TNFα stimulates NKG2D-mediated lytic activity of acute myeloid leukemic cells

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Cutaneous mastocytosis in adults with a serum tryptase level < 20 ng mL –1: why we should investigate further

International audienceDear Editor, Mastocytosis is a rare disease characterized by the accumulation/proliferation of abnormal mast cells (MCs).1 Mastocytosis is categorized into isolated cutaneous mastocytosis (CM), where only the skin is infiltrated by abnormal MC, and systemic mastocytosis (SM), where at least one internal organ is involved.2 SM is diagnosed according to the criteria defined by the World Health Organization (WHO).3 The major criterion consists of the presence of multifocal dense infiltrates of MC in a bone marrow (BM) biopsy or extracutaneous tissues. The minor criteria comprise the following: the presence of > 25% of MC with abnormal cytology out of all MCs in a BM biopsy or in other nonskin tissues; abnormal expression of CD2 and/or CD25 on MCs in an immunohistochemistry study and/or by flow cytometry analysis; the presence of the KIT codon D816V mutation in BM aspirate and a serum tryptase level (STL) > 20 ng mL–1. SM is diagnosed if the major criterion and at least one minor criterion or three minor criteria are present. For the diagnosis of SM, performing a BM aspirate and/or a BM biopsy is mandatory. For a patient presenting with CM, the first question for the physician is whether the disease is limited to the skin or does it involve internal organs? Answering this question is of relevance as specific treatments are available or under investigation in patients with SM – especially those with disabling MC activation symptoms or advanced SM. Screening basal STL in patients with CM is considered to be a cost-effective first-line tool to distinguish possible SM from isolated CM

P477: PHENOTYPICALLY-DEFINED STAGES OF LEUKEMIA ARREST PREDICT MAIN DRIVER MUTATIONS SUBGROUPS, AND OUTCOME IN ACUTE MYELOID LEUKEMIA

Classifications of acute myeloid leukemia (AML) patients rely on morphologic, cytogenetic, and molecular features. Here we have established a novel flow cytometry-based immunophenotypic stratification showing that AML blasts are blocked at specific stages of differentiation where features of normal myelopoiesis are preserved. Six stages of leukemia differentiation-arrest categories based on CD34, CD117, CD13, CD33, MPO, and HLA-DR expression were identified in two independent cohorts of 2087 and 1209 AML patients. Hematopoietic stem cell/multipotent progenitor-like AMLs display low proliferation rate, inv(3) or RUNX1 mutations, and high leukemic stem cell frequency as well as poor outcome, whereas granulocyte–monocyte progenitor-like AMLs have CEBPA mutations, RUNX1-RUNX1T1 or CBFB-MYH11 translocations, lower leukemic stem cell frequency, higher chemosensitivity, and better outcome. NPM1 mutations correlate with most mature stages of leukemia arrest together with TET2 or IDH mutations in granulocyte progenitors-like AML or with DNMT3A mutations in monocyte progenitors-like AML. Overall, we demonstrate that AML is arrested at specific stages of myeloid differentiation (SLA classification) that significantly correlate with AML genetic lesions, clinical presentation, stem cell properties, chemosensitivity, response to therapy, and outcome

Human acute myelogenous leukemia stem cells are rare and heterogeneous when assayed in NOD/SCID/IL2Rγc-deficient mice

Human leukemic stem cells, like other cancer stem cells, are hypothesized to be rare, capable of incomplete differentiation, and restricted to a phenotype associated with early hematopoietic progenitors or stem cells. However, recent work in other types of tumors has challenged the cancer stem cell model. Using a robust model of xenotransplantation based on NOD/SCID/IL2Rγc-deficient mice, we confirmed that human leukemic stem cells, functionally defined by us as SCID leukemia-initiating cells (SL-ICs), are rare in acute myelogenous leukemia (AML). In contrast to previous results, SL-ICs were found among cells expressing lineage markers (i.e., among Lin+ cells), CD38, or CD45RA, all markers associated with normal committed progenitors. Remarkably, each engrafting fraction consistently recapitulated the original phenotypic diversity of the primary AML specimen and contained self-renewing leukemic stem cells, as demonstrated by secondary transplants. While SL-ICs were enriched in the Lin–CD38– fraction compared with the other fractions analyzed, SL-ICs in this fraction represented only one-third of all SL-ICs present in the unfractionated specimen. These results indicate that human AML stem cells are rare and enriched but not restricted to the phenotype associated with normal primitive hematopoietic cells. These results suggest a plasticity of the cancer stem cell phenotype that we believe has not been previously described

