Afucosylated IgG characterizes enveloped viral responses and correlates with COVID-19 severity

Comprehensive Immunoglobulin G, A, and M glycopeptide profiling for large-scale biomedical research

Glycosylation of immunoglobulin G (IgG) is recognized as a key modulator of cellular effector functions. At the same time, an increasing body of evidence underlines the importance of other antibody isotypes, especially IgA and IgM, in pathophysiological conditions. Therefore, methods to efficiently study the complex interplay between isotypes, subclasses, and glycosylation of antibodies during acute and chronic states of inflammation are needed. As a solution, we present an integrated and comprehensive method combining simultaneous affinity enrichment of IgG, IgA, and IgM with a single measurement, glycopeptide-centered LC-MS analysis of all isotypes which provides protein-specific (isotype and subclass), and site-specific N- and O-glycosylation quantitation. A two-protease approach provided individual peptides for each glycosylation site, allowing unambiguous compositional assignment and relative quantitation of glycoforms on the MS1 level as well as structural confirmation and partial isomer assignment on the MS/MS level. We demonstrate that our methodology can be efficiently applied to large clinical studies revealing differences of antibody glycosylation in woman during and after pregnancy, as well as between healthy donors and patients with rheumatoid arthritis. In addition, this showcased the advantages of our method in comprehensiveness and resolution of isotypes, subclasses, and glycosylation sites as well as its precision and robustness.

IgA displays site- and subclass-specific glycoform differences despite equal glycoenzyme expression

BACKGROUND

Glycosylation is an important posttranslational modification of proteins and in most cases indispensable for proper protein function. Like most soluble proteins, IgA, the second most prevalent antibody in human serum, contains several N- and O-glycosylation sites. While for IgG the impact of Fc glycosylation on effector functions and inflammatory potential has been studied intensively, only little is known for IgA. In addition, only glimpses exist regarding the regulation of IgA glycosylation. We have previously shown that IgA1 and IgA2 differ functionally and also show differences in their glycosylation pattern. The more pro-inflammatory IgA2 which is linked to autoimmune diseases displays decreased sialylation, galactosylation, fucosylation and bisection as compared to IgA1. In the present study, we aimed to investigate these differences in glycosylation in detail and to explore the mechanisms underlying them.

METHODS

IgA1 and IgA2 was isolated from serum of 12 healthy donors. Site specific glycosylation was analyzed by mass spectrometry. In addition, human bone marrow plasma cells were investigated using single cell mRNA sequencing, flow cytometry and ELISpot.

RESULTS

We found that certain glycoforms greatly differ in their abundance between IgA1 and IgA2 while others are equally abundant. Overall, the IgA2 glycans displayed a more immature phenotype with a higher prevalence of oligomannose and fewer fully processed glycans. Of note, these differences can't be explained by differences in the glycosylation enzyme machinery as mRNA sequencing and flow cytometry analysis showed equal enzyme expression in IgA1 and IgA2 producing plasma cells. ELISpot analysis suggested a slightly increased antibody production rate in IgA2 producing plasma cells which might contribute to its lower glycan processing rates. But this difference was only minor, suggesting that further factors such as steric accessibility determine glycan processing. This is supported by the fact that glycans at different positions on the same IgA chain differ dramatically in fucosylation, sialylation and bisection.

CONCLUSION

In summary, our detailed overview of IgA1 and IgA2 glycosylation shows a class, subclass, and site-specific glycosylation fingerprint, most likely due to structural differences of the protein backbones.

Roles of core fucosylation modification in immune system and diseases

Core fucosylation, catalyzed by α1,6-fucosyltransferase (FUT8), is an important N-glycosylation modification process that attaches a fucose residue via an α1,6-linkage to the core N-acetylglucosamine of N-glycans in mammals. Research over the past three decades has revealed the critical role of FUT8-mediated core fucosylation modification in various physiological and pathological processes, including cell growth, adhesion, receptor activation, antibody-dependent cellular cytotoxicity (ADCC), tumor metastasis and infections. This review discusses the immune system function involving FUT8 and the mechanisms by which core fucosylation regulates immunity and contributes to disease. A deeper understanding of these mechanisms can provide insights into cellular biology and suggest new therapeutic approaches and targets for related diseases.

Individual patient and donor seroprofiles in convalescent plasma treatment of COVID-19 in REMAP-CAP clinical trial

OBJECTIVES

Convalescent plasma (CP) treatment of COVID-19 has shown significant therapeutic effect only when administered early. We investigated the importance of patient and CP seroprofiles on treatment outcome in REMAP-CAP CP trial.

METHODS

We evaluated neutralising antibodies (nAb), anti-spike (S) IgM, IgG, IgG avidity, IgG fucosylation and respiratory viral loads in a sub-set of patients (n=80) and controls (n=51) before and after transfusion, comparing them to those in the CP units (n=157) they received.

RESULTS

Most patients were SARS-CoV-2 seropositive pre-transfusion (72% nAb; 89% S-IgG seropositivity). The majority (80%) had higher pre-transfusion S-IgG levels (median 1.7×106 arbitrary units (AU); 56%) or S-IgG production rates (median 1.1×106 AU/day; 64%) than they received from CP (median 2.2×105 AU). Only 22% of the patients demonstrated significant (median 24-fold) increase in their S-IgG levels acquired from transfusion. Better outcomes, measured by organ support-free days, were associated with increase in S-IgM levels (p=0.007), decreased S-IgG fucosylation (p<0.001), lower patient age (p<0.001) but not with receiving CP (p=0.337).

CONCLUSIONS

Based on our data, increased S-antibody levels linked to transfused CP were only observed in pre-seroconversion or immunodeficient patients lacking their own SARS-CoV-2 antibodies, representing the groups where CP treatment has previously shown most benefit.

Unveiling unique effector function-related bulk antibody profiles in long-term hemodialysis patients following COVID-19 mRNA booster vaccination

BACKGROUND

Hemodialysis patients exhibit a reduced response to vaccination and have different vaccine dose regimens. Vaccines induce antibodies and affect the inflammatory balance through antibody glycosylation and effector functions. Therefore, we aimed to analyze the antibody glycosylation profiles in hemodialysis patients who were vaccinated against severe acute respiratory syndrome coronavirus 2, infected with the virus, or both, and compare them with those of dialysis patients in a control group.

METHODS

Plasma samples from 112 hemodialysis patients were assigned to four groups: control, infected, vaccinated, and post-vaccine-infected. Paired plasma samples from 47 people with vaccination (vaccinees) were analyzed before and after the booster dose. The same analytical approach was applied to the four groups for a cross-sectional comparison.

RESULTS

Our study found that both vaccination and infection groups showed decreased fucosylation of IgG1, which is associated with a proinflammatory biosignature. However, vaccination also leads to increased galactosylation and bisection of IgG antibodies, which are associated with anti-inflammatory effects and the additional regulation of immune responses. In contrast, infection led to an additional decrease in the fucosylation of IgG2 and IgA, demonstrating a more intense proinflammatory biosignature than vaccination.

CONCLUSIONS

Our findings emphasize the proinflammatory biosignature of afucosylation in both vaccination and infection groups. Additionally, we uncovered further regulated profiles related to galactosylation in vaccinees. These findings suggest that antibody investigation for vaccination or infection should not solely focus on neutralization but should also consider effector function-related glycosylation profiling. This comprehensive information can be valuable for fine-tuning vaccine development in the future.

