Enhanced sialylation of a human chimeric IgG1 variant produced in human and rodent cell lines

Loss of a Newly Discovered microRNA in Chinese Hamster Ovary Cells Leads to Upregulation of NGNA Sialylation on Monoclonal Antibodies

Chinese hamster ovary (CHO) cells are known not to express appreciable levels of the sialic acid residue N‐glycolylneuraminic acid (NGNA) on monoclonal antibodies. However, we actually have identified a recombinant CHO cell line expressing an IgG with unusually high levels of NGNA sialylation (>30%). Comprehensive multi‐OMICs based experimental analyses unraveled the root cause of this atypical sialylation: (1) expression of the cytidine monophosphate‐N‐acetylneuraminic acid hydroxylase (CMAH) gene was spontaneously switched on, (2) CMAH mRNA showed an anti‐correlated expression to the newly discovered Cricetulus griseus (cgr) specific microRNA cgr‐miR‐111 and exhibits two putative miR‐111 binding sites, (3) miR‐111 expression depends on the transcription of its host gene SDK1, and (4) a single point mutation within the promoter region of the sidekick cell adhesion molecule 1 (SDK1) gene generated a binding site for the transcriptional repressor histone H4 transcription factor HINF‐P. The resulting transcriptional repression of SDK1 led to a downregulation of its co‐expressed miR‐111 and hence to a spontaneous upregulation of CMAH expression finally increasing NGNA protein sialylation.

The interplay of protein engineering and glycoengineering to fine-tune antibody glycosylation and its impact on effector functions

The N-glycan pattern of an IgG antibody, attached at a conserved site within the fragment crystallizable (Fc) region, is a critical antibody quality attribute whose structural variability can also impact antibody function. For tailoring the Fc glycoprofile, glycoengineering in cell lines as well as Fc amino acid mutations have been applied. Multiple glycoengineered Chinese hamster ovary cell lines were generated, including defucosylated (FUT8KO), α-2,6-sialylated (ST6KI), and defucosylated α-2,6-sialylated (FUT8KOST6KI), expressing either a wild-type anti-CD20 IgG (WT) or phenylalanine to alanine (F241A) mutant. Matrix-assisted laser desorption ionization-time of flight mass spectrometry characterization of antibody N-glycans revealed that the F241A mutation significantly increased galactosylation and sialylation content and glycan branching. Furthermore, overexpression of recombinant human α-2,6-sialyltransferase resulted in a predominance of α-2,6-sialylation rather than α-2,3-sialylation for both WT and heavily sialylated F241A antibody N-glycans. Interestingly, knocking out α-1,6-fucosyltransferase (FUT8KO), which removed core fucose, lowered the content of N-glycans with terminal Gal and increased levels of terminal GlcNAc and Man5 groups on WT antibody. Further complement-dependent cytotoxicity (CDC) analysis revealed that, regardless of the production cells, WT antibody samples have higher cytotoxic CDC activity with more exposed Gal residues compared to their individual F241A mutants. However, the FUT8KO WT antibody, with a large fraction of bi-GlcNAc structures (G0), displayed the lowest CDC activity of all WT antibody samples. Furthermore, for the F241A mutants, a higher CDC activity was observed for α-2,6- compared to α-2,3-sialylation. Antibody-dependent cellular cytotoxicity (ADCC) analysis revealed that the defucosylated WT and F241A mutants showed enhanced in vitro ADCC performance compared to their fucosylated counterparts, with the defucosylated WT antibodies displaying the highest overall ADCC activity, regardless of sialic acid substitution. Moreover, the FcγRIIIA receptor binding by antibodies did not always correspond directly with ADCC result. This study demonstrates that glycoengineering and protein engineering can both promote and inhibit antibody effector functions and represent practical approaches for varying glycan composition and functionalities during antibody development.

