The Emerging Importance of IgG Fab Glycosylation in Immunity

Immune checkpoint therapy-elicited sialylation of IgG antibodies impairs antitumorigenic type I interferon responses in hepatocellular carcinoma

The reinvigoration of anti-tumor T cells in response to immune checkpoint blockade (ICB) therapy is well established. Whether and how ICB therapy manipulates antibody-mediated immune response in cancer environments, however, remains elusive. Using tandem mass spectrometric analysis of modification of immunoglobulin G (IgG) from hepatoma tissues, we identified a role of ICB therapy in catalyzing IgG sialylation in the Fc region. Effector T cells triggered sialylation of IgG via an interferon (IFN)-γ-ST6Gal-I-dependent pathway. DC-SIGN⁺ macrophages represented the main target cells of sialylated IgG. Upon interacting with sialylated IgG, DC-SIGN stimulated Raf-1-elicited elevation of ATF3, which inactivated cGAS-STING pathway and eliminated subsequent type-I-IFN-triggered antitumorigenic immunity. Although enhanced IgG sialylation in tumors predicted improved therapeutic outcomes for patients receiving ICB therapy, impeding IgG sialylation augmented antitumorigenic T cell immunity after ICB therapy. Thus, targeting antibody-based negative feedback action of ICB therapy has potential for improving efficacy of cancer immunotherapies.

Emerging Methods in Biosensing of Immunoglobin G-A Review

Human antibodies are produced due to the activation of immune system components upon exposure to an external agent or antigen. Human antibody G, or immunoglobin G (IgG), accounts for 75% of total serum antibody content. IgG controls several infections by eradicating disease-causing pathogens from the body through complementary interactions with toxins. Additionally, IgG is an important diagnostic tool for certain pathological conditions, such as autoimmune hepatitis, hepatitis B virus (HBV), chickenpox and MMR (measles, mumps, and rubella), and coronavirus-induced disease 19 (COVID-19). As an important biomarker, IgG has sparked interest in conducting research to produce robust, sensitive, selective, and economical biosensors for its detection. To date, researchers have used different strategies and explored various materials from macro- to nanoscale to be used in IgG biosensing. In this review, emerging biosensors for IgG detection have been reviewed along with their detection limits, especially electrochemical biosensors that, when coupled with nanomaterials, can help to achieve the characteristics of a reliable IgG biosensor. Furthermore, this review can assist scientists in developing strategies for future research not only for IgG biosensors but also for the development of other biosensing systems for diverse targets.

Glycobiology of rheumatic diseases

Glycosylation has a profound influence on protein activity and cell biology through a variety of mechanisms, such as protein stability, receptor interactions and signal transduction. In many rheumatic diseases, a shift in protein glycosylation occurs, and is associated with inflammatory processes and disease progression. For example, the Fc-glycan composition on (auto)antibodies is associated with disease activity, and the presence of additional glycans in the antigen-binding domains of some autoreactive B cell receptors can affect B cell activation. In addition, changes in synovial fibroblast cell-surface glycosylation can alter the synovial microenvironment and are associated with an altered inflammatory state and disease activity in rheumatoid arthritis. The development of our understanding of the role of glycosylation of plasma proteins (particularly (auto)antibodies), cells and tissues in rheumatic pathological conditions suggests that glycosylation-based interventions could be used in the treatment of these diseases.

Factors affecting IgG4-mediated complement activation

Of the four human immunoglobulin G (IgG) subclasses, IgG4 is considered the least inflammatory, in part because it poorly activates the complement system. Regardless, in IgG4 related disease (IgG4-RD) and in autoimmune disorders with high levels of IgG4 autoantibodies, the presence of these antibodies has been linked to consumption and deposition of complement components. This apparent paradox suggests that conditions may exist, potentially reminiscent of in vivo deposits, that allow for complement activation by IgG4. Furthermore, it is currently unclear how variable glycosylation and Fab arm exchange may influence the ability of IgG4 to activate complement. Here, we used well-defined, glyco-engineered monoclonal preparations of IgG4 and determined their ability to activate complement in a controlled system. We show that IgG4 can activate complement only at high antigen and antibody concentrations, via the classical pathway. Moreover, elevated or reduced Fc galactosylation enhanced or diminished complement activation, respectively, with no apparent contribution from the lectin pathway. Fab glycans slightly reduced complement activation. Lastly, we show that bispecific, monovalent IgG4 resulting from Fab arm exchange is a less potent activator of complement than monospecific IgG4. Taken together, these results imply that involvement of IgG4-mediated complement activation in pathology is possible but unlikely.

A glyco-engineering approach for site-specific conjugation to Fab glycans

Effective processes for synthesizing antibody-drug conjugates (ADCs) require: 1) site-specific incorporation of the payload to avoid interference with binding to the target epitope, 2) optimal drug/antibody ratio to achieve sufficient potency while avoiding aggregation or solubility problems, and 3) a homogeneous product to facilitate approval by regulatory agencies. In conventional ADCs, the drug molecules are chemically attached randomly to antibody surface residues (typically Lys or Cys), which can interfere with epitope binding and targeting, and lead to overall product heterogeneity, long-term colloidal instability and unfavorable pharmacokinetics. Here, we present a more controlled process for generating ADCs where drug is specifically conjugated to only Fab N-linked glycans in a narrow ratio range through functionalized sialic acids. Using a bacterial sialytransferase, we incorporated N-azidoacetylneuraminic acid (Neu5NAz) into the Fab glycan of cetuximab. Since only about 20% of human IgG1 have a Fab glycan, we extended the application of this approach by using molecular modeling to introduce N-glycosylation sites in the Fab constant region of other therapeutic monoclonal antibodies. We used trastuzumab as a model for the incorporation of Neu5NAz in the novel Fab glycans that we designed. ADCs were generated by clicking the incorporated Neu5NAz with monomethyl auristatin E (MMAE) attached to a self-immolative linker terminated with dibenzocyclooctyne (DBCO). Through this process, we obtained cetuximab-MMAE and trastuzumab-MMAE with drug/antibody ratios in the range of 1.3 to 2.5. We confirmed that these ADCs still bind their targets efficiently and are as potent in cytotoxicity assays as control ADCs obtained by standard conjugation protocols. The site-directed conjugation to Fab glycans has the additional benefit of avoiding potential interference with effector functions that depend on Fc glycan structure.

Impact of N-Linked Glycosylation on Therapeutic Proteins

Therapeutic proteins have unique advantages over small-molecule drugs in the treatment of various diseases, such as higher target specificity, stronger pharmacological efficacy and relatively low side effects. These advantages make them increasingly valued in drug development and clinical practice. However, although highly valued, the intrinsic limitations in their physical, chemical and pharmacological properties often restrict their wider applications. As one of the most important post-translational modifications, glycosylation has been shown to exert positive effects on many properties of proteins, including molecular stability, and pharmacodynamic and pharmacokinetic characteristics. Glycoengineering, which involves changing the glycosylation patterns of proteins, is therefore expected to be an effective means of overcoming the problems of therapeutic proteins. In this review, we summarize recent efforts and advances in the glycoengineering of erythropoietin and IgG monoclonal antibodies, with the goals of illustrating the importance of this strategy in improving the performance of therapeutic proteins and providing a brief overview of how glycoengineering is applied to protein-based drugs.

BNT162b2-induced neutralizing and non-neutralizing antibody functions against SARS-CoV-2 diminish with age

Each severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variant renews concerns about decreased vaccine neutralization weakening efficacy. However, while prevention of infection varies, protection from disease remains and implicates immunity beyond neutralization in vaccine efficacy. Polyclonal antibodies function through Fab domains that neutralize virus and Fc domains that induce non-neutralizing responses via engagement of Fc receptors on immune cells. To understand how vaccines promote protection, we leverage sera from 51 SARS-CoV-2 uninfected individuals after two doses of the BNT162b2 mRNA vaccine. We show that neutralizing activities against clinical isolates of wild-type and five SARS-CoV-2 variants, including Omicron BA.2, link to FcγRIIIa/CD16 non-neutralizing effector functions. This is associated with post-translational afucosylation and sialylation of vaccine-specific antibodies. Further, polyfunctional neutralizing and non-neutralizing breadth, magnitude, and coordination diminish with age. Thus, studying Fc functions in addition to Fab-mediated neutralization provides greater insight into vaccine efficacy for vulnerable populations, such as the elderly, against SARS-CoV-2 and novel variants.

