Glycosylation and biological activity of CAMPATH-1H expressed in different cell lines and grown under different culture conditions

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.

Glycoconjugates: Synthesis, Functional Studies, and Therapeutic Developments

Glycoconjugates are major constituents of mammalian cells that are formed via covalent conjugation of carbohydrates to other biomolecules like proteins and lipids and often expressed on the cell surfaces. Among the three major classes of glycoconjugates, proteoglycans and glycoproteins contain glycans linked to the protein backbone via amino acid residues such as Asn for N-linked glycans and Ser/Thr for O-linked glycans. In glycolipids, glycans are linked to a lipid component such as glycerol, polyisoprenyl pyrophosphate, fatty acid ester, or sphingolipid. Recently, glycoconjugates have become better structurally defined and biosynthetically understood, especially those associated with human diseases, and are accessible to new drug, diagnostic, and therapeutic developments. This review describes the status and new advances in the biological study and therapeutic applications of natural and synthetic glycoconjugates, including proteoglycans, glycoproteins, and glycolipids. The scope, limitations, and novel methodologies in the synthesis and clinical development of glycoconjugates including vaccines, glyco-remodeled antibodies, glycan-based adjuvants, glycan-specific receptor-mediated drug delivery platforms, etc., and their future prospectus are discussed.

ADCC enhancement: A conundrum or a boon to mAb therapy?

The ability of antibodies to distinctly identify the antigens is an important feature exploited by the scientific community for the treatment of various diseases. The therapeutic action of monoclonal antibodies (mAbs) is mediated along with the cells of the immune system, such as natural killer cells, T cells and macrophages. The two major mechanisms that govern the therapeutic efficacy of mAbs are the antibody dependent cell mediated cytotoxicity (ADCC) and the complement dependent cytotoxicity (CDC). Consequently, much of the research dedicated to improving their action is focussed on enhancing either of these mechanisms. This manuscript focuses on the strategies to enhance ADCC, for providing more efficacious mAb therapeutics. These approaches essentially bring about changes in the elements of ADCC mechanism, such as the effector cell or the antibody itself and thus favour an enhanced therapeutic response. Several technologies of ADCC enhancement have been developed, based on the success of various strategies advanced by the researchers. These technologies show success with a few antibody therapeutics while they do not work with others. This review presents a detailed overview on these strategies and presents perspectives regarding the same.

Strategies for Glycoengineering Therapeutic Proteins

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

l-fucose, a sugary regulator of antitumor immunity and immunotherapies

l-fucose is a dietary sugar that is used by cells in a process called fucosylation to posttranslationally modify and regulate protein behavior and function. As fucosylation plays essential cellular functions in normal organ and immune developmental and homeostasis, it is perhaps not surprising that it has been found to be perturbed in a number of pathophysiological contexts, including cancer. Increasing studies over the years have highlighted key roles that altered fucosylation can play in cancer cell-intrinsic as well as paracrine signaling and interactions. In particular, studies have demonstrated that fucosylation impact tumor:immunological interactions and significantly enhance or attenuate antitumor immunity. Importantly, fucosylation appears to be a posttranslational modification that can be therapeutically targeted, as manipulating the molecular underpinnings of fucosylation has been shown to be sufficient to impair or block tumor progression and to modulate antitumor immunity. Moreover, the fucosylation of anticancer agents, such as therapeutic antibodies, has been shown to critically impact their efficacy. In this review, we summarize the underappreciated roles that fucosylation plays in cancer and immune cells, as well as the fucosylation of therapeutic antibodies or the manipulation of fucosylation and their implications as new therapeutic modalities for cancer.

Characterization of glycosylation in monoclonal antibodies and its importance in therapeutic antibody development

Glycosylation is one of the structurally diverse and complex forms of post translational modifications observed in proteins which influence the effector functions of IgG-Fc. Although the glycosylation constitutes 2-3% of the total mass of the IgG antibody, a thorough assessment of glycoform distribution present on the antibody is a critical quality attribute (cQA) for the majority of novel and biosimilar monoclonal antibody (mAb) development. This review paper will highlight the impact of different glycoforms such as galactose, fucose, high mannose, NANA (N-acetylneuraminic acid), and NGNA (N-glycoylneuraminic acid) on the safety/immunogeneicity, efficacy/biological activity and clearance (pharmacodynamics/pharmacokinetic property (PD/PK)) of biological molecules. In addition, this paper will summarize routinely employed reliable analytical techniques such as hydrophilic interaction chromatography (HILIC), high performance anion exchange chromatography with pulsed amperometric detection (HPAEC-PAD) and mass spectrometry (MS) for characterizing and monitoring glycosylation in monoclonal antibodies (mAbs). The advantages and disadvantages of each of the methods are addressed. The scope of this review paper is limited to only N-linked and O-linked glycosylation.

Immunoglobulin G Glycosylation in Diseases

Changes in immunoglobulin G (IgG) glycosylation pattern have been observed in a vast array of auto- and alloimmune, infectious, cardiometabolic, malignant, and other diseases. This chapter contains an updated catalog of over 140 studies within which IgG glycosylation analysis was performed in a disease setting. Since the composition of IgG glycans is known to modulate its effector functions, it is suggested that a changed IgG glycosylation pattern in patients might be involved in disease development and progression, representing a predisposition and/or a functional effector in disease pathology. In contrast to the glycopattern of bulk serum IgG, which likely relates to the systemic inflammatory background, the glycosylation profile of antigen-specific IgG probably plays a direct role in disease pathology in several infectious and allo- and autoimmune antibody-dependent diseases. Depending on the specifics of any given disease, IgG glycosylation read-out might therefore in the future be developed into a useful clinical biomarker or a supplementary to currently used biomarkers.