Engineered Fc-glycosylation switch to eliminate antibody effector function

Antibodies mediate effector functions through Fcγ receptor (FcγR) interactions and complement activation, causing cytokine release, degranulation, phagocytosis, and cell death. They are often undesired for development of therapeutic antibodies where only antigen binding or neutralization would be ideal. Effector elimination has been successful with extensive mutagenesis, but these approaches can potentially lead to manufacturability and immunogenicity issues. By switching the native glycosylation site from position 297 to 298, we created alternative antibody glycosylation variants in the receptor interaction interface as a novel strategy to eliminate the effector functions. The engineered glycosylation site at Asn298 was confirmed by SDS-PAGE, mass spectrometry, and X-ray crystallography (PDB code 6X3I). The lead NNAS mutant (S298N/T299A/Y300S) shows no detectable binding to mouse or human FcγRs by surface plasmon resonance analyses. The effector functions of the mutant are completely eliminated when measured in antibody-dependent cell-meditated cytotoxicity (ADCC) and complement-dependent cytotoxicity (CDC) assays. In vivo, the NNAS mutant made on an antibody against a human lymphocyte antigen does not deplete T cells or B cells in transgenic mice, in contrast to wild-type antibody. Structural study confirms the successful glycosylation switch to the engineered Asn298 site. The engineered glycosylation would clash with approaching FcγRs based on reported Fc-FcγR co-crystal structures. In addition, the NNAS mutants of multiple antibodies retain binding to antigens and neonatal Fc receptor, exhibit comparable purification yields and thermal stability, and display normal circulation half-life in mice and non-human primate. Our work provides a novel approach for generating therapeutic antibodies devoid of any ADCC and CDC activities with potentially lower immunogenicity.

Neuroimmunological therapies for treating spinal cord injury: Evidence and future perspectives

Spinal cord injury (SCI) has a complex pathophysiology. Following the initial physical trauma to the spinal cord, which may cause vascular disruption, hemorrhage, mechanical injury to neural structures and necrosis, a series of biomolecular cascades is triggered to evoke secondary injury. Neuroinflammation plays a major role in the secondary injury after traumatic SCI. To date, the administration of systemic immunosuppressive medications, in particular methylprednisolone sodium succinate, has been the primary pharmacological treatment. This medication is given as a complement to surgical decompression of the spinal cord and maintenance of spinal cord perfusion through hemodynamic augmentation. However, the impact of neuroinflammation is complex with harmful and beneficial effects. The use of systemic immunosuppressants is further complicated by the natural onset of post-injury immunosuppression, which many patients with SCI develop. It has been hypothesized that immunomodulation to attenuate detrimental aspects of neuroinflammation after SCI, while avoiding systemic immunosuppression, may be a superior approach. To accomplish this, a detailed understanding of neuroinflammation and the systemic immune responses after SCI is required. Our review will strive to achieve this goal by first giving an overview of SCI from a clinical and basic science context. The role that neuroinflammation plays in the pathophysiology of SCI will be discussed. Next, the positive and negative attributes of the innate and adaptive immune systems in neuroinflammation after SCI will be described. With this background established, the currently existing immunosuppressive and immunomodulatory therapies for treating SCI will be explored. We will conclude with a summary of topics that can be explored by neuroimmunology research. These concepts will be complemented by points to be considered by neuroscientists developing therapies for SCI and other injuries to the central nervous system.

Quality by Design-Based Assessment for Analytical Similarity of Adalimumab Biosimilar HLX03 to Humira®

Quality by design (QbD) is an efficient but challenging approach for the development of biosimilar due to the complex relationship among process, quality, and efficacy. Here, the analytical similarity of adalimumab biosimilar HLX03 to Humira® was successfully established following a QbD quality study. Quality target product profile (QTPP) of HLX03 was first generated according to the public available information and initial characterization of 3 batches of Humira®. The critical quality attributes (CQAs) were then identified through risk assessment according to impact of each quality attribute on efficacy and safety. The anticipated range for each CQA was derived from similarity acceptance range and/or the corresponding regulatory guidelines. Finally, a panel of advanced and orthogonal physicochemical and functional tests and comparison of 6 batches of HLX03 and 10 batches of the reference standard demonstrated high similarity of HLX03 to Humira®, except for slightly lower percentage of high mannosylated glycans (%HM) in HLX03 which had no effect on FcγRIII binding and antibody-dependent cell-mediated cytotoxicity (ADCC) activity in human peripheral blood mononuclear cell (PBMC). All above demonstrated the feasibility and efficiency of QbD-based similarity assessment of a biosimilar monoclonal antibody (mAb).

