Effect of posttranslational modifications and subclass on IgG activity: from immunity to immunotherapy

Cancer therapy with antibodies

The greatest challenge in cancer therapy is to eradicate cancer cells with minimal damage to normal cells. Targeted therapy has been developed to meet that challenge, showing a substantially increased therapeutic index compared with conventional cancer therapies. Antibodies are important members of the family of targeted therapeutic agents because of their extraordinarily high specificity to the target antigens. Therapeutic antibodies use a range of mechanisms that directly or indirectly kill the cancer cells. Early antibodies were developed to directly antagonize targets on cancer cells. This was followed by advancements in linker technologies that allowed the production of antibody-drug conjugates (ADCs) that guide cytotoxic payloads to the cancer cells. Improvement in our understanding of the biology of T cells led to the production of immune checkpoint-inhibiting antibodies that indirectly kill the cancer cells through activation of the T cells. Even more recently, bispecific antibodies were synthetically designed to redirect the T cells of a patient to kill the cancer cells. In this Review, we summarize the different approaches used by therapeutic antibodies to target cancer cells. We discuss their mechanisms of action, the structural basis for target specificity, clinical applications and the ongoing research to improve efficacy and reduce toxicity.

Emerging trends and therapeutic applications of monoclonal antibodies

Monoclonal antibodies (mAbs) are being used to prevent, detect, and treat a broad spectrum of malignancies and infectious and autoimmune diseases. Over the past few years, the market for mAbs has grown exponentially. They have become a significant part of many pharmaceutical product lines, and more than 250 therapeutic mAbs are undergoing clinical trials. Ever since the advent of hybridoma technology, antibody-based therapeutics were realized using murine antibodies which further progressed into humanized and fully human antibodies, reducing the risk of immunogenicity. Some of the benefits of using mAbs over conventional drugs include a drastic reduction in the chances of adverse reactions, interactions between drugs, and targeting specific proteins. While antibodies are very efficient, their higher production costs impede the process of commercialization. However, their cost factor has been improved by developing biosimilar antibodies, which are affordable versions of therapeutic antibodies. Along with biosimilars, innovations in antibody engineering have helped to design bio-better antibodies with improved efficacy than the conventional ones. These novel mAb-based therapeutics are set to revolutionize existing drug therapies targeting a wide spectrum of diseases, thereby meeting several unmet medical needs. In the future, mAbs generated by applying next-generation sequencing (NGS) are expected to become a powerful tool in clinical therapeutics. This article describes the methods of mAb production, pre-clinical and clinical development of mAbs, approved indications targeted by mAbs, and novel developments in the field of mAb research.

Agonist Antibodies for Cancer Immunotherapy: History, Hopes, and Challenges

Immunotherapy is among the most promising new treatment modalities to arise over the last two decades; antibody drugs are delivering immunotherapy to millions of patients with many different types of cancer. Initial success with antibody therapeutics came in the form of direct targeting or cytotoxic antibodies, such as rituximab and trastuzumab, which bind directly to tumor cells to elicit their destruction. These were followed by immunomodulatory antibodies that elicit antitumor responses by either stimulating immune cells or relieving tumor-mediated suppression. By far the most successful approach in the clinic to date has been relieving immune suppression, with immune checkpoint blockade now a standard approach in the treatment of many cancer types. Despite equivalent and sometimes even more impressive effects in preclinical models, agonist antibodies designed to stimulate the immune system have lagged behind in their clinical translation. In this review, we document the main receptors that have been targeted by agonist antibodies, consider the various approaches that have been evaluated to date, detail what we have learned, and consider how their anticancer potential can be unlocked.

