Genetics and clonal architecture of Juvenile Myelomonocytic Leukemia

La LMMJ est un syndrome myéloprolifératif et myélodysplasique rare du jeune enfant, initiée par des mutations classiquement décrites comme mutuellement exclusives de RAS (NRAS, KRAS) ou de régulateurs de la voie RAS (PTPN11, NF1 ou CBL). Ces mutations, somatiques ou constitutionnelles, entraînent l’hyperactivation de cette voie de signalisation et une hypersensibilité spécifique au GM-CSF. La LMMJ est une hémopathie sévère dont le seul traitement est l’allogreffe de moelle osseuse. Cependant sa présentation et son évolution sont particulièrement hétérogènes puisqu’une transformation en leucémie aiguë myéloide survient chez un tiers des patients quand d’autres présentent des formes plus indolentes, voire des rémissions spontanées en l’absence de greffe. Cette hétérogénéité n’est que partiellement liée à la mutation initiatrice et pourrait s’expliquer par la présence de mutations additionnelles et/ou par une variabilité dans la cellule initiatrice de la leucémie, qui n’a jamais été précisément caractérisée.La caractérisation génétique de 118 LMMJ nous a permis de montrer que les anomalies génétiques additionnelles sont peu nombreuses dans les LMMJ sporadiques, et exceptionnelles dans les LMMJ syndromiques sauf en cas de neurofibromatose de type-1. Ces anomalies se concentrent sur deux grands systèmes, la voie RAS et le PRC2, et leur présence s’accompagne d’un pronostic défavorable (particulièrement en cas de mutations multiples de la voie RAS). L’absence d’anomalie additionnelle permet à l’inverse de distinguer un sous-groupe de patients qui présentent une forte probabilité de survie à long terme sans greffe et pour lesquels une soultion attentiste serait à privilégier. Une collaboration avec l’équipe de D Bonnet (Crick Institute) nous a ensuite permis d’établir un modèle murin de xénotransplantation dans des souris immunodéficientes de type NSG ou NSG-S et de montrer que la capacité de propagation de la leucémie est bien portée par la fraction souche, mais s’étend aussi chez certains patients à des fractions plus différenciées. Le profil génétique des 15 xénogreffes étudiées reproduit fidèlement l’architecture clonale des LMMJ natives, tant dans les souris NSG que NSG-S. L’architecture clonale des LMMJ est dans la majorité des cas compatible avec une acquisition linéaire des altérations, mais une architecture complexe est parfois observée, avec coexistence de clones distincts, dont les plus faiblement représentés sont susceptibles de devenir dominants lors de la rechute. Le séquençage de sous-populations isolées a montré que l’ensemble des mutations (initiatrice et additionnelles) est présent dès les fractions les plus immatures (HSC/MPP/MLP). Le séquençage de colonies obtenues par culture des progéniteurs en méthylcellulose révèle que les mutations coexistent dans les mêmes cellules, sans qu’il soit possible de hiérarchiser leur ordre de survenue, témoignant d’un avantage sélectif majeur de leur association dès la cellule souche. Au total, nos résultats remettent en cause le dogme de l’exclusivité mutuelle des mutations activant RAS dans les LMMJ, confirment le rôle central et initiateur de cette voie oncogénique dans la leucémogénèse et suggérent un effet-dose de l’activation de RAS, en particulier en cas de mutation de NRAS. La présence d’altérations multiples ciblant la voie RAS marque des LMMJ agressives et rapidement évolutives. La mise en évidence d’une fréquente dérégulation du PRC2 offre de nouvelles perspectives therapeutiques (comme l’utilisation des inhibiteurs de bromodomaine). La mise en place d’un modèle de souris xénotransplantée devrait de plus faciliter les études biologiques et la mise en place d’évaluations précliniques.JMML is a rare myeloproliferative and myelodysplastic neoplasm of early childhood, initiated by mutations classically described as mutually exclusive of RAS (NRAS, KRAS) or RAS pathway regulators (PTPN11, NF1 or CBL). These mutations, either germline or somatically aquired, lead to an hyperactivation of the RAS signalling pathway and a to a specific hypersensitivity to GM-CSF. JMML is a severe hemopathy, and the only curative treatment is allogenic bone marrow transplantation. However, its presentation and evolution are particularly heterogeneous since transformation into acute myeloid leukaemia occurs in about one third of patients, when others present more indolent forms, or even spontaneous remissions in the absence of transplantation. This heterogeneity is only partially accounted for by the initiating mutation and could be related to the presence of additional mutations, or some variability in the leukemia initiating cell, which has never been precisely characterized so far.Establishing the genetic landscape of 118 LMMJ allowed us to show that additional genetic abnormalities are scarse in sporadic JMML and exceptional in syndromic JMML, except in the case of type-1 neurofibromatosis. These additional abnormalities mainly target two major biologic components, the RAS pathway and the PRC2, and their presence is associated with an unfavourable prognosis (particularly in the case of multiple mutations targeting the RAS pathway). On the other hand, the absence of any additional abnormality allows to delineate a subgroup of patients who have a high probability of long-term survival in the absence of bone marrow transplantation, and for whom a wait-and-see approach would be preferable. A collaboration with D. Bonnet’s group (Crick Institute) allowed us to establish a mouse model of xenotransplantation in immunodeficient NSG or NSG-S mice and to demonstrate that the leukemia propagating cell is present in the stem cell fractions (HSC, CD34+/CD38-…) but also extends in certain patients to more differentiated fractions, such as CMP. The genetic profile of xenografts established from 15 JMML faithfully reproduced the clonal architecture of the native leukemia, either in NSG or NSG-S mice. The clonal architecture of JMML is linear in the great majority of cases, with linear acquisition of alterations, but a complex architecture is sometimes observed, with coexistence of distinct clones, the weakest of which being susceptible to become dominant at relapse. Sequencing of sorted cell populations showed that all mutations (initiating and additional) are present in the most immature fractions (HSC/MPP/MLP). The sequencing of colonies obtained by culturing progenitors into methylcellulose revealed that mutations coexist in the same cells, their order of appearance being often impossible to determine, showing a major selective advantage of their association from the most immature compartment. In conclusion, our findings confirm the central role of RAS activation in JMML leukemogenesis. The identification of multiple alterations targeting the RAS pathway challenges the dogma of the mutual exclusivity of these mutations and defines a subset of aggressive and rapidly evolving JMML, suggesting a dose-effect of RAS activation, particularly in case with NRAS mutation. Recurrent deregulation of PRC2 in JMML may offer new therapeutic approaches, such as bromodomain inhibitors. The implementation of a xenotransplanted mouse model should also facilitate biological studies and the implementation of preclinical evaluations

