Human mast cells express receptors for IL-3, IL-5 and GM-CSF; a partial map of receptors on human mast cells cultured in vitro

Insight into IL-5 as a Potential Target for the Treatment of Allergic Diseases

Interleukin-5 functions as a B-cell differentiation factor, but more importantly, in the context of this review, it plays a variety of roles in eosinophil biology, including eosinophil differentiation and maturation in the bone marrow, and facilitates eosinophil migration to tissue sites, usually in the context of an allergic reaction. Given the availability of selective anti-IL-5 drugs such as mepolizumab and reslizumab, as well as the IL-5 receptor antagonist benralizumab, it is worth investigating whether they could be used in some cases of allergic disease. Asthma has a well-documented involvement of IL-5 in its pathophysiology and has clear benefits in the case of anti-IL-5 therapy; therefore, current knowledge is presented to provide a reference point for the study of less-described diseases such as atopic dermatitis, chronic rhinosinusitis, chronic spontaneous urticaria, and its association with both IL-5 and anti-IL-5 treatment options. We then review the current literature on these diseases, explain where appropriate potential reasons why anti-IL-5 treatments are ineffective, and then point out possible future directions for further research.

Coronavirus Receptor Expression Profiles in Human Mast Cells, Basophils, and Eosinophils

A major problem in SARS-CoV-2-infected patients is the massive tissue inflammation in certain target organs, including the lungs. Mast cells (MC), basophils (BA), and eosinophils (EO) are key effector cells in inflammatory processes. These cells have recently been implicated in the pathogenesis of SARS-CoV-2 infections. We explored coronavirus receptor (CoV-R) expression profiles in primary human MC, BA, and EO, and in related cell lines (HMC-1, ROSA, MCPV-1, KU812, and EOL-1). As determined using flow cytometry, primary MC, BA, and EO, and their corresponding cell lines, displayed the CoV-R CD13 and CD147. Primary skin MC and BA, as well as EOL-1 cells, also displayed CD26, whereas primary EO and the MC and BA cell lines failed to express CD26. As assessed using qPCR, most cell lines expressed transcripts for CD13, CD147, and ABL2, whereas ACE2 mRNA was not detectable, and CD26 mRNA was only identified in EOL-1 cells. We also screened for drug effects on CoV-R expression. However, dexamethasone, vitamin D, and hydroxychloroquine did not exert substantial effects on the expression of CD13, CD26, or CD147 in the cells. Together, MC, BA, and EO express distinct CoV-R profiles. Whether these receptors mediate virus-cell interactions and thereby virus-induced inflammation remains unknown at present.

Th2 cells inhibit growth of colon and pancreas cancers by promoting anti-tumorigenic responses from macrophages and eosinophils

BACKGROUND

Immunotherapy of gastrointestinal cancers is challenging; however, several lines of evidence suggest that adoptive transfer of stimulated or modified immune cells support not only protective role of immune cells in tumor microenvironment, but actively participate in the elimination of cancer cells.

METHODS

In vivo studies employing cancer cell-derived allograft murine models of gastrointestinal cancers were performed. The effects of T helper (Th) 2 cells on gastrointestinal cancers growth and tumor microenvironment composition using adoptive transfer of Th2 cells, interleukin (IL)-5 treatment, and immunofluorescence, multiplex and real-time PCR were explored.

RESULTS

Here, we show that Th2 cells play an essential role in the inhibition of colon and pancreas cancers progression. In murine models of gastrointestinal tumors using adoptive transfer of Th2 cells, we identify that Th2 cells are responsible for generation of apoptotic factors and affect macrophage as well as eosinophil recruitment into tumors where they produce cytotoxic factors. Moreover, we found that Th2 cells lead to IL-5 hypersecretion, which links the anti-tumorigenic function of Th2 cells and eosinophils. Importantly, we noted that recombinant IL-5 administration is also related with inhibition of gastrointestinal tumor growth. Finally, using an in vitro approach, we documented that both Th2 cells and eosinophils are directly responsible for gastrointestinal cancer cell killing.

CONCLUSIONS

These data demonstrate the significance of Th2 cells, eosinophils and IL-5 in the inhibition of gastrointestinal tumor growth, and pointed toward tumor microenvironment reprogramming as a Th2 cell-mediated anti-tumorigenic mechanism of action.

Histamine Activates Human Eosinophils via H2R and H4R Predominantly in Atopic Dermatitis Patients

Atopic dermatitis (AD) is maintained by a variety of cells and inflammatory mediators, including eosinophils and histamine. We recently reported that eosinophils from AD patients highly express the H₄R. However, its immunomodulatory function in eosinophils is still largely unexplored. In this study, transcriptome analysis of blood eosinophils from AD patients stimulated with histamine and the H₄R agonist ST-1006 revealed several regulated genes (e.g., IL-18R, IL-1RL1, PDE4B, CXCR4) involved in inflammation. Subsequently, the impact of histamine on one of the strongly regulated genes, the IL-18 receptor (IL-18Rα), was investigated in detail. Stimulation with histamine induced the upregulation of IL-18Rα at mRNA and at the protein level in human eosinophils, which was more pronounced in cells from AD patients than in cells from healthy controls. IL-18 was upregulated via histamine as well. After pre-incubation with histamine and IFN-γ, subsequent stimulation with IL-18 resulted in an increased ECP mRNA expression. The activation of eosinophils by histamine, in combination with IFN-γ and IL-5, was also accompanied by an upregulation of CD69. Thus, our results indicate a crucial role of histamine in the upregulation of the IL-18/IL-18R axis and in the activation of human eosinophils from AD patients.

Structural and evolutionary exploration of the IL-3 family and its alpha subunit receptors

Interleukin-3 (IL-3) is a cytokine belonging to the family of common β (βc) and is involved in various biological systems. Its activity is mediated by the interaction with its receptor (IL-3R), a heterodimer composed of two distinct subunits: IL-3Rα and βc. IL-3 and its receptor, especially IL-3Rα, play a crucial role in pathologies like inflammatory diseases and therefore are interesting therapeutic targets. Here, we have performed an analysis of these proteins and their interaction based on structural and evolutionary information. We highlighted that IL-3 and IL-3Rα structural architectures are conserved across evolution and shared with other proteins belonging to the same βc family interleukin-5 (IL-5) and granulocyte-macrophage colony-stimulating factor (GM-CSF). The IL-3Rα/IL-3 interaction is mediated by a large interface in which most residues are surprisingly not conserved during evolution and across family members. In spite of this high variability, we suggested small regions constituted by few residues conserved during the evolution in both proteins that could be important for the binding affinity.

CD123-targeted therapy in acute myeloid leukemia

INTRODUCTION

Acute myeloid leukemia (AML) results from the neoplastic transformation of a hematopoietic stem cell. While therapeutic progress has stagnated for several decades, recent progress in the genomic classification of AML has paved the way for multiple new drug approvals. These long-awaited achievements represent a paradigm shift in the approach to a disease that has largely been managed with conventional chemotherapy since the 1970s. With the evolution of targeted AML therapies, novel agents continue to be developed with the goal to improve efficacy while minimizing toxicity. Monoclonal antibodies targeting AML-specific surface markers have emerged as promising candidates to improve outcomes. CD123, interleukin-3 receptor alpha chain [IL-3 Rα], is highly expressed in AML, particularly within the AML stem cell compartment. Several CD123-targeted strategies are currently being evaluated in clinical trials.

