Ontogenic Changes in Hematopoietic Hierarchy Determine Pediatric Specificity and Disease Phenotype in Fusion Oncogene-Driven Myeloid Leukemia.

Fusion oncogenes are prevalent in several pediatric cancers, yet little is known about the specific associations between age and phenotype. We observed that fusion oncogenes, such as ETO2-GLIS2, are associated with acute megakaryoblastic or other myeloid leukemia subtypes in an age-dependent manner. Analysis of a novel inducible transgenic mouse model showed that ETO2-GLIS2 expression in fetal hematopoietic stem cells induced rapid megakaryoblastic leukemia whereas expression in adult bone marrow hematopoietic stem cells resulted in a shift toward myeloid transformation with a strikingly delayed in vivo leukemogenic potential. Chromatin accessibility and single-cell transcriptome analyses indicate ontogeny-dependent intrinsic and ETO2-GLIS2-induced differences in the activities of key transcription factors, including ERG, SPI1, GATA1, and CEBPA. Importantly, switching off the fusion oncogene restored terminal differentiation of the leukemic blasts. Together, these data show that aggressiveness and phenotypes in pediatric acute myeloid leukemia result from an ontogeny-related differential susceptibility to transformation by fusion oncogenes. SIGNIFICANCE: This work demonstrates that the clinical phenotype of pediatric acute myeloid leukemia is determined by ontogeny-dependent susceptibility for transformation by oncogenic fusion genes. The phenotype is maintained by potentially reversible alteration of key transcription factors, indicating that targeting of the fusions may overcome the differentiation blockage and revert the leukemic state.See related commentary by Cruz Hernandez and Vyas, p. 1653.This article is highlighted in the In This Issue feature, p. 1631

Acquired TET2 mutation in one patient with familial platelet disorder with predisposition to AML led to the development of pre-leukaemic clone resulting in T2-ALL and AML-M0

International audienceFamilial platelet disorder with predisposition to acute myeloid leukaemia (FPD/AML) is characterized by germline RUNX1 mutations, thrombocy-topaenia, platelet dysfunction and a risk of developing acute myeloid and in rare cases lymphoid T leukaemia. Here, we focus on a case of a man with a familial history of RUNX1 R174Q mutation who developed at the age of 42 years a T2-ALL and, 2 years after remission, an AML-M0. Both AML-M0 and T2-ALL blast populations demonstrated a loss of 1p36.32-23 and 17q11.2 regions as well as other small deletions, clonal rearrangements of both TCRc and TCRd and a presence of 18 variants at a frequency of more than 40%. Additional variants were identified only in T2-ALL or in AML-M0 evoking the existence of a common original clone, which gave rise to subclonal populations. Next generation sequen-cing (NGS) performed on peripheral blood-derived CD34 + cells 5 years prior to T2-ALL development revealed only the missense TET2 P1962T mutation at a frequency of 1%, which increases to more than 40% in fully transformed leukaemic T2-ALL and AML-M0 clones. This result suggests that TET2 P1962T mutation in association with germline RUNX1 R174Q mutation leads to amplification of a haematopoietic clone susceptible to acquire other transforming alterations

Genetic characterization of B-cell prolymphocytic leukemia: a prognostic model involving and MYC and TP53

B-cell prolymphocytic leukemia (B-PLL) is a rare hematological disorder whose underlying oncogenic mechanisms are poorly understood. Our cytogenetic and molecular assessment of 34 patients with B-PLL revealed several disease-specific features and potential therapeutic targets. The karyotype was complex ({greater than or equal to}3 abnormalities) in 73% of the patients and highly complex (5 abnormalities) in 45%. The most frequent chromosomal aberrations were translocations involving [t()] (62%), deletion (del)17p (38%), trisomy (tri)18 (30%), del13q (29%), tri3 (24%), tri12 (24%), and del8p (23%). Twenty-six of the 34 patients (76%) exhibit aberration, resulting from mutually exclusive translocations or gains. Whole-exome sequencing revealed frequent mutations in , , , , , , , , and The majority of B-PLL used the or subgroups (89%), and displayed significantly mutated genes (79%). We identified three distinct cytogenetic risk groups: low-risk (no aberration), intermediate-risk ( aberration but no del17p), and high-risk ( aberration and del17p) (p=.0006). drug response profiling revealed that the combination of a B-cell receptor or BCL2 inhibitor with OTX015 (a bromodomain and extra-terminal motif (BET) inhibitor targeting ) was associated with significantly lower viability of B-PLL cells harboring a t(). We conclude that cytogenetic analysis is a useful diagnostic and prognostic tool in B-PLL. Targeting may be a useful treatment option in this disease

Presence of atypical thrombopoietin receptor (MPL) mutations in triple negative essential thrombocythemia patients.

