Enhanced Fc-dependent cellular cytotoxicity of Fc fusion proteins derived from TNF receptor II and LFA-3 by fucose removal from Asn-linked oligosaccharides

Treatment of Parkinson's disease with biologics that penetrate the blood-brain barrier via receptor-mediated transport

Parkinson's disease (PD) is characterized by neurodegeneration of nigral-striatal neurons in parallel with the formation of intra-neuronal α-synuclein aggregates, and these processes are exacerbated by neuro-inflammation. All 3 components of PD pathology are potentially treatable with biologics. Neurotrophins, such as glial derived neurotrophic factor or erythropoietin, can promote neural repair. Therapeutic antibodies can lead to disaggregation of α-synuclein neuronal inclusions. Decoy receptors can block the activity of pro-inflammatory cytokines in brain. However, these biologic drugs do not cross the blood-brain barrier (BBB). Biologics can be made transportable through the BBB following the re-engineering of the biologic as an IgG fusion protein, where the IgG domain targets an endogenous receptor-mediated transcytosis (RMT) system within the BBB, such as the insulin receptor or transferrin receptor. The receptor-specific antibody domain of the fusion protein acts as a molecular Trojan horse to ferry the biologic into brain via the BBB RMT pathway. This review describes the re-engineering of all 3 classes of biologics (neurotrophins, decoy receptor, therapeutic antibodies) for BBB delivery and treatment of PD. Targeting the RMT pathway at the BBB also enables non-viral gene therapy of PD using lipid nanoparticles (LNP) encapsulated with plasmid DNA encoding therapeutic genes. The surface of the lipid nanoparticle is conjugated with a receptor-specific IgG that triggers RMT of the LNP across the BBB in vivo.

Engineering protein-based therapeutics through structural and chemical design

Protein-based therapeutics have led to new paradigms in disease treatment. Projected to be half of the top ten selling drugs in 2023, proteins have emerged as rivaling and, in some cases, superior alternatives to historically used small molecule-based medicines. This review chronicles both well-established and emerging design strategies that have enabled this paradigm shift by transforming protein-based structures that are often prone to denaturation, degradation, and aggregation in vitro and in vivo into highly effective therapeutics. In particular, we discuss strategies for creating structures with increased affinity and targetability, enhanced in vivo stability and pharmacokinetics, improved cell permeability, and reduced amounts of undesired immunogenicity.

A Historical Review of Brain Drug Delivery

The history of brain drug delivery is reviewed beginning with the first demonstration, in 1914, that a drug for syphilis, salvarsan, did not enter the brain, due to the presence of a blood-brain barrier (BBB). Owing to restricted transport across the BBB, FDA-approved drugs for the CNS have been generally limited to lipid-soluble small molecules. Drugs that do not cross the BBB can be re-engineered for transport on endogenous BBB carrier-mediated transport and receptor-mediated transport systems, which were identified during the 1970s-1980s. By the 1990s, a multitude of brain drug delivery technologies emerged, including trans-cranial delivery, CSF delivery, BBB disruption, lipid carriers, prodrugs, stem cells, exosomes, nanoparticles, gene therapy, and biologics. The advantages and limitations of each of these brain drug delivery technologies are critically reviewed.

Coupling CRISPR interference with FACS enrichment: New approach in glycoengineering of CHO cell lines for therapeutic glycoprotein production

Difficulties in obtaining and maintaining the desired level of the critical quality attributes (CQAs) of therapeutic proteins as well as the pace of the development are major challenges of current biopharmaceutical development. Therapeutic proteins, both innovative and biosimilars, are mostly glycosylated. Glycans directly influence the stability, potency, plasma half-life, immunogenicity, and effector functions of the therapeutic. Hence, glycosylation is widely recognized as a process-dependent CQA of therapeutic glycoproteins. Due to the typically high heterogeneity of glycoforms attached to the proteins, control of glycosylation represents one of the most challenging aspects of biopharmaceutical development. Here, we explored a new glycoengineering approach in therapeutic glycoproteins development, which enabled us to achieve the targeted glycoprofile of the Fc-fusion protein in a fast manner. Coupling CRISPRi technology with lectin-FACS sorting enabled downregulation of the endogenous gene involved in fucosylation and further enrichment of CHO cells producing Fc-fusion proteins with reduced fucosylation levels. Enrichment of cells with targeted glycoprofile can lead to time-optimized clone screening and speed up cell line development. Moreover, the presented approach allows isolation of clones with varying levels of fucosylation, which makes it applicable to a broad range of glycoproteins differing in target fucosylation level. This article is protected by copyright. All rights reserved.

