IgG Fc receptors

Phenotype analyses of IL-10-producing Foxp3- CD4+ T cells increased by subcutaneous immunotherapy in allergic airway inflammation

INTRODUCTION

The mechanisms of allergen immunotherapy are not fully elucidated. Here, we sought to develop a murine model to demonstrate the effectiveness of subcutaneous immunotherapy (SCIT) for allergic responses. As excessive antigen dosages may induce immune tolerance in sensitized mice, the effects of SCIT were assessed by varying the antigen dosage. The mechanisms of SCIT were analyzed by focusing on the induction of Foxp3⁺ Treg cells and IL-10-producing Foxp3^- CD4⁺ T cells, as well as on the phenotype of the latter cells.

METHODS

Ovalbumin (OVA) + Al(OH)₃-sensitized mice received subcutaneous dosages of OVA at 0.01, 0.1 or 1 mg/animal for SCIT, followed by intratracheal challenges with OVA at 5, 50 or 500 μg/animal.

RESULTS

The maximum effects of SCIT were observed with 1 mg/animal of OVA for airway inflammation induced by 5 μg/animal of OVA, in which airway eosinophilia and Th2 cytokine production were markedly suppressed. The increase in the OVA-specific IgE level was significantly suppressed by SCIT. The development of bronchial epithelial thickening and mucus accumulation were also suppressed by SCIT. Concomitantly, IL-10-producing Foxp3^- CD4⁺ T cells were increased in the lungs by SCIT, but Foxp3⁺ Treg cells were not. Most of the induced IL-10-producing Foxp3^- CD4⁺ T cells were negative for either IL-5 or LAG-3, but positive for CD49b.

CONCLUSION

We successfully developed an airway allergic model for SCIT. It was suggested that most of IL-10-producing Foxp3^- CD4⁺ regulatory T cells increased by SCIT in the lungs were CD49b⁺ CD4⁺ regulatory T cells, but neither Th2 cells nor Tr1 cells.

Lineage-Specific Functionality of an Interferon Regulatory Factor 5 Lupus Risk Haplotype: Lack of B Cell Intrinsic Effects

Interferon regulatory factor 5 (IRF5) is widely recognized as a risk locus for systemic lupus erythematosus (SLE). Risk gene and IRF5 activation is triggered through toll-like receptor signaling. In myeloid cells, this leads to production of type I interferon and inflammatory cytokines, with enhanced production in cells of individuals harboring IRF5 risk alleles. Mouse models have also demonstrated the importance of IRF5 in B cell function, particularly plasma cell differentiation and isotype switching. Here, we evaluated the major SLE risk haplotype of IRF5 on the functional attributes of freshly isolated B cells from human subjects who do not have evidence of SLE or other forms of autoimmunity. We took this approach to avoid the complications of studying genotype-phenotype relationships in B cells that have been chronically exposed to an inflammatory disease environment before isolation. We focused on B cell endophenotypes that included gene expression, antibody secretion, class switching, and apoptotic susceptibility. We performed IRF5 overexpression studies, genetic reporter assays and electro-mobility shift assays on B and myeloid cell lines. Somewhat surprisingly, the results of our analyses indicate that IRF5 risk genotypes do not have a B cell intrinsic effect on these B cell functions. By contrast, we confirmed that the IRF5 risk and non-risk haplotypes exert differential effects in myeloid cells, including an increased susceptibility to apoptosis conferred by the risk haplotype. We also demonstrated an increased binding of the transcription factor specificity protein 1 to an insertion/deletion present in the risk haplotype. Our findings raise the specter that genetic risk alleles can have complex and unexpected lineage-specific effects, and these must be carefully considered when guiding or developing therapies based on understanding disease risk haplotypes.

Neutrophils and neutrophil extracellular traps in the liver and gastrointestinal system

Neutrophil extracellular traps (NETs) have an important role during infection by helping neutrophils to capture and kill pathogens. However, evidence is accumulating that uncontrolled or excessive production of NETs is related to the exacerbation of inflammation and the development of autoimmunity, cancer metastasis and inappropriate thrombosis. In this Review, we focus on the role of NETs in the liver and gastrointestinal system, outlining their protective and pathological effects. The latest mechanistic insights in NET formation, interactions between microorganisms and NETs and the relationship between neutrophil subtypes and their functions are also discussed. Additionally, we describe the potential importance of NET-related molecules, including cell-free DNA and hypercitrullinated histones, as biomarkers and targets for therapeutic intervention in gastrointestinal diseases.

Low pH impairs complement-dependent cytotoxicity against IgG-coated target cells

Local acidosis is a common feature of allergic, vascular, autoimmune, and cancer diseases. However, few studies have addressed the effect of extracellular pH on the immune response. Here, we analyzed whether low pH could modulate complement-dependent cytotoxicity (CDC) against IgG-coated cells. Using human serum as a complement source, we found that extracellular pH values of 5.5 and 6.0 strongly inhibit CDC against either B lymphoblast cell lines coated with the chimeric anti-CD20 mAb rituximab or PBMCs coated with the humanized anti-CD52 mAb alemtuzumab. Suppression of CDC by low pH was observed either in cells suspended in culture medium or in whole blood assays. Interestingly, not only CDC against IgG-coated cells, but also the activation of the complement system induced by the alternative and lectin pathways was prevented by low pH. Tumor-targeting mAbs represent one of the most successful tools for cancer therapy, however, the use of mAb monotherapy has only modest effects on solid tumors. Our present results suggest that severe acidosis, a hallmark of solid tumors, might impair complement-mediated tumor destruction directed by mAb.

Antibody Functional Assays as Measures of Fc Receptor-Mediated Immunity to HIV - New Technologies and their Impact on the HIV Vaccine Field

Background:

There is now intense interest in the role of HIV-specific antibodies and the engagement of FcγR functions in the control and prevention of HIV infection. The analyses of the RV144 vaccine trial, natural progression cohorts, and macaque models all point to a role for Fc-dependent effector functions, such as cytotoxicity (ADCC) or phagocytosis (ADCP), in the control of HIV. However, reliable assays that can be reproducibly used across different laboratories to measure Fc-dependent functions, such as antibody dependent cellular cytotoxicity (ADCC) are limited.

Method:

This brief review highlights the importance of Fc properties for immunity to HIV, particular-ly via FcγR diversity and function. We discuss assays used to study FcR mediated functions of HIV-specific Ab, including our recently developed novel cell-free ELISA using homo-dimeric FcγR ecto-domains to detect functionally relevant viral antigen-specific antibodies.

Results:

The binding of these dimeric FcγR ectodomains, to closely spaced pairs of IgG Fc, mimics the engagement and cross-linking of Fc receptors by IgG opsonized virions or infected cells as the es-sential prerequisite to the induction of Ab-dependent effector functions. The dimeric FcγR ELISA reli-ably correlates with ADCC in patient responses to influenza. The assay is amenable to high throughput and could be standardized across laboratories.

Conclusion:

We propose the assay has broader implications for the evaluation of the quality of anti-body responses in viral infections and for the rapid evaluation of responses in vaccine development campaigns for HIV and other viral infections.