Acquisition of Fc-afucosylation of PfEMP1-specific IgG is age-dependent and associated with clinical protection against malaria

Protective immunity to malaria depends on acquisition of parasite-specific antibodies, with Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1) being one of the most important target antigens. The effector functions of PfEMP1-specific IgG include inhibition of infected erythrocyte (IE) sequestration and opsonization of IEs for cell-mediated destruction. IgG glycosylation modulates antibody functionality, with increased affinity to FcγRIIIa for IgG lacking fucose in the Fc region (Fc-afucosylation). We report here that selective Fc-afucosylation of PfEMP1-specific IgG1 increases with age in P. falciparum-exposed children and is associated with reduced risk of anemia, independent of the IgG levels. A similar association was found for children having PfEMP1-specific IgG1 inducing multiple effector functions against IEs, particularly those associated with antibody-dependent cellular cytotoxicity (ADCC) by NK cells. Our findings provide new insights regarding protective immunity to P. falciparum malaria and highlight the importance of cell-mediated destruction of IgG-opsonized IEs.

Mechanisms of antibody-dependent enhancement of infectious disease

Antibody-dependent enhancement (ADE) of infectious disease is a phenomenon whereby host antibodies increase the severity of an infection. It is well established in viral infections but ADE also has an underappreciated role during bacterial, fungal and parasitic infections. ADE can occur during both primary infections and re-infections with the same or a related pathogen; therefore, understanding the underlying mechanisms of ADE is critical for understanding the pathogenesis and progression of many infectious diseases. Here, we review the four distinct mechanisms by which antibodies increase disease severity during an infection. We discuss the most established mechanistic explanation for ADE, where cross-reactive, disease-enhancing antibodies bound to pathogens interact with Fc receptors, thereby enhancing pathogen entry or replication, ultimately increasing the total pathogen load. Additionally, we explore how some pathogenic antibodies can shield bacteria from complement-dependent killing, thereby enhancing bacterial survival. We interrogate the molecular mechanisms by which antibodies can amplify inflammation to drive severe disease, even in the absence of increased pathogen replication. We also examine emerging roles for autoantibodies in enhancing the pathogenesis of infectious diseases. Finally, we discuss how we can leverage these insights to improve vaccine design and future treatments for infectious diseases.

Antibodies to the RBD of SARS-CoV-2 spike mediate productive infection of primary human macrophages

The role of myeloid cells in the pathogenesis of SARS-CoV-2 is well established, in particular as drivers of cytokine production and systemic inflammation characteristic of severe COVID-19. However, the potential for myeloid cells to act as bona fide targets of productive SARS-CoV-2 infection, and the specifics of entry, remain unclear. Using a panel of anti-SARS-CoV-2 monoclonal antibodies (mAbs) we performed a detailed assessment of antibody-mediated infection of monocytes/macrophages. mAbs with the most consistent potential to mediate infection were those targeting a conserved region of the receptor binding domain (RBD; group 1/class 4). Infection was closely related to the neutralising concentration of the mAbs, with peak infection occurring below the IC50, while pre-treating cells with remdesivir or FcγRI-blocking antibodies inhibited infection. Studies performed in primary macrophages demonstrated high-level and productive infection, with infected macrophages appearing multinucleated and syncytial. Infection was not seen in the absence of antibody with the same quantity of virus. Addition of ruxolitinib significantly increased infection, indicating restraint of infection through innate immune mechanisms rather than entry. High-level production of pro-inflammatory cytokines directly correlated with macrophage infection levels. We hypothesise that infection via antibody-FcR interactions could contribute to pathogenesis in primary infection, systemic virus spread or persistent infection.

Simultaneous Protein Quantitation and Glycosylation Profiling of Antigen-Specific Immunoglobulin G1 in Large Clinical Studies

Antibodies have a key role in the immune system, making their characterization essential to biomedical, biopharmaceutical, and clinical research questions. Antibody effector functions are mainly controlled by quantity, subclass, and Fc glycosylation. We describe an integrated method to measure these three critical dimensions simultaneously. The subclass-specific immunoglobulin G (IgG) Fc glycosylation analysis combines immunosorbance with glycopeptide-centered LC-MS detection. For integrated IgG1-specific quantitation, a commercial, stable isotope labeled IgG1 protein standard was spiked into the immunosorbent eluates. Robust quantitation was achieved, relying on a combination of a proteotypic peptide and the most abundant glycopeptides, generated through proteolytic cleavage from a mixture of natural IgG1 and the recombinant IgG1 standard. Method performance was demonstrated in a large coronavirus vaccination cohort at a throughput of 100 samples/day. LC-MS-derived, anti-SARS-CoV-2 spike protein IgG1 concentrations ranged from 100 to 10000 ng/mL and correlated well with a clinically relevant immunoassay. Technical variation was 200 times lower than biological variation; intermediate precision was 44%. In conclusion, we present a method capable of robustly and simultaneously assessing quantity, subclass, and Fc glycosylation of antigen-specific IgG in large clinical studies. This method will facilitate a broader understanding of immune responses, especially the important interplay among the three dimensions.

The Circulating Proteome─Technological Developments, Current Challenges, and Future Trends

Recent improvements in proteomics technologies have fundamentally altered our capacities to characterize human biology. There is an ever-growing interest in using these novel methods for studying the circulating proteome, as blood offers an accessible window into human health. However, every methodological innovation and analytical progress calls for reassessing our existing approaches and routines to ensure that the new data will add value to the greater biomedical research community and avoid previous errors. As representatives of HUPO's Human Plasma Proteome Project (HPPP), we present our 2024 survey of the current progress in our community, including the latest build of the Human Plasma Proteome PeptideAtlas that now comprises 4608 proteins detected in 113 data sets. We then discuss the updates of established proteomics methods, emerging technologies, and investigations of proteoforms, protein networks, extracellualr vesicles, circulating antibodies and microsamples. Finally, we provide a prospective view of using the current and emerging proteomics tools in studies of circulating proteins.

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.

A multivalent binding model infers antibody Fc species from systems serology

Systems serology aims to broadly profile the antigen binding, Fc biophysical features, immune receptor engagement, and effector functions of antibodies. This experimental approach excels at identifying antibody functional features that are relevant to a particular disease. However, a crucial limitation of this approach is its incomplete description of what structural features of the antibodies are responsible for the observed immune receptor engagement and effector functions. Knowing these antibody features is important for both understanding how effector responses are naturally controlled through antibody Fc structure and designing antibody therapies with specific effector profiles. Here, we address this limitation by modeling the molecular interactions occurring in these assays and using this model to infer quantities of specific antibody Fc species among the antibodies being profiled. We used several validation strategies to show that the model accurately infers antibody properties and then applied the model to infer previously unavailable antibody fucosylation information from existing systems serology data. Using this capability, we find that COVID-19 vaccine efficacy is associated with the induction of afucosylated spike protein-targeting IgG. Our results also question an existing assumption that controllers of HIV exhibit gp120-targeting IgG that are less fucosylated than those of progressors. Additionally, we confirm that afucosylated IgG is associated with membrane-associated antigens for COVID-19 and HIV, and present new evidence indicating that this relationship is specific to the host cell membrane. Finally, we use the model to identify redundant assay measurements and subsets of information-rich measurements from which Fc properties can be inferred. In total, our modeling approach provides a quantitative framework for the reasoning typically applied in these studies, improving the ability to draw mechanistic conclusions from these data.

Crosstalk Between Cytokines and IgG N-Glycosylation: Bidirectional Effects and Relevance to Clinical Innovation for Inflammatory Diseases

The crosstalk between cytokines and immunoglobulin G (IgG) N-glycosylation forms a bidirectional regulatory network that significantly impacts inflammation and immune function. This review examines how various cytokines, both pro- and anti-inflammatory, modulate IgG N-glycosylation, shaping antibody activity and influencing inflammatory responses. In addition, we explore how altered IgG N-glycosylation patterns affect cytokine production and immune signaling, either promoting or reducing inflammation. Through a comprehensive analysis of current studies, this review underscores the dynamic relationship between cytokines and IgG N-glycosylation. These insights enhance our understanding of the mechanisms underlying inflammatory diseases and contribute to improved strategies for disease prevention, diagnosis, monitoring, prognosis, and the exploration of novel treatment options. By focusing on this crosstalk, we identify new avenues for developing innovative diagnostic tools and therapies to improve patient outcomes in inflammatory diseases.