Modulation of high mannose levels in N-linked glycosylation through cell culture process conditions to increase antibody-dependent cell-mediated cytotoxicity activity for an antibody biosimilar

The regulatory approval of a biosimilar product is contingent on the favorable comparability of its safety and efficacy to that of the innovator product. As such, it is important to match the critical quality attributes of the biosimilar product to that of the innovator product. The N-glycosylation profile of a monoclonal antibody (mAb) can influence effector function activities such as antibody-dependent cell-mediated cytotoxicity (ADCC) and complement-dependent cytotoxicity. In this study, we describe efforts to modulate the high-mannose (HM) levels of a biosimilar mAb produced in a Chinese hamster ovary cell fed-batch process. Because the HM level of the mAb was observed to impact ADCC activity, it was desirable to match it to the innovator mAb's levels. Several cell culture process related factors known to modulate the HM content of N-glycosylation were investigated, including osmolality, ammonium chloride (NH₄ Cl) addition, glutamine concentration, monensin addition, and the addition of alternate sugars and amino sugars to the feed medium. The process conditions evaluated varied in impact on HM levels, process performance and product quality. One condition, the addition of alternate sugars and amino sugars to feed medium, was identified as the preferred method for increasing HM levels with minimal disruptions to process performance or other product quality attributes. Interestingly, a secondary interaction between sugar and amino sugar supplemented feeds and osmolality was observed during process scale-up. These studies demonstrate sugar and amino sugar concentrations and osmolality are critical variables to evaluate to match HM content in biosimilar and their innovator mAbs.

Profiling of N-Linked Oligosaccharides of a Glycoprotein by UPLC-FLR-ESI-MS After Derivatization with Fluorescent Anthranilamide

N-glycans are described to have a large influence on the properties of therapeutic proteins, including safety and efficacy. For this reason, the extent and type of glycosylation is a characterization parameter for the analysis of antibodies and other therapeutic proteins. The method described here is a fast and high-throughput method for identification and semiquantification of N-glycans by HILIC-FLR-ESI-MS. Sample preparation has been optimized and simultaneous preparation of a large number of samples can be achieved within a day. The use of MS coupled to fluorescence detection is an additional tool for identifying the N-glycan type.

Engineering of Humanized Antibodies Against Human Interleukin 5 Receptor Alpha Subunit That Cause Potent Antibody-Dependent Cell-Mediated Cytotoxicity

Patients with severe eosinophilic asthma (SEA; characterized by persistent eosinophilia in blood and airway tissues) experience frequent asthma exacerbations with poor clinical outcomes. Interleukin 5 (IL-5) and IL-5 receptor alpha subunit (IL-5α) play key roles in eosinophilia maintenance, and relevant therapeutic strategies include the development of antibodies (Abs) against IL-5 or IL-5α to control eosinophilia. Benralizumab, an anti–IL-5α Ab that depletes eosinophils mainly via Ab-dependent cell-mediated cytotoxicity and through blockage of IL-5 function on eosinophils, has been clinically approved for patients with SEA. Here, we report engineering of a new humanized anti–IL-5Rα Ab with potent biological activity. We first raised murine Abs against human IL-5Rα, humanized a leading murine Ab, and then further engineered the humanized Abs to enhance their affinity for IL-5Rα using the yeast surface display technology. The finally engineered version of the Ab, 5R65.7, with affinity (K_D ≈ 4.64 nM) stronger than that of a clinically relevant benralizumab analogue (K_D ≈ 26.8 nM) showed improved neutralizing activity toward IL-5–dependent cell proliferation in a reporter cell system. Domain level Ab epitope mapping revealed that 5R65.7 recognizes membrane-proximal domain 3 of IL-5Rα, distinct from domain I epitope of the benralizumab analogue. In ex vivo assays with peripheral eosinophils from patients with SEA and healthy donors, 5R65.7 manifested more potent biological activities than the benralizumab analogue did, including inhibition of IL-5–dependent proliferation of eosinophils and induction of eosinophil apoptosis through autologous natural-killer-cell–mediated Ab-dependent cell-mediated cytotoxicity. Our study provides a potent anti–IL-5Rα Ab, 5R65.7, which is worthy of further testing in preclinical and clinical trials against SEA as a potential alternative to the current therapeutic arsenal.

