Interactions Between Eosinophils and IL5Rα+ Mast Cells in Non-Advanced Systemic Mastocytosis.

BACKGROUND: Bidirectional interactions between eosinophils and mast cells (MCs) have been reported in various allergic diseases. Bone marrow (BM) eosinophilia, and to a lesser extent blood eosinophilia, is common in systemic mastocytosis (SM), but its significance remains unknown. OBJECTIVE: To describe blood and BM eosinophil characteristics in SM. METHODS: A large collection of BM biopsies was analyzed using immunohistochemical staining and whole-slide imaging. Eosinophil and extracellular granules were detected by eosinophil peroxidase (EPX) staining, and MCs by KIT staining. Complementary analyses were conducted using flow cytometry and immunofluorescence. RESULTS: Eosinophil infiltrates and large areas of eosinophil degranulation were observed within or around BM MC infiltrates in SM. EPX staining surface, highlighting intact eosinophils and eosinophil degranulation, was higher in non-advanced-SM (n=37 BM biopsies) compared to both controls (n=8, p=0.0003) and to advanced SM (n=24, p=0.014). In non-advanced SM, positive correlations were observed between serum tryptase levels and percentages of eosinophil counts in BM aspirations (Spearman r coefficient r=0.38, p=0.038), eosinophils count in BM biopsies (r=0.45, p=0.007), EPX staining (r=0.37, p=0.035) and eosinophil degranulation (r=0.39, p=0.023). Eosinophil counts in BM biopsies also correlated with MC counts (r=0.47, p=0.006) and KIT staining surface (r=0.49, p=0.003). BM MCs expressed interleukin-5 receptor and other usual eosinophil cytokine/chemokine receptors, and blood eosinophils display several increased surface markers compared to controls, suggesting an activated state. CONCLUSION: Our data suggest a possible crosstalk between MCs and eosinophils, supporting MC tryptase release and MC activation-related symptoms. This suggests a rationale for targeting eosinophils in non-advanced-SM not fully controlled by other therapies.

Sputum interleukin-6 level as a marker of severity during acute chest syndrome in children with sickle cell disease.

Acute chest syndrome (ACS) is a leading cause of morbimortality in sickle cell disease (SCD). In this prospective observational study, we investigated sputum interleukin-6 (IL-6) level as an ACS severity marker during 30 ACS episodes in 26 SCD children. Sputum IL-6 levels measured within the first 72 h of hospitalisation for ACS were significantly higher in patients with oxygen requirement ≥2 L/min, ventilation (invasive and/or non-invasive) length ≥5 days, bilateral and/or extensive opacities on chest X-ray or erythrocytapheresis requirement. Sputum IL-6 could serve as an ACS severity marker to help identify patients requiring targeted anti-inflammatory treatments such as tocilizumab.

Oral famotidine reduces the plasma level of soluble P-selectin in children with sickle cell disease.

Plasma histamine levels are increased in patients with sickle cell disease (SCD), potentially promoting endothelial P-selectin expression and vaso-occlusion via histamine type 2 (H2) receptors. We conducted a prospective, non-comparative, single-centre study to determine whether famotidine, a H2 receptor antagonist, reduces P-selectin expression in SCD children. The median plasma P-selectin level was significantly reduced after 29 days of oral famotidine (53.2 ng/mL [IQR: 46.7-63.4] vs. 69.9 ng/mL [IQR: 53.6-84.2], median difference -10.2 ng/mL [IQR: -21.8 to -2.7], p = 0.005) in 28 patients. No effect was observed on other adhesion molecules, inflammation or haemolysis markers, except decreased reticulocyte count. No adverse events deemed related to famotidine were observed. Randomized controlled trials are now needed to assess the efficacy of famotidine in preventing vaso-occlusion in SCD.

Dramatic efficacy of cannabidiol on refractory chronic pain in an adolescent with sickle cell disease.

Here, we report a dramatic efficacy of cannabidiol in an adolescent with SCD suffering from chronic pain refractory to other analgesics, with complete regression of chronic pain and rapid plasma histamine level normalization after treatment.

Mast cell-mediated inflammation relies on insulin-regulated aminopeptidase controlling cytokine export from the Golgi.