Production of α2,6-sialylated and non-fucosylated recombinant alpha-1-antitrypsin in CHO cells

Alpha-1-antitrypsin (A1AT) is an abundant serum inhibitor of serine proteases. A1AT deficiency is a common genetic disorder which is currently treated with augmentation therapies. These treatments involve weekly injections of patients with purified plasma-derived A1AT. Such therapies can be extremely expensive and rely on plasma donors. Hence, large-scale production of recombinant A1AT (rA1AT) could greatly benefit these patients, as it could decrease the cost of treatments, reduce biosafety concerns and ensure quantitative and qualitative controls of the protein. In this report, we sought to produce α2,6-sialylated rA1AT with our cumate-inducible stable CHO pool expression system. Our different CHO pools could reach volumetric productivities of 1,2 g/L. The human α2,6-sialyltransferase was stably expressed in these cells in order to mimic elevated α2,6-sialylation levels of native A1AT protein. Sialylation of the recombinant protein was stable over the duration of the fed-batch production phase and was higher in a pool where cells were sorted and enriched by FACS based on cell-surface α2,6-sialylation. Addition of ManNAc to the cell culture media during production enhanced both α2,3 and α2,6 A1AT sialylation levels whereas addition of 2F-peracetylfucose potently inhibited fucosylation of the protein. Finally, we demonstrated that rA1AT proteins exhibited human neutrophil elastase inhibitory activities similar to the commercial human plasma-derived A1AT.

The impact of sialylation linkage-type on the pharmacokinetics of recombinant butyrylcholinesterases

Chinese hamster ovary (CHO) cells typically produce glycoproteins with N-glycans terminating in α-2,3 sialylation. Human cells produce glycoproteins that include α-2,3 and α-2,6 sialic acids. To examine the impact of altering protein sialylation on pharmacokinetic properties, recombinant human butyrylcholinesterase (BChE) was produced in CHO cells by knocking out the α-2,3 sialyltransferase genes followed by overexpression of the α-2,6 sialyltransferase (26BChE) enzyme. The N-glycan composition of 26BChE was compared to BChE with α-2,3 sialylation (23BChE) derived from wild-type CHO cells. Both 23BChE and 26BChE exhibited comparable antennarity distributions with bi-antennary di-sialylated glycans representing the most abundant glycoform. CD-1 mice were intravenously injected with the 23BChE or 26BChE, and residual BChE activities from blood collected at various time points for pharmacokinetic analyses. Although 23BChE contained a slightly lower initial sialylation level compared to 26BChE, the molecule exhibited higher residual activity between 5 and 24 hr postinjection. Pharmacokinetic analyses indicated that 23BChE exhibited an increase in area under the curve and a lower volume of distribution at steady state than that of 26BChE. These findings suggest that the type of sialylation linkage may play a significant role in the pharmacokinetic behavior of a biotherapeutic when tested in in vivo animal models.

Translation of genome to glycome: role of the Golgi apparatus

Glycans are one of the four biopolymers of the cell and they play important roles in cellular and organismal physiology. They consist of both linear and branched structures and are synthesized in a nontemplated manner in the secretory pathway of mammalian cells with the Golgi apparatus playing a key role in the process. In spite of the absence of a template, the glycans synthesized by a cell are not a random collection of possible glycan structures but a distribution of specific glycans in defined quantities that is unique to each cell type (Cell type here refers to distinct cell forms present in an organism that can be distinguished based on morphological, phenotypic and/or molecular criteria.) While information to produce cell type-specific glycans is encoded in the genome, how this information is translated into cell type-specific glycome (Glycome refers to the quantitative distribution of all glycan structures present in a given cell type.) is not completely understood. We summarize here the factors that are known to influence the fidelity of glycan biosynthesis and integrate them into known glycosylation pathways so as to rationalize the translation of genetic information to cell type-specific glycome.