AREAS COVERED

The authors herein discuss recent clinical data in CD123-directed therapy in AML. A computerized PubMed search was conducted using key words relevant to the various sections of this article. Relevant abstracts presented at the American Society of Hematology, the European Hematology Association, and the American Society of Clinical Oncology were also reviewed.

EXPERT OPINION

CD123 represents a suitable therapeutic target that has the potential to improve AML patient outcomes.

Novel Strategies to Target Mast Cells in Disease

Mast cells (MCs) are versatile effector cells of the immune system, characterized by a large content of secretory granules containing a variety of inflammatory mediators. They are implicated in the host protection toward various external insults, but are mostly well known for their detrimental impact on a variety of pathological conditions, including allergic disorders such as asthma and a range of additional disease settings. Based on this, there is currently a large demand for therapeutic regimens that can dampen the detrimental impact of MCs in these respective pathological conditions. This can be accomplished by several strategies, including targeting of individual mediators released by MCs, blockade of receptors for MC-released compounds, inhibition of MC activation, limiting mast cell growth or by inducing mast cell apoptosis. Here, we review the currently available and emerging regimens to interfere with harmful mast cell activities in asthma and other pathological settings and discuss the advantages and limitations of such strategies.

Altered plasma levels of βC and γC chain cytokines and post-treatment modulation in tuberculous lymphadenitis

BACKGROUND

Alterations in β common (βC) and γ common (γC) chain cytokines have been described in pulmonary tuberculosis. However, their role in tuberculous lymphadenitis (TBL) disease has not been assessed.

METHODS

Thus, in the present study, we have examined the systemic levels of βC and γC chain cytokines in TBL, latent tuberculosis (LTB) and healthy control (HC) individuals. We have examined the discriminatory potential of both family of cytokines using ROC analysis. Finally, we measured the pre and post-treatment responses of these cytokines after anti-tuberculosis treatment.

RESULTS

TBL individuals exhibit significantly increased (IL-3) and diminished systemic levels of (IL-5, GM-CSF) βC cytokines compared to LTB and HC individuals. TBL individuals also exhibit significantly diminished (IL-2, IL-7) and elevated (IL-4, IL-9) levels of γC cytokines compared to LTB and/or HC. ROC analysis shows a clear discriminatory capacity of both βC (IL-5) and γC (IL-2) chain cytokines to distinguish TBL from LTB and HCs. The systemic levels of βC chain cytokines were not significantly altered, but in contrast γC (IL-2 and IL-7) cytokines were significantly modulated after treatment. Finally, no significant correlation was observed for βC and γC chain cytokines with their respective lymphocyte count of TBL individuals.

CONCLUSIONS

Hence, we conclude that altered plasma levels of βC and γC cytokines are the characteristics of immune alteration in TBL disease and certain cytokines were modulated after treatment.

Switching between biologics in severe asthma patients. When the first choice is not proven to be the best

During the last decades, new treatments targeting disease mechanisms referred as biologics have been introduced in the therapy of asthma and currently, five monoclonal antibodies have been approved. Although these therapeutic agents have been formulated to target specific asthma endotypes, it is often difficult for the treating physician to identify which patient is the best candidate for each one of these specific treatments especially in the clinical scenario of a patient in whom clinical characteristics overlap between different endotypes, allowing the selection of more than one biologic agent. As no head-to-head comparisons between these biologics have been attempted, there is no evidence on the superiority of one biologic agent over the other. Furthermore, a physician's first therapeutic decision, no matter how carefully has been made, may often result in suboptimal clinical response and drug discontinuation, indicating the need for switching to a different biologic. In this short review, we discuss the available evidence regarding the switching between biologics in patients with severe asthma and we propose a simple algorithm on switching possibilities in case that the physicians' initial choice is proven not to be the best.

Solanum nigrum Linne improves DNCB‑induced atopic dermatitis‑like skin disease in BALB/c mice

The present study aimed to investigate the effects of Solanum nigrum Linne (SNL) in a model of 1-chloro-2,4-dinitrobenzene (DNCB)-induced atopic dermatitis (AD) and in TNF-α/IFN-γ-stimulated HaCaT cells. AD is a chronic inflammatory skin disease and is characterized by erythema, edema, increased pruritus and eczema. Steroids are most commonly used for anti-inflammatory therapy; however, their long-term use is limited due to side-effects, such as osteoporosis, brittle skin, muscle weaknesses and diabetes. Therefore, patients with AD require alternative treatment strategies. In previous studies, SNL has been reported to be effective against oxidants and cancer. However, to the best of our knowledge, the effects of SNL on AD have not yet been investigated. The present study examined the effects of SNL ethanol extract on a model of DNCB induced AD and on TNF-α/IFN-γ-stimulated HaCaT cells. The skin tissue was sectioned to measure the thicknesses of the epidermis and dermis, as well as the numbers of eosinophils, mast cells and CD8 infiltration by H&E, toluidine blue, Masson's trichrome and IHC staining. ELISA was performed using serum to measure IgE levels. The present study also examined the expression of various inflammatory cytokines, MAPK and NF-κB in TNF-α/IFN-γ-stimulated HaCaT cells. SNL significantly reduced the levels of cytokines released from HaCaT cells stimulated with TNF-α/IFN-γ. SNL also significantly reduced the levels of p-p38 at 30 min and significantly reduced the activation of NF-κB in a time course experiment. In addition, SNL significantly reduced the level of serum IgE and dermal thickness and the infiltration of mast cells and CD8 in the BALB/c mouse model of DNCB-induced AD. The results of the current study suggest that SNL exerts a suppressive effect on pro-inflammatory cytokines in vitro and in vivo through the regulation of the immune system.

In utero exposure to low doses of genistein and di-(2-ethylhexyl) phthalate (DEHP) alters innate immune cells in neonatal and adult rat testes

BACKGROUND

Although humans are exposed to mixtures of endocrine disruptor chemicals, few studies have examined their toxicity on male reproduction. We previously found that fetal exposure to a mixture of the phytoestrogen genistein (GEN) and the plasticizer di(2-ethylhexyl) phthalate (DEHP) altered gene expression in adult rat testes.

OBJECTIVES

Our goal was to investigate the effects of fetal exposure to GEN-DEHP mixtures at two doses relevant to humans on testicular function and transcriptome in neonatal and adult rats.

MATERIALS AND METHODS

Pregnant SD rats were gavaged with vehicle, GEN or DEHP, alone or mixed at 0.1 and 10 mg/kg/day, from gestation day 14 to birth. Fertility, steroid levels, and testis morphology were examined in neonatal and adult rats. Testicular transcriptomes were examined by gene array and functional pathway analyses. Cell-specific genes/proteins were determined by quantitative real-time PCR and immunohistochemistry.

