Improved effector functions of a therapeutic monoclonal Lewis Y-specific antibody by glycoform engineering

Complement System: An Immunotherapy Target in Colorectal Cancer

Colorectal cancer (CRC) is the third most common malignant tumor and the second most fatal cancer worldwide. Several parts of the immune system contribute to fighting cancer including the innate complement system. The complement system is composed of several players, namely component molecules, regulators and receptors. In this review, we discuss the complement system activation in cancer specifically CRC and highlight the possible interactions between the complement system and the various TME components. Additionally, the role of the complement system in tumor immunity of CRC is reviewed. Hence, such work could provide a framework for researchers to further understand the role of the complement system in CRC and explore the potential therapies targeting complement activation in solid tumors such as CRC.

Malignant tissues produce divergent antibody glycosylation of relevance for cancer gene therapy effectiveness

Gene therapy approaches now allow for the production of therapeutic antibodies by healthy or cancerous human tissues directly in vivo, and, with an increasing number of gene delivery methods available, the cell type for expression can be chosen. Yet, little is known about the biophysical changes introduced by expressing antibodies from producer cells or tissues targeted by gene therapy approaches, nor about the consequences for the type of glycosylation. The effects of different glycosylation on therapeutic antibodies have been well studied by controlling their glycan compositions in non-human mammalian production cells, i.e., Chinese hamster ovary cells. Therefore, we investigated the glycosylation state of clinically approved antibodies secreted from cancer tissues frequently targeted by in vivo gene therapy, using native mass spectrometry and glycoproteomics. We found that antibody sialylation and fucosylation depended on the producer tissue and the antibody isotype, allowing us to identify optimal producer cell types according to the desired mode of action of the antibody. Furthermore, we discovered that high amounts (>20%) of non-glycosylated antibodies were produced in cells sensitive to the action of the produced antibodies. Different glycosylation in different producer cells can translate into an altered potency of in-vivo produced antibodies, depending on the desired mode of action, and can affect their serum half-lives. These results increase our knowledge about antibodies produced from cells targeted by gene therapy, enabling development of improved cancer gene therapy vectors that can include in vivo glycoengineering of expressed antibodies to optimize their efficacies, depending on the desired mode of action.

Immunotherapeutic strategies to target vulnerabilities in the Ebolavirus glycoprotein

The 2014 Ebola virus disease (EVD) outbreak in West Africa and the subsequent outbreaks of 2018-2020 in Equator and North Kivu provinces of the Democratic Republic of the Congo illustrate the public health challenges of emerging and reemerging viruses. EVD has a high case fatality rate with a rapidly progressing syndrome of fever, rash, vomiting, diarrhea, and bleeding diathesis. Recently, two monoclonal-antibody-based therapies received United States Food and Drug Administration (FDA) approval, and there are several other passive immunotherapies that hold promise as therapeutics against other species of Ebolavirus. Here, we review concepts needed to understand mechanisms of action, present an expanded schema to define additional sites of vulnerability on the viral glycoprotein, and review current antibody-based therapeutics. The concepts described are used to gain insights into the key characteristics that represent functional targets for immunotherapies against Zaire Ebolavirus and other emerging viruses within the Ebolavirus genus.

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.

Engineering a bacterial sialyltransferase for di-sialylation of a therapeutic antibody

Terminal α-2,6-sialylation of N-glycans is a humanized glycosylation that affects the properties and efficacy of therapeutic glycoproteins. Fc di-sialylation (a biantennary N-glycan with two α-2,6-linked sialic acids) of IgG antibodies imparts them with enhanced anti-inflammatory activity and other roles. However, the microheterogeneity of N-glycoforms presents a challenge for therapeutic development. Therefore, controlled sialylation has drawn considerable attention, but direct access to well-defined di-sialylated antibodies remains limited. Herein, a one-pot three-enzyme protocol was developed by engineering a bacterial sialyltransferase to facilitate the modification of therapeutic antibodies with N-acetylneuraminic acid or its derivatives towards optimized glycosylation. To overcome the low proficiency of bacterial sialyltransferase in antibody remodeling, the Photobacterium sp. JT-ISH-224 α-2,6-sialyltransferase (Psp2,6ST) was genetically engineered by terminal truncation and site-directed mutagenesis based on its protein crystal structure. With the optimized reaction conditions and using activity-based screening of various Psp2,6ST variants, a truncated mutant Psp2,6ST (111-511)-His6 A235M/A366G was shown to effectively improve the catalytic efficiency of antibody di-sialylation. Herceptin and the donor substrate promiscuity allow the introduction of bioorthogonal modifications of N-acetylneuraminic acid into antibodies for site-specific conjugation. 2-AB hydrophilic interaction chromatography analysis of the released N-glycans and intact mass characterization confirmed the high di-sialylation of Herceptin via the optimized one-pot three-enzyme reaction. This study established a versatile enzymatic approach for producing highly di-sialylated IgG antibodies. It provides new insights into engineering bacterial sialyltransferase for adaptation to the enzymatic glycoengineering of therapeutic antibodies and the glycosite-specific conjugation of antibodies.