Human erythroleukemia genetics and transcriptomes identify master transcription factors as functional disease drivers

Acute erythroleukemia (AEL or acute myeloid leukemia [AML]-M6) is a rare but aggressive hematologic malignancy. Previous studies showed that AEL leukemic cells often carry complex karyotypes and mutations in known AML-associated oncogenes. To better define the underlying molecular mechanisms driving the erythroid phenotype, we studied a series of 33 AEL samples representing 3 genetic AEL subgroups including TP53-mutated, epigenetic regulator-mutated (eg, DNMT3A, TET2, or IDH2), and undefined cases with low mutational burden. We established an erythroid vs myeloid transcriptome-based space in which, independently of the molecular subgroup, the majority of the AEL samples exhibited a unique mapping different from both non-M6 AML and myelodysplastic syndrome samples. Notably, >25% of AEL patients, including in the genetically undefined subgroup, showed aberrant expression of key transcriptional regulators, including SKI, ERG, and ETO2. Ectopic expression of these factors in murine erythroid progenitors blocked in vitro erythroid differentiation and led to immortalization associated with decreased chromatin accessibility at GATA1-binding sites and functional interference with GATA1 activity. In vivo models showed development of lethal erythroid, mixed erythroid/myeloid, or other malignancies depending on the cell population in which AEL-associated alterations were expressed. Collectively, our data indicate that AEL is a molecularly heterogeneous disease with an erythroid identity that results in part from the aberrant activity of key erythroid transcription factors in hematopoietic stem or progenitor cells

Oncogenic FLT3-ITD supports autophagy via ATF4 in acute myeloid leukemia

International audienceIn acute myeloid leukemia (AML), internal tandem duplication mutations in the FLT3 tyrosine kinase receptor (FLT3-ITD) account for up to 25% of cases and are associated with a poor outcome. In order to better target this AML subtype, a comprehensive view of how FLT3-ITD impacts AML cell biology is required. Here, we found that FLT3-ITD expression increased basal autophagy in AML cells, and that both pharmacological and genetic inhibition of the receptor reduced autophagy in primary AML samples and cell lines. Conditional expression of shRNAs against key autophagy proteins demonstrated that autophagy is required for AML cell proliferation in vitro and for leukemic cells survival in a mouse model of xenograft. Importantly, autophagy inhibition also overcame FLT3 inhibitor resistance both in vitro and in vivo. The transcription factor ATF4 was identified as an essential actor of FLT3-ITD-induced autophagy. Cellular levels of ATF4 were highly dependent on FLT3-ITD activity, and downregulation of ATF4 inhibited autophagy-dependent AML cell proliferation and improved overall mouse survival similarly to autophagy inhibition. These results suggest that targeting autophagy or ATF4 in patients expressing FLT3 mutations may represent a novel promising and innovative therapeutic strategy for AML

C/EBPa confers dependence to fatty acid anabolic pathways and vulnerability to lipid oxidative stress-induced ferroptosis in FLT3-mutant leukemia.

While transcription factor C/AAT-enhancer binding protein a (C/EBPa) is critical for normal and leukemic differentiation, its role on cell and metabolic homeostasis is largely unknown in cancer. Here, multi-omics analyses uncovered a coordinated activation of C/EBPa and Fms-like tyrosine kinase 3 (FLT3) that increased lipid anabolism in vivo and in patients with FLT3-mutant acute myeloid leukemia (AML). Mechanistically, C/EBPa regulated FASN-SCD axis to promote fatty acid (FA) biosynthesis and desaturation. We further demonstrated that FLT3 or C/EBPa inactivation decreased mono-unsaturated FA incorporation to membrane phospholipids through SCD downregulation. Consequently, SCD inhibition enhanced susceptibility to lipid redox stress that was exploited by combining FLT3 and glutathione peroxidase 4 inhibition to trigger lipid oxidative stress, enhancing ferroptotic death of FLT3-mutant AML cells. Altogether, our study reveals a C/EBPa function in lipid homeostasis and adaptation to redox stress, and a previously unreported vulnerability of FLT3-mutant AML to ferroptosis with promising therapeutic application