Gene-modified NK-92MI cells expressing a chimeric CD16-BB-ζ or CD64-BB-ζ receptor exhibit enhanced cancer-killing ability in combination with therapeutic antibody

Natural killer (NK) cells play a pivotal role in monoclonal antibody-mediated immunotherapy through the antibody-dependent cell-mediated cytotoxicity (ADCC) mechanism. NK-92MI is an interleukin-2 (IL-2)-independent cell line, which was derived from NK-92 cells with superior cytotoxicity toward a wide range of tumor cells in vitro and in vivo. Nonetheless, the Fc-receptor (CD16) that usually mediates ADCC is absent in NK-92 and NK-92MI cells. To apply NK-92MI cell-based immunotherapy to cancer treatment, we designed and generated two chimeric receptors in NK-92MI cells that can bind the Fc portion of human immunoglobulins. The construct includes the low-affinity Fc receptor CD16 (158F) or the high-affinity Fc receptor CD64, with the addition of the CD8a extracellular domain, CD28 transmembrane domains, two costimulatory domains (CD28 and 4-1BB), and the signaling domain from CD3ζ. The resulting chimeric receptors, termed CD16-BB-ζ and CD64-BB-ζ, were used to generate modified NK-92MI cells expressing the chimeric receptor, which were named NK-92MI^hCD16 and NK-92MI^hCD64 cells, respectively. We found that NK-92MI^hCD16 and NK-92MI^hCD64 cells significantly improved cytotoxicity against CD20-positive non-Hodgkin's lymphoma cells in the presence of rituximab. These results suggest that the chimeric receptor-expressing NK-92MI cells may enhance the clinical responses to currently available anticancer monoclonal antibodies.

Evaluation of analytical similarity between trastuzumab biosimilar CT-P6 and reference product using statistical analyses

The evaluation of analytical similarity has been a challenging issue for the biosimilar industry because the number of lots for reference and biosimilar products available at the time of development are limited, whilst measurable quality attributes of target molecule are numerous, which can lead to potential bias or false negative/positive conclusions regarding biosimilarity. Therefore, appropriate statistical analyses are highly desirable to achieve a high level of confidence in the similarity evaluation. A recent guideline for the risk-based statistical approaches recommended by the US Food and Drug Administration provides useful tools to systematically evaluate analytical similarity of biosimilar products compared with reference products. Here, we evaluated analytical similarity of CT-P6, a biosimilar product of trastuzumab, with the reference products (EU-Herceptin® or US-Herceptin®) following these statistical approaches. Various quality attributes of trastuzumab were first ranked based on the clinical impact of each attribute and subsequently adjusted to one of three tiers (Tier 1, Tier 2 and Tier 3) considering the characteristics of the assay, the level of attribute present and the feasibility of statistical analysis. Two biological activities with highest potential clinical impact were evaluated by an equivalent test (Tier 1), and other bioactivities and structural/physicochemical properties relevant to the clinical impact were evaluated by a quality range approach (Tier 2). The attributes with low risk ranking or qualitative assay were evaluated by visual comparison (Tier 3). Analytical similarity assessment analyzed by the three tiers clearly demonstrated that CT-P6 exhibits highly similar structural and physicochemical properties, as well as functional activities, compared with the reference products. There were small differences observed in a few quality attributes between CT-P6 and the reference products, but the differences were very minor, and unlikely to impact on clinical outcome. The recently reported equivalent clinical efficacy of CT-P6 with the reference product further supports that CT-P6 is highly similar compared with the reference product in the view of totality-of-evidence.

Analytical similarity assessment of rituximab biosimilar CT-P10 to reference medicinal product

CT-P10 (Truxima™) was recently approved as the world's first rituximab biosimilar product in the European Union (EU) and South Korea. To demonstrate biosimilarity of CT-P10 with the reference medicinal product (RMP), extensive 3-way similarity assessment has been conducted between CT-P10, EU-Rituximab and US-Rituximab, focusing on the physicochemical and biological quality attributes. A multitude of state-of-the-art analyses revealed that CT-P10 has identical primary and higher order structures compared to the original product. Purity/impurity profiles of CT-P10 measured by the levels of aggregates, fragments, non-glycosylated form and process-related impurities were also found to be comparable with those of RMPs. In terms of the post-translational modification, CT-P10 contains slightly less N-terminal pyro-glutamate variant, which has been known not to affect product efficacy or safety. Oligosaccharide profiling has revealed that, although CT-P10 contains the same conserved glycan species and relative proportion with the RMPs, the content of total afucosylated glycan in CT-P10 was slightly higher than in EU- or US-Rituximab. Nevertheless, the effect of the observed level of afucosylation in CT-P10 drug product on Fc receptor binding affinity or antibody-dependent cell-mediated cytotoxicity was found to be negligible based on the spiking study with highly afucosylated sample. Arrays of biological assays representative of known and putative mechanisms of action for rituximab have shown that biological activities of CT-P10 are within the quality range of RMPs. Recent results of clinical studies have further confirmed that the CT-P10 exhibits equivalent clinical efficacy and safety profiles compared to EU- and US-Rituximab. The current 3-way similarity assessment together with clinical study results confidently demonstrate that CT-P10 is highly similar with EU- and US-Rituximab in terms of physicochemical properties, biological activities, efficacy, and safety for its final approval as a biosimilar product.

Curing tumor-bearing mice by shifting a Th2 to a Th1 anti-tumor response

Over the past several years remarkable therapeutic responses have been obtained with immunomodulatory monoclonal antibodies (mAbs), both in mice \cite{10,18,20,48,54,61} and human cancer patients \cite{1,3,14,28,30,39,80}. However, complete regressions and cures are infrequent and not predictable and some tumor types respond much worse than others. As an attempt to increase curability, we have investigated in mouse models the therapeutic efficacy of several mAb combinations, focusing on anti-PD-1/CTLA-4/CD137 and anti-PD-1/CTLA-4/CD137/CD19, and we have also combined mAbs with the chemotherapeutic drug cisplatin. Our data demonstrate an important contribution of anti-CD19 mAb to therapeutic efficacy, they show that intratumoral delivery of the mAbs is therapeutically more effective than systemic delivery, and that there is synergy when the mAbs are combined with cisplatin. In an attempt to improve predictability, we developed an in vitro model that may also be employed to search for novel immunomodulatory agents and combinations. This article reviews our data and discusses what is known about the underlying mechanisms.

Anti-CD11b antibody treatment suppresses the osteoclast generation, inflammatory cell infiltration, and autoantibody production in arthritis-prone FcγRIIB-deficient mice

BACKGROUND

Previously we established an arthritis-prone FcγRIIB-deficient mouse strain (designated KO1). Anti-mouse CD11b mAb (5C6) has been reported to inhibit the recruitment of peripheral CD11b⁺ myelomonocytic cells from the blood to the inflammatory site. These cells include neutrophils and monocytes, both of which play important roles in the development of arthritis. Here we treated KO1 mice with 5C6 mAb in order to study its effect on arthritis development.

METHODS

To evaluate the disease-preventive effect of 5C6, 4-month-old preclinical KO1 mice were divided into three groups: the first treated with 5C6 for 6 months, the second treated with normal rat IgG for 6 months, as a control, and the third left untreated. Arthritis severity and immunological abnormalities were compared among the groups, along with transcriptional levels of several important arthritis-related factors in ankle joints, spleen, and peripheral blood cells.

RESULTS

The 5C6 treatment ameliorated arthritis in KO1 mice, showing decreases in inflammatory cell infiltration and osteoclast formation. Analysis of transcriptional levels in ankle joints revealed that compared with the two control groups, the 5C6-treated group showed downregulated expression of RANK, RANKL, MCP-1, RANTES, TNFα, and IL-6, and at the same time showed significantly up-regulated expression of the decoy receptor for RANKL, i.e. osteoprotegerin. In addition, the disease suppression was associated with the lower serum levels of autoantibodies, and the decreased frequencies of activated B cells and plasma cells. The expression levels of B cell activation/differentiation-related cytokines were suppressed in spleen and peripheral leukocytes of the 5C6-treated mice. Intriguingly, while untreated KO1 mice spontaneously developed marked monocytosis, the 5C6-treated mice showed the significantly down-regulated frequency of monocytes.

CONCLUSIONS

The outcome of 5C6 treatment was complex, in which the 5C6-mediated disease-preventive effect is likely due on one hand to the decrease in the recruitment of inflammatory cells and osteoclast precursor monocytes from the periphery into the joints, and on the other hand to the suppression of B cell activation/maturation and of autoantibody production via the suppression of B cell stimulating cytokine production. The lower levels of these cytokines may be the secondary effect of the lower frequency of monocytes, since monocytes/macrophages are the major producers of these cytokines.