Protein Glycoengineering: An Approach for Improving Protein Properties

Natural proteins are an important source of therapeutic agents and industrial enzymes. While many of them have the potential to be used as highly effective medical treatments for a wide range of diseases or as catalysts for conversion of a range of molecules into important product types required by modern society, problems associated with poor biophysical and biological properties have limited their applications. Engineering proteins with reduced side-effects and/or improved biophysical and biological properties is therefore of great importance. As a common protein modification, glycosylation has the capacity to greatly influence these properties. Over the past three decades, research from many disciplines has established the importance of glycoengineering in overcoming the limitations of proteins. In this review, we will summarize the methods that have been used to glycoengineer proteins and briefly discuss some representative examples of these methods, with the goal of providing a general overview of this research area.

Construction of a Mammalian IRES-based Expression Vector to Amplify a Bispecific Antibody; Blinatumomab

Blinatumomab, the bispecific T cell engager antibody (BsAb), has been demonstrated as the most successful BsAb to date. Throughout the past decade, vector design has great importance for the expression of monoclonal antibody in Chinese hamster ovary (CHO) cells. It has been indicated that expression vectors based on the elongation factor-1 alpha (EF-1 alpha) gene and DHFR selection marker can be highly effective to produce populations of stably transfected cells in the selection medium. Moreover, the phiC31 integrase system is considered as an attractive and safe protein expression system in mammalian cells and it could integrate a donor plasmid of any size, as a single copy, in to the host genome with no cofactors. In this study, phiC31 integrase technology in combination with DHFR amplification system was used to have an expression vector for future expression of blinatumomab in CHO cells. The gene of interest (BsAb gene) could be joined to DHFR selection marker with the insertion of an internal ribosome entry site (IRES). By positioning the DHFR downstream of BsAb gene and IRES, the transcription of the selection marker can depend on the successful transcription of the BsAb gene, which was located upstream in the expression construct. In this study, FC550A-1 vector was used as the backbone and DHFR selection marker was successfully combined with phiC31 integrase technology to generate a high-expressing construct for BsAb expression in CHO-DG44 cells in future studies.

Strategies to Augment Natural Killer (NK) Cell Activity against Solid Tumors

The immune system plays a crucial role to prevent local growth and dissemination of cancer. Therapies based on activating the immune system can result in beneficial responses in patients with metastatic disease. Treatment with antibodies targeting the immunological checkpoint axis PD-1 / PD-L1 can result in the induction of anti-tumor T cell activation leading to meaningful long-lasting clinical responses. Still, many patients acquire resistance or develop dose-limiting toxicities to these therapies. Analysis of tumors from patients who progress on anti-PD-1 treatment reveal defective interferon-signaling and antigen presentation, resulting in immune escape from T cell-mediated attack. Natural killer (NK) cells are innate lymphocytes that can kill tumor cells without prior sensitization to antigens and can be activated to kill tumor cells that have an impaired antigen processing and presentation machinery. Thus, NK cells may serve as useful effectors against tumor cells that have become resistant to classical immune checkpoint therapy. Various approaches to activate NK cells are being increasingly explored in clinical trials against cancer. While clinical benefit has been demonstrated in patients with acute myeloid leukemia receiving haploidentical NK cells, responses in patients with solid tumors are so far less encouraging. Several hurdles need to be overcome to provide meaningful clinical responses in patients with solid tumors. Here we review the recent developments to augment NK cell responses against solid tumors with regards to cytokine therapy, adoptive infusion of NK cells, NK cell engagers, and NK cell immune checkpoints.

MS-based conformation analysis of recombinant proteins in design, optimization and development of biopharmaceuticals

Mass spectrometry (MS)-based methods for analyzing protein higher order structures have gained increasing application in the field of biopharmaceutical development. The predominant methods used in this area include native MS, hydrogen deuterium exchange-MS, covalent labeling, cross-linking and limited proteolysis. These MS-based methods will be briefly described in this article, followed by a discussion on how these methods contribute at different stages of discovery and development of protein therapeutics.

Differential Inhibition of Nav1.7 and Neuropathic Pain by Hybridoma-Produced and Recombinant Monoclonal Antibodies that Target Nav1.7 : Differential activities of Nav1.7-targeting monoclonal antibodies

The voltage-gated Na+ channel subtype Nav1.7 is important for pain and itch in rodents and humans. We previously showed that a Nav1.7-targeting monoclonal antibody (SVmab) reduces Na+ currents and pain and itch responses in mice. Here, we investigated whether recombinant SVmab (rSVmab) binds to and blocks Nav1.7 similar to SVmab. ELISA tests revealed that SVmab was capable of binding to Nav1.7-expressing HEK293 cells, mouse DRG neurons, human nerve tissue, and the voltage-sensor domain II of Nav1.7. In contrast, rSVmab showed no or weak binding to Nav1.7 in these tests. Patch-clamp recordings showed that SVmab, but not rSVmab, markedly inhibited Na+ currents in Nav1.7-expressing HEK293 cells. Notably, electrical field stimulation increased the blocking activity of SVmab and rSVmab in Nav1.7-expressing HEK293 cells. SVmab was more effective than rSVmab in inhibiting paclitaxel-induced mechanical allodynia. SVmab also bound to human DRG neurons and inhibited their Na+ currents. Finally, potential reasons for the differential efficacy of SVmab and rSVmab and future directions are discussed.

