Multi-Angle Effector Function Analysis of Human Monoclonal IgG Glycovariants

Underappreciated layers of antibody-mediated immune synapse architecture and dynamics

The biologic activities of antibody drugs are dictated by structure-function relationships-emerging from the kind, composition, and degree of interactions with a target antigen and with soluble and cellular antibody receptors of the innate immune system. These activities are canonically understood to be both modular: antigen recognition is driven by the heterodimeric antigen-binding fragment, and innate immune recruitment by the homodimeric constant/crystallizable fragment. The model that treats these domains with a high degree of independence has served the field well but is not without limitations. Here, we consider how new insights, particularly from structural studies, complicate the model of neat biophysical separation between these domains and shape our understanding of antibody effector functions. The emerging model endeavors to explain the phenotypic impact of both antibody intrinsic characteristics and extrinsic features-fitting them within a spatiotemporal paradigm that better accounts for observed antibody activities. In this review, we will use insights from recent models of classical complement complexes and T cell immune synapse formation to explore how structural differences in antibody-mediated immune synapses may relate to their functional diversity.

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.

Therapeutic antibodies in oncology: an immunopharmacological overview

The biotechnological development of monoclonal antibodies and their immunotherapeutic use in oncology have grown exponentially in the last decade, becoming the first-line therapy for some types of cancer. Their mechanism of action is based on the ability to regulate the immune system or by interacting with targets that are either overexpressed in tumor cells, released into the extracellular milieu or involved in processes that favor tumor growth. In addition, the intrinsic characteristics of each subclass of antibodies provide specific effector functions against the tumor by activating antibody-dependent cellular cytotoxicity, complement-dependent cytotoxicity, and antibody-dependent cellular phagocytosis, among other mechanisms. The rational design and engineering of monoclonal antibodies have improved their pharmacokinetic and pharmacodynamic features, thus optimizing the therapeutic regimens administered to cancer patients and improving their clinical outcomes. The selection of the immunoglobulin G subclass, modifications to its crystallizable region (Fc), and conjugation of radioactive substances or antineoplastic drugs may all improve the antitumor effects of therapeutic antibodies. This review aims to provide insights into the immunological and pharmacological aspects of therapeutic antibodies used in oncology, with a rational approach at molecular modifications that can be introduced into these biological tools, improving their efficacy in the treatment of cancer.

Engineering of pH-dependent antigen binding properties for toxin-targeting IgG1 antibodies using light-chain shuffling

Immunoglobulin G (IgG) antibodies that bind their cognate antigen in a pH-dependent manner (acid-switched antibodies) can release their bound antigen for degradation in the acidic environment of endosomes, while the IgGs are rescued by the neonatal Fc receptor (FcRn). Thus, such IgGs can neutralize multiple antigens over time and therefore be used at lower doses than their non-pH-responsive counterparts. Here, we show that light-chain shuffling combined with phage display technology can be used to discover IgG1 antibodies with increased pH-dependent antigen binding properties, using the snake venom toxins, myotoxin II and α-cobratoxin, as examples. We reveal differences in how the selected IgG1s engage their antigens and human FcRn and show how these differences translate into distinct cellular handling properties related to their pH-dependent antigen binding phenotypes and Fc-engineering for improved FcRn binding. Our study showcases the complexity of engineering pH-dependent antigen binding IgG1s and demonstrates the effects on cellular antibody-antigen recycling.

Benchmarking glycoform-resolved affinity separation - mass spectrometry assays for studying FcγRIIIa binding

The antibody- FcγRIIIa interaction triggers key immunological responses such as antibody dependent cellular cytotoxicity (ADCC), making it highly important for therapeutic mAbs. Due to the direct glycan-glycan interaction with FcγRIIIa receptor, differences in antibody glycosylation can drastically influence the binding affinity. Understanding the differential binding of mAb glycoforms is a very important, yet challenging task due to the co-existence of multiple glycoforms in a sample. Affinity liquid chromatography (AC) and affinity capillary electrophoresis (ACE) hyphenated with mass spectrometry (MS) can provide glycoform-resolved affinity profiles of proteins based on their differences in either dissociation (AC) or equilibrium (ACE) constants. To cross-validate the affinity ranking provided by these complementary novel approaches, both techniques were benchmarked using the same FcγRIIIa constructs. Both approaches were able to assess the mAb - FcγRIIIa interaction in a glycoform selective manner and showed a clear increase in binding for fully versus hemi-fucosylated mAbs. Also, other features, such as increasing affinity with elevated galactosylation or the binding affinity for high mannose glycoforms were consistent. We further applied these approaches to assess the binding towards the F158 allotype of FcγRIIIa, which was not reported before. The FcγRIIIa F158 allotype showed a very similar profile compared to the V158 receptor with the strongest increase in binding due to afucosylation and only a slight increase in binding with additional galactosylation. Both techniques showed a decrease of the binding affinity for high mannose glycoforms for FcγRIIIa F158 compared to the V158 variant. Overall, both approaches provided very comparable results in line with orthogonal methods proving the capabilities of separation-based affinity approaches to study FcγR binding of antibody glycoforms.

Immunogenicity at delivery after Tdap vaccination in successive pregnancies

Background

Tetanus, diphtheria, acellular pertussis (Tdap) vaccination is recommended to be administered in every pregnancy. Although the safety of this strategy has been confirmed, the immunogenicity of Tdap vaccination in two successive pregnancies has not yet been described. This study investigated Tdap-specific immunity levels and transplacental transfer in two successive pregnancies after repeated Tdap-vaccination.

Methods

Women enrolled in prior studies on Tdap vaccination during pregnancy were invited to participate in a follow-up study if they became pregnant again. Women who received a Tdap vaccine in both pregnancies were considered for this analysis. Tdap-specific total IgG and IgG subclasses were measured with a multiplex immunoassay.

Results

In total, 27 participants with a mean interval between deliveries of 2.4 years were included in the analysis. In maternal serum, Tdap-specific total IgG levels were comparable at both deliveries whereas in cord serum, all Tdap-specific total IgG antibody levels were reduced at the second compared to the first delivery. This was largely reflected in the IgG1 levels in maternal and cord serum. Transplacental transfer ratios of total IgG and IgG1 were also mostly reduced in the second compared to the first pregnancy.

Conclusion

This study reports for the first time Tdap-specific total IgG and IgG subclass levels and transfer ratios after repeated Tdap vaccination in successive pregnancies. We found reduced transfer of most Tdap-specific IgG and IgG1 antibodies in the successive pregnancy. As pertussis-specific antibodies wane quickly, Tdap vaccination in each pregnancy remains beneficial. However, more research is needed to understand the impact of closely spaced booster doses during pregnancy on early infant protection against pertussis.

The elusive nature of the oligoclonal bands in multiple sclerosis

Intrathecal immunoglobulin G (IgG) and oligoclonal bands (OCBs) detected in both the brain and cerebrospinal fluid (CSF) are seminal features of multiple sclerosis (MS). The presence of OCBs correlates with elevated disease burden and severity and supports the diagnosis of MS. Despite numerous investigations into the potential viral and autoantigen targets, the precise antigenic specificity of OCBs has remained elusive. We have little knowledge of the nature regarding these oligoclonal IgG bands. Here, we present compelling evidence highlighting the key findings that both OCBs and intrathecal IgG antibodies are under genetic control and that OCBs originate from clonal B-cells in both the periphery and CNS. We propose that MS OCBs are IgG immune complexes composed of IgG1 and IgG3 antibodies and that the pathological role of OCB stems from the IgG effector functions of these complexes, leading to demyelination and axonal injuries. We present additional evidence regarding the nature of MS OCBs: (1) disease-modifying therapies have been shown to affect CSF OCB; (2) OCBs have also been detected in several neuroinfectious diseases; (3) Epstein-Barr virus (EBV) has been particularly linked with MS pathogenesis, and its association with OCB is an important area of study. Although OCBs are closely associated with MS, more meticulously planned research is necessary to clarify the precise role of OCB in MS, both in terms of disease pathogenesis and diagnosis.

