Lack of fucose on human IgG1 N-linked oligosaccharide improves binding to human Fcgamma RIII and antibody-dependent cellular toxicity

Structural basis for Fc gammaRIIa recognition of human IgG and formation of inflammatory signaling complexes

The interaction of Abs with their specific FcRs is of primary importance in host immune effector systems involved in infection and inflammation, and are the target for immune evasion by pathogens. FcγRIIa is a unique and the most widespread activating FcR in humans that through avid binding of immune complexes potently triggers inflammation. Polymorphisms of FcγRIIa (high responder/low responder [HR/LR]) are linked to susceptibility to infections, autoimmune diseases, and the efficacy of therapeutic Abs. In this article, we define the three-dimensional structure of the complex between the HR (arginine, R134) allele of FcγRIIa (FcγRIIa-HR) and the Fc region of a humanized IgG1 Ab, hu3S193. The structure suggests how the HR/LR polymorphism may influence FcγRIIa interactions with different IgG subclasses and glycoforms. In addition, mutagenesis defined the basis of the epitopes detected by FcR blocking mAbs specific for FcγRIIa (IV.3), FcγRIIb (X63-21), and a pan FcγRII Ab (8.7). The epitopes detected by these Abs are distinct, but all overlap with residues defined by crystallography to contact IgG. Finally, crystal structures of LR (histidine, H134) allele of FcγRIIa and FcγRIIa-HR reveal two distinct receptor dimers that may represent quaternary states on the cell surface. A model is presented whereby a dimer of FcγRIIa-HR binds Ag-Ab complexes in an arrangement that possibly occurs on the cell membrane as part of a larger signaling assembly.

Placental immunology and maternal alloimmune responses

During pregnancy, women are tolerant of their semi-allogeneic fetus whilst not being immunosuppressed and indeed readily form alloantibodies. This 'Immunological Paradox of Pregnancy' may be explained by an understanding of placental anatomy and immunology. Trophoblast cells form the interface between the fetus and maternal tissues and blood and escape allorecognition because they lack classical human leucocyte antigen (HLA) class I and II molecules. Local immunoregulation, or tolerance, in the decidua is mediated partly by HLA-G(+) extravillous trophoblasts (EVT) that invade the tissue and prevent killing by maternal natural killer cells, cytotoxic T cells and macrophages. Placental hormones orchestrate the composition and regulatory function of maternal immune cells. In contrast, syncytiotrophoblast cells at the surface of chorionic villi, in contact with maternal blood, maintain a state of mild maternal systemic immunity via activation of innate immunity and skewing towards humoral immunity. This enables maintenance of a healthy immune system in pregnant women and robust protective antibody responses to pathogens whilst enabling survival of the fetus. However, this has the unfortunate consequence that pregnant women readily form alloantibodies to incompatible alloantigens on fetal red cells, platelets and leucocytes if fetomaternal haemorrhage (FMH) occurs. The antibodies are initially low affinity but after re-immunization with further FMH become functionally effective, high-titre IgG.

Biochemical and biophysical characterization of humanized IgG1 produced in Pichia pastoris

The first full length IgG produced in Pichia pastoris was reported in late 1980. However, use of a wild-type Pichia expression system to produce IgGs with human-like N-linked glycans was not possible until recently. Advances in glycoengineering have enabled organisms such as Pichia to mimic human N-glycan biosynthesis and produce IgGs with human glycans on an industrial scale. Since there are only a few reports of the analytical characterization of Pichia-produced IgG, we summarize the results known in this field, and provide additional characterization data generated in our laboratories. The data suggest that Pichia-produced IgG has the same stability as that produced in Chinese hamster ovary (CHO) cells. It has similar aggregation profiles, charge variant distribution and oxidation levels as those for a CHO IgG. It contains human N-linked glycans and O-linked single mannose. Because of the comparable biophysical and biochemical characteristics, glycoengineered Pichia pastoris is an attractive expression system for therapeutic IgG productions.

Fucose content of monoclonal antibodies can be controlled by culture medium osmolality for high antibody-dependent cellular cytotoxicity

Antibody-dependent cellular cytotoxicity (ADCC) is dependent on the fucose content of oligosaccharides bound to monoclonal antibodies (MAbs). As MAbs with a low fucose content exhibit high ADCC activity, it is important to control the defucosylation levels (deFuc%) of MAbs and to analyze the factors that affect deFuc%. In this study, we observed that the deFuc% was inversely related to culture medium osmolality for MAbs produced in the rat hybridoma cell line YB2/0, with r (2) values as high as 0.92. Moreover, deFuc% exhibited the same correlation irrespective of the type of compound used for regulating osmolality (NaCl, KCl, fucose, fructose, creatine, or mannitol) at a culture scale ranging from 1 to 400 L. We succeeded in controlling MAb deFuc% by maintaining a constant medium osmolality in both perfusion and fed-batch cultures. In agreement with these observations, reverse transcription PCR analyses revealed decreased transcription of genes involved in glycolysis, GDP-fucose supply, and fucose transfer under hypoosmotic conditions.

