The Emerging Importance of IgG Fab Glycosylation in Immunity

A Novel, Site-Specific N-Linked Glycosylation Model Provides Mechanistic Insights Into the Process-Condition Dependent Distinct Fab and Fc Glycosylation of an IgG1 Monoclonal Antibody Produced by CHO VRC01 Cells

The CHO VRC01 cell line produces an anti-HIV IgG1 monoclonal antibody containing N-linked glycans on both the Fab (variable) and Fc (constant) regions. Site-specific glycan analysis was used to measure the complex effects of cell culture process conditions on Fab and Fc glycosylation. Experimental data revealed major differences in glycan fractions across the two sites. Bioreactor pH was found to influence fucosylation, galactosylation, and sialylation in the Fab region and galactosylation in the Fc region. To understand the complex effects of process conditions on site-specific N-linked glycosylation, a kinetic model of site-specific N-linked glycosylation was developed. The model parameters provided mechanistic insights into the differences in glycan fractions observed in the Fc and Fab regions. Enzyme activities calculated from the model provided insights into the effect of bioreactor pH on site-specific N-linked glycosylation. Model predictions were experimentally tested by measuring glycosyltransferase-enzyme mRNA-levels and intracellular nucleotide sugar concentrations. The model was used to demonstrate the effect of increasing galactosyltransferase activity on site-specific N-linked glycan fractions. Experiments involving galactose and MnCl2 supplementation were used to test model predictions. The model is capable of providing insights into experimentally measured data and also of making predictions that can be used to design media supplementation strategies.

Variable domain glycosylation as a marker and modulator of immune responses: Insights into autoimmunity and B-cell malignancies

Glycosylation of antibodies is essential for shaping immune responses, as it contributes significantly to antibody function and diversity. While immunoglobulin G (IgG) Fc glycosylation is well-characterized, variable domain glycosylation (VDG) introduces an additional and less understood layer of complexity. Notably, VDG is associated with rheumatoid arthritis, where disease-specific IgG autoantibodies abundantly express this modification. Moreover, its presence on these antibodies correlates with disease progression in at-risk individuals and therapeutic outcomes. Emerging evidence links increased VDG levels to other autoimmune diseases and B-cell malignancies, highlighting its potential as both a marker and modulator in disease onset and progression. Importantly, VDG on IgG is now recognized to influence antigen binding, enhance antibody stability, and modulate interactions with the human neonatal Fc receptor. In addition, glycans in the antigen-binding domains of autoreactive B-cell receptors (BCRs) can significantly impact B cell activation. In follicular lymphoma and other B-cell malignancies, the presence of N-glycosylation sites in the immunoglobulin variable domains leads to the introduction of oligomannose glycans, which are postulated to bind to mannose-specific lectins. This interaction might promote antigen-independent activation of BCRs, thereby supporting malignant B cell survival and proliferation. Here, we explore the regulatory pathways of VDG and its functional roles across both physiological and pathological conditions, underscoring its prevalence and significance in various autoimmune diseases and B-cell malignancies. Ultimately, advancing our understanding of the regulatory factors influencing VDG and its functional implications could be highly rewarding for identifying potential therapeutic targets and strategies to prevent and treat autoimmune diseases and B-cell malignancies.

Humoral immune response to 10-valent pneumococcal conjugate vaccine (PCV10) in individuals with type 2 diabetes mellitus

BACKGROUND

Pneumococcal infections pose a significant health problem in individuals with comorbid conditions such as Type 2 diabetes mellitus. Although pneumococcal vaccines are recommended in individuals with type 2 diabetes, there is a lack of data on the immunogenicity of pneumococcal vaccines in the type 2 diabetes population. This pilot study was therefore developed to determine if the humoral immune response to the 10-valent pneumococcal conjugate vaccine (PCV10) in those with and without type 2 diabetes is comparable.

METHODS

A total of 40 (24 with type 2 diabetes and 16 without type 2 diabetes) adults were immunized with PCV10. WHO reference ELISA and multiplexed opsonophagocytic killing assay (MOPA) were used to measure the concentration and functionality of serotype-specific IgG at baseline and 14 days, 1 month, and 8 months post-vaccination.

RESULTS

The geometric mean IgG concentrations and opsonic titers increased significantly in post-immunization (T1-14 days, T2-1 month, and T3-8 month) serum samples compared to baseline (T0) in individuals with and without type 2 diabetes. In both groups, the highest post-immunization IgG concentrations were measured for serotype 19F at T2. Individuals with type 2 diabetes showed significantly lower IgG concentrations and opsonic titers for serotype 19F and 9V post-immunization compared to age and sex-matched non-diabetes individuals. Serotype-specific IgG concentrations declined rapidly in those with type 2 diabetes at 8 months post-immunization. Obese diabetes individuals had lower IgG concentrations compared to non-Obese individuals with type 2 diabetes.

CONCLUSION

Individuals with type 2 diabetes demonstrated a significant protective humoral immune response to the 10-valent pneumococcal conjugate vaccine (PCV10); however, the response was comparatively less robust and declined faster in those with type 2 diabetes compared to age and sex-matched non-diabetes controls.

Role of Antibody Glycosylation in Health, Disease, and Therapy

Immunoglobulin G (IgG) antibodies are an essential component of humoral immunity protecting the host from recurrent infections. Among all antibody isotypes, IgG antibodies have a uniquely long half-life, can basically reach any tissue in the body, and have the ability to kill opsonized target cells, which has made them the molecule of choice for therapeutic interventions in cancer and autoimmunity. Moreover, IgG antibodies in the form of pooled serum IgG preparations from healthy donors are used to treat chronic inflammatory and autoimmune diseases, providing evidence that serum IgG antibodies can have an active immunomodulatory activity. Research over the last two decades has established that the single sugar moiety attached to each IgG heavy chain plays a very important role in modulating the pro- and anti-inflammatory activities of IgG. Moreover, specific sugar moieties such as sialic acid and galactose residues can serve as highly specific biomarkers for ongoing inflammatory processes. This chapter will summarize how different sugar residues in the IgG sugar moiety change upon inflammation and how such changes may translate to altered IgG function and hence maybe useful for optimizing or modulating the function of therapeutic antibodies.

New insights into antibody structure with implications for specificity, variable region restriction and isotype choice

The mystery surrounding the mechanisms by which antibody diversity is generated was largely settled in the 1970s by the discoveries of variable gene rearrangements and somatic hypermutation. This led to the paradigm that immunoglobulins are composed of two independent domains - variable and constant - that confer specificity and effector functions, respectively. However, since these early discoveries, there have been a series of observations of communication between the variable and constant domains that affects the overall antibody structure, which suggests that immunoglobulins have a more complex, interconnected functionality than previously thought. Another unresolved issue has been the genesis of 'restricted' antibody responses, characterized by the use of only a few variable region gene segments, despite the enormous potential combinatorial diversity. In this Perspective, we place recent findings related to immunoglobulin structure and function in the context of these immunologically important, historically unsolved problems to propose a new model for how antibody specificity is achieved without autoreactivity.

Site-specific immunoglobulin G N-glycosylation is associated with gastric cancer progression

BACKGROUND

The relationship between cancer development and alterations in IgG N-glycosylation has been well-established. However, comprehensive profiling of the N-glycome and N-glycoproteome in gastric cancer (GC) remains limited. Furthermore, the prognostic potential of IgG N-glycan patterns in identifying precursors to GC has yet to be fully elucidated.

METHODS

The IgG N-glycome in GC was characterized using a custom high-throughput orthogonal mass spectrometry approach. Multivariate analysis was employed to identify and assess glycomic alterations. A comprehensive bioinformatics analysis was also conducted to investigate the differential expression of N-glycosylation-related genes and their potential roles in GC pathogenesis. Additionally, interleukin-11 (IL-11) levels were quantified using a standardized enzyme-linked immunosorbent assay (ELISA).

RESULTS

Galactosylation and sialylation of IgG decreased mainly in the IgG1 and IgG2 subclasses in GC, with subclass-specific changes in IgG3 and IgG4 galactosylation. These glycan modifications were represented by unique glycopeptides (IgG1_H5N5, IgG2_H4N3F1, IgG2_H4N4, IgG2_H4N4F1S1, IgG3/4_H4N4F1, IgG3/4_H4N4F1S1), which outperformed CA72-4 for GC diagnosis. Analysis of key glycogenes revealed differential expression patterns, implicating a functional role for IgG N-glycosylation in GC. Notably, the abundance of specific IgG glycosylation exhibited a significant correlation with serum level of IL-11.

CONCLUSIONS

Alterations in subclass-specific IgG N-glycosylation represent promising biomarkers for the detection and monitoring of GC progression, potentially influenced by cytokine-driven inflammation. Understanding these changes could improve our knowledge of molecular mechanisms, aiding in diagnostic improvements and therapeutic development.