Unravelling Immunoglobulin G Fc N-Glycosylation: A Dynamic Marker Potentiating Predictive, Preventive and Personalised Medicine

Multiple factors influence immunoglobulin G glycosylation, which in turn affect the glycoproteins’ function on eliciting an anti-inflammatory or pro-inflammatory response. It is prudent to underscore these processes when considering the use of immunoglobulin G N-glycan moieties as an indication of disease presence, progress, or response to therapeutics. It has been demonstrated that the altered expression of genes that encode enzymes involved in the biosynthesis of immunoglobulin G N-glycans, receptors, or complement factors may significantly modify immunoglobulin G effector response, which is important for regulating the immune system. The immunoglobulin G N-glycome is highly heterogenous; however, it is considered an interphenotype of disease (a link between genetic predisposition and environmental exposure) and so has the potential to be used as a dynamic biomarker from the perspective of predictive, preventive, and personalised medicine. Undoubtedly, a deeper understanding of how the multiple factors interact with each other to alter immunoglobulin G glycosylation is crucial. Herein we review the current literature on immunoglobulin G glycoprotein structure, immunoglobulin G Fc glycosylation, associated receptors, and complement factors, the downstream effector functions, and the factors associated with the heterogeneity of immunoglobulin G glycosylation.

Epigenetic and Posttranscriptional Regulation of CD16 Expression during Human NK Cell Development

The surface receptor FcγRIIIA (CD16a) is encoded by the FCGR3A gene and is acquired by human NK cells during maturation. NK cells bind the Fc portion of IgG via CD16a and execute Ab-dependent cell-mediated cytotoxicity, which is critical for the effectiveness of several antitumor mAb therapies. The role of epigenetic regulatory mechanisms controlling transcriptional and posttranscriptional CD16 expression in NK cells is unknown. In this study, we compared specific patterns of DNA methylation and expression of FCGR3A with FCGR3B, which differ in cell type-specific expression despite displaying nearly identical genomic sequences. We identified a sequence within the FCGR3A promoter that selectively exhibits reduced methylation in CD16a+ NK cells versus CD16a- NK cells and neutrophils. This region contained the transcriptional start site of the most highly expressed CD16a isoform in NK cells. Luciferase assays revealed remarkable cell-type specificity and methylation-dependent activity of FCGR3A- versus FCGR3B-derived sequences. Genomic differences between FCGR3A and FCGR3B are enriched at CpG dinucleotides, and mutation of variant CpGs reversed cell-type specificity. We further identified miR-218 as a posttranscriptional negative regulator of CD16a in NK cells. Forced overexpression of miR-218 in NK cells knocked down CD16a mRNA and protein expression. Moreover, miR-218 was highly expressed in CD16a- NK cells compared with CD16a+ NK cells. Taken together, we propose a system of FCGR3A regulation in human NK cells in which CpG dinucleotide sequences and concurrent DNA methylation confer developmental and cell type-specific transcriptional regulation, whereas miR-218 provides an additional layer of posttranscriptional regulation during the maturation process.

Engineering of Fc Fragments with Optimized Physicochemical Properties Implying Improvement of Clinical Potentials for Fc-Based Therapeutics

Therapeutic monoclonal antibodies and Fc-fusion proteins are successfully used in treatment of various diseases mainly including cancer, immune disease, and viral infection, which belong to the Fc-based therapeutics. In recent years, engineered Fc-derived antibody domains have also shown potential for Fc-based therapeutics. To increase the druggability of Fc-based therapeutic candidates, many efforts have been made in optimizing physicochemical properties and functions mediated by Fc fragment. The desired result is that we can simultaneously obtain Fc variants with increased physicochemical properties in vitro and capacity of mediating appropriate functions in vivo. However, changes of physicochemical properties of Fc may result in alternation of Fc-mediated functions and vice versa, which leads to undesired outcomes for further development of Fc-based therapeutics. Therefore, whether modified Fc fragments are suitable for achievement of expected clinical results or not needs to be seriously considered. Now, this question comes to be noticed and should be figured out to make better translation from the results of laboratory into clinical applications. In this review, we summarize different strategies on engineering physicochemical properties of Fc, and preliminarily elucidate the relationships between modified Fc in vitro and the subsequent therapeutic influence in vivo.

Recent Advances in the Generation of Antibody-Nanomaterial Conjugates

Targeted nanomedicines have significantly changed the way new therapeutics are designed to treat disease. Central to successful therapeutics is the ability to control the dynamics of protein-nanomaterial interactions to enhance the therapeutic effect of the nanomedicine. The aim of this review is to illustrate the diversity and versatility of the conjugation approaches involved in the synthesis of antibody-nanoparticle conjugates, and highlight significant new advances in the field of bioconjugation. Such nanomedicines have found utility as both advanced therapeutic agents, as well as more complex imaging contrast agents that can provide both anatomical and functional information of diseased tissue. While such conjugates show significant promise as next generation targeted nanomedicines, it is recognized that there are in fact no clinically approved targeted therapeutics on the market. This fact is reflected upon within this review, and attempts are made to draw some reasoning from the complexities associated with the bioconjugation chemistry approaches that are typically utilized. Present trends, as well as future directions of next generation targeted nanomedicines are also discussed.

Elucidating the interplay between IgG-Fc valency and FcγR activation for the design of immune complex inhibitors

Autoantibody immune complex (IC) activation of Fcγ receptors (FcγRs) is a common pathogenic hallmark of multiple autoimmune diseases. Given that the IC structural features that elicit FcγR activation are poorly understood and the FcγR system is highly complex, few therapeutics can directly block these processes without inadvertently activating the FcγR system. To address these issues, the structure activity relationships of an engineered panel of multivalent Fc constructs were evaluated using sensitive FcγR binding and signaling cellular assays. These studies identified an Fc valency with avid binding to FcγRs but without activation of immune cell effector functions. These observations directed the design of a potent trivalent immunoglobulin G-Fc molecule that broadly inhibited IC-driven processes in a variety of immune cells expressing FcγRs. The Fc trimer, Fc3Y, was highly efficacious in three different animal models of autoimmune diseases. This recombinant molecule may represent an effective therapeutic candidate for FcγR-mediated autoimmune diseases.

Glycosylation of autoantibodies: Insights into the mechanisms of immune thrombocytopenia

Immune thrombocytopenia (ITP) is a bleeding disorder caused by IgG autoantibodies (AAbs) directed against platelets (PLTs). IgG effector functions depend on their Fc-constant region which undergoes post-translational glycosylation. We investigated the role of Asn279-linked N-glycan of AAbs in vitro and in vivo. AAbs were purified from ITP patients (n=15) and N-glycans were enzymatically cleaved by endoglycosidase F. The effects of native AAbs and deglycosylated AAbs were compared in vitro on enhancement of phagocytosis of platelets by monocytes and complement fixation and activation applying flow cytometry, laser scanning microscopy, and a complement consumption assay. AAb-induced platelet phagocytosis was inhibited by N-glycan cleavage (median phagocytic activity: 8% vs 0.8%, p=0.004). Seven out of 15 native AAbs bound C1q and activated complement. N-glycan cleavage significantly reduced both effects. In vivo survival of human PLTs was assessed after co-transfusion with native or N-glycan cleaved AAbs in a NOD/SCID mouse model. Injection of AAbs resulted in rapid clearance of human platelets compared to control (platelet clearance after 5h (CL5h) 75% vs 30%, p<0.001). AAbs that were able to activate complement induced more pronounced platelet clearance in the presence of complement compared to the clearance in the absence of complement (CL5h 82% vs 62%, p=0.003). AAbs lost their ability to destroy platelets in vivo after deglycosylation (CL5h 42%, p<0.001). N-glycosylation of human ITP AAbs appears to be required for platelet phagocytosis and complement activation, reducing platelet survival in vivo. Posttranslational modification of AAbs may constitute an important determinant for the clinical manifestation of ITP.