Immunoglobulin G glycans - Biomarkers and molecular effectors of aging

Immunoglobulin G (IgG) antibodies are post-translationally modified by the addition of complex carbohydrate molecules - glycans, which have profound effects on the IgG function, most significantly as modulators of its inflammatory capacity. Therefore, it is not surprising that the changes in IgG glycosylation pattern are associated with various physiological states and diseases, including aging and age-related diseases. Importantly, within the inflammaging concept, IgG glycans are considered not only biomarkers but one of the molecular effectors of the aging process. The exact mechanism by which they exert their function, however, remains unknown. In this review, we list and comment on, to our knowledge, all studies that examined changes in IgG glycosylation during aging in humans. We focus on the information obtained from studies on general population, but we also cover the insights obtained from studies of long-lived individuals and people with age-related diseases. We summarize the current knowledge on how levels of different IgG glycans change with age (i.e., the extent and direction of the change with age) and discuss the potential mechanisms and possible functional roles of changes in IgG glycopattern that accompany aging.

Glycosylation of immunoglobin G in tumors: Function, regulation and clinical implications

Immunoglobulin G (IgG) is the predominant component in humoral immunity and the major effector of neutralizing heterogeneous antigens. Glycosylation, as excessive posttranscriptional modification, can modulate IgG immune function. Glycosylated IgG has been reported to correlate with tumor progression, presenting several characteristic modifications, including the core fucose, galactose, sialic acid, and the bisect N-acetylglucosamine (GlcNAc). Meanwhile, IgG glycosylation regulates tumor immunity involved in tumor progression and is thus a potential target. Herein, we summarized the research progression to provide novel insight into the application of IgG glycosylation in tumor diagnosis and treatment.

Highly sensitive characterization of non-human glycan structures of monoclonal antibody drugs utilizing tandem mass spectrometry

Glycosylation is an important attribute of monoclonal antibodies (mAbs) for assessing manufacturing quality. Analysis of non-human glycans containing terminal galactose-α1,3-galactose and N-glycolylneuraminic acid is essential due to the potential immunogenicity and insufficient efficacy caused by mAb expression in non-human mammalian cells. Using parallel sequencing of isobaric glycopeptides and isomeric glycans that were separated by reversed-phase and porous graphitic carbon LC, we report a highly sensitive LC MS/MS method for the comprehensive characterization of low-abundance non-human glycans and their closely related structural isomers. We demonstrate that the straightforward use of high-abundance diagnostic ions and complementary fragments under the positive ionization low-energy collision-induced dissociation is a universal approach to rapidly discriminate branch-linkage structures of biantennary glycans. Our findings reveal the structural diversity of non-human glycans and sulfation of α-galactosylated glycans, providing both an analytical method and candidate structures that could potentially be used in the crucial quality control of therapeutic mAb products.

BNT162b2 induced neutralizing and non-neutralizing antibody functions against SARSCoV-2 diminish with age

Each novel SARS-CoV-2 variant renews concerns about decreased vaccine efficacy caused by evasion of vaccine induced neutralizing antibodies. However, accumulating epidemiological data show that while vaccine prevention of infection varies, protection from severe disease and death remains high. Thus, immune responses beyond neutralization could contribute to vaccine efficacy. Polyclonal antibodies function through their Fab domains that neutralize virus directly, and Fc domains that induce non-neutralizing host responses via engagement of Fc receptors on immune cells. To understand how vaccine induced neutralizing and non-neutralizing activities synergize to promote protection, we leverage sera from 51 SARS-CoV-2 uninfected health-care workers after two doses of the BNT162b2 mRNA vaccine. We show that BNT162b2 elicits antibodies that neutralize clinical isolates of wildtype and five variants of SARS-CoV-2, including Omicron BA.2, and, critically, induce Fc effector functions. FcγRIIIa/CD16 activity is linked to neutralizing activity and associated with post-translational afucosylation and sialylation of vaccine specific antibodies. Further, neutralizing and non-neutralizing functions diminish with age, with limited polyfunctional breadth, magnitude and coordination observed in those ≥65 years old compared to <65. Thus, studying Fc functions in addition to Fab mediated neutralization provides greater insight into vaccine efficacy for vulnerable populations such as the elderly against SARS-CoV-2 and novel variants.

IgG N-Glycosylation from Patients with Pemphigus Treated with Rituximab

Pemphigus is a life-threatening auto-immune blistering disease of the skin and mucous membrane that is caused by the production of auto-antibodies (auto-Abs) directed against adhesion proteins: desmoglein 1 and 3. We demonstrated in the “Ritux3” trial, the high efficacy of rituximab, an anti-CD20 recombinant monoclonal antibody, as the first-line treatment for pemphigus. However, 25% of patients relapsed during the six-month period after rituximab treatment. These early relapses were associated with a lower decrease in anti-desmoglein auto-Abs after the initial cycle of rituximab. The N-glycosylation of immunoglobulin-G (IgG) can affect their affinity for Fc receptors and their serum half-life. We hypothesized that the extended half-life of Abs could be related to modifications of IgG N-glycans. The IgG N-glycome from pemphigus patients and its evolution under rituximab treatment were analyzed. Pemphigus patients presented a different IgG N-glycome than healthy donors, with less galactosylated, sialylated N-glycans, as well as a lower level of N-glycans bearing an additional N-acetylglucosamine. IgG N-glycome from patients who achieved clinical remission was not different to the one observed at baseline. Moreover, our study did not identify the N-glycans profile as discriminating between relapsing and non-relapsing patients. We report that pemphigus patients present a specific IgG N-glycome. The changes observed in these patients could be a biomarker of autoimmunity susceptibility rather than a sign of inflammation.

Expanding the Malaria Antibody Toolkit: Development and Characterisation of Plasmodium falciparum RH5, CyRPA, and CSP Recombinant Human Monoclonal Antibodies

Malaria, an infection caused by apicomplexan parasites of the genus Plasmodium, continues to exact a significant toll on public health with over 200 million cases world-wide, and annual deaths in excess of 600,000. Considerable progress has been made to reduce malaria burden in endemic countries in the last two decades. However, parasite and mosquito resistance to frontline chemotherapies and insecticides, respectively, highlights the continuing need for the development of safe and effective vaccines. Here we describe the development of recombinant human antibodies to three target proteins from Plasmodium falciparum: reticulocyte binding protein homologue 5 (PfRH5), cysteine-rich protective antigen (PfCyRPA), and circumsporozoite protein (PfCSP). All three proteins are key targets in the development of vaccines for blood-stage or pre-erythrocytic stage infections. We have developed potent anti-PfRH5, PfCyRPA and PfCSP monoclonal antibodies that will prove useful tools for the standardisation of assays in preclinical research and the assessment of these antigens in clinical trials. We have generated some very potent anti-PfRH5 and anti-PfCyRPA antibodies with some clones >200 times more potent than the polyclonal anti-AMA-1 antibodies used for the evaluation of blood stage antigens. While the monoclonal and polyclonal antibodies are not directly comparable, the data provide evidence that these new antibodies are very good at blocking invasion. These antibodies will therefore provide a valuable resource and have potential as biological standards to help harmonise pre-clinical malaria research.