Physicochemical and functional assessments demonstrating analytical similarity between rituximab biosimilar HLX01 and the MabThera®

Development of bio-therapeutics has exhibited exponential growth in China over the past decade. However, no biosimilar drug has been approved in China (CN) due to the lack of a national biosimilar regulatory guidance. HLX01, a rituximab biosimilar developed in China under European Medicines Agency biosimilar guidelines and requirements, was the first such drug submitted for regulatory review in China, and it is expected to receive approval there as a biosimilar product. To demonstrate the analytical similarities of HLX01, CN-rituximab (sourced in China but manufactured in Europe) and EU-rituximab (sourced and manufactured in Europe), an extensive 3-way physicochemical and functional similarity assessment using a series of orthogonal and state-of-the-art techniques was conducted, following the similarity requirement guidelines recently published by China’s Center for Drug Evaluation. The results of the similarity study showed an identical protein amino acid sequence and highly similar primary structures between HLX01 and the reference product (RP) MabThera®, along with high similarities in higher order structures, potency, integrity, purity and impurity profiles, biological and immunological binding functions, as well as degradation behaviors under stress conditions. In addition, HLX01 presented slightly lower aggregates and better photostability compared with the RP. Despite slight changes in relative abundance of glycan moieties and heavy chain C-terminal lysine modification, no differences in biological activities and immunological properties were observed between the RP and HLX01. In conclusion, HLX01 is highly similar to CN- and EU-sourced RP in terms of physicochemical properties and biological activities, suggesting similar product quality, efficacy, and safety. The regulatory requirements interpreted and applied towards the HLX01 marketing application sets a precedent for analytical similarity assessment of biosimilar products in China.

Fc Sialylation Prolongs Serum Half-Life of Therapeutic Antibodies

The long serum t _1/2 of IgGs is ensured by their interaction with the neonatal Fc receptor (FcRn), which salvages IgG from intracellular degradation. Fc glycosylation is thought not to influence FcRn binding and IgG longevity in vivo. In this article, we demonstrate that hypersialylation of asparagine 297 (N297) enhances IgG serum persistence. This polarized glycosylation is achieved using a novel Fc mutation, a glutamate residue deletion at position 294 (Del) that endows IgGs with an up to 9-fold increase in serum lifespan. The strongest impact was observed when the Del was combined with Fc mutations improving FcRn binding (Del-FcRn⁺). Enzymatic desialylation of a Del-FcRn⁺ mutant or its production in a cell line unable to hypersialylate reduced the in vivo serum t _1/2 of the desialylated mutants to that of native FcRn⁺ mutants. Consequently, our study proves that sialylation of the N297 sugar moiety has a direct impact on human IgG serum persistence.

Transient CHO expression platform for robust antibody production and its enhanced N-glycan sialylation on therapeutic glycoproteins

Large-scale transient expression in mammalian cells is a rapid protein production technology often used to shorten overall timelines for biotherapeutics drug discovery. In this study we demonstrate transient expression in a Chinese hamster ovary (CHO) host (ExpiCHO-S™) cell line capable of achieving high recombinant antibody expression titers, comparable to levels obtained using human embryonic kidney (HEK) 293 cells. For some antibodies, ExpiCHO-S™ cells generated protein materials with better titers and improved protein quality characteristics (i.e., less aggregation) than those from HEK293. Green fluorescent protein imaging data indicated that ExpiCHO-S™ displayed a delayed but prolonged transient protein expression process compared to HEK293. When therapeutic glycoproteins containing non-Fc N-linked glycans were expressed in transient ExpiCHO-S™, the glycan pattern was unexpectedly found to have few sialylated N-glycans, in contrast to glycans produced within a stable CHO expression system. To improve N-glycan sialylation in transient ExpiCHO-S™, we co-transfected galactosyltransferase and sialyltransferase genes along with the target genes, as well as supplemented the culture medium with glycan precursors. The authors have demonstrated that co-transfection of glycosyltransferases combined with medium addition of galactose and uridine led to increased sialylation content of N-glycans during transient ExpiCHO-S™ expression. These results have provided a scientific basis for developing a future transient CHO system with N-glycan compositions that are similar to those profiles obtained from stable CHO protein production systems. © 2018 American Institute of Chemical Engineers Biotechnol. Prog., 35: e2724, 2019.