Combined Fc-protein- and Fc-glyco-engineering of scFv-Fc fusion proteins synergistically enhances CD16a binding but does not further enhance NK-cell mediated ADCC

Protein- or glyco-engineering of antibody molecules can be used to enhance Fc-mediated effector functions. ScFv-Fc fusion proteins (scFv-Fc) represent interesting antibody derivatives due to their relatively simple design and increased tissue penetration. Here, the impact of protein- and glyco-engineering on ADCC potency of a panel of human IgG1-based scFv-Fc was tested. Three matched sets of scFv-Fc variants targeting CD7, CD20 or HLA class II and optimized for CD16a binding by mutagenesis, lack of core-fucose, or their combination, were generated and functionally tested in comparison to the corresponding wild type scFv-Fc. Antigen binding activity was not compromised by altered glycosylation or Fc mutagenesis, whereas Fc binding to CD16a was significantly enhanced in the order: non-core fucosylated/Fc-mutated double-engineered≫Fc-mutated≥non-core-fucosylated>wild-type IgG1-Fc. All engineered variants triggered potent ADCC with up to 100-fold reduced EC50 values compared to non-engineered variants. Interestingly, double-engineered variants were similarly effective in triggering ADCC compared to single-engineered variants irrespective of their 1 log greater CD16a binding affinity. Thus, these data demonstrate that protein- and glyco-engineering enhances NK-cell mediated ADCC of scFv-Fc similarly and show that enhancing CD16a affinity beyond a certain threshold does not result in a further increase of NK-cell mediated ADCC.

Methods development for Analysis of Partially Deglycosylated Proteins and Application to an HIV Envelope Protein Vaccine Candidate

The work presented herein describes the first comprehensive analysis of a partially deglycosylated HIV vaccine candidate envelope protein (Env). The Env, JRFL gp140 ΔCF, with 27 potential glycosylation sites, was partially deglycosylated with PNGase F as part of a strategy to generate a more immunogenic HIV vaccine, and the resulting protein's glycosylation was characterized in a unique workflow using two different glycosidases, Endo H and Endo F3. This unique analysis protocol provided for coverage on 26 of the 27 glycosylation sites, and the data showed that the biochemical treatment with PNGase F resulted in a highly heterogeneous glycoprotein product that had been partially deglycosylated at most of the glycosylation sites. The protocols described in this work could be useful for characterizing the glycosylation site occupancy of other native or biochemically deglycosylated proteins.

Unique carbohydrate-carbohydrate interactions are required for high affinity binding between FcgammaRIII and antibodies lacking core fucose

Antibody-mediated cellular cytotoxicity (ADCC), a key immune effector mechanism, relies on the binding of antigen-antibody complexes to Fcγ receptors expressed on immune cells. Antibodies lacking core fucosylation show a large increase in affinity for FcγRIIIa leading to an improved receptor-mediated effector function. Although afucosylated IgGs exist naturally, a next generation of recombinant therapeutic, glycoenginereed antibodies is currently being developed to exploit this finding. In this study, the crystal structures of a glycosylated Fcγ receptor complexed with either afucosylated or fucosylated Fc were determined allowing a detailed, molecular understanding of the regulatory role of Fc-oligosaccharide core fucosylation in improving ADCC. The structures reveal a unique type of interface consisting of carbohydrate-carbohydrate interactions between glycans of the receptor and the afucosylated Fc. In contrast, in the complex structure with fucosylated Fc, these contacts are weakened or nonexistent, explaining the decreased affinity for the receptor. These findings allow us to understand the higher efficacy of therapeutic antibodies lacking the core fucose and also suggest a unique mechanism by which the immune system can regulate antibody-mediated effector functions.

Pharmacokinetics of IgG1 monoclonal antibodies produced in humanized Pichia pastoris with specific glycoforms: a comparative study with CHO produced materials

A glycoengineered Pichia pastoris host was used to produce an IgG1 with either afucosylated N-glycosylation (afucosylated biantennary complex) or without N-glycosylation (N297A) while a wild type P. pastoris host was used to produce an IgG1 containing fungal-type N- and O-linked glycosylation. The PK properties of these antibodies were compared to a commercial IgG1 produced in CHO cells following intravenous administration in wild type C57B6, FcγR-/- or hFcRn transgenic mice. MAbs produced in glycoengineered yeast exhibited similar PK properties in wild type mice or FcγR-/- mice with respect to clearance (CL), volume of distribution at steady-state (Vss) and half-life (t(1/2)) to that produced in mammalian (CHO) cells, while the mAb produced in wild type yeast exhibited ∼2-3-fold faster CL, which might be due to the high mannose content interacting with mannose receptors. Furthermore, in vitro binding affinity to human FcRn or mouse FcRn was similar between the reference mAb and mAbs produced in humanized yeast, and the glycovariants produced in humanized yeast exhibited similar PK patterns in human FcRn transgenic mice and in wild type mice. These results suggest the potential application of P. pastoris as a production platform for clinically viable mAbs.