Perspectives for Glyco-Engineering of Recombinant Biopharmaceuticals from Microalgae

Microalgae exhibit great potential for recombinant therapeutic protein production, due to lower production costs, immunity to human pathogens, and advanced genetic toolkits. However, a fundamental aspect to consider for recombinant biopharmaceutical production is the presence of correct post-translational modifications. Multiple recent studies focusing on glycosylation in microalgae have revealed unique species-specific patterns absent in humans. Glycosylation is particularly important for protein function and is directly responsible for recombinant biopharmaceutical immunogenicity. Therefore, it is necessary to fully characterise this key feature in microalgae before these organisms can be established as industrially relevant microbial biofactories. Here, we review the work done to date on production of recombinant biopharmaceuticals in microalgae, experimental and computational evidence for N- and O-glycosylation in diverse microalgal groups, established approaches for glyco-engineering, and perspectives for their application in microalgal systems. The insights from this review may be applied to future glyco-engineering attempts to humanize recombinant therapeutic proteins and to potentially obtain cheaper, fully functional biopharmaceuticals from microalgae.

How Ginsenosides Trigger Apoptosis in Human Lung Adenocarcinoma Cells

Panax ginseng is a natural medicine that has been used globally for a long time. Moreover, several studies have reported the effective activity of ginseng in treating malignancies. Various agents containing ginseng were widely used as an antitumor treatment nowadays. Lung cancer is the most common fatal cancer in China, and lung adenocarcinoma is the most common histological type of non-small cell lung cancer (NSCLC). What's worse, many patients may have a failed response to conventional therapy including chemotherapy, radiotherapy, or molecule-targeted therapy due to drug resistance. Apoptosis is a highly ordered cellular suicidal process that plays an essential role in maintaining normal homeostasis. The pharmacological mechanism of many antineoplastic drugs involves triggering of apoptotic process. In several recent studies, ginsenosides are regarded as major active components of ginseng that have the potential to control lung cancer. Most of these results have proved that ginsenosides induce apoptosis in lung cancer cells through many different signaling pathways such as PI3K/Akt, NF-κB, EGFR, and so on. This study is aimed at reviewing the signaling pathways that underlie ginsenosides-triggered apoptotic process and encourage further studies to target promising agents against lung cancer treatment.

Antibody-mediated protection against Ebola virus

Recent Ebola virus disease epidemics have highlighted the need for effective vaccines and therapeutics to prevent future outbreaks. Antibodies are clearly critical for control of this deadly disease; however, the specific mechanisms of action of protective antibodies have yet to be defined. In this Perspective we discuss the antibody features that correlate with in vivo protection during infection with Ebola virus, based on the results of a systematic and comprehensive study of antibodies directed against this virus. Although neutralization activity mediated by the Fab domains of the antibody is strongly correlated with protection, recruitment of immune effector functions by the Fc domain has also emerged as a complementary, and sometimes alternative, route to protection. For a subset of antibodies, Fc-mediated clearance and killing of infected cells seems to be the main driver of protection after exposure and mirrors observations in vaccination studies. Continued analysis of antibodies that achieve protection partially or wholly through Fc-mediated functions, the precise functions required, the intersection with specificity and the importance of these functions in different animal models is needed to identify and begin to capitalize on Fc-mediated protection in vaccines and therapeutics alike.

Unusual N-type glycosylation of salivary prolactin-inducible protein (PIP): multiple LewisY epitopes generate highly-fucosylated glycan structures

Prolactin-inducible protein (PIP) is a glycoprotein found in body secretions from exocrine glands like saliva and seminal plasma. Important biological functions of PIP concentrations have been demonstrated, e.g. in tumor diagnosis and progression. PIP quantity has been also found useful to determine the success of chemotherapy of mammary carcinoma. Here, we present the analysis of the N-glycosylation of PIP isolated from different sources by LC-MS(/MS) and ¹H-NMR. We found a very uncommon N-type glycosylation of PIP in healthy individuals from both, seminal fluid and saliva. PIP carries unusual highly fucosylated N-linked glycans with multiple Lewis^y (Le^y) epitopes on bi-, tri- and tetraantennary structures resulting in up to nine fucosyl residues on a tetraantennary glycan. In most organs, Le^y epitopes are not present on N-glycans except in case of a tumor when it is highly up-regulated and important for prognosis. Here, for the first time on a specific glycoprotein Le^y antigens are unambiguously characterized on an N-type glycan by NMR spectroscopy. So far, for specific glycoproteins Le^y epitopes had only been reported on O-glycans. Furthermore, a correlation between a nonsynonymous single nucleotide polymorphism (SNP) and glycosylation pattern was detected: individuals heterozygous for the SNP causing the amino acid exchange ⁵¹Gln to ⁵¹His have glycan structures with a higher degree of sialylation compared to individuals lacking the SNP.