Site-Specific Glycosylation Analysis of Murine and Human Fcγ Receptors Reveals High Heterogeneity at Conserved N-Glycosylation Site

Fc γ-receptors (FcγRs) on leukocytes bind immunoglobulin G (IgG) immune complexes to mediate effector functions. Dysregulation of FcγR-mediated processes contributes to multiple inflammatory diseases, including rheumatoid arthritis, lupus, and immune thrombocytopenia. Critically, immunoregulatory N-glycan modifications on both FcγRs and IgGs alter FcγR-IgG binding affinity. Rapid methods for the characterization of N-glycans across multiple Fcγ receptors are needed to propel investigations into disease-specific contributions of FcγR N-glycans. Here, we utilize nanoliquid chromatography tandem mass spectrometry (nLC-MS/MS) to characterize FcγR glycosylation and report quantitative and site-specific N-glycan characterization of recombinant human FcγRI, FcγRIIIA V158, and FcγRIIIA F158 from CHO cells and murine FcγRI, FcγRIII, and FcγRIV from NS0 cells. Data are available via ProteomeXchange with identifier PXD043966. Broad glycoform distribution (≥30) was observed at mouse FcγRIV site N159 and human FcγRIIIA site N162, an evolutionarily conserved site. Further, mouse FcγRIII N-glycopeptides spanning all four predicted N-glycosylation sequons were detected. Glycoform relative abundances for hFcγRIIIA V/F158 polymorphic variants are reported, demonstrating the clinical potential of this workflow to measure differences in glycosylation between common human FcγRIIIA allelic variants with disease-associated outcomes. The multi-Fcγ receptor glycoproteomic workflow reported here will empower studies focused on the role of FcγR N-glycosylation in autoimmune diseases.

Antibodies, repertoires and microdevices in antibody discovery and characterization

Therapeutic antibodies are paramount in treating a wide range of diseases, particularly in auto-immunity, inflammation and cancer, and novel antibody candidates recognizing a vast array of novel antigens are needed to expand the usefulness and applications of these powerful molecules. Microdevices play an essential role in this challenging endeavor at various stages since many general requirements of the overall process overlap nicely with the general advantages of microfluidics. Therefore, microfluidic devices are rapidly taking over various steps in the process of new candidate isolation, such as antibody characterization and discovery workflows. Such technologies can allow for vast improvements in time-lines and incorporate conservative antibody stability and characterization assays, but most prominently screenings and functional characterization within integrated workflows due to high throughput and standardized workflows. First, we aim to provide an overview of the challenges of developing new therapeutic candidates, their repertoires and requirements. Afterward, this review focuses on the discovery of antibodies using microfluidic systems, technological aspects of micro devices and small-scale antibody protein characterization and selection, as well as their integration and implementation into antibody discovery workflows. We close with future developments in microfluidic detection and antibody isolation principles and the field in general.

Internal Fragments Enhance Middle-Down Mass Spectrometry Structural Characterization of Monoclonal Antibodies and Antibody-Drug Conjugates

Monoclonal antibodies (mAbs) and antibody-drug conjugates (ADCs) are important large biotherapeutics (∼150 kDa) and high structural complexity that require extensive sequence and structure characterization. Middle-down mass spectrometry (MD-MS) is an emerging technique that sequences and maps subunits larger than those released by trypsinolysis. It avoids potentially introducing artifactual modifications that may occur in bottom-up MS while achieving higher sequence coverage compared to top-down MS. However, returning complete sequence information by MD-MS is still challenging. Here, we show that assigning internal fragments in direct infusion MD-MS of a mAb and an ADC substantially improves their structural characterization. For MD-MS of the reduced NIST mAb, including internal fragments recovers nearly 100% of the sequence by accessing the middle sequence region that is inaccessible by terminal fragments. The identification of important glycosylations can also be improved after the inclusion of internal fragments. For the reduced lysine-linked IgG1-DM1 ADC, we show that considering internal fragments increases the DM1 conjugation sites coverage to 80%, comparable to the reported 83% coverage achieved by peptide mapping on the same ADC (Luo et al. Anal. Chem. 2016, 88, 695-702). This study expands our work on the application of internal fragment assignments in top-down MS of mAbs and ADCs and can be extended to other heterogeneous therapeutic molecules such as multispecifics and fusion proteins for more widespread applications.

