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• Pediatric Non-Down Syndrome Acute Megakaryoblastic Leukemia is Characterized by Distinct Genomic Subsets with Varying Outcomes

  Acute Megakaryoblastic Leukemia (AMKL) is a subtype of acute myeloid leukemia (AML) in which cells morphologically resemble abnormal megakaryoblasts.  While extremely rare in adults, AMKL accounts for 4-15% of newly diagnosed childhood AML1-3.  A significant proportion of pediatric AMKL cases occur in children with Down syndrome (DS).  These patients have excellent outcomes and are characterized at the genomic level by a founding GATA1 mutation4-6.  In contrast, AMKL in patients without DS (non-DS-AMKL) is frequently associated with poor outcomes.  Previous efforts have identified chimeric oncogenes in a significant number of cases, including RBM15-MKL1, CBFA2T3-GLIS2, KMT2A gene rearrangements and NUP98-KDM5A7-9.  The etiology of 30-40% of cases, however, remains unknown.  To better understand the genomic landscape of non-DS-AMKL, we performed RNA and exome sequencing on specimens from 99 patients (75 pediatric and 24 adult).  We demonstrate that pediatric non-DS-AMKL is a heterogeneous malignancy that can be divided into seven subgroups with varying outcomes.  These subgroups are characterized by chimeric oncogenes with cooperating mutations in epigenetic and kinase signaling genes.  Overall, these data shed light on the etiology of AMKL and provide useful information for treatment tailoring. 

  Study EGAS00001002183

• CancerLocator: Non-Invasive Cancer Diagnosis and Tissue-of-Origin Prediction Using Methylation Profiles of Cell-Free DNA

  Background: The detection and characterization of cell-free DNA in plasma is one of the most promising new areas in cancer diagnosis. Liquid biopsy, unlike traditional tissue biopsy, has the potential to diagnose a variety of different malignancies. Results: Here we propose a probabilistic method, CancerLocator, which exploits the diagnostic potential of cell-free DNA by determining not only the presence but also the location of tumors. CancerLocator simultaneously infers the proportions and the tissue-of-origin of tumor-derived cell-free DNA in a blood sample using genome-wide DNA methylation data. We comprehensively evaluate CancerLocator with simulations and real data, and compare its performance with that of two established multi-class classification methods. We show that the predicted tumor burdens are highly consistent with the true values. In addition, when the proportion of tumor-derived DNAs in the cell-free DNAs is low, the two popular machine learning methods completely fail for cancer diagnosis, while CancerLocator successfully overcomes the challenge. CancerLocator also achieves promising results on patient plasma samples, despite the fact that the DNA methylation data from these samples has very low sequencing coverage. Conclusions: CfDNA methylation may be developed as an important approach for non-invasive early cancer diagnosis.

  Study EGAS00001002211

• Whole genome sequencing of tumour and normal paired samples of diffuse intrinsic pontine gliomas

  Diffuse intrinsic pontine glioma (DIPG) have a universally dismal prognosis (median 9-12 months), with neither chemotherapeutic nor targeted agents showing any substantial survival benefit in clinical trials in children with these tumours. DIPG are highly infiltrative malignant glial neoplasms of the ventral pons, which due to their location within the brain, make them unsuitable for surgical resection and consequently have a universally dismal clinical outcome. Recent high-throughput sequencing approaches have revealed a striking prevalence of K27M mutations in the genes encoding the histone variants H3.3 (H3F3A) or H3.1 (HIST1H3B) in the childhood brain tumour DIPG. This K-to-M substitution confers a trans-dominant ablation of global H3K27 trimethylation, which likely profoundly alters gene expression through de-repression of polycomb repressive complex 2 (PRC2) target genes. Despite these advances in our understanding of the distinct biology of these tumours, approaches for specific novel therapeutic interventions are not clear, and little has been reported of the secondary mutations accompanying these changes. We carried out whole genome sequencing on a series of 20 tumour normal pairs of pre-treatment biopsy samples of DIPG, for which the patients underwent a safe stereotactic procedure, and whole exome sequencing on a further six tumour normal pairs obtained at autopsy.