Escherichia coli and Pichia pastoris: microbial cell-factory platform for -full-length IgG production

Owing to the unmet demand, the pharmaceutical industry is investigating an alternative host to mammalian cells to produce antibodies for a variety of therapeutic and research applications. Regardless of some disadvantages, Escherichia coli and Pichia pastoris are the preferred microbial hosts for antibody production. Despite the fact that the production of full-length antibodies has been successfully demonstrated in E. coli, which has mostly been used to produce antibody fragments, such as: antigen-binding fragments (Fab), single-chain fragment variable (scFv), and nanobodies. In contrast, Pichia, a eukaryotic microbial host, is mostly used to produce glycosylated full-length antibodies, though hypermannosylated glycan is a major challenge. Advanced strategies, such as the introduction of human-like glycosylation in endotoxin-edited E. coli and cell-free system-based glycosylation, are making progress in creating human-like glycosylation profiles of antibodies in these microbes. This review begins by explaining the structural and functional requirements of antibodies and continues by describing and analyzing the potential of E. coli and P. pastoris as hosts for providing a favorable environment to create a fully functional antibody. In addition, authors compare these microbes on certain features and predict their future in antibody production. Briefly, this review analyzes, compares, and highlights E. coli and P. pastoris as potential hosts for antibody production.

GRP78 as a potential therapeutic target in cancer treatment: an updated review of its role in chemoradiotherapy resistance of cancer cells

GRP78 (Glucose-related protein 78, BiP/HSPA5) is commonly overexpressed in cancer cells. Acting as an activator of endoplasmic reticulum stress, GRP78 is involved in the resistance of cancer cells to injury. Current evidence suggests that GRP78 plays a significant role in the radiotherapy resistance and chemotherapy resistance of cancers, which is accomplished through a variety of complex pathways. These include the promotion of tumor stemness, inhibition of apoptosis, regulation of autophagy, maintenance of tumor microenvironment homeostasis, protection of dormant cells, evasion of senescence, counteraction of autoantibodies against GRP78, facilitation of DNA damage repair, suppression of ferroptosis, and modulation of metabolic reprogramming in tumor cells. Importantly, chemoradiotherapy resistance in cancers are the main reasons for treatment failure in patients, severely affecting their survival. Investigating the mechanisms of GRP78 in tumor therapeutic resistance is essential. In this article, we review the mechanisms by which GRP78 mediates cell survival and chemoradiotherapy resistance in cancers and provide an overview of clinical trials targeting GRP78 therapy.

Developing a Label-Free Infrared Spectroscopic Analysis with Chemometrics and Computational Enhancement for Assessing Lupus Nephritis Activity

Patterns of disease and therapeutic responses vary widely among patients with autoimmune glomerulonephritis. This study introduces groundbreaking personalized infrared (IR)-based diagnostics for real-time monitoring of disease status and treatment responses in lupus nephritis (LN). We have established a relative absorption difference (RAD) equation to assess characteristic spectral indices based on the temporal peak heights (PHs) of two characteristic serum absorption bands: ν1 as the target signal and ν2 as the PH reference for the ν1 absorption band, measured at each dehydration time (t) during dehydration. The RAD gap (Ψ), defined as the difference in the RAD values between the initial and final stages of serum dehydration, enables the measurement of serum levels of IgG glycosylation (ν1 (1030 cm-1), ν2 (1171 cm-1)), serum lactate (ν1 (1021 cm-1), ν2 (1171 cm-1)), serum hydrophobicity (ν1 (2930 cm-1), ν2 (2960 cm-1)), serum hydrophilicity (ν1 (1550 cm-1), ν2 (1650 cm-1)), and albumin (ν1 (1400 cm-1), ν2 (1450 cm-1)). Furthermore, this IR-based assay incorporates an innovative algorithm and our proprietary iPath software (ver. 1.0), which calculates the prognosis prediction function (PPF, Φ) from the RAD gaps of five spectral markers and correlates these with conventional clinical renal biomarkers. We propose that this algorithm-assisted, IR-based approach can augment the patient-centric care of LN patients, particularly by focusing on changes in serum IgG glycosylation.

B Cell Responses to the Placenta and Fetus

Pregnancy has fascinated immunologists ever since Peter Medawar's observation that reproduction runs contrary to the founding tenets of immunology. During healthy pregnancy, maternal B cells interact with antigens of the foreign conceptus (placenta and fetus) yet do not elicit rejection. Instead, robust and redundant fetomaternal tolerance pathways generally prevent maternal B cells and antibodies from harming the placenta and fetus. Fetomaternal tolerance is not absolute, and unfortunately there exist several pregnancy complications that arise from breaks therein. Here, important historic and recent developments in the field of fetomaternal tolerance pertaining to maternal B cells and antibodies are reviewed. General rules from which to conceptualize humoral tolerance to the placenta and fetus are proposed. Significant but underexplored ideas are highlighted and topics for future research are suggested, findings from which are predicted to provide insight into the fundamental nature of tolerance and bolster efforts to combat immune-mediated pregnancy complications.

Flux balance analysis and peptide mapping elucidate the impact of bioreactor pH on Chinese hamster ovary (CHO) cell metabolism and N-linked glycosylation in the fab and Fc regions of the produced IgG

Culture conditions have a profound impact on therapeutic protein production and glycosylation, a critical therapeutic-quality attribute, especially for monoclonal antibodies (mAbs). While the critical culture parameter of pH has been known since the early 1990s to affect protein glycosylation and production, detailed glycan and metabolic characterization and mechanistic understanding are critically lacking. Here, Chinese Hamster Ovary (CHO) cells were grown in bioreactors at pH 6.75, 7, and 7.25 (± 0.03) to examine how pH affects cell metabolism and site-specific N-linked glycosylation of the produced broadly neutralizing anti-HIV IgG1 mAb. VRC01 has N-linked glycosylation sites in both the Fc region and the Fab region, a situation not previously examined with respect to mAb glycosylation as affected by culture conditions. Using parsimonious Flux Balance Analysis (pFBA) and Flux Variability Analysis (FVA), we dissect and quantitate the impact of pH on cell growth, glucose/lactate metabolism, accumulation of the toxic metabolite ammonia, IgG production rates, and nonessential amino acid metabolism. pFBA revealed that beyond the established mechanism of glutamine conversion to glutamate, ammonia is also produced by the reaction converting serine to pyruvate, especially in the later phases of culture. pFBA also provided insights into the switch from ammonia production to consumption, notably due to depletion of glutamine, and consumption of glutamate and aspartate. We document that culture duration and pH alter the complex bimodal patterns (production/uptake) of several essential and non-essential amino acids. Site-specific N-linked glycan analysis using glycopeptide mapping demonstrated that pH significantly affects the glycosylation profiles of the two IgG1 sites. Fc region glycans were completely fucosylated but did not contain any sialylation. The Fab region glycans were not completely fucosylated but contained sialylated glycans. Bioreactor pH affected both the fucosylation and sialylation indexes in the Fab region and the galactosylation index of the Fc region. However, fucosylation in the Fc region was unaffected thus demonstrating that the effect of pH on site-specific N-linked glycosylation is complex.

Antibodies disrupt bacterial adhesion by ligand mimicry and allosteric interference

A critical step in infections is the attachment of many microorganisms to host cells using lectins that bind surface glycans, making lectins promising antimicrobial targets. Upon binding mannosylated glycans, FimH, the most studied lectin adhesin of type 1 fimbriae in E. coli, undergoes an allosteric transition from an inactive to an active conformation that can act as a catch-bond. Monoclonal antibodies that alter FimH glycan binding in various ways are available, but the mechanisms of these antibodies remain unclear. Here, we use cryoEM, mass spectrometry, binding assays, and molecular dynamics simulations to determine the structure-function relationships underlying antibody-FimH binding. Our study reveals four distinct antibody mechanisms of action: ligand mimicry by an N-linked, high-mannose glycan; stabilization of the ligand pocket in the inactive state; conformational trapping of the active and inactive states; and locking of the ligand pocket through long-range allosteric effects. These structures reveal multiple mechanisms of antibody responses to an allosteric protein and provide blueprints for new antimicrobial that target adhesins.

IgG Glycosylation: Biomarker, Functional Modulator, and Structural Component

The family of IgG Abs is a crucial component of adaptive immunity. Glycosylation of IgG maintains its structural integrity and modulates its effector functions. In this review, we discuss IgG glycosylation covering cell biological as well as therapeutic and disease-related aspects, focusing on the glycan structures in distinct IgG regions (Fab versus Fc). We also cover the impact of IgG glycosylation on disease modulation and therapeutic outcomes, alongside the potential for development of vaccines designed to induce Ag-specific IgG with glycoforms for optimal immune responses. Overall, we emphasize the significance of studying glycosylation to enhance our understanding of the dynamics and functional impacts of IgG glycosylation. These insights could be beneficial for advancing future research and clinical applications.