Evolutional and clinical implications of the epigenetic regulation of protein glycosylation

Protein N glycosylation is an ancient posttranslational modification that enriches protein structure and function. The addition of one or more complex oligosaccharides (glycans) to the backbones of the majority of eukaryotic proteins makes the glycoproteome several orders of magnitude more complex than the proteome itself. Contrary to polypeptides, which are defined by a sequence of nucleotides in the corresponding genes, glycan parts of glycoproteins are synthesized by the activity of hundreds of factors forming a complex dynamic network. These are defined by both the DNA sequence and the modes of regulating gene expression levels of all the genes involved in N glycosylation. Due to the absence of a direct genetic template, glycans are particularly versatile and apparently a large part of human variation derives from differences in protein glycosylation. However, composition of the individual glycome is temporally very constant, indicating the existence of stable regulatory mechanisms. Studies of epigenetic mechanisms involved in protein glycosylation are still scarce, but the results suggest that they might not only be important for the maintenance of a particular glycophenotype through cell division and potentially across generations but also for the introduction of changes during the adaptive evolution.

High throughput isolation and glycosylation analysis of IgG-variability and heritability of the IgG glycome in three isolated human populations

All immunoglobulin G molecules carry N-glycans, which modulate their biological activity. Changes in N-glycosylation of IgG associate with various diseases and affect the activity of therapeutic antibodies and intravenous immunoglobulins. We have developed a novel 96-well protein G monolithic plate and used it to rapidly isolate IgG from plasma of 2298 individuals from three isolated human populations. N-glycans were released by PNGase F, labeled with 2-aminobenzamide and analyzed by hydrophilic interaction chromatography with fluorescence detection. The majority of the structural features of the IgG glycome were consistent with previous studies, but sialylation was somewhat higher than reported previously. Sialylation was particularly prominent in core fucosylated glycans containing two galactose residues and bisecting GlcNAc where median sialylation level was nearly 80%. Very high variability between individuals was observed, approximately three times higher than in the total plasma glycome. For example, neutral IgG glycans without core fucose varied between 1.3 and 19%, a difference that significantly affects the effector functions of natural antibodies, predisposing or protecting individuals from particular diseases. Heritability of IgG glycans was generally between 30 and 50%. The individual's age was associated with a significant decrease in galactose and increase of bisecting GlcNAc, whereas other functional elements of IgG glycosylation did not change much with age. Gender was not an important predictor for any IgG glycan. An important observation is that competition between glycosyltransferases, which occurs in vitro, did not appear to be relevant in vivo, indicating that the final glycan structures are not a simple result of competing enzymatic activities, but a carefully regulated outcome designed to meet the prevailing physiological needs.

High-mannose N-glycan-specific lectin from the red alga Kappaphycus striatum (Carrageenophyte)

From a fresh sample (1 kg) of cultivated red alga Kappaphycus striatum, three isolectins, KSA-1 (15.1 mg), KSA-2 (58.0 mg) and KSA-3 (6.9 mg), were isolated by a combination of extraction with aqueous ethanol, ethanol precipitation, and ion exchange chromatography. Isolated KSAs were monomeric proteins of about 28kDa having identical 20N-terminal amino acid sequences to each other. Their hemagglutination activities were not inhibited by monosaccharides, but inhibited by glycoproteins bearing high-mannose N-glycans. In a binding experiment with pyridylaminated oligosaccharides by centrifugal ultrafiltration-HPLC assay, the isolectin KSA-2 was exclusively bound to high-mannose type N-glycans, but not to other glycans. Including complex types and a pentasaccharide core of N-glycans, indicating that it recognized branched oligomannosides. The binding activity of KSA-2 was slightly different among high-mannose N-glycans examined, indicating that the lectin has a higher affinity for those having the exposed (α1-3) Man in the D2 arm. On the other hand, KSA-2 did not bind to a free oligomannose that is a constituent of the branched oligomannosides, implying that the portion of the core GlcNAc residue(s) of the N-glycans is also essential for binding. Thus, KSA-2 appears to recognize the extended carbohydrate structure with a minimal length of a tetrasaccharide, Man(α1-3)Man(α1-6)Man(β1-4)GlcNAc. This study indicates that K. striatum, which has extensively been cultivated as a source of carrageenan, is a good source of a valuable lectin(s) that is strictly specific for high-mannose N-glycans.