Glycoengineering in CHO Cells: Advances in Systems Biology

For several decades, glycoprotein biologics have been successfully produced from Chinese hamster ovary (CHO) cells. The therapeutic efficacy and potency of glycoprotein biologics are often dictated by their post-translational modifications, particularly glycosylation, which unlike protein synthesis, is a non-templated process. Consequently, both native and recombinant glycoprotein production generate heterogeneous mixtures containing variable amounts of different glycoforms. Stability, potency, plasma half-life, and immunogenicity of the glycoprotein biologic are directly influenced by the glycoforms. Recently, CHO cells have also been explored for production of therapeutic glycosaminoglycans (e.g., heparin), which presents similar challenges as producing glycoproteins biologics. Approaches to controlling heterogeneity in CHO cells and directing the biosynthetic process toward desired glycoforms are not well understood. A systems biology approach combining different technologies is needed for complete understanding of the molecular processes accounting for this variability and to open up new venues in cell line development. In this review, we describe several advances in genetic manipulation, modeling, and glycan and glycoprotein analysis that together will provide new strategies for glycoengineering of CHO cells with desired or enhanced glycosylation capabilities.

Development of a pre-glycoengineered CHO-K1 host cell line for the expression of antibodies with enhanced Fc mediated effector function

Novel biotherapeutic glycoproteins, like recombinant monoclonal antibodies (mAbs) are widely used for the treatment of numerous diseases. The N-glycans attached to the constant region of an antibody have been demonstrated to be crucial for the biological efficacy. Even minor modifications of the N-glycan structure can dictate the potency of IgG effector functions such as the antibody-dependent cell-mediated cytotoxicity (ADCC) and complement-dependent cytotoxicity (CDC).

Here, we present the development of a glycoengineered CHO-K1 host cell line (HCL), stably expressing β1,4-N-Acetylglucoseaminyltransferase III (GnT-III) and α-mannosidase II (Man-II), for the expression of a-fucosylated antibodies with enhanced Fc-mediated effector function. Glycoengineered HCLs were generated in a two-step strategy, starting with generating parental HCLs by stable transfection of CHO-K1 cells with GnT-III and Man-II. In a second step, parental HCLs were stably transfected a second time with these two transgenes to increase their copy number in the genetic background. Generated glycoengineered CHO-K1 cell lines expressing two different mAbs deliver antibody products with a content of more than 60% a-fucosylated glycans. In-depth analysis of the N-glycan structure revealed that the majority of the Fc-attached glycans of the obtained mAbs were of complex bisected type. Furthermore, we showed the efficient use of FcγRIIIa affinity chromatography as a novel method for the fast assessment of the mAbs a-fucosylation level. By testing different cultivation conditions for the pre-glycoengineered recombinant CHO-K1 clones, we identified key components essential for the production of a-fucosylated mAbs. The prevalent effect could be attributed to the trace element manganese, which leads to a strong increase of a-fucosylated complex- and hybrid-type glycans. In conclusion, the novel pre-glycoengineered CHO-K1 HCL can be used for the production of antibodies with high ratios of a-fucosylated Fc-attached N-glycans. Application of our newly developed FcγRIIIa affinity chromatography method during cell line development and use of optimized cultivation conditions can ultimately support the efficient development of a-fucosylated mAbs.

Immune recruitment or suppression by glycan engineering of endogenous and therapeutic antibodies

Human serum IgG contains multiple glycoforms which exhibit a range of binding properties to effector molecules such as cellular Fc receptors. Emerging knowledge of how the Fc glycans contribute to the antibody structure and effector functions has opened new avenues for the exploitation of defined antibody glycoforms in the treatment of diseases. Here, we review the structure and activity of antibody glycoforms and highlight developments in antibody glycoengineering by both the manipulation of the cellular glycosylation machinery and by chemoenzymatic synthesis. We discuss wide ranging applications of antibody glycoengineering in the treatment of cancer, autoimmunity and inflammation. This article is part of a Special Issue entitled "Glycans in personalised medicine" Guest Editor: Professor Gordan Lauc.