Decoding the mannose receptor-mAb interaction: the importance of high-mannose N-glycans and glycan-pairing

During the development process of therapeutic monoclonal antibodies (mAbs), it is crucial to control (critical) quality attributes such as N-glycosylation influencing pharmacokinetics (PK) and Fc effector functions. Previous reports have shown that mAbs containing high-mannose N-glycans are cleared faster from blood circulation, leading to reduced half-lives. The high-mannose N-glycan content of mAbs can be influenced during the cell culture process by factors such as cell lines, process conditions, and media. Furthermore, mAbs have either one high mannose N-glycan (asymmetrical high-mannose glyco-pair) or two high mannose N-glycans (symmetrical high-mannose glyco-pair). The hypothesis that the mannose receptor (MR, CD206) accelerates clearance by facilitating their internalization and subsequent lysosomal degradation is widespread. However, the interaction between MR and mAbs has not been explicitly demonstrated. This study aimed to investigate this interaction, providing the first systematic demonstration of MR binding to the Fc region of mAbs with high-mannose N-glycans. Two novel analytical methods, MR surface plasmon resonance and MR affinity chromatography, were developed and applied to investigate the MR-mAb interaction. The interaction is found to be dependent on high-mannose content, but is independent of the mAb format or sequence. However, different glyco-pairs exhibited varying binding affinities to the MR, with the symmetrical high-mannose glyco-pair showing the strongest binding properties. These findings strengthen the hypothesis for the MR-mediated mAb interaction and contribute to a deeper understanding of the MR-mAb interaction, which could affect the criticality of high-mannose containing mAbs development strategies of IgG-based molecules and improve their PK profiles.

Immunomodulation of Antibody Glycosylation through the Placental Transfer

Establishing an immune balance between the mother and fetus during gestation is crucial, with the placenta acting as the epicenter of immune tolerance. The placental transfer of antibodies, mainly immunoglobulin G (IgG), is critical in protecting the developing fetus from infections. This review looks at how immunomodulation of antibody glycosylation occurs during placental transfer and how it affects fetal health. The passage of maternal IgG antibodies through the placental layers, including the syncytiotrophoblast, stroma, and fetal endothelium, is discussed. The effect of IgG subclass, glycosylation, concentration, maternal infections, and antigen specificity on antibody transfer efficiency is investigated. FcRn-mediated IgG transport, influenced by pH-dependent binding, is essential for placental transfer. Additionally, this review delves into the impact of glycosylation patterns on antibody functionality, considering both protective and pathological effects. Factors affecting the transfer of protective antibodies, such as maternal vaccination, are discussed along with reducing harmful antibodies. This in-depth examination of placental antibody transfer and glycosylation provides insights into improving neonatal immunity and mitigating the effects of maternal autoimmune and alloimmune conditions.

Glycosylation differences of an anti-VEGF monoclonal antibody (PRO-169) and its extensive comparison with Bevacizumab

PRO-169 is an anti-VEGF monoclonal antibody developed by Laboratorios Sophia that shares its sequence with Bevacizumab (BVZ); though, PRO-169 is intended for intravitreal administration. In this study, analytical characterization showed that PRO-169 had glycosylation differences in comparison to BVZ reference product (RP); since it had more content of G1F, G2F, sialic acid and high mannose. Further investigation was performed to evaluate if differences between both products would affect the efficacy and safety profile of PRO-169. PRO-169 had no alteration in its in vitro biological activity; moreover, no cytotoxicity or immunogenicity concerns should be expected as demonstrated by different orthogonal methods at analytical, in vitro and in vivo assays. These results support moving to the clinical testing of PRO-169 since no major complications will be expected with its clinical use for the treatment of ophthalmic diseases.

Fc-Engineered Therapeutic Antibodies: Recent Advances and Future Directions

Monoclonal therapeutic antibodies have revolutionized the treatment of cancer and other diseases. Fc engineering aims to enhance the effector functions or half-life of therapeutic antibodies by modifying their Fc regions. Recent advances in the Fc engineering of modern therapeutic antibodies can be considered the next generation of antibody therapy. Various strategies are employed, including altering glycosylation patterns via glycoengineering and introducing mutations to the Fc region, thereby enhancing Fc receptor or complement interactions. Further, Fc engineering strategies enable the generation of bispecific IgG-based heterodimeric antibodies. As Fc engineering techniques continue to evolve, an expanding portfolio of Fc-engineered antibodies is advancing through clinical development, with several already approved for medical use. Despite the plethora of Fc-based mutations that have been analyzed in in vitro and in vivo models, we focus here in this review on the relevant Fc engineering strategies of approved therapeutic antibodies to finetune effector functions, to modify half-life and to stabilize asymmetric bispecific IgGs.

Antibody attributes, Fc receptor expression, gestation and maternal SARS-CoV-2 infection modulate HSV IgG placental transfer

Antibody-dependent cellular cytotoxicity (ADCC) is associated with protection against neonatal herpes. We hypothesized that placental transfer of ADCC-mediating herpes simplex virus (HSV) immunoglobulin G (IgG) is influenced by antigenic target, function, glycans, gestational age, and maternal severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. Maternal and cord blood were collected from HSV-seropositive (HSV+) mothers pre-COVID and HSV+/SARS-CoV-2+ mothers during the pandemic. Transfer of HSV neutralizing IgG was significantly lower in preterm versus term dyads (transfer ratio [TR] 0.84 vs. 2.44) whereas the TR of ADCC-mediating IgG was <1.0 in both term and preterm pre-COVID dyads. Anti-glycoprotein D IgG, which had only neutralizing activity, and anti-glycoprotein B (gB) IgG, which displayed neutralizing and ADCC activity, exhibited different relative affinities for the neonatal Fc receptor (FcRn) and expressed different glycans. The transfer of ADCC-mediating IgG increased significantly in term SARS-CoV-2+ dyads. This was associated with greater placental colocalization of FcRn with FcγRIIIa. These findings have implications for strategies to prevent neonatal herpes.

The role of N-glycosylation in B-cell biology and IgG activity. The aspects of autoimmunity and anti-inflammatory therapy

The immune system is strictly regulated by glycosylation through the addition of highly diverse and dynamically changing sugar structures (glycans) to the majority of immune cell receptors. Although knowledge in the field of glycoimmunology is still limited, numerous studies point to the key role of glycosylation in maintaining homeostasis, but also in reflecting its disruption. Changes in oligosaccharide patterns can lead to impairment of both innate and acquired immune responses, with important implications in the pathogenesis of diseases, including autoimmunity. B cells appear to be unique within the immune system, since they exhibit both innate and adaptive immune activity. B cell surface is rich in glycosylated proteins and lectins which recognise glycosylated ligands on other cells. Glycans are important in the development, selection, and maturation of B cells. Changes in sialylation and fucosylation of cell surface proteins affect B cell signal transduction through BCRs, CD22 inhibitory coreceptor and Siglec-G. Plasmocytes, as the final stage of B cell differentiation, produce and secrete immunoglobulins (Igs), of which IgGs are the most abundant N-glycosylated proteins in human serum with the conserved N-glycosylation site at Asn297. N-oligosaccharide composition of the IgG Fc region affects its secretion, structure, half-life and effector functions (ADCC, CDC). IgG N-glycosylation undergoes little change during homeostasis, and may gradually be modified with age and during ongoing inflammatory processes. Hyperactivated B lymphocytes secrete autoreactive antibodies responsible for the development of autoimmunity. The altered profile of IgG N-glycans contributes to disease progression and remission and is sensitive to the application of therapeutic substances and immunosuppressive agents. In this review, we focus on the role of N-glycans in B-cell biology and IgG activity, the rearrangement of IgG oligosaccharides in aging, autoimmunity and immunosuppressive therapy.