BACKGROUND: On activation, mast cells rapidly release preformed inflammatory mediators from large cytoplasmic granules via regulated exocytosis. This acute degranulation is followed by a late activation phase involving synthesis and secretion of cytokines, growth factors, and other inflammatory molecules via the constitutive pathway that remains ill defined. OBJECTIVE: We investigated the role for an insulin-responsive vesicle-like endosomal compartment, marked by insulin-regulated aminopeptidase (IRAP), in the secretion of TNF-α and IL-6 in mast cells and macrophages. METHODS: Murine knockout (KO) mouse models (IRAP-KO and kit-Wsh/sh) were used to study inflammatory disease models and to measure and mechanistically investigate cytokine secretion and degranulation in bone marrow-derived mast cells in vitro. RESULTS: IRAP-KO mice are protected from TNF-α-dependent kidney injury and inflammatory arthritis. In the absence of IRAP, TNF-α and IL-6 but not IL-10 fail to be efficiently secreted. Moreover, chemical targeting of IRAP endosomes reduced proinflammatory cytokine secretion. Mechanistically, impaired TNF-α export from the Golgi and reduced colocalization of vesicle-associated membrane protein (VAMP) 3-positive TNF-α transport vesicles with syntaxin 4 (aka Stx4) was observed in IRAP-KO mast cells, while VAMP8-dependent exocytosis of secretory granules was facilitated. CONCLUSION: IRAP plays a novel role in mast cell-mediated inflammation through the regulation of exocytic trafficking of cytokines.

HbS promotes TLR4-mediated monocyte activation and proinflammatory cytokine production in sickle cell disease.

Monocytes are considered crucial actors of inflammation in sickle cell disease (SCD), being responsible for an increased production of proinflammatory cytokines such as tumor necrosis factor α (TNF-α), interleukin-1ß (IL-1ß), and IL-6. Although a role of free heme released by intravascular hemolysis has been suspected, the mechanisms underlying monocyte activation in patients with SCD remain unknown. Using purified human hemoglobin (Hb), we demonstrate herein, that cell-free HbS, unlike HbA or heme, is responsible for a major enhancement in the expression of proinflammatory cytokines by human monocytes. This effect was found mediated by direct interaction with the Toll-like receptor 4 (TLR4)/myeloid differentiation factor 2 (MD-2) complex, resulting in the activation of both the nuclear factor-κB (NF-κB) and type I interferon pathways. In Townes SCD mice, injection of HbS, unlike HbA, was responsible for an increased production of proinflammatory cytokines, which was prevented by the TLR4 inhibitor, TAK-242. Our results reveal a novel mechanism of monocyte activation and systemic inflammation in SCD, which opens new promising therapeutic perspectives targeting the HbS-TLR4 interaction.

Long-Term Effects of Allogeneic Hematopoietic Stem Cell Transplantation on Systemic Inflammation in Sickle Cell Disease Patients.

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is the only currently available curative treatment for sickle cell disease (SCD). However, the effects of HSCT on SCD pathophysiology are poorly elucidated. Here, we assessed red blood cell (RBC) adhesiveness, intensity of hemolysis, vascular tone markers and systemic inflammation, in SCD patients treated with allogeneic HSCT. Thirty-two SCD patients were evaluated before and on long-term follow-up after HSCT. Overall survival was 94% with no severe (grade III-IV) graft-vs-host disease and a 22% rejection rate (graft failure). Hematological parameters, reticulocyte counts, and levels of lactate dehydrogenase (LDH), endothelin-1 and VCAM-1 normalized in SCD patients post-HSCT. Expression of adhesion molecules on reticulocytes and RBC was lower in patients with sustained engraftment. Levels of IL-18, IL-15 and LDH were higher in patients that developed graft failure. Increased levels of plasma pro-inflammatory cytokines, mainly TNF-α, were found in SCD patients long-term after transplantation. SCD patients with sustained engraftment after allo-HSCT showed decreased reticulocyte counts and adhesiveness, diminished hemolysis, and lower levels of vascular tonus markers. Nevertheless, systemic inflammation persists for at least five years after transplantation, indicating that allo-HSCT does not equally affect all aspects of SCD pathophysiology.

XPO1 regulates erythroid differentiation and is a new target for the treatment of ß-thalassemia.

ß-thalassemia major (ß-TM) is an inherited hemoglobinopathy caused by a quantitative defect in the synthesis of ß-globin chains of hemoglobin, leading to the accumulation of free a-globin chains that aggregate and cause ineffective erythropoiesis. We have previously demonstrated that terminal erythroid maturation requires a transient activation of caspase-3 and that the chaperone Heat Shock Protein 70 (HSP70) accumulates in the nucleus to protect GATA-1 transcription factor from caspase-3 cleavage. This nuclear accumulation of HSP70 is inhibited in human ß-TM erythroblasts due to HSP70 sequestration in the cytoplasm by free a-globin chains, resulting in maturation arrest and apoptosis. Likewise, terminal maturation can be restored by transduction of a nuclear-targeted HSP70 mutant. Here we demonstrate that in normal erythroid progenitors, HSP70 localization is regulated by the exportin-1 (XPO1), and that treatment of ß-thalassemic erythroblasts with an XPO1 inhibitor increased the amount of nuclear HSP70, rescued GATA-1 expression and improved terminal differentiation, thus representing a new therapeutic option to ameliorate ineffective erythropoiesis of ß-TM.