Modulating Cytotoxic Effector Functions by Fc Engineering to Improve Cancer Therapy

In the last two decades, monoclonal antibodies have revolutionized the therapy of cancer patients. Although antibody therapy has continuously been improved, still a significant number of patients do not benefit from antibody therapy. Therefore, rational optimization of the antibody molecule by Fc engineering represents a major area of translational research to further improve this potent therapeutic option. Monoclonal antibodies are able to trigger a variety of effector mechanisms. Especially Fc-mediated effector functions such as antibody-dependent cell-mediated cytotoxicity (ADCC), antibody-dependent cellular phagocytosis (ADCP), and complement- dependent cytotoxicity (CDC) are considered important in antibody therapy of cancer. Novel mechanistic insights into the action of monoclonal antibodies allowed the development of various Fc engineering approaches to modulate antibodies' effector functions. Strategies in modifying the Fc glycosylation profile (Fc glyco-engineering) or approaches in engineering the protein backbone (Fc protein engineering) have been intensively evaluated. In the current review, Fc engineering strategies resulting in improved ADCC, ADCP and CDC activity are summarized and discussed.

Effect of Fc-Glycan Structure on the Conformational Stability of IgG Revealed by Hydrogen/Deuterium Exchange and Limited Proteolysis

Human therapeutic immunoglobulin gamma (IgG) molecules contain an N-glycan on each of their Fc CH2 domains. These glycans include high-mannose, hybrid, and complex types. Recombinant IgG molecules containing high-mannose glycans have been shown to clear faster in human blood, and exhibit decreased thermal stability. The molecular mechanism behind these observations, however, is not well understood. In this work, we used hydrogen/deuterium exchange combined with mass spectrometry (HDX MS), as well as proteolytic degradation under a native-like condition, to assess the impact of different glycoforms on the molecular structure and stability of recombinant IgG1 and IgG2 molecules expressed from Chinese hamster ovary cells. Our HDX MS data indicate that the conformation of these IgG molecules was indeed influenced by the glycan structure. IgG molecules containing high-mannose and hybrid glycans showed more conformational flexibility in the CH2 domain. This conclusion was further supported by the analysis of glycopeptides released from these molecules by trypsin digestion under a native-like condition. The higher CH2 conformational flexibility of IgG molecules with high-mannose and hybrid glycans contributes to their decreased thermal stability. IgG molecules containing sialylated glycans in the CH2 domain exhibited similar enzymatic degradation behavior as high-mannose glycans, suggesting decreased CH2-domain stability compared to shorter complex glycans, likely resulting from steric effect that decreased the glycan-CH2 domain interaction.

Transient Glyco-Engineering to Produce Recombinant IgA1 with Defined N- and O-Glycans in Plants

The production of therapeutic antibodies to combat pathogens and treat diseases, such as cancer is of great interest for the biotechnology industry. The recent development of plant-based expression systems has demonstrated that plants are well-suited for the production of recombinant monoclonal antibodies with defined glycosylation. Compared to immunoglobulin G (IgG), less effort has been undertaken to express immunoglobulin A (IgA), which is the most prevalent antibody class at mucosal sites and a promising candidate for novel recombinant biopharmaceuticals with enhanced anti-tumor activity. Here, we transiently expressed recombinant human IgA1 against the VP8* rotavirus antigen in glyco-engineered ΔXT/FT Nicotiana benthamiana plants. Mass spectrometric analysis of IgA1 glycopeptides revealed the presence of complex biantennary N-glycans with terminal N-acetylglucosamine present on the N-glycosylation site of the CH2 domain in the IgA1 alpha chain. Analysis of the peptide carrying nine potential O-glycosylation sites in the IgA1 alpha chain hinge region showed the presence of plant-specific modifications including hydroxyproline formation and the attachment of pentoses. By co-expression of enzymes required for initiation and elongation of human O-glycosylation it was possible to generate disialylated mucin-type core 1 O-glycans on plant-produced IgA1. Our data demonstrate that ΔXT/FT N. benthamiana plants can be engineered toward the production of recombinant IgA1 with defined human-type N- and O-linked glycans.

Pro-inflammatory pattern of IgG1 Fc glycosylation in multiple sclerosis cerebrospinal fluid

BACKGROUND

Immunoglobulin G (IgG) effector functions are regulated by the composition of glycans attached to a conserved N-glycosylation site in the Fc part. Intrathecal production of IgG, especially IgG1, is a hallmark of multiple sclerosis (MS), but nothing is known about IgG Fc glycosylation in MS and in cerebrospinal fluid (CSF) in general.

METHODS

We applied mass spectrometry of tryptic Fc glycopeptides to analyze IgG Fc glycosylation (sialylation, galactosylation, fucosylation, and bisecting N-acetylglucosamine (GlcNAc)) in 48 paired CSF and serum samples from adult patients with MS or a first demyelinating event highly suggestive of MS (designated as MS cases), and from healthy volunteers and patients with other non-inflammatory diseases (control group). p values were adjusted for multiple testing.

RESULTS

Our experiments revealed four main results. First, IgG1 glycosylation patterns were different in CSF vs. serum, in the MS group and even in control donors without intrathecal IgG synthesis. Second, in MS patients vs. controls, IgG1 glycosylation patterns were altered in CSF, but not in serum. Specifically, in CSF from the MS group, bisecting GlcNAc were elevated, and afucosylation and galactosylation were reduced. Elevated bisecting GlcNAc and reduced galactosylation are known to enhance IgG effector functions. Third, hypothesis-free regression analysis revealed that alterations of afucosylation and bisecting GlcNAc in CSF from MS cases peaked 2-3 months after the last relapse. Fourth, CSF IgG1 glycosylation correlated with the degree of intrathecal IgG synthesis and CSF cell count.