A variant human IgG1-Fc mediates improved ADCC

Ribosome display was applied to the Fc region of human immunoglobulin G (IgG1) to select for improved binding to human FcγRIIIa, the receptor expressed on human natural killer cells that mediates antibody-dependent cellular cytotoxicity (ADCC). A library of human Fcγ1 variants was generated using error-prone polymerase chain reaction, and subjected to multiple rounds of ribosome display selection against progressively decreasing concentrations of soluble human FcγRIIIa, to enrich for improved binders. Radioimmunoassay and alphascreen analyses of the aglycosylated IgG-Fc output revealed variants with improved binding to FcγRIIIa relative to wild-type IgG-Fc. Subsequent expression in human (HEK-EBNA) cells generated glycosylated IgGs with modified activity in ADCC assays. One particular variant, 125_B01 triggered enhanced ADCC (EC(50) up to four-fold reduced with increased maximal lysis) relative to wild-type antibody, having more equal levels of ADCC for each allotype (V158/F158) of FcγRIIIa. Deconvolution of individual replacements within the variant showed that improved function arose from the Phe243Leu replacement within the CH2 domain, rather than the CH3 domain replacements Thr393Ala or His433Pro. Surprisingly, the oligosaccharide profiles of 125_B01 indicated more oligosaccharide chains lacking fucose, or with bisecting N-acetylglucosamine relative to wild-type IgG1, which correlates with improved function and the replacement Phe243Leu that is a carbohydrate contact residue within the C(H)2 domain.

Glycoengineered Pichia produced anti-HER2 is comparable to trastuzumab in preclinical study

Mammalian cell culture systems are used predominantly for the production of therapeutic monoclonal antibody (mAb) products. A number of alternative platforms, such as Pichia engineered with a humanized N-linked glycosylation pathway, have recently been developed for the production of mAbs. The glycosylation profiles of mAbs produced in glycoengineered Pichia are similar to those of mAbs produced in mammalian systems. This report presents for the first time the comprehensive characterization of an anti-human epidermal growth factor receptor 2 (HER2) mAb produced in a glycoengineered Pichia, and a study comparing the anti-HER2 from Pichia, which had an amino acid sequence identical to trastuzumab, with trastuzumab. The comparative study covered a full spectrum of preclinical evaluation, including bioanalytical characterization, in vitro biological functions, in vivo anti-tumor efficacy and pharmacokinetics in both mice and non-human primates. Cell signaling and proliferation assays showed that anti-HER2 from Pichia had antagonist activities comparable to trastuzumab. However, Pichia-produced material showed a 5-fold increase in binding affinity to FcγIIIA and significantly enhanced antibody dependant cell-mediated cytotoxicity (ADCC) activity, presumably due to the lack of fucose on N-glycans. In a breast cancer xenograft mouse model, anti-HER2 was comparable to trastuzumab in tumor growth inhibition. Furthermore, comparable pharmacokinetic profiles were observed for anti-HER2 and trastuzumab in both mice and cynomolgus monkeys. We conclude that glycoengineered Pichia provides an alternative production platform for therapeutic mAbs and may be of particular interest for production of antibodies for which ADCC is part of the clinical mechanism of action.

Recombinant antibodies: engineering and production in yeast and bacterial hosts

After the appearance of the first FDA-approved antibody 25 years ago, antibodies have become major therapeutic agents in the treatment of many human diseases, including cancer and infectious diseases, and the use of antibodies as therapeutic/diagnostic agents is expected to increase in the future. So far, a variety of strategies have been devised for engineering of these fascinating molecules to develop superior properties and functions. Recent progress in systems biology has provided more information about the structures and cellular networks of antibodies, and, in addition, recent development of biotechnology tools, particularly in regard to high-throughput screening, has made it possible to perform more intensive engineering on these substances. Based on a sound understanding and new technologies, antibodies are now being developed as more powerful drugs. In this review, we highlight the recent, significant progress that has been made in antibody engineering, with a particular focus on Fc engineering and glycoengineering for improved functions, and cellular engineering for enhanced production of antibodies in yeast and bacterial hosts.

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.