Prognostic relevance of HER2/neu in acute lymphoblastic leukemia and induction of NK cell reactivity against primary ALL blasts by trastuzumab

The epidermal growth factor receptor HER2/neu is expressed on various cancers and represents a negative prognostic marker, but is also a target for the therapeutic monoclonal antibody Trastuzumab. In about 30% of cases, HER2/neu is expressed on acute lymphoblastic leukemia (ALL) cells and was proposed to be associated with a deleterious prognosis. Here we evaluated clinical data from 65 ALL patients (HER2/neu+, n = 17; HER2/neu-, n = 48) with a median follow-up of 19.4 months (range 0.6-176.5 months) and observed no association of HER2/neu expression with response to chemotherapy, disease free or overall survival. In vitro, treatment of primary ALL cells (CD20+HER2/neu+, CD20+HER2/neu- and CD20-HER2/neu-) with Rituximab and Trastuzumab led to activation of NK cells in strict dependence of the expression of the respective antigen. NK reactivity was more pronounced with Rituximab as compared to Trastuzumab, and combined application could lead to additive effects in cases where both antigens were expressed. Besides providing evidence that HER2/neu expression is no risk factor in ALL patients, our data demonstrates that HER2/neu can be a promising target for Trastuzumab therapy in the subset of ALL patients with the potential to improve disease outcome.

Neutrophil CD16b crosslinking induces lipid raft-mediated activation of SHP-2 and affects cytokine expression and retarded neutrophil apoptosis

Two different types of FcRs for IgG are constitutively expressed on the surface of human neutrophils, namely, FcγRIIA (CD32a) and FcγRIIIB (CD16b). Unlike FcγRIIA, FcγRIIIb is GPI anchored to the cell membrane and its signal transduction is still ambiguous. To further understand the signal transduction of CD16b, we compared neutrophil cytokine expression and apoptosis by the cross-linking of CD32a and CD16b respectively. We found that both CD32a and CD16b crosslinking can activate neutrophils, but did not exactly share cytokine expression profiles. On the other hand, CD16b cross-linking retarded neutrophil apoptosis while CD32a promoted it. By interrupting the lipid raft with methyl-β-cyclodextrin (MβCD) and inhibiting the ITAM-SYK pathway with an SYK inhibitor (piceatannol), we found reduced apoptosis was at least partially mediated by lipid raft structure, but not the ITAM-SYK pathway. Additionally, CD16b but not CD32a cross-linking triggered SHP-2 phosphorylation and led to its translocation into lipid rafts. SHP-2 phosphorylation and translocation were inhibited by MβCD. Moreover, pre-inhibition of SHP-2 by a specific inhibitor (SHP099) converted IL-10 and SOCS3 expression level and promoted neutrophil apoptosis after CD16b crosslinking. In conclusion, these results, for the first time, collectively indicate that SHP-2 is activated by CD16b crosslinking in neutrophils and functions as a component of the raft-mediated signaling pathway.

Immune complex negatively regulates toll-like receptor 3-triggered tumour necrosis factor α production in B cells

Inappropriate activation of toll-like receptor 3 (TLR3) has been implicated in the pathogenesis of autoimmune diseases, so the negative regulation of TLR3-triggered immune response has received increasing attention. Nonpathogenic immune complex (IC) has been used as treatment for many inflammatory and autoimmune diseases. However, the role of IC in the regulation of TLR3-triggered immune responses and the underlying mechanisms need to be investigated. In this study we demonstrate that IC or intravenous immunoglobulin (Ig) stimulation of B cells attenuates polyinosinic:polycytidylic acid (poly I:C)-induced CD40 expression; IC, but not Ig, can significantly inhibit poly I:C-induced pro-inflammatory tumour necrosis factor α (TNF-α) production by B cells. Moreover, IC/Ig stimulation does not alter the expression of TLR3 in B cells. Further experiments suggest that receptor for the Fc portion of IgGIIb (FcγRIIb) is involved in the suppressive effect of IC on TLR3-mediated TNF-α production, but not CD40 expression. Thus, we provide a new means of negative regulation of TLR3-triggered immune responses in B cells via FcγRIIb, and we provide a new mechanistic explanation of the therapeutic effect of nonpathogenic IC on inflammatory or autoimmune diseases.

An astrocyte derived extracellular matrix coating reduces astrogliosis surrounding chronically implanted microelectrode arrays in rat cortex

Available evidence suggests that the magnitude of the foreign body response (FBR) to implants placed in cortical brain tissue is affected by the extent of vasculature damage following device insertion and the magnitude of the ensuing macrophage response. Since the extracellular matrix (ECM) serves as a natural hemostatic and immunomodulatory agent, we examined the ability of an FDA-approved neurosurgical hemostatic coating and an ECM coating derived from primary rat astrocytes to reduce the FBR surrounding a penetrating microelectrode array chronically implanted in rat cortex. Using quantitative methods, we examined various components of the FBR in vitro and after implantation. In vitro assays showed that both coatings accelerated coagulation in a similar fashion but only the astrocyte-derived material suppressed macrophage activation. In addition, the ECM coating derived from astrocytes, also decreased the astrogliotic response 8 weeks after implantation. Neither coating had a significant influence on the intensity or spatial distribution of FBR biomarkers 1 week after implantation or on degree of macrophage activation or neuronal survival at the later time point. The results show that microelectrode coatings with similar hemostatic properties but different immunomodulatory characteristics differentially affect the FBR to an anchored, single-shank, silicon microelectrode array. The results also support the concept that divergent biological pathways affect the various components of the FBR in the CNS and suggests that decreasing its impact will require a multifaceted approach.

Immunotherapy as an Option for Cancer Treatment

The progress in melanoma immunotherapy highlights the importance of immunotherapy for cancer treatment. Although the concept of immunotherapy emerged in the beginning of the twentieth century, the end of the century signaled the start of modern immunotherapy, which has recently allowed a staggering progress in the field of cancer immunotherapy. Currently, there is a wide variety of immunotherapeutic approaches and critical improvements are continually being made. Among different immunotherapeutic strategies, therapies based on the blockade of immune checkpoint molecules have shown unparalleled efficacy in late-stage cancer patients. Pre-clinical research using ex vivo and in vivo approaches demonstrates the promise of numerous novel strategies for the immunotherapy of cancer.

FcγRIIb attenuates TLR4‑mediated NF‑κB signaling in B cells

Toll‑like receptors (TLRs) serve a vital role in activating the innate immune system by sensing conserved microbial products. Fc γ receptor IIb (FcγRIIb), the inhibitory Fc receptor, exerts its immune regulatory functions by binding to the immunoglobulin G Fc domain. Although the individual roles of TLRs and FcγRIIb have been studied intensively, the cross‑talk between FcγRIIb and TLR4 on B cells remains unknown. The present study demonstrated that FcγRIIb ligation by the immune complex (IC) attenuated the TLR4‑triggered nuclear factor (NF)‑κΒ activation, and decreased the release of interleukin (IL)‑6 from B cells, via enhancing LYN proto‑oncogene (Lyn) phosphorylation. In addition, IC treatment protected mice from lethal endotoxic shock. Accordingly, IC decreased the LPS‑induced serum levels of IL‑6, as well as intracellular IL‑6 production in B cells in vivo. However, these protective and inhibitory effects of IC were not observed in FcγRIIb‑/‑ mice. In conclusion, the present data demonstrated that FcγRIIb inhibited TLR4 signaling in B cells by activating Lyn phosphorylation and by inhibiting NF‑κΒ signaling. The present study elucidated the mechanism associated with the TLR4 and FcγRIIb cross‑talk in B cells.