CONCLUSIONS

The CNS compartment as well as the inflammatory milieu in MS affect IgG1 Fc glycosylation. In MS, the CSF IgG1 glycosylation has features that enhance Fc effector functions.

Surrogate target cells expressing surface anti-idiotype antibody for the clinical evaluation of an internalizing CD22-specific antibody

SM03, a chimeric antibody that targets the B-cell restricted antigen CD22, is currently being clinically evaluated for the treatment of lymphomas and other autoimmune diseases in China. SM03 binding to surface CD22 leads to rapid internalization, making the development of an appropriate cell-based bioassay for monitoring changes in SM03 bioactivities during production, purification, storage, and clinical trials difficult. We report herein the development of an anti-idiotype antibody against SM03. Apart from its being used as a surrogate antigen for monitoring SM03 binding affinities, the anti-idiotype antibody was engineered to express as fusion proteins on cell surfaces in a non-internalizing manner, and the engineered cells were used as novel "surrogate target cells" for SM03. SM03-induced complement-mediated cytotoxicity (CMC) against these "surrogate target cells" proved to be an effective bioassay for monitoring changes in Fc functions, including those resulting from minor structural modifications borne within the Fc-appended carbohydrates. The approach can be generally applied for antibodies that target rapidly internalizing or non-surface bound antigens. The combined use of the anti-idiotype antibody and the surrogate target cells could help evaluate clinical parameters associated with safety and efficacies, and possibly the mechanisms of action of SM03.

Site-specific antibody-drug conjugates: the nexus of bioorthogonal chemistry, protein engineering, and drug development

Antibody–drug conjugates (ADCs) combine the specificity of antibodies with the potency of small molecules to create targeted drugs. Despite the simplicity of this concept, generation of clinically successful ADCs has been very difficult. Over the past several decades, scientists have learned a great deal about the constraints on antibodies, linkers, and drugs as they relate to successful construction of ADCs. Once these components are in hand, most ADCs are prepared by nonspecific modification of antibody lysine or cysteine residues with drug-linker reagents, which results in heterogeneous product mixtures that cannot be further purified. With advances in the fields of bioorthogonal chemistry and protein engineering, there is growing interest in producing ADCs by site-specific conjugation to the antibody, yielding more homogeneous products that have demonstrated benefits over their heterogeneous counterparts in vivo. Here, we chronicle the development of a multitude of site-specific conjugation strategies for assembly of ADCs and provide a comprehensive account of key advances and their roots in the fields of bioorthogonal chemistry and protein engineering.

Glycans in the immune system and The Altered Glycan Theory of Autoimmunity: a critical review

Herein we will review the role of glycans in the immune system. Specific topics covered include: the glycosylation sites of IgE, IgM, IgD, IgE, IgA, and IgG; how glycans can encode "self" identity by functioning as either danger associated molecular patterns (DAMPs) or self-associated molecular patterns (SAMPs); the role of glycans as markers of protein integrity and age; how the glycocalyx can dictate the migration pattern of immune cells; and how the combination of Fc N-glycans and Ig isotype dictate the effector function of immunoglobulins. We speculate that the latter may be responsible for the well-documented association between alterations of the serum glycome and autoimmunity. Due to technological limitations, the extent of these autoimmune-associated glycan alterations and their role in disease pathophysiology has not been fully elucidated. Thus, we also review the current technologies available for glycan analysis, placing an emphasis on Multiple Reaction Monitoring (MRM), a rapid high-throughput technology that has great potential for glycan biomarker research. Finally, we put forth The Altered Glycan Theory of Autoimmunity, which states that each autoimmune disease will have a unique glycan signature characterized by the site-specific relative abundances of individual glycan structures on immune cells and extracellular proteins, especially the site-specific glycosylation patterns of the different immunoglobulin(Ig) classes and subclasses.

In vitro and in vivo modifications of recombinant and human IgG antibodies

Tremendous knowledge has been gained in the understanding of various modifications of IgG antibodies, driven mainly by the fact that antibodies are one of the most important groups of therapeutic molecules and because of the development of advanced analytical techniques. Recombinant monoclonal antibody (mAb) therapeutics expressed in mammalian cell lines and endogenous IgG molecules secreted by B cells in the human body share some modifications, but each have some unique modifications. Modifications that are common to recombinant mAb and endogenous IgG molecules are considered to pose a lower risk of immunogenicity. On the other hand, modifications that are unique to recombinant mAbs could potentially pose higher risk. The focus of this review is the comparison of frequently observed modifications of recombinant monoclonal antibodies to those of endogenous IgG molecules.

Clearance of human IgG1-sensitised red blood cells in vivo in humans relates to the in vitro properties of antibodies from alternative cell lines