Predicting Structural Consequences of Antibody Light Chain N-Glycosylation in AL Amyloidosis

Background/Objectives: Antibody light chains form amyloid fibrils that lead to progressive tissue damage in amyloid light chain (AL) amyloidosis. The properties of each patient's unique light chain appear to determine its propensity to form amyloid. One factor is N-glycosylation, which is more frequent in amyloid-associated light chains than in light chains from the normal immune repertoire. However, the mechanisms underlying this association are unknown. Here, we investigate the frequency and position within the light chain sequence of the N-glycosylation sequence motif, or sequon. Methods: Monoclonal light chains from AL amyloidosis and multiple myeloma were identified from the AL-Base repository. Polyclonal light chains were obtained from the Observed Antibody Space resource. We compared the fraction of light chains from each group harboring an N-glycosylation sequon, and the positions of these sequons within the sequences. Results: Sequons are enriched among AL-associated light chains derived from a subset of precursor germline genes. Sequons are observed at multiple positions, which differ between the two types of light chains, κ and λ, but are similar between light chains from AL amyloidosis and multiple myeloma. Positions of sequons map to residues with surface-exposed sidechains that are compatible with the folded structures of light chains. Within the known structures of λ AL amyloid fibrils, many residues where sequons are observed are buried, inconsistent with N-glycosylation. Conclusions: There is no clear structural rationale for why N-glycosylation of κ light chains is associated with AL amyloidosis. A better understanding of the roles of N-glycosylation in AL amyloidosis is required before it can be used as a marker for disease risk.

Potent neutralization by a RBD antibody with broad specificity for SARS-CoV-2 JN.1 and other variants

SARS-CoV-2 continues to be a public health burden, driven in-part by its continued antigenic diversification and resulting emergence of new variants. By increasing herd immunity, current vaccines have improved infection outcomes for many. However, prophylactic and treatment interventions that are not compromised by viral evolution of the Spike protein are still needed. Using a differential staining strategy with a rationally designed SARS-CoV-2 Receptor Binding Domain (RBD) - ACE2 fusion protein and a native Omicron RBD protein, we developed a recombinant human monoclonal antibody (hmAb) from a convalescent individual following SARS-CoV-2 Omicron infection. The resulting hmAb, 1301B7 potently neutralized a wide range of SARS-CoV-2 variants including the original Wuhan-1, the more recent Omicron JN.1 strain, and SARS-CoV. 1301B7 contacts the ACE2 binding site of RBD exclusively through its VH1-69 heavy chain. Broad specificity is achieved through 1301B7 binding to many conserved residues of Omicron variants including Y501 and H505. Consistent with its extensive binding epitope, 1301B7 is able to potently diminish viral burden in the upper and lower respiratory tract and protect mice from challenge with Omicron XBB1.5 and Omicron JN.1 viruses. These results suggest 1301B7 has broad potential to prevent or treat clinical SARS-CoV-2 infections and to guide development of RBD-based universal SARS-CoV-2 prophylactic vaccines and therapeutic approaches.

The importance of IgG glycosylation-What did we learn after analyzing over 100,000 individuals

All four subclasses of immunoglobulin G (IgG) antibodies have glycan structures attached to the protein part of the IgG molecules. Glycans linked to the Fc portion of IgG are found in all IgG antibodies, while about one-fifth of IgG antibodies in plasma also have glycans attached to the Fab portion of IgG. The IgG3 subclass is characterized by more complex glycosylation compared to other IgG subclasses. In this review, we discuss the significant influence that glycans exert on the structural and functional properties of IgG. We provide a comprehensive overview of how the composition of these glycans can affect IgG's effector functions by modulating its interactions with Fcγ receptors and other molecules such as the C1q component of complement, which in turn influence various immune responses triggered by IgG, including antibody-dependent cell-mediated cytotoxicity (ADCC) and complement-dependent cytotoxicity (CDC). In addition, the importance of glycans for the efficacy of therapeutics like monoclonal antibodies and intravenous immunoglobulin (IVIg) therapy is discussed. Moreover, we offer insights into IgG glycosylation characteristics and roles derived from general population, disease-specific, and interventional studies. These studies indicate that IgG glycans are important biomarkers and functional effectors in health and disease.

Pathogenic role of anti-nuclear autoantibodies in systemic sclerosis: Insights from other rheumatic diseases

Systemic sclerosis (SSc) is a severe autoimmune disease characterized by vasculopathy, fibrosis, and dysregulated immunity, with hallmark autoantibodies targeting nuclear antigens such as centromere protein (ACA) and topoisomerase I (ATA). These autoantibodies are highly prevalent and disease-specific, rarely coexisting, thus serving as crucial biomarkers for SSc diagnosis. Despite their diagnostic value, their roles in SSc pathogenesis remain unclear. This review summarizes current literature on ACA and ATA in SSc, comparing them to autoantibodies in other rheumatic diseases to elucidate their potential pathogenic roles. Similarities are drawn with anti-citrullinated protein antibodies (ACPA) in rheumatoid arthritis, particularly regarding disease specificity and minimal pathogenic impact of antigen binding. In addition, differences between ANA and ACPA in therapeutic responses and Fab glycosylation patterns are reviewed. While ACA and ATA are valuable for disease stratification and monitoring activity, understanding their origins and the associated B cell responses is critical for advancing therapeutic strategies for SSc.

The role of antibody glycosylation in autoimmune and alloimmune kidney diseases

Immunoglobulin glycosylation is a pivotal mechanism that drives the diversification of antibody functions. The composition of the IgG glycome is influenced by environmental factors, genetic traits and inflammatory contexts. Differential IgG glycosylation has been shown to intricately modulate IgG effector functions and has a role in the initiation and progression of various diseases. Analysis of IgG glycosylation is therefore a promising tool for predicting disease severity. Several autoimmune and alloimmune disorders, including critical and potentially life-threatening conditions such as systemic lupus erythematosus, anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis and antibody-mediated kidney graft rejection, are driven by immunoglobulin. In certain IgG-driven kidney diseases, including primary membranous nephropathy, IgA nephropathy and lupus nephritis, particular glycome characteristics can enhance in situ complement activation and the recruitment of innate immune cells, resulting in more severe kidney damage. Hypofucosylation, hypogalactosylation and hyposialylation are the most common IgG glycosylation traits identified in these diseases. Modulating IgG glycosylation could therefore be a promising therapeutic strategy for regulating the immune mechanisms that underlie IgG-driven kidney diseases and potentially reduce the burden of immunosuppressive drugs in affected patients.

Structural basis for inhibition of coagulation factor VIII reveals a shared antigenic hotspot on the C1 domain

BACKGROUND

Hemophilia A arises from dysfunctional or deficient coagulation factor (F)VIII and leads to inefficient fibrin clot formation and uncontrolled bleeding events. The development of antibody inhibitors is a clinical complication in hemophilia A patients receiving FVIII replacement therapy. LE2E9 is an anti-C1 domain inhibitor previously isolated from a mild/moderate hemophilia A patient and disrupts FVIII interactions with von Willebrand factor and FIXa, though the intermolecular contacts that underpin LE2E9-mediated FVIII neutralization are undefined.

OBJECTIVES

To determine the structure of the complex between FVIII and LE2E9 and characterize its mechanism of inhibition.

METHODS

FVIII was bound to the antigen binding fragment (Fab) of NB2E9, a recombinant construct of LE2E9, and its structure was determined by cryogenic electron microscopy.

RESULTS

This report communicates the 3.46 Å structure of FVIII bound to NB2E9, with its epitope comprising FVIII residues S2040 to Y2043, K2065 to W2070, and R2150 to H2155. Structural analysis reveals that the LE2E9 epitope overlaps with portions of the epitope for 2A9, a murine-derived inhibitor, suggesting that these residues represent a shared antigenic region on the C1 domain between FVIII-/- mice and hemophilia A patients. Furthermore, the FVIII:NB2E9 structure elucidates the orientation of the LE2E9 glycan, illustrating how the glycan sterically blocks interactions between the FVIII C1 domain and the von Willebrand factor D' domain. A putative model of the FVIIIa:FIXa complex suggests potential clashing between the NB2E9 glycan and FIXa light chain.

CONCLUSION

These results describe an antigenic "hotspot" on the FVIII C1 domain and provide a structural basis for engineering FVIII replacement therapeutics with reduced antigenicity.

Glycosylation in cancer as a source of biomarkers

INTRODUCTION

Glycosylation, the process of glycan synthesis and attachment to target molecules, is a crucial and common post-translational modification (PTM) in mammalian cells. It affects the protein's hydrophilicity, charge, solubility, structure, localization, function, and protection from proteolysis. Aberrant glycosylation in proteins can reveal new detection and therapeutic Glyco-biomarkers, which help to improve accurate early diagnosis and personalized treatment. This review underscores the pivotal role of glycans and glycoproteins as a source of biomarkers in human diseases, particularly cancer.

AREAS COVERED

This review delves into the implications of glycosylation, shedding light on its intricate roles in cancer-related cellular processes influencing biomarkers. It is underpinned by a thorough examination of literature up to June 2024 in PubMed, Scopus, and Google Scholar; concentrating on the terms: (Glycosylation[Title/Abstract]) OR (Glycan[Title/Abstract]) OR (glycoproteomics[Title/Abstract]) OR (Proteoglycans[Title/Abstract]) OR (Glycomarkers[Title/Abstract]) AND (Cancer[Title/Abstract]) AND ((Diagno*[Title/Abstract]) OR (Progno*[Title/Abstract])).

EXPERT OPINION

Glyco-biomarkers enhance early cancer detection, allow early intervention, and improve patient prognoses. However, the abundance and complex dynamic glycan structure may make their scientific and clinical application difficult. This exploration of glycosylation signatures in cancer biomarkers can provide a detailed view of cancer etiology and instill hope in the potential of glycosylation to revolutionize cancer research.