A whole blood-based functional assay to characterize immunoglobulin A effector functions

Most investigations on the immune cell-activating potency of IgA used purified total IgA and/or specific isolated cell populations. As IgA2 has been reported to be more pro-inflammatory than IgA1, we aimed to employ a fast and convenient whole blood-based assay to individually probe the capacity of the two IgA subclasses to activate immune cells in close physiological conditions. To this end, whole blood from healthy donors (n = 10) was stimulated with immobilized IgA1, IgA2m1 or IgA2m2 (the two main allotypic variants of IgA2). Activation of major leukocyte subsets was measured using a 10-color flow cytometry panel providing access to the expression of 5 activation markers on 6 different immune cell subsets. While capturing some heterogeneity of responses among donors, IgA2m1 and IgA2m2 systematically showed a stronger activation profile compared to IgA1 in a variety of dimensions. For example, both IgA2 allotypes led to stronger modulations of CD54, CD11b, CD62L, CD66b or CD69, on both or either monocytes or neutrophils, indicating a more pronounced pro-inflammatory effect for this subclass than IgA1. By taking into account donor-specific soluble and cellular components this whole blood-based functional approach provides new perspectives to further investigate IgA effector functions in mechanistic studies and/or translational research.

Vaccine Strategies Against RNA Viruses: Current Advances and Future Directions

The development of vaccines against RNA viruses has undergone a rapid evolution in recent years, particularly driven by the COVID-19 pandemic. This review examines the key roles that RNA viruses, with their high mutation rates and zoonotic potential, play in fostering vaccine innovation. We also discuss both traditional and modern vaccine platforms and the impact of new technologies, such as artificial intelligence, on optimizing immunization strategies. This review evaluates various vaccine platforms, ranging from traditional approaches (inactivated and live-attenuated vaccines) to modern technologies (subunit vaccines, viral and bacterial vectors, nucleic acid vaccines such as mRNA and DNA, and phage-like particle vaccines). To illustrate these platforms' practical applications, we present case studies of vaccines developed for RNA viruses such as SARS-CoV-2, influenza, Zika, and dengue. Additionally, we assess the role of artificial intelligence in predicting viral mutations and enhancing vaccine design. The case studies underscore the successful application of RNA-based vaccines, particularly in the fight against COVID-19, which has saved millions of lives. Current clinical trials for influenza, Zika, and dengue vaccines continue to show promise, highlighting the growing efficacy and adaptability of these platforms. Furthermore, artificial intelligence is driving improvements in vaccine candidate optimization and providing predictive models for viral evolution, enhancing our ability to respond to future outbreaks. Advances in vaccine technology, such as the success of mRNA vaccines against SARS-CoV-2, highlight the potential of nucleic acid platforms in combating RNA viruses. Ongoing trials for influenza, Zika, and dengue demonstrate platform adaptability, while artificial intelligence enhances vaccine design by predicting viral mutations. Integrating these innovations with the One Health approach, which unites human, animal, and environmental health, is essential for strengthening global preparedness against future RNA virus threats.

Fc-Afucosylation of VAR2CSA-Specific Immunoglobulin G and Clinical Immunity to Placental Plasmodium falciparum Malaria

BACKGROUND

Acquired immunity to Plasmodium falciparum malaria is mainly mediated by immunoglobulin G (IgG) targeting erythrocyte membrane protein 1 (PfEMP1). These adhesins mediate infected erythrocyte (IE) sequestration, protecting IEs from splenic destruction. PfEMP1-specific IgG is therefore thought to protect mainly by inhibiting IE sequestration. VAR2CSA-type PfEMP1 mediates placental IE sequestration, putting pregnant women exposed to P falciparum parasites at risk of placental malaria (PM).

METHODS

Levels and Fc-afucosylation of VAR2CSA-specific plasma IgG were measured by a modified enzyme-linked immunosorbent assay (FEASI). We also measured the ability of the IgG to inhibit IE adhesion and to induce natural killer (NK) cell degranulation. The results were related to parity and clinical pregnancy outcomes.

RESULTS

Parity was positively correlated with levels and Fc-afucosylation of VAR2CSA-specific IgG, and with birth weight and plasma IgG inhibition of IE adhesion in vitro. Fc-afucosylation of VAR2CSA-specific IgG increased NK-cell degranulation. Women with Fc-afucosylated VAR2CSA-specific IgG had a reduced risk of delivering a low birth weight (LBW) baby, but not of PM or anemia.

CONCLUSIONS

Fc-afucosylated VAR2CSA-specific IgG effectively induced NK-cell degranulation and was associated with protection against LBW, independent of IgG levels. Our study has implications for the development of VAR2CSA-based subunit vaccines, which exclusively induce Fc-fucosylated IgG.

Sugar Highs: Recent Notable Breakthroughs in Glycobiology

Glycosylation is biochemically complex and functionally critical to a wide range of processes and disease states, making it a vibrant area of contemporary research. Here, we highlight a selection of notable recent advances in the glycobiology of SARS-CoV-2 infection and immunity, cancer biology and immunotherapy, and newly discovered glycosylated RNAs. Together, these studies illustrate the significance of glycosylation in normal biology and the great promise of manipulating glycosylation for therapeutic benefit in disease.

Altered Spike Immunoglobulin G Fc N-Linked Glycans Are Associated With Hyperinflammatory State in Adult Coronavirus Disease 2019 and Multisystem Inflammatory Syndrome in Children

Background

Severe coronavirus disease 2019 (COVID-19) and multisystem inflammatory syndrome (MIS-C) are characterized by excessive inflammatory cytokines/chemokines. In adults, disease severity is associated with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-specific immunoglobulin G (IgG) Fc afucosylation, which induces proinflammatory cytokine secretion from innate immune cells. This study aimed to define spike IgG Fc glycosylation following SARS-CoV-2 infection in adults and children and following SARS-CoV-2 vaccination in adults and the relationships between glycan modifications and cytokines/chemokines.

Methods

We analyzed longitudinal (n = 146) and cross-sectional (n = 49) serum/plasma samples from adult and pediatric COVID-19 patients, MIS-C patients, adult vaccinees, and adult and pediatric controls. We developed methods for characterizing bulk and spike IgG Fc glycosylation by capillary electrophoresis and measured levels of 10 inflammatory cytokines/chemokines by multiplexed enzyme-linked immunosorbent assay.

Results

Spike IgG was more afucosylated than bulk IgG during acute adult COVID-19 and MIS-C. We observed an opposite trend following vaccination, but it was not significant. Spike IgG was more galactosylated and sialylated and less bisected than bulk IgG during adult COVID-19, with similar trends observed during pediatric COVID-19/MIS-C and following SARS-CoV-2 vaccination. Spike IgG glycosylation changed with time following adult COVID-19 or vaccination. Afucosylated spike IgG exhibited inverse and positive correlations with inflammatory markers in MIS-C and following vaccination, respectively; galactosylated and sialylated spike IgG inversely correlated with proinflammatory cytokines in adult COVID-19 and MIS-C; and bisected spike IgG positively correlated with inflammatory cytokines/chemokines in multiple groups.

Conclusions

We identified previously undescribed relationships between spike IgG glycan modifications and inflammatory cytokines/chemokines that expand our understanding of IgG glycosylation changes that may impact COVID-19 and MIS-C immunopathology.