We previously produced a recombinant version of the human anti-RhD antibody Fog-1 in the rat myeloma cell line, YB2/0. When human, autologous RhD-positive red blood cells (RBC) were sensitised with this IgG1 antibody and re-injected, they were cleared much more rapidly from the circulation than had been seen earlier with the original human-mouse heterohybridoma-produced Fog-1. Since the IgG have the same amino acid sequence, this disparity is likely to be due to alternative glycosylation that results from the rat and mouse cell lines. By comparing the in vitro properties of YB2/0-produced Fog-1 IgG1 and the same antibody produced in the mouse myeloma cell line NS0, we now have a unique opportunity to pinpoint the cause of the difference in ability to clear RBC in vivo. Using transfected cell lines that express single human FcγR, we showed that IgG1 made in YB2/0 and NS0 cell lines bound equally well to receptors of the FcγRI and FcγRII classes but that the YB2/0 antibody was superior in FcγRIII binding. When measuring complexed IgG binding, the difference was 45-fold for FcγRIIIa 158F, 20-fold for FcγRIIIa 158V and approximately 40-fold for FcγRIIIb. The dissimilarity was greater at 100-fold in monomeric IgG binding assays with FcγRIIIa. When used to sensitise RBC, the YB2/0 IgG1 generated 100-fold greater human NK cell antibody-dependent cell-mediated cytotoxicity and had a 10³-fold advantage over the NS0 antibody in activating NK cells, as detected by CD54 levels. In assays of monocyte activation and macrophage adherence/phagocytosis, where FcγRI plays major roles, RBC sensitised with the two antibodies produced much more similar results. Thus, the alternative glycosylation profiles of the Fog-1 antibodies affect only FcγRIII binding and FcγRIII-mediated functions. Relating this to the in vivo studies confirms the importance of FcγRIII in RBC clearance.

LC-MS/MS peptide mapping with automated data processing for routine profiling of N-glycans in immunoglobulins

Protein N-Glycan analysis is traditionally performed by high pH anion exchange chromatography (HPAEC), reversed phase liquid chromatography (RPLC), or hydrophilic interaction liquid chromatography (HILIC) on fluorescence-labeled glycans enzymatically released from the glycoprotein. These methods require time-consuming sample preparations and do not provide site-specific glycosylation information. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) peptide mapping is frequently used for protein structural characterization and, as a bonus, can potentially provide glycan profile on each individual glycosylation site. In this work, a recently developed glycopeptide fragmentation model was used for automated identification, based on their MS/MS, of N-glycopeptides from proteolytic digestion of monoclonal antibodies (mAbs). Experimental conditions were optimized to achieve accurate profiling of glycoforms. Glycan profiles obtained from LC-MS/MS peptide mapping were compared with those obtained from HPAEC, RPLC, and HILIC analyses of released glycans for several mAb molecules. Accuracy, reproducibility, and linearity of the LC-MS/MS peptide mapping method for glycan profiling were evaluated. The LC-MS/MS peptide mapping method with fully automated data analysis requires less sample preparation, provides site-specific information, and may serve as an alternative method for routine profiling of N-glycans on immunoglobulins as well as other glycoproteins with simple N-glycans.

Purification of chimeric heavy chain monoclonal antibody EG2-hFc using hydrophobic interaction membrane chromatography: an alternative to protein-A affinity chromatography

Heavy chain monoclonal antibodies are being considered as alternative to whole-IgG monoclonal antibodies for certain niche applications. Protein-A chromatography which is widely used for purifying IgG monoclonal antibodies is also used for purifying heavy chain monoclonal antibodies as these molecules possess fully functional Fc regions. However, the acidic conditions used to elute bound antibody may sometimes also leach protein-A, which is immunotoxic. Low pH conditions also tend to make the mAb molecules unstable and prone to aggregation. Moreover, protein-A affinity chromatography does not remove aggregates already present in the feed. Hydrophobic interaction membrane chromatography (or HIMC) has already been studied as an alternative to protein-A chromatography for purifying whole-IgG monoclonal antibodies. This paper describes the use of HIMC for capturing a humanized chimeric heavy chain monoclonal antibody (EG2-hFC). Binding and eluting conditions were suitably optimized using pure EG2-hFC. Based on this, an HIMC method was developed for capture of EG2-hFC directly from cell culture supernatant. The EG2-hFc purity obtained in this single-step process was high. The glycan profiles of protein-A and HIMC purified monoclonal antibody samples were similar, clearly demonstrating that both techniques captured similarly glycosylated population of EG2-hFc. Moreover, this technique was able to resolve aggregates from monomeric form of the EG2-hFc.

Antibody Engineering

Advanced molecular biology techniques developed during the past few decades have allowed the industry to exploit and commercialize the natural defense mechanisms that antibodies provide. This review discusses the latest advances in antibody-engineering technologies to enhance clinical efficacy and outcomes. For the constant regions, the choice of the antibody class and isotype has to be made carefully to suit the therapeutic applications. Engineering of the Fc region, either by direct targeted mutagenesis or by modifying the nature of its N -glycan, has played an important role in recent years in increasing half-life or controlling effector functions. The variable regions of the antibody are responsible for binding affinity and exquisite specificity to the target molecule, which together with the Fc determine the drug's efficacy and influence the drug dose required to obtain the desired effectiveness. A key requirement during antibody development is therefore to affinity mature the variable regions when necessary, so that they bind the therapeutic target with sufficiently high affinity to guarantee effective occupancy over prolonged periods. If the antibody was obtained from a non-human source, such as rodents, a humanization process has to be applied to minimize immunogenicity while maintaining the desired binding affinity and selectivity. Finally, we discuss the next next-generation antibodies, such as antibody-drug conjugates, bispecific antibodies, and immunocytokines, which are being developed to meet future challenges.