A Comparative Analysis of the Immunoglobulin Repertoire in Leukemia Cells and B Cells in Chinese Acute Myeloid Leukemia by High-Throughput Sequencing

It is common knowledge that immunoglobulin (Ig) is produced by B lymphocytes and mainly functions as an antibody. However, it has been shown recently that myeloblasts from acute myeloid leukemia (AML) could also express Ig and that AML-Ig played a role in leukemogenesis and AML progression. The difference between Ig from myeloblasts and B cells has not been explored. Studying the characteristics of the Ig repertoire in myeloblasts and B cells will be helpful to understand the function and significance of AML-Ig. We performed 5' RACE-related PCR coupled with PacBio sequencing to analyze the Ig repertoire in myeloblasts and B cells from Chinese AML patients. Myeloblasts expressed all five classes of IgH, especially Igγ, with a high expression frequency. Compared with B-Ig in the same patient, AML-Ig showed different biased V(D)J usages and mutation patterns. In addition, the CDR3 length distribution of AML-Ig was significantly different from those of B-Ig. More importantly, mutations of AML-IgH, especially Igμ, Igα, and Igδ, were different from that of B-IgH in each AML patient, and the mutations frequently occurred at the sites of post-translational modification. AML-Ig has distinct characteristics of variable regions and mutations, which may have implications for disease monitoring and personalized therapy.

Naturally acquired antibodies against 4 Streptococcus pneumoniae serotypes in Pakistani adults with type 2 diabetes mellitus

Immune response elicited during pneumococcal carriage has been shown to protect against subsequent colonization and infection by Streptococcus pneumoniae. The study was designed to measure the baseline serotype-specific anti-capsular IgG concentration and opsonic titers elicited in response to asymptomatic carriage in adults with and without type 2-diabetes. Level of IgG to capsular polysaccharide was measured in a total of 176 samples (124 with type 2 diabetes and 52 without type 2 diabetes) against serotype 1, 19F, 9V, and 18C. From within 176 samples, a nested cohort of 39 samples was selected for measuring the functional capacity of antibodies by measuring opsonic titer to serotypes 19F, 9V, and 18C. Next, we measured levels of IgG to PspA in 90 samples from individuals with and without diabetes (22 non-diabetes and 68 diabetes). Our results demonstrated comparable IgG titers against all serotypes between those with and without type 2-diabetes. Overall, we observed higher opsonic titers in those without diabetes as compared to individuals with diabetes for serotypes 19F and 9V. The opsonic titers for 19F and 9V significantly negatively correlated with HbA1c. For 19F, 41.66% (n = 10) showed opsonic titers ≥ 1:8 in the diabetes group as compared to 66.66% (n = 10) in the non-diabetes group. The percentage was 29.6% (n = 7) vs 66.66% (n = 10) for 9V and 70.83% (n = 17) vs 80% (n = 12) for 18C in diabetes and non-diabetes groups respectively. A comparable anti-PspA IgG (p = 0.409) was observed in those with and without diabetes, indicating that response to protein antigen is likely to remain intact in those with diabetes. In conclusion, we demonstrated comparable IgG titers to both capsular polysaccharide and protein antigens in those with and without diabetes, however, the protective capacity of antibodies differed between the two groups.

Immunoglobulin G glycosylation and its alterations in aging-related diseases

Immunoglobulin G (IgG) is an important serum glycoprotein and a major component of antibodies. Glycans on IgG affect the binding of IgG to the Fc receptor or complement C1q, which in turn affects the biological activity and biological function of IgG. Altered glycosylation patterns on IgG emerge as important biomarkers in the aging process and age-related diseases. Key aging-related alterations observed in IgG glycosylation include reductions in galactosylation and sialylation, alongside increases in agalactosylation, and bisecting GlcNAc. Understanding the role of IgG glycosylation in aging-related diseases offers insights into disease mechanisms and provides opportunities for the development of diagnostic and therapeutic strategies. This review summarizes five aspects of IgG: an overview of IgG, IgG glycosylation, IgG glycosylation with inflammation mediation, IgG glycan changes with normal aging, as well as the relevance of IgG glycan changes to aging-related diseases. This review provides a reference for further investigation of the regulatory mechanisms of IgG glycosylation in aging-related diseases, as well as for evaluating the potential of IgG glycosylation changes as markers of aging and aging-related diseases.

In silico evaluation of the role of Fab glycosylation in cetuximab antibody dynamics

Introduction

N-glycosylation is a post-translational modification that is highly important for the development of monoclonal antibodies (mAbs), as it regulates their biological activity, particularly in terms of immune effector functions. While typically added at the Fc level, approximately 15-25% of circulating antibodies exhibit glycosylation in the Fab domains as well. To the best of our knowledge, cetuximab (Erbitux®) is the only therapeutic antibody presenting Fab glycosylation approved world-wide targeting the epidermal growth factor receptor for the treatment of metastatic-colorectal and head and neck cancers. Additionally, it can trigger antibody-dependent cell cytotoxicity (ADCC), a response that typically is influenced by N-glycosylation at Fc level. However, the role of Fab glycosylation in cetuximab remains poorly understood. Hence, this study aims to investigate the structural role of Fab glycosylation on the conformational behavior of cetuximab.

Methods

The study was performed in silico via accelerated molecular dynamics simulations. The commercial cetuximab was compared to its form without Fab glycosylation and structural descriptors were evaluated to establish conformational differences.

Results

The results clearly show a correlation between the Fab glycosylation and structural descriptors that may modulate the conformational freedom of the antibody, potentially affecting Fc effector functions, and suggesting a negative role of Fab glycosylation on the interaction with FcγRIIIa.

Conclusion

Fab glycosylation of cetuximab is the most critical challenge for biosimilar development, but the differences highlighted in this work with respect to its aglycosylated form can improve the knowledge and represent also a great opportunity to develop novel strategies of biotherapeutics.

Core fucosylation within the Fc-FcγR degradation pathway promotes enhanced IgG levels via exogenous L-fucose

α1,6-Fucosyltransferase (Fut8) is the enzyme responsible for catalyzing core fucosylation. Exogenous L-fucose upregulates fucosylation levels through the GDP-fucose salvage pathway. This study investigated the relationship between core fucosylation and immunoglobulin G (IgG) amounts in serum utilizing WT (Fut8+/+), Fut8 heterozygous knockout (Fut8+/-), and Fut8 knockout (Fut8-/-) mice. The IgG levels in serum were lower in Fut8+/- and Fut8-/- mice compared with Fut8+/+ mice. Exogenous L-fucose increased IgG levels in Fut8+/- mice, while the ratios of core fucosylated IgG versus total IgG showed no significant difference among Fut8+/+, Fut8+/-, and Fut8+/- mice treated with L-fucose. These ratios were determined by Western blot, lectin blot, and mass spectrometry analysis. Real-time PCR results demonstrated that mRNA levels of IgG Fc and neonatal Fc receptor, responsible for protecting IgG turnover, were similar among Fut8+/+, Fut8+/-, and Fut8+/- mice treated with L-fucose. In contrast, the expression levels of Fc-gamma receptor Ⅳ (FcγRⅣ), mainly expressed on macrophages and neutrophils, were increased in Fut8+/- mice compared to Fut8+/+ mice. The effect was reversed by administrating L-fucose, suggesting that core fucosylation primarily regulates the IgG levels through the Fc-FcγRⅣ degradation pathway. Consistently, IgG internalization and transcytosis were suppressed in FcγRⅣ-knockout cells while enhanced in Fut8-knockout cells. Furthermore, we assessed the expression levels of specific antibodies against ovalbumin and found they were downregulated in Fut8+/- mice, with potential recovery observed with L-fucose administration. These findings confirm that core fucosylation plays a vital role in regulating IgG levels in serum, which may provide insights into a novel mechanism in adaptive immune regulation.

N-linked glycosylation of the M-protein variable region: glycoproteogenomics reveals a new layer of personalized complexity in multiple myeloma

OBJECTIVES

Multiple myeloma (MM) is a plasma cell malignancy characterized by a monoclonal expansion of plasma cells that secrete a characteristic M-protein. This M-protein is crucial for diagnosis and monitoring of MM in the blood of patients. Recent evidence has emerged suggesting that N-glycosylation of the M-protein variable (Fab) region contributes to M-protein pathogenicity, and that it is a risk factor for disease progression of plasma cell disorders. Current methodologies lack the specificity to provide a site-specific glycoprofile of the Fab regions of M-proteins. Here, we introduce a novel glycoproteogenomics method that allows detailed M-protein glycoprofiling by integrating patient specific Fab region sequences (genomics) with glycoprofiling by glycoproteomics.

METHODS

Glycoproteogenomics was used for the detailed analysis of de novo N-glycosylation sites of M-proteins. First, Genomic analysis of the M-protein variable region was used to identify de novo N-glycosylation sites. Subsequently glycopeptide analysis with LC-MS/MS was used for detailed analysis of the M-protein glycan sites.

RESULTS

Genomic analysis uncovered a more than two-fold increase in the Fab Light Chain N-glycosylation of M-proteins of patients with Multiple Myeloma compared to Fab Light Chain N-glycosylation of polyclonal antibodies from healthy individuals. Subsequent glycoproteogenomics analysis of 41 patients enrolled in the IFM 2009 clinical trial revealed that the majority of the Fab N-glycosylation sites were fully occupied with complex type glycans, distinguishable from Fc region glycans due to high levels of sialylation, fucosylation and bisecting structures.