Innate immune cells, major protagonists of sickle cell disease pathophysiology.

Sickle cell disease (SCD), considered the most common monogenic disease worldwide, is a severe hemoglobin disorder. Although the genetic and molecular bases have long been characterized, the pathophysiology remains incompletely elucidated and therapeutic options are limited. It has been increasingly suggested that innate immune cells, including monocytes, neutrophils, invariant natural killer T cells, platelets and mast cells, have a role in promoting inflammation, adhesion and pain in SCD. Here we provide a thorough review of the involvement of these novel, major protagonists in SCD pathophysiology, highlighting recent evidence for innovative therapeutic perspectives.

Vitamin D Receptor Controls Cell Stemness in Acute Myeloid Leukemia and in Normal Bone Marrow.

Vitamin D (VD) is a known differentiating agent, but the role of VD receptor (VDR) is still incompletely described in acute myeloid leukemia (AML), whose treatment is based mostly on antimitotic chemotherapy. Here, we present an unexpected role of VDR in normal hematopoiesis and in leukemogenesis. Limited VDR expression is associated with impaired myeloid progenitor differentiation and is a new prognostic factor in AML. In mice, the lack of Vdr results in increased numbers of hematopoietic and leukemia stem cells and quiescent hematopoietic stem cells. In addition, malignant transformation of Vdr-/- cells results in myeloid differentiation block and increases self-renewal. Vdr promoter is methylated in AML as in CD34+ cells, and demethylating agents induce VDR expression. Association of VDR agonists with hypomethylating agents promotes leukemia stem cell exhaustion and decreases tumor burden in AML mouse models. Thus, Vdr functions as a regulator of stem cell homeostasis and leukemic propagation.

Erdheim-Chester Disease: a Concise Review.

PURPOSE OF REVIEW: This report provides an overview of the current knowledge of molecular characterization, clinical description, and treatment of Erdheim-Chester disease (ECD), a multi-systemic adult histiocytosis of the L group. RECENT FINDINGS: The recent identification of several MAPK mutations in histiocytes of ECD lesions. Leading to targeted therapies. The discovery of the BRAFV600E mutation in ECD lesions followed by several other kinase mutations in the MAPK pathway has revolutionized our understanding of the disease pathogenesis and led to trials with targeted therapies that demonstrated robust efficacy.

Innate-like T cells in children with sickle cell disease.

BACKGROUND: The implication of lymphocytes in sickle cell disease pathogenesis is supported by a number of recent reports. These studies provided evidence for the activation of invariant natural killer T (iNKT) cells in adult patients, but did not investigate the involvement of other innate-like T cell subsets so far. METHODS: Here we present a monocentric prospective observational study evaluating the number and functional properties of both circulating conventional and innate-like T cells, namely iNKT, Mucosal-Associated Invariant T (MAIT) and gammadelta (γδ) T cells in a cohort of 39 children with sickle cell disease. RESULTS: Relative to age-matched healthy controls, we found that patients had a higher frequency of IL-13- and IL-17-producing CD4+ T cells, as well as higher MAIT cell counts with an increased frequency of IL-17-producing MAIT cells. Patients also presented increased Vδ2 γδ T cell counts, especially during vaso-occlusive crisis, and a lower frequency of IFNγ-producing Vδ2 γδ T cells, except during crisis. iNKT cell counts and the frequency of IFNγ-producing iNKT cells were unchanged compared to controls. Our study revealed positive correlations between 1) the frequency of IFNγ-producing CD4+, CD8+ and Vδ2 γδ T cells and the number of hospitalizations for vaso-occlusive crisis in the previous year; 2) the frequency of IFNγ-producing iNKT cells and patients' age and 3) the frequency of IL-17-producing Vδ2 γδ T cells and hemoglobin S level. CONCLUSION: These results strongly suggest a role of innate-like T cells in sickle cell disease pathophysiology, especially that of IL-17-producing MAIT and γδ T cells.

Lessons to Learn From Low-Dose Cyclosporin-A: A New Approach for Unexpected Clinical Applications.

Cyclosporin-A has been known and used for a long time, since its "fast track" approval in the early 80's. This molecule has rapidly demonstrated unexpected immunosuppressive properties, transforming the history of organ transplantation. Cyclosporin's key effect relies on modulation on T-lymphocyte activity, which explains its role in the prevention of graft rejection. However, whether cyclosporin-A exerts other effects on immune system remains to be determined. Until recently, cyclosporin-A was mainly used at a high-dose, but given the drug toxicity and despite the fear of losing its immunosuppressive effects, there is nowadays a tendency to decrease its dose. The literature has been reporting data revealing a paradoxical effect of low dosage of cyclosporin-A. These low-doses appear to have immunomodulatory properties, with different effects from high-doses on CD8+ T lymphocyte activation, auto-immune diseases, graft-vs.-host disease and cancer. The aim of this review is to discuss the role of cyclosporin-A, not only as a consecrated immunosuppressive agent, but also as an immunomodulatory drug when administrated at low-dose. The use of low-dose cyclosporin-A may become a new therapeutic strategy, particularly to treat cancer.