Study on antibody Fc-glycosylation for optimal effector functions

A comprehensive structure-activity relationship study on antibody Fc-glycosylation has been performed using the chimeric anti-SSEA4 antibody chMC813-70 as a model. The α-2,6 sialylated biantennary complex type glycan was identified as the optimal Fc-glycan with significant enhancement in antibody effector functions, including binding to different Fc receptors and ADCC.

Evidence for the Role of a Second Fc-Binding Receptor in Placental IgG Transfer in Nonhuman Primates

Transplacental transfer of maternal antibodies provides the fetus and newborn with passive protection against infectious diseases. While the role of the highly conserved neonatal Fc receptor (FcRn) in transfer of IgG in mammals is undisputed, recent reports have suggested that a second receptor may contribute to transport in humans. We report poor transfer efficiency of plant-expressed recombinant HIV-specific antibodies, including engineered variants with high FcRn affinity, following subcutaneous infusion into rhesus macaques close to parturition. Unexpectedly, unlike those derived from mammalian tissue culture, plant-derived antibodies were essentially unable to cross macaque placentas. This defect was associated with poor Fcγ receptor binding and altered Fc glycans and was not recapitulated in mice. These results suggest that maternal-fetal transfer of IgG across the three-layer primate placenta may require a second receptor and suggest a means of providing maternal antibody treatments during pregnancy while avoiding fetal harm. IMPORTANCE This study compared the ability of several human HIV envelope-directed monoclonal antibodies produced in plants with the same antibodies produced in mammalian cells for their ability to cross monkey and mouse placentas. We found that the two types of antibodies have comparable transfer efficiencies in mice, but they are differentially transferred across macaque placentas, consistent with a two-receptor IgG transport model in primates. Importantly, plant-produced monoclonal antibodies have excellent binding characteristics for human FcRn receptors, permitting desirable pharmacokinetics in humans. The lack of efficient transfer across the primate placenta suggests that therapeutic plant-based antibody treatments against autoimmune diseases and cancer could be provided to the mother while avoiding transfer and preventing harm to the fetus.

Enhancing pharmacokinetic and pharmacodynamic properties of recombinant therapeutic proteins by manipulation of sialic acid content

The circulatory half-life of recombinant therapeutic proteins is an important pharmacokinetic attribute because it determines the dosing frequency of these drugs, translating directly to treatment cost. Thus, recombinant therapeutic glycoproteins such as monoclonal antibodies have been chemically modified by various means to enhance their circulatory half-life. One approach is to manipulate the N-glycan composition of these agents. Among the many glycan constituents, sialic acid (specifically, N-acetylneuraminic acid) plays a critical role in extending circulatory half-life by masking the terminal galactose that would otherwise be recognised by the hepatic asialoglycoprotein receptor (ASGPR), resulting in clearance of the biotherapeutic from the circulation. This review aims to provide an illustrative overview of various strategies to enhance the pharmacokinetic/pharmacodynamic properties of recombinant therapeutic proteins through manipulation of their sialic acid content.

CD3 Target Affinity Chromatography Mass Spectrometry as a New Tool for Function-Structure Characterization of T-Cell Engaging Bispecific Antibody Proteoforms and Product-Related Variants

T-cell engaging bispecific antibodies (TCBs) targeting CD3 and tumor-specific antigens are very promising therapeutic modalities. Since CD3 binding is crucial for the potency of TCBs, understanding the functional impact of CD3 antigen-binding fragment modifications is of utmost importance for defining critical quality attributes (CQA). The current CQA assessment strategy requires the integration of structure-based physicochemical separation and functional cell-based potency assays. However, this strategy is tedious, and coexisting proteoforms with potentially different functionalities may not be individually assessed. This increases the degree of ambiguities for defining meaningful CQAs, particularly for complex bispecific antibody formats such as TCBs. Here, we report for the first time a proof-of-concept study to separate and identify critically modified proteoforms of TCBs using functional CD3 target affinity chromatography (AC) coupled with online mass spectrometry (MS). Our method enabled functional distinction of relevant deamidated and glycosylated proteoforms and the simultaneous assessment of product-related variants such as TCB mispairings. For example, CD3 AC-MS allowed us to separate TCB mispairings with increased CD3 binding (i.e., knob-knob homodimers) within the bound fraction. The functional separation of proteoforms was validated using an established workflow for CQA identification based on thoroughly characterized ion-exchange fractions of a 2+1 TCB. In addition, the new method facilitated the criticality assessment of post-translational modifications in stress studies and structural variants in early stage clone selection. CD3 AC-MS has high impact for streamlining the integration of functional and structural characterizations of the large landscape of therapeutic CD3 targeting TCBs from early stage research to late stage characterization.

IgG Fab Glycans Hinder FcRn-Mediated Placental Transport

Abs can be glycosylated in both their Fc and Fab regions with marked effects on Ab function and binding. High levels of IgG Fab glycosylation are associated with malignant and autoimmune conditions, exemplified by rheumatoid arthritis and highly Fab-glycosylated (∼90%) anti-citrullinated protein Abs (ACPAs). Important properties of IgG, such as long half-life and placental transport, are facilitated by the human neonatal Fc receptor (hFcRn). Although it is known that glycosylation of Abs can affect binding to Fc receptors, little is known on the impact of IgG Fab glycosylation on hFcRn binding and transplacental transport. Therefore, we analyzed the interaction between hFcRn and IgG with and without Fab glycans in vitro with various methods as well as in vivo by studying placental transfer of Fab-glycosylated Abs from mothers to newborns. No effect of Fab glycosylation on IgG binding to hFcRn was found by surface plasmon resonance and hFcRn affinity chromatography. In contrast, studies in a cell membrane context revealed that Fab glycans negatively impacted IgG-hFcRn interaction. In line with this, we found that Fab-glycosylated IgGs were transported ∼20% less efficiently across the placenta. This appeared to be a general phenomenon, observed for ACPAs, non-ACPAs, as well as total IgG in rheumatoid arthritis patients and healthy controls. Our results suggest that, in a cellular context, Fab glycans inhibit IgG-hFcRn interaction and thus negatively affect the transplacental transfer of IgG. As Fab-glycosylated Abs are frequently associated with autoimmune and malignant disorders and may be potentially harmful, this might encompass a regulatory mechanism, limiting the half-life and transport of such Abs.