A novel bispecific DARPin targeting FcγRIIB and FcεRI-bound IgE inhibits allergic responses

BACKGROUND

Binding of allergen-specific IgE to its high-affinity receptor FcεRI on basophils and mast cells is a central event in the development of allergies. Exposure of these cells to allergens induces the release of soluble mediators causing allergic symptoms. The inhibitory low-affinity IgG Fc-receptor FcγRIIB is co-expressed on allergic effector cells and has been implicated in negative regulation of immediate hypersensitivity responses. In order to harvest the inhibitory function of this receptor, we aimed to select specific binders against FcγRIIB and to generate a bispecific molecule simultaneously targeting FcγRIIB and FcεRI-bound IgE on the surface of allergic effector cells.

METHODS

We selected FcγRIIB-specific binding molecules from a library of designed ankyrin repeat proteins using ribosome display technology. The bispecific binding modality was generated by molecular cloning and recombinant protein expression. We determined binding characteristics on molecular and cellular levels using SPR, ELISA, and flow cytometry. The inhibitory potential of the newly described molecules was assessed in different cellular degranulation assays ex vivo and in a mouse model of passive systemic anaphylaxis.

RESULTS

We demonstrate that the selected DARPin^® proteins recognize FcγRIIB with high affinity. Furthermore, the bispecific binding protein successfully interferes with allergen-induced cell degranulation and efficiently inhibits systemic anaphylaxis in vivo. Mechanistically, we report that FcγRIIB-mediated inhibition of effector cell activation requires direct ligation to an activating FcεRI receptor.

CONCLUSION

The described bispecific DARPin protein has the ability to co-ligate FcγRIIB with FcεRI-bound IgE on allergic effector cells and represents an efficient dual-modality to interfere with allergic hypersensitivity reactions.

The influence of FCGR2A and FCGR3A polymorphisms on the survival of patients with recurrent or metastatic squamous cell head and neck cancer treated with cetuximab

FCGR2A-H131R and FCGR3A-V157F are single-nucleotide polymorphisms known to influence the outcome of patients treated with rituximab, cetuximab and trastuzumab. We investigated the impact of these polymorphisms on the clinical outcome of 103 patients with recurrent or metastatic squamous cell carcinoma of the head and neck treated with a platinum compound, fluorouracil and cetuximab as palliative first-line therapy. The survival of patients with FCGR2A-131H/H and/or FCGR3A-157V/V genotypes was significantly longer compared with patients carrying 131R and 157F alleles (median progression-free survival (PFS): 5.5 vs 4.1 months, P=0.02; median overall survival: 10.2 vs 7.2 months, P=0.04). In multivariate analysis, the FCGR2A and 3A genotypes as well as the time between initial diagnosis and relapse of disease not amenable to curative therapy remained the only independent prognostic factors for PFS. The results are in line with previous reports in colorectal cancer patients and confirm the possible value of genetic polymorphisms of immunocompetent cells for the success of cetuximab treatment.

The Role and Function of Fcγ Receptors on Myeloid Cells

A key determinant for the survival of organisms is their capacity to recognize and respond efficiently to foreign antigens. This is largely accomplished by the orchestrated activity of the innate and adaptive branches of the immune system. Antibodies are specifically generated in response to foreign antigens, facilitating thereby the specific recognition of antigens of almost infinite diversity. Receptors specific for the Fc domain of antibodies, Fc receptors, are expressed on the surface of the various myeloid leukocyte populations and mediate the binding and recognition of antibodies by innate leukocytes. By directly linking the innate and the adaptive components of immunity, Fc receptors play a central role in host defense and the maintenance of tissue homeostasis through the induction of diverse proinflammatory, anti-inflammatory, and immunomodulatory processes that are initiated upon engagement by the Fc domain. In this chapter, we discuss the mechanisms that regulate Fc domain binding to the various types of Fc receptors and provide an overview of the astonishing diversity of effector functions that are mediated through Fc-FcR interactions on myeloid cells. Lastly, we discuss the impact of FcR-mediated interactions in the context of IgG-mediated inflammation, autoimmunity, susceptibility to infection, and responsiveness to antibody-based therapeutics.

Cγ1 Deficiency Exacerbates Collagen-Induced Arthritis

OBJECTIVE

IgG antibodies protect by aggregating pathogens and activating complement and stimulatory Fcγ receptors (FcγR). Although IgG1 accounts for a large percentage of murine serum antibodies, it poorly activates complement, binds more avidly to inhibitory FcγRIIb than to stimulatory FcγRIII, and has a relatively low aggregating ability. We previously demonstrated that IgG1 protects against complement- and FcγR-independent renal disease by inhibiting immune complex obstruction of glomerular capillaries. The purpose of this study was to determine whether IgG1 also protects against the complement- and FcγR-dependent disorder, collagen-induced arthritis (CIA).

METHODS

CIA was induced by injecting mice with type II collagen (CII) (active model) or with IgG2a and IgG2b anti-CII monoclonal antibodies (ArthritoMab) (passive model). Arthritis severity was assessed, and CII-specific IgG was titered.

RESULTS

Cγ1-deficient C57BL/6 mice lack IgG1 (IgG1(-/-) ); in these mice, arthritis developed at a higher frequency and was more severe compared with IgG1(+/+) mice in the active model. Disease was FcγRIII- and C3-dependent in both the IgG(+/+) and IgG(-/-) mouse strains and was not influenced by interleukin-4 receptor α in either strain. CII-specific IgG2a/c titers were considerably higher in IgG1(-/-) than in IgG1(+/+) mice and correlated with CIA incidence and severity. IgG1(+/+) mice that developed CIA had higher CII-specific IgG1 and IgG2a/c levels than did those without CIA. CII-inoculated BALB/c IgG1(+/+) and IgG1(-/-) mice had much lower CII-specific IgG2a/c titers than did C57BL/6 mice and failed to develop CIA but developed passive CIA when given ArthritoMab.

CONCLUSION

The absence of a functional Cγ1 gene indirectly promotes the development of CIA, likely through increased production of IgG2a/c, an isotype that strongly activates complement and stimulatory FcγR.

Natural Killer Cells Response to IL-2 Stimulation Is Distinct between Ascites with the Presence or Absence of Malignant Cells in Ovarian Cancer Patients

Peritoneal ascites are a distinguishable feature of patients with advanced epithelial ovarian cancer (EOC). The presence of different lymphocyte subsets has been reported in EOC-associated ascites, which also can or not contain malignant cells. The goal of this study was to analyze the functional characteristics of natural killer (NK) cells from EOC-associated ascites in terms of their expression of activating receptors and ascites’ contents of lymphocyte subtypes, cytokine profile and presence of EOC cells. NK cell function was evaluated by the expression of the degranulation marker CD107a in resting and interleukin (IL)-2 stimulated NK cells from ascites and blood. Degranulation of NK cells from EOC cell-free ascites was significantly (p < 0.05) higher than all the other groups, either in their resting state or after IL-2 stimulation, suggesting a previous local stimulation. In contrast, treatment with IL-2 had no effect on NK cells from ascites with EOC cells. The amount of regulatory T cells was significantly higher in ascites with EOC cells compared to EOC cell-free ascites. Ascites with EOC cells also had higher levels of tumor necrosis factor (TNF)-α, suggesting inflammation related to the malignancy. In conclusion, the functional performance of NK cells was distinct between EOC cell-free ascites and ascites with EOC cells. The impairment of NK cell response to IL-2 in ascites with EOC cells was consistent with an immunosuppressive tumor microenvironment.

