1 (5%), EBF1 (4%), ETV6 (4%), while PAR1 region genes were predominantly duplicated (20%). EBF1 deletions selectively associated with adults, IKZF1 deletions occurred frequently in high WCC and BCR-ABL1 cases, while PAR1 region gains significantly associated with MLL-AF4 cases. IKZF1 haploinsufficiency group was predominant, especially in adults (65%), high WCC (60%) patients and BCR-ABL1-negative (78%) patients. Most cases harbored multiple concurrent CNA, with IKZF1 concomitantly occurring with CDNK2A/B, PAX5 and BTG1, while JAK2 occurred with CDNK2A/B and PAX5. Mutually exclusive CNA included ETV6 and IKZF1/RB1, and EBF1 and JAK2. Our results corroborate with global reports, aggregating molecular markers in Indian HR B-ALL cases. Integration of CNA data from rapid methods like MLPA, onto background of existing gold-standard methods detecting significant chromosomal abnormalities, provides a comprehensive genetic profile in B-ALL.