Immunoglobulin G glycans - Biomarkers and molecular effectors of aging

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

Affinity capillary electrophoresis – mass spectrometry permits direct binding assessment of IgG and FcγRIIa in a glycoform-resolved manner

The impact of antibody glycoforms on FcγRIIa activation and immune responses is poorly understood. Yet, glycoform binding assessment remains one of the major analytical challenges requiring long enrichment or glycoengineering steps. Here, we developed and applied an affinity capillary electrophoresis-mass spectrometry approach to selectively assess the binding of different antibody glycoforms to the FcγIIa receptor without the need of glycoengineering. The approach required only low microgram amounts of antibody and receptor and enables assessing the binding of high and low-abundance glycoforms. The approach indicated clear differences in binging between doubly-, hemi-glycosylated and non-glycosylated antibodies as well as for mutated (Leu234Ala, Leu235Ala – Pro329-Gly (LALA-PG)) IgG1 antibodies silenced for Fcγ binding. The LALA-PG mutated antibody showed no binding to the FcγIIa receptor (excluding potential non-specific binding effects) while the non-glycosylated IgG1 showed a strongly reduced, but still minor binding. The highest binding affinity was for the antibody carrying two complex-type glycans. Man5 glycans resulted in decreased binding compared to complex-type glycans, with the lowest binding for the IgG containing two Man5. For complex-type glycans, galactosylation showed a subtle increase in binding to the FcγIIa receptor, and sialylation showed an increase in binding for lower sialylated species. Fucosylation did not influence binding to the FcγIIa receptor. Finally, the assay was evaluated for the two variants of the FcγRIIa receptor (allotypes H131 and R131) showing highly comparable glycoform selectivity. Overall, the proposed approach allows the direct comparison of binding affinities of different antibody species in mixtures promising a fast establishment of their structure-function relationships.

Contribution of the ex vivo placental perfusion model in understanding transplacental immunoglobulin G transfer

INTRODUCTION

The acquisition of humoral immunity in utero is essential for the fetus. The crucial protein, which is responsible for this part of immunity, is immunoglobulin-G (IgG). Immune functions of IgGs are mediated via the interaction of the crystallizable fragment (Fc) region of IgG with specific Fc γ receptors (FcγRs). However, an atypical FcγR, the neonatal Fc receptor (FcRn), is a key regulator of IgG transfer across the human placenta. During the last four decades ex vivo placental perfusion studies have contributed significantly to the study of mechanisms of IgG transfer across the multicellular placental barrier.

METHOD

A PubMed search was conducted by using specific keywords: placenta, perfusion and IgG to review manuscripts using human placental perfusion to study the transplacental transfer of IgG. Relevant studies found in reference lists of these manuscripts were also added to the review, and references were included that supported or gave nuance to the discussion of the mechanisms of IgG kinetics in the placenta.

RESULTS AND DISCUSSION

We found twenty publications on the study of transplacental transfer of IgG using human ex vivo placental perfusion, by research groups with partly different settings. This review summarizes knowledge about placental IgG transfer, with a strong focus on the contributions from ex vivo placental perfusion studies.

HIV-associated alterations of the biophysical features of maternal antibodies correlate with their reduced transfer across the placenta

BACKGROUND

Human Immunodeficiency Virus (HIV) infection during pregnancy is associated with reduced transplacental transfer of maternal antibodies and increased risk of severe infections in children who are exposed and uninfected with HIV (CHEU). The basis of this reduced transfer of maternal immunity has not yet been defined but could involve modifications in the biophysical features of antibodies.

OBJECTIVE

To assess the impact of maternal HIV infection on the biophysical features of serum IgG and transplacental antibody transfer.

METHODS

Maternal serum IgG subclass levels, Fc glycosylation, Fc Receptor (FcR) binding, and transplacental transfer of pathogen-specific maternal IgG were measured in pregnant women living with HIV (WWH) and pregnant women testing negative for HIV (WNH) in Cape Town, South Africa.

RESULTS

Maternal antibody profiles were strikingly different between pregnant WWH and WNH. Antibody binding to FcγR2a and FcγR2b, IgG1 and IgG3 antibodies, and agalactosylated antibodies were all elevated in WLHIV, whereas digalactosylated and sialylated antibodies were reduced as compared to pregnant WNH. Antibody features that were elevated in WWH were also correlated with reduced transplacental transfer of vaccine antigen-specific antibodies.

CONCLUSION

HIV infection is associated with marked alterations of biophysical features of maternal IgG and reduced placental transfer-potentially impairing antimicrobial immunity.

Streamlining the Transition From Yeast Surface Display of Antibody Fragment Immune Libraries to the Production as IgG Format in Mammalian Cells

Yeast-surface display (YSD) is commonly applied to screen Fab immune or naïve libraries for binders of predefined target molecules. However, reformatting of isolated variants represents a time-intensive bottleneck. Herein, we present a novel approach to facilitate a lean transition from antibody screening using YSD Fab libraries to the production of full-length IgG antibodies in Expi293-F cells. In this study, utilizing Golden Gate Cloning (GGC) and a bidirectional promoter system, an exemplary Fab-displaying YSD library was generated based on immunised transgene rats. After subsequent screening for antigen-specific antibody candidates by fluorescence-activated cell sorting (FACS), the Fab-encoding genes were subcloned into a bidirectional mammalian expression vector, exhibiting CH2-CH3 encoding genes, in a GGC-mediated, PCR-free manner. This novel, straightforward and time-saving workflow allows the VH/VL pairing to be preserved. This study resulted in antibody variants exhibiting suitable biophysical properties and covered a broad VH diversity after two rounds of FACS screening, as revealed by NGS analysis. Ultimately, we demonstrate that the implication of such a gene transfer system streamlines antibody hit discovery efforts, allowing the faster characterisation of antibodies against a plethora of targets that may lead to new therapeutic agents.

Therapeutic antibody glycosylation impacts antigen recognition and immunogenicity

In this study we show that glycosylation is relevant for immune recognition of therapeutic antibodies, and that defined glycan structures can modulate immunogenicity. Concerns regarding immunogenicity arise from the high heterogeneity in glycosylation that is difficult to control and can deviate from human glycosylation if produced in non-human cell lines. While non-human glycosylation is thought to cause hypersensitivity reactions and immunogenicity, less is known about effects of Fc-associated glycan structures on immune cell responses. We postulated that glycosylation influences antigen recognition and subsequently humoral responses to therapeutic antibodies by modulating 1) recognition and uptake by dendritic cells (DCs), and 2) antigen routing, processing and presentation. Here, we compared different glycosylation variants of the antibody rituximab (RTX) in in vitro assays using human DCs and T cells as well as in in vivo studies. We found that human DCs bind and internalize unmodified RTX stronger compared to its aglycosylated form suggesting that glycosylation mediates uptake after recognition by glycan-specific receptors. Furthermore, we show that DC-uptake of RTX increases or decreases if glycosylation is selectively modified to recognize activating (by mannosylation) or inhibitory lectin receptors (by sialylation). Moreover, glycosylation seems to influence antigen presentation by DCs because specific glycovariants tend to induce either stronger or weaker T cell activation. Finally, we demonstrate that antibody glycosylation impacts anti-drug antibody (ADA) responses to RTX in vivo. Hence, defined glycan structures can modulate immune recognition and alter ADA responses. Glyco-engineering may help to decrease clinical immunogenicity and ADA-associated adverse events such as hypersensitivity reactions.

Studying protein structure and function by native separation–mass spectrometry

Alterations in protein structure may have profound effects on biological function. Analytical techniques that permit characterization of proteins while maintaining their conformational and functional state are crucial for studying changes in the higher order structure of proteins and for establishing structure-function relationships. Coupling of native protein separations with mass spectrometry is emerging rapidly as a powerful approach to study these aspects in a reliable, fast and straightforward way. This Review presents the available native separation modes for proteins, covers practical considerations on the hyphenation of these separations with mass spectrometry and highlights the involvement of affinity-based separations to simultaneously obtain structural and functional information of proteins. The impact of these approaches is emphasized by selected applications addressing biomedical and biopharmaceutical research questions.