Comparison of the glycosylation of in vitro generated polyclonal human IgG and therapeutic immunoglobulins

We have recently developed an in vitro culture model enabling the large-scale expansion of switched-memory B lymphocytes, producing a polyclonal human IgG repertoire. Given the importance of glycosylation for the functions of immunoglobulins, we analyzed the N-glycosylation profiles of the immunoglobulin G (IgG) in this model. Switched-memory B cells were cultured for 38 days and, using liquid chromatography-mass spectrometry, we analyzed IgGs' glycosylation profiles which were then compared to the glycosylation patterns of commercial intravenous immunoglobulin (IVIG). We observed a reproducible proliferation rate, high viability through the cultures as well as a good maintenance of the switched-memory B cells repertoire. The glycosylation pattern analyses revealed a variety of the typical biantennary N-glycan structures with diverse terminal monosaccharides. While many similarities were detected in comparison to the glycosylation profile of IVIG, in vitro-produced polyclonal IgGs were bearing higher levels of bisecting GlcNAc known to affect the effector functions of therapeutic antibodies. This data highlights the need for monitoring of the glycoform distribution in antibodies produced in vitro.

Glycosylation: impact, control and improvement during therapeutic protein production

The emergence of the biopharmaceutical industry represented a major revolution for modern medicine, through the development of recombinant therapeutic proteins that brought new hope for many patients with previously untreatable diseases. There is a ever-growing demand for these therapeutics that forces a constant technological evolution to increase product yields while simultaneously reducing costs. However, the process changes made for this purpose may also affect the quality of the product, a factor that was initially overlooked but which is now a major focus of concern. Of the many properties determining product quality, glycosylation is regarded as one of the most important, influencing, for example, the biological activity, serum half-life and immunogenicity of the protein. Consequently, monitoring and control of glycosylation is now critical in biopharmaceutical manufacturing and a requirement of regulatory agencies. A rapid evolution is being observed in this context, concerning the influence of glycosylation in the efficacy of different therapeutic proteins, the impact on glycosylation of a diversity of parameters/processes involved in therapeutic protein production, the analytical methodologies employed for glycosylation monitoring and control, as well as strategies that are being explored to use this property to improve therapeutic protein efficacy (glycoengineering). This work reviews the main findings on these subjects, providing an up-to-date source of information to support further studies.

Expression of recombinant antibodies

Recombinant antibodies are highly specific detection probes in research, diagnostics, and have emerged over the last two decades as the fastest growing class of therapeutic proteins. Antibody generation has been dramatically accelerated by in vitro selection systems, particularly phage display. An increasing variety of recombinant production systems have been developed, ranging from Gram-negative and positive bacteria, yeasts and filamentous fungi, insect cell lines, mammalian cells to transgenic plants and animals. Currently, almost all therapeutic antibodies are still produced in mammalian cell lines in order to reduce the risk of immunogenicity due to altered, non-human glycosylation patterns. However, recent developments of glycosylation-engineered yeast, insect cell lines, and transgenic plants are promising to obtain antibodies with "human-like" post-translational modifications. Furthermore, smaller antibody fragments including bispecific antibodies without any glycosylation are successfully produced in bacteria and have advanced to clinical testing. The first therapeutic antibody products from a non-mammalian source can be expected in coming next years. In this review, we focus on current antibody production systems including their usability for different applications.

Boosting ADCC and CDC activity by Fc engineering and evaluation of antibody effector functions

In recent years, therapy with monoclonal antibodies has become standard of care in various clinical applications. Despite obvious clinical activity, not all patients respond and benefit from this generally well tolerated treatment option. Therefore, rational optimization of antibody therapy represents a major area of interest in translational research. Animal models and clinical data suggested important roles of Fc-mediated effector mechanisms such as antibody dependent cell-mediated cytotoxicity (ADCC) or complement dependent cytotoxicity (CDC) in antibody therapy. These novel insights into the mechanisms of action mediated by monoclonal antibodies inspired the development of different engineering approaches to enhance/optimize antibodies' effector functions. Fc-engineering approaches by altering the Fc-bound glycosylation profile or by exchanging amino acids in the protein backbone have been intensively studied. Here, advanced and emerging technologies in Fc-engineering resulting in altered ADCC and CDC activity are summarized and experimental strategies to evaluate antibodies' effector functions are discussed.

Different glycosylation pattern of human IgG1 and IgG3 antibodies isolated from transiently as well as permanently transfected cell lines

The effector functions of IgG depend on the presence of carbohydrates attached to asparagine 297 in the Fc-portion. In this report, glycosylation profiles of recombinant wild-type and mutant IgG1 and IgG3 antibodies produced from three cell lines were analysed using LC-ESI-Orbitrap. Clear differences were detected between IgG1 and IgG3 glycoforms, where IgG1 generally contained fucosylated glycoforms, whilst IgG3 mainly were non-fucosylated. When using NS-0 and J558L cells for permanent transfection, IgG1 wt glycoforms differed between the two cell lines, whilst IgG3 wt glycoforms did not. Transiently transfected HEK 293E cells were used to produce IgG1 and IgG3 wt and mutants, affecting complement activation. Cell supernatants were harvested at early and late time points and analysed separately. IgGs harvested late showed simpler and less developed glycosylation structure compared to those harvested early. The IgG harvested early was slightly more effective in complement activation than those harvested late, whilst the antibody-dependent cell-mediated cytotoxicity was unaltered. Generally, the glycosylation pattern of the mutants tested, including a hinge truncate mutant of IgG3, did not differ significantly from the wild-type IgGs. The striking difference in glycosylation pattern of IgG1 compared to IgG3 therefore appears not to be due to the long hinge region of IgG3 (62 amino acids) relative to the IgG1 hinge region (15 amino acids). Furthermore, mutation variants at or near the C1q binding site showed similar glycosylation structure and difference in their complement activation activity observed earlier is thus most likely due to differences in protein structure only.