CONCLUSIONS

Together, glycoproteogenomics is a powerful tool to study de novo Fab N-glycosylation in plasma cell dyscrasias.

The peculiar features, diversity and impact of citrulline-reactive autoantibodies

Since entering the stage 25 years ago as a highly specific serological biomarker for rheumatoid arthritis, anti-citrullinated protein antibodies (ACPAs) have been a topic of extensive research. This hallmark B cell response arises years before disease onset, displays interpatient autoantigen variability, and is associated with poor clinical outcomes. Technological and scientific advances have revealed broad clonal diversity and intriguing features including high levels of somatic hypermutation, variable-domain N-linked glycosylation, hapten-like peptide interactions, and clone-specific multireactivity to citrullinated, carbamylated and acetylated epitopes. ACPAs have been found in different isotypes and subclasses, in both circulation and tissue, and are secreted by both plasmablasts and long-lived plasma cells. Notably, although some disease-promoting features have been reported, results now demonstrate that certain monoclonal ACPAs therapeutically block arthritis and inflammation in mouse models. A wealth of functional studies using patient-derived polyclonal and monoclonal antibodies have provided evidence for pathogenic and protective effects of ACPAs in the context of arthritis. To understand the roles of ACPAs, one needs to consider their immunological properties by incorporating different facets such as rheumatoid arthritis B cell biology, environmental triggers and chronic antigen exposure. The emerging picture points to a complex role of citrulline-reactive autoantibodies, in which the diversity and dynamics of antibody clones could determine clinical progression and manifestations.

Biological Surface Layer Formation on Bioceramic Particles for Protein Adsorption

In the biomedical fields of bone regenerative therapy, the immobilization of proteins on the bioceramic particles to maintain their highly ordered structures is significantly important. In this review, we comprehensively discussed the importance of the specific surface layer, which can be called "non-apatitic layer", affecting the immobilization of proteins on particles such as hydroxyapatite and amorphous silica. It was suggested that the water molecules and ions contained in the non-apatitic layer can determine and control the protein immobilization states. In amorphous silica particles, the direct interactions between proteins and silanol groups make it difficult to immobilize the proteins and maintain their highly ordered structures. Thus, the importance of the formation of a surface layer consisting of water molecules and ions (i.e., a non-apatitic layer) on the particle surfaces for immobilizing proteins and maintaining their highly ordered structures was suggested and described. In particular, chlorine-containing amorphous silica particles were also described, which can effectively form the surface layer of protein immobilization carriers. The design of the bio-interactive and bio-compatible surfaces for protein immobilization while maintaining the highly ordered structures will improve cell adhesion and tissue formation, thereby contributing to the construction of social infrastructures to support super-aged society.

IgG sialylation occurs in B cells pre antibody secretion

Sialic acids as terminal sugar residues on cell surface or secreted proteins have many functional roles. In particular, the presence or absence of α2,6-linked sialic acid residues at the immunoglobulin G (IgG) Fc fragment can switch IgG effector functions from pro- to anti-inflammatory activity. IgG glycosylation is considered to take place inside the plasma blast/plasma cell while the molecule travels through the endoplasmic reticulum and Golgi apparatus before being secreted. However, more recent studies have suggested that IgG sialylation may occur predominantly post-antibody secretion. To what extent this extracellular IgG sialylation process contributes to overall IgG sialylation remains unclear, however. By generating bone marrow chimeric mice with a B cell-specific deletion of ST6Gal1, the key enzyme required for IgG sialylation, we now show that sialylation of the IgG Fc fragment exclusively occurs within B cells pre-IgG secretion. We further demonstrate that B cells expressing ST6Gal1 have a developmental advantage over B cells lacking ST6Gal1 expression and thus dominate the plasma cell pool and the resulting serum IgG population in mouse models in which both ST6Gal1-sufficient and -deficient B cells are present.

Control of Biological Surface States on Chlorine-Doped Amorphous Silica Particles and Their Effective Absorptive Ability for Antibody Protein

Amorphous silica particles (ASPs) have low biotoxicity and are used in foodstuffs; however, the adsorption states of proteins on their surfaces have not yet been clarified. If the adsorption states can be clarified and controlled, then a wide range of biological and medical applications can be expected. The conventional amorphous silica particles have the problem of protein adsorption due to the strong interaction with their dense silanol groups and denaturation. In this study, the surfaces of amorphous silica particles with a lower silanol group density were modified with a small amount of chlorine during the synthesis process to form a specific surface layer by adsorbing water molecules and ions in the biological fluid, thereby controlling the protein adsorption state. Specifically, the hydration state on the surface of the amorphous silica particles containing trace amounts of chlorine was evaluated, and the surface layer (especially the hydration state) for the adsorption of antibody proteins while maintaining their steric structures was evaluated and discussed. The results showed that the inclusion of trace amounts of chlorine increased the silanol groups and Si-Cl bonds in the topmost surface layer of the particles, thereby inducing the adsorption of ions and water molecules in the biological fluid. Then, it was found that a novel surface layer was formed by the effective adsorption of Na and phosphate ions, which would change the proportion of the components in the hydration layer. In particular, the proportion of the free water component increased by 21% with the doping of chlorine. Antibody proteins were effectively adsorbed on the particles doped with trace amounts of chlorine, and their steric adsorption states were evaluated. It was found that the proteins were clearly adsorbed and maintained the steric state of their secondary structure. In the immunoreactivity tests using streptavidin and biotin, biotin bound to the chlorine-doped particles showed efficient reactivity. In conclusion, this study is the first to discover the surface layer of the amorphous silica particles to maintain the steric structures of adsorbed proteins, which is expected to be used as a carrier particle for antibody test kits and immunochromatography.

Structural Characterization of a Pathogenic Antibody Underlying Vaccine-Induced Immune Thrombotic Thrombocytopenia (VITT)

Vaccine-induced immune thrombotic thrombocytopenia (VITT) is a rare but dangerous side effect of adenoviral-vectored COVID-19 vaccines. VITT had been linked to production of autoantibodies recognizing platelet factor 4 (PF4). Here, we characterize anti-PF4 antibodies obtained from a VITT patient's blood. Intact mass measurements indicate that a significant fraction of these antibodies represent a limited number of clones. MS analysis of large antibody fragments (the light chain and the Fc/2 and Fd fragments of the heavy chain) confirms the monoclonal nature of this component of the anti-PF4 antibodies repertoire and reveals the presence of a mature complex biantennary N-glycan within the Fd segment. Peptide mapping using two complementary proteases and LC-MS/MS was used to determine the amino acid sequence of the entire light chain and over 98% of the heavy chain (excluding a short N-terminal segment). The sequence analysis allows the monoclonal antibody to be assigned to the IgG2 subclass and verifies that the light chain belongs to the λ-type. Incorporation of enzymatic de-N-glycosylation into the peptide mapping routine allows the N-glycan in the Fab region of the antibody to be localized to the framework 3 region of the VH domain. This novel N-glycosylation site is the result of a single mutation within the germline sequence. Peptide mapping also provides information on lower-abundance (polyclonal) components of the anti-PF4 antibody ensemble, revealing the presence of all four subclasses (IgG1-IgG4) and both types of the light chain (λ and κ). This case study demonstrates the power of combining the intact, middle-down, and bottom-up MS approaches for meaningful characterization of ultralow quantities of pathogenic antibodies extracted directly from patients' blood.

Changes in the N-glycosylation of porcine immune globulin G during postnatal development

N-glycosylation influences the effectiveness of immune globulin G (IgG) and thus the immunological downstream responses of immune cells. This impact arises from the presence of N-glycans within the Fc region, which not only alters the conformation of IgG but also influences its steric hindrance. Consequently, these modifications affect the interaction between IgG and its binding partners within the immune system. Moreover, this posttranslational modification vary according to the physiological condition of each individual. In this study, we examined the N-glycosylation of IgG in pigs from birth to five months of age. Our analysis identified a total of 48 distinct N-glycan structures. Remarkably, we observed defined changes in the composition of these N-glycans during postnatal development. The presence of agalactosylated and sialylated structures increases in relation to the number of N-glycans terminated by galactose residues during the first months of life. This shift may indicate a transition from passively transferred antibodies from the colostrum of the sow to the active production of endogenous IgG by the pig's own immune system.

Development and validation of online SPE purification coupled to HILIC-fluorescence-MS analysis for the characterization of N-glycans

N-glycans of therapeutic glycoproteins is a critical quality attribute to be addressed. We developed a sensitive method for N-glycan characterization using procainamide (ProcA) labelling and online solid phase extraction (online SPE). N-glycans were enzymatically released, then labeled with ProcA and cleaned up via the online SPE using HILIC chemistry (online HILIC SPE). Two preparation protocols were optimized: a short one (1 h 30) and a long one (18 h). Furthermore, the developed approach was compared to RapiFluor-MS (RFMS) kit (from Waters) and to InstantPC kit (from Agilent) which both include a classical HILIC μElution plate SPE purification. Samples were analyzed using HILIC separation coupled to fluorescence and MS detection (HILIC-FLD-MS) with or without the online HILIC SPE. During the validation, repeatability, intermediate precision, stability, response function and injection volume were tested. Human IgG mix (Multigam®) and NIST mAb standard were used as references as their glycoprofiles are well described. A comparison of three batches of a rituximab biosimilar (Truxima®) and one batch of its originator (MabThera®) was also performed. Online HILIC SPE sample cleanup shows a higher sensitivity and repeatability compared to the classical HILIC μElution SPE. Our online HILIC SPE approach also offers the highest MS signal compared to both commercial kits. However, InstantPC shows the highest FLD signal. The analyses of rituximab samples were in line with the literature showing the efficiency of the method for N-glycan monitoring of biotherapeutics. In conclusion, the results demonstrated the usefulness and ease of application of the developed protocol with the online HILIC SPE purification.