HDX-MS and MD Simulations Provide Evidence for Stabilization of the IgG1-FcγRIa (CD64a) Immune Complex Through Intermolecular Glycoprotein Bonds

Previous reports present different models for the stabilization of the Fc-FcγRI immune complex. Although accord exists on the importance of L235 in IgG1 and some hydrophobic contacts for complex stabilization, discord exists regarding the existence of stabilizing glycoprotein contacts between glycans of IgG1 and a conserved FG-loop (¹⁷¹MGKHRY¹⁷⁶) of FcγRIa. Complexes formed from the FcγRIa receptor and IgG1s containing biantennary glycans with N-acetylglucosamine, galactose, and α2,6-N-acetylneuraminic terminations were measured by hydrogen-deuterium exchange mass spectrometry (HDX-MS), classified for dissimilarity with Welch's ANOVA and Games-Howell post hoc procedures, and modeled with molecular dynamics (MD) simulations. For each glycoform of the IgG1-FcγRIa complex peptic peptides of Fab, Fc and FcγRIa report distinct H/D exchange rates. MD simulations corroborate the differences in the peptide deuterium content through calculation of the percent of time that transient glycan-peptide bonds exist. These results indicate that stability of IgG1-FcγRIa complexes correlate with the presence of intermolecular glycoprotein interactions between the IgG1 glycans and the ¹⁷³KHR¹⁷⁵ motif within the FG-loop of FcγRIa. The results also indicate that intramolecular glycan-protein bonds stabilize the Fc region in isolated and complexed IgG1. Moreover, HDX-MS data evince that the Fab domain has glycan-protein binding contacts within the IgG1-FcγRI complex.

Affinity Capillary Electrophoresis-Mass Spectrometry as a Tool to Unravel Proteoform-Specific Antibody-Receptor Interactions

Monoclonal antibody (mAb) pharmaceuticals consist of a plethora of different proteoforms with different functional characteristics, including pharmacokinetics and pharmacodynamics, requiring their individual assessment. Current binding techniques do not distinguish between coexisting proteoforms requiring tedious production of enriched proteoforms. Here, we have developed an approach based on mobility shift-affinity capillary electrophoresis-mass spectrometry (ACE-MS), which permitted us to determine the binding of coexisting mAb proteoforms to Fc receptors (FcRs). For high-sensitivity MS analysis, we used a sheathless interface providing adequate mAb sensitivity allowing functional characterization of mAbs with a high sensitivity and dynamic range. As a model system, we focused on the interaction with the neonatal FcR (FcRn), which determines the half-life of mAbs. Depending on the oxidation status, proteoforms exhibited different electrophoretic mobility shifts in the presence of FcRn, which could be used to determine their affinity. We confirmed the decrease of the FcRn affinity with antibody oxidation and observed a minor glycosylation effect, with higher affinities for galactosylated glycoforms. Next to relative binding, the approach permits the determination of individual K_D values in solution resulting in values of 422 and 139 nM for double-oxidized and non-oxidized variants. Hyphenation with native MS provides unique capabilities for simultaneous heterogeneity assessment for mAbs, FcRn, and complexes formed. The latter provides information on binding stoichiometry revealing 1:1 and 1:2 for antibody/FcRn complexes. The use of differently engineered Fc-only constructs allowed distinguishing between symmetric and asymmetric binding. The approach opens up unique possibilities for proteoform-resolved antibody binding studies to FcRn and can be extended to other FcRs and protein interactions.

Implementation of in vitro glycoengineering of monoclonal antibodies into downstream processing of industrial production

In vitro glycoengineering using exoenzymes for specific modification is recognized as appropriate method to tailor sugar moieties of glycan structures during the recombinant production of monoclonal antibodies (mAbs). This report describes enhanced in vitro glycoengineering approaches using β1,4-galactosyltransferase and α2,6-sialyltransferase to improve the efficiency of galactosylation and sialylation with the aim to implement in vitro glycoengineering into common mAb purification processes. Feasibility studies tested the potential of different in vitro glycoengineering protocols (2-step vs. 1-step) to facilitate the overall procedure. Scalability of the reactions was demonstrated for mAb amounts ranging from 1 mg to 1 g. Additionally, the reactions of β1,4-galactosyltransferase and α2,6-sialyltransferase were shown to work on column during affinity chromatography using Protein A or KappaSelect, the latter providing more efficient galactosylation and sialylation of IgG1 and IgG4 mAbs. Performing in vitro glycoengineering on column enabled the use of cell culture harvest which yielded results comparable to that of purified bulk. Based thereon, an optimized 2-step mixed mode approach was found most appropriate to integrate in vitro glycoengineering of the IgG1 mAb into the overall manufacturing process. Using harvest for on-column reaction of β1,4-galactosyltransferase combined with in-solution reaction of α2,6-sialyltransferase, this approach yielded 100 percent biantennary galactosylation and 61 percent biantennary sialylation. Moreover, the enzymes applied in in vitro glycoengineering could be separated, recycled, and reused in further reactions to improve economic efficiency. Overall, the study provides a toolbox for in vitro glycoengineering and presents an optimized easy-to-handle workflow to implement this method into the downstream processing of industrial mAb production.

Fc gamma receptor IIIb binding of individual antibody proteoforms resolved by affinity chromatography-mass spectrometry

The crystallizable fragment (Fc) of immunoglobulin G (IgG) activates key immunological responses by interacting with Fc gamma receptors (FcɣR). FcɣRIIIb contributes to neutrophil activation and is involved in antibody-dependent cellular cytotoxicity (ADCC) and antibody-dependent cellular phagocytosis (ADCP). These processes present important mechanisms-of-actions of therapeutic antibodies. The very low affinity of IgG toward FcɣRIIIb (K_D ~ 10 µM) is a technical challenge for interaction studies. Additionally, the interaction is strongly dependent on IgG glycosylation, a major contributor to proteoform heterogeneity. We developed an affinity chromatography–mass spectrometry (AC-MS) assay for analyzing IgG-FcɣRIIIb interactions in a proteoform-resolved manner. This proved to be well suited to study low-affinity interactions. The applicability and selectivity of the method were demonstrated on a panel of nine different IgG monoclonal antibodies (mAbs), including no-affinity, low-affinity and high-affinity Fc-engineered or glycoengineered mAbs. Thereby, we could reproduce reported affinity rankings of different IgG glycosylation features and IgG subclasses. Additional post-translational modifications (IgG1 Met252 oxidation, IgG3 hinge-region O-glycosylation) showed no effect on FcɣRIIIb binding. Interestingly, we observed indications of an effect of the variable domain sequence on the Fc-binding that deserves further attention. Our new AC-MS method is a powerful tool for expanding knowledge on structure–function relationships of the IgG-FcɣRIIIb interaction. Hence, this assay may substantially improve the efficiency of assessing critical quality attributes of therapeutic mAbs with respect to an important aspect of neutrophil activation.