Production, Characterization, and Biological Evaluation of Well-Defined IgG1 Fc Glycoforms as a Model System for Biosimilarity Analysis

Four different well-defined IgG1 Fc glycoforms are proposed as a model system to examine important biological and physicochemical features for protein drug biosimilar analyses. The IgG1 Fc glycoforms were produced by yeast expression combined with in vitro enzymatic synthesis as a series of sequentially truncated high-mannose IgG1 Fc glycoforms with an anticipated range of biological activity and structural stability. Initial characterization with mass spectrometry, SDS-PAGE, size exclusion HPLC, and capillary isoelectric focusing confirmed that the glycoproteins are overall highly similar with the only major difference being glycosylation state. Binding to the activating Fc receptor, FcγRIIIa was used to evaluate the potential biological activity of the IgG1 Fc glycoproteins. Two complementary methods using biolayer interferometry, 1 with protein G-immobilized IgG1 Fc and the other with streptavidin-immobilized FcγRIIIa, were developed to assess FcγRIIIa affinity in kinetic binding studies. The high-mannose IgG1 Fc and Man5-IgG1 Fc glycoforms were highly similar to one another with high affinity for FcγRIIIa, whereas GlcNAc-Fc had weak affinity, and the nonglycosylated N297Q-Fc had no measurable affinity for FcγRIIIa. These 4 IgG1 Fc glycoforms were also evaluated in terms of physical and chemical stability profiles and then used as a model system to mathematically assess overall biosimilarity, as described in a series of companion articles.

Enhancement of antibody-dependent cell mediated cytotoxicity: a new era in cancer treatment

The therapeutic efficacy of some anti-tumor monoclonal antibodies (mAbs) depends on the capacity of the mAb to recognize the tumor-associated antigen and induce cytotoxicity via a network of immune effector cells. This process of antibody-dependent cell-mediated cytotoxicity (ADCC) against tumor cells is triggered by the interaction of the fragment crystallizable (Fc) portion of the mAb with the Fc receptors on effector cells like natural killer cells, macrophages, γδ T cells, and dendritic cells. By augmenting ADCC, the antitumor activity of mAbs can be significantly increased. Currently, identifying and developing therapeutic agents that enhance ADCC is a growing area of research. Combining existing tumor-targeting mAbs and ADCC-promoting agents that stimulate effector cells will translate to greater clinical responses. In this review, we discuss strategies for enhancing ADCC and emphasize the potential of combination treatments that include US Food and Drug Administration-approved mAbs and immunostimulatory therapeutics.

Strategies for Engineering Protein N-Glycosylation Pathways in Mammalian Cells

Complexity and heterogeneity of oligosaccharides present a considerable challenge to the biopharmaceutical industry to manufacture biotherapeutics with reproducible and consistent glycoform profiles. Mammalian cells, especially Chinese hamster ovary cells, are the most widely used platform for the production of biotherapeutics. The glycans produced are predominantly of the complex type, with some differences between human and nonhuman mammalian glycosylation existing. This review briefly summarizes metabolic glyco-engineering strategies used in mammalian cells in order to alter the glycosylation patterns attached to proteins applied for diverse biotechnology applications.

Opportunities to exploit non-neutralizing HIV-specific antibody activity

Antibodies act as a nexus between innate and adaptive immunity: they provide a means to engage a spectrum of innate immune effector cells in order to clear viral particles and infected cells and prime antigen presentation. This functional landscape is remarkably complex, and depends on antibody isotype, subclass, and glycosylation; the expression levels and patterns of a suite of Fc receptors with both complementary and opposing activities; and a host of innate immune cells capable of differential responses to opsonized particles and present at different sites. In vivo, even neutralizing antibodies rely on their ability to act as molecular beacons and recruit innate immune effector cells in order to provide protection, and results from both human and macaque studies have implicated these effector functions in vaccinemediated protection. Thus, while enhancing effector function is a tractable handle for potentiating antibody-mediated protection from HIV infection, success will depend critically on leveraging understanding of the means by which antibodies with specific functional profiles could be elicited, which effector functions could provide optimal protection, and perhaps most critically, how to efficiently recruit the innate effector cells present at sites of infection.