RESULTS

GEN-DEHP mixtures increased the rates of infertility and abnormal testes in adult rats. Gene array analysis identified more genes exclusively altered by the mixtures than individual compounds. Altered top canonical pathways included urogenital/reproductive developmental and inflammatory processes. GEN-DEHP mixtures increased innate immune cells and macrophages markers at both doses and ages, more strongly and consistently than DEHP or GEN alone. Genes exclusively increased by the mixture in adult testis related to innate immune cells and macrophages included Kitlg, Rps6ka3 (Rsk2), Nr3c1, Nqo1, Lif, Fyn, Ptprj (Dep-1), Gpr116, Pfn2, and Ptgr1.

DISCUSSION AND CONCLUSION

These findings demonstrate that GEN-DEHP mixtures at doses relevant to human induce adverse testicular phenotypes, concurrent with age-dependent and non-monotonic changes in testicular transcriptomes. The involvement of innate immune cells such as macrophages suggests immediate and delayed inflammatory responses which may contribute to testicular dysfunction. Moreover, these effects are complex and likely involve multiple interactions between immune and non-immune testicular cell types that will entail further studies.

Relationship of sputum mast cells with clinical and inflammatory characteristics of asthma

BACKGROUND

Mast cells (MCs) are innate immune cells that regulate atopic and non-atopic inflammation in the airways. MCs play a critical role in the pathogenesis of asthma, yet their relationship to airway and systemic inflammation and clinical characteristics of asthma is poorly understood.

OBJECTIVE

To quantify MCs in induced sputum samples and understand their relationship to airway and circulatory immune cells, and clinical variables in asthma.

METHODS

We employed flow cytometry of sputum samples to quantify MCs, basophils and other immune cells in 51 participants (45 asthma and 6 non-asthma controls). Relationship of MCs to airway (n = 45) and blood (n = 19) immune cells, participant demographics, asthma history, spirometry and airways hyperresponsiveness (AHR) to hypertonic saline was determined by correlation and comparison of cut-off-based sputum MC high vs low participants.

RESULTS

Mast cells, basophils and eosinophils were increased in asthma vs non-asthma control sputum. In asthma sputum, MCs, basophils and eosinophils were significantly intercorrelated, and MCs and basophils were elevated in participants with eosinophilic asthma. MCs and basophils, but not eosinophils, correlated with AHR. Sputum MC high asthma was characterized by an increased proportion of participants with uncontrolled asthma and reduced FEV₁ and FVC. Trends towards similar clinical associations with elevated MCs were observed in a paucigranulocytic subpopulation (n = 15) lacking airway eosinophilia or neutrophilia. Receiver operator characteristic (ROC) analysis showed peripheral blood eosinophil (PBE) count predicted elevated sputum eosinophils and basophils, but not MCs.

CONCLUSIONS AND CLINICAL RELEVANCE

Sputum MCs are elevated in asthma, and their measurement may be useful as they relate to key clinical features of asthma (spirometry, asthma control, AHR). PBE count did not predict airway MC status, suggesting direct measurement of airway MCs by sensitive methods such as flow cytometry should be further developed.

Anti-IL-5 in Mild Asthma Alters Rhinovirus-induced Macrophage, B-Cell, and Neutrophil Responses (MATERIAL). A Placebo-controlled, Double-Blind Study

RATIONALE

Eosinophils drive pathophysiology in stable and exacerbating eosinophilic asthma, and therefore treatment is focused on the reduction of eosinophil numbers. Mepolizumab, a humanized monoclonal antibody that neutralizes IL-5 and efficiently attenuates eosinophils, proved clinically effective in severe eosinophilic asthma but not in mild asthma.

OBJECTIVES

To study the effect of mepolizumab on virus-induced immune responses in mild asthma.

METHODS

Patients with mild asthma, steroid-naive and randomized for eosinophil numbers, received 750 mg mepolizumab intravenously in a placebo-controlled double-blind trial, 2 weeks after which patients were challenged with rhinovirus (RV) 16. FEV₁, FVC, fractional exhaled nitric oxide, symptom scores (asthma control score), viral load (PCR), eosinophil numbers, humoral (luminex, ELISA), and cellular (flow cytometry) immune parameters in blood, BAL fluid, and sputum, before and after mepolizumab and RV16, were assessed.

MEASUREMENTS AND MAIN RESULTS

Mepolizumab attenuated baseline blood eosinophils and their activation, attenuated trendwise sputum eosinophils, and enhanced circulating natural killer cells. Mepolizumab did not affect FEV₁, FVC, and fractional exhaled nitric oxide, neither at baseline nor after RV16. On RV16 challenge mepolizumab did not prevent eosinophil activation but did enhance local B lymphocytes and macrophages and reduce neutrophils and their activation. Mepolizumab also enhanced secretory IgA and reduced tryptase in BAL fluid. Finally, mepolizumab affected particularly RV16-induced macrophage inflammatory protein-3a, vascular endothelial growth factor-A, and IL-1RA production in BAL fluid.

CONCLUSIONS

Mepolizumab failed to prevent activation of remaining eosinophils and changed RV16-induced immune responses in mild asthma. Although these latter effects likely are caused by attenuated eosinophil numbers, we cannot exclude a role for basophils. Clinical trial registered with www.clinicaltrials.gov (NCT 01520051).

Identification and Immunophenotypic Characterization of Normal and Pathological Mast Cells

Mast cells (MCs) are secretory cells that are central players in human allergic disease and immune responses. With the exception of a few pathological situations, MCs are usually present at relatively low frequencies in most tissues. Since their first description, MCs in tissues were identified mostly using their morphological characteristics and their typical coloration when stained with aniline dyes. However, increasing availability of highly specific antibodies now permits the use of fluorescence-based flow cytometry as the method of choice for the quantification, characterization, and purification of cells in suspension. This technique allows for a rapid analysis of thousands of events and for the identification of cells present at frequencies as low as one event in 10⁶ unwanted cells. This method also permits for simultaneous characterization of multiple antigens at a single cell level, which is ideal in order to study rare populations of cells like MCs. Here we describe the basis of flow cytometry-based immunophenotyping applied to the study of MC. The protocol focuses on the study of human MCs present in body fluids (mainly bone marrow) but can easily be adapted to studying MCs from other tissues and species.

Mast Cells as a Double-Edged Sword in Immunity: Their Function in Health and Disease. First of Two Parts

Mast cells (MCs) have recently been re-interpreted in the context of the immune scenario in the sense that their pro-allergic role is no longer exclusive. In fact, MCs even in steady state conditions maintain homeostatic functions, producing mediators and intensively cross-talking with other immune cells. Here, emphasis will be placed on the array of receptors expressed by MCs and the variety of cytokines they produce. Then, the bulk of data discussed will provide readers with a wealth of information on the dual ability of MCs not only to defend but also to offend the host. This double attitude of MCs relies on many variables, such as their subsets, tissues of residency and type of stimuli ranging from microbes to allergens and food antigens. Finally, the relationship between MCs with basophils and eosinophils will be discussed.