  Study EGAS00001000572

• Accurate sample assignment in a multiplexed, ultra-sensitive, high-throughput sequencing assay for minimal residual disease

  High throughput sequencing (HTS) (next generation sequencing) of the rearranged immunoglobulin and T-cell receptor genes promises to be cheaper and more sensitive than current methods for monitoring minimal residual disease (MRD) in patients with acute lymphoblastic leukemia. However, adoption of new approaches by clinical laboratories requires careful evaluation of all potential sources of error and the development of strategies to ensure the highest accuracy. Timely and efficient clinical use of HTS platforms will depend on combining multiple samples (multiplexing) in each sequencing run. Here we examine immunoglobulin heavy chain gene HTS on the Illumina MiSeq platform for MRD (HTS-MRD). We identify errors associated with multiplexing that could potentially impact on the accuracy of MRD analysis. We optimise a strategy combining high purity, sequence-optimised oligonucleotides, dual-indexing and an error-aware demultiplexing approach to minimise errors and maximise sensitivity. We present a probability-based demultiplexing pipeline, Error-Aware Demultiplexer (EAD) - that is suitable for all MiSeq sequencing strategies and accurately assigns samples to the correct identifier without excessive loss of data. Finally using controls quantified by digital PCR, we show that HTS-MRD can accurately detect as few as 1 in 106 copies of specific leukemic MRD.

  Study EGAS00001001303

• Biallelic mutations in the ubiquitin ligase RFWD3 cause Fanconi anemia

  The WD40-containing E3 ubiquitin ligase RFWD3 has been recently linked to the repair of DNA damage by Homologous Recombination (HR). Here we show that an RFWD3 mutation within the WD40 domain is connected to the genetic disease Fanconi anemia (FA). An individual revealed congenital abnormalities characteristic for FA. Cells from the patient, carrying the compound heterozygous mutations c.205_206dupCC and c.1916T>A in RFWD3, show increased sensitivity to DNA interstrand cross-linking agents in terms of increased chromosomal breakage, reduced survival and cell cycle arrest in G2 phase. The cellular phenotype is mirrored in genetically engineered human and avian cells by inactivation of RFWD3 or by introduction of the patient-derived missense mutation, and is rescued by expression of wildtype RFWD3 protein. HR is disrupted in RFWD3 mutant cells, caused by impaired relocation of mutant RFWD3 to chromatin and defective physical interaction with RPA. Rfwd3 knockout mice exhibit increased embryonic lethality, are sub-fertile, show ovarian and testicular atrophy and have a reduced life span in which they resemble other FA mouse models. Although mutation was detected in a single child with FA yet, we propose RFWD3 as a novel FA gene, FANCW, supported by cellular paradigm systems and an animal model.

  Study EGAS00001002440

• High Grade Serous Ovarian Carcinomas Originate in the Fallopian Tube

  High-grade serous ovarian carcinoma (HGSOC) is the most frequent type of ovarian cancer and has a poor outcome. It has been proposed that fallopian tube cancers may be precursors of HGSOC but evolutionary evidence for this hypothesis has been limited. To provide insights into the origins of HGSOC, we We performed whole-exome sequence and copy number analyses of laser-capture microdissected fallopian tube lesions (p53 signatures, serous tubal intraepithelial carcinomas (STICs), and fallopian tube carcinomas), ovarian cancers, and metastases from nine patients with HGSOC. The majority of tumor-specific sequence and structural alterations in ovarian cancers were present in STICs, including those affecting TP53, BRCA1, BRCA2 or PTEN genes. An eEvolutionary analyseis revealed that p53 signatures and STICs were are the precursors of ovarian carcinoma which in turn gave rise to metastatic lesionsand identify a. In one patient we identified a second STIC as a metastasis in the fallopian tube opposite from the affected ovary. These analyses revealed a window of seven years between the development of a STIC and the initiation of ovarian carcinomas, with development of metastases following rapidly thereafter. Our results provide insights into the etiology of ovarian cancer and have implications for the prevention, early detection and therapeutic intervention of this disease.

  Study EGAS00001002589

• Whole-exome and targeted sequencing of pediatric hyperdiploid B-cell precursor acute lymphoblastic leukemia

  High hyperdiploidy defines the largest genetic entity of childhood acute lymphoblastic leukemia (ALL). Despite its relatively low recurrence risk, this subgroup generates a high proportion of relapses. The cause and origin of these relapses remains obscure. We therefore explored the mutational landscape in high hyperdiploid (HD) ALL with whole-exome (n=19) and subsequent targeted deep sequencing of 60 genes in 100 relapsing and 51 non-relapsing cases. We identified multiple clones at diagnosis that were primarily defined by a variety of mutations in receptor tyrosine kinase (RTK)/Ras pathway and chromatin-modifying genes. The relapse clones consisted of reappearing as well as new mutations, and overall contained more mutations. Although RTK/Ras pathway mutations were similarly frequent between diagnosis and relapse, both intergenic and intragenic heterogeneity was essentially lost at relapse. CREBBP mutations, however, increased from initially 18-30% at relapse, then commonly co-occurred with KRAS mutations (P<0.001) and these relapses appeared primarily early (P=0.012). Our results confirm the exceptional susceptibility of HD ALL to RTK/Ras pathway and CREBBP mutations, but, more importantly, suggest that mutant KRAS and CREBBP might cooperate and equip cells with the necessary capacity to evolve into a relapse-generating clone.