Complement activation and cellular inflammation in Fabry disease patients despite enzyme replacement therapy

Defective α-galactosidase A (AGAL/GLA) due to missense or nonsense mutations in the GLA gene results in accumulation of the glycosphingolipids globotriaosylceramide (Gb3) and its deacylated derivate globotriaosylsphingosine (lyso-Gb3) in cells and body fluids. The aberrant glycosphingolipid metabolism leads to a progressive lysosomal storage disorder, i. e. Fabry disease (FD), characterized by chronic inflammation leading to multiorgan damage. Enzyme replacement therapy (ERT) with agalsidase-alfa or -beta is one of the main treatment options facilitating cellular Gb3 clearance. Proteome studies have shown changes in complement proteins during ERT. However, the direct activation of the complement system during FD has not been explored. Here, we demonstrate strong activation of the complement system in 17 classical male FD patients with either missense or nonsense mutations before and after ERT as evidenced by high C3a and C5a serum levels. In contrast to the strong reduction of lyso-Gb3 under ERT, C3a and C5a markedly increased in FD patients with nonsense mutations, most of whom developed anti-drug antibodies (ADA), whereas FD patients with missense mutations, which were ADA-negative, showed heterogenous C3a and C5a serum levels under treatment. In addition to the complement activation, we found increased IL-6, IL-10 and TGF-ß1 serum levels in FD patients. This increase was most prominent in patients with missense mutations under ERT, most of whom developed mild nephropathy with decreased estimated glomerular filtration rate. Together, our findings demonstrate strong complement activation in FD independent of ERT therapy, especially in males with nonsense mutations and the development of ADAs. In addition, our data suggest kidney cell-associated production of cytokines, which have a strong potential to drive renal damage. Thus, chronic inflammation as a driver of organ damage in FD seems to proceed despite ERT and may prove useful as a target to cope with progressive organ damage.

Impact of structural modifications of IgG antibodies on effector functions

Immunoglobulin G (IgG) antibodies are a critical component of the adaptive immune system, binding to and neutralizing pathogens and other foreign substances. Recent advances in molecular antibody biology and structural protein engineering enabled the modification of IgG antibodies to enhance their therapeutic potential. This review summarizes recent progress in both natural and engineered structural modifications of IgG antibodies, including allotypic variation, glycosylation, Fc engineering, and Fc gamma receptor binding optimization. We discuss the functional consequences of these modifications to highlight their potential for therapeutical applications.

Benchmark Glycan Profile of Therapeutic Monoclonal Antibodies Produced by Mammalian Cell Expression Systems

PURPOSE

This study aims to establish a benchmark glycan profile for commercial therapeutic monoclonal antibodies (mAbs) approved by the US Food and Drug Administration (FDA).

METHODS

We conducted a rigorous comparison of glycosylation data from the regulatory submissions for FDA-approved therapeutic antibodies up to May 2023. This analysis includes over 150 mAbs produced by various mammalian cell expression systems.

RESULTS

The study identified nine prevalent glycan epitopes across all FDA-approved monoclonal antibodies produced by different expression systems. These epitopes include terminal N-acetylglucosamine, core fucose, terminal galactose, high mannose, α-galactose, terminal α2,3-linked N-acetylneuraminic acid, terminal α2,6-linked N-glycolylneuraminic acid, triantennary structure, and bisecting N-acetylglucosamine, thus establishing a benchmark glycan profile.

CONCLUSIONS

The findings of this study have significant implications for therapeutic antibody development, quality control, and regulatory compliance. The benchmark glycan profile enables the assessment of glycosylation consistency and comparability across a diverse range of antibody products, ensuring improved product quality within the biopharmaceutical industry.

Platelet transfusion refractoriness due to HLA alloimmunization: Evolving paradigms in mechanisms and management

Platelet transfusion refractoriness due to HLA alloimmunization presents a significant medical problem, particularly among multiply transfused patients with hematologic malignancies and those undergoing hematopoietic stem cell transplants. HLA compatible platelet transfusions also impose significant financial burden on these patients. Recently, several novel mechanisms have been described in the development of HLA alloimmunization and platelet transfusion refractoriness. We review the history of platelet transfusions and mechanisms of HLA-sensitization and transfusion refractoriness. We also summarize advances in the diagnosis and treatment of platelet transfusion refractoriness due to HLA alloimmunization.

Can we suppress chronic systemic inflammation and postpone age-related diseases by targeting the IgG glycome?

INTRODUCTION

Glycans attached to immunoglobulin G are an important regulator of chronic systemic inflammation, one of the key drivers of aging. As people age, glycans that suppress inflammation are being replaced with inflammation-promoting glycans, but the rate of this conversion is highly individual and is affected by genetic, epigenetic, and environmental factors.