Antibody-mediated control mechanisms of viral infections

Antibodies generated after vaccination or natural pathogen exposure are essential mediators of protection against many infections. Most studies with viruses have focused on antibody neutralization, in which protection is conferred by the fragment antigen binding region (Fab) through targeting of different steps in the viral lifecycle including attachment, internalization, fusion, and egress. Beyond neutralization, the fragment crystallizable (Fc) region of antibodies can integrate innate and adaptive immune responses by engaging complement components and distinct Fc gamma receptors (FcγR) on different host immune cells. In this review, we discuss recent advances in our understanding of antibody neutralization and Fc effector functions, and the assays used to measure them. Additionally, we describe the contexts in which these mechanisms are associated with protection against viruses and highlight how Fc-FcγR interactions can improve the potency of antibody-based therapies.

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.

Fc-FcγR interactions during infections: From neutralizing antibodies to antibody-dependent enhancement

Advances in antibody technologies have resulted in the development of potent antibody-based therapeutics with proven clinical efficacy against infectious diseases. Several monoclonal antibodies (mAbs), mainly against viruses such as SARS-CoV-2, HIV-1, Ebola virus, influenza virus, and hepatitis B virus, are currently undergoing clinical testing or are already in use. Although these mAbs exhibit potent neutralizing activity that effectively blocks host cell infection, their antiviral activity results not only from Fab-mediated virus neutralization, but also from the protective effector functions mediated through the interaction of their Fc domains with Fcγ receptors (FcγRs) on effector leukocytes. Fc-FcγR interactions confer pleiotropic protective activities, including the clearance of opsonized virions and infected cells, as well as the induction of antiviral T-cell responses. However, excessive or inappropriate activation of specific FcγR pathways can lead to disease enhancement and exacerbated pathology, as seen in the context of dengue virus infections. A comprehensive understanding of the diversity of Fc effector functions during infection has guided the development of engineered antiviral antibodies optimized for maximal effector activity, as well as the design of targeted therapeutic approaches to prevent antibody-dependent enhancement of disease.

One N-glycan regulates natural killer cell antibody-dependent cell-mediated cytotoxicity and modulates Fc γ receptor IIIa/CD16a structure

Both endogenous antibodies and a subset of antibody therapeutics engage Fc gamma receptor (FcγR)IIIa/CD16a to stimulate a protective immune response. Increasing the FcγRIIIa/IgG1 interaction improves the immune response and thus represents a strategy to improve therapeutic efficacy. FcγRIIIa is a heavily glycosylated receptor and glycan composition affects antibody-binding affinity. Though our laboratory previously demonstrated that natural killer (NK) cell N-glycan composition affected the potency of one key protective mechanism, antibody-dependent cell-mediated cytotoxicity (ADCC), it was unclear if this effect was due to FcγRIIIa glycosylation. Furthermore, the structural mechanism linking glycan composition to affinity and cellular activation remained undescribed. To define the role of individual amino acid and N-glycan residues, we measured affinity using multiple FcγRIIIa glycoforms. We observed stepwise affinity increases with each glycan truncation step, with the most severely truncated glycoform displaying the highest affinity. Removing the N162 glycan demonstrated its predominant role in regulating antibody-binding affinity, in contrast to four other FcγRIIIa N-glycans. We next evaluated the impact of the N162 glycan on NK cell ADCC. NK cells expressing the FcγRIIIa V158 allotype exhibited increased ADCC following kifunensine treatment to limit N-glycan processing. Notably, an increase was not observed with cells expressing the FcγRIIIa V158 S164A variant that lacks N162 glycosylation, indicating that the N162 glycan is required for increased NK cell ADCC. To gain structural insight into the mechanisms of N162 regulation, we applied a novel protein isotope labeling approach in combination with solution NMR spectroscopy. FG loop residues proximal to the N162 glycosylation site showed large chemical shift perturbations following glycan truncation. These data support a model for the regulation of FcγRIIIa affinity and NK cell ADCC whereby composition of the N162 glycan stabilizes the FG loop and thus the antibody-binding site.

Glycosylation signature of plasma IgA of critically ill COVID-19 patients

Thromboembolic complications are common in severe COVID-19 and are thought to result from excessive neutrophil-extracellular-trap (NET)-driven immunothrombosis. Glycosylation plays a vital role in the efficiency of immunoglobulin A (IgA) effector functions, with significant implications for NET formation in infectious diseases. This study represents the first comprehensive analysis of plasma IgA glycosylation during severe SARS-CoV-2 or Influenza A infection, revealing lower sialylation and higher galactosylation of IgA1 O-glycans in acute respiratory distress syndrome (ARDS), regardless of the underlying cause of the disease. Importantly, N-glycans displayed an infection-specific pattern, with N47 of IgA2 showing diminished sialylation and bisection, and N340/N327 of IgA1/2 demonstrating lower fucosylation and antennarity along with higher non-complex glycans in COVID-19 compared to Influenza. Notably, COVID-19 IgA possessed strong ability to induce NET formation and its glycosylation patterns correlated with extracellular DNA levels in plasma of critically ill COVID-19 patients. Our data underscores the necessity of further research on the role of IgA glycosylation in the modulation of pathogen-specific immune responses in COVID-19 and other infectious diseases.

Recent Endemic Coronavirus Infection Associates With Higher SARS-CoV-2 Cross-Reactive Fc Receptor Binding Antibodies

Recent documented infection with an endemic coronavirus (eCoV) associates with less severe coronavirus disease 2019 (COVID-19), yet the immune mechanism behind this protection has not been fully explored. We measured both antibody and T cell responses against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in SARS-CoV-2 naïve individuals classified into two groups, either with or without presumed recent eCoV infections. There was no difference in neutralizing antibodies and T cell responses against SARS-CoV-2 antigens between the two groups. SARS-CoV-2 naïve individuals with recent presumed eCoV infection, however, had higher levels of Fc receptor (FcR) binding antibodies against eCoV spikes (S) and SARS-CoV-2 S2. There was also a significant correlation between eCoV and SARS-CoV-2 FcR binding antibodies. Recent eCoV infection boosts cross-reactive antibodies that can mediate Fc effector functions, and this may play a role in the observed heterotypic immune protection against severe COVID-19.

A single-dose circular RNA vaccine prevents Zika virus infection without enhancing dengue severity in mice

Antibody-dependent enhancement (ADE) is a potential concern for the development of Zika virus (ZIKV) vaccines. Cross-reactive but poorly neutralizing antibodies, usually targeting viral pre-membrane or envelope (E) proteins, can potentially enhance dengue virus (DENV) infection. Although E domain III (EDIII) contains ZIKV-specific epitopes, its immunogenicity is poor. Here, we show that dimeric EDIII, fused to human IgG1 Fc fragment (EDIII-Fc) and encoded by circular RNA (circRNA), induces better germinal center reactions and higher neutralizing antibodies compared to circRNAs encoding monomeric or trimeric EDIII. Two doses of circRNAs encoding EDIII-Fc and ZIKV nonstructural protein NS1, another protective antigen, prevent lethal ZIKV infection in neonates born to immunized C57BL/6 mice and in interferon-α/β receptor knockout adult C57BL/6 mice. Importantly, a single-dose optimized circRNA vaccine with improved antigen expression confers potent and durable protection without inducing obvious DENV ADE in mice, laying the groundwork for developing flavivirus vaccines based on circRNAs encoding EDIII-Fc and NS1.

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.

Safety and immunogenicity of PIKA-adjuvanted recombinant SARS-CoV-2 spike protein subunit vaccine as a booster against SARS-CoV-2: a phase II, open-label, randomized, double-blinded study

Purpose

This study evaluated the safety and immunogenicity of the PIKA-adjuvanted recombinant severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike protein subunit vaccine as a booster dose for healthy adults who had previously received two or more doses of an inactivated coronavirus disease 2019 (COVID-19) vaccine.