Alpha1,6-fucosyltransferase-deficient mice exhibit multiple behavioral abnormalities associated with a schizophrenia-like phenotype: importance of the balance between the dopamine and serotonin systems

Previously, we reported that α1,6-fucosyltransferase (Fut8)-deficient (Fut8(-/-)) mice exhibit emphysema-like changes in the lung and severe growth retardation due to dysregulation of TGF-β1 and EGF receptors and to abnormal integrin activation, respectively. To study the role of α1,6-fucosylation in brain tissue where Fut8 is highly expressed, we examined Fut8(-/-) mice using a combination of neurological and behavioral tests. Fut8(-/-) mice exhibited multiple behavioral abnormalities consistent with a schizophrenia-like phenotype. Fut8(-/-) mice displayed increased locomotion compared with wild-type (Fut8(+/+)) and heterozygous (Fut8(+/-)) mice. In particular, Fut8(-/-) mice showed strenuous hopping behavior in a novel environment. Working memory performance was impaired in Fut8(-/-) mice as evidenced by the Y-maze tests. Furthermore, Fut8(-/-) mice showed prepulse inhibition (PPI) deficiency. Intriguingly, although there was no significant difference between Fut8(+/+) and Fut8(+/-) mice in the PPI test under normal conditions, Fut8(+/-) mice showed impaired PPI after exposure to a restraint stress. This result suggests that reduced expression of Fut8 is a plausible cause of schizophrenia and related disorders. The levels of serotonin metabolites were significantly decreased in both the striatum and nucleus accumbens of the Fut8(-/-) mice. Likewise, treatment with haloperidol, which is an antipsychotic drug that antagonizes dopaminergic and serotonergic receptors, significantly reduced hopping behaviors. The present study is the first to clearly demonstrate that α1,6-fucosylation plays an important role in the brain, and that it might be related to schizophrenia-like behaviors. Thus, the results of the present study provide new insights into the underlying mechanisms responsible for schizophrenia and related disorders.

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.

Advances in the assessment and control of the effector functions of therapeutic antibodies

The Fc (crystallizable fragment) region of therapeutic antibodies can have an important role in their safety and efficacy. Although much is known about the structure-activity relationship of antibodies and the factors that influence Fc effector functions, a process has not yet been defined to clearly delineate how Fc functionality should be assessed and controlled during antibody development and manufacturing. In this article, we summarize the current knowledge of antibody Fc functionality, provide a strategy for assessing the effector functions of different classes of therapeutic antibodies (including Fc fusion proteins) and propose a path for routine testing and controls for manufacturers of antibody products.

Bypassing glycosylation: engineering aglycosylated full-length IgG antibodies for human therapy

In recent years a number of aglycosylated therapeutic antibodies have entered the clinic. The clinical evaluation of these antibodies has served to dispel concerns that the absence of the ubiquitous N297 glycan in the Fc of IgG might result in immunogenicity, poor in vivo stability or unfavorable pharmacokinetics. Importantly, recent studies have now demonstrated that aglycosylated antibodies can be engineered to display novel effector functions and mechanisms of action that do not appear to be possible with their glycosylated counterparts. Moreover, the ability to manufacture aglycosylated antibodies in lower eukaryotes or in bacteria provides significant bioprocessing advantages in terms of shorter bioprocess development and running times and by completely bypassing the problems associated with the glycan heterogeneity of conventional antibodies. These advantages are poised to catapult aglycosylated antibodies to the forefront of protein therapeutics.

Fc-glycosylation of IgG1 is modulated by B-cell stimuli

We have recently shown that IgG1 directed against antigens thought to be involved in the pathogenesis of rheumatoid arthritis harbor different glycan moieties on their Fc-tail, as compared with total sera IgG1. Given the crucial roles of Fc-linked N-glycans for the structure and biological activity of IgG, Fc-glycosylation of antibodies is receiving considerable interest. However, so far little is known about the signals and factors that could influence the composition of these carbohydrate structures on secreted IgG produced by B lymphocytes. Here we show that both "environmental" factors, such as all-trans retinoic acid (a natural metabolite of vitamin A), as well as factors stimulating the innate immune system (i.e. CpG oligodeoxynucleotide, a ligand for toll-like receptor 9) or coming from the adaptive immune system (i.e. interleukin-21, a T-cell derived cytokine) can modulate IgG1 Fc-glycosylation. These factors affect Fc-glycan profiles in different ways. CpG oligodeoxynucleotide and interleukin-21 increase Fc-linked galactosylation and reduce bisecting N-acetylglucosamine levels, whereas all-trans retinoic acid significantly decreases galactosylation and sialylation levels. Moreover, these effects appeared to be stable and specific for secreted IgG1 as no parallel changes of the corresponding glycans in the cellular glycan pool were observed. Interestingly, several other cytokines and molecules known to affect B-cell biology and antibody production did not have an impact on IgG1 Fc-coupled glycan profiles. Together, these data indicate that different stimuli received by B cells during their activation and differentiation can modulate the Fc-linked glycosylation of secreted IgG1 without affecting the general cellular glycosylation machinery. Our study, therefore, furthers our understanding of the regulation of IgG1 glycosylation at the cellular level.

