Interleukin-18 produced by bone marrow- derived stromal cells supports T-cell acute leukaemia progression

International audienceDevelopment of novel therapies is critical for T-cell acute leukae-mia (T-ALL). Here, we investigated the effect of inhibiting the MAPK/MEK/ERK pathway on T-ALL cell growth. Unexpectedly, MEK inhibitors (MEKi) enhanced growth of 70% of human T-ALL cell samples cultured on stromal cells independently of NOTCH activa-tion and maintained their ability to propagate in vivo. Similar results were obtained when T-ALL cells were cultured with ERK1/ 2-knockdown stromal cells or with conditioned medium from MEKi-treated stromal cells. Microarray analysis identified interleu-kin 18 (IL-18) as transcriptionally up-regulated in MEKi-treated MS5 cells. Recombinant IL-18 promoted T-ALL growth in vitro, whereas the loss of function of IL-18 receptor in T-ALL blast cells decreased blast proliferation in vitro and in NSG mice. The NFKB pathway that is downstream to IL-18R was activated by IL-18 in blast cells. IL-18 circulating levels were increased in T-ALL-xeno-grafted mice and also in T-ALL patients in comparison with controls. This study uncovers a novel role of the pro-inflammatory cytokine IL-18 and outlines the microenvironment involvement in human T-ALL development

Oncogenic Drivers in Myeloproliferative Neoplasms: From JAK2 to Calreticulin Mutations.

During the past 10 years, major progress has been accomplished with the discovery of activating mutations that are associated with the vast majority of BCR-ABL negative human myeloproliferative neoplasms (MPNs). The identification in 2005 of JAK2 V617F triggered great interest in the JAK2-STAT5/STAT3 pathway. Discovery in 2006 of mutants of thrombopoietin receptor (TPO-R/MPL) and later on of mutants in negative regulators of JAK-STAT pathway led to the notion that persistent JAK2 activation is a hallmark of MPNs. In 2013, mutations in the gene coding for the chaperone calreticulin were reported in 20-30 % of essential thrombocythemia and primary myelofibrosis patients. Here, we will address the question: what do we know about calreticulin that could help us understand its role in MPNs? In addition to oncogenic driver mutations, certain MPNs also exhibit epigenetic mutations. Targeting of both oncogenic drivers and epigenetic defects could be required for effective therapy

Peripheral Blood Plasmacytoid Dendritic Cells at Day 100 Can Predict Outcome after Allogeneic Stem Cell Transplantation

International audienceThe rapidly increasing use of allogeneic stem cell transplantation (allo-SCT) emphasizes the need for identifying variables predictive of its outcome. Plasmacytoid dendritic cells (pDCs) play a major role in establishing immune competence and in several autoimmune diseases. Thus, we investigated whether pDCs might influence the outcome of patients after allo-SCT in 79 consecutive patients who underwent this procedure. pDCs were identified in the blood of patients at day 100 after allo-SCT by staining peripheral blood mono-nuclear cells for surface markers and intracellular cytokines and analyzing them on a flow cytometer. We found the pDC level at day 100 was not influenced by patient or graft characteristics, and only the absence of previous grades II to IV acute graft-versus-host disease was significantly associated with higher levels of blood pDCs after allo-SCT (OR, .67; 95% CI, .54 to .83; P ¼ .0004). Using the median value of pDCs at day 100 to divide the patients into 2 distinct groups, we observed that a low pDC level was correlated with a worse overall survival (55% versus 86%, P ¼ .007). In a multivariate analysis, only low pDC level (OR, 3.41; 95% CI, 1.19 to 9.79; P ¼ .02) and older patient age (OR, 5.16; 95% CI, 1.15 to 23.14; P ¼ .03) were significantly predictive of increased risk of death. We conclude that monitoring of pDC may be useful for patient management and may have a significant impact on the probability of a favorable outcome of allo-SCT. INTRODUCTION Allogeneic stem cell transplantation (allo-SCT) has evolved into a curative therapy for a variety of hematological and nonhematological malignancies. In the treatment of the former, high-intensity conditioning therapy before allo-SCT eradicates malignant cells, and the infusion of donor stem cells enables reconstitution of the recipient's hematopoietic system and also triggers a graft-versus-leukemia (GVL) effect. However, the main limitation of treating a broader spectrum of diseases and patients with allo-SCT is graft-versus-host disease (GVHD), a reaction closely associated to GVL. Both GVHD and GVL occur when donor T lymphocytes respond to genetically defined proteins on host cells. Den-dritic cells (DCs) are key antigen-presenting cells tha

Uncoupling JAK2 V617F activation from cytokine-induced signaling by modulation of JH2 αC helix.

The mechanisms by which JAK2 is activated by the prevalent pseudokinase (JH2) V617F mutation in blood cancers remain elusive. Via structure-guided mutagenesis and transcriptional and functional assays, we identify a community of residues from the JH2 helix αC, SH2-JH2 linker and JH1 kinase domain that mediate V617F-induced activation. This circuit is broken by altering the charge of residues along the solvent-exposed face of the JH2 αC, which is predicted to interact with the SH2-JH2 linker and JH1. Mutations that remove negative charges or add positive charges, such as E596A/R, do not alter the JH2 V617F fold, as shown by the crystal structure of JH2 V617F E596A. Instead, they prevent kinase domain activation via modulation of the C-terminal residues of the SH2-JH2 linker. These results suggest strategies for selective V617F JAK2 inhibition, with preservation of wild type function

Bone marrow sites differently imprint dormancy and chemoresistance to T-cell acute lymphoblastic leukemia

International audienceT-cell acute lymphoblastic leukemia (T-ALL) expands in various bonemarrow (BM) sites of the body. We investigated whether different BM sites could differently modulate T-ALL propagation using in vivo animal models. We observed that mouse and human T-ALL develop slowly in the BM of tail vertebrae compared with the BM from thorax vertebrae. T-ALL recovered from tail BM displays lower cell-surfacemarker expression and decreased metabolism and cell-cycle progression, demonstrating a dormancy phenotype. Functionally, tailderived T-ALL exhibit a deficient short-term ex vivo growth and a delayed in vivo propagation. These features are noncell-autonomous because T-ALL fromtail and thorax shares identical genomic abnormalities and functional disparities disappear in vivo and in prolonged in vitro assays. Importantly tail-derived T-ALL displays higher intrinsic resistance to cell-cycle-related drugs (ie, vincristine sulfate and cytarabine). Of note, T-ALL recovered from gonadal adipose tissues or from cocultures with adipocytes shares metabolic, cell-cycle, and phenotypic or chemoresistance features, with tail-derived T-ALL suggesting adipocytes may participate in the tail BM imprints on T-ALL. Altogether these results demonstrate that BM sites differentially orchestrate T-ALL propagation stamping specific features to leukemic cells such as quiescence and decreased response to cell-cycle-dependent chemotherapy