Sugar-coated bullets: Unveiling the enigmatic mystery 'sweet arsenal' in osteoarthritis

Glycosylation is a crucial post-translational modification process where sugar molecules (glycans) are covalently linked to proteins, lipids, or other biomolecules. In this highly regulated and complex process, a series of enzymes are involved in adding, modifying, or removing sugar residues. This process plays a pivotal role in various biological functions, influencing the structure, stability, and functionality of the modified molecules. Glycosylation is essential in numerous biological processes, including cell adhesion, signal transduction, immune response, and biomolecular recognition. Dysregulation of glycosylation is associated with various diseases. Glycation, a post-translational modification characterized by the non-enzymatic attachment of sugar molecules to proteins, has also emerged as a crucial factor in various diseases. This review comprehensively explores the multifaceted role of glycation in disease pathogenesis, with a specific focus on its implications in osteoarthritis (OA). Glycosylation and glycation alterations wield a profound influence on OA pathogenesis, intertwining with disease onset and progression. Diverse studies underscore the multifaceted role of aberrant glycosylation in OA, particularly emphasizing its intricate relationship with joint tissue degradation and inflammatory cascades. Distinct glycosylation patterns, including N-glycans and O-glycans, showcase correlations with inflammatory cytokines, matrix metalloproteinases, and cellular senescence pathways, amplifying the degenerative processes within cartilage. Furthermore, the impact of advanced glycation end-products (AGEs) formation in OA pathophysiology unveils critical insights into glycosylation-driven chondrocyte behavior and extracellular matrix remodeling. These findings illuminate potential therapeutic targets and diagnostic markers, signaling a promising avenue for targeted interventions in OA management. In this comprehensive review, we aim to thoroughly examine the significant impact of glycosylation or AGEs in OA and explore its varied effects on other related conditions, such as liver-related diseases, immune system disorders, and cancers, among others. By emphasizing glycosylation's role beyond OA and its implications in other diseases, we uncover insights that extend beyond the immediate focus on OA, potentially revealing novel perspectives for diagnosing and treating OA.

Genetic insights into across pancreatitis types: the causal influence of immunoglobulin G N-glycosylation variants on disease risk

Background

While a few case-control studies indicated a possible correlation of IgG N-glycosylation patterns with pancreatitis, their restricted sample sizes and methodologies prevented conclusive insights into causality or distinguishing traits across pancreatitis types.

Method

We conducted a two-sample Mendelian Randomization (MR) analysis to investigate the causal relationship between 77 IgG N-glycosylation traits and various types of pancreatitis, including acute pancreatitis (AP), chronic pancreatitis (CP), alcohol acute pancreatitis (AAP), and alcohol chronic pancreatitis (ACP). This analysis utilized summary-level data from genome-wide association studies (GWAS), employing methods such as IVW, MR-Egger, and weighted median. To ensure the robustness of our findings, several sensitivity analyses, including Cochran's Q statistic, leave-one-out, MR-Egger intercept, and MR-PRESSO global test were conducted.

Result

Our study uncovered the causal relationship between specific IgG N-glycosylation traits and various types of pancreatitis. Notably, an increase in genetically predicted IGP7 levels was associated with a decreased risk of developing AP. For CP, our data suggested a protective effect associated with higher levels of both IGP7 and IGP31, contrasting with increased levels of IGP27 and IGP65, which were linked to a heightened risk. Moreover, in the case of AAP, elevated IGP31 levels were causatively associated with a lower incidence, while higher IGP26 levels correlated with an increased risk for ACP.

Conclusion

This study establishes causal relationship between specific IgG N-glycosylation patterns and varying risks of different pancreatitis forms, underscoring their potential as predictive biomarkers. These findings necessitate further exploration into the underlying mechanisms, promising to inform more personalized diagnostic and therapeutic strategies in pancreatitis management.

A monoclonal antibody targeting a large surface of the receptor binding motif shows pan-neutralizing SARS-CoV-2 activity

Here we report the characterization of 17T2, a SARS-CoV-2 pan-neutralizing human monoclonal antibody isolated from a COVID-19 convalescent individual infected during the first pandemic wave. 17T2 is a class 1 VH1-58/κ3-20 antibody, derived from a receptor binding domain (RBD)-specific IgA+ memory B cell, with a broad neutralizing activity against former and new SARS-CoV-2 variants, including XBB.1.16 and BA.2.86 Omicron subvariants. Consistently, 17T2 demonstrates in vivo prophylactic and therapeutic activity against Omicron BA.1.1 infection in K18-hACE2 mice. Cryo-electron microscopy reconstruction shows that 17T2 binds the BA.1 spike with the RBD in "up" position and blocks the receptor binding motif, as other structurally similar antibodies do, including S2E12. Yet, unlike S2E12, 17T2 retains its neutralizing activity against all variants tested, probably due to a larger RBD contact area. These results highlight the impact of small structural antibody changes on neutralizing performance and identify 17T2 as a potential candidate for future clinical interventions.

Anastrozole and Tamoxifen Impact on IgG Glycome Composition Dynamics in Luminal A and Luminal B Breast Cancers

This study examines the intricate relationship between protein glycosylation dynamics and therapeutic responses in Luminal A and Luminal B breast cancer subtypes, focusing on anastrozole and tamoxifen impacts. The present methods inadequately monitor and forecast patient reactions to these treatments, leaving individuals vulnerable to the potential adverse effects of these medications. This research investigated glycan structural changes by following patients for up to 9 months. The protocol involved a series of automated steps including IgG isolation, protein denaturation, glycan labelling, purification, and final analysis using capillary gel electrophoresis with laser-induced fluorescence. The results suggested the significant role of glycan modifications in breast cancer progression, revealing distinctive trends in how anastrozole and tamoxifen elicit varied responses. The findings indicate anastrozole's association with reduced sialylation and increased core fucosylation, while tamoxifen correlated with increased sialylation and decreased core fucosylation. These observations suggest potential immunomodulatory effects: anastrozole possibly reducing inflammation and tamoxifen impacting immune-mediated cytotoxicity. This study strongly emphasizes the importance of considering specific glycan traits to comprehend the dynamic mechanisms driving breast cancer progression and the effects of targeted therapies. The nuanced differences observed in glycan modifications between these two treatments underscore the necessity for further comprehensive research aimed at thoroughly evaluating the long-term implications and therapeutic efficacy for breast cancer patients.

Unveiling the multifaceted landscape of N-glycosylation in antibody variable domains: Insights and implications

N-glycosylation at the antibody variable domain has emerged as an important modification influencing antibody function. Despite its significance, information regarding its role and regulation remains limited. To address this gap, we comprehensively explored antibody structures housing N-glycosylation within the Protein Data Bank, yielding fresh insights into this intricate landscape. Our findings revealed that among 208 structures, N-glycosylation was more prevalent in human and mouse antibodies containing IGHV1-8 and IGHV2-2 germline genes, respectively. Moreover, our research highlights the potential for somatic hypermutation to introduce N-glycosylation sites by substituting polar residues (Ser or Thr) in germline variable genes with asparagine. Notably, our study underscores the prevalence of N-glycosylation in antiviral antibodies, especially anti-HIV. Besides antigen-antibody interaction, our findings suggest that N-glycosylation may impact antibody specificity, affinity, and avidity by influencing Fab dimer formation and complementary-determining region orientation. We also identified different glycan structures in HIV and SARS-CoV-2 antibody proteomic datasets, highlighting disparities from the N-glycan structures between PDB antibodies and biological repertoires further highlighting the complexity of N-glycosylation patterns. Our findings significantly enrich our understanding of the N-glycosylation's multifaceted characteristics within the antibody variable domain. Additionally, they underscore the pressing imperative for a more comprehensive characterization of its impact on antibody function.

A novel Fc-engineered cathepsin D-targeting antibody enhances ADCC, triggers tumor-infiltrating NK cell recruitment, and improves treatment with paclitaxel and enzalutamide in triple-negative breast cancer

INTRODUCTION

Triple-negative breast cancer (TNBC) prognosis is poor. Immunotherapies to enhance the antibody-induced natural killer (NK) cell antitumor activity are emerging for TNBC that is frequently immunogenic. The aspartic protease cathepsin D (cath-D), a tumor cell-associated extracellular protein with protumor activity and a poor prognosis marker in TNBC, is a prime target for antibody-based therapy to induce NK cell-mediated antibody-dependent cellular cytotoxicity (ADCC). This study investigated whether Fc-engineered anti-cath-D antibodies trigger ADCC, their impact on antitumor efficacy and tumor-infiltrating NK cells, and their relevance for combinatory therapy in TNBC.