Eosinophils, the IL-5/IL-5Rα axis, and the biologic effects of benralizumab in severe asthma

Bronchial asthma is a chronic inflammatory disease characterized, in a percentage of patients, as an eosinophilic inflammation of the airways. Eosinophils are recognized as a proinflammatory granulocyte playing a major role in the T2-high phenotype, which includes severe eosinophilic asthma. Eosinophilic asthma represents the majority of the phenotypic variants clinically characterized by severity and frequent exacerbations. For patients with severe uncontrolled asthma, monoclonal antibodies are used as add-on treatments. Among them, in addition to anti-immunoglobulin E therapy, biologic agents directed toward the interleukin (IL)-5/IL-5Rα axis and, thus, interfering with the pathologic functions of eosinophils, are now available. Unlike the other anti‒IL-5 monoclonal antibodies which exert an indirect effect on eosinophils, benralizumab, an afucosylated IgG₁ kappa antibody directed against the α subunit of IL-5R, directly depletes eosinophils and their associated bone marrow progenitor cells through induction of antibody-dependent cell-mediated cytotoxicity, through recruitment of natural killer cells. This article reviews the role of eosinophils in the pathogenesis of bronchial asthma and discusses the potential advantageous biologic effects of benralizumab in comparison with other monoclonal antibodies targeting the IL-5 ligand.

Deciphering the differentiation trajectory from hematopoietic stem cells to mast cells

Hematopoietic stem cells differentiate into all types of blood cells, including peripheral tissue-resident mast cells. The early mast cell differentiation takes place in the bone marrow, after which the progenitor cells enter the circulation and mature once reaching their target organ. Early results from single-cell culture experiments and colony-forming assays have produced the classic hierarchical tree model of hematopoiesis. The introduction of high-throughput, single-cell RNA sequencing is now revolutionizing our understanding of the differentiation process, questioning the classic tree-based models. By integrating the results from early cell culture experiments with single-cell transcriptomics, we present a differentiation landscape model of hematopoiesis and discuss it with focus on mast cells. The review also describes how the hematologic neoplasm systemic mastocytosis can be used to model human hematopoiesis using naturally occurring cell barcoding by means of the common KIT D816V mutation.

Eosinophils: Nemeses of Pulmonary Pathogens?

PURPOSE OF REVIEW

Eosinophils are short-lived granulocytes that contain a variety of proteins and lipids traditionally associated with host defense against parasites. The primary goal of this review is to examine more recent evidence that challenged this rather outdated role of eosinophils in the context of pulmonary infections with helminths, viruses, and bacteria.

RECENT FINDINGS

While eosinophil mechanisms that counter parasites, viruses, and bacteria are similar, the kinetics and impact may differ by pathogen type. Major antiparasitic responses include direct killing and immunoregulation, as well as some mechanisms by which parasite survival/growth is supported. Antiviral defenses may be as unembellished as granule protein-induced direct killing or more urbane as serving as a conduit for better adaptive immune responses to the invading virus. Although sacrificial, eosinophil DNA emitted in response to bacteria helps trap bacteria to limit dissemination. Herein, we discuss the current research redefining eosinophils as multifunctional cells that are active participants in host defense against lung pathogens. Eosinophils recognize and differentially respond to invading pathogens, allowing them to deploy innate defense mechanisms to contain and clear the infection, or modulate the immune response. Modern technology and animal models have unraveled hitherto unknown capabilities of this surreptitious cell that indubitably has more functions awaiting discovery.

Benralizumab for PDGFRA-Negative Hypereosinophilic Syndrome

BACKGROUND

Hypereosinophilic syndrome is a group of diseases defined by marked eosinophilia in blood or tissue and eosinophil-related clinical manifestations. Benralizumab is a monoclonal antibody against interleukin-5 receptor α, which is expressed on human eosinophils.

METHODS

In this randomized, double-blind, placebo-controlled, phase 2 trial, we administered a series of three monthly subcutaneous injections of either benralizumab (at a dose of 30 mg) or placebo in 20 symptomatic patients who had PDGFRA-negative hypereosinophilic syndrome and an absolute eosinophil count of at least 1000 cells per cubic millimeter; all the patients were receiving stable therapy (drugs or dietary changes) for this disease. This regimen was followed by an open-label phase, during which the patient's background therapy could be tapered as tolerated, and an extension phase. The primary end point of the randomized phase was a reduction of at least 50% in the absolute eosinophil count at week 12.

RESULTS

During the randomized phase, the primary end point occurred in more patients in the benralizumab group than in the placebo group (9 of 10 patients [90%] vs. 3 of 10 patients [30%], P = 0.02). During the open-label phase, clinical and hematologic responses were observed in 17 of 19 patients (89%) and were sustained for 48 weeks in 14 of 19 patients (74%); in the latter group, in 9 of 14 patients (64%), background therapies could be tapered. Bone marrow and tissue eosinophilia were also suppressed with benralizumab therapy. The most common drug-related adverse events, headache and an elevated lactate dehydrogenase level, occurred in 32% of the patients after the first dose of benralizumab and resolved within 48 hours in all patients. Other adverse events occurred with similar frequency in the two groups. Of the many potential predictors of response that were examined, only clinical disease subtype appeared to be associated with the initial response or relapse.

CONCLUSIONS

In this small phase 2 trial, patients with PDGFRA-negative hypereosinophilic syndrome who received benralizumab for 12 weeks had lower absolute eosinophil counts than those who received placebo. During the open-label phase, clinical and hematologic responses were sustained for 48 weeks in 74% of the patients. Adverse events did not limit treatment. (Funded by the National Institute of Allergy and Infectious Diseases; ClinicalTrials.gov numbers, NCT00001406 and NCT02130882.).

CD33 recruitment inhibits IgE-mediated anaphylaxis and desensitizes mast cells to allergen

Allergen immunotherapy for patients with allergies begins with weekly escalating doses of allergen under medical supervision to monitor and treat IgE mast cell-mediated anaphylaxis. There is currently no treatment to safely desensitize mast cells to enable robust allergen immunotherapy with therapeutic levels of allergen. Here, we demonstrated that liposomal nanoparticles bearing an allergen and a high-affinity glycan ligand of the inhibitory receptor CD33 profoundly suppressed IgE-mediated activation of mast cells, prevented anaphylaxis in Tg mice with mast cells expressing human CD33, and desensitized mice to subsequent allergen challenge for several days. We showed that high levels of CD33 were consistently expressed on human skin mast cells and that the antigenic liposomes with CD33 ligand prevented IgE-mediated bronchoconstriction in slices of human lung. The results demonstrated the potential of exploiting CD33 to desensitize mast cells to provide a therapeutic window for administering allergen immunotherapy without triggering anaphylaxis.