AREAS COVERED

This review summarizes key studies of IgG glycosylation changes in aging and disease, effects of lifestyle and pharmacological interventions, and mechanisms that regulate IgG glycosylation.

EXPERT OPINION

IgG glycome is an important contributor to the process of aging that can be modulated by both lifestyle and pharmacological interventions. Small molecule drugs that would suppress chronic systemic inflammation by modulation of the IgG glycome are still not available, but since gene network regulating IgG glycosylation has been identified and a high-throughput in vitro screening system is available, it is likely that this highly innovative approach to manage chronic systemic inflammation will be developed soon.

Function-structure approach reveals novel insights on the interplay of Immunoglobulin G 1 proteoforms and Fc gamma receptor IIa allotypes

Human Fc gamma receptor IIa (FcγRIIa) or CD32a has two major allotypes with a single amino acid difference at position 131 (histidine or arginine). Differences in FcγRIIa allotypes are known to impact immunological responses such as the clinical outcome of therapeutic monoclonal antibodies (mAbs). FcγRIIa is involved in antibody-dependent cellular phagocytosis (ADCP), which is an important contributor to the mechanism-of-action of mAbs by driving phagocytic clearance of cancer cells. Hence, understanding the impact of individual mAb proteoforms on the binding to FcγRIIa, and its different allotypes, is crucial for defining meaningful critical quality attributes (CQAs). Here, we report a function-structure based approach guided by novel FcγRIIa affinity chromatography-mass spectrometry (AC-MS) assays to assess individual IgG1 proteoforms. This allowed to unravel allotype-specific differences of IgG1 proteoforms on FcγRIIa binding. FcγRIIa AC-MS confirmed and refined structure-function relationships of IgG1 glycoform interactions. For example, the positive impact of afucosylation was higher than galactosylation for FcγRIIa Arg compared to FcγRIIa His. Moreover, we observed FcγRIIa allotype-opposing and IgG1 proteoform integrity-dependent differences in the binding response of stress-induced IgG1 proteoforms comprising asparagine 325 deamidation. The FcγRIIa-allotype dependent binding differences resolved by AC-MS were in line with functional ADCP-surrogate bioassay models. The molecular basis of the observed allotype specificity and proteoform selectivity upon asparagine 325 deamidation was elucidated using molecular dynamics. The observed differences were attributed to the contributions of an inter-molecular salt bridge between IgG1 and FcγRIIa Arg and the contribution of an intra-molecular hydrophobic pocket in IgG1. Our work highlights the unprecedented structural and functional resolution of AC-MS approaches along with predictive biological significance of observed affinity differences within relevant cell-based methods. This makes FcγRIIa AC-MS an invaluable tool to streamline the CQA assessment of therapeutic mAbs.

Inhibitory Fc-Gamma IIb Receptor Signaling Induced by Multivalent IgG-Fc Is Dependent on Sialylation

Immunoglobulin (IgG) Fc glycosylation has been shown to be important for the biological activity of antibodies. Fc sialylation is important for the anti-inflammatory activity of IgGs. However, evaluating the structure-activity relationship (SAR) of antibody Fc glycosylation has been hindered using simplified in vitro models in which antibodies are often displayed in monomeric forms. Presenting antibodies in monomeric forms may not accurately replicate the natural environment of the antibodies when binding their antigen in vivo. To address these limitations, we used different Fc-containing molecules, displaying their Fc domains in monovalent and multivalent fashion. Given the inhibitory role of Fc gamma receptor IIb (FcγRIIb) in autoimmune and inflammatory diseases, we focused on evaluating the impact of Fc sialylation on the activation of FcγRIIb. We report for the first time that in human cellular systems, sialic acid mediates the induction of FcγRIIb phosphorylation by IgG-Fc when the IgG-Fc is displayed in a multivalent fashion. This effect was observed with different types of therapeutic agents such as sialylated anti-TNFα antibodies, sialylated IVIg and sialylated recombinant multivalent Fc products. These studies represent the first report of the specific effects of Fc sialylation on FcγRIIb signaling on human immune cells and may help in the characterization of the anti-inflammatory activity of Fc-containing therapeutic candidates.