A new approach for identifying positional isomers of glycans cleaved from monoclonal antibodies

Glycosylation patterns in monoclonal antibodies (mAbs) can vary significantly between different host cell types, and these differences may affect mAbs safety, efficacy, and immunogenicity. Recent studies have demonstrated that glycan isomers with the terminal galactose position on either the Man α1-3 arm or the Man α1-6 arm have an impact on the effector functions and dynamic structure of mAbs. The development of a robust method to distinguish positional isomers of glycans is thus critical to guarantee mAb quality. In this work, we apply high-resolution ion mobility combined with cryogenic infrared spectroscopy to distinguish isomeric glycans with different terminal galactose positions, using G1F as an example. Selective enzymatic synthesis of the G1(α1-6)F isomer allows us to assign the peaks in the arrival-time distributions and the infrared spectra to their respective isomeric forms. Moreover, we demonstrate the impact of the host cell line (CHO and HEK-293) on the IgG G1F gycan profile at the isomer level. This work illustrates the potential of our approach for glycan analysis of mAbs.

Use of 5-Thio-L-Fucose to modulate binding affinity of therapeutic proteins

The reduction of antibody core-fucosylation is known to enhance antibody-dependent cellular cytotoxicity (ADCC). In this study, 5-Thio-l-Fucose (ThioFuc) was investigated as a media and feed supplement for modulating the fucosylation profile of therapeutic proteins and, thereby, improving the resulting effector functions. Glycan analysis of five different therapeutic proteins produced by a diverse set of Chinese hamster ovary cell lines demonstrated a clone dependent impact of ThioFuc treatment. Using rituximab as a model, an efficient dose- and time-dependent reduction of core-fucosylation up to a minimum of 5% were obtained by ThioFuc. Besides a concomitant increase in the afucosylation level up to 48%, data also revealed up to 47% incorporation of ThioFuc in place of core-fucosylation. In accordance with the glycan data, antibodies produced in the presence of ThioFuc revealed an enhanced FcγRIIIa binding up to 7.7-fold. Furthermore, modified antibodies subjected to a cell-based ADCC reporter bioassay proved to exert both a 1.5-fold enhanced ADCC efficacy and 2.6-fold enhancement in potency in comparison to their native counterparts-both of which contribute to an improvement in the ADCC activity. In conclusion, ThioFuc is a potent fucose derivative with potential applications in drug development processes.

Antibody mediated activation of natural killer cells in malaria exposed pregnant women

Immune effector responses against Plasmodium falciparum include antibody-mediated activation of innate immune cells, which can induce Fc effector functions, including antibody-dependent cellular cytotoxicity, and the secretion of cytokines and chemokines. These effector functions are regulated by the composition of immunoglobulin G (IgG) Fc N-linked glycans. However, a role for antibody-mediated natural killer (NK) cells activation or Fc N-linked glycans in pregnant women with malaria has not yet been established. Herein, we studied the capacity of IgG antibodies from pregnant women, with placental malaria or non-placental malaria, to induce NK cell activation in response to placental malaria-associated antigens DBL2 and DBL3. Antibody-mediated NK cell activation was observed in pregnant women with malaria, but no differences were associated with susceptibility to placental malaria. Elevated anti-inflammatory glycosylation patterns of IgG antibodies were observed in pregnant women with or without malaria infection, which were not seen in healthy non-pregnant controls. This suggests that pregnancy-associated anti-inflammatory Fc N-linked glycans may dampen the antibody-mediated activation of NK cells in pregnant women with malaria infection. Overall, although anti-inflammatory glycans and antibody-dependent NK cell activation were detected in pregnant women with malaria, a definitive role for these antibody features in protecting against placental malaria remains to be proven.

Glycosylation of recombinant rabbit immunoglobulins influences protease susceptibility as shown by comprehensive mass spectrometric glycan analysis

Recombinant immunoglobulins (rIgGs) have become increasingly important as therapeutic agents and diagnostic tools in recent years. Genetic engineering allows the introduction of non-natural features such as the Sortase motif for site-directed labeling. In this study, the enzyme Sortase A (SrtA) was used for the proteolytic cleavage of rIgGs to produce their biotinylated Fab fragments by locating the cleavage site close to the hinge region. However, SrtA cleavage of engineered rabbit IgGs (rRb-IgGs) derived from human embryonic kidney (HEK) 293 cells showed significantly lower yields compared with their mouse counterparts. Nonrecombinant Rb-IgGs have N- and O-glycans, and the presence of O-glycans close to the hinge region of the rRb-IgGs might affect the susceptibility of these antibodies to SrtA cleavage. In addition, the glycosylation pattern of rIgGs differs depending on the host cell used for expression. Therefore, we analyzed the N- and O-glycans of various rRb-IgGs expressed in HEK293 cells, detecting and quantifying 13 different N-glycan and 3 different O-glycan structures. The distribution of the different detected glycoforms in our rRb-IgG N-glycan analysis is in agreement with previous studies on recombinant human IgG N-glycans, confirming the hypothesis that the host cell defines the glycosylation of the recombinant produced IgGs. O-glycosylation could be mapped onto the threonine residue within the hinge region sequence XPTCPPPX, as already described previously for nonrecombinant Rb-IgGs. Substitution of this threonine allowed an almost complete Fab fragment cleavage. Therefore, we could confirm the hypothesis that the O-glycans affect the SrtA activity, probably due to steric hindrance.

Modeling of the Biological Activity of Monoclonal Antibodies Based on the Glycosylation Profile

The influence of the glycosylation profile of IgG on biological activity is known, but it is not clear which glycoforms have the highest impact on the main mechanism of action. The aim of this study was to design a mathematical model for predicting the antibody-dependent cellular cytotoxicity (ADCC) activity and the Fc gamma IIIa receptors' (FcɣRIIIa) relative binding of rituximab drug products based on their glycosylation profile. An additional goal was to identify the glycoforms that have the greatest impact on these mechanisms of action. For these purposes, the glycosylation profile was examined by hydrophilic interaction ultra-performance liquid chromatography (HILIC-UPLC), ADCC was assessed using a Promega kit, and FcɣRIIIa's binding affinity was assessed by surface plasmon resonance (SPR) analysis of a group of >50 rituximab drug products. Based on the results, mathematical models for the ADCC and FcɣRIIIa binding affinity prediction were designed using JMP 13.2.0. The quality of the model and the influence of sample size and heterogeneity on the reliability were verified. The results allow for the evaluation of rituximab drug products' activity based on their glycosylation profile and show that with a sufficiently large and differentiated dataset, it is possible to generate models for different monoclonal antibodies.

Sweet Rules: Linking Glycosylation to Antibody Function

Antibodies produced upon infections with pathogenic microorganisms are essential for clearing primary infections and for providing the host with long-lasting immunity. Moreover, antibodies have become the most widely used platform for developing novel therapies against cancer and autoimmunity, requiring an in-depth understanding of how antibodies mediate their activity in vivo and which factors modulate pro- or anti-inflammatory antibody activities. Since the discovery that select residues present in the sugar domain attached to the immunoglobulin G (IgG) fragment crystallizable (Fc) region can modulate both, pro- and anti-inflammatory effector functions, a wealth of studies has focused on understanding how IgG glycosylation is regulated and how this knowledge can be used to optimize therapeutic antibody activity. With the introduction of glycoengineered afucosylated antibodies in cancer therapy and the initiation of clinical testing of highly sialylated anti-inflammatory antibodies the proof-of-concept that understanding antibody glycosylation can lead to clinical innovation has been provided. The focus of this review is to summarize recent insights into how antibody glycosylation is regulated in vivo and how select sugar residues impact IgG function.