Fcγ1 fragment of IgG1 as a powerful affinity tag in recombinant Fc-fusion proteins: immunological, biochemical and therapeutic properties

Affinity tags are vital tools for the production of high-throughput recombinant proteins. Several affinity tags, such as the hexahistidine tag, maltose-binding protein, streptavidin-binding peptide tag, calmodulin-binding peptide, c-Myc tag, glutathione S-transferase and FLAG tag, have been introduced for recombinant protein production. The fragment crystallizable (Fc) domain of the IgG1 antibody is one of the useful affinity tags that can facilitate detection, purification and localization of proteins and can improve the immunogenicity, modulatory effects, physicochemical and pharmaceutical properties of proteins. Fcγ recombinant forms a group of recombinant proteins called Fc-fusion proteins (FFPs). FFPs are widely used in drug discovery, drug delivery, vaccine design and experimental research on receptor-ligand interactions. These fusion proteins have become successful alternatives to monoclonal antibodies for drug developments. In this review, the physicochemical, biochemical, immunological, pharmaceutical and therapeutic properties of recombinant FFPs were discussed as a new generation of bioengineering strategies.

In vivo anti-tumor efficacy of afucosylated anti-CS1 monoclonal antibody produced in glycoengineered Pichia pastoris

Monoclonal antibody (mAb) therapy has been successfully used for the treatment of B-cell lymphomas and is currently extended for the treatment of multiple myeloma (MM). New developments in MM therapeutics have achieved significant survival gains in patients but the disease still remains incurable. Elotuzumab (HuLuc63), an anti-CS1 monoclonal IgG1 antibody, is believed to induce anti-tumor activity and MM cytotoxicity through antibody dependent cellular cytotoxicity (ADCC) and inhibition of MM cell adhesion to bone marrow stromal cells (BMSCs). Modulations of the Fc glycan composition at the N297 site by selective mutations or afucosylation have been explored as strategies to develop bio-better therapeutics with enhanced ADCC activity. Afucosylated therapeutic antibodies with enhanced ADCC activity have been reported to possess greater efficacy in tumor growth inhibition at lower doses when compared to fucosylated therapeutic antibodies. The N-linked glycosylation pathway in Pichia pastoris has been engineered to produce human-like N-linked glycosylation with uniform afucosylated complex type glycans. The purpose of this study was to compare afucosylated anti-CS1 mAb expressed in glycoengineered Pichia pastoris with fucosylated anti-CS1 mAb expressed in mammalian HEK293 cells through in vitro ADCC and in vivo tumor inhibition models. Our results indicate that Fc glycosylation is critical for in vivo efficacy and afucosylated anti-CS1 mAb expressed in glycoengineered Pichia pastoris shows a better in vivo efficacy in tumor regression when compared to fucosylated anti-CS1 mAb expressed in HEK293 cells. Glycoengineered Pichia pastoris could provide an alternative platform for generating homogeneous afucosylated recombinant antibodies where Fc mediated immune effector function is important for efficacy.

A method for high-throughput, sensitive analysis of IgG Fc and Fab glycosylation by capillary electrophoresis

The N-glycan of the IgG constant region (Fc) plays a central role in tuning and directing multiple antibody functions in vivo, including antibody-dependent cellular cytotoxicity, complement deposition, and the regulation of inflammation, among others. However, traditional methods of N-glycan analysis, including HPLC and mass spectrometry, are technically challenging and ill suited to handle the large numbers of low concentration samples analyzed in clinical or animal studies of the N-glycosylation of polyclonal IgG. Here we describe a capillary electrophoresis-based technique to analyze plasma-derived polyclonal IgG-glycosylation quickly and accurately in a cost-effective, sensitive manner that is well suited for high-throughput analyses. Additionally, because a significant fraction of polyclonal IgG is glycosylated on both Fc and Fab domains, we developed an approach to separate and analyze domain-specific glycosylation in polyclonal human, rhesus and mouse IgGs. Overall, this protocol allows for the rapid, accurate, and sensitive analysis of Fc-specific IgG glycosylation, which is critical for population-level studies of how antibody glycosylation may vary in response to vaccination or infection, and across disease states ranging from autoimmunity to cancer in both clinical and animal studies.