Pregnancy enables antibody protection against intracellular infection

Adaptive immune components are thought to exert non-overlapping roles in antimicrobial host defence, with antibodies targeting pathogens in the extracellular environment and T cells eliminating infection inside cells1,2. Reliance on antibodies for vertically transferred immunity from mothers to babies may explain neonatal susceptibility to intracellular infections3,4. Here we show that pregnancy-induced post-translational antibody modification enables protection against the prototypical intracellular pathogen Listeria monocytogenes. Infection susceptibility was reversed in neonatal mice born to preconceptually primed mothers possessing L. monocytogenes-specific IgG or after passive transfer of antibodies from primed pregnant, but not virgin, mice. Although maternal B cells were essential for producing IgGs that mediate vertically transferred protection, they were dispensable for antibody acquisition of protective function, which instead required sialic acid acetyl esterase5 to deacetylate terminal sialic acid residues on IgG variable-region N-linked glycans. Deacetylated L. monocytogenes-specific IgG protected neonates through the sialic acid receptor CD226,7, which suppressed IL-10 production by B cells leading to antibody-mediated protection. Consideration of the maternal-fetal dyad as a joined immunological unit reveals protective roles for antibodies against intracellular infection and fine-tuned adaptations to enhance host defence during pregnancy and early life.

Physiological Roles of the Autoantibodies to the 78-Kilodalton Glucose-Regulated Protein (GRP78) in Cancer and Autoimmune Diseases

The 78 kDa glucose-regulated protein (GRP78), a member of the 70 kDa heat-shock family of molecular chaperones (HSP70), is essential for the regulation of the unfolded protein response (UPR) resulting from cellular endoplasmic reticulum (ER) stress. During ER stress, GRP78 evades retention mechanisms and is translocated to the cell surface (csGRP78) where it functions as an autoantigen. Autoantibodies to GRP78 appear in prostate, ovarian, gastric, malignant melanoma, and colorectal cancers. They are also found in autoimmune pathologies such as rheumatoid arthritis (RA), neuromyelitis optica (NMO), anti-myelin oligodendrocyte glycoprotein antibody-associated disorder (AMOGAD), Lambert-Eaton myasthenic syndrome (LEMS), multiple sclerosis (MS), neuropsychiatric systemic lupus erythematosus (NPSLE) and type 1 diabetes (T1D). In NMO, MS, and NPSLE these autoantibodies disrupt and move across the blood-brain barrier (BBB), facilitating their entry and that of other pathogenic antibodies to the brain. Although csGRP78 is common in both cancer and autoimmune diseases, there are major differences in the specificity of its autoantibodies. Here, we discuss how ER mechanisms modulate csGRP78 antigenicity and the production of autoantibodies, permitting this chaperone to function as a dual compartmentalized receptor with independent signaling pathways that promote either pro-proliferative or apoptotic signaling, depending on whether the autoantibodies bind csGRP78 N- or C-terminal regions.

α-2,6-sialic acid/IgG anti-dsDNA ratios correlate with human lupus disease activity and possible mechanisms: A pilot study

Objective

To study the association of α2,6-sialic acid (SIA) content in serum IgG anti-dsDNA with human systemic lupus erythematosus disease activity index (SLEDAI) and the effect of sialylated and desialylated (deSIA) IgG anti-dsDNA on lupus B cells.

Methods

Blood from lupus patients was collected to determine the ratio of SIA in isolated IgG anti-dsDNA over serum IgG anti-dsDNA (SIA/IgG anti-dsDNA) ratios, which were plotted against SLEDAI using a receiver-operating-characteristics curve. Lupus B cells were cultured in vitro with chimeric sialylated IgG anti-dsDNA and its deSIA form. Culture supernatants were assayed for anti-inflammatory IL-10 and SIA/IgG anti-dsDNA ratios, which were compared among different pre-treatment groups using t-tests.

Results

The area-under-the-curve (AUC) for anti-dsDNA levels against SLEDAI was 0.791 positively (95% confidence interval [C.I.]: 0.699–0.884) and SIA/IgG anti-dsDNA ratios against SLEDAI yielded an AUC of 0.705 inversely (95% C.I: 0.601–0.809): not significantly different. SIA/IgG anti-dsDNA ratios discriminated significantly between patients without and patients with proteinuria ( p = .046). SIA/IgG anti-dsDNA ratios correlated significantly and positively with serum C3c and C4 levels. Pre-treatment with IgG anti-dsDNA and its immune complexes (dsDNA/IgG anti-dsDNA IC) induced higher IL-10 from lupus B cells than medium pre-treatment (most p < .01 from day 2 to day 5 culture). DeSIA IgG anti-dsDNA IC induced lower IL-10 ( p < .05) and lower SIA/IgG anti-dsDNA ratios ( p < .001) from lupus B cells than medium and dsDNA pre-treatment.

Conclusion

α2,6-SIA/IgG anti-dsDNA ratios inversely forecasted SLEDAI scores. Possible mechanisms may be due to the different effects of sialylated and deSIA IgG anti-dsDNA on lupus B cells in terms of IL-10 secretion and SIA/IgG anti-dsDNA ratios.

Immunoglobulin G N-glycan Biomarkers for Autoimmune Diseases: Current State and a Glycoinformatics Perspective

The effective treatment of autoimmune disorders can greatly benefit from disease-specific biomarkers that are functionally involved in immune system regulation and can be collected through minimally invasive procedures. In this regard, human serum IgG N-glycans are promising for uncovering disease predisposition and monitoring progression, and for the identification of specific molecular targets for advanced therapies. In particular, the IgG N-glycome in diseased tissues is considered to be disease-dependent; thus, specific glycan structures may be involved in the pathophysiology of autoimmune diseases. This study provides a critical overview of the literature on human IgG N-glycomics, with a focus on the identification of disease-specific glycan alterations. In order to expedite the establishment of clinically-relevant N-glycan biomarkers, the employment of advanced computational tools for the interpretation of clinical data and their relationship with the underlying molecular mechanisms may be critical. Glycoinformatics tools, including artificial intelligence and systems glycobiology approaches, are reviewed for their potential to provide insight into patient stratification and disease etiology. Challenges in the integration of such glycoinformatics approaches in N-glycan biomarker research are critically discussed.

Sialylation as an Important Regulator of Antibody Function

Antibodies play a critical role in linking the adaptive immune response to the innate immune system. In humans, antibodies are categorized into five classes, IgG, IgM, IgA, IgE, and IgD, based on constant region sequence, structure, and tropism. In serum, IgG is the most abundant antibody, comprising 75% of antibodies in circulation, followed by IgA at 15%, IgM at 10%, and IgD and IgE are the least abundant. All human antibody classes are post-translationally modified by sugars. The resulting glycans take on many divergent structures and can be attached in an N-linked or O-linked manner, and are distinct by antibody class, and by position on each antibody. Many of these glycan structures on antibodies are capped by sialic acid. It is well established that the composition of the N-linked glycans on IgG exert a profound influence on its effector functions. However, recent studies have described the influence of glycans, particularly sialic acid for other antibody classes. Here, we discuss the role of glycosylation, with a focus on terminal sialylation, in the biology and function across all antibody classes. Sialylation has been shown to influence not only IgG, but IgE, IgM, and IgA biology, making it an important and unappreciated regulator of antibody function.

Functional and structural modifications of influenza antibodies during pregnancy

Pregnancy represents a unique tolerogenic immune state which may alter susceptibility to infection and vaccine response. Here, we characterized humoral immunity to seasonal influenza vaccine strains in pregnant and non-pregnant women. Although serological responses to influenza remained largely intact during late pregnancy, distinct modifications were observed. Pregnant women had reduced hemagglutinin subtype-1 (H1)- IgG, IgG1, IgG2, and IgG3, hemagglutination inhibition, and group 1 and 2 stem IgG titers. Intriguingly, H1-specific avidity and FcγR1 binding increased, and influenza antibodies had distinct Fc and Fab glycans characterized by increased di-galactosylation and di-sialylation. H1-specific Fc-functionality (i.e. monocyte phagocytosis and complement deposition) was moderately reduced in pregnancy. Multivariate antibody analysis revealed two distinct populations (pregnant vs. non-pregnant) segregated by H1 FcγR1 binding, H1-IgG levels, and Fab and Fc glycosylation. Our results demonstrated a structural and functional modulation of influenza humoral immunity during pregnancy that was antigen-specific and consistent with reduced inflammation and efficient placental transport

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Pregnancy resulted in structural and functional modulation of influenza antibodies.