Structural documentation of glycan epitopes: sequential mass spectrometry and spectral matching

Documenting mass spectral data is a fundamental aspect of accepted protocols. In this report, we contrast MS(n) sequential disassembly spectra obtained from natural and synthetic glycan epitopes. The epitopes considered are clusters found on conjugate termini of lipids and N- and O-glycans of proteins. The latter are most frequently pendant through a CID-labile HexNAc glycosidic linkage. The synthetic samples were supplied by collaborating colleagues and commercial sources and usually possessed a readily released reducing-end linker, a by-product of synthesis. All samples were comparably methylated, extracted, and MS(n) disassembled to compare their linkage and branching spectral details. Both sample types provide B-ion type fragments early in a disassembly pathway and their compositions are a suggestion of structure. Further steps of disassembly are necessary to confirm the details of linkage and branching. Included in this study were various Lewis and H antigens, 3- and 6-linked sialyl-lactosamine, NeuAc-2,8-NeuAc dimer, and Galα1,3Gal. Sample infusion provided high quality spectral data whereas disassembly to small fragments generates reproducible high signal/noise spectra for spectral matching. All samples were analyzed as sodium adducted positive ions. This study includes comparability statistics and evaluations on several mass spectrometers.

The role of complement in tumor growth

Complement is a central part of the immune system that has developed as a first defense against non-self cells. Neoplastic transformation is accompanied by an increased capacity of the malignant cells to activate complement. In fact, clinical data demonstrate complement activation in cancer patients. On the basis of the use of protective mechanisms by malignant cells, complement activation has traditionally been considered part of the body's immunosurveillance against cancer. Inhibitory mechanisms of complement activation allow cancer cells to escape from complement-mediated elimination and hamper the clinical efficacy of monoclonal antibody-based cancer immunotherapies. To overcome this limitation, many strategies have been developed with the goal of improving complement-mediated effector mechanisms. However, significant work in recent years has identified new and surprising roles for complement activation within the tumor microenvironment. Recent reports suggest that complement elements can promote tumor growth in the context of chronic inflammation. This chapter reviews the data describing the role of complement activation in cancer immunity, which offers insights that may aid the development of more effective therapeutic approaches to control cancer.

Plant glyco-biotechnology on the way to synthetic biology

Plants are increasingly being used for the production of recombinant proteins. One reason is that plants are highly amenable to glycan engineering processes and allow the production of therapeutic proteins with increased efficacies due to optimized glycosylation profiles. Removal and insertion of glycosylation reactions by knock-out/knock-down approaches and introduction of glycosylation enzymes have paved the way for the humanization of the plant glycosylation pathway. The insertion of heterologous enzymes at exactly the right stage of the existing glycosylation pathway has turned out to be of utmost importance. To enable such precise targeting chimeric enzymes have been constructed. In this short review we will exemplify the importance of correct targeting of glycosyltransferases, we will give an overview of the targeting mechanism of glycosyltransferases, describe chimeric enzymes used in plant N-glycosylation engineering and illustrate how plant glycoengineering builds on the tools offered by synthetic biology to construct such chimeric enzymes.

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.

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.

Generation of a potent recombinant homophilic chimeric anti-CD20 antibody

Previously we increased the potency of therapeutic antibodies in targeting, induction of apoptosis, and growth inhibition in vitro and in vivo by chemically conjugating a homophilic peptide to the antibody. Here, we describe the construction of a chimeric fusion gene derived from the murine anti-CD20 antibody (1F5) variable region, with an engineered homophilic domain at the C-terminus of the human IgG1 sequence. The construct was expressed in CHO suspension cells and purified. The potency of the homophilic anti-CD20 antibody was compared to a chimeric antibody without the engineered homophilic domain. In this comparison, the homophilic anti-CD20 antibody showed increased binding to a human CD20 cell line, and significantly more ADCC, CDC, and induction of apoptosis in three cell lines. In addition, the homophilic anti-CD20 antibody demonstrated increased inhibition of proliferation of two cell lines. These data show that homophilic fusion protein antibodies with enhanced therapeutic potency can be produced with industry-standard fermentation protocols.

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.

Antibody-drug conjugates: using monoclonal antibodies for delivery of cytotoxic payloads to cancer cells

One approach to improving activity of anticancer drugs is to conjugate them to antibodies that recognize tumor-associated, cell-surface antigens. The antibody-drug conjugate concept evolved following major advances, first, in the development of humanized and fully human antibodies; second, in the discoveries of highly cytotoxic compounds ('drugs) linkable to antibodies; and finally, in the optimization of linkers that couple the drug to the antibody and provide sufficient stability of the antibody-drug conjugate in the circulation, optimal activation of the drug in the tumor, and the ability of the activated drug to overcome multidrug resistance. In this article, we will review the considerations for selecting a target antigen, the design of the conjugate, and the pre-clinical and clinical experiences with the current generation of antibody-drug conjugates.