Fc-fusion proteins: new developments and future perspectives

Since the first description in 1989 of CD4-Fc-fusion antagonists that inhibit human immune deficiency virus entry into T cells, Fc-fusion proteins have been intensely investigated for their effectiveness to curb a range of pathologies, with several notable recent successes coming to market. These promising outcomes have stimulated the development of novel approaches to improve their efficacy and safety, while also broadening their clinical remit to other uses such as vaccines and intravenous immunoglobulin therapy. This increased attention has also led to non-clinical applications of Fc-fusions, such as affinity reagents in microarray devices. Here we discuss recent results and more generally applicable strategies to improve Fc-fusion proteins for each application, with particular attention to the newer, less charted areas.

Quantitative evaluation of fucose reducing effects in a humanized antibody on Fcγ receptor binding and antibody-dependent cell-mediated cytotoxicity activities

The presence or absence of core fucose in the Fc region N-linked glycans of antibodies affects their binding affinity toward FcγRIIIa as well as their antibody-dependent cell-mediated cytotoxicity (ADCC) activity. However, the quantitative nature of this structure-function relationship remains unclear. In this study, the in vitro biological activity of an afucosylated anti-CD20 antibody was fully characterized. Further, the effect of fucose reduction on Fc effector functions was quantitatively evaluated using the afucosylated antibody, its "regular" fucosylated counterpart and a series of mixtures containing varying proportions of "regular" and afucosylated materials. Compared with the "regular" fucosylated antibody, the afucosylated antibody demonstrated similar binding interactions with the target antigen (CD20), C1q and FcγRIa, moderate increases in binding to FcγRIIa and IIb, and substantially increased binding to FcγRIIIa. The afucosylated antibodies also showed comparable complement-dependent cytotoxicity activity but markedly increased ADCC activity. Based on EC 50 values derived from dose-response curves, our results indicate that the amount of afucosylated glycan in antibody samples correlate with both FcγRIIIa binding activity and ADCC activity in a linear fashion. Furthermore, the extent of ADCC enhancement due to fucose depletion was not affected by the FcγRIIIa genotype of the effector cells.

Novel roles for the IgG Fc glycan

IgG antibodies trigger leukocyte activation and inflammation by forming immune complexes that crosslink activating Fcγ receptors (FcγRs). This is essential to combat infection, but detrimental if antibodies target or cross-react with autoantigens. The high specificity and long serum half-life of IgG antibodies confers tremendous therapeutic potential. Indeed, antibodies have been successfully employed to target cancers, autoreactive B cells, and pro-inflammatory cytokines. Conversely, IgG antibodies can also initiate anti-inflammatory responses. In the form of intravenous immunoglobulin (IVIG), IgGs are routinely administered to treat inflammatory autoimmune diseases. Importantly, the N-linked glycans on the IgG Fc are absolutely required for initiating these IgG effector functions. In fact, the Fc glycan composition dictates IgG affinity to individual FcγRs, and in a broader sense, binding to different FcγRs classes: activating, inhibitory, and anti-inflammatory (dendritic cell-specific ICAM-3 grabbing nonintegrin, DC-SIGN). The Fc glycan requirements to initiate and suppress inflammation will be discussed herein.

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.