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Antibodies had differential binding capacity, Fc/Fab glycosylation, and function.

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Antibody glycans directed toward low inflammation and efficient placental transfer.

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Multivariate analysis of immune markers segregated pregnant and non-pregnant women.

Strategies for Glycoengineering Therapeutic Proteins

Almost all therapeutic proteins are glycosylated, with the carbohydrate component playing a long-established, substantial role in the safety and pharmacokinetic properties of this dominant category of drugs. In the past few years and moving forward, glycosylation is increasingly being implicated in the pharmacodynamics and therapeutic efficacy of therapeutic proteins. This article provides illustrative examples of drugs that have already been improved through glycoengineering including cytokines exemplified by erythropoietin (EPO), enzymes (ectonucleotide pyrophosphatase 1, ENPP1), and IgG antibodies (e.g., afucosylated Gazyva^®, Poteligeo^®, Fasenra™, and Uplizna^®). In the future, the deliberate modification of therapeutic protein glycosylation will become more prevalent as glycoengineering strategies, including sophisticated computer-aided tools for “building in” glycans sites, acceptance of a broad range of production systems with various glycosylation capabilities, and supplementation methods for introducing non-natural metabolites into glycosylation pathways further develop and become more accessible.

Distinct N-Linked Immunoglobulin G Glycosylation Patterns Are Associated With Chronic Pathology and Asymptomatic Infections in Human Lymphatic Filariasis

Lymphatic filariasis presents a complex spectrum of clinical manifestations ranging from asymptomatic microfilariaemic (MF+) to chronic pathology (CP), including lymphedema and elephantiasis. Emerging evidence suggests a link between the physiopathology of filarial infections and antibody properties. Post-translational glycosylation has been shown to play a key role in the modulation of antibodies’ effector functions. Here, we investigated the link between total IgG-N-glycosylation patterns and the physiopathology of human lymphatic filariasis using UPLC-FLD/ESI-MS comparison of N-glycan profiles of total IgG purified from endemic normals (EN), MF+, and CP patients. We detected a total of 19 glycans released from all IgG samples. Strikingly, agalactosylated glycan residues were more prominent in EN, whereas sialylation and bisecting GlcNac correlated with asymptomatic infections. While IgG from all three clinical groups expressed high levels of fucosylated residues, significantly lower expressions of afucosylated IgG were seen in MF+ individuals compared to EN and CP. Our data reveal distinct N-linked IgG glycan profiles in EN, MF+, and CP and suggest that IgG galactosylation and sialylation are associated with chronic pathology, whereas agalactosylation correlates with putative immunity. The results also indicate a role for sialylation, fucosylation, and bisecting GlcNac in immune tolerance to the parasite. These findings highlight the link between N-glycosylation and the physiopathology of lymphatic filariasis and open new research avenues for next-generation therapeutic formulations against infectious diseases.

Fc Domain-Imprinted Stealth Nanogels Capable of Orientational Control of Immunoglobulin G Adsorbed In Vivo

Regulation of nanomaterial-cell interaction is an important requisite for a variety of biomedical applications such as drug delivery systems and theranostics. Here, we demonstrate the regulation of nanomaterial-cell interaction using the oriented adsorption of intrinsic immunoglobulin G (IgG) on molecularly imprinted polymer nanogels (MIP-NGs) capable of recognizing the fragment crystallizable (Fc) domain of IgG. The unique domain recognition property resulted in the suppression of the immune response in Fc domain receptor-possessing macrophages and natural killer cells due to the regulation of protein corona based on the oriented adsorption of IgG. This resulted in the hindrance of the Fc domain, which is the trigger of an immune response. Furthermore, the acquisition of stealth capability was successfully demonstrated in vivo using intravital confocal laser scanning microscopy. The domain imprinting proposed in this study will provide a new strategy for creating nanomaterials capable of domain recognition-based oriented adsorption of intrinsic proteins in situ, thus regulating the protein corona formed on the nanomaterials. Thus, the unique Fc domain-recognition nanomaterial developed in our study can be used for various biomedical applications to target specific cells without triggering an immune response.

Changes of IgG N-Glycosylation in Thyroid Autoimmunity: The Modulatory Effect of Methimazole in Graves' Disease and the Association With the Severity of Inflammation in Hashimoto's Thyroiditis

The N-glycome of immunoglobulin G (IgG), the most abundant glycoprotein in human blood serum, reflects pathological conditions of autoimmunity and is sensitive to medicines applied in disease therapy. Due to the high sensitivity of N-glycosylation, the IgG N-glycan profile may serve as an indicator of an ongoing inflammatory process. The IgG structure and its effector functions are strongly dependent on the composition of N-glycans attached to the Fc fragment, and the binding of antigens is regulated by Fab sugar moieties. Because of the crucial role of N-glycans in IgG function, remodeling of its N-oligosaccharides can induce pathological changes that ultimately contribute to the development of autoimmunity; restoration of their physiological structure is critical to the reduction of disease symptoms. Our recently published data have shown that the pathology of autoimmune thyroid diseases (AITDs), including Hashimoto’s thyroiditis (HT) and Graves’ disease (GD), is accompanied by alterations of the composition of IgG N-glycans. The present study is a more in-depth investigation of IgG glycosylation in both AITDs, designed to determine the relationship between the severity of thyroid inflammation and IgG N-glycan structures in HT, and to assess the impact of immunosuppressive therapy on the N-glycan profile in GD patients. The study material consisted of human serum samples collected from donors with elevated anti-thyroglobulin (Tg) and/or anti-thyroperoxidase (TPO) IgGs without symptoms of hypothyroidism (n=68), HT patients characterized by high autoantibody titers and advanced destruction of the thyroid gland (n=113), GD patients with up-regulated IgG against thyroid-stimulating hormone receptor (TSHR) before (n=62) and after (n=47) stabilization of TSH level as a result of methimazole therapy (study groups), and healthy donors (control group, n=90). IgG was isolated from blood serum using protein G affinity chromatography. N-glycans were released from IgG by PNGase F digestion and analyzed by ultra-performance liquid chromatography-mass spectrometry (UPLC-MS) after 2-aminobenzamide (2-AB) labeling. UPLC-MS chromatograms were integrated into 25 peaks (GP) in the Waters UNIFI Scientific Information System, and N-glycans were assigned based on the glucose unit values and mass-to-charge ratios (m/z) of the detected ions. The Kruskal-Wallis non-parametric test was used to determine the statistical significance of the results (p<0.05). The obtained results suggest that modifications of IgG sialylation, galactosylation and core-fucosylation are associated with the severity of HT symptoms. Methimazole therapy implemented in GD patients affected the IgG N-glycan profile; as a result, the content of the sialylated and galactosylated oligosaccharides with core fucose differed after treatment. Our results suggest that N-glycosylation of IgG undergoes dynamic changes during the intensification of thyroiditis in HT, and that in GD autoimmunity it is affected significantly by immunosuppressive therapy.

Glycans as a key factor in self and non-self discrimination: Impact on the breach of immune tolerance

Glycans are carbohydrates that are made by all organisms and covalently conjugated to other biomolecules. Glycans cover the surface of both human cells and pathogens and are fundamental to defining the identity of a cell or an organism, thereby contributing to discriminating self from non-self. As such, glycans are a class of "Self-Associated Molecular Patterns" that can fine-tune host inflammatory processes. In fact, glycans can be sensed and recognized by a variety of glycan-binding proteins (GBP) expressed by immune cells, such as galectins, siglecs and C-type lectins, which recognize changes in the cellular glycosylation, instructing both pro-inflammatory or anti-inflammatory responses. In this review, we introduce glycans as cell-identification structures, discussing how glycans modulate host-pathogen interactions and how they can fine-tune inflammatory processes associated with infection, inflammation and autoimmunity. Finally, from the clinical standpoint, we discuss how glycoscience research can benefit life sciences and clinical medicine by providing a source of valuable biomarkers and therapeutic targets for immunity.