V. RK, Miyoshi R, Yokoi Y, Tanaka M, Hinou H, Nishimura SI. Synthetic Glycopeptides Allow for the Quantitation of Scarce Nonfucosylated IgG Fc N-Glycans of Therapeutic Antibody

Glycans attached to the IgG Fc domain affect strongly biological activities such as antibody-dependent cellular cytotoxicity (ADCC) and complement-dependent cytotoxicity (CDC) of therapeutic antibodies. However, molecular mechanism in the glycoform-dependent functional modulation of the IgGs remains elusive. The present study communicates that selected reaction monitoring (SRM)-based assay of tryptic IgG Fc glycopeptides is a promising approach for the characterization of antibodies when combined with structure-defined synthetic Fc peptides having a focused N-glycoform as a calibration standard. We describe a novel synthetic approach to the human IgG1 Fc peptide having a bisected decasaccharide and its nonbisected counterpart compound, the signatures of antibodies involving Fc domain with rare N-glycans expected to show much higher ADCC/CDC than abundant IgG N-glycans, and their application to the SRM-based quantitative glycoproteomics. Use of a key intermediate, phenyl (2-O-benzyl-4,6-O-benzylidine-β-d-mannopyranosyl)-(1 → 4)-3,6-di-O-benzyl-2-azido-2-deoxy-1-thio-β-d-glucopyranoside, derived from locust bean gum galactomannan, facilitated greatly the synthesis of a bisected nonasaccharide as a stable precursor of oxazoline derivative needed for the enzymatic trans-glycosylation with Fc nonapeptide carrying a GlcNAc at Asn297 residue, while the coupling reaction catalyzed by mutant endo-M-N175Q proceeded very slowly. Strikingly, SRM assay using the synthetic Fc glycopeptides as calibration standards uncovered the occurrence of the targeted IgG1 Fc fragment carrying a nonfucosylated and bisected (315 fmol, 0.20%) and its nonbisected counterpart (1154 fmol, 0.73%) in the tryptic digests from 158 pmol of anticancer antibody Herceptin (trastuzumab). The results suggest that aberrantly glycosylated IgG Fc variants may contribute to the total biological activities of the therapeutic antibodies.

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.

Glycosylation engineering of therapeutic IgG antibodies: challenges for the safety, functionality and efficacy

Glycosylation of the Fc region of IgG has a profound impact on the safety and clinical efficacy of therapeutic antibodies. While the biantennary complex-type oligosaccharide attached to Asn297 of the Fc is essential for antibody effector functions, fucose and outer-arm sugars attached to the core heptasaccharide that generate structural heterogeneity (glycoforms) exhibit unique biological activities. Hence, efficient and quantitative glycan analysis techniques have been increasingly important for the development and quality control of therapeutic antibodies, and glycan profiles of the Fc are recognized as critical quality attributes. In the past decade our understanding of the influence of glycosylation on the structure/function of IgG-Fc has grown rapidly through X-ray crystallographic and nuclear magnetic resonance studies, which provides possibilities for the design of novel antibody therapeutics. Furthermore, the chemoenzymatic glycoengineering approach using endoglycosidase-based glycosynthases may facilitate the development of homogeneous IgG glycoforms with desirable functionality as next-generation therapeutic antibodies. Thus, the Fc glycans are fertile ground for the improvement of the safety, functionality, and efficacy of therapeutic IgG antibodies in the era of precision medicine.