Neuroprotection with a brain-penetrating biologic tumor necrosis factor inhibitor

Biologic tumor necrosis factor (TNF)-α inhibitors do not cross the blood-brain barrier (BBB). A BBB-penetrating TNF-α inhibitor was engineered by fusion of the extracellular domain of the type II human TNF receptor (TNFR) to the carboxyl terminus of the heavy chain of a mouse/rat chimeric monoclonal antibody (MAb) against the mouse transferrin receptor (TfR), and this fusion protein is designated cTfRMAb-TNFR. The cTfRMAb-TNFR fusion protein and etanercept bound human TNF-α with high affinity and K(D) values of 374 ± 77 and 280 ± 80 pM, respectively. Neuroprotection in brain in vivo after intravenous administration of the fusion protein was examined in a mouse model of Parkinson's disease. Mice were also treated with saline or a non-BBB-penetrating TNF decoy receptor, etanercept. After intracerebral injection of the nigral-striatal toxin, 6-hydroxydopamine, mice were treated every other day for 3 weeks. Treatment with the cTfRMAb-TNFR fusion protein caused an 83% decrease in apomorphine-induced rotation, a 67% decrease in amphetamine-induced rotation, a 82% increase in vibrissae-elicited forelimb placing, and a 130% increase in striatal tyrosine hydroxylase (TH) enzyme activity. In contrast, chronic treatment with etanercept, which does not cross the BBB, had no effect on neurobehavior or striatal TH enzyme activity. A bridging enzyme-linked immunosorbent assay specific for the cTfRMAb-TNFR fusion protein showed that the immune response generated in the mice was low titer. In conclusion, a biologic TNF inhibitor is neuroprotective after intravenous administration in a mouse model of neurodegeneration, providing that the TNF decoy receptor is reengineered to cross the BBB.

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.

Biopharmaceutical drug targeting to the brain

Biopharmaceuticals are large molecule drugs that do not cross the blood-brain barrier (BBB). The limiting factor in the drug development of biopharmaceuticals as new drugs for the human brain is the engineering of effective brain drug targeting technology platforms. Recombinant proteins, enzymes, and monoclonal antibodies can be re-engineered for transport across the human BBB with the molecular Trojan horse technology. The most active BBB molecular Trojan horse is a monoclonal antibody to the human insulin receptor. The genetic engineering of IgG fusion proteins has been demonstrated for neurotrophic factors, decoy receptors, therapeutic enzymes, single chain Fv antibodies, and avidin. The IgG fusion proteins are not toxic on repeated administration in high doses to primates and do not interfere with glycemic control in plasma or brain. IgG fusion proteins contain amino acid sequences that induce immune tolerance, and show low immunogenicity in primates. The IgG fusion proteins are new bifunctional biopharmaceuticals that are both targeted to brain via transport on endogenous BBB receptors, and exert pharmacological effects in brain at the cognate receptor, ligand, or enzyme substrate.

Tumor necrosis factor receptor-IgG fusion protein for targeted drug delivery across the human blood-brain barrier

The tumor necrosis factor-alpha receptor (TNFR) extracellular domain (ECD) is a decoy receptor that could be developed as a neurotherapeutic for stroke, brain injury, or chronic neurodegeneration. However, the TNFR ECD is a large molecule therapeutic that does not cross the blood-brain barrier (BBB). Human TNFR ECD was re-engineered by fusion of the receptor protein to the carboxyl terminus of the chimeric monoclonal antibody (mAb) to the human insulin receptor (HIR). The HIRMAb-TNFR fusion protein is bifunctional, and binds both the HIR, to trigger receptor-mediated transport across the BBB, and TNFalpha, to sequester this cytotoxic cytokine. COS cells were dual transfected with the heavy chain (HC) and light chain fusion protein expression plasmids, and the HC of the fusion protein was immunoreactive with antibodies to both human IgG and TNFR. The HIRMAb-TNFR fusion protein bound to the extracellular domain of the HIR with an affinity comparable to the HIRMAb, and bound TNFalpha with a K(D) of 0.34 +/- 0.17 nM. Both the TNFR:Fc fusion protein and the HIRMAb-TNFR fusion protein blocked the cytotoxic actions of TNFalpha on human cells in a bioassay. In conclusion, these studies describe the re-engineering of the TNFR ECD to make this decoy receptor transportable across the human BBB.