Cytokines in the Immune Microenvironment Change the Glycosylation of IgG by Regulating Intracellular Glycosyltransferases

Background

Changes in IgG glycosylation, as a novel pathological feature, are observed in various autoimmune diseases (AIDs). The glycosylation patterns of IgG play a critical role in regulating the biological function and stability of IgG involved in the pathophysiology of many AIDs. However, the intracellular regulatory mechanisms underlying the effects of disturbances in various cytokines on IgG glycosylation are poorly understood. Thus, we investigated the regulatory effects of elevated cytokines in AIDs on intracellular IgG glycosylation within B cells.

Methods

First, we established a controlled primary culture system in vitro to differentiate human CD19+ B cells into antibody-secreting cells (ASCs). Then, the IgG concentrations in the supernatants were measured by enzyme-linked immunoassay (ELISA) under IFN-γ, TNF-α, IL-21, IL-17A, BAFF, or APRIL stimulation. Next, the glycosylation levels of IgG under different stimuli were compared via a lectin microarray. The fine carbohydrate structures of IgG were confirmed by matrix-assisted laser desorption/ionization-quadrupole ion trap-time of flight-mass spectrometry (MALDI-TOF-MS). Finally, the expression of glycosyltransferases and glycosidases in B cells under stimulation with several cytokines was detected by real-time PCR and western blotting.

Results

We found that cytokines significantly promoted IgG production in vitro and led to considerably different IgG glycan patterns. Specifically, the results of lectin microarray showed the galactose level of IgG was increased by IFN-γ stimulation (p&lt;0.05), and the sialylation of IgG was increased by IL-21 and IL-17A (p&lt;0.05). The MALDI-TOF-MS data showed that the frequency of agalactosylation was decreased by IFN-γ with the increased frequency of mono-galactosylation and decreased frequency of digalactosylation, accompanied by upregulation of β-1,4-galactosyltransferase 1. Both frequencies of mono-sialylated and disialylated N-glycans were increased by IL-21 and IL-17A with decreased frequency of asialylation, and the expression of β-galactoside α-2,6-sialyltransferase 1 was upregulated by IL-21 and IL-17A.

Conclusion

Abnormally elevated cytokines in the microenvironment regulates IgG glycan patterns by regulating intracellular glycosyltransferases in human B cells.

The Alterations of Serum IgG Fucosylation as a Potential Additional New Diagnostic Marker in Advanced Endometriosis

BACKGROUND

Endometriosis is an inflammatory disease leading to the growth of endometrial-like tissue outside of the uterus, which affects approximately 10% of young women of reproductive potential. The diagnosis of this disease is difficult, often invasive and time-consuming, therefore non-invasive diagnostic methods are strongly desirable in endometriosis detection. The aim of our project was to investigate whether any associations exist between the expression of serum IgG fucosylation and advanced stages of endometriosis. We were also interested in whether native serum IgG (s-IgG) fucosylation analysis, without prior IgG isolation, could provide a panel of parameters helpful in non-invasive diagnostics of advanced endometriosis.

METHODS

IgG fucosylation was examined using a lectin-ELISA test with fucose-specific lectins: AAL and LCA, specific for core fucose α1,6-linked, as well as LTA and UEA which recognize α1,3- and α1,2-linked fucose, respectively.

RESULTS

ROC curve and cluster analysis showed s-IgG reactivities with the panel of fucose-specific lectins AAL, LCA and LTA.

CONCLUSION

s-IgG reactivity with the panel of fucose-specific lectins AAL, LCA and LTA can be taken into account as a useful diagnostic and clinical tool to differentiate women with advanced endometriosis. Moreover, it has been shown that the analysis of native IgG fucosylation directly in serum, without prior time-consuming, expensive IgG isolation, is sufficient to distinguish advanced stages of endometriosis from a control group of healthy women.

Engineering an Enhanced EGFR Engager: Humanization of Cetuximab for Improved Developability

The epidermal growth factor receptor (EGFR) is a receptor tyrosine kinase whose proliferative effects can contribute to the development of many types of solid tumors when overexpressed. For this reason, EGFR inhibitors such as cetuximab can play an important role in treating cancers such as colorectal cancer and head and neck cancer. Cetuximab is a chimeric monoclonal antibody containing mouse variable regions that bind to EGFR and prevent it from signaling. Although cetuximab has been used clinically since 2004 to successfully control solid tumors, advances in protein engineering have created the opportunity to address some of its shortcomings. In particular, the presence of mouse sequences could contribute to immunogenicity in the form of anti-cetuximab antibodies, and an occupied glycosylation site in FR3 can contribute to hypersensitivity reactions and product heterogeneity. Using simple framework graft or sequence-/structure-guided approaches, cetuximab was humanized onto 11 new frameworks. In addition to increasing humanness and removing the VH glycosylation site, dynamic light scattering revealed increases in stability, and bio-layer interferometry confirmed minimal changes in binding affinity, with patterns emerging across the humanization method. This work demonstrates the potential to improve the biophysical and clinical properties of first-generation protein therapeutics and highlights the advantages of computationally guided engineering.

Anti-citrullinated Protein Antibody Generation, Pathogenesis, Clinical Application, and Prospects

Anti-citrullinated protein antibodies (ACPAs) are autoantibodies commonly observed in patients with rheumatoid arthritis (RA). Currently, most of the mechanisms of ACPA formation and bone destruction are well-understood, however, some unknown mechanisms still exist. There have been many new advances in ACPA-related clinical applications and targeted therapies. However, the existence of different ACPA subtypes is a limitation of targeted therapy. Herein, we present an overview of the process of ACPA generation, the underlying pathogenesis, and relevant clinical application and prospects.

New Opportunities in Glycan Engineering for Therapeutic Proteins

Glycans as sugar polymers are important metabolic, structural, and physiological regulators for cellular and biological functions. They are often classified as critical quality attributes to antibodies and recombinant fusion proteins, given their impacts on the efficacy and safety of biologics drugs. Recent reports on the conjugates of N-acetyl-galactosamine and mannose-6-phosphate for lysosomal degradation, Fab glycans for antibody diversification, as well as sialylation therapeutic modulations and O-linked applications, have been fueling the continued interest in glycoengineering. The current advancements of the human glycome and the development of a comprehensive network in glycosylation pathways have presented new opportunities in designing next-generation therapeutic proteins.

OUP accepted manuscript

Host carbohydrates, or glycans, have been implicated in the pathogenesis of many bacterial infections. Group A Streptococcus (GAS) is a Gram-positive bacterium that readily colonises the skin and oropharynx, and is a significant cause of mortality in humans. While the glycointeractions orchestrated by many other pathogens are increasingly well-described, the understanding of the role of human glycans in GAS disease remains incomplete. Although basic investigation into the mechanisms of GAS disease is ongoing, several glycointeractions have been identified and are examined herein. The majority of research in this context has focussed on bacterial adherence, however, glycointeractions have also been implicated in carbohydrate metabolism; evasion of host immunity; biofilm adaptations; and toxin-mediated haemolysis. The involvement of human glycans in these diverse avenues of pathogenesis highlights the clinical value of understanding glycointeractions in combatting GAS disease.

A versatile design platform for glycoengineering therapeutic antibodies

Manipulation of glycosylation patterns, i.e., glycoengineering, is incorporated in the therapeutic antibody development workflow to ensure clinical safety, and this approach has also been used to modulate the biological activities, functions, or pharmacological properties of antibody drugs. Whereas most existing glycoengineering strategies focus on the canonical glycans found in the constant domain of immunoglobulin G (IgG) antibodies, we report a new strategy to leverage the untapped potential of atypical glycosylation patterns in the variable domains, which naturally occur in 15% to 25% of IgG antibodies. Glycosylation sites were added to the antigen-binding regions of two functionally divergent, interleukin-2-binding monoclonal antibodies. We used computational tools to rationally install various N-glycosylation consensus sequences into the antibody variable domains, creating "glycovariants" of these molecules. Strikingly, almost all the glycovariants were successfully glycosylated at their newly installed N-glycan sites, without reduction of the antibody's native function. Importantly, certain glycovariants exhibited modified activities compared to the parent antibody, showing the potential of our glycoengineering strategy to modulate biological function of antibodies involved in multi-component receptor systems. Finally, when coupled with a high-flux sialic acid precursor, a glycovariant with two installed glycosylation sites demonstrated superior in vivo half-life. Collectively, these findings validate a versatile glycoengineering strategy that introduces atypical glycosylation into therapeutic antibodies in order to improve their efficacy and, in certain instances, modulate their activity early in the drug development process.