Allogenic natural killer cell immunotherapy of sizeable ovarian cancer: A case report

Masses are often detected in the abdomen of patients with sizeable ovarian cancer. There are currently no effective treatments available for late-stage ovarian cancer. Immunotherapy is gaining increasing attention worldwide in the clinical setting due to its ability to eliminate tumor cells and its favorable toxicity profile. We herein report the case of a 60-year-old woman who received allogenic natural killer (NK) cell immunotherapy for a sizeable ovarian carcinoma and achieved a noteworthy response. NK cells were isolated from the donor's peripheral blood mononuclear cells, and the cell numbers were increased to 8-10 billion [corrected]. The activated cells were expanded ex vivo for 14 days prior to intravenous infusion. After six infusions of NK cell therapy >3 months, the level of carbohydrate antigen 125 decreased significantly (from 11,270 to 580 U/ml). Furthermore, the size of the masses in the abdomen was markedly reduced. Overall, the treatment had few adverse effects and it prolonged patient survival. The present data and the patient response suggest that allogenic NK cell immunotherapy is a promising approach for ovarian cancer, with few treatment-related adverse effects. The patient received six intravenous infusions of allogenic HANK cells between March, 2015 and June, 2015, but discontinued in October, 2015 and succumbed to the disease in March, 2016 following relapse.

The lack of BTK does not impair monocytes and polymorphonuclear cells functions in X-linked agammaglobulinemia under treatment with intravenous immunoglobulin replacement

The lack of BTK in X-linked agammaglobulinemia (XLA) patients does not affect monocytes and polymorphonuclear cells (PMN) phenotype and functions. In this study, we show that XLA patients had an increased frequency of the intermediate monocytes subset and that BTK-deficient monocytes and PMN had a normal expression of receptors involved in the activation and cellular responses. We demonstrate that BTK is not required for migration, phagocytosis and the production of reactive oxygen species (ROS) following engagement of FC gamma receptors (FcγR). XLA monocytes and PMN showed an efficient calcium (Ca2+)-independent activation of oxidative burst, suggesting that oxidative burst is less dependent by Ca2+ mobilization. The phagocytosis was functional and it remained unaltered also after Ca2+ chelation, confirming the independence of phagocytosis on Ca2+ mobilization. Intravenous immunoglobulin (IVIg) infusion exerted an anti-inflammatory effect by reducing the frequency of pro-inflammatory monocytes. In monocytes, the IVIg reduce the oxidative burst and phagocytosis even if these functions remained efficient.

Molecular cloning of IgZ heavy chain isotype in Catla catla and comparative expression profile of IgZ and IgM following pathogenic infection

Immunoglobulins serve as a crucial arm of the adaptive immune system against detrimental pathogenic threats in teleosts. However, whether the novel Ig isotype IgZ is present in the Indian major carp, Catla catla, has not yet been elucidated. The present study reports the presence of IgZ ortholog in C. catla (CcIgZ) and further demonstrates its comparative tissue specific expression with IgM (CcIgM) in response to bacterial and parasitic stimulation. The putative 139 amino acid sequence of IgZ heavy chain cDNA of C. catla showed homology with IgZ constant domains of other teleosts. Phylogenetic analysis of the predicted IgZ transcript sequence clustered with previously identified IgZ heavy chain sequences of Cyprinidae family members. The inductive expression profiles of IgZ and IgM genes were evaluated in immunologically relevant tissues at 24, 48 and 72 hr post infection with Aeromonas hydrophila, Streptococcus uberis and Argulus sp. Both CcIgZ and CcIgM were expressed most strongly in the kidneys of healthy fish. Basal expression of CcIgM transcript was higher than that of CcIgZ in all the examined tissues. Stimulation with bacteria triggered significant increase of IgZ in the intestine (P < 0.001) and spleen (P < 0.01), whereas IgM was relatively up-regulated in blood (P < 0.001) after stimulation with each of the three pathogens assessed. The study is the first to report identification of IgZ in C. catla. Further, it provides insights into the differential expression profiles of IgZ and IgM isotypes against various pathogenic infection in C. catla, which may facilitate better prophylaxis again such infections.

Fc or not Fc; that is the question: Antibody Fc-receptor interactions are key to universal influenza vaccine design

A universal vaccine that provides long-lasting protection from both epidemic and pandemic influenza viruses remains the "holy grail" of influenza vaccine research. Though virus neutralization assays are the current benchmark of measuring vaccine effectiveness, it is clear that Fc-receptor functions can drastically improve the effectiveness of antibodies and vaccines in vivo. Antibodies that kill virus-infected cells and/or elicit an antiviral environment, termed antibody-dependent cellular cytotoxicity (ADCC)-mediating antibodies, provide a link between the innate and adaptive immune response. New technologies allowing the rapid isolation and characterization of monoclonal antibodies (mAb) have yielded a plethora of mAbs which target conserved regions of influenza virus, such as the hemagglutinin (HA) stem region. Many such mAbs have been used to gain a better understanding of Fc-receptor functions in vivo. In parallel, several studies have characterized the induction of polyclonal ADCC following influenza vaccination and infection in humans. Taken together, these studies suggest that ADCC-mediating antibodies (ADCC-Abs) significantly contribute to host immunity against influenza virus and may be a mechanism to exploit for rational vaccine and therapeutic design. We discuss recent research on influenza-specific ADCC and potential future avenues to extend our understanding.

Fcγ Receptor Heterogeneity in Leukocyte Functional Responses

Antibodies participate in defense of the organism from all types of pathogens, including viruses, bacteria, fungi, and protozoa. IgG antibodies recognize their associated antigen via their two Fab portions and are in turn recognized though their Fc portion by specific Fcγ receptors (FcγRs) on the membrane of immune cells. Multiple types and polymorphic variants of FcγR exist. These receptors are expressed in many cells types and are also redundant in inducing cell responses. Crosslinking of FcγR on the surface of leukocytes activates several effector functions aimed toward the destruction of pathogens and the induction of an inflammatory response. In the past few years, new evidence on how the particular IgG subclass and the glycosylation pattern of the antibody modulate the IgG-FcγR interaction has been presented. Despite these advances, our knowledge of what particular effector function is activated in a certain cell and in response to a specific type of FcγR remains very limited today. On one hand, each immune cell could be programmed to perform a particular cell function after FcγR crosslinking. On the other, each FcγR could activate a particular signaling pathway leading to a unique cell response. In this review, I describe the main types of FcγRs and our current view of how particular FcγRs activate various signaling pathways to promote unique leukocyte functions.

Early induction of NRF2 antioxidant pathway by RHBDF2 mediates rapid cutaneous wound healing

Rhomboid family protein RHBDF2, an upstream regulator of the epidermal growth factor (EGF) receptor signaling, has been implicated in cutaneous wound healing. However, the underlying molecular mechanisms are still emerging. In humans, a gain-of-function mutation in the RHBDF2 gene accelerates cutaneous wound healing in an EGFR-dependent manner. Likewise, a gain-of-function mutation in the mouse Rhbdf2 gene (Rhbdf2^cub/cub) shows a regenerative phenotype (rapid ear-hole closure) resulting from constitutive activation of the EGFR pathway. Because the RHBDF2-regulated EGFR pathway is relevant to cutaneous wound healing in humans, we used Rhbdf2^cub/cub mice to investigate the biological networks and pathways leading to accelerated ear-hole closure, with the goal of identifying therapeutic targets potentially effective in promoting wound healing in humans. Comparative transcriptome analysis of ear pinna tissue from Rhbdf2^cub/cub and Rhbdf2^+/+ mice at 0h, 15min, 2h, and 24h post-wounding revealed an early induction of the nuclear factor E2-related factor 2 (NRF2)-mediated anti-oxidative pathway (0h and 15min), followed by the integrin-receptor aggregation pathway (2h) as early-stage events immediately and shortly after wounding in Rhbdf2^cub/cub mice. Additionally, we observed genes enriched for the Fc fragment of the IgG receptor IIIa (FCGR3A)-mediated phagocytosis pathway 24h post-wounding. Although cutaneous wound repair in healthy individuals is generally non-problematic, it can be severely impaired due to aging, diabetes, and chronic inflammation. This study suggests that activation of the NRF2-antioxidant pathway by rhomboid protein RHBDF2 might be beneficial in treating chronic non-healing wounds.