Impact of host cell line choice on glycan profile

Protein glycosylation is post-translational modification (PTM) which is important for pharmacokinetics and immunogenicity of recombinant glycoprotein therapeutics. As a result of variations in monosaccharide composition, glycosidic linkages and glycan branching, glycosylation introduces considerable complexity and heterogeneity to therapeutics. The host cell line used to produce the glycoprotein has a strong influence on the glycosylation because different host systems may express varying repertoire of glycosylation enzymes and transporters that contributes to specificity and heterogeneity in glycosylation profiles. In this review, we discuss the types of host cell lines currently used for recombinant therapeutic production, their glycosylation potential and the resultant impact on glycoprotein properties. In addition, we compare the reported glycosylation profiles of four recombinant glycoproteins: immunoglobulin G (IgG), coagulation factor VII (FVII), erythropoietin (EPO) and alpha-1 antitrypsin (A1AT) produced in different mammalian cells to establish the influence of mammalian host cell lines on glycosylation.

Antibody blood-brain barrier efflux is modulated by glycan modification

BACKGROUND

Drug delivery to the brain is a major roadblock to treatment of Alzheimer's disease. Recent results of the PRIME study indicate that increasing brain penetration of antibody drugs improves Alzheimer's treatment outcomes. New approaches are needed to better accomplish this goal. Based on prior evidence, the hypothesis that glycan modification alters antibody blood-brain barrier permeability was tested here.

METHODS

The blood-brain barrier permeability coefficient Pe of different glycosylated states of anti-amyloid IgG was measured using in vitro models of brain microvascular endothelial cells. Monoclonal antibodies 4G8, with sialic acid, and 6E10, lacking sialic acid, were studied. The amount of sialic acid was determined using quantitative and semi-quantitative surface plasmon resonance methods.

RESULTS

Influx of IgG was not saturable and was largely insensitive to IgG species and glycosylation state. By contrast, efflux of 4G8 efflux was significantly lower than both albumin controls and 6E10. Removal of α2,6-linked sialic acid group present on 12% of 4G8 completely restored efflux to that of 6E10 but increasing the α2,6-sialylated fraction to 15% resulted in no change. Removal of the Fc glycan from 4G8 partially restored efflux. Alternate sialic acid groups with α2,3 and α2,8 linkages, nor on the Fc glycan, were not detected at significant levels on either 4G8 or 6E10.

CONCLUSIONS

These results support a model in which surface-sialylated 4G8 inhibits its own efflux and that of asialylated 4G8.

GENERAL SIGNIFICANCE

Glycan modification has the potential to increase antibody drug penetration into the brain through efflux inhibition.

Engineering the fragment crystallizable (Fc) region of human IgG1 multimers and monomers to fine-tune interactions with sialic acid-dependent receptors

Multimeric fragment crystallizable (Fc) regions and Fc-fusion proteins are actively being explored as biomimetic replacements for IVIG therapy, which is deployed to manage many diseases and conditions but is expensive and not always efficient. The Fc region of human IgG1 (IgG1-Fc) can be engineered into multimeric structures (hexa-Fcs) that bind their cognate receptors with high avidity. The critical influence of the unique N-linked glycan attached at Asn-297 on the structure and function of IgG1-Fc is well documented; however, whether the N-linked glycan has a similarly critical role in multimeric, avidly binding Fcs, is unknown. Hexa-Fc contains two N-linked sites at Asn-77 (equivalent to Asn-297 in the Fc of IgG1) and Asn-236 (equivalent to Asn-563 in the tail piece of IgM). We report here that glycosylation at Asn-297 is critical for interactions with Fc receptors and complement and that glycosylation at Asn-563 is essential for controlling multimerization. We also found that introduction of an additional fully occupied N-linked glycosylation site at the N terminus at position 1 (equivalent to Asp-221 in the Fc of IgG1) dramatically enhances overall sialic acid content of the Fc multimers. Furthermore, replacement of Cys-575 in the IgM tail piece of multimers resulted in monomers with enhanced sialic acid content and differential receptor-binding profiles. Thus insertion of additional N-linked glycans into either the hinge or tail piece of monomers or multimers leads to molecules with enhanced sialylation that may be suitable for managing inflammation or blocking pathogen invasion.