Engineered anti-CD20 antibodies with enhanced complement-activating capacity mediate potent anti-lymphoma activity

One of the major issues in current antibody therapy is insufficient efficacy. Various biological factors relating to the host's immune system or tumor cells have been suggested to reduce the efficacy of anti-CD20 therapy in B-cell malignancies. In this study, we characterized the in vitro anti-lymphoma activity of anti-CD20 antibodies having a novel engineered heavy chain with enhanced complement-dependent cytotoxicity (CDC). Anti-CD20 antibodies having a variant heavy constant region of mixed IgG1/IgG3 isotype, which have previously been found to enhance CDC, were investigated for their in vitro CDC against lymphoma cells and whole blood B-cell depletion activity. Use of the variant constant region greatly increased the CDC of an anti-CD20 antibody having variable regions identical to those of rituximab to the level shown by an IgG1 antibody of ofatumumab. Although the whole blood assay showed different cytotoxicity patterns among individual blood donors, the CDC-enhancing variant of rituximab showed higher activity than the parent IgG1 and consistently showed maximized activity when further combined with antibody-dependent cellular cytotoxicity (ADCC)-enhancing modification by fucose removal from Fc-linked oligosaccharides. In addition, the rituximab variant showed potent CDC against transfectant cells with lower CD20 expression and chronic lymphocytic leukemia-derived cell lines with higher complement regulatory proteins. These findings suggest that CDC enhancement, both alone and in combination with ADCC enhancement, increases the anti-lymphoma activity of anti-CD20 antibodies irrespective of individual differences in effector functions, and renders current anti-CD20 therapy capable of overcoming the potential resistance mechanisms.

Engineered therapeutic antibodies with improved effector functions

In the past decade, more than 20 therapeutic antibodies have been approved for clinical use and many others are now at the clinical and preclinical stage of development. Fragment crystallizable (Fc)-dependent antibody functions, such as antibody-dependent cell-mediated cytotoxicity (ADCC), complement-dependent cytotoxicity (CDC), and a long half-life, have been suggested as important clinical mechanisms of therapeutic antibodies. These functions are primarily triggered through direct interaction of the Fc domain with its corresponding receptors: FcgammaRIIIa for ADCC, C1q for CDC, and neonatal Fc receptor for prolongation of the clearance rate. However, current antibody therapy still faces the critical issues of insufficient efficacy and the high cost of the therapeutic agents. A possible solution to these issues could be to engineer antibody molecules to enhance their antitumor activity, leading to improved therapeutic outcomes and reduced doses. Here, we review advanced Fc engineering approaches for the enhancement of effector functions, some of which are now ready for evaluation of their effectiveness in clinical trials.

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.

Immunoglobulin 1 (IgG1) Fc-glycosylation profiling of anti-citrullinated peptide antibodies from human serum

In several autoimmune disorders, including rheumatoid arthritis (RA), autoantibodies are thought to be the driving force of pathogenicity. Glycosylation of the Fc-part of human Igs is known to modulate biological activity. Hitherto, glycosylation of human IgG-Fc has been analyzed predominantly at the level of total serum IgG, revealing reduced galactosylation in RA. Given the pathogenic relevance of autoantibodies in RA, we wished, in the present study, to address the question whether distinct Fc-glycosylation features are observable at the level of antigen-specific IgG subpopulations. For this purpose, we have developed a method for the microscale purification and Fc-glycosylation analysis of anti-citrullinated peptide antibodies (ACPA). ACPA represent a group of autoantibodies that occur with unique specificity in RA patients. Their presence is associated with increased inflammatory disease activity and rapid joint destruction. Results indicate that ACPA of the IgG1 subclass vary considerably from total serum IgG1 with respect to Fc-galactosylation, with galactosylation being higher on ACPA than on serum IgG1 for some patients, while other patients show higher galactosylation on serum IgG1 than on ACPA. Using this method, studies can be performed on the biological and clinical relevance of ACPA glycosylation within RA patient cohorts.