Enhancement of antibody production by the addition of Coenzyme-Q(10)

Recently, there has been a growing demand for therapeutic monoclonal antibodies (MAbs) on the global market. Because therapeutic MAbs are more expensive than low-molecular-weight drugs, there have been strong demands to lower their production costs. Therefore, efficient methods to minimize the cost of goods are currently active areas of research. We have screened several enhancers of specific MAb production rate (SPR) using a YB2/0 cell line and found that coenzyme-Q(10) (CoQ(10)) is a promising enhancer candidate. CoQ(10) is well known as a strong antioxidant in the respiratory chain and is used for healthcare and other applications. Because CoQ(10) is negligibly water soluble, most studies are limited by low concentrations. We added CoQ(10) to a culture medium as dispersed nanoparticles at several concentrations (Q-Media) and conducted a fed-batch culture. Although the Q-Media had no effect on cumulative viable cell density, it enhanced SPR by 29%. In addition, the Q-Media had no effect on the binding or cytotoxic activity of MAbs. Q-Media also enhanced SPR with CHO and NS0 cell lines by 30%. These observations suggest that CoQ(10) serves as a powerful aid in the production of MAbs by enhancing SPR without changing the characteristics of cell growth, or adversely affecting the quality or biological activity of MAbs.

Production of complex multiantennary N-glycans in Nicotiana benthamiana plants

In recent years, plants have been developed as an alternative expression system to mammalian hosts for the production of therapeutic proteins. Many modifications to the plant glycosylation machinery have been made to render it more human because of the importance of glycosylation for functionality, serum half-life, and the safety profile of the expressed proteins. These modifications include removal of plant-specific β1,2-xylose and core α1,3-fucose, and addition of bisecting N-acetylglucosamine, β1,4-galactoses, and sialic acid residues. Another glycosylation step that is essential for the production of complex human-type glycans is the synthesis of multiantennary structures, which are frequently found on human N-glycans but are not generated by wild-type plants. Here, we report both the magnICON-based transient as well as stable introduction of the α1,3-mannosyl-β1,4-N-acetylglucosaminyltransferase (GnT-IV isozymes a and b) and α1,6-mannosyl-β1,6-N-acetylglucosaminyltransferase (GnT-V) in Nicotiana benthamiana plants. The enzymes were targeted to the Golgi apparatus by fusing their catalytic domains to the plant-specific localization signals of xylosyltransferase and fucosyltransferase. The GnT-IV and -V modifications were tested in the wild-type background, but were also combined with the RNA interference-mediated knockdown of β1,2-xylosyltransferase and α1,3-fucosyltransferase. Results showed that triantennary Gn[GnGn] and [GnGn]Gn N-glycans could be produced according to the expected activities of the respective enzymes. Combination of the two enzymes by crossing stably transformed GnT-IV and GnT-V plants showed that up to 10% tetraantennary [GnGn][GnGn], 25% triantennary, and 35% biantennary N-glycans were synthesized. All transgenic plants were viable and showed no aberrant phenotype under standard growth conditions.

Modulation of antibody galactosylation through feeding of uridine, manganese chloride, and galactose

Through process transfer and optimization for increased antibody production to 3 g/L for a GS-CHO cell line, an undesirable drop in antibody Fc galactosylation was observed. Uridine (U), manganese chloride (M), and galactose (G), constituents involved in the intracellular galactosylation process, were evaluated in 2-L bioreactors for their potential to specifically increase antibody galactosylation. These components were placed in the feed medium at proportionally increasing concentrations from 0 to 20 × UMG, where a 1× concentration of U was 1 mM, a 1× concentration of M was 0.002 mM, and a 1× concentration of G was 5 mM. Antibody galactosylation increased rapidly from 3% at 0× UMG up to 21% at 8× UMG and then more slowly to 23% at 20× UMG. The increase was primarily due to a shift from G0F to G1F, with minimal impact on other glycoforms or product quality attributes. Cell culture performance was largely not impacted by addition of up to 20× UMG except for suppression of glucose consumption and lactate production at 16 and 20× UMG and a slight drop in antibody concentration at 20× UMG. Higher accumulation of free galactose in the medium was observed at 8× UMG and above, coincident with achieving the plateau of maximal galactosylation. A concentration of 4× UMG resulted in achieving the target of 18% galactosylation at 2-L scale, a result that was reproduced in a 1,000-L run. Follow-up studies to evaluate the addition of each component individually up to 12× concentration revealed that the effect was synergistic; the combination of all three components gave a higher level of galactosylation than addition of the each effect independently. The approach was found generally useful since a second cell line responded similarly, with an increase in galactosylation from 5% to 29% from 0 to 8× UMG and no further increase or impact on culture performance up to 12× UMG. These results demonstrate a useful approach to provide exact and specific control of antibody galactosylation through manipulation of the concentrations of uridine, manganese chloride, and galactose in the cell culture medium.