Materials and Methods

The study was a phase II multicenter, double-blinded, comparator-controlled, randomized trial. Participants were randomly assigned to receive either the PIKA COVID-19 vaccine booster dose or an inactivated COVID-19 vaccine (Sinovac, China). Safety was assessed based on adverse events, while immunogenicity was measured by neutralizing antibodies against SARS-CoV-2 and serum immunoglobulin G (IgG) levels. Data on safety and immunogenicity were collected in the short-term (within 14 days after the booster dose) and long-term (from 90 to 365 days after the booster dose).

Results

The PIKA-adjuvanted vaccine demonstrated a significant increase in neutralizing antibodies against the Omicron variant (geometric mean ratio [GMR]=2.0 on day 7, p-value <0.001; GMR=2.7 on day 14, p-value <0.001) and the wild type SARS-CoV-2 virus (GMR=2.3 on day 7, p-value <0.001; GMR=2.8 on day 14, p-value<0.001) in the early post-vaccination period when compared to the inactivated vaccine. Additionally, the PIKA COVID-19 vaccine showed higher seroconversion rates for neutralizing antibodies against both variants during the first 14 days post-vaccination. However, there were no significant differences in neutralizing antibody levels between the two vaccines from day 90 to day 360 post-vaccination. Serum IgG antibody levels for the PIKA COVID-19 vaccine were also higher throughout the study period. The incidence of adverse events was slightly higher in the PIKA COVID-19 group, with the most common events being pain at the injection site and headache. All adverse events were mild or moderate, with no reports of severe or life-threatening adverse events in either group.

Conclusion

The PIKA COVID-19 vaccine, when administered as a booster dose, showed promising short- and long-term immunogenicity with no emergent safety issues identified. The booster dose of the PIKA COVID-19 vaccine elicited a robust immune response against various SARS-CoV-2 variants and provided some seroprotection for up to 360 days (ClinicalTrials.gov registration number: NCT05463419).

Characterization of the Antibody Response to SARS-CoV-2 Infection in COVID-19 Transplant versus Nontransplant Recipients by Ig-MS

Solid organ transplant recipients with immunosuppressant regimens to prevent rejection are less able to mount effective immune responses to pathogenic infection. Here, we apply a recently reported mass spectrometry-based serological approach known as Ig-MS to characterize immune responses against infection with SARS-CoV-2 in cohorts of transplant recipients and immunocompetent controls, both at a single early time point following COVID-19 diagnosis as well as over the course of one-month postdiagnosis. We found that the antibody repertoires generated by transplant recipients against SARS-CoV-2 do not differ significantly compared to immunocompetent individuals with regard to repertoire titer, clonality, or glycan composition. Importantly, our study is the first to characterize the evolution of antibody glycan profiles in transplant recipients with COVID-19 disease, presenting evidence that the evolution of glycan composition in these immunocompromised individuals is similar to that in immunocompetent people.

Infection and the Glycome─New Insights into Host Response

Glycans play critical roles in the host-pathogen interactions leading to infection. However, we still understand very little about the dynamic nature of glycosylation in response to infection and its function in modulating host immunity. Many of the host proteins involved in immune defense are glycoproteins. Furthermore, the innate immune system recognizes glycans. The glycoform of a protein can impact proteolytic stability, receptor interactions, serum half-life, and other aspects. New, cutting-edge chemical biology tools are shedding light on the interplay between infection and the host glycome. In this review, we highlight new work on the importance of dynamic glycosylation of host proteins in the innate and adaptive immune pathways in response to infection. These include recent findings on altered glycoprofiles of mucins, complement components, and antibodies.

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.

Protective non-neutralizing SARS-CoV-2 monoclonal antibodies

Recent studies show an important role for non-neutralizing anti-spike antibodies, including monoclonal antibodies (mAbs), in robustly protecting against SARS-CoV-2 infection. These mAbs use Fc-mediated functions such as complement activation, phagocytosis, and cellular cytotoxicity. There is an untapped potential for using non-neutralizing mAbs in durable antibody treatments; because of their available conserved epitopes, they may not be as sensitive to virus mutations as neutralizing mAbs. Here, we discuss evidence of non-neutralizing mAb-mediated protection against SARS-CoV-2 infection. We explore how non-neutralizing mAb Fc-mediated functions can be enhanced via novel antibody-engineering techniques. Important questions remain to be answered regarding the characteristics of protective non-neutralizing mAbs, including the models and assays used for study, the risks of ensuing detrimental inflammation, as well as the durability and mechanisms of protection.

Primary SARS-CoV-2 infection in children and adults results in similar Fc-mediated antibody effector function patterns

Objectives

Increasing evidence suggests that Fc-mediated antibody effector functions have an important role in protection against respiratory viruses, including SARS-CoV-2. However, limited data are available on the potential differences in the development, heterogeneity and durability of these responses in children compared to adults.

Methods

Here, we assessed the development of spike S1-specific serum antibody-dependent cellular phagocytosis (ADCP), complement deposition (ADCD) and natural killer cell activation (ADNKA), alongside specific antibody binding concentrations (IgG, IgA and IgM) and IgG avidity in healthy adults (n = 38, 18-56 years) and children (n = 21, 5-16 years) following primary SARS-CoV-2 infection, with a 10-month longitudinal follow-up. Differences between groups were assessed using a nonparametric Kruskal-Wallis test with Dunn's multiple comparisons test.

Results

We found similar (functional) antibody responses in children compared to adults, with a tendency for increased durability in children, which was statistically significant for ADCD (P < 0.05). While ADNKA was strongly reduced in both adults (P < 0.001) and children (P < 0.05) at the latest time point, ADCP remained relatively stable over time, possibly relating to an increase in avidity of the spike-specific antibodies (P < 0.001). Finally, the ADNKA capacity relative to antibody concentration appeared to decrease over time in both children and adults.

Conclusion

In conclusion, our data provide novel insights into the development of SARS-CoV-2-specific antibody Fc-mediated effector functions in children and adults. An increased understanding of these characteristics in specific age populations is valuable for the future design of novel and improved vaccination strategies for respiratory viruses such as SARS-CoV-2.

iPSC-derived NK cells expressing high-affinity IgG Fc receptor fusion CD64/16A to mediate flexible, multi-tumor antigen targeting for lymphoma

Introduction

NK cells can mediate tumor cell killing by natural cytotoxicity and by antibody-dependent cell-mediated cytotoxicity (ADCC), an anti-tumor mechanism mediated through the IgG Fc receptor CD16A (FcγRIIIA). CD16A polymorphisms conferring increased affinity for IgG positively correlate with clinical outcomes during monoclonal antibody therapy for lymphoma, linking increased binding affinity with increased therapeutic potential via ADCC. We have previously reported on the FcγR fusion CD64/16A consisting of the extracellular region of CD64 (FcγRI), a high-affinity Fc receptor normally expressed by myeloid cells, and the transmembrane/cytoplasmic regions of CD16A, to create a highly potent and novel activating fusion receptor. Here, we evaluate the therapeutic potential of engineered induced pluripotent stem cell (iPSC)-derived NK (iNK) cells expressing CD64/16A as an "off-the-shelf", antibody-armed cellular therapy product with multi-antigen targeting potential.

Methods

iNK cells were generated from iPSCs engineered to express CD64/16A and an interleukin (IL)-15/IL-15Rα fusion (IL-15RF) protein for cytokine independence. iNK cells and peripheral blood NK cells were expanded using irradiated K562-mbIL21-41BBL feeder cells to examine in in vitro and in vivo assays using the Raji lymphoma cell line. ADCC was evaluated in real-time by IncuCyte assays and using a xenograft mouse model with high circulating levels of human IgG.