Modulation of blood inflammatory markers by benralizumab in patients with eosinophilic airway diseases

Background

Benralizumab, a humanized, afucosylated, monoclonal antibody that targets interleukin-5 receptor α, depletes eosinophils and basophils by enhanced antibody-dependent cell-mediated cytotoxicity. It demonstrated efficacy for patients with moderate to severe asthma and, in a Phase IIa trial, for chronic obstructive pulmonary disease (COPD) with eosinophilic inflammation. We investigated effects of benralizumab 100 mg every 8 weeks (first three doses every 4 weeks) subcutaneous on blood inflammatory markers through proteomic and gene-expression analyses collected during two Phase II studies of patients with eosinophilic asthma and eosinophilic COPD.

Methods

Serum samples for proteomic analysis and whole blood for gene expression analysis were collected at baseline and 52 weeks (asthma study) or 32 weeks (COPD study) post-treatment. Proteomic analyses were conducted on a custom set of 90 and 147 Rules-Based Medicine analytes for asthma and COPD, respectively. Gene expression was profiled by Affymetrix Human Genome U133 plus 2 arrays (~ 54 K probes). Gene set variation analysis (GSVA) was used to determine transcriptomic activity of immune signatures. Treatment-related differences between analytes, genes, and gene signatures were analyzed for the overall population and for patient subgroups stratified by baseline blood eosinophil count (eosinophil-high [≥300 cells/μL] and eosinophil-low [< 300 cells/μL]) via t-test and repeated measures analysis of variance.

Results

Eosinophil chemokines eotaxin-1 and eotaxin-2 were significantly upregulated (false discovery rate [FDR] < 0.05) by approximately 2.1- and 1.4-fold in the asthma study and by 2.3- and 1.7-fold in the COPD study following benralizumab treatment. Magnitude of upregulation of these two chemokines was greater for eosinophil-high patients than eosinophil-low patients in both studies. Benralizumab was associated with significant reductions (FDR < 0.05) in expression of genes associated with eosinophils and basophils, such as CLC, IL-5Rα, and PRSS33; immune-signaling complex genes (FCER1A); G-protein–coupled receptor genes (HRH4, ADORA3, P2RY14); and further immune-related genes (ALOX15 and OLIG2). The magnitude of downregulation of gene expression was greater for eosinophil-high than eosinophil-low patients. GSVA on immune signatures indicated significant treatment reductions (FDR < 0.05) in eosinophil-associated signatures.

Conclusions

Benralizumab is highly selective, modulating blood proteins or genes associated with eosinophils or basophils. Modulated protein and gene expression patterns are most prominently altered in eosinophil-high vs. eosinophil-low patients.

Trial registration

NCT01227278 and NCT01238861.

Electronic supplementary material

The online version of this article (10.1186/s12931-018-0968-8) contains supplementary material, which is available to authorized users.

Human eosinophils and mast cells: Birds of a feather flock together

While the origin of the phrase "birds of a feather flock together" is unclear, it has been in use for centuries and is typically employed to describe the phenomenon that people with similar tastes or interests tend to seek each other out and congregate together. In this review, we have co-opted this phrase to compare innate immune cells of related origin, the eosinophil and mast cell, because they very often accumulate together in tissue sites under both homeostatic and inflammatory conditions. To highlight overlapping yet distinct features, their hematopoietic development, cell surface phenotype, mediator release profiles and roles in diseases have been compared and contrasted. What emerges is a sense that these two cell types often interact with each other and their tissue environment to provide synergistic contributions to a variety of normal and pathologic immune responses.

Immunological and hematological effects of IL-5(Rα)-targeted therapy: An overview

IL‐5 is an important cytokine for priming and survival of mature eosinophils and for proliferation and maturation of their progenitors. Hence, IL‐5(Rα) targeting will be increasingly used in diseases where eosinophils are the key immune effector cells such as eosinophilic asthma (EA), hypereosinophilic syndrome (HES), eosinophilic esophagitis (EE), and eosinophilic granulomatosis with polyangiitis (EGPA). Therefore, several neutralizing monoclonal antibodies directed against IL‐5 (mepolizumab and reslizumab) and its receptor IL‐5Rα (benralizumab) have found or will find their way to the clinic. While the clinical effect of these drugs has been extensively investigated and reviewed, the understanding of the underlying immunological and hematological mechanisms remains less clear. This review will discuss the translational outcomes of treatment with these monoclonal antibodies in humans to shed light on the mechanisms underlying the main immunological and hematological findings from these clinical trials in humans.

Mast Cell Disease Assessment by Flow Cytometric Analysis

Mast cells are present at a low frequency in bone marrow, rendering high-sensitivity multiparametric flow cytometric analysis an ideal method to assess antigen expression on mast cells. This article discusses the normal antigen expression profile of mast cells, established criteria to identify neoplastic mast cells, and new immunophenotypic markers and approaches to identify the presence of neoplastic mast cells in cases of mastocytosis.

KIT signaling is dispensable for human mast cell progenitor development

Human hematopoietic progenitors are generally assumed to require stem cell factor (SCF) and KIT signaling during differentiation for the formation of mast cells. Imatinib treatment, which inhibits KIT signaling, depletes mast cells in vivo. Furthermore, the absence of SCF or imatinib treatment prevents progenitors from developing into mast cells in vitro. However, these observations do not mean that mast cell progenitors require SCF and KIT signaling throughout differentiation. Here, we demonstrate that circulating mast cell progenitors are present in patients undergoing imatinib treatment. In addition, we show that mast cell progenitors from peripheral blood survive, mature, and proliferate without SCF and KIT signaling in vitro. Contrary to the prevailing consensus, our results show that SCF and KIT signaling are dispensable for early mast cell development.

Bidirectional Mast Cell-Eosinophil Interactions in Inflammatory Disorders and Cancer

Human mast cells (MCs) and eosinophils were first described and named by Paul Ehrlich. These cells have distinct myeloid progenitors and differ morphologically, ultrastructurally, immunologically, biochemically, and pharmacologically. However, MCs and eosinophils play a pivotal role in several allergic disorders. In addition, these cells are involved in autoimmune disorders, cardiovascular diseases, and cancer. MCs are distributed throughout all normal human tissues, whereas eosinophils are present only in gastrointestinal tract, secondary lymphoid tissues, and adipose tissue, thymus, mammary gland, and uterus. However, in allergic disorders, MCs and eosinophils can form the "allergic effector unit." Moreover, in several tumors, MCs and eosinophils can be found in close proximity. Therefore, it is likely that MCs have the capacity to modulate eosinophil functions and vice versa. For example, interleukin 5, stem cell factor, histamine, platelet-activating factor (PAF), prostaglandin D2 (PGD2), cysteinyl leukotrienes, and vascular endothelial growth factors (VEGFs), produced by activated MCs, can modulate eosinophil functions through the engagement of specific receptors. In contrast, eosinophil cationic proteins such as eosinophil cationic protein and major basic protein (MBP), nerve growth factor, and VEGFs released by activated eosinophils can modulate MC functions. These bidirectional interactions between MCs and eosinophils might be relevant not only in allergic diseases but also in several inflammatory and neoplastic disorders.