Glycovariant anti-CD37 monospecific protein therapeutic exhibits enhanced effector cell-mediated cytotoxicity against chronic and acute B cell malignancies

TRU-016 is a SMIP(TM) (monospecific protein therapeutic) molecule against the tetraspanin transmembrane family protein CD37 that is currently in Phase 2 trials in Chronic Lymphocytic Leukemia (CLL) and Non-Hodgkin Lymphoma (NHL). In an attempt to enhance the ADCC function of SMIP-016, the chimeric version of TRU-016, SMIP-016(GV) was engineered with a modification in a glycosylation site in the Fc domain. The wild-type and glycovariant SMIP proteins mediate comparable Type I antibody-like direct cytotoxicity in the presence of anti-human Fc crosslinker and show a similar tyrosine phosphorylation pattern post-treatment. However, NK cells stimulated with the SMIP-016(GV) exhibit enhanced activation and release 3-fold more interferon-γ compared with SMIP-016. SMIP-016(GV) shows enhanced ADCC function against cells expressing CD37 with NK cell effectors derived from both normal and CLL-affected individuals. Enhanced ADCC is observed against CLL cells and is sustained at concentrations of SMIP-016(GV) as low at 5E(-6) µg/mL on cells expressing minimal CD37 antigen. In support of the biological relevance of this, SMIP-016(GV) mediates effective ADCC against primary acute lymphoblastic leukemia (ALL) cells with low surface expression of CD37. Collectively, these data suggest potential use of the novel therapeutic agent SMIP-016(GV) with enhanced effector function for B cell malignancies, including CLL and ALL therapy.

Natural killer cell mediated antibody-dependent cellular cytotoxicity in tumor immunotherapy with therapeutic antibodies

In the last decade several therapeutic antibodies have been Federal Drug Administration (FDA) and European Medicines Agency (EMEA) approved. Although their mechanisms of action in vivo is not fully elucidated, antibody-dependent cellular cytotoxicity (ADCC) mediated by natural killer (NK) cells is presumed to be a key effector function. A substantial role of ADCC has been demonstrated in vitro and in mouse tumor models. However, a direct in vivo effect of ADCC in tumor reactivity in humans remains to be shown. Several studies revealed a predictive value of FcγRIIIa-V158F polymorphism in monoclonal antibody treatment, indicating a potential effect of ADCC on outcome for certain indications. Furthermore, the use of therapeutic antibodies after allogeneic hematopoietic stem cell transplantation is an interesting option. Studying the role of the FcγRIIIa-V158F polymorphism and the influence of Killer-cell Immunoglobuline-like Receptor (KIR) receptor ligand incompatibility on ADCC in this approach may contribute to future transplantation strategies. Despite the success of approved second-generation antibodies in the treatment of several malignancies, efforts are made to further augment ADCC in vivo by antibody engineering. Here, we review currently used therapeutic antibodies for which ADCC has been suggested as effector function.

IgG-Fc glycoengineering in non-mammalian expression hosts

The remarkable success of therapeutic applications of immunoglobulin G (IgG) in form of monoclonal antibodies and pooled immunoglobulin G preparations has directed attention to this class of glycoproteins. It is commonly appreciated that oligosaccharides attached to the Fc-region play a critical role in the biological activity of IgGs. Thus, glycosylation has been a focus of interest for many scientists and the biopharmaceutical industry and expression hosts have been engineered in order to optimize antibody products. In this review we focus on efforts towards a targeted manipulation of IgG-Fc N-glycans using non-mammalian expression hosts, i.e. yeast, insect cells and plants. Current achievements in generating human-like N-glycan structures will be presented and recent data on the molecular mechanisms that might explain how these potent drugs mediate in vivo activities will be discussed.

The use of serum-free medium for the production of functionally active humanised monoclonal antibody from NS0 mouse myeloma cells engineered using glutamine synthetase as a selectable marker

A protein-free growth medium (W38 medium) had previously been developed for the NS0 mouse myeloma cell line which is cholesterol-auxotrophic. This paper describes the development of a protein-free growth medium for NS0 cells expressing humanised monoclonal antibody using GS (glutamine synthetase) as a selectable marker. Several GS-engineered NS0 cell lines expressing humanised monoclonal antibody grew in a modification of W38 medium which maintained GS-selection, supplemented with cholesterol, phosphatidylcholine and β-cyclodextrin. Further studies showed that additional glutamic acid, asparagine, ribonucleosides and choline chloride improved cell growth. Amino acid analysis identified a number of amino acids that were being depleted from the culture medium. NS0 cell lines 9D4 and 2H5 expressing CAMPATH-1H(*) were adapted to enable them to grow serum-free in the absence of cholesterol and β-cyclodextrin. Cholesterol-independent 9D4 (9D4.CF) cells grown in shake flask culture using an enriched protein-free medium (WNSD medium), supplemented with human recombinant insulin (Nucellin), reached a maximum cell density to 1.86×10(6) cells ml(-1) producing 76.6 mg l(-1) of antibody. CAMPATH-1H antibody produced using serum-free medium was found to be functionally activein vitro in the Antibody Dependant Cellular Cytotoxicity (ADCC) assay.

Fucose-specific conjugation of hydrazide derivatives to a vascular-targeting monoclonal antibody in IgG format

We describe a method that enables specific and efficient conjugation of hydrazide-moieties to an IgG targeting the tumor neovasculature. The resulting chemically defined, homogeneous hydrazone-linked IgG conjugates remain immunoreactive and have a half-life of approximately 18 hours at physiological pH and temperature suitable for localized delivery of toxic drugs.