Influence of Maternal Microbiome and Inflammatory Response in Preterm Birth: Recent Aspects of the Prevention of Preterm Birth

Preterm birth (PTB) is a global health issue and one of the most challenging problems affecting 12.9 million births worldwide. PTB is a multi-etiological disease and remains incompletely understood. The major cause of PTB is infection or inflammation and disruption of the vaginal microbiome, which affects the maternal immunologic response leading to PTB. The vaginal microbiome composition changes by a shift in the community are typically dominated by Lactobacillus during pregnancy. There are complex interactions between the maternal microbiome in pregnancy and the development of PTB, therefore, researchers have struggled to connect the maternal microbiome with the dysregulation of the maternal immune response in cases of PTB. The host microbiome affects alterations of the microorganisms with external stimuli such as disease, nutrition, immunity, and behavior. In this review, we discuss the complex association between the maternal microbiome and the risk of PTB and also focus on recent aspects of the prevention of PTB.

The current status of anti-citrullinated protein antibodies and citrullinated protein-reactive B cells in the pathogenesis of rheumatoid arthritis

Anti-citrullinated protein antibodies are a hallmark of rheumatoid arthritis. It is widely acknowledged that the presence of ACPAs is the result of the interaction of genes, the environment and epigenetic modifications. The mechanism by which the factors, especially citrullination and ACPA glycosylation, affect ACPAs is still unclear. In this article, we review the presence of the ACPAs in RA and their relationship with clinical manifestations. The pathogenicity of ACPAs and B cells in RA was also summarized. A growing body of evidence has shown that ACPA-positive patients have more serious bone erosion and destruction and poor clinical prognosis than ACPA-negative patients. Recently, with the direct study of citrullinated protein-reactive B cells, their role in the development of rheumatoid arthritis has been further understood. It indicates that further understanding of the mechanism of ACPAs and CP-reactive B cells would beneficial in the prevention and treatment of RA.

IgG N-glycans

Glycosylation, one of the most common post-translational modifications in mammalian cells, impacts many biological processes such as cell adhesion, proliferation and differentiation. As the most abundant glycoprotein in human serum, immunoglobulin G (IgG) plays a vital role in immune response and protection. There is a growing body of evidence suggests that IgG structure and function are modulated by attached glycans, especially N-glycans, and aberrant glycosylation is associated with disease states. In this chapter, we review IgG glycan repertoire and function, strategies for profiling IgG N-glycome and recent studies. Mass spectrometry (MS) based techniques are the most powerful tools for profiling IgG glycome. IgG glycans can be divided into high-mannose, biantennary complex and hybrid types, modified with mannosylation, core-fucosylation, galactosylation, bisecting GlcNAcylation, or sialylation. Glycosylation of IgG affects antibody half-life and their affinity and avidity for antigens, regulates crystallizable fragment (Fc) structure and Fcγ receptor signaling, as well as antibody effector function. Because of their critical roles, IgG N-glycans appear to be promising biomarkers for various disease states. Specific IgG glycosylation can convert a pro-inflammatory response to an anti-inflammatory activity. Accordingly, IgG glycoengineering provides a powerful approach to potentially develop effective drugs and treat disease. Based on the understanding of the functional role of IgG glycans, the development of vaccines with enhanced capacity and long-term protection are possible in the near future.

Investigation of the causal relationships between human IgG N-glycosylation and twelve common diseases associated with changes in the IgG N-glycome

Changes in the N-glycosylation of immunoglobulin G (IgG) are often observed in pathological states, such as autoimmune, inflammatory, neurodegenerative, cardiovascular diseases and some types of cancer. However, in most cases it is not clear if the disease onset causes these changes, or if the changes in IgG N-glycosylation are among the risk factors for the diseases. The aim of this study was to investigate the casual relationships between IgG N-glycosylation traits and 12 diseases, in which the alterations of IgG N-glycome were previously reported, using Two Sample Mendelian Randomization (MR) approach. We have performed Two Sample MR using publicly available summary statistics of genome-wide association studies of IgG N-glycosylation and disease risks. Our results indicate positive causal effect of systemic lupus erythematosus (SLE) on the abundance of N-glycans with bisecting N-acetylglucosamine in the total IgG N-glycome. Therefore, we suggest regarding this IgG glycosylation trait as a biomarker of SLE. We also emphasize the need for more powerful GWAS studies of IgG N-glycosylation to further elucidate the causal effect of IgG N-glycome on the diseases.

Immunoglobulin Glycosylation - An Unexploited Potential for Immunomodulatory Strategies in Farm Animals

The function of antibodies, namely the identification and neutralization of pathogens, is mediated by their antigen binding site (Fab). In contrast, the subsequent signal transduction for activation of the immune system is mediated by the fragment crystallizable (Fc) region, which interacts with receptors or other components of the immune system, such as the complement system. This aspect of binding and interaction is more precise, readjusted by covalently attached glycan structures close to the hinge region of immunoglobulins (Ig). This fine-tuning of Ig and its actual state of knowledge is the topic of this review. It describes the function of glycosylation at Ig in general and the associated changes due to corresponding glycan structures. We discuss the functionality of IgG glycosylation during different physiological statuses, like aging, lactation and pathophysiological processes. Further, we point out what is known to date about Ig glycosylation in farm animals and how new achievements in vaccination may contribute to improved animal welfare.

Glycoengineering of Therapeutic Antibodies with Small Molecule Inhibitors

Monoclonal antibodies (mAbs) are one of the cornerstones of modern medicine, across an increasing range of therapeutic areas. All therapeutic mAbs are glycoproteins, i.e., their polypeptide chain is decorated with glycans, oligosaccharides of extraordinary structural diversity. The presence, absence, and composition of these glycans can have a profound effect on the pharmacodynamic and pharmacokinetic profile of individual mAbs. Approaches for the glycoengineering of therapeutic mAbs—the manipulation and optimisation of mAb glycan structures—are therefore of great interest from a technological, therapeutic, and regulatory perspective. In this review, we provide a brief introduction to the effects of glycosylation on the biological and pharmacological functions of the five classes of immunoglobulins (IgG, IgE, IgA, IgM and IgD) that form the backbone of all current clinical and experimental mAbs, including an overview of common mAb expression systems. We review selected examples for the use of small molecule inhibitors of glycan biosynthesis for mAb glycoengineering, we discuss the potential advantages and challenges of this approach, and we outline potential future applications. The main aim of the review is to showcase the expanding chemical toolbox that is becoming available for mAb glycoengineering to the biology and biotechnology community.

Elevated N-Linked Glycosylation of IgG V Regions in Myasthenia Gravis Disease Subtypes

Elevated N-linked glycosylation of IgG V regions (IgG-V^N-Glyc) is an emerging molecular phenotype associated with autoimmune disorders. To test the broader specificity of elevated IgG-V^N-Glyc, we studied patients with distinct subtypes of myasthenia gravis (MG), a B cell-mediated autoimmune disease. Our experimental design focused on examining the B cell repertoire and total IgG. It specifically included adaptive immune receptor repertoire sequencing to quantify and characterize N-linked glycosylation sites in the circulating BCR repertoire, proteomics to examine glycosylation patterns of the total circulating IgG, and an exploration of human-derived recombinant autoantibodies, which were studied with mass spectrometry and Ag binding assays to respectively confirm occupation of glycosylation sites and determine whether they alter binding. We found that the frequency of IgG-V^N-Glyc motifs was increased in the total BCR repertoire of patients with MG when compared with healthy donors. The elevated frequency was attributed to both biased V gene segment usage and somatic hypermutation. IgG-V^N-Glyc could be observed in the total circulating IgG in a subset of patients with MG. Autoantigen binding, by four patient-derived MG autoantigen-specific mAbs with experimentally confirmed presence of IgG-V^N-Glyc, was not altered by the glycosylation. Our findings extend prior work on patterns of Ig V region N-linked glycosylation in autoimmunity to MG subtypes.