Recombinant plant-derived human IgE glycoproteomics

The increasing biotechnological interest in human IgE antibodies demands advanced systems which allow their proper expression. However, this is still a challenge due to the complexity of the molecule, particularly regarding the diverse N-glycosylation pattern. Here, we present the expression of recombinant IgE in wild type and glycan-engineered Nicotiana benthamiana plants and in-depth N-glycosylation analyses. Mass spectrometric profiling revealed that plant IgE has a site occupancy rate that ranges from non-occupied at glycosite 6 (GS6) to 100% occupancy at GS1 and 2. Similarly to human cell-derived IgE, plant versions carry complex N-glycans at GS1-5 and oligomannosidic structures at GS7. Computational modelling suggests that spatial position (or orientation) of glycans can impair processing or site occupancy on adjacent glycosites. IgE expressed in glycoengineered and wild type plants carry, respectively, GnGn and plant-typical GnGnXF structures at large homogeneity. This contrasts with the glycan diversity of HEK cell-derived IgE, carrying at least 20 different glycoforms. Importantly, IgE glycoengineering allows the control of its glycosylation, a so far unmet need when using well-established expression systems. This enables the elucidation of possible carbohydrate-dependent IgE functions.

SIGNIFICANCE

Targeted glycosylation of recombinant proteins may provide an advantage in therapeutic applications. Despite increasing biotechnological interest in IgE antibodies, knowledge and impact of glycosylation on this antibody class are scarce. With the ability to glyco-engineer recombinant IgE, we provide an important step towards the generation of IgE with other targeted N-glycans. This will facilitate detailed structure-function studies and may lead to the production of IgE with optimized activities.

Integrated Genome and Protein Editing Swaps α-2,6 Sialylation for α-2,3 Sialic Acid on Recombinant Antibodies from CHO

Immunoglobin G with α-2,6 sialylation has been reported to have an impact on antibody-dependent cellular cytotoxicity and anti-inflammatory efficacy. However, production of antibodies with α-2,6 sialylation from Chinese hamster ovary cells is challenging due to the inaccessibility of sialyltransferases for the heavy chain N-glycan site and the presence of exclusively α-2,3 sialyltransferases. In this study, combining mutations on the Fc regions to allow sialyltransferase accessibility with overexpression of α-2,6 sialyltransferase produced IgG with significant levels of both α-2,6 and α-2,3 sialylation. Therefore, ST3GAL4 and ST3GAL6 genes were disrupted by CRISPR/Cas9 to minimize the α-2,3 sialylation. Sialidase treatment and SNA lectin blot indicated greatly increased α-2,6 sialylation level relative to α-2,3 sialylation for the α-2,3 sialyltransferase knockouts when combined with α-2,6 sialyltransferase overexpression. Indeed, α-2,3 linked sialic acids were not detected on IgG produced from the α-2,3 sialyltransferase knockout-α-2,6 sialyltransferase overexpression pools. Finally, glycoprofiling of IgG with four amino acid substitutions expressed from an α-2,3 sialyltransferase knockout-α-2,6 sialyltransferase stable clone resulted in more than 77% sialylated glycans and more than 62% biantennary disialylated glycans as indicated by both MALDI-TOF and LC-ESI-MS. Engineered antibodies from these modified Chinese hamster ovary cell lines will provide biotechnologists with IgGs containing N-glycans with different structural variations for examining the role of glycosylation on protein performance.

10% liquid human immunoglobulin (KIOVIG®) for immunomodulation in autoimmune disorders

Intravenous immunoglobulins have been used to treat autoimmune disorders (ADs) for over 50 years. The etiologies of various ADs are not fully understood and although intravenous immunoglobulin treatment has proved its immunomodulatory properties, the roles of proposed mechanisms of action also remain a matter of speculation. A systemic search of the literature regarding KIOVIG® (Baxalta US, Inc., MA, USA) use in clinical trials on patients with ADs and a detailed review of retrieved articles revealed eight relevant publications. These articles reported KIOVIG use in multifocal motor neuropathy, chronic inflammatory demyelinating polyneuropathy, idiopathic thrombocytopenic purpura, Kawasaki disease, Guillain–Barré syndrome and other autoimmune and neurologic disorders and showed that KIOVIG is an effective, safe and well-tolerated treatment in the studied populations. Nevertheless, further studies on larger patient cohorts are needed.