METHODS

Cath-D expression and localization in TNBC samples were evaluated by western blotting, immunofluorescence, and immunohistochemistry. The binding of human anti-cath-D F1M1 and Fc-engineered antibody variants, which enhance (F1M1-Fc+) or prevent (F1M1-Fc-) affinity for CD16a, to secreted human and murine cath-D was analyzed by ELISA, and to CD16a by surface plasmon resonance and flow cytometry. NK cell activation was investigated by flow cytometry, and ADCC by lactate dehydrogenase release. The antitumor efficacy of F1M1 Fc-variants was investigated using TNBC cell xenografts in nude mice. NK cell recruitment, activation, and cytotoxic activity were analyzed in MDA-MB-231 cell xenografts by immunophenotyping and RT-qPCR. NK cells were depleted using an anti-asialo GM1 antibody. F1M1-Fc+ antitumor effect was assessed in TNBC patient-derived xenografts (PDXs) and TNBC SUM159 cell xenografts, and in combination with paclitaxel or enzalutamide.

RESULTS

Cath-D expression on the TNBC cell surface could be exploited to induce ADCC. F1M1 Fc-variants recognized human and mouse cath-D. F1M1-Fc+ activated NK cells in vitro and induced ADCC against TNBC cells and cancer-associated fibroblasts more efficiently than F1M1. F1M1-Fc- was ineffective. In the MDA-MB-231 cell xenograft model, F1M1-Fc+ displayed higher antitumor activity than F1M1, whereas F1M1-Fc- was less effective, reflecting the importance of Fc-dependent mechanisms in vivo. F1M1-Fc+ triggered tumor-infiltrating NK cell recruitment, activation and cytotoxic activity in MDA-MB-231 cell xenografts. NK cell depletion impaired F1M1-Fc+ antitumor activity, demonstrating their key role. F1M1-Fc+ inhibited growth of SUM159 cell xenografts and two TNBC PDXs. In combination therapy, F1M1-Fc+ improved paclitaxel and enzalutamide therapeutic efficacy without toxicity.

CONCLUSIONS

F1M1-Fc+ is a promising immunotherapy for TNBC that could be combined with conventional regimens, including chemotherapy or antiandrogens.

The functional roles of protein glycosylation in human maternal-fetal crosstalk

BACKGROUND

The establishment of maternal-fetal crosstalk is vital to a successful pregnancy. Glycosylation is a post-translational modification in which glycans (monosaccharide chains) are attached to an organic molecule. Glycans are involved in many physiological and pathological processes. Human endometrial epithelium, endometrial gland secretions, decidual immune cells, and trophoblasts are highly enriched with glycoconjugates and glycan-binding molecules important for a healthy pregnancy. Aberrant glycosylation in the placenta and uterus has been linked to repeated implantation failure and various pregnancy complications, but there is no recent review summarizing the functional roles of glycosylation at the maternal-fetal interface and their associations with pathological processes.

OBJECTIVE AND RATIONALE

This review aims to summarize recent findings on glycosylation, glycosyltransferases, and glycan-binding receptors at the maternal-fetal interface, and their involvement in regulating the biology and pathological conditions associated with endometrial receptivity, placentation and maternal-fetal immunotolerance. Current knowledge limitations and future insights into the study of glycobiology in reproduction are discussed.

SEARCH METHODS

A comprehensive PubMed search was conducted using the following keywords: glycosylation, glycosyltransferases, glycan-binding proteins, endometrium, trophoblasts, maternal-fetal immunotolerance, siglec, selectin, galectin, repeated implantation failure, early pregnancy loss, recurrent pregnancy loss, preeclampsia, and fetal growth restriction. Relevant reports published between 1980 and 2023 and studies related to these reports were retrieved and reviewed. Only publications written in English were included.

OUTCOMES

The application of ultrasensitive mass spectrometry tools and lectin-based glycan profiling has enabled characterization of glycans present at the maternal-fetal interface and in maternal serum. The endometrial luminal epithelium is covered with highly glycosylated mucin that regulates blastocyst adhesion during implantation. In the placenta, fucose and sialic acid residues are abundantly presented on the villous membrane and are essential for proper placentation and establishment of maternal-fetal immunotolerance. Glycan-binding receptors, including selectins, sialic-acid-binding immunoglobulin-like lectins (siglecs) and galectins, also modulate implantation, trophoblast functions and maternal-fetal immunotolerance. Aberrant glycosylation is associated with repeated implantation failure, early pregnancy loss and various pregnancy complications. The current limitation in the field is that most glycobiological research relies on association studies, with few studies revealing the specific functions of glycans. Technological advancements in analytic, synthetic and functional glycobiology have laid the groundwork for further exploration of glycans in reproductive biology under both physiological and pathological conditions.

WIDER IMPLICATIONS

A deep understanding of the functions of glycan structures would provide insights into the molecular mechanisms underlying their involvement in the physiological and pathological regulation of early pregnancy. Glycans may also potentially serve as novel early predictive markers and therapeutic targets for repeated implantation failure, pregnancy loss, and other pregnancy complications.

Comparison of Non B-Ig and B-Ig

Immunoglobulin (Ig) has been widely acknowledged to be produced solely by B-lineage cells. However, growing evidence has demonstrated the expression of Ig in an array of cancer cells, as well as normal cells including epithelial cells, epidermal cells, mesangial cells, monocytes, and neutrophils. Ig has even been found to be expressed in non-B cells at immune-privileged sites such as neurons and spermatogenic cells. Despite these non-B cell-derived Igs (non-B-Igs) sharing the same symmetric structures with conventional Igs (B-Igs), further studies have revealed unique characteristics of non-B-Ig, such as restricted variable region and aberrant glycosylation. Moreover, non-B-Ig exhibits properties of promoting malignant behaviours of cancer cells, therefore it could be utilised in the clinic as a potential therapeutic biomarker or target. The elucidation of the generation and regulation of non-B-Ig will certainly broaden our understanding of immunology.

Introduction of Carbonyl Groups into Antibodies

Antibodies and their derivatives (scFv, Fabs, etc.) represent a unique class of biomolecules that combine selectivity with the ability to target drug delivery. Currently, one of the most promising endeavors in this field is the development of molecular diagnostic tools and antibody-based therapeutic agents, including antibody-drug conjugates (ADCs). To meet this challenge, it is imperative to advance methods for modifying antibodies. A particularly promising strategy involves the introduction of carbonyl groups into the antibody that are amenable to further modification by biorthogonal reactions, namely aliphatic, aromatic, and α-oxo aldehydes, as well as aliphatic and aryl-alkyl ketones. In this review, we summarize the preparation methods and applications of site-specific antibody conjugates that are synthesized using this approach.

Anti-cathepsin D immunotherapy triggers both innate and adaptive anti-tumour immunity in breast cancer

BACKGROUND AND PURPOSE

Triple-negative breast cancer (TNBC) has poorer outcomes than other breast cancers (BC), including HER2+ BC. Cathepsin D (CathD) is a poor prognosis marker overproduced by BC cells, hypersecreted in the tumour microenvironment with tumour-promoting activity. Here, we characterized the immunomodulatory activity of the anti-CathD antibody F1 and its improved Fab-aglycosylated version (F1M1) in immunocompetent mouse models of TNBC (C57BL/6 mice harbouring E0771 cell grafts) and HER2-amplified BC (BALB/c mice harbouring TUBO cell grafts).

EXPERIMENTAL APPROACH

CathD expression was evaluated by western blotting and immunofluorescence, and antibody binding to CathD by ELISA. Antibody anti-tumour efficacy was investigated in mouse models. Immune cell recruitment and activation were assessed by immunohistochemistry, immunophenotyping, and RT-qPCR.

KEY RESULTS

F1 and F1M1 antibodies remodelled the tumour immune landscape. Both antibodies promoted innate antitumour immunity by preventing the recruitment of immunosuppressive M2-polarized tumour-associated macrophages (TAMs) and by activating natural killer cells in the tumour microenvironment of both models. This translated into a reduction of T-cell exhaustion markers in the tumour microenvironment that could be locally supported by enhanced activation of anti-tumour antigen-presenting cell (M1-polarized TAMs and cDC1 cells) functions. Both antibodies inhibited tumour growth in the highly-immunogenic E0771 model, but only marginally in the immune-excluded TUBO model, indicating that anti-CathD immunotherapy is more relevant for BC with a high immune cell infiltrate, as often observed in TNBC.

CONCLUSION AND IMPLICATION

Anti-CathD antibody-based therapy triggers the anti-tumour innate and adaptive immunity in preclinical models of BC and is a promising immunotherapy for immunogenic TNBC.