Platform for analysis of anthranilic acid N-glycan derivatives utilizing multipolarity mode LC-MS with hydrophilic interaction chromatography separation and ion trap MS/MS

BACKGROUND

The structure of glycans is complex compared with linear polymers such as proteins and nucleic acids. Structural assignment of these compounds is particularly challenging to the bioanalyst. Here we present a multipolarity mode LC-MS platform for analysis of anthranilic acid-derivatized N-glycans.

RESULTS

Multipolarity mode LC-MS analysis of N-glycan anthranilic aid (2AA) derivatives, collected under conditions that stabilize sialyloligosaccharides, provided more complete structural coverage than either mode when used alone. Structural assignment was simplified by the use of 2AA, which localizes charge to the reducing end in both modes facilitating the production of reducing end fragment dominant spectra.

CONCLUSION

Multimode analysis of high-mannose, hybrid and complex N-glycans, under conditions used in this method, is superior to either mode when used alone.

Fc receptor-targeted therapies for the treatment of inflammation, cancer and beyond

The direct or indirect targeting of antibody Fc receptors (FcRs) presents unique opportunities and interesting challenges for the treatment of inflammatory diseases, cancer and infection. Biological responses induced via the Fc portions of antibodies are powerful, complex and unusual, and comprise both activating and inhibitory effects. These properties can be exploited in the engineering of therapeutic monoclonal antibodies to improve their activity in vivo. FcRs have also emerged as key participants in the pathogenesis of several important autoimmune diseases, including systemic lupus erythematosus and rheumatoid arthritis. Therapeutic approaches based on antagonizing FcR function with small molecules or biological drugs such as monoclonal antibodies and recombinant soluble FcR ectodomains have gained momentum. This Review addresses various strategies to manipulate FcR function to overcome immune complex-mediated inflammatory diseases, and considers approaches to improve antibody-based anticancer therapies.

Methods to measure the binding of therapeutic monoclonal antibodies to the human Fc receptor FcγRIII (CD16) using real time kinetic analysis and flow cytometry

Two different methods have been developed to measure the binding of therapeutic antibodies to the low affinity human Fc receptor FcγRIII (CD16). The first measures binding of antibody to recombinant soluble receptor by surface plasmon resonance and the second uses flow cytometry to measure antibody binding to cells which express the receptor. Both methods have been formatted as parallel line assays and show high levels of accuracy, precision and linearity, making them suitable for comparability, potency and stability assays. They are both readily able to detect structural differences such as glycosylation, which affect Fc receptor binding. The same approaches can be used to measure the binding of any antibody to any Fc receptor. These assays show greater internal precision and long-term reproducibility than traditional cell-based assays such as antibody-dependent cell-mediated cytotoxicity. A combinational approach with a target binding might be appropriate for routine drug batch release as these assays are likely to be significantly more sensitive to small changes in drug structure or activity.

The antibody paradigm: present and future development as a scaffold for biopharmaceutical drugs

Early studies of the humoral immune response revealed an apparent paradox: an infinite diversity of antibody specificities encoded within a finite genome. In consequence antibodies became a focus of interest for biochemists and geneticists. It resulted in the elucidation of the basic structural unit, the immunoglobulin (Ig) domain, comprised of ~ 100 amino acid residues that generate the characteristic "immunoglobulin (Ig) fold". The Ig fold has an anti-parallel ß-pleated sheet (barrel) structure that affords structural stability whilst the ß-bends allow for essentially infinite structural variation and functional diversity. This versatility is reflected in the Ig domain being the most widely utilised structural unit within the proteome. Human antibodies are comprised of multiple Ig domains and their structural diversity may be enhanced through the attachment of oligosaccharides. This review summarizes our current understanding of the immunoglobulin structure/function relationships and the application of protein and oligosaccharide engineering to further develop the Ig domain as a scaffold for the generation of new and novel antibody based therapeutics.

Isolation and characterization of IgG1 with asymmetrical Fc glycosylation

N-glycosylation of immunoglobulin G (IgG) at asparigine residue 297 plays a critical role in antibody stability and immune cell-mediated Fc effector function. Current understanding pertaining to Fc glycosylation is based on studies with IgGs that are either fully glycosylated [both heavy chain (HC) glycosylated] or aglycosylated (neither HC glycosylated). No study has been reported on the properties of hemi-glycosylated IgGs, antibodies with asymmetrical glycosylation in the Fc region such that one HC is glycosylated and the other is aglycosylated. We report here for the first time a detailed study of how hemi-glycosylation affects the stability and functional activities of an IgG1 antibody, mAb-X, in comparison to its fully glycosylated counterpart. Our results show that hemi-glycosylation does not impact Fab-mediated antigen binding, nor does it impact neonatal Fc receptor binding. Hemi-glycosylated mAb-X has slightly decreased thermal stability in the CH2 domain and a moderate decrease (∼20%) in C1q binding. More importantly, the hemi-glycosylated form shows significantly decreased binding affinities toward all Fc gamma receptors (FcγRs) including the high-affinity FcγRI, and the low-affinity FcγRIIA, FcγRIIB, FcγRIIIA and FcγRIIIB. The decreased binding affinities to FcγRs result in a 3.5-fold decrease in antibody-dependent cell cytotoxicity (ADCC). As ADCC often plays an important role in therapeutic antibody efficacy, glycosylation status will not only affect the antibody quality but also may impact the biological function of the product.

Modulation of antibody effector function

Several novel technologies have evolved over the last decade for the modification of antibodies to enhance their inherent effector functions. All focus on the constant Fc domain and utilize either amino acid substitutions or glycoform perturbations to modulate their interaction with Fc receptors and the effector cells that bear them. We review these technologies with an emphasis on their validation with animal models and human clinical data.