Correlation of ADCC activity with cytokine release induced by the stably expressed, glyco-engineered humanized Lewis Y-specific monoclonal antibody MB314

A major limitation to the application of therapeutic monoclonal antibodies (mAbs) is their reduced in vivo efficacy compared with the high efficacy measured in vitro. Effector functions such as antibody-dependent cell-mediated cytotoxicity (ADCC) are dramatically reduced in vivo by the presence of high amounts of endogenous IgG in the serum. Recent studies have shown that modification of the glycosylation moieties attached to the Fc part of the mAb can enhance binding affinity to FcγRIIIα receptors on natural killer cells and thus may counteract the reduced in vivo efficacy. In the present study, a humanized IgG1/κ monoclonal antibody recognizing the tumor-associated carbohydrate antigen Lewis Y was stably produced in a moss expression system that allows glyco-engineering. The glyco-modified mAb (designated MB314) showed a highly homogeneous N-glycosylation pattern lacking core-fucose. A side-by-side comparison to its parental counterpart produced in conventional mammalian cell-culture (MB311, formerly known as IGN311) by fluorescence-activated cell sorting analysis confirmed that the target specificity of MB314 is similar to that of MB311. In contrast, ADCC effector function of MB314 was increased up to 40-fold whereas complement dependent cytotoxicity activity was decreased 5-fold. Notably, a release of immunostimulatory cytokines, including interferon γ, monocyte chemotactic protein-1 (MCP-1), interleukin-6 and tumor necrosis factor (TNF) was particularly induced with the glyco-modified antibody. TNF release was associated with CD14 (+) cells, indicating activation of monocytes.

Glycans in sera of amyotrophic lateral sclerosis patients and their role in killing neuronal cells

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease caused by degeneration of upper and lower motor neurons. To date, glycosylation patterns of glycoproteins in fluids of ALS patients have not been described. Moreover, the aberrant glycosylation related to the pathogenesis of other neurodegenerative diseases encouraged us to explore the glycome of ALS patient sera. We found high levels of sialylated glycans and low levels of core fucosylated glycans in serum-derived N-glycans of patients with ALS, compared to healthy volunteer sera. Based on these results, we analyzed the IgG Fc N²⁹⁷-glycans, as IgG are major serum glycoproteins affected by sialylation or core fucosylation and are found in the motor cortex of ALS patients. The analyses revealed a distinct glycan, A2BG2, in IgG derived from ALS patient sera (ALS-IgG). This glycan increases the affinity of IgG to CD16 on effector cells, consequently enhancing Antibody-Dependent Cellular Cytotoxicity (ADCC). Therefore, we explore whether the Fc-N²⁹⁷-glycans of IgG may be involved in ALS disease. Immunostaining of brain and spinal cord tissues revealed over-expression of CD16 and co-localization of intact ALS-IgG with CD16 and in brain with activated microglia of G93A-SOD1 mice. Intact ALS-IgG enhanced effector cell activation and ADCC reaction in comparison to sugar-depleted or control IgG. ALS-IgG were localized in the synapse between brain microglia and neurons of G93A-SOD1 mice, manifesting a promising in vivo ADCC reaction. Therefore, glycans of ALS-IgG may serve as a biomarker for the disease and may be involved in neuronal damage.

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.

Optimizing therapeutic antibody function: progress with Fc domain engineering

Since the establishment of monoclonal antibody production using hybridoma technology in the mid-1970s, there has been expanding progress and continuous technological improvement in the development of therapeutic antibodies. The initial technological breakthroughs involved reduction of immunogenicity and thus enabled repeated administration. The establishment of chimeric, humanized, and fully human antibodies has led to the great success of several ‘second-generation’ therapeutic antibodies, such as rituximab, trastuzumab, cetuximab, and bevacizumab. However, there still exists an urgent demand for improvement in the efficacy of the current antibody therapeutics, which is not yet fully satisfactory for patients. Based on the current understanding of the clinical mechanisms of several therapeutic antibodies, many now believe that Fc-mediated functions (e.g. antibody-dependent cellular cytotoxicity, complement-dependent cytotoxicity, and neonatal Fc receptor [FcRn]-mediated storage) will improve the clinical outcomes of therapeutic antibodies. The present review focuses on the recent progress in the development of ‘Fc engineering,’ which dramatically improves (and sometimes silences) Fc-mediated functions. These achievements can be classified into two technological approaches: (i) introducing amino acid mutations and (ii) modifying Fc-linked oligosaccharide structures. The effectiveness of multiple third-generation therapeutic antibodies armed with various engineered Fcs is now ready to be tested in clinical trials.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: an update for the period 2005-2006

This review is the fourth update of the original review, published in 1999, on the application of MALDI mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2006. The review covers fundamental studies, fragmentation of carbohydrate ions, method developments, and applications of the technique to the analysis of different types of carbohydrate. Specific compound classes that are covered include carbohydrate polymers from plants, N- and O-linked glycans from glycoproteins, glycated proteins, glycolipids from bacteria, glycosides, and various other natural products. There is a short section on the use of MALDI-TOF mass spectrometry for the study of enzymes involved in glycan processing, a section on industrial processes, particularly the development of biopharmaceuticals and a section on the use of MALDI-MS to monitor products of chemical synthesis of carbohydrates. Large carbohydrate-protein complexes and glycodendrimers are highlighted in this final section.