International audienceMutations in signaling molecules of the cytokine receptor axis play a central role in myeloproliferative neoplasm (MPN) pathogenesis. Polycythemia Vera is mainly related to JAK2 mutations, whereas a wider mutational spectrum is detected in Essential Thrombocythemia (ET) with mutations in JAK2, the thrombopoietin receptor (MPL) and the calreticulin (CALR) genes. Here, we studied the mutational profile of 17 ET patients negative for JAK2V617F, MPLW515K/L and CALR mutations, using Whole Exome Sequencing and Next Generation Sequencing (NGS) targeted on JAK2 and MPL. We found several signaling mutations including JAK2V617F at very low allele frequency, one homozygous SH2B3 mutation, one MPLS505N, one MPLW515R and two MPLS204P mutations. In the remaining patients, four presented a clonal and seven a polyclonal hematopoiesis, suggesting that certain triple negative ETs are not MPNs. NGS on 26 additional triple negative ETs detected only one MPLY591N mutation. Functional studies on MPLS204P and MPLY591N revealed that they are weak gain-of-function mutants increasing MPL signaling and conferring either TPO hypersensitivity or independence to expressing cells, but with a low efficiency. Further studies should be performed to precisely determine the frequency of MPLS204 and MPLY591 mutants in a bigger cohort of MPN

Genetic characterization of B-cell prolymphocytic leukemia: a prognostic model involving MYC and TP53

International audienceB-cell prolymphocytic leukemia (B-PLL) is a rare hematological disorder whose underlying oncogenic mechanisms are poorly understood. Our cytogenetic and molecular assessment of 34 patients with B-PLL revealed several disease-specific features and potential therapeutic targets. The karyotype was complex ({greater than or equal to}3 abnormalities) in 73% of the patients and highly complex (>5 abnormalities) in 45%. The most frequent chromosomal aberrations were translocations involving MYC [t(MYC)] (62%), deletion (del)17p (38%), trisomy (tri)18 (30%), del13q (29%), tri3 (24%), tri12 (24%), and del8p (23%). Twenty-six of the 34 patients (76%) exhibit MYC aberration, resulting from mutually exclusive translocations or gains. Whole-exome sequencing revealed frequent mutations in TP53, MYD88, BCOR, MYC, SF3B1, SETD2, CHD2, CXCR4, and BCLAF1 The majority of B-PLL used the IGHV3 or IGHV4 subgroups (89%), and displayed significantly mutated IGHV genes (79%). We identified three distinct cytogenetic risk groups: low-risk (no MYC aberration), intermediate-risk (MYC aberration but no del17p), and high-risk (MYC aberration and del17p) (p=.0006). In vitro drug response profiling revealed that the combination of a B-cell receptor or BCL2 inhibitor with OTX015 (a bromodomain and extra-terminal motif (BET) inhibitor targeting MYC) was associated with significantly lower viability of B-PLL cells harboring a t(MYC). We conclude that cytogenetic analysis is a useful diagnostic and prognostic tool in B-PLL. Targeting MYC may be a useful treatment option in this disease

Germline duplication of ATG2B and GSKIP predisposes to familial myeloid malignancies

No major predisposition gene for familial myeloproliferative neoplasms (MPN) has been identified. Here we demonstrate that the autosomal dominant transmission of a 700-kb duplication in four genetically related families predisposes to myeloid malignancies, including MPN, frequently progressing to leukemia. Using induced pluripotent stem cells and primary cells, we demonstrate that overexpression of ATG2B and GSKIP enhances hematopoietic progenitor differentiation, including of megakaryocytes, by increasing progenitor sensitivity to thrombopoietin (TPO). ATG2B and GSKIP cooperate with acquired JAK2, MPL and CALR mutations during MPN development. Thus, the germline duplication may change the fitness of cells harboring signaling pathway mutations and increases the probability of disease development