Longitudinal Pathogenic Properties and N-Glycosylation Profile of Antibodies from Patients with Pemphigus after Corticosteroid Treatment

Pemphigus vulgaris is an autoimmune disease that occurs due to pathogenic autoantibodies that recognize the following epidermal adhesion proteins: desmogleins. Systemic corticosteroids usually decrease the titers of anti-desmoglein autoantibodies and improve patients’ conditions. Since modifications of IgG N-glycosylation have been described in some autoimmune diseases, we hypothesized that changes in the pathogenic activity of pemphigus IgG could be related to changes in their N-glycosylation profile. The purpose of this study was to assess, longitudinally, the pathogenicity of pemphigus serum IgG and their N-glycosylation profile during phases of disease activity and clinical remission. The pathogenic activity of serum IgG was measured in vitro on immortalized keratinocytes, by immunofluorescence and dissociation assays, and IgG N-glycans were analyzed by mass spectrometry. We showed (i) a correlation between pemphigus clinical activity and the pathogenicity of serum IgG at baseline and at month 6, while the persistence of the in vitro pathogenic activity of IgG during its evolution, even in patients in clinical remission, seemed to be predictive of relapse; (ii) that modifications of the N-glycan structure were altered the in vitro pathogenicity of patients’ autoantibodies; (iii) that the pathogenic properties of pemphigus IgG did not appear to be related to the disparity in IgG N-glycans during the course of pemphigus.

Shotgun scanning glycomutagenesis: A simple and efficient strategy for constructing and characterizing neoglycoproteins

Asparagine-linked (N-linked) protein glycosylation—the covalent attachment of complex sugars to the nitrogen atom in asparagine side chains—is the most widespread posttranslational modification to proteins and also the most complex. N-glycosylation affects a significant number of cellular proteins and can have profound effects on their most important attributes such as biological activity, chemical solubility, folding and stability, immunogenicity, and serum half-life. Accordingly, the strategic installation of glycans at naïve sites has become an attractive means for endowing proteins with advantageous biological and/or biophysical properties. Here, we describe a glycoprotein engineering strategy that enables systematic investigation of the structural and functional consequences of glycan installation at every position along a protein backbone and provides a new route to bespoke glycoproteins.

As a common protein modification, asparagine-linked (N-linked) glycosylation has the capacity to greatly influence the biological and biophysical properties of proteins. However, the routine use of glycosylation as a strategy for engineering proteins with advantageous properties is limited by our inability to construct and screen large collections of glycoproteins for cataloguing the consequences of glycan installation. To address this challenge, we describe a combinatorial strategy termed shotgun scanning glycomutagenesis in which DNA libraries encoding all possible glycosylation site variants of a given protein are constructed and subsequently expressed in glycosylation-competent bacteria, thereby enabling rapid determination of glycosylatable sites in the protein. The resulting neoglycoproteins can be readily subjected to available high-throughput assays, making it possible to systematically investigate the structural and functional consequences of glycan conjugation along a protein backbone. The utility of this approach was demonstrated with three different acceptor proteins, namely bacterial immunity protein Im7, bovine pancreatic ribonuclease A, and human anti-HER2 single-chain Fv antibody, all of which were found to tolerate N-glycan attachment at a large number of positions and with relatively high efficiency. The stability and activity of many glycovariants was measurably altered by N-linked glycans in a manner that critically depended on the precise location of the modification. Structural models suggested that affinity was improved by creating novel interfacial contacts with a glycan at the periphery of a protein–protein interface. Importantly, we anticipate that our glycomutagenesis workflow should provide access to unexplored regions of glycoprotein structural space and to custom-made neoglycoproteins with desirable properties.

Rarely Recognized Antibody Diversification in Covid-19 Evolution to Counteract Advanced SARS-CoV-2 Evasion Strategies, and Implications for Prophylactic Treatment

The ongoing Covid-19 pandemic underscores the importance of finding effective and safe ways to combat the virus, and to optimally understand the immune response elicited upon natural infection. This likely involves all components of the immune system, both innate and adaptive. The impetus for the rapid development of prophylactic treatment options has led to an intense focus on neutralizing antibodies (Abs), and many novel and specialized platforms have been designed to achieve that goal. B-cell immunity relies on the generation of a diverse repertoire of Abs. Their structural variation is defined in terms of amino acid composition that is encoded in the genome or acquired through somatic mutations. Yet, key examples of frequently neglected antibody diversification mechanisms involving post-translational modifications such as N- or O-linked glycosylation are present in significant portions of the population. During the last few years, these and other beyond gene sequence determined humoral immune response mechanisms have in some specific cases revealed their potent immunomodulatory effects. Nonetheless, such more unusual mechanisms have not received much attention in the context of SARS-CoV-2. Thus, with specific focus on the latter, this paper presents, (1) the rationale for considering beyond sequence determined strategies, (2) evidence for their possible involvement in Covid-19 disease evolution, (3) consequences for vaccine design exemplified by one of the vaccine candidates that is currently undergoing trial, and (4) more general implications. Based on a critical interpretation of published literature, the hypotheses developed in this study point to a crucial role of non-genetic antibody diversification mechanisms in disease evolution to counteract unique immunogenicity determinants of SARS-CoV-2 infection. The involvement of post translational mechanisms may also help explain the widely varied immune response observed, not only among different patient groups, but also in terms of their observed incompatibility with SARS-CoV-2 infection in several human cell types. The article highlights potentials and challenges of these refined humoral immune response mechanisms to most optimally target non-genetic viral evasion strategies.

Glycosylation decreases aggregation and immunogenicity of adalimumab Fab secreted from Pichia pastoris

Glycoengineering of therapeutic proteins has been applied to improve the clinical efficacy of several therapeutics. Here, we examined the effect of glycosylation on the properties of the Fab of the therapeutic antibody, adalimumab. An N-glycosylation site was introduced at position 178 of the H chain constant region of adalimumab Fab through site-directed mutagenesis (H:L178N Fab), and the H:L178N Fab was produced in Pichia pastoris. Expressed mutant Fab contained long and short glycan chains (L-glyco Fab and S-glyco Fab, respectively). Under the condition of aggregation of Fab upon pH shift-induced stress, both of L-glyco Fab and S-glyco Fab were less prone to aggregation, with L-glyco Fab suppressing aggregation more effectively than the S-glyco Fab. Moreover, the comparison of the antigenicity of glycosylated and wild-type Fabs in mice revealed that glycosylation resulted in the suppression of antigenicity. Analysis of the pharmacokinetic behaviour of the Fab, L-glyco Fab and S-glyco Fab indicated that the half-lives of glycosylated Fabs in the rats were shorter than that of wild-type Fab, with L-glyco Fab having a shorter half-life than S-glyco Fab. Thus, we demonstrated that the glycan chain influences Fab aggregation and immunogenicity, and glycosylation reduces the elimination half-life in vivo.

Creation of monoclonal antibody expressing CHO cell lines grown with sodium butyrate and characterization of resulting antibody glycosylation

Chinese hamster ovary (CHO) cells are the primary mammalian cell lines utilized to produce monoclonal antibodies (mAbs). The upsurge in biosimilar development and the proven health benefits of mAb treatments reinforces the need for innovative methods to generate robust CHO clones and enhance production, while maintaining desired product quality attributes. Among various product titer-enhancing approaches, the use of histone deacetylase inhibitors (HDACis) such as sodium butyrate (NaBu) has yielded promising results. The titer-enhancing effect of HDACi treatment has generally been observed in lower producer cell lines but those studies are typically done on individual clones. Here, we describe a cell line development (CLD) platform approach for creating clones with varying productivities. We then describe a method for selecting an optimal NaBu concentration to evaluate potential titer-enhancing capabilities in a fed-batch study. Finally, a method for purifying the mAb using protein A chromatography, followed by glycosylation analysis using mass spectrometry, is described. The proposed workflow can be applied for a robust CLD process optimization to generate robust clones, enhance product expression, and improve product quality attributes.