The therapeutic value of monoclonal antibodies directed against immunogenic tumor glycoproteins

Monoclonal antibodies developed against immunogenic proteins (Tumor Specific Antigens/TSA's) that are expressed in human cancers, display a unique behavioral pattern. They appear to serve in a dual role. This includes the early recognition of these immunogenic membrane proteins that can serve as diagnostic markers, and the targeting of such markers for the destruction of the tumor, primarily thru ADCC.

The monoclonals (mAbs) that we have developed against specific immunogenic tumor membrane proteins have been studied in detail. These tumor proteins, when first defined, were referred to as tumor associated antigens. With the ability of the mAbs to demonstrate therapeutic antitumor activity in those patients with relatively advanced malignancies, the term tumor specific was introduced. Monoclonals that we were able to develop from tumor specific proteins derived from colon and pancreas cancer were found capable of targeting those tumors to induce apoptosis. We were also able to define immunogenic membrane proteins from lung (squamous and adenoCa) as well as prostate neoplasms. Monoclonals developed from these tumor antigens are in the initial phases of investigation with regard to their specificity and antitumor activity.

Mabs capable of targeting the malignancies noted above were produced following immunization of BALBc mice with the Tumor Specific Antigens. The hybridomas that were screened and found to express the antibodies of interest appeared for the most part as IgG2a's. It became apparent after a short period of time that stability of the Fab CDR loops as well as the therapeutic efficacy of the hybridoma mAbs could be lost. Stability was achieved by chimerization and or humanization. The resulting mAbs were found to switch their isotypes to an IgG1 subsequent to chimerization and or humanization, when expressed in CHO cells. The monoclonals, so produced, were not only more efficient in controlling tumor growth but minimized the development of a HAMA response.

Because of 1) the specificity of this group of monoclonal antibodies in targeting well defined immunogenic proteins that were expressed on the tumor cell membrane,2) their lack of cross reactivity to normal tissue, 3) relatively low toxicity when delivered intravenously, 4) rapid targeting of tumor cell populations (4-6 hrs in vitro) and their 5) ability to destroy xenograft transplants (in vivo) within days of delivery, these mAbs were felt to be ideal for possible use in the treatment of patients with recurrent and or metastatic tumors.

Initial clinical studies have been planned for following the filing of an IND. It is required by FDA that the potential effects of tumor control and toxicity be defined using the naked antibodies produced under GMP conditions, In those situations where patients with recurrent malignancies are to be studied we have come to realize that a number of factors can influence the response to monoclonal therapy. This includes the amount of shed antigen in the serum at the time of treatment that could initiate immune complex formation as well as the shedding of inhibitory material into the serum possibly effecting an immune response. As such we plan to eventually employ the therapeutic mAbs in combination with chemotherapy as a means of enhancing the immunogenicity of the tumor system being treated and to possibly weaken the malignant growth for easier destruction by the mAb. We will also look at the combination of mAbs with immunostimulants such as GMCSF and IL-2 (fusion proteins) and eventual conjugation of the mAbs with alpha and possibly B-emitters to help in targeting bystander cells. The present paper reviews the potential therapeutic value of such mAbs in the treatment of recurrent malignancies, especially those having failed chemotherapy in established clinical trials.

Rapid production of recombinant human IgG With improved ADCC effector function in a transient expression system

Rapid production of recombinant human IgG with improved antibody dependent cell-mediated cytotoxicity (ADCC) effector function is presented. The technique employs transient expression of IgG in suspension growing HEK-293F cells in the presence of the glycosidase inhibitor kifunensine. The procedure takes approximately 7 days, provided that expression plasmids encoding the IgG of interest are available. Kifunensine inhibits the N-linked glycosylation pathway of HEK-293F cells in the endoplasmatic reticulum, resulting in IgG with oligomannose type glycans lacking core-fucose. IgG1 transiently produced in kifunensine- treated HEK-293F cells has improved affinity for the FcgammaRIIIA molecule as measured in an ELISA based assay, and almost eightfold enhanced ADCC using primary peripheral blood mononuclear effector cells.

Humanised IgG1 antibody variants targeting membrane-bound carcinoembryonic antigen by antibody-dependent cellular cytotoxicity and phagocytosis

BACKGROUND

The effect of glycoengineering a membrane specific anti-carcinoembryonic antigen (CEA) (this paper uses the original term CEA for the formally designated CEACAM5) antibody (PR1A3) on its ability to enhance killing of colorectal cancer (CRC) cell lines by human immune effector cells was assessed. In vivo efficacy of the antibody was also tested.