TNF receptor II fusion protein with tandemly repeated Fc domains

The extracellular domain of tumour necrosis factor (TNF) receptor II fused with the human IgG1 Fc region (TNFRII-Fc), as well as antibodies against TNF, has been used to treat rheumatoid arthritis. However, TNFRII-Fc is less effective than these antibodies in terms of antibody-dependent cellular cytotoxicity (ADCC) and complement-dependent cytotoxicity (CDC) against cells bearing TNF on the cell surface. We hypothesized that these activities could be increased by fusing TNFRII with tandemly repeated Fc (TNFRII-Fc-Fc). The affinities of TNFRII-Fc-Fc for soluble TNF-α and transmembrane TNF-α and the TNF-α cytotoxicity-inhibitory activity were as potent as those of TNFRII-Fc. TNFRII-Fc-Fc showed much higher binding avidity for Fcγ receptors than TNFRII-Fc and was more potent in terms of both ADCC and CDC against cells expressing transmembrane TNF-α. TNFRII-Fc-Fc of 80 kDa, as well as TNFRII-Fc-Fc of 200 kDa, was detected. TNFRII-Fc-Fc (80 kDa) was as potent as TNFRII-Fc in terms of both ADCC and CDC. These results suggest that Fc multimerization of receptor-Fc fusion proteins can augment effector functions such as ADCC and CDC, and thereby have the potential to provide a superior therapeutic effect. This may be the case not only for TNFRII-Fc but also for other receptor-Fc fusion proteins.

Molecular cloning, characterization, genomic organization and promoter analysis of the α1,6-fucosyltransferase gene (fut8) expressed in the rat hybridoma cell line YB2/0

Background

The rat hybridoma cell line YB2/0 appears a good candidate for the large-scale production of low fucose recombinant mAbs due to its lower expression of fut8 gene than other commonly used rodent cell lines. However, important variations of the fucose content of recombinant mAbs are observed in production culture conditions. To improve our knowledge on the YB2/0 fucosylation capacity, we have cloned and characterized the rat fut8 gene.

Results

The cDNAs encoding the rat α1,6-fucosyltransferase (FucT VIII) were cloned from YB2/0 cells by polymerase chain reaction-based and 5' RNA-Ligase-Mediated RACE methods. The cDNAs contain an open reading frame of 1728 bp encoding a 575 amino acid sequence showing 94% and 88% identity to human and pig orthologs, respectively. The recombinant protein expressed in COS-7 cells exhibits a α1,6-fucosyltransferase activity toward human asialo-agalacto-apotransferrin. The rat fut8 gene is located on chromosome 6 q and spans over 140 kbp. It contains 9 coding exons and four 5'-untranslated exons. FISH analysis shows a heterogeneous copy number of fut8 in YB2/0 nuclei with 2.8 ± 1.4 mean copy number. The YB2/0 fut8 gene is expressed as two main transcripts that differ in the first untranslated exon by the usage of distinct promoters and alternative splicing. Luciferase assays allow defining the minimal promoting regions governing the initiation of the two transcripts, which are differentially expressed in YB2/0 as shown by duplex Taqman QPCR analysis. Bioinformatics analysis of the minimal promoter regions upstream exons E-2 and E-3, governing the transcription of T1 and T2 transcripts, respectively, evidenced several consensus sequences for potential transcriptional repressors. Transient transfections of Rat2 cells with transcription factor expression vectors allowed identifying KLF15 as a putative repressor of T1 transcript in Rat2 cells.

Conclusion

Altogether, these data contribute to a better knowledge of fut8 expression in YB2/0 that will be useful to better control the fucosylation of recombinant mAbs produced in these cells.

Protein glycosylation control in mammalian cell culture: past precedents and contemporary prospects

Protein glycosylation is a post-translational modification of paramount importance for the function, immunogenicity, and efficacy of recombinant glycoprotein therapeutics. Within the repertoire of post-translational modifications, glycosylation stands out as having the most significant proven role towards affecting pharmacokinetics and protein physiochemical characteristics. In mammalian cell culture, the understanding and controllability of the glycosylation metabolic pathway has achieved numerous successes. However, there is still much that we do not know about the regulation of the pathway. One of the frequent conclusions regarding protein glycosylation control is that it needs to be studied on a case-by-case basis since there are often conflicting results with respect to a control variable and the resulting glycosylation. In attempts to obtain a more multivariate interpretation of these potentially controlling variables, gene expression analysis and systems biology have been used to study protein glycosylation in mammalian cell culture. Gene expression analysis has provided information on how glycosylation pathway genes both respond to culture environmental cues, and potentially facilitate changes in the final glycoform profile. Systems biology has allowed researchers to model the pathway as well-defined, inter-connected systems, allowing for the in silico testing of pathway parameters that would be difficult to test experimentally. Both approaches have facilitated a macroscopic and microscopic perspective on protein glycosylation control. These tools have and will continue to enhance our understanding and capability of producing optimal glycoform profiles on a consistent basis.