Induced Remodeling of Porcine Tendons to Human Anterior Cruciate Ligaments by α-GAL Epitope Removal and Partial Cross-Linking

This review describes a novel method developed for processing porcine tendon and other ligament implants that enables in situ remodeling into autologous ligaments in humans. The method differs from methods using extracellular matrices (ECMs) that provide postoperative orthobiological support (i.e., augmentation grafts) for healing of injured ligaments, in that the porcine bone-patellar-tendon-bone itself serves as the graft replacing ruptured anterior cruciate ligament (ACL). The method allows for gradual remodeling of porcine tendon into autologous human ACL while maintaining the biomechanical integrity. The method was first evaluated in a preclinical model of monkeys and subsequently in patients. The method overcomes detrimental effects of the natural anti-Gal antibody and harnesses anti-non-gal antibodies for the remodeling process in two steps: Step 1. Elimination of α-gal epitopes—this epitope that is abundant in pigs (as in other nonprimate mammals) binds the natural anti-Gal antibody, which is the most abundant natural antibody in humans. This interaction, which can induce fast resorption of the porcine implant, is avoided by enzymatic elimination of α-gal epitopes from the implant with recombinant α-galactosidase. Step 2. Partial cross-linking of porcine tendon with glutaraldehyde—this cross-linking generates covalent bonds in the ECM, which slow infiltration of macrophages into the implant. Anti-non-gal antibodies are produced in recipients against the multiple porcine antigenic proteins and proteoglycans because of sequence differences between human and porcine homologous proteins. Anti-non-gal antibodies bind to the implant ECM, recruit macrophages, and induce the implant destruction by directing proteolytic activity of macrophages. Partial cross-linking of the tendon ECM decreases the extent of macrophage infiltration and degradation of the implant and enables concomitant infiltration of fibroblasts that follow the infiltrating macrophages. These fibroblasts align with the implant collagen fibers and secrete their own collagen and other ECM proteins, which gradually remodel the porcine tendon into human ACL. This ligamentization process lasts ∼2 years and the biomechanical integrity of the graft is maintained throughout the whole period. These studies are the first, and so far the only, to demonstrate remodeling of porcine tendon implants into permanently functional autologous ACL in humans.

B cells interactions in lipid immune responses: implications in atherosclerotic disease

Atherosclerosis is considered as an inflammatory and chronic disorder with an important immunologic component, which underlies the majority of cardiovascular diseases; condition that belongs to a group of noncommunicable diseases that to date and despite of prevention and treatment approaches, they remain as the main cause of death worldwide, with 17.5 million of deaths every year. The impact of lipids in human health and disease is taking center stage in research, due to lipotoxicity explained by elevated concentration of circulating lipids, in addition to altered adipose tissue metabolism, and aberrant intracellular signaling. Immune response and metabolic regulation are highly integrated systems and the proper function of each one is dependent on the other. B lymphocytes express a variety of receptors that can recognize foreign, endogenous or modified self-antigens, among them oxidized low density lipoproteins, which are the main antigens in atherosclerosis. Mechanisms of B cells to recognize, remove and present lipids are not completely clear. However, it has been reported that B cell can recognize/remove lipids through a range of receptors, such as LDLR, CD1d, FcR and SR, which might have an atheroprotector or proatherogenic role during the course of atherosclerotic disease. Pertinent literature related to these receptors was examined to inform the present conclusions.

Potential importance of B cells in aging and aging-associated neurodegenerative diseases

Our understanding of B cells as merely antibody producers is slowly changing. Alone or in concert with antibody, they control outcomes of seemingly different diseases such as cancer, rheumatoid arthritis, diabetes, and multiple sclerosis. While their role in activation of effector immune cells is beneficial in cancer but bad in autoimmune diseases, their immunosuppressive and regulatory subsets (Bregs) inhibit autoimmune and anticancer responses. These pathogenic and suppressive functions are not static and appear to be regulated by the nature and strength of inflammation. Although aging increases inflammation and changes the composition and function of B cells, surprisingly, little is known whether the change affects aging-associated neurodegenerative disease, such as Alzheimer's disease (AD). Here, by analyzing B cells in cancer and autoimmune and neuroinflammatory diseases, we elucidate their potential importance in AD and other aging-associated neuroinflammatory diseases.

The role of macrophages in the susceptibility of Fc gamma receptor IIb deficient mice to Cryptococcus neoformans

Dysfunctional polymorphisms of FcγRIIb, an inhibitory receptor, are associated with Systemic Lupus Erythaematosus (SLE). Cryptococcosis is an invasive fungal infection in SLE, perhaps due to the de novo immune defect. We investigated cryptococcosis in the FcγRIIb-/- mouse-lupus-model. Mortality, after intravenous C. neoformans-induced cryptococcosis, in young (8-week-old) and older (24-week-old) FcγRIIb-/- mice, was higher than in age-matched wild-types. Severe cryptococcosis in the FcγRIIb-/- mice was demonstrated by high fungal burdens in the internal organs with histological cryptococcoma-like lesions and high levels of TNF-α and IL-6, but not IL-10. Interestingly, FcγRIIb-/- macrophages demonstrated more prominent phagocytosis but did not differ in killing activity in vitro and the striking TNF-α, IL-6 and IL-10 levels, compared to wild-type cells. Indeed, in vivo macrophage depletion with liposomal clodronate attenuated the fungal burdens in FcγRIIb-/- mice, but not wild-type mice. When administered to wild-type mice, FcγRIIb-/- macrophages with phagocytosed Cryptococcus resulted in higher fungal burdens than FcγRIIb+/+ macrophages with phagocytosed Cryptococcus. These results support, at least in part, a model whereby, in FcγRIIb-/- mice, enhanced C. neoformans transmigration occurs through infected macrophages. In summary, prominent phagocytosis, with limited effective killing activity, and high pro-inflammatory cytokine production by FcγRIIb-/- macrophages were correlated with more severe cryptococcosis in FcγRIIb-/- mice.

Biosimilars in IBD: from theory to practice

Biologic agents have revolutionized the care management of many life-threatening and debilitating diseases. As patents for older biologic therapies have begun to expire, the market has opened to copy versions of the originators - commonly referred to as biosimilars, follow-on biologic agents or subsequent-entry biologic agents - which are expected to gain a portion of the market, reduce health-care spending and increase treatment access worldwide. Importantly for patients with IBD, CT-P13 was the first biosimilar to infliximab that obtained regulatory approval by the European Medicines Agency in September 2013 and by the FDA in April 2016. In May 2016, SB2 was the second biosimilar to infliximab receiving marketing authorization in Europe. Currently, >20 other biosimilars to infliximab and adalimumab are in the development pipeline. Their similar-but-not-identical nature, and the concept of extrapolating efficacy and safety data from one therapeutic indication to another, seem to be confusing to physicians and cause concerns about the efficacy and safety of biosimilar products. A relevant debate is still ongoing in the field of IBD. This Review discusses the scientific principles underlying the biosimilar concept established in Europe and the USA, and discusses the current state of knowledge on biosimilar use in IBD.

FCRLA-A Resident Endoplasmic Reticulum Protein that Associates with Multiple Immunoglobulin Isotypes in B Lineage Cells

FCRLA is homologous to receptors for the Fc portion of IgG (FcγR) and is located in the same region of human chromosome one, but has several unusual and unique features. It is a soluble resident ER protein retained in this organelle by unknown mechanisms involving the N-terminal domain, a disordered domain with three Cys residues in close proximity in the human protein. Unlike the FcγRs, FCRLA is not glycosylated and has no transmembrane region. FCRLA is included in this CTMI volume on IgM-binding proteins because it binds IgM in the ER, but quite surprisingly, given the isotype-restricted ligand specificity of the other FcRs, it also binds all other Ig isotypes so far tested, IgG and IgA. In the case of IgM, there is even preferential binding of the secretory and not the transmembrane form. Among B cells, FCRLA is most highly expressed in the germinal center and shows little expression in plasma cells. Based on these observations, we propose that one human FCRLA function is to stop GC B cells from secreting IgM, which would act as a decoy receptor, thus preventing the B cells from capturing antigen, processing it, and presenting the antigen-derived peptides to T follicular helper cells. Without help from these T cells, there would be limited B cell isotype switching, proliferation, and differentiation. On the other hand, FCRLA is downregulated in plasma cells, where IgM secretion is an essential function. FCRLA may also act as a chaperone involved by unknown mechanisms in the proper assembly of Ig molecules of all isotypes.