Results

Our data show that CD64/16A expressing iNK cells can mediate potent anti-tumor activity against human B cell lymphoma. In particular, (i) under suboptimal conditions, including low antibody concentrations and low effector-to-target ratios, iNK-CD64/16A cells mediate ADCC, (ii) iNK-CD64/16A cells can be pre-loaded with tumor-targeting antibodies (arming) to elicit ADCC, (iii) armed iNK-CD64/16A cells can be repurposed with additional antibodies to target new tumor antigens, and (iv) cryopreserved, armed iNK-CD64/16A are capable of sustained ADCC in a tumor xenograft model under saturating levels of human IgG.

Discussion

iNK-CD64/16A cells allow for a flexible use of antibodies (antibody arming and antibody targeting), and an "off-the-shelf" platform for multi-antigen recognition to overcome limitations of adoptive cell therapies expressing fixed antigen receptors leading to cancer relapse due to antigen escape variants.

Total plasma N-glycomic signature of SARS-CoV-2 infection

Total plasma protein N-glycosylation (TPNG) changes are a hallmark of many diseases. Here, we analyzed the TPNG of 169 COVID-19 patients and 12 healthy controls, using mass spectrometry, resulting in the relative quantification of 85 N-glycans. We found a COVID-19 N-glycomic signature, with 59 glycans differing between patients and controls, many of them additionally differentiating between severe and mild COVID-19. Tri- and tetra-antennary N-glycans were increased in patients, showing additionally elevated levels of antennary α2,6-sialylation. Conversely, bisection of di-antennary, core-fucosylated, nonsialylated glycans was low in COVID-19, particularly in severe cases, potentially driven by the previously observed low levels of bisection on antibodies of severely diseased COVID-19 patients. These glycomic changes point toward systemic changes in the blood glycoproteome, particularly involvement of acute-phase proteins, immunoglobulins and the complement cascade. Further research is needed to dissect glycosylation changes in a protein- and site-specific way to obtain specific functional leads.

Influence of AAV vector tropism on long-term expression and Fc-γ receptor binding of an antibody targeting SARS-CoV-2

Long-acting passive immunization strategies are needed to protect immunosuppressed vulnerable groups from infectious diseases. To further explore this concept for COVID-19, we constructed Adeno-associated viral (AAV) vectors encoding the human variable regions of the SARS-CoV-2 neutralizing antibody, TRES6, fused to murine constant regions. An optimized vector construct was packaged in hepatotropic (AAV8) or myotropic (AAVMYO) AAV capsids and injected intravenously into syngeneic TRIANNI-mice. The highest TRES6 serum concentrations (511 µg/ml) were detected 24 weeks after injection of the myotropic vector particles and mean TRES6 serum concentrations remained above 100 µg/ml for at least one year. Anti-drug antibodies or TRES6-specific T cells were not detectable. After injection of the AAV8 particles, vector mRNA was detected in the liver, while the AAVMYO particles led to high vector mRNA levels in the heart and skeletal muscle. The analysis of the Fc-glycosylation pattern of the TRES6 serum antibodies revealed critical differences between the capsids that coincided with different binding activities to murine Fc-γ-receptors. Concomitantly, the vector-based immune prophylaxis led to protection against SARS-CoV-2 infection in K18-hACE2 mice. High and long-lasting expression levels, absence of anti-drug antibodies and favourable Fc-γ-receptor binding activities warrant further exploration of myotropic AAV vector-based delivery of antibodies and other biologicals.

New technologies in therapeutic antibody development: The next frontier for treating infectious diseases

Adaptive immunity to viral infections requires time to neutralize and clear viruses to resolve infection. Fast growing and pathogenic viruses are quickly established, are highly transmissible and cause significant disease burden making it difficult to mount effective responses, thereby prolonging infection. Antibody-based passive immunotherapies can provide initial protection during acute infection, assist in mounting an adaptive immune response, or provide protection for those who are immune suppressed or immune deficient. Historically, plasma-derived antibodies have demonstrated some success in treating diseases caused by viral pathogens; nonetheless, limitations in access to product and antibody titer reduce success of this treatment modality. Monoclonal antibodies (mAbs) have proven an effective alternative, as it is possible to manufacture highly potent and specific mAbs against viral targets on an industrial scale. As a result, innovative technologies to discover, engineer and manufacture specific and potent antibodies have become an essential part of the first line of treatment in pathogenic viral infections. However, a mAb targeting a specific epitope will allow escape variants to outgrow, causing new variant strains to become dominant and resistant to treatment with that mAb. Methods to mitigate escape have included combining mAbs into cocktails, creating bi-specific or antibody drug conjugates but these strategies have also been challenged by the potential development of escape mutations. New technologies in developing antibodies made as recombinant polyclonal drugs can integrate the strength of poly-specific antibody responses to prevent mutational escape, while also incorporating antibody engineering to prevent antibody dependent enhancement and direct adaptive immune responses.

Suppressed IgG4 class switching in dupilumab- and TNF inhibitor-treated patients after mRNA vaccination

BACKGROUND

The noninflammatory immunoglobulin G4 (IgG4) is linked to tolerance and is unique to humans. Although poorly understood, prolonged antigenic stimulation and IL-4-signaling along the T helper 2-axis may be instrumental in IgG4 class switching. Recently, repeated SARS-CoV-2 mRNA vaccination has been linked to IgG4 skewing. Although widely used immunosuppressive drugs have been shown to only moderately affect humoral responses to SARS-CoV-2 mRNA vaccination, the effect on IgG4 switching has not been investigated.

METHODS

Here we study the impact of such immunosuppressive drugs, including the IL-4 receptor-blocking antibody dupilumab, on IgG4 skewing upon repeated SARS-CoV-2 mRNA vaccination. Receptor-binding domain (RBD) specific antibody responses were longitudinally measured in 600 individuals, including patients with immune-mediated inflammatory diseases treated with a TNF inhibitor (TNFi) and/or methotrexate (MTX), dupilumab, and healthy/untreated controls, after repeated mRNA vaccination.

RESULTS

We observed a substantial increase in the proportion of RBD-specific IgG4 antibodies (median 21%) in healthy/untreated controls after third vaccination. This IgG4 skewing was profoundly reduced in dupilumab-treated patients (<1%). Unexpectedly, an equally strong suppression of IgG4 skewing was observed in TNFi-treated patients (<1%), whereas MTX caused a modest reduction (7%). RBD-specific total IgG levels were hardly affected by these immunosuppressive drugs. Minimal skewing was observed, when primary vaccination was adenoviral vector-based.

CONCLUSIONS

Our results imply a critical role for IL-4/IL-13 as well as TNF in vivo IgG4 class switching. These novel findings advance our understanding of IgG4 class switch dynamics, and may benefit humoral tolerance induction strategies, treatment of IgG4 pathologies and mRNA vaccine optimization.

IgG1 glycosylation highlights premature aging in Down syndrome

Down syndrome (DS) is characterized by lowered immune competence and premature aging. We previously showed decreased antibody response following SARS-CoV-2 vaccination in adults with DS. IgG1 Fc glycosylation patterns are known to affect the effector function of IgG and are associated with aging. Here, we compare total and anti-spike (S) IgG1 glycosylation patterns following SARS-CoV-2 vaccination in DS and healthy controls (HC). Total and anti-Spike IgG1 Fc N-glycan glycoprofiles were measured in non-exposed adults with DS and controls before and after SARS-CoV-2 vaccination by liquid chromatography-mass spectrometry (LC-MS) of Fc glycopeptides. We recruited N = 44 patients and N = 40 controls. We confirmed IgG glycosylation patterns associated with aging in HC and showed premature aging in DS. In DS, we found decreased galactosylation (50.2% vs. 59.0%) and sialylation (6.7% vs. 8.5%) as well as increased fucosylation (97.0% vs. 94.6%) of total IgG. Both cohorts showed similar bisecting GlcNAc of total and anti-S IgG1 with age. In contrast, anti-S IgG1 of DS and HC showed highly comparable glycosylation profiles 28 days post vaccination. The IgG1 glycoprofile in DS exhibits strong premature aging. The combination of an early decrease in IgG1 Fc galactosylation and sialylation and increase in fucosylation is predicted to reduce complement activity and decrease FcγRIII binding and subsequent activation, respectively. The altered glycosylation patterns, combined with decreased antibody concentrations, help us understand the susceptibility to severe infections in DS. The effect of premature aging highlights the need for individuals with DS to receive tailored vaccines and/or vaccination schedules.