Glycoform-resolved pharmacokinetic studies in a rat model employing glycoengineered variants of a therapeutic monoclonal antibody

Good pharmacokinetic (PK) behavior is a key prerequisite for sufficient efficacy of therapeutic monoclonal antibodies (mAbs). Fc glycosylation is a critical quality attribute (CQA) of mAbs, due to its impact on stability and effector functions. However, the effects of various IgG Fc glycoforms on antibody PK remain unclear. We used a combination of glycoengineering and glycoform-resolved PK measurements by mass spectrometry (MS) to assess glycoform effects on PK. Four differently glycoengineered mAbs, each still containing multiple glycoforms, were separately injected into rats. Rat models have been shown to be predictive of human PK. At different time points, blood was taken, from which the mAbs were purified and analyzed with a liquid chromatography-MS-based bottom-up glycoproteomics approach. This allowed us to follow changes in the glycosylation profiles of each glycoengineered mAb over time. Enzyme-linked immunosorbent assay measurements provided an absolute concentration in the form of a sum value for all glycoforms. Information from both readouts was then combined to calculate PK parameters per glycoform. Thereby, multiple glycoform kinetics were resolved within one mAb preparation. We confirmed increased clearance of high-mannose (Man5) and hybrid-type (Man5G0) glycoforms. Specifically, Man5 showed a 1.8 to 2.6-fold higher clearance than agalactosylated, complex glycans (G0F). Unexpectedly, clearance was even higher (4.7-fold) for the hybrid-type glycan Man5G0. In contrast, clearance of agalactosylated, monoantennary glycoforms (G0F-N) was only slightly increased over G0F (1.2 to 1.4-fold). Thus, monoantennary, hybrid-type and high-mannose glycoforms should be distinguished in CQA assessments. Strikingly, α2,3-linked sialylation did not affect clearance, contradicting the involvement of the asialoglycoprotein receptor in mAb clearance.

Monitoring of immunoglobulin N- and O-glycosylation in health and disease

Protein N- and O-glycosylation are well known co- and post-translational modifications of immunoglobulins. Antibody glycosylation on the Fab and Fc portion is known to influence antigen binding and effector functions, respectively. To study associations between antibody glycosylation profiles and (patho) physiological states as well as antibody functionality, advanced technologies and methods are required. In-depth structural characterization of antibody glycosylation usually relies on the separation and tandem mass spectrometric (MS) analysis of released glycans. Protein- and site-specific information, on the other hand, may be obtained by the MS analysis of glycopeptides. With the development of high-resolution mass spectrometers, antibody glycosylation analysis at the intact or middle-up level has gained more interest, providing an integrated view of different post-translational modifications (including glycosylation). Alongside the in-depth methods, there is also great interest in robust, high-throughput techniques for routine glycosylation profiling in biopharma and clinical laboratories. With an emphasis on IgG Fc glycosylation, several highly robust separation-based techniques are employed for this purpose. In this review, we describe recent advances in MS methods, separation techniques and orthogonal approaches for the characterization of immunoglobulin glycosylation in different settings. We put emphasis on the current status and expected developments of antibody glycosylation analysis in biomedical, biopharmaceutical and clinical research.

Impact of IgG1 N-glycosylation on their interaction with Fc gamma receptors

The effector functions of the IgGs are modulated by the N-glycosylation of their Fc region. Particularly, the absence of core fucosylation is known to increase the affinity of IgG1s for the Fcγ receptor IIIa expressed by immune cells, in turn translating in an improvement in the antibody-dependent cellular cytotoxicity. However, the impact of galactosylation and sialylation is still debated in the literature. In this study, we have investigated the influence of high and low levels of core fucosylation, terminal galactosylation and terminal α2,6-sialylation of the Fc N-glycans of trastuzumab on its affinity for the FcγRIIIa. A large panel of antibody glycoforms (i.e., highly α2,6-sialylated or galactosylated IgG1s, with high or low levels of core fucosylation) were generated and characterized, while their interactions with the FcγRs were analysed by a robust surface plasmon resonance-based assay as well as in a cell-based reporter bioassay. Overall, IgG1 glycoforms with reduced fucosylation display a stronger affinity for the FcγRIIIa. In addition, fucosylation, and the presence of terminal galactose and sialic acids are shown to increase the affinity for the FcγRIIIa as compared to the agalactosylated forms. These observations perfectly translate in the response observed in our reporter bioassay.

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Rapid production in CHO cells of IgGs bearing defined and relevant N-glycans

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IgG1 N-glycosylation influence upon FcγRs binding studied in a robust SPR assay

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Excellent correlation between the EC₅₀ from a cell-based assay and the affinities

Soluble dimeric prion protein ligand activates Adgrg6 receptor but does not rescue early signs of demyelination in PrP-deficient mice

The adhesion G-protein coupled receptor Adgrg6 (formerly Gpr126) is instrumental in the development, maintenance and repair of peripheral nervous system myelin. The prion protein (PrP) is a potent activator of Adgrg6 and could be used as a potential therapeutic agent in treating peripheral demyelinating and dysmyelinating diseases. We designed a dimeric Fc-fusion protein comprising the myelinotrophic domain of PrP (FT2Fc), which activated Adgrg6 in vitro and exhibited favorable pharmacokinetic properties for in vivo treatment of peripheral neuropathies. While chronic FT2Fc treatment elicited specific transcriptomic changes in the sciatic nerves of PrP knockout mice, no amelioration of the early molecular signs demyelination was detected. Instead, RNA sequencing of sciatic nerves revealed downregulation of cytoskeletal and sarcomere genes, akin to the gene expression changes seen in myopathic skeletal muscle of PrP overexpressing mice. These results call for caution when devising myelinotrophic therapies based on PrP-derived Adgrg6 ligands. While our treatment approach was not successful, Adgrg6 remains an attractive therapeutic target to be addressed in other disease models or by using different biologically active Adgrg6 ligands.

A Detailed Protocol for Generation of Therapeutic Antibodies with Galactosylated Glycovariants at Laboratory Scale Using In-Vitro Glycoengineering Technology

N-linked glycosylation is an important post translational modification that occurs on Asparagine 297 residue or a homologous position on the Fc portion of monoclonal antibodies (mAbs). mAb Fc glycans play important roles in antibody structure, stability, and function including effector function and pharmacokinetics. The Fc glycans are made up of a wide variety of sugars including galactose, mannose, and sialic acid. The role of galactose in mediating antibody effector functions is not well understood. Hence, there is widespread interest in the antibody research community to understand the role of galactose in antibody effector functions as galactose is a major constituent of antibody glycans. This requires generation of highly enriched galactosylated variants that has been very challenging via cell culture process. To tackle this challenge, we developed a laboratory scale biochemical process to produce highly enriched galactosylated variants. In this article, we report optimized lab-scale workflows and detailed protocols for generation of deglycosylated, hypo-galactosylated and hyper-galactosylated variants of IgG therapeutic antibodies using the in-vitro glycoengineering technology. The optimized workflows offer short turnaround time and produce highly enriched deglycosylated/hypo-galactosylated/hyper-galactosylated IgG glycovariants, with high purity & molecular integrity as demonstrated by data from an example IgG.