  Study EGAS00001001113

• Single cell transcriptomic landscape of pediatric B-cell acute lymphoblastic leukemia: dissection of transcriptional heterogeneity and B-cell developmental state

  Introduction: Genomic analyses of bulk ALL samples have improved our understanding of the genetic basis and risk stratification of B-ALL, but do not directly examine intratumor heterogeneity or enable inference of leukemia developmental state and cell of origin. Methods: We profiled 89 B-ALL samples by single-cell RNA-seq (scRNA-seq) (10X Genomics 5’v2) and compared them to a scRNA-seq reference map of normal human B-cell development. Results: Analysis of heterogeneity of inferred DNA copy number alterations at single cell level showed that aneuploid ALL with near haploidy and hyperdiploid harbor chromosomal losses or gains in all blasts, consistent with early, synchronous origin rather than sequential accumulation. Intra-sample heterogeneity was driven by five gene expression signatures: cell cycle, metabolism, differentiation, inflammation, refining leukemic subtyping. An atlas of B cell development was established to map B-ALL samples to specific developmental states. Hyperdiploid samples resembled pro-B cells, while MEF2D-r and TCF3::PBX1 showed high pre-B abundance. Patients with high early lymphoid abundance had poorer outcomes. Conclusions: Understanding variation in transcriptional programs and developmental states of B-ALL blasts by sc transcriptome refines existing clinical and genomic classifications and provides novel prognostic markers.

  Study EGAS00001007512

• Ewing and Ewing-like-sarcoma tumoroid biobank reveals distinct drug sensitivities: translocation makes the difference

  Ewing sarcoma (ES) and Ewing-like sarcomas (ELS) are highly aggressive tumors found in soft tissues and bone of mostly children and young adults. Despite being different in many aspects, including genetics, possible cell-of-origin, and pathology, patients with any of these entities all receive the same therapeutic regimen. Currently, there is a lack of preclinical cell models that can predict drug response of these entities in vitro. Here, we describe a pediatric ES and ELS tumor organoid (tumoroid) biobank containing tumoroids with different translocations, including EWSR1::FLI1, EWSR1::ERG, CIC::DUX4, and BCOR-rearrangements. Using histology, whole genome sequencing and RNA sequencing, we demonstrate that these tumoroids retain key properties of their matching patient tumors. In addition, we traced tumor subclones in the tumoroids across patient-matched longitudinal samples, which showed that cellular heterogeneity was maintained. We subsequently performed drug screening on the tumoroid models, which unveiled entity-specific drug sensitivity to various cytotoxic compounds and targeted compounds, including MCL-1 inhibitors for CIC::DUX4 sarcomas. Taken together, this newly established ES and ELS patient-derived tumoroid biobank generates a unique source of material for future basic cancer research and drug-screening.

  Study EGAS00001007941

• Pooled scRNA-seq of iPSC-derived neural stem cells from ADHD and control individuals

  This dataset comprises paired-end FASTQ files from single-cell RNA sequencing (scRNA-seq) of neural stem cells (NSCs) derived from induced pluripotent stem cells (iPSCs). The iPSCs were reprogrammed from somatic cells (keratinocytes, PBMCs, or lymphoblastoid cell lines) collected from individuals diagnosed with attention-deficit hyperactivity disorder (ADHD) and age-matched healthy controls (ages 6–18 years). Reprogramming was carried out using the non-integrative Sendai virus system (CytoTune-iPS 2.0, Thermo Fisher Scientific), introducing OCT3/4, SOX2, KLF4, and cMYC. iPSCs were cultured in Essential 8 medium on vitronectin and underwent rigorous quality control including immunocytochemistry, qRT-PCR, mycoplasma testing, and SNP genotyping (Illumina Global Screening Array). NSCs were generated using a standardized neural induction protocol and validated via qRT-PCR and immunostaining for markers including PAX6, SOX2, NESTIN, TUJ1, and FOXG1. Two independent scRNA-seq multiplexed experiments were performed: Experiment 1 (ADHD: n = 7; Control: n = 6) and Experiment 2 (ADHD: n = 9; Control: n = 7). Samples were pooled and demultiplexed using the Ensemblex algorithm, incorporating prior genotype data. After quality control filtering (>500 unique RNA molecules per cell), 30,433 single-cell transcriptomes were retained. Differential gene expression analysis was conducted to identify transcriptional signatures associated with ADHD compared to controls.

  Study EGAS00001008169