Regulation of intracellular activity of N-glycan branching enzymes in mammals

Most proteins in the secretory pathway are glycosylated, and N-glycans are estimated to be attached to over 7000 proteins in humans. As structural variation of N-glycans critically regulates the functions of a particular glycoprotein, it is pivotal to understand how structural diversity of N-glycans is generated in cells. One of the major factors conferring structural variation of N-glycans is the variable number of N-acetylglucosamine branches. These branch structures are biosynthesized by dedicated glycosyltransferases, including GnT-III (MGAT3), GnT-IVa (MGAT4A), GnT-IVb (MGAT4B), GnT-V (MGAT5), and GnT-IX (GnT-Vb, MGAT5B). In addition, the presence or absence of core modification of N-glycans, namely, core fucose (included as an N-glycan branch in this manuscript), synthesized by FUT8, also confers large structural variation on N-glycans, thereby crucially regulating many protein-protein interactions. Numerous biochemical and medical studies have revealed that these branch structures are involved in a wide range of physiological and pathological processes. However, the mechanisms regulating the activity of the biosynthetic glycosyltransferases are yet to be fully elucidated. In this review, we summarize the previous findings and recent updates regarding regulation of the activity of these N-glycan branching enzymes. We hope that such information will help readers to develop a comprehensive overview of the complex system regulating mammalian N-glycan maturation.

Specific long-term changes in anti-SARS-CoV-2 IgG modifications and antibody functions in mRNA, adenovector, and protein subunit vaccines

Various vaccine platforms were developed and deployed against the COVID-19 disease. The Fc-mediated functions of IgG antibodies are essential in the adaptive immune response elicited by vaccines. However, the long-term changes of protein subunit vaccines and their combinations with messenger RNA (mRNA) vaccines are unknown. A total of 272 serum and plasma samples were collected from individuals who received first to third doses of the protein subunit Medigen, the mRNA (BNT, Moderna), or the adenovector AstraZeneca vaccines. The IgG subclass level was measured using enzyme-linked immunosorbent assay, and Fc-N glycosylation was measured using liquid chromatography coupled to tandem mass spectrometry. Antibody-dependent-cellular-phagocytosis (ADCP) and complement deposition (ADCD) of anti-spike (S) IgG antibodies were measured by flow cytometry. IgG1 and 3 reached the highest anti-S IgG subclass level. IgG1, 2, and 4 subclass levels significantly increased in mRNA- and Medigen-vaccinated individuals. Fc-glycosylation was stable, except in female BNT vaccinees, who showed increased bisection and decreased galactosylation. Female BNT vaccinees had a higher anti-S IgG titer than that of males. ADCP declined in all groups. ADCD was significantly lower in AstraZeneca-vaccinated individuals. Each vaccine produced specific long-term changes in Fc structure and function. This finding is critical when selecting a vaccine platform or combination to achieve the desired immune response.

GlYcoLISA: antigen-specific and subclass-specific IgG Fc glycosylation analysis based on an immunosorbent assay with an LC-MS readout

Immunoglobulin G (IgG) fragment crystallizable (Fc) glycosylation modulates effector functions such as antibody-dependent cellular cytotoxicity and complement-dependent cytotoxicity. Consequently, assessing IgG Fc glycosylation is important for understanding the role of antibodies in infectious, alloimmune and autoimmune diseases. GlYcoLISA determines the Fc glycosylation of antigen-specific IgG by an immunosorbent assay with a liquid chromatography-mass spectrometry (LC-MS) readout. Detection of antigen-specific IgG glycosylation in a subclass- and site-specific manner is realized by LC-MS-based glycopeptide analysis after proteolytic cleavage. GlYcoLISA addresses challenges related to the low abundance of specific IgG and the high background of total IgG by using well-established immunosorbent assays for purifying antibodies of the desired specificity using immobilized antigen. Alternative methods with sufficient glycan resolution lack these important specificities. GlYcoLISA is performed in a 96-well plate format, and the analysis of 160 samples takes ~5 d, with 1 d for sample preparation, 2 d of LC-MS measurement and 2 d for partially automated data processing. GlYcoLISA requires expertise in LC-MS operation and data processing.

ITAM-based receptors in natural killer cells

The ability of cells of the immune system to acquire features such as increased longevity and enhanced secondary responses was long thought to be restricted to cells of the adaptive immune system. Natural killer (NK) cells have challenged this notion by demonstrating that they can also gain adaptive features. This has been observed in both humans and mice during infection with cytomegalovirus (CMV). The generation of adaptive NK cells requires antigen-specific recognition of virally infected cells through stimulatory NK receptors. These receptors lack the ability to signal on their own and rather rely on adaptor molecules that contain ITAMs for driving signals. Here, we highlight our understanding of how these receptors influence the production of adaptive NK cells and propose areas in the field that merit further investigation.

SARS-CoV-2 membrane protein-specific antibodies from critically ill SARS-CoV-2-infected individuals interact with Fc receptor-expressing cells but do not neutralize the virus

The membrane (M) glycoprotein of SARS-CoV-2 is one of the key viral proteins regulating virion assembly and morphogenesis. Immunologically, the M protein is a major source of peptide antigens driving T cell responses, and most individuals who have been infected with SARS-CoV-2 make antibodies to the N-terminal, surface-exposed peptide of the M protein. We now report that although the M protein is abundant in the viral particle, antibodies to the surface-exposed N-terminal epitope of M do not appear to neutralize the virus. M protein-specific antibodies do, however, activate antibody-dependent cell-mediated cytotoxicity and cytokine secretion by primary human natural killer cells. Interestingly, while patients with severe or mild disease make comparable levels of M antigen-binding antibodies, M-specific antibodies from the serum of critically ill patients are significantly more potent activators of antibody-dependent cell-mediated cytotoxicity than antibodies found in individuals with mild or asymptomatic infection.

Immunoglobulin G N-glycan markers of accelerated biological aging during chronic HIV infection

People living with HIV (PLWH) experience increased vulnerability to premature aging and inflammation-associated comorbidities, even when HIV replication is suppressed by antiretroviral therapy (ART). However, the factors associated with this vulnerability remain uncertain. In the general population, alterations in the N-glycans on IgGs trigger inflammation and precede the onset of aging-associated diseases. Here, we investigate the IgG N-glycans in cross-sectional and longitudinal samples from 1214 women and men, living with and without HIV. PLWH exhibit an accelerated accumulation of pro-aging-associated glycan alterations and heightened expression of senescence-associated glycan-degrading enzymes compared to controls. These alterations correlate with elevated markers of inflammation and the severity of comorbidities, potentially preceding the development of such comorbidities. Mechanistically, HIV-specific antibodies glycoengineered with these alterations exhibit a reduced ability to elicit anti-HIV Fc-mediated immune activities. These findings hold potential for the development of biomarkers and tools to identify and prevent premature aging and comorbidities in PLWH.

Distinctive domains and activity regulation of core fucosylation enzyme FUT8

BACKGROUND

Core fucose, a structure added to the reducing end N-acetylglucosamine of N-glycans, has been shown to regulate various physiological and pathological processes, including melanoma metastasis, exacerbation of chronic obstructive pulmonary disease, and severe outcomes in COVID-19.