Biolayer Interferometry-based FcγRIIa binding assay for a therapeutic antibody with strong effector function

FcγRIIa receptor binding is part of the mechanism of action for many therapeutic antibodies. AlphaScreen® technology and Biolayer Interferometry (BLI) are often used to assess protein-protein interactions. Recently we demonstrated that the presence of aggregates in samples significantly increased binding potency values in AlphaScreen®-based FcRn binding assays, sometimes masking the loss of potency. Even bigger effect of aggregates was observed in an AlphaScreen®-based FcγRIIa binding assay for a monoclonal antibody with strong effector function. To resolve this issue a novel BLI-based FcγRIIa binding assay was developed and qualified. The assay measures association binding responses and calculates the binding potency of the samples relative to the standard using Parallel Line Analysis. The method overcomes interference of aggregates present in the samples, distinguishes different Fc glycosylation patterns, and is stability-indicating. It can be used for sample characterization, drug product release and stability testing.

The role of antibodies in Bacille Calmette Guérin-mediated immune responses and protection against tuberculosis in humans: A systematic review

BACKGROUND

The mechanisms underlying Bacille Calmette-Guérin (BCG) vaccine's protective effects against tuberculosis (TB) are incompletely understood but are proposed to involve a predominantly cell-mediated process. However, there is increasing evidence for the involvement of antibodies in the control of Mycobacteria tuberculosis and in the immune response to BCG.

METHODS

We did a systematic review of studies investigating anti-BCG antibodies in individuals with active or latent TB, and in the response to BCG vaccination.

RESULTS

Of 1417 articles screened, 70 were relevant, comprising 52 investigating anti-BCG antibodies in TB and 18 investigating the anti-BCG antibody response to BCG-vaccination. Individuals with active TB have higher levels of anti-BCG antibodies compared with individuals with latent TB or healthy individuals. Antibodies to BCG are present after BCG vaccination. There is some evidence for the in utero transfer of maternal anti-BCG antibodies to infants.

CONCLUSIONS

BCG vaccination induces a humoral response. Antibodies targeted against BCG and its antigens may play a role in protection against active TB.

N-Glycosylation of IgG and IgG-Like Recombinant Therapeutic Proteins: Why Is It Important and How Can We Control It?

Regulatory bodies worldwide consider N-glycosylation to be a critical quality attribute for immunoglobulin G (IgG) and IgG-like therapeutics. This consideration is due to the importance of posttranslational modifications in determining the efficacy, safety, and pharmacokinetic properties of biologics. Given its critical role in protein therapeutic production, we review N-glycosylation beginning with an overview of the myriad interactions of N-glycans with other biological factors. We examine the mechanism and drivers for N-glycosylation during biotherapeutic production and the several competing factors that impact glycan formation, including the abundance of precursor nucleotide sugars, transporters, glycosidases, glycosyltransferases, and process conditions. We explore the role of these factors with a focus on the analytical approaches used to characterize glycosylation and associated processes, followed by the current state of advanced glycosylation modeling techniques. This combination of disciplines allows for a deeper understanding of N-glycosylation and will lead to more rational glycan control.

Demonstrating Analytical Similarity of Trastuzumab Biosimilar HLX02 to Herceptin® with a Panel of Sensitive and Orthogonal Methods Including a Novel FcγRIIIa Affinity Chromatography Technology

BACKGROUND

A biosimilar needs to demonstrate its similarity to the originator reference product (RP) in terms of structural and functional properties as well as nonclinical and clinical outcomes.

OBJECTIVES

The aim was to assess the analytical similarity between the trastuzumab biosimilar HLX02 and Europe-sourced Herceptin® (EU-Herceptin®) and China-sourced Herceptin® (CN-Herceptin®) following a quality-by-design (QbD) quality study and tier-based quality attribute evaluation.

METHODS

A panel of highly sensitive and orthogonal methods, including a novel Fc gamma receptor IIIa (FcγRIIIa) affinity chromatography technique that enables quantitative comparison of glycan effects on effector function, was developed for the assessment. To ensure the full product variability was captured, ten batches of HLX02 were compared with 39 RP batches with expiry dates from August 2017 to March 2021.

RESULTS

The extensive three-way similarity assessment demonstrated that HLX02 is highly similar to the RPs. Furthermore, the %afucose, %galactose, and FcγRIIIa affinity of the RPs were observed to first decrease and then return to the original level in relation to their expiry dates, and the RP batches can be subgrouped by their FcγRIIIa affinity chromatograms. HLX02 is demonstrated to be more similar to the RPs of the high FcγRIIIa affinity group.

CONCLUSION

Besides having an overall high analytical similarity to both EU-Herceptin® and CN-Herceptin®, HLX02 is more similar to Herceptin® with high FcγRIIIa affinity, a result that demonstrates the power of the novel FcγRIIIa affinity chromatography technology in biosimilarity evaluation.

An Inflammatory Story: Antibodies in Tuberculosis Comorbidities

Mycobacterium tuberculosis (Mtb) resides in a quarter of the world's population and is the causative agent for tuberculosis (TB), the most common infectious reason of death in humans today. Although cellular immunity has been firmly established in the control of Mtb, there is growing evidence that antibodies may also modulate the infection. More specifically, certain antibody features are associated with inflammation and are divergent in different states of human infection and disease. Importantly, TB impacts not just the healthy but also those with chronic conditions. While HIV represents the quintessential comorbid condition for TB, recent epidemiological evidence shows that additional chronic conditions such as diabetes and kidney disease are rising. In fact, the prevalence of diabetes as a comorbid TB condition is now higher than that of HIV. These chronic diseases are themselves independently associated with pro-inflammatory immune states that encompass antibody profiles. This review discusses isotypes, subclasses, post-translational modifications and Fc-mediated functions of antibodies in TB infection and in the comorbid chronic conditions of HIV, diabetes, and kidney diseases. We propose that inflammatory antibody profiles, which are a marker of active TB, may be an important biomarker for detection of TB disease progression within comorbid individuals. We highlight the need for future studies to determine which inflammatory antibody profiles are the consequences of comorbidities and which may potentially contribute to TB reactivation.

Proteoform-Resolved FcɤRIIIa Binding Assay for Fab Glycosylated Monoclonal Antibodies Achieved by Affinity Chromatography Mass Spectrometry of Fc Moieties

Fcɤ receptors (FcɤR) mediate key functions in immunological responses. For instance, FcɤRIIIa is involved in antibody-dependent cell-mediated cytotoxicity (ADCC). FcɤRIIIa interacts with the fragment crystallizable (Fc) of immunoglobulin G (IgG). This interaction is known to be highly dependent on IgG Fc glycosylation. Thus, the impact of glycosylation features on this interaction has been investigated in several studies by numerous analytical and biochemical techniques. FcɤRIIIa affinity chromatography (AC) hyphenated to mass spectrometry (MS) is a powerful tool to address co-occurring Fc glycosylation heterogeneity of monoclonal antibodies (mAbs). However, MS analysis of mAbs at the intact level may provide limited proteoform resolution, for example, when additional heterogeneity is present, such as antigen-binding fragment (Fab) glycosylation. Therefore, we investigated middle-up approaches to remove the Fab and performed AC-MS on the IgG Fc to evaluate its utility for FcɤRIIIa affinity assessment compared to intact IgG analysis. We found the protease Kgp to be particularly suitable for a middle-up FcɤRIIIa AC-MS workflow as demonstrated for the Fab glycosylated cetuximab. The complexity of the mass spectra of Kgp digested cetuximab was significantly reduced compared to the intact level while affinity was fully retained. This enabled a reliable assignment and relative quantitation of Fc glycoforms in FcɤRIIIa AC-MS. In conclusion, our workflow allows a functional separation of differentially glycosylated IgG Fc. Consequently, applicability of FcɤRIIIa AC-MS is extended to Fab glycosylated IgG, i.e., cetuximab, by significantly reducing ambiguities in glycoform assignment vs. intact analysis.