Therapeutic monoclonal antibodies and consistent ends: terminal heterogeneity, detection, and impact on quality

Adaptation of Aglycosylated Monoclonal Antibodies for Improved Production in Komagataella phaffii

Monoclonal antibodies (mAbs) are a major class of biopharmaceuticals manufactured by well-established processes using Chinese Hamster Ovary (CHO) cells. Next-generation biomanufacturing using alternative hosts like Komagataella phaffii could improve the accessibility of these medicines, address broad societal goals for sustainability, and offer financial advantages for accelerated development of new products. Antibodies produced by K. phaffii, however, may manifest unique molecular quality attributes, like host-dependent, product-related variants, that could raise potential concerns for clinical use. We demonstrate here conservative modifications to the amino acid sequence of aglycosylated antibodies based on the human IgG1 isotype that minimize product-related variations when secreted by K. phaffii. A combination of 2-3 changes of amino acids reduced variations across six different aglycosylated versions of commercial mAbs. Expression of a modified sequence of NIST mAb in both K. phaffii and CHO cells showed comparable biophysical properties and molecular variations. These results suggest a path toward the production of high-quality mAbs that could be expressed interchangeably by either yeast or mammalian cells. Improving molecular designs of proteins to enable a range of manufacturing strategies for well-characterized biopharmaceuticals could accelerate global accessibility and innovations.

Removal of signal peptide variants by cation exchange chromatography: A case study

Signal peptide (SP) is required for secretion of recombinant proteins and typically cleaved by signal peptidase at its C-region to generate the mature proteins. Miscleavage of the SP is reported occasionally, resulting in a truncated- or elongated-terminal sequence. In the present work, we demonstrated that cation exchange (CEX) chromatography is an effective means for removing SP variants with a case study. With the selected resin/conditions, the chromatographic performance is comparable between runs performed at the low end and high end of load density and elution range. The procedure described in this work can be used as a general approach for resin selection and optimization of chromatographic conditions to remove byproducts that bind more strongly than the product to the selected resin.

Coupling cation and anion exchange chromatography for fast separation of monoclonal antibody charge variants

A design procedure for the separation of charge variants of a monoclonal antibody (mAb) was developed, which was based on the coupling of cation-exchange chromatography (CEX) and anion-exchange chromatography (AEX) under high loading conditions. The design of the coupled process was supported by a dynamic model. The model was calibrated on the basis of band profiles of variants determined experimentally for the mAb materials of different variant compositions. The numerical simulations were used to select the coupling configuration and the loading conditions that allowed for efficient separation of the mAb materials into three products enriched with each individual variant: the acidic (av), main (mv) and basic (bv) one. In the CEX section, a two-step pH gradient was used to split the loaded mass of mAb into a weakly bound fraction enriched with av and mv, and a strongly bound fraction containing the bv-rich product. The weakly bound fraction was further processed in the AEX section, where the mv-rich product was eluted in flowthrough, while the av-rich product was collected by a step change in pH. The choice of flow distribution and the number of columns in the CEX and AEX sections depended on the variant composition of the mAb material. For the selected configurations, the optimized mAb loading density in the CEX columns ranged from 10 to 26 mg mL-1, while in the AEX columns it was as high as 300 or 600 mg mL-1, depending on the variant composition of the mAb material. By proper selection of the loading condition, a trade-off between yield and purity of the products could be reached.

Stability of Protein Pharmaceuticals: Recent Advances

There have been significant advances in the formulation and stabilization of proteins in the liquid state over the past years since our previous review. Our mechanistic understanding of protein-excipient interactions has increased, allowing one to develop formulations in a more rational fashion. The field has moved towards more complex and challenging formulations, such as high concentration formulations to allow for subcutaneous administration and co-formulation. While much of the published work has focused on mAbs, the principles appear to apply to any therapeutic protein, although mAbs clearly have some distinctive features. In this review, we first discuss chemical degradation reactions. This is followed by a section on physical instability issues. Then, more specific topics are addressed: instability induced by interactions with interfaces, predictive methods for physical stability and interplay between chemical and physical instability. The final parts are devoted to discussions how all the above impacts (co-)formulation strategies, in particular for high protein concentration solutions.'