Targeted Radionuclide Therapy of Melanoma

An estimated 60,000 individuals in the United States and 132,000 worldwide are yearly diagnosed with melanoma. Until recently, treatment options for patients with stages III-IV metastatic disease were limited and offered marginal, if any, improvement in overall survival. The situation changed with the introduction of B-RAF inhibitors and anti-cytotoxic T-lymphocyte antigen 4 and anti-programmed cell death protein 1 immunotherapies into the clinical practice. With only some patients responding well to the immune therapies and with very serious side effects and high costs of immunotherapy, there is still room for other approaches for the treatment of metastatic melanoma. Targeted radionuclide therapy of melanoma could be divided into the domains of radioimmunotherapy (RIT), radiolabeled peptides, and radiolabeled small molecules. RIT of melanoma is currently experiencing a renaissance with the clinical trials of alpha-emitter (213)Bi-labeled and beta-emitter (188)Rhenium-labeled monoclonal antibodies in patients with metastatic melanoma producing encouraging results. The investigation of the mechanism of efficacy of melanoma RIT points at killing of melanoma stem cells by RIT and involvement of immune system such as complement-dependent cytotoxicity. The domain of radiolabeled peptides for targeted melanoma therapy has been preclinical so far, with work concentrated on radiolabeled peptide analogues of melanocyte-stimulating hormone receptor and on melanin-binding peptides. The field of radiolabeled small molecule produced radioiodinated benzamides that cross the cellular membrane and bind to the intracellular melanin. The recent clinical trial demonstrated measurable antitumor effects and no acute or midterm toxicities. We are hopeful that the targeted radionuclide therapy of metastatic melanoma would become a clinical reality as a stand-alone therapy or in combination with the immunotherapies such as anti-PD1 programmed cell death protein 1 monoclonal antibodies within the next few years.

Immunoglobulin G (IgG)-Based Imaging Probe Accumulates in M1 Macrophage-Infiltrated Atherosclerotic Plaques Independent of IgG Target Molecule Expression

PURPOSE

Vulnerable plaques are key factors for ischemic diseases. Thus, their precise detection is necessary for the diagnosis of such diseases. Immunoglobulin G (IgG)-based imaging probes have been developed for imaging biomolecules related to plaque formation for the diagnosis of atherosclerosis. However, IgG accumulates nonspecifically in atherosclerotic regions, and its accumulation mechanisms have not yet been clarified in detail. Therefore, we explored IgG accumulation mechanisms in atherosclerotic lesions and examined images of radiolabeled IgG for the diagnosis of atherosclerosis.

PROCEDURES

Mouse IgG without specificity to biomolecules was labeled with technetium-99m via 6-hydrazinonicotinate to yield [^99mTc]IgG. ApoE^-/- or C57BL/6J mice were injected intravenously with [^99mTc]IgG, and their aortas were excised 24 h after injection. After radioactivity measurement, serial aortic sections were autoradiographically and histopathologically examined. RAW264.7 macrophages were polarized into M1 or M2 and then treated with [^99mTc]IgG. The radioactivities in the cells were measured after 1 h of incubation. [^99mTc]IgG uptake in M1 macrophages was also evaluated after the pretreatment with an anti-Fcγ receptor (FcγR) antibody. The expression levels of FcγRs in the cells were measured by western blot analysis.

RESULTS

[^99mTc]IgG accumulation levels in the aortas were significantly higher in apoE^-/- mice than in C57BL/6J mice (5.1 ± 1.4 vs 2.8 ± 0.5 %ID/g, p < 0.05). Autoradiographic images showed that the accumulation areas highly correlated with the macrophage-infiltrated areas. M1 macrophages showed significantly higher levels of [^99mTc]IgG than M2 or M0 (nonpolarized) macrophages [2.2 ± 0.3 (M1) vs 0.5 ± 0.1 (M2), 0.4 ± 0.1 (M0) %dose/mg protein, p < 0.01] and higher expression levels of FcγRI and FcγRII. [^99mTc]IgG accumulation in M1 macrophages was suppressed by pretreatment with the anti-FcγR antibody [2.2 ± 0.3 (nonpretreatment) vs 1.2 ± 0.2 (pretreatment) %ID/mg protein, p < 0.01].

CONCLUSIONS

IgG accumulated in pro-inflammatory M1 macrophages via FcγRs in atherosclerotic lesions. Thus, the target biomolecule-independent imaging of active inflammation should be taken into account in the diagnosis of atherosclerosis using IgG-based probes.

Advances in Therapeutic Fc Engineering - Modulation of IgG-Associated Effector Functions and Serum Half-life

Today, monoclonal immunoglobulin gamma (IgG) antibodies have become a major option in cancer therapy especially for the patients with advanced or metastatic cancers. Efficacy of monoclonal antibodies (mAbs) is achieved through both its antigen-binding fragment (Fab) and crystallizable fragment (Fc). Fab can specifically recognize tumor-associated antigen (TAA) and thus modulate TAA-linked downstream signaling pathways that may lead to the inhibition of tumor growth, induction of tumor apoptosis, and differentiation. The Fc region can further improve mAbs’ efficacy by mediating effector functions such as antibody-dependent cellular cytotoxicity, complement-dependent cytotoxicity, and antibody-dependent cell-mediated phagocytosis. Moreover, Fc is the region interacting with the neonatal Fc receptor in a pH-dependent manner that can slow down IgG’s degradation and extend its serum half-life. Loss of the antibody Fc region dramatically shortens its serum half-life and weakens its anticancer effects. Given the essential roles that the Fc region plays in the modulation of the efficacy of mAb in cancer treatment, Fc engineering has been extensively studied in the past years. This review focuses on the recent advances in therapeutic Fc engineering that modulates its related effector functions and serum half-life. We also discuss the progress made in aglycosylated mAb development that may substantially reduce the cost of manufacture but maintain similar efficacies as conventional glycosylated mAb. Finally, we highlight several Fc engineering-based mAbs under clinical trials.

Fc gamma receptors: glycobiology and therapeutic prospects

Therapeutic antibodies hold great promise for the treatment of cancer and autoimmune diseases, and developments in antibody–drug conjugates and bispecific antibodies continue to enhance treatment options for patients. Immunoglobulin (Ig) G antibodies are proteins with complex modifications, which have a significant impact on their function. The most important of these modifications is glycosylation, the addition of conserved glycans to the antibody Fc region, which is critical for its interaction with the immune system and induction of effector activities such as antibody-dependent cell cytotoxicity, complement activation and phagocytosis. Communication of IgG antibodies with the immune system is controlled and mediated by Fc gamma receptors (FcγRs), membrane-bound proteins, which relay the information sensed and gathered by antibodies to the immune system. These receptors are also glycoproteins and provide a link between the innate and adaptive immune systems. Recent information suggests that this receptor glycan modification is also important for the interaction with antibodies and downstream immune response. In this study, the current knowledge on FcγR glycosylation is discussed, and some insight into its role and influence on the interaction properties with IgG, particularly in the context of biotherapeutics, is provided. For the purpose of this study, other Fc receptors such as FcαR, FcεR or FcRn are not discussed extensively, as IgG-based antibodies are currently the only therapeutic antibody-based products on the market. In addition, FcγRs as therapeutics and therapeutic targets are discussed, and insight into and comment on the therapeutic aspects of receptor glycosylation are provided.