Novel diagnostic and therapeutic options for KMT2A-rearranged acute leukemias

The KMT2A (MLL) gene rearrangements (KMT2A-r) are associated with a diverse spectrum of acute leukemias. Although most KMT2A-r are restricted to nine partner genes, we have recently revealed that KMT2A-USP2 fusions are often missed during FISH screening of these genetic alterations. Therefore, complementary methods are important for appropriate detection of any KMT2A-r. Here we use a machine learning model to unravel the most appropriate markers for prediction of KMT2A-r in various types of acute leukemia. A Random Forest and LightGBM classifier was trained to predict KMT2A-r in patients with acute leukemia. Our results revealed a set of 20 genes capable of accurately estimating KMT2A-r. The SKIDA1 (AUC: 0.839; CI: 0.799–0.879) and LAMP5 (AUC: 0.746; CI: 0.685–0.806) overexpression were the better markers associated with KMT2A-r compared to CSPG4 (also named NG2; AUC: 0.722; CI: 0.659–0.784), regardless of the type of acute leukemia. Of importance, high expression levels of LAMP5 estimated the occurrence of all KMT2A-USP2 fusions. Also, we performed drug sensitivity analysis using IC50 data from 345 drugs available in the GDSC database to identify which ones could be used to treat KMT2A-r leukemia. We observed that KMT2A-r cell lines were more sensitive to 5-Fluorouracil (5FU), Gemcitabine (both antimetabolite chemotherapy drugs), WHI-P97 (JAK-3 inhibitor), Foretinib (MET/VEGFR inhibitor), SNX-2112 (Hsp90 inhibitor), AZD6482 (PI3Kβ inhibitor), KU-60019 (ATM kinase inhibitor), and Pevonedistat (NEDD8-activating enzyme (NAE) inhibitor). Moreover, IC50 data from analyses of ex-vivo drug sensitivity to small-molecule inhibitors reveals that Foretinib is a promising drug option for AML patients carrying FLT3 activating mutations. Thus, we provide novel and accurate options for the diagnostic screening and therapy of KMT2A-r leukemia, regardless of leukemia subtype