Reverse Engineering of a Pathogenic Antibody Reveals the Molecular Mechanism of Vaccine-Induced Immune Thrombotic Thrombocytopenia

The massive COVID-19 vaccine roll-out campaign illuminated a range of rare side effects, the most dangerous of which─vaccine-induced immune thrombotic thrombocytopenia (VITT)─is caused by adenoviral (Ad)-vectored vaccines. VITT occurrence had been linked to the production of pathogenic antibodies that recognize an endogenous chemokine, platelet factor 4 (PF4). Mass spectrometry (MS)-based evaluation of the ensemble of anti-PF4 antibodies obtained from a VITT patient's blood indicates that the major component is a monoclonal antibody. Structural characterization of this antibody reveals several unusual characteristics, such as the presence of an N-glycan in the Fab segment and high density of acidic amino acid residues in the complementarity-determining regions. A recombinant version of this antibody (RVT1) was generated by transient expression in mammalian cells based on the newly determined sequence. It captures the key properties of VITT antibodies such as their ability to activate platelets in a PF4 concentration-dependent fashion. Homology modeling of the Fab segment reveals a well-defined polyanionic paratope, and the docking studies indicate that the polycationic segment of PF4 readily accommodates two Fab segments, cross-linking the antibodies to yield polymerized immune complexes. Their existence was verified with native MS by detecting assemblies as large as (RVT1)3(PF4)2, pointing out at FcγRIIa-mediated platelet activation as the molecular mechanism underlying VITT clinical manifestations. In addition to the high PF4 affinity, RVT1 readily binds other polycationic targets, indicating a polyreactive nature of this antibody. This surprising promiscuity not only sheds light on VITT etiology but also opens up a range of opportunities to manage this pathology.

The unique properties of IgG4 and its roles in health and disease

IgG4 is the least abundant subclass of IgG in human serum and has unique functional features. IgG4 is largely unable to activate antibody-dependent immune effector responses and, furthermore, undergoes Fab (fragment antigen binding)-arm exchange, rendering it bispecific for antigen binding and functionally monovalent. These properties of IgG4 have a blocking effect, either on the immune response or on the target protein of IgG4. In this Review, we discuss the unique structural characteristics of IgG4 and how these contribute to its roles in health and disease. We highlight how, depending on the setting, IgG4 responses can be beneficial (for example, in responses to allergens or parasites) or detrimental (for example, in autoimmune diseases, in antitumour responses and in anti-biologic responses). The development of novel models for studying IgG4 (patho)physiology and understanding how IgG4 responses are regulated could offer insights into novel treatment strategies for these IgG4-associated disease settings.

Rheumatoid Arthritis-Specific Autoimmunity in the Lung Before and at the Onset of Disease

OBJECTIVE

The lung is implicated as a site for breach of tolerance prior to onset of seropositive rheumatoid arthritis (RA). To substantiate this, we investigated lung-resident B cells in bronchoalveolar lavage (BAL) samples from untreated early RA patients and anti-citrullinated protein antibody (ACPA)-positive individuals at risk for developing RA.

METHODS

Single B cells (n = 7,680) were phenotyped and isolated from BAL samples from individuals at risk of RA (n = 3) and at RA diagnosis (n = 9). The immunoglobulin variable region transcripts were sequenced and selected for expression as monoclonal antibodies (n = 141). Monoclonal ACPAs were tested for reactivity patterns and binding to neutrophils.

RESULTS

Using our single-cell approach, we found significantly increased proportions of B lymphocytes in ACPA+ compared to ACPA- individuals. Memory and double-negative B cells were prominent in all subgroups. Upon antibody re-expression, 7 highly mutated citrulline-autoreactive clones originating from different memory B cell subsets were identified, both in individuals at risk of RA and early RA patients. Lung IgG variable gene transcripts from ACPA+ individuals carried frequent mutation-induced N-linked Fab glycosylation sites (P < 0.001), often in the framework 3 of the variable region. Two of the lung ACPAs bound to activated neutrophils, 1 from an individual at risk of RA and 1 from an early RA patient.

CONCLUSION

T cell-driven B cell differentiation resulting in local class switching and somatic hypermutation are evident in lungs before as well as in early stages of ACPA+ RA. Our findings add to the notion of lung mucosa being a site for initiation of citrulline autoimmunity preceding seropositive RA.

A photoaffinity glycan-labeling approach to investigate immunoglobulin glycan-binding partners

Glycans play a pivotal role in biology. However, because of the low-affinity of glycan-protein interactions, many interaction pairs remain unknown. Two important glycoproteins involved in B-cell biology are the B-cell receptor and its secreted counterpart, antibodies. It has been indicated that glycans expressed by these B-cell-specific molecules can modulate immune activation via glycan-binding proteins. In several autoimmune diseases, an increased prevalence of variable domain glycosylation of IgG autoantibodies has been observed. Especially, the hallmarking autoantibodies in rheumatoid arthritis, anti-citrullinated protein antibodies, carry a substantial amount of variable domain glycans. The variable domain glycans expressed by these autoantibodies are N-linked, complex-type, and α2-6 sialylated, and B-cell receptors carrying variable domain glycans have been hypothesized to promote selection of autoreactive B cells via interactions with glycan-binding proteins. Here, we use the anti-citrullinated protein antibody response as a prototype to study potential in solution and in situ B-cell receptor-variable domain glycan interactors. We employed SiaDAz, a UV-activatable sialic acid analog carrying a diazirine moiety that can form covalent bonds with proximal glycan-binding proteins. We show, using oligosaccharide engineering, that SiaDAz can be readily incorporated into variable domain glycans of both antibodies and B-cell receptors. Our data show that antibody variable domain glycans are able to interact with inhibitory receptor, CD22. Interestingly, although we did not detect this interaction on the cell surface, we captured CD79 β glycan-B-cell receptor interactions. These results show the utility of combining photoaffinity labeling and oligosaccharide engineering for identifying antibody and B-cell receptor interactions and indicate that variable domain glycans appear not to be lectin cis ligands in our tested conditions.

Native SEC and Reversed-Phase LC-MS Reveal Impact of Fab Glycosylation of Anti-SARS-COV-2 Antibodies on Binding to the Receptor Binding Domain

The binding affinity of monoclonal antibodies (mAbs) for their intended therapeutic targets is often affected by chemical and post-translational modifications in the antigen binding (Fab) domains. A new two-dimensional analytical approach is described here utilizing native size exclusion chromatography (SEC) to separate populations of antibodies and bound antibody-antigen complexes for subsequent characterization of these modifications by reversed-phase (RP) liquid chromatography-mass spectrometry (LC-MS) at the intact antibody level. Previously, we utilized peptide mapping to measure modifications impacting binding. However, in this study, the large size of the modification (N-glycosylation) allowed assessing its impact from small amounts (∼20 ug) of intact antibody, without the need for peptide mapping. Here, we apply the native SEC-based competitive binding assay to quickly and qualitatively investigate the effects of Fab glycosylation of four antispike protein mAbs that were developed for use in the treatment of COVID-19 disease. Three of the mAbs were observed to have consensus N-glycosylation sites (N-X-T/S) in the Fab domains, a relatively rare occurrence in therapeutic mAbs. The goal of the study was to characterize the levels of Fab glycosylation present, as well as determine the impact of glycosylation on binding to the spike protein receptor binding domain (RBD) and the ability of the mAbs to inhibit RBD-ACE2 interaction at the intact antibody level, with minimal sample treatment and preparation. The three mAbs with Fab N-glycans were found to have glycosylation profiles ranging from full occupancy at each Fab (in one mAb) to partially glycosylated with mixed populations of two, one, or no glycan moieties. Competitive SEC analysis of mAb-RBD revealed that the glycosylated antibody populations outcompete their nonglycosylated counterparts for the available RBD molecules. This competitive SEC binding analysis was applied to investigate the three-body interaction of a glycosylated mAb blocking the interaction between endogenous binding partners RBD-ACE2, finding that both glycosylated and nonglycosylated mAb populations bound to RBD with high enough affinity to block RBD-ACE2 binding.

Cell-culture process optimization via model-based predictions of metabolism and protein glycosylation

In order to meet the rising demand for biologics and become competitive on the developing biosimilar market, there is a need for process intensification of biomanufacturing processes. Process development of biologics has historically relied on extensive experimentation to develop and optimize biopharmaceutical manufacturing. Experimentation to optimize media formulations, feeding schedules, bioreactor operations and bioreactor scale up is expensive, labor intensive and time consuming. Mathematical modeling frameworks have the potential to enable process intensification while reducing the experimental burden. This review focuses on mathematical modeling of cellular metabolism and N-linked glycosylation as applied to upstream manufacturing of biologics. We review developments in the field of modeling cellular metabolism of mammalian cells using kinetic and stoichiometric modeling frameworks along with their applications to simulate, optimize and improve mechanistic understanding of the process. Interest in modeling N-linked glycosylation has led to the creation of various types of parametric and non-parametric models. Most published studies on mammalian cell metabolism have performed experiments in shake flasks where the pH and dissolved oxygen cannot be controlled. Efforts to understand and model the effect of bioreactor-specific parameters such as pH, dissolved oxygen, temperature, and bioreactor heterogeneity are critically reviewed. Most modeling efforts have focused on the Chinese Hamster Ovary (CHO) cells, which are most commonly used to produce monoclonal antibodies (mAbs). However, these modeling approaches can be generalized and applied to any mammalian cell-based manufacturing platform. Current and potential future applications of these models for Vero cell-based vaccine manufacturing, CAR-T cell therapies, and viral vector manufacturing are also discussed. We offer specific recommendations for improving the applicability of these models to industrially relevant processes.