Significant Associations of IgG Glycan Structures With Chronic Graft-Versus-Host Disease Manifestations: Results of the Cross-Sectional NIH Cohort Study

Chronic graft-versus-host disease (cGvHD) is a systemic alloimmune and autoimmune disorder and a major late complication of allogeneic hematopoietic stem cell transplantation (alloHSCT). The disease is characterized by an altered homeostasis of the humoral immune response. Immunoglobulin G (IgG) glycoprotein is the main effector molecule of the humoral immune response. Changes in IgG glycosylation are associated with a number of autoimmune diseases. IgG glycosylation analysis was done by the means of liquid chromatography in the National Institutes of Health (NIH) cohort of 213 cGvHD patients. The results showed statistically significant differences with regards to cGvHD NIH joint/fascia and skin score, disease activity and intensity of systemic immunosuppression. ROC analysis confirmed that IgG glycosylation increases specificity and sensitivity of models using laboratory parameters and markers of inflammation associated with cGvHD (eosinophil count, complement components C3 and C4 and inflammation markers: albumin, CRP and thrombocyte count). This research shows that IgG glycosylation may play a significant role in cGvHD pathology. Further research could contribute to the understanding of the disease biology and lead to the clinical biomarker development to allow personalized approaches to chronic GvHD therapy.

A study of the possible role of Fab-glycosylated IgG in tumor immunity

Previously we reported that administration of IgG could inhibit tumor progression in mouse models. At the same time, we also found that some IgGs have glycosylation modifications on their Fab fragments, which may have different biological functions than non-glycosylated IgG. In this study, we employed mouse tumor models to explore the roles of two different forms of IgG, i.e. Fab-glycosylated and Fab-non-glycosylated IgG, in tumor progression. The two types of IgGs were separated with ConA absorption which could react with glycan on the Fab arm but could not access glycan on the Fc fragment. In addition, we performed cytokine array, ELISA, western blotting, immunocytochemistry and other techniques to investigate the possible mechanisms of the actions of Fab-glycosylated IgG in the models. We found that Fab-glycosylated IgG, unlike Fab-non-glycosylated IgG, did not inhibit tumor growth and metastasis in the model. On the contrary, Fab-glycosylated IgG may bind to antigen-bound IgG molecules and macrophages through the glycosidic chain on the Fab fragment to affect antigen-antibody binding and macrophage polarization, which are likely to help tumor cells to evade the immune surveillance. A new mechanism of immune evasion with Fab-glycosylated IgG playing a significant role was proposed.

Characterisation of a highly potent and near pan-neutralising anti-HIV monoclonal antibody expressed in tobacco plants

BACKGROUND

HIV remains one of the most important health issues worldwide, with almost 40 million people living with HIV. Although patients develop antibodies against the virus, its high mutation rate allows evasion of immune responses. Some patients, however, produce antibodies that are able to bind to, and neutralise different strains of HIV. One such 'broadly neutralising' antibody is 'N6'. Identified in 2016, N6 can neutralise 98% of HIV-1 isolates with a median IC50 of 0.066 µg/mL. This neutralisation breadth makes N6 a very promising therapeutic candidate.

RESULTS

N6 was expressed in a glycoengineered line of N. benthamiana plants (pN6) and compared to the mammalian cell-expressed equivalent (mN6). Expression at 49 mg/kg (fresh leaf tissue) was achieved in plants, although extraction and purification are more challenging than for most plant-expressed antibodies. N-glycoanalysis demonstrated the absence of xylosylation and a reduction in α(1,3)-fucosylation that are typically found in plant glycoproteins. The N6 light chain contains a potential N-glycosylation site, which was modified and displayed more α(1,3)-fucose than the heavy chain. The binding kinetics of pN6 and mN6, measured by surface plasmon resonance, were similar for HIV gp120. pN6 had a tenfold higher affinity for FcγRIIIa, which was reflected in an antibody-dependent cellular cytotoxicity assay, where pN6 induced a more potent response from effector cells than that of mN6. pN6 demonstrated the same potency and breadth of neutralisation as mN6, against a panel of HIV strains.

CONCLUSIONS

The successful expression of N6 in tobacco supports the prospect of developing a low-cost, low-tech production platform for a monoclonal antibody cocktail to control HIV in low-to middle income countries.

Fc Glycosylation Characterization of Human Immunoglobulins G Using Immunocapture and LC-MS

Immunoglobulins G (IgG) are proteins produced by the immune system of higher life forms that play a central role in the defense against microbial pathogens. IgG bind pathogens with the hypervariable Fab component and mediate a diversity of effector functions by binding to immune effector cells via their crystallizable (Fc) component. All IgG Fc carry a polymorphic N-glycan that regulates its binding properties and thereby its effector functions. The glycosylation profile of IgG Fc is modulated by physiological and pathological conditions, including infectious diseases and inflammatory disorders. Characterization of IgG Fc glycosylation profiles is a promising approach to understand the pathogenesis of diseases involving the immune system and to develop novel biomarkers of disease activity. Measuring the proportion of the different IgG Fc glycoforms remains an analytical challenge, that requires a sensitive and reproducible analytical approach.This chapter describes an optimized approach for the preparation and the analysis of Fc N-glycans from total serum or plasma IgG using magnetic beads, RapiFluor MS label©, and LC-MS.

Low-density PD-1 expression on resting human natural killer cells is functional and upregulated after transplantation

Expression of programmed cell death protein 1 (PD-1) on natural killer (NK) cells has been difficult to analyze on human NK cells. By testing commercial clones and novel anti-PD-1 reagents, we found expression of functional PD-1 on resting human NK cells in healthy individuals and reconstituting NK cells early after allogeneic hematopoietic stem cell transplantation (allo-HSCT). Peripheral blood samples from healthy individuals and transplant recipients were stained for PD-1 expression using the commercial anti-PD-1 clone PD1.3.1.3, fluorescein isothiocyanate (FITC)-labeled pembrolizumab, or an FITC-labeled single-chain variable fragment (scFv) reagent made from pembrolizumab. These reagents identified low yet consistent basal PD-1 expression on resting NK cells, a finding verified by finding lower PD-1 transcripts in sorted NK cells compared with those in resting or activated T cells. An increase in PD-1 expression was identified on paired resting NK cells after allo-HSCT. Blockade of PD-1 on resting NK cells from healthy donors with pembrolizumab did not enhance NK function against programmed death-ligand 1 (PD-L1)-expressing tumor lines, but blocking with its scFv derivative resulted in a twofold increase in NK cell degranulation and up to a fourfold increase in cytokine production. In support of this mechanism, PD-L1 overexpression of K562 targets suppressed NK cell function. Interleukin-15 (IL-15) activity was potent and could not be further enhanced by PD-1 blockade. A similar increase in function was observed with scFv PD-1 blockade on resting blood NK cells after allo-HSCT. We identify the functional importance of the PD-1/PD-L1 axis on human NK cells in which blockade or activation to overcome inhibition will enhance NK cell-mediated antitumor control.

B Cell Activation and Escape of Tolerance Checkpoints: Recent Insights from Studying Autoreactive B Cells

Autoreactive B cells are key drivers of pathogenic processes in autoimmune diseases by the production of autoantibodies, secretion of cytokines, and presentation of autoantigens to T cells. However, the mechanisms that underlie the development of autoreactive B cells are not well understood. Here, we review recent studies leveraging novel techniques to identify and characterize (auto)antigen-specific B cells. The insights gained from such studies pertaining to the mechanisms involved in the escape of tolerance checkpoints and the activation of autoreactive B cells are discussed. In addition, we briefly highlight potential therapeutic strategies to target and eliminate autoreactive B cells in autoimmune diseases.