A standardized conversion of IgG antibody to bispecific form with inversely altered affinities for Fcγ-receptors II and III

This work aims to enhance killing of antibody-coated human tumor cells by altering the antibody's affinity for two effector-cell Fcγ-receptors (FcγR). Affinity for the activating FcγRIII is raised, affinity for the inhibitory FcγRIIB is reduced, with the ratio between the two association constants increasing >1000-fold. We use as a standard tool the Fab'γ from a monoclonal antibody specific for human FcγRIII. This Fab'γ module is bonded to an IgG antibody by a tandem thioether link running between cysteine residues in the hinge vicinity of each protein, thus forming a bispecific FabIgG construct. Simultaneously, effector function of the IgG module is adjusted by leaving its hinge open and adding negative charges. FabIgG constructs derived from the chimeric IgG1 antibody rituximab show the following properties. (1) The titer for antibody-dependent cellular cytotoxicity is enhanced by 12-100-fold, reflecting the affinity of the Fab'γ module for effector-cell FcγRIII. (2) Two functions of the construct's Fcγ, activation of complement and prolonged metabolic survival, are moderately reduced. (3) In contrast, affinities of the Fcγ for all FcγR are severely reduced, with two anticipated consequences. First, attacks by macrophages on antibody-coated cells are favored by reduced engagement of the inhibitory FcγRIIB. Second, reduced engagement of activating FcγR by the Fcγ lowers the probability of untoward crosslinkings of FcγR, which have been shown to provoke toxicity. If the Fab'γ module possesses human constant regions, the linkage strategy requires prior genetic deletion of at least one cysteine residue. With both Fab'γ and IgG modules available, FabIgG can be prepared in 35 h.

A robust, high-throughput assay to determine the phagocytic activity of clinical antibody samples

Phagocytosis can be induced via the engagement of Fcγ receptors by antibody-opsonized material. Furthermore, the efficiency of antibody-induced effector functions has been shown to be dramatically modulated by changes in antibody glycosylation. Because infection can modulate antibody glycans, which in turn modulate antibody functions, assays capable of determining the induction of effector functions rather than neutralization or titer provide a valuable opportunity to more fully characterize the quality of the adaptive immune response. Here we describe a robust and high-throughput flow cytometric assay to define the phagocytic activity of antigen-specific antibodies from clinical samples. This assay employs a monocytic cell line that expresses numerous Fc receptors: including inhibitory and activating, and high and low affinity receptors--allowing complex phenotypes to be studied. We demonstrate the adaptability of this high-throughput, flow-based assay to measure antigen-specific antibody-mediated phagocytosis against an array of viruses, including influenza, HIV, and dengue. The phagocytosis assay format further allows for simultaneous analysis of cytokine release, as well as determination of the role of specific Fcγ-receptor subtypes, making it a highly useful system for parsing differences in the ability of clinical and vaccine induced antibody samples to recruit this critical effector function.

Identification of IgG(1) variants with increased affinity to FcγRIIIa and unaltered affinity to FcγRI and FcRn: comparison of soluble receptor-based and cell-based binding assays

Clinical response to the anti-CD20 antibody rituximab has been demonstrated to correlate with the polymorphism in the FcγRIIIa receptor where patients homozygous for the higher affinity V158 allotype showed a better response rate. This finding suggests that engineering of anti-CD20 for increased FcγRIIIa affinity could result in improved clinical outcome. To identify variants with increased affinity to FcγRIIIa, we developed quantitative assays using soluble receptors as well as engineered cell lines expressing FcγRI or FcγRIIIa on the cell surface. We assayed a set of anti-CD20 IgG(1) variants that had identical Fab regions, but alterations in the Fc regions, in both the soluble receptor-based and cell-based FcγRIIIa binding assays. We obtained similar relative binding affinity increases and assay precisions. The increase in affinity for FcγRIIIa correlated with the increase in activity in the antibody-dependent cellular cytotoxicity assay. These variants had unaltered FcγRI binding. In addition to Fcγ receptors, IgG also binds to FcRn, the receptor responsible for the long circulating half-life of IgG. The mutations in the anti-CD20 variants were previously found not to affect FcRn binding in the soluble receptor-based assays; consequently, we used anti-Her2 variants with different binding affinities to FcRn to study FcRn binding assays. We generated a cell line expressing FcRn on the cell surface to measure IgG binding and obtained similar ranking of these anti-Her2 variants in the cell-based and the soluble receptor-based FcRn binding assays. In conclusion, both the soluble receptor-based and cell-based binding assays can be used to identify IgG(1) variants with increased affinity to FcγRIIIa and unaltered affinity to FcγRI and FcRn.