The prognostic value of IKZF1(plus) in B‐cell progenitor acute lymphoblastic leukemia : results from the EORTC 58951 trial

BackgroundIKZF1 gene deletion is an indicator of poor prognosis in childhood B-cell precursor acute lymphoblastic leukemia (BCP-ALL). The AEIOP/BFM group proposed that the prognostic strength of IKZF1 deletion could be remarkably improved by taking into account additional genetic deletions and reported that among patients with an IKZF1 deletion those with deletions in CDKN2A/2B, PAX5, or PAR1 in the absence of ERG deletion, grouped as IKZF1(plus), had the worst outcome. ProcedureBetween 1998 and 2008, 1636 patients under 18 years of age with previously untreated BCP-ALL were registered in the EORTC 58951 trial. Those with multiplex ligation-dependent probe amplification data were included in this analysis. Unadjusted and adjusted Cox model was used to investigate the additional prognostic value of IKZF1(plus). ResultsAmong 1200 patients included in the analysis, 1039 (87%) had no IKZF1 deletion (IKZF1(WT)), 87 (7%) had an IKZF1 deletion but not IKZF1(plus) (IKZF1(del)) and 74 (6%) had IKZF1(plus). In the unadjusted analysis, both patients with IKZF1(del) (hazard ratio [HR] = 2.10, 95% confidence interval [CI]: 1.34-3.31) and IKZF1(plus) (HR = 3.07, 95% CI: 2.01-4.67) had a shorter event-free survival compared with IKZF1(WT). However, although the IKZF1(plus) status was associated with patients' characteristics indicating poor prognosis, the difference between IKZF1(plus) and IKZF1(del) was not statistically significant (HR = 1.46, 95% CI: 0.83-2.57, p = .19). The results of the adjusted analysis were similar to the unadjusted analysis. ConclusionsIn patients with BCP-ALL from the EORTC 58951 trial, the improvement of the prognostic importance of IKZF1 by considering IKZF1(plus) was not statistically significant

Large deletions of the 5' region of IKZF1 lead to haploinsufficiency in B-cell precursor acute lymphoblastic leukaemia

No abstract availabl

Targeted High-throughput Sequencing for Hematological Malignancies: A GBMHM Survey of Practice and Cost Evaluation in France

The objective of this study was to assess the clinical impact and financial costs of next-generation sequencing (NGS) in 5 categories of pediatric and adult hematological cancers. NGS prescriptions were prospectively collected from 26 laboratories, with varied technical and reporting practice (all or only significant targets). Impact was defined by the identification of (1) an actionable mutation, (2) a mutation with prognostic and/or theranostic value, and/or (3) a mutation allowing nosological refinement, reported by local investigators. A microcosting study was undertaken in 4 laboratories, identifying the types and volumes of resources required for each procedural step. Individual index prescriptions for 3961 patients were available for impact analysis on the management of myeloid disorders (two thirds) and, mainly mature B, lymphoid disorders (one third). NGS results were considered to impact the management for 73.4% of prescriptions: useful for evaluation of prognostic risk in 34.9% and necessary for treatment adaptation (actionable) in 19.6%, but having no immediate individual therapeutic impact in 18.9%. The average overall cost per sample was 191 € for the restricted mature lymphoid amplicon panel. Capture panel costs varied from 369 € to 513 €. Unit costs varied from 0.5 € to 5.7 € per kb sequenced, from 3.6 € to 11.3 € per target gene/hot-spot sequenced and from 4.3 € to 73.8 € per target gene/hot-spot reported. Comparable costs for the Amplicon panels were 5–8 € per kb and 10.5–14.7 € per target gene/hot-spot sequenced and reported, demonstrating comparable costs with greater informativity/flexibility for capture strategies. Sustainable funding of precision medicine requires a transparent discussion of its impact on care pathways and its financial aspects