Targeting glutaminolysis has antileukemic activity in acute myeloid leukemia and synergizes with BCL-2 inhibition.

Cancer cells require glutamine to adapt to increased biosynthetic activity. The limiting step in intracellular glutamine catabolism involves its conversion to glutamate by glutaminase (GA). Different GA isoforms are encoded by the genes GLS1 and GLS2 in humans. Herein, we show that glutamine levels control mitochondrial oxidative phosphorylation (OXPHOS) in acute myeloid leukemia (AML) cells. Glutaminase C (GAC) is the GA isoform that is most abundantly expressed in AML. Both knockdown of GLS1 expression and pharmacologic GLS1 inhibition by the drug CB-839 can reduce OXPHOS, leading to leukemic cell proliferation arrest and apoptosis without causing cytotoxic activity against normal human CD34(+) progenitors. Strikingly, GLS1 knockdown dramatically inhibited AML development in NSG mice. The antileukemic activity of CB-839 was abrogated by both the expression of a hyperactive GAC(K320A) allele and the addition of the tricarboxyclic acid cycle product α-ketoglutarate, indicating the critical function of GLS1 in AML cell survival. Finally, glutaminolysis inhibition activated mitochondrial apoptosis and synergistically sensitized leukemic cells to priming with the BCL-2 inhibitor ABT-199. These findings show that targeting glutamine addiction via GLS1 inhibition offers a potential novel therapeutic strategy for AML.

HSP70 sequestration by free α-globin promotes ineffective erythropoiesis in ß-thalassaemia.

ß-Thalassaemia major (ß-TM) is an inherited haemoglobinopathy caused by a quantitative defect in the synthesis of ß-globin chains of haemoglobin, leading to the accumulation of free α-globin chains that form toxic aggregates. Despite extensive knowledge of the molecular defects causing ß-TM, little is known of the mechanisms responsible for the ineffective erythropoiesis observed in the condition, which is characterized by accelerated erythroid differentiation, maturation arrest and apoptosis at the polychromatophilic stage. We have previously demonstrated that normal human erythroid maturation requires a transient activation of caspase-3 at the later stages of maturation. Although erythroid transcription factor GATA-1, the master transcriptional factor of erythropoiesis, is a caspase-3 target, it is not cleaved during erythroid differentiation. We have shown that, in human erythroblasts, the chaperone heat shock protein70 (HSP70) is constitutively expressed and, at later stages of maturation, translocates into the nucleus and protects GATA-1 from caspase-3 cleavage. The primary role of this ubiquitous chaperone is to participate in the refolding of proteins denatured by cytoplasmic stress, thus preventing their aggregation. Here we show in vitro that during the maturation of human ß-TM erythroblasts, HSP70 interacts directly with free α-globin chains. As a consequence, HSP70 is sequestrated in the cytoplasm and GATA-1 is no longer protected, resulting in end-stage maturation arrest and apoptosis. Transduction of a nuclear-targeted HSP70 mutant or a caspase-3-uncleavable GATA-1 mutant restores terminal maturation of ß-TM erythroblasts, which may provide a rationale for new targeted therapies of ß-TM.

Inhibiting glutamine uptake represents an attractive new strategy for treating acute myeloid leukemia.

Cancer cells require nutrients and energy to adapt to increased biosynthetic activity, and protein synthesis inhibition downstream of mammalian target of rapamycin complex 1 (mTORC1) has shown promise as a possible therapy for acute myeloid leukemia (AML). Glutamine contributes to leucine import into cells, which controls the amino acid/Rag/mTORC1 signaling pathway. We show in our current study that glutamine removal inhibits mTORC1 and induces apoptosis in AML cells. The knockdown of the SLC1A5 high-affinity transporter for glutamine induces apoptosis and inhibits tumor formation in a mouse AML xenotransplantation model. l-asparaginase (l-ase) is an anticancer agent also harboring glutaminase activity. We show that l-ases from both Escherichia coli and Erwinia chrysanthemi profoundly inhibit mTORC1 and protein synthesis and that this inhibition correlates with their glutaminase activity levels and produces a strong apoptotic response in primary AML cells. We further show that l-ases upregulate glutamine synthase (GS) expression in leukemic cells and that a GS knockdown enhances l-ase-induced apoptosis in some AML cells. Finally, we observe a strong autophagic process upon l-ase treatment. These results suggest that l-ase anticancer activity and glutamine uptake inhibition are promising new therapeutic strategies for AML.