METHODS

The antibody was modified using EBNA cells cotransfected with beta-1,4-N-acetylglucosaminyltransferase III and the humanised hPR1A3 antibody genes.

RESULTS

The resulting alteration of the Fc segment glycosylation pattern enhances the antibody's binding affinity to the FcgammaRIIIa receptor on human immune effector cells but does not alter the antibody's binding capacity. Antibody-dependent cellular cytotoxicity (ADCC) is inhibited in the presence of anti-FcgammaRIII blocking antibodies. This glycovariant of hPR1A3 enhances ADCC 10-fold relative to the parent unmodified antibody using either unfractionated peripheral blood mononuclear or natural killer (NK) cells and CEA-positive CRC cells as targets. NK cells are far more potent in eliciting ADCC than either freshly isolated monocytes or granulocytes. Flow cytometry and automated fluorescent microscopy have been used to show that both versions of hPR1A3 can induce antibody-dependent cellular phagocytosis (ADCP) by monocyte-derived macrophages. However, the glycovariant antibody did not mediate enhanced ADCP. This may be explained by the relatively low expression of FcgammaRIIIa on cultured macrophages. In vivo studies show the efficacy of glycoengineered humanised IgG1 PR1A3 in significantly improving survival in a CRC metastatic murine model.

CONCLUSION

The greatly enhanced in vitro ADCC activity of the glycoengineered version of hPR1A3 is likely to be clinically beneficial.

Production of therapeutic antibodies with controlled fucosylation

The clinical success of therapeutic antibodies is demonstrated by the number of antibody therapeutics that have been brought to market and the increasing number of therapeutic antibodies in development. Recombinant antibodies are molecular-targeted therapeutic agents and represent a major new class of drugs. However, it is still very important to optimize and maximize the clinical efficacy of therapeutic antibodies, in part to help lower the cost of therapeutic antibodies by potentially reducing the dose or the duration of treatment. Clinical trials using therapeutic antibodies fully lacking core fucose residue in the Fc oligosaccharides are currently underway, and their remarkable physiological activities in humans in vivo have attracted attention as next-generation therapeutic antibody approaches with improved efficacy. Thus, an industrially applicable antibody production process that provides consistent yields of fully non-fucosylated antibody therapeutics with fixed quality has become a key goal in the successful development of next-generation therapeutic agents. In this article, we review the current technologies for production of therapeutic antibodies with control of fucosylation of the Fc N-glycans.

Generation and validation of affinity reagents on a proteome-wide level

There is a need for protein-specific affinity reagents to explore the gene products encoded by the genome. Recently, systematic efforts to generate validated affinity reagents on a whole human proteome level have been initiated. There are several issues for such efforts, including choice of antigen, type of affinity reagent, and the subsequent validation of the generated protein-specific binders. The advantages and disadvantages with the different approaches are discussed and the problems related to quality assessment of antibodies to be used in multi-platform applications are addressed. This review also describes the efforts to create a virtual resource of validated antibodies using a community-based portal and summarizes the status and visions for the publicly available human protein atlas (http://www.proteinatlas.org) showing the human protein profiles in a large number of normal and cancer tissues as well as a large set of human cell lines.

Antibody fucosylation differentially impacts cytotoxicity mediated by NK and PMN effector cells

Glycosylation of the antibody Fc fragment is essential for Fc receptor–mediated activity. Carbohydrate heterogeneity is known to modulate the activity of effector cells in the blood, in which fucosylation particularly affects NK cell–mediated killing. Here, we investigated how the glycosylation profile of 2F8, a human IgG1 monoclonal antibody against epidermal growth factor receptor in clinical development, impacted effector function. Various 2F8 batches differing in fucosylation, galactosylation, and sialylation of the complex-type oligosaccharides in the Fc fragment were investigated. Our results confirmed that low fucose levels enhance mononuclear cell–mediated antibody-mediated cellular cytotoxicity (ADCC). In contrast, polymorphonuclear cells were found to preferentially kill via high-fucosylated antibody. Whole blood ADCC assays, containing both types of effector cells, revealed little differences in tumor cell killing between both batches. Significantly, however, high-fucose antibody induced superior ADCC in blood from granulocyte colony-stimulating factor–primed donors containing higher numbers of activated polymorphonuclear cells. In conclusion, our data demonstrated for the first time that lack of fucose does not generally increase the ADCC activity of therapeutic antibodies and that the impact of Fc glycosylation on ADCC is critically dependent on the recruited effector cell type.