Gene therapy for radioprotection

Radiation therapy is a critical component of cancer treatment with over half of patients receiving radiation during their treatment. Despite advances in image-guided therapy and dose fractionation, patients receiving radiation therapy are still at risk for side effects due to off-target radiation damage of normal tissues. To reduce normal tissue damage, researchers have sought radioprotectors, which are agents capable of protecting tissue against radiation by preventing radiation damage from occurring or by decreasing cell death in the presence of radiation damage. Although much early research focused on small-molecule radioprotectors, there has been a growing interest in gene therapy for radioprotection. The amenability of gene therapy vectors to targeting, as well as the flexibility of gene therapy to accomplish ablation or augmentation of biologically relevant genes, makes gene therapy an excellent strategy for radioprotection. Future improvements to vector targeting and delivery should greatly enhance radioprotection through gene therapy.

IgE and IgA produced by OX40-OX40L or CD40-CD40L interaction in B cells-mast cells re-activate FcεRI or FcαRI on mast cells in mouse allergic asthma

Mast cells are major effector cells of allergic diseases related to IgE. This study was undertaken to determine whether IgE or IgA, produced by CD40-CD40L or OX40-OX40L interactions between B cells and mast cells, re-activate FcεRI or FcαRI on mast cell surface. C57BL mice were sensitized and subjected to OVA challenge to induce asthma. Bone marrow-derived mast cells (BMMCs) and primary B cells were co-cultured. Mast cell recruitment into airways was stained by May-Grünwald Giemsa, the expression of markers or signaling molecules were determined by immunohistochemistry or Western blotting, and co-localization of B cells and mast cells by immunofluorescence. Anti-CD40 plus anti-OX40L Abs synergistically reduced IgE and IgA production, and mediators (histamine, LTs and cytokines) released in mast cells, and additively reduced other responses, such as, numbers of mast cells, the expression of markers (tryptase, mMCP5, B220 and CD19), surface molecules (CD40, CD40L, OX40 and OX40L), FcεRI or FcαRI and the co-localization of BMMCs and B cells, and IgE- or IgA-producing cells, as compared with individual blocking Ab treatment which reducedresponses in BAL cells or lung tissues of OVA-challenged mice or in co-culture of B and mast cells. The data suggest that IgE and IgA, produced by OX40-OX40L or CD40-CD40L interaction between B cells and mast cells, may re-activate receptors of FCεRI and FcαRI on mast cell surfaces, followed by more mediator release, and furthermore, that treatment with anti-CD40 plus anti-OX40L Abs offers a potential treatment for allergic asthma.

The immunophenotype of mast cells and its utility in the diagnostic work-up of systemic mastocytosis

SM comprises a heterogeneous group of disorders, characterized by an abnormal accumulation of clonal MCs in 1 or more tissues, frequently involving the skin and BM. Despite the fact that most adult patients (>90%) carry the same genetic lesion (D816V KIT mutation), the disease presents with multiple variants with very distinct clinical and biologic features, a diverse prognosis, and different therapeutic requirements. Recent advances in the standardization of the study of BM MC by MFC allowed reproducible identification and characterization of normal/reactive MCs and their precursors, as well as the establishment of the normal MC maturational profiles. Analysis of large groups of patients versus normal/reactive samples has highlighted the existence of aberrant MC phenotypes in SM, which are essential for the diagnosis of the disease. In turn, 3 clearly distinct and altered maturation-associated immunophenotypic profiles have been reported recently in SM, which provide criteria for the distinction between ISM patients with MC-restricted and multilineage KIT mutation; thus, immunphenotyping also contributes to prognostic stratification of ISM, particularly when analysis of the KIT mutation on highly purified BM cells is not routinely available in the diagnostic work-up of the disease.

Mast cell function: a new vision of an old cell

Since first described by Paul Ehrlich in 1878, mast cells have been mostly viewed as effectors of allergy. It has been only in the past two decades that mast cells have gained recognition for their involvement in other physiological and pathological processes. Mast cells have a widespread distribution and are found predominantly at the interface between the host and the external environment. Mast cell maturation, phenotype and function are a direct consequence of the local microenvironment and have a marked influence on their ability to specifically recognize and respond to various stimuli through the release of an array of biologically active mediators. These features enable mast cells to act as both first responders in harmful situations as well as to respond to changes in their environment by communicating with a variety of other cells implicated in physiological and immunological responses. Therefore, the critical role of mast cells in both innate and adaptive immunity, including immune tolerance, has gained increased prominence. Conversely, mast cell dysfunction has pointed to these cells as the main offenders in several chronic allergic/inflammatory disorders, cancer and autoimmune diseases. This review summarizes the current knowledge of mast cell function in both normal and pathological conditions with regards to their regulation, phenotype and role.

Critical role for mast cell Stat5 activity in skin inflammation

Atopic dermatitis (AD) is a chronic inflammatory skin disease. Here, we show that phospholipase C-β3 (PLC-β3)-deficient mice spontaneously develop AD-like skin lesions and more severe allergen-induced dermatitis than wild-type mice. Mast cells were required for both AD models and remarkably increased in the skin of Plcb3(-/-) mice because of the increased Stat5 and reduced SHP-1 activities. Mast cell-specific deletion of Stat5 gene ameliorated allergen-induced dermatitis, whereas that of Shp1 gene encoding Stat5-inactivating SHP-1 exacerbated it. PLC-β3 regulates the expression of periostin in fibroblasts and TSLP in keratinocytes, two proteins critically involved in AD pathogenesis. Furthermore, polymorphisms in PLCB3, SHP1, STAT5A, and STAT5B genes were associated with human AD. Mast cell expression of PLC-β3 was inversely correlated with that of phospho-STAT5, and increased mast cells with high levels of phospho-STAT5 were found in lesional skin of some AD patients. Therefore, STAT5 regulatory mechanisms in mast cells are important for AD pathogenesis.

Identification and immunophenotypic characterization of normal and pathological mast cells

Mast cells (MCs) are secretory cells that are central players in human allergic disease and immune responses. With the exception of a few pathological situations, MCs are usually present at relatively low frequencies in most tissues. Since their first description, MCs in tissues were identified mostly using their morphological characteristics and their typical coloration when stained with aniline dyes. However, increasing availability of highly specific antibodies now permits the use of fluorescence-based flow cytometry as the method of choice for the quantification, characterization, and purification of cells in suspension. This technique allows for a rapid analysis of thousands of events and for the identification of cells present at frequencies as low as one event in 10(6) unwanted cells. This method also permits for simultaneous characterization of multiple antigens at a single-cell level, which is ideal in order to study rare populations of cells like MCs. Here we describe the basis of flow cytometry-based immunophenotyping applied to the study of MC. The protocol focuses on the study of human MCs present in body fluids (mainly bone marrow) but can easily be adapted to study MCs from other tissues and species.