Engineered antibodies of IgG1/IgG3 mixed isotype with enhanced cytotoxic activities

Enhancement of multiple effector functions of an antibody may be a promising approach for antibody therapy. We have previously reported that fucose removal from Fc-linked oligosaccharides greatly enhances antibody-dependent cellular cytotoxicity (ADCC) of therapeutic antibodies. Here, we report a unique approach to enhance complement-dependent cytotoxicity (CDC), another important effector function of antitumor antibodies, by using engineered constant region of human IgG1/IgG3 chimeric isotypes. We systematically shuffled constant domains of IgG1 and IgG3 to generate a comprehensive set of mixed chimeric isotypes of anti-CD20 antibodies. Among these, the variant 1133, consisting of the CH1 and the hinge each from IgG1 and the Fc from IgG3, was unexpectedly found to exhibit markedly enhanced CDC that exceeded wild-type levels. However, it lacked protein A-binding capacity, an important feature for the industrial production. To eliminate this deficiency, a portion in COOH-terminal CH3 domain of 1133 was substituted with IgG1, resulting in full recovery of protein A binding without compromising the enhanced CDC and ADCC activities. The CDC-enhancing effect using a chimeric isotype was also shown in CD52 antigen/antibody system. The ADCC activity of the variants was also maximized by the absence of fucose from its carbohydrate structure, a phenomenon that has previously been observed for wild-type antibodies. Enhanced cytotoxicity of a variant was confirmed in a cynomolgus monkey model. These findings suggest that the variant antibodies with IgG1/IgG3 chimeric constant regions and nonfucosylated oligosaccharides that possess dual-enhanced cytotoxic functions may be an improvement for the next generation of therapeutic antitumor antibodies.

Glycosylation profiling of immunoglobulin G (IgG) subclasses from human serum

All four subclasses of human serum IgG contain a single N-glycosylation site in the constant region of their heavy chain, which is occupied by biantennary, largely core-fucosylated and partially truncated oligosaccharides, that may carry a bisecting N-acetylglucosamine and sialic acid residues. IgG glycosylation has been shown to be altered under various physiological and pathological circumstances. IgG N-glycan profiles vary with age, and galactosylation for example is enhanced during pregnancy. Several diseases including rheumatoid arthritis are associated with a reduction in galactosylation of the IgG N-glycans. Here, we describe a robust method for the isolation of IgG subclasses using protein A (binds IgG1, IgG2, and IgG4) and protein G (binds additionally IgG3) at the 96-well plate level, which is suitable for automation. Isolated IgGs were digested with trypsin, and obtained glycopeptides were analyzed by nano-LC-MS. Glycopeptides were characterized by CID as well as electron transfer dissociation (ETD). The method provided glycosylation profiles for IgG1, IgG2, IgG3, and IgG4 and revealed distinct differences in N-glycosylation between the four IgG subclasses. The changes in galactosylation associated with rheumatoid arthritis could readily be monitored. This method is suitable for the subclass-specific analysis of IgG glycosylation from clinical samples.

Comparative analyses of complex formation and binding sites between human tumor necrosis factor-alpha and its three antagonists elucidate their different neutralizing mechanisms

Tumor necrosis factor-alpha (TNFalpha)-blocking therapy, using biologic TNFalpha antagonists, has been approved for the treatment of several diseases including rheumatoid arthritis, psoriasis and Crohn's disease. There have been few detailed studies of binding characterizations for the complex formation by TNFalpha and clinically relevant antagonists, particularly Infliximab (Remicade) and Etanercept (Enbrel). Here we characterized the binding stoichiometry and size of soluble TNFalpha-antagonist complexes and identified energetically important binding sites on TNFalpha for the three antagonists, Etanercept, Infliximab, and the recently developed humanized TNFalpha neutralizing monoclonal antibody, YHB1411-2. Size-exclusion chromatography and dynamic light scattering analyses revealed that the three antagonists formed distinct thermodynamically stable TNFalpha-antagonist complexes that exhibited differences in their size and composition. Energetically important binding residues on TNFalpha were identified for each antagonist by a sequence of experiments that consisted of competition binding assays, fragmentations, loop mutations, and single-point mutations using yeast surface-displayed TNFalpha, which was further confirmed for solubly purified TNFalpha mutants by surface plasmon resonance technique. Analyses of the binding geometry based on binding site location, spatial constraints, and valency satisfaction allowed us to interpret the thermodynamically stable complexes as follows: one molecule of Etanercept and one molecule of trimeric TNFalpha (Etanercept1-TNFalpha1), Infliximab6-TNFalpha3, and YHB1411-2(4)-TNFalpha2. The distinct features of the soluble antagonist-TNFalpha complex formation among the antagonists may give further insights into their different neutralizing mechanisms and pharmacokinetic profiles.