SCOPE OF REVIEW

Recent research has shed light on regulation of the activity and subcellular localization of a1,6-fucosyltransferase (FUT8), the glycosyltransferase responsible for core fucose biosynthesis, unraveling the mechanisms for controlling core fucosylation in vivo.

MAJOR CONCLUSIONS

This review summarizes the various features of FUT8, including its domains, structures, and substrate specificity. Additionally, we discuss the potential involvement of FUT8-binding proteins, such as oligosaccharyltransferase subunits, in the regulation of FUT8 activity, substrate specificity, and the secretion of FUT8.

GENERAL SIGNIFICANCE

We anticipate that this review will contribute to a deeper understanding of the control of core fucose levels in vivo and involvement of core fucosylation in FUT8-relevant functions and diseases.

PfEMP1 and var genes - Still of key importance in Plasmodium falciparum malaria pathogenesis and immunity

The most severe form of malaria, caused by infection with Plasmodium falciparum parasites, continues to be an important cause of human suffering and poverty. The P. falciparum erythrocyte membrane protein 1 (PfEMP1) family of clonally variant antigens, which mediates the adhesion of infected erythrocytes to the vascular endothelium in various tissues and organs, is a central component of the pathogenesis of the disease and a key target of the acquired immune response to malaria. Much new knowledge has accumulated since we published a systematic overview of the PfEMP1 family almost ten years ago. In this chapter, we therefore aim to summarize research progress since 2015 on the structure, function, regulation etc. of this key protein family of arguably the most important human parasite. Recent insights regarding PfEMP1-specific immune responses and PfEMP1-specific vaccination against malaria, as well as an outlook for the coming years are also covered.

The association between plasma IgG N-glycosylation and neonatal hypoxic-ischemic encephalopathy: a case-control study

Introduction

Hypoxic-ischemic encephalopathy (HIE) is one of severe neonatal brain injuries, resulting from inflammation and the immune response after perinatal hypoxia and ischemia. IgG N-glycosylation plays a crucial role in various inflammatory diseases through mediating the balance between anti-inflammatory and pro-inflammatory responses. This study aimed to explore the effect of IgG N-glycosylation on the development of HIE.

Methods

This case-control study included 53 HIE patients and 57 control neonates. An ultrahigh-performance liquid chromatography (UPLC) method was used to determine the features of the plasma IgG N-glycans, by which 24 initial glycan peaks (GPs) were quantified. Multivariate logistic regression was used to examine the association between initial glycans and HIE, by which the significant parameters were used to develop a diagnostic model. Though receiver operating characteristic (ROC) curves, area under the curve (AUC) and 95% confidence interval (CI) were calculated to assess the performance of the diagnostic model.

Results

There were significant differences in 11 initial glycans between the patient and control groups. The levels of fucosylated and galactosylated glycans were significantly lower in HIE patients than in control individuals, while sialylated glycans were higher in HIE patients (p < 0.05). A prediction model was developed using three initial IgG N-glycans and fetal distress, low birth weight, and globulin. The ROC analysis showed that this model was able to discriminate between HIE patients and healthy individuals [AUC = 0.798, 95% CI: (0.716-0.880)].

Discussion

IgG N-glycosylation may play a role in the pathogenesis of HIE. Plasma IgG N-glycans are potential noninvasive biomarkers for screening individuals at high risk of HIE.

Filamentous fungus-produced human monoclonal antibody provides protection against SARS-CoV-2 in hamster and non-human primate models

Monoclonal antibodies are an increasingly important tool for prophylaxis and treatment of acute virus infections like SARS-CoV-2 infection. However, their use is often restricted due to the time required for development, variable yields and high production costs, as well as the need for adaptation to newly emerging virus variants. Here we use the genetically modified filamentous fungus expression system Thermothelomyces heterothallica (C1), which has a naturally high biosynthesis capacity for secretory enzymes and other proteins, to produce a human monoclonal IgG1 antibody (HuMab 87G7) that neutralises the SARS-CoV-2 variants of concern (VOCs) Alpha, Beta, Gamma, Delta, and Omicron. Both the mammalian cell and C1 produced HuMab 87G7 broadly neutralise SARS-CoV-2 VOCs in vitro and also provide protection against VOC Omicron in hamsters. The C1 produced HuMab 87G7 is also able to protect against the Delta VOC in non-human primates. In summary, these findings show that the C1 expression system is a promising technology platform for the development of HuMabs in preventive and therapeutic medicine.

Are Changes in Serum IgG Glycosylation Related to the Severe Course of SARS-CoV-2 Infection and Recovery Process? In Search of New Diagnostic and Prognostic Biomarkers

Introduction

Immunoglobulin G (IgG) glycosylation affects its effector functions and is essential in many steps of the inflammatory cascade. Therefore, it may be an important parameter for assessing the body's immune response during the course of COVID-19 (Coronavirus disease 2019).

Methods

The N- and O-glycosylation of serum IgG in severe COVID-19 patients (n=87), convalescents (n=50), and healthy subjects (n=65) were examined using a modified lectin-ELISA method with specific biotinylated lectins. The obtained data were analyzed using STATISTICA 13.3PL software.

Results

We showed significantly higher expression of Lewisx oligosaccharide structures in severe COVID-19 patients than in the other two groups. Moreover, significantly lower expression of Lewisy sugar structures in IgG glycans was observed in the convalescents when compared with COVID-19 patients and healthy subjects. The lowest expression of highly branched N-glycans in cases of severe COVID-19 indicates that the development of the disease is associated with the presence of typical IgG biantennary N-glycans. The lack of significant differences in the expression of Tn antigen in IgG between studied groups and the significantly lower expression of T antigen in convalescents compared to the patients with severe COVID-19 and healthy subjects indicates a decrease in the content of the T antigen in IgG O-glycans in subjects recovered from COVID-19. Substantially higher reactivities of IgG O-glycans with Jacalin observed in COVID-19 patients and convalescents in comparison to the control group were most probably caused by increased expression of core 3 O-glycans in IgG.

Conclusion

Severe COVID-19 is accompanied by the expression in serum IgG of sialylated biantennary and highly branched N-glycans, decorated by fucose of Lewisx and Lewisy structures. The higher reactivity of IgG O-glycans with Jacalin in severe COVID-19 patients and convalescents indicates that the disease development and the recovery process are most probably accompanied by increased expression of the core 3 O-glycans.

Assessment of IgG-Fc glycosylation from individual RhD-specific B cell clones reveals regulation at clonal rather than clonotypic level

The type and strength of effector functions mediated by immunoglobulin G (IgG) antibodies rely on the subclass and the composition of the N297 glycan. Glycosylation analysis of both bulk and antigen-specific human IgG has revealed a marked diversity of the glycosylation signatures, including highly dynamic patterns as well as long-term stability of profiles, yet information on how individual B cell clones would contribute to this diversity has hitherto been lacking. Here, we assessed whether clonally related B cells share N297 glycosylation patterns of their secreted IgG. We differentiated single antigen-specific peripheral IgG+ memory B cells into antibody-secreting cells and analysed Fc glycosylation of secreted IgG. Furthermore, we sequenced the variable region of their heavy chain, which allowed the grouping of the clones into clonotypes. We found highly diverse glycosylation patterns of culture-derived IgG, which, to some degree, mimicked the glycosylation of plasma IgG. Each B cell clone secreted IgG with a mixture of different Fc glycosylation patterns. The majority of clones produced fully fucosylated IgG. B cells producing afucosylated IgG were scattered across different clonotypes. In contrast, the remaining glycosylation traits were, in general, more uniform. These results indicate IgG-Fc fucosylation to be regulated at the single-clone level, whereas the regulation of other glycosylation traits most likely occurs at a clonotypic or systemic level. The discrepancies between plasma IgG and culture-derived IgG, could be caused by the origin of the B cells analysed, clonal dominance or factors from the culture system, which need to be addressed in future studies.