High yield production of a soluble human interleukin-3 variant from E. coli with wild-type bioactivity and improved radiolabeling properties

Human interleukin-3 (hIL-3) is a polypeptide growth factor that regulates the proliferation, differentiation, survival and function of hematopoietic progenitors and many mature blood cell lineages. Although recombinant hIL-3 is a widely used laboratory reagent in hematology, standard methods for its preparation, including those employed by commercial suppliers, remain arduous owing to a reliance on refolding insoluble protein expressed in E. coli. In addition, wild-type hIL-3 is a poor substrate for radio-iodination, which has been a long-standing hindrance to its use in receptor binding assays. To overcome these problems, we developed a method for expression of hIL-3 in E. coli as a soluble protein, with typical yields of >3mg of purified hIL-3 per litre of shaking microbial culture. Additionally, we introduced a non-native tyrosine residue into our hIL-3 analog, which allowed radio-iodination to high specific activities for receptor binding studies whilst not compromising bioactivity. The method presented herein provides a cost-effective and convenient route to milligram quantities of a hIL-3 analog with wild-type bioactivity that, unlike wild-type hIL‑3, can be efficiently radio-iodinated for receptor binding studies.

Anti-IL-5 therapy reduces mast cell and IL-9 cell numbers in pediatric patients with eosinophilic esophagitis

BACKGROUND

Eosinophilic esophagitis (EoE) is a clinicopathologic entity of increasing worldwide prevalence. IL-5 is essential for eosinophil trafficking, and anti-IL-5 therapy decreases esophageal eosinophilia. EoE is associated with prominent mast cell infiltration.

OBJECTIVE

We investigated whether anti-IL-5 (mepolizumab) treatment reduced esophageal mast cell accumulation in biopsy specimens from pediatric patients with EoE from a previous randomized anti-IL-5 trial.

METHODS

A subanalysis was completed for children treated with 0.55, 2.5, or 10 mg/kg mepolizumab monthly for 12 weeks followed by no treatment until week 24. Quantitative immunochemistry was used to assess the numbers of eosinophils, tryptase-positive mast cells, IL-9(+) cells, and mast cell-eosinophil couplets before and after treatment.

RESULTS

Forty-three biopsy specimens had adequate tissue for paired analysis. Forty percent of subjects responded to anti-IL-5 (defined as <15 eosinophils per high-power field [hpf] after mepolizumab therapy), and 77% of all subjects had decreased numbers of mast cells after anti-IL-5. In responders epithelial mast cell numbers decreased from 62 to 19 per hpf (P < .001), were significantly lower than in nonresponders after therapy (P < .05), and correlated with eosinophil numbers (r = 0.75, P < .0001). Mast cells and eosinophils were found in couplets before therapy, and these were significantly decreased only in responders after anti-IL-5 (P < .001). Esophageal eosinophils comprised the majority of cells that made the mast cell growth factor IL-9. IL-9(+) cell numbers decreased from 102 to 71 per hpf (P < .001) after anti-IL-5.

CONCLUSIONS

Pediatric patients with EoE had significantly fewer mast cells, IL-9(+) cells, and mast cell-eosinophil couplets in the esophageal epithelium after anti-IL-5 therapy. Because eosinophils were one source of IL-9, they might support esophageal mastocytosis.

A genetic effect of IL-5 receptor α polymorphism in patients with aspirin-exacerbated respiratory disease

Persistent eosinophil activation in both the upper and lower airway mucosa is a central feature of aspirin-exacerbated respiratory disease (AERD). Eosinophil activation and survival are profoundly influenced by interleukin 5 (IL-5) and its receptor, IL-5R. In patients susceptible to allergic disorders, IL-5 receptor α (IL5RA) polymorphisms have been reported; however, an association with AERD remains unclear. We hypothesize that IL5RA polymorphisms may contribute to eosinophil activation in AERD patients. We recruited 139 AERD patients, 171 aspirin-tolerant asthma patients and 160 normal controls. IL5RA polymorphisms (−5993G>A, −5567C>G and −5091G>A) were genotyped and functional activity of polymorphism was assessed by luciferase reporter assay and electrophoretic mobility shift assay (EMSA). There was no significant difference in the genotype frequency of the three polymorphisms among the three groups. AERD patients carrying the AA genotype at −5993G>A had a significantly higher presence of serum-specific immunoglobulin E (IgE) to staphylococcal enterotoxin A (P=0.008) than those with the GG/GA genotype. In vitro, the −5993A allele had a higher promoter activity compared with the −5993G allele in human mast cell (HMC-1; P=0.030) and human promyelocytic leukemia (HL-60; P=0.013) cells. In EMSA, a −5993A probe produced a specific shifted band than the −5993G had. These findings suggest that a functional polymorphism in IL5RA may contribute to eosinophil and mast cell activation along with specific IgE responses to staphylococcal enterotoxin A in AERD patients.

The GM-CSF/IL-3/IL-5 cytokine receptor family: from ligand recognition to initiation of signaling

Granulocyte-macrophage colony-stimulating factor (GM-CSF), interleukin-3 (IL-3), and IL-5 are members of a discrete family of cytokines that regulates the growth, differentiation, migration and effector function activities of many hematopoietic cells and immunocytes. These cytokines are involved in normal responses to infectious agents, bridging innate and adaptive immunity. However, in certain cases, the overexpression of these cytokines or their receptors can lead to excessive or aberrant initiation of signaling resulting in pathological conditions, with chronic inflammatory diseases and myeloid leukemias the most notable examples. Recent crystal structures of the GM-CSF receptor ternary complex and the IL-5 binary complex have revealed new paradigms of cytokine receptor activation. Together with a wealth of associated structure-function studies, they have significantly enhanced our understanding of how these receptors recognize cytokines and initiate signals across cell membranes. Importantly, these structures provide opportunities for structure-based approaches for the discovery of novel and disease-specific therapeutics. In addition, recent biochemical evidence has suggested that the GM-CSF/IL-3/IL-5 receptor family is capable of interacting productively with other membrane proteins at the cell surface. Such interactions may afford additional or unique biological activities and might be harnessed for selective modulation of the function of these receptors in disease.

Osteocalcin positive CD133+/CD34-/KDR+ progenitor cells as an independent marker for unstable atherosclerosis

AIMS

For the characterization of endothelial progenitor cells (EPCs), commonly the markers CD34 and KDR have been used. CD133+/CD34-/KDR+ cells may represent more immature 'early' progenitors. In patients with coronary artery disease (CAD), a large fraction of EPCs carry the osteoblastic marker osteocalcin (OCN), which may mediate vascular calcification and abnormal repair. The aim of this study was to evaluate the expression of OCN+ 'early' EPCs in patients with risk factors (RFs) and a history of stable (history of stenting/coronary artery bypass grafting) or unstable CAD (myocardial infarction).

METHODS AND RESULTS

Medical history and blood samples from 282 patients (age 58 ± 16 years) with CAD or at least one RF (mean 2.5 ± 1.5) were analysed. For the analysis of EPC markers (CD133, CD34, KDR) and OCN, the flow cytometry of peripheral blood mononuclear cells was performed. Circulating OCN+/CD133+/CD34-/KDR+ cells (median counts [interquartile range] per 100 000 events) were 15 [4-41] in patients with RF (n = 199), 26 [1-136] in those with a history of stable (n = 57), and 246 [105-308] in those with a history of unstable CAD (n = 26; P < 0.001). The association with unstable CAD remained highly significant even after multivariate adjusting for RFs and the different characteristics of the groups. Osteocalcin positive 'early' EPCs trend to predict further events [HR for each doubling of the cell number: 1.20 (95% CI: 1.00-1.46), P = 0.06].

CONCLUSION

Circulating OCN+ 'early' EPCs are strongly associated with unstable CAD. Therefore, this particular subset of EPCs could mediate abnormal vascular repair and may help identifying patients with a more unstable phenotype of atherosclerosis.

Generation, selection and preclinical characterization of an Fc-optimized FLT3 antibody for the treatment of myeloid leukemia

The therapeutic efficacy of humanized or chimeric second-generation antitumor antibodies is clearly established, but often limited. In recent years, defined modifications of the glycosylation pattern or the amino-acid sequence of the human immunoglobulin G1 Fc part have resulted in the development of third-generation antibodies with improved capability to recruit Fc receptor-bearing effector cells. The first antibodies of this kind, currently evaluated in early clinical trials, are directed against lymphoma-associated antigens. Fc-engineered antibodies targeting myeloid leukemia are not yet available. We here report on the generation and preclinical characterization of an Fc-optimized antibody directed to the FMS-related tyrosine kinase 3 (FLT3), an antigen expressed on the leukemic blasts of all investigated patients with acute myeloid leukemia (AML). This antibody, termed 4G8SDIEM, mediated markedly enhanced cellular cytotoxicity against FLT3-expressing cell lines as well as blasts of AML patients. FLT3 expression levels on AML cells varied between 300 and 4600 molecules/cell and, in most cases, were substantially higher than those detected on normal hematopoietic precursor cells and dendritic cells (approximately 300 molecules/cell). Antibody-mediated cytotoxicity against these normal cells was not detectable. 4G8SDIEM has been produced in pharmaceutical quality in a university-owned production unit and is currently used for the treatment of leukemia patients.

Molecular and clinical rationale for therapeutic targeting of interleukin-5 and its receptor

Interleukin-5 is a Th2 homodimeric cytokine involved in the differentiation, maturation, migration, development, survival, trafficking and effector function of blood and local tissue eosinophils, in addition to basophils and mast cells. The IL-5 receptor (IL-5R) consists of an IL-5-specific α subunit that interacts in conformationally dynamic ways with the receptor's βc subunit, an aggregate of domains it shares with binding sites of IL-3 and granulocyte-macrophage colony-stimulating factor. IL-5 and IL-5R drive allergic and inflammatory immune responses characterizing numerous diseases, such as asthma, atopic dermatitis, chronic obstructive pulmonary disease, eosinophilic gastrointestinal diseases, hyper-eosinophilic syndrome, Churg-Strauss syndrome and eosinophilic nasal polyposis. Although corticosteroid therapy is the primary treatment for these diseases, a substantial number of patients exhibit incomplete responses and suffer side-effects. Two monoclonal antibodies have been designed to neutralize IL-5 (mepolizumab and reslizumab). Both antibodies have demonstrated the ability to reduce blood and tissue eosinophil counts. One additional monoclonal antibody, benralizumab (MEDI-563), has been developed to target IL-5R and attenuate eosinophilia through antibody-dependent cellular cytotoxicity. All three monoclonal antibodies are being clinically evaluated. Antisense oligonucleotide technology targeting the common βc IL-5R subunit is also being used therapeutically to inhibit IL-5-mediated effects (TPI ASM8). Small interfering RNA technology has also been used therapeutically to inhibit the expression of IL-5 in animal models. This review summarizes the structural interactions between IL-5 and IL-5R and the functional consequences of such interactions, and describes the pre-clinical and clinical evidence supporting IL-5R as a therapeutic target.

IL-5 receptor α levels in patients with marked eosinophilia or mastocytosis

BACKGROUND

IL-5 plays a central role in the development and maintenance of eosinophilia (EO) and eosinophil activation in a wide variety of eosinophilic disorders. Although IL-5, IL-3, and GM-CSF can modulate the expression of IL-5 receptor α (IL-5Rα) on eosinophils in vitro, little is known about soluble and surface IL-5Rα levels in vivo.

OBJECTIVE

To assess soluble and surface IL-5Rα levels in patients with EO and/or mastocytosis.

METHODS

Surface IL-5Rα expression was assessed by flow cytometry in blood and/or bone marrow from subjects with EO (n = 39) and systemic mastocytosis (n = 8) and from normal volunteers (n = 28). Soluble IL-5Rα (sIL-5Rα) level was measured in a cohort of 177 untreated subjects and correlated with EO, eosinophil activation, and serum tryptase and cytokine levels.

RESULTS

IL-5Rα expression on eosinophils inversely correlated with EO (r = -0.48; P < .0001), whereas serum levels of sIL-5Rα increased with the eosinophil count (r = 0.56; P < .0001) and serum IL-5 (r = 0.40; P < .0001) and IL-13 (r = 0.29; P = .004) levels. Of interest, sIL-5Rα level was significantly elevated in patients with systemic mastocytosis without EO. Although sIL-5Rα levels correlated with serum tryptase levels in these patients, eosinophil activation, assessed by CD69 expression on eosinophils and serum eosinophil-derived neurotoxin levels, was increased compared with that in normal subjects.

CONCLUSIONS

These data are consistent with an in vivo IL-5Rα regulatory pathway in human eosinophils similar to that described in vitro and involving a balance between soluble and surface receptor levels. This may have implications with respect to the use of novel therapeutic agents targeting IL-5 and its receptor in patients with EO and/or mastocytosis.

Physical interactions between mast cells and eosinophils: a novel mechanism enhancing eosinophil survival in vitro

BACKGROUND

Mast cells (MCs) and eosinophils (Eos) are the key effector cells of the allergic reaction. Although classically associated with different stages of the response, the cells co-exist in the inflamed tissue in the late and chronic phases in high numbers and are likely to cross-talk. While some mediators of MCs are known to affect Eos biology and vice versa, paracrine and physical interplay between the two cells has not been described yet. We aimed to investigate whether intercellular MC-Eos communication could take place in the allergic response and exert functional bidirectional changes on the cells.

METHODS

Tissue sections from various allergic disorders were specifically stained for both cells. Human cord blood-derived MCs and peripheral blood Eos, co-cultured under different conditions, were studied by advanced microscopy and flow cytometry.

RESULTS

Several co-localized MC-Eos pairs were detected in human nasal polyps and asthmatic bronchi, as well in mouse atopic dermatitis. In vitro, MCs and Eos formed stable conjugates at high rates, with clear membrane contact. In the presence of MCs, Eos were significantly more viable under several co-culture conditions and at both IgE-activated and steroid-inhibited settings. MC regulation of Eos survival required communication through soluble mediators but was even more dependent on physical cell-cell contact.

CONCLUSIONS

Our findings provide the first evidence for a complex network of paracrine and membrane interactions between MCs and Eos. The prosurvival phenotype induced by this MC-Eos interplay may be critical for sustaining chronic allergic inflammation.