Development of a novel, high-throughput imaged capillary isoelectric focusing-Western method to characterize charge heterogeneity of monoclonal antibody heavy and light chains

Charge heterogeneity is one of the commonly monitored quality attributes in biotherapeutics. It can impact the stability, efficacy, and safety of products, but it can also affect the pharmacokinetics, binding affinity, and overall biological activity of the molecules. Given the substantial size and complexity of antibodies, subtle variations or specific modifications that result in charge heterogeneity might be concealed when mAbs are analyzed under native conditions. Two-dimensional gel electrophoresis has traditionally been used to characterize antibody heavy chain (HC) and light chain (LC) charge variants. The procedures, however, are laborious, and the method is only qualitative. ChromiCE was developed as an alternative approach to provide quantitative analysis, but the method is also labor intensive, requiring separation of the HC and LC by chromatography before imaged capillary isoelectric focusing (iCIEF) analysis. We thus developed a novel, automated high-throughput iCIEF-Western method to directly quantify the HC and LC charge variants with high sensitivity under denatured and reduced conditions. The HC and LC charge variants are selectively characterized using detection antibodies specific to the HC or LC. In addition, the reduced, denatured iCIEF-Western method allows for the analysis of up to 96 samples overnight, offering good precision and high throughput with minimal analyst hands-on time. Further, the developed method can be applied in different aspects of drug development, such as comparability, release or stability testing given its ability to provide identity, as well as qualitative and quantitative comparative analysis.

Improved process design for monoclonal antibody charge variants separation with multicolumn counter-current solvent gradient purification

The multicolumn counter-current solvent gradient purification (MCSGP) method has proven effective in addressing the issue of elution profile overlap for difficult-to-separate proteins, leading to improved purity and recovery. However, during the MCSGP process, the flow rate and proportion of loaded proteins undergo changes, causing a significant discrepancy between the elution profiles of batch process design and the actual MCSGP process. This mismatch negatively impacts the purity and recovery of the target protein. To address this challenge, an improved process design (reDesign) was proposed with the first-run MCSGP to mimic the actual continuous process and obtain elution profiles that closely resemble the real ones. The reDesign was demonstrated with both a model protein mixture and a sample of monoclonal antibody (mAb) with charge variants. For model protein mixture, the reDesign-based MCSGP process (reMCSGP) showed a remarkable improvement in recovery, increasing from 83.6% to 97.8% while maintaining a purity of more than 95%. For mAb sample, the recovery of reMCSGP improved significantly to 93.9%, surpassing the performance of normal MCSGP processes at a given purity level of more than 84%. In general, the new process design strategy developed in this work could generate a more representative elution profile that closely mirrors actual conditions in continuous processes, which enhances the separation performance of MCSGP.

Yields and product comparison between Escherichia coli BL21 and W3110 in industrially relevant conditions: anti-c-Met scFv as a case study

INTRODUCTION

In the biopharmaceutical industry, Escherichia coli is one of the preferred expression hosts for large-scale production of therapeutic proteins. Although increasing the product yield is important, product quality is a major factor in this industry because greatest productivity does not always correspond with the highest quality of the produced protein. While some post-translational modifications, such as disulphide bonds, are required to achieve the biologically active conformation, others may have a negative impact on the product's activity, effectiveness, and/or safety. Therefore, they are classified as product associated impurities, and they represent a crucial quality parameter for regulatory authorities.

RESULTS

In this study, fermentation conditions of two widely employed industrial E. coli strains, BL21 and W3110 are compared for recombinant protein production of a single-chain variable fragment (scFv) in an industrial setting. We found that the BL21 strain produces more soluble scFv than the W3110 strain, even though W3110 produces more recombinant protein in total. A quality assessment on the scFv recovered from the supernatant was then performed. Unexpectedly, even when our scFv is correctly disulphide bonded and cleaved from its signal peptide in both strains, the protein shows charge heterogeneity with up to seven distinguishable variants on cation exchange chromatography. Biophysical characterization confirmed the presence of altered conformations of the two main charged variants.

CONCLUSIONS

The findings indicated that BL21 is more productive for this specific scFv than W3110. When assessing product quality, a distinctive profile of the protein was found which was independent of the E. coli strain. This suggests that alterations are present in the recovered product although the exact nature of them could not be determined. This similarity between the two strains' generated products also serves as a sign of their interchangeability. This study encourages the development of innovative, fast, and inexpensive techniques for the detection of heterogeneity while also provoking a debate about whether intact mass spectrometry-based analysis of the protein of interest is sufficient to detect heterogeneity in a product.

Coupling of chromatography and precipitation for adjusting acidic variant content in a monoclonal antibody pool

The acidic charge variants (av) of monoclonal antibodies (mAb) are often reported to have reduced therapeutic potency compared with the main (mv) and basic variants (bv), therefore reduction in the av content in mAb pools is often prioritized over reduction in the bv content. In previous studies we described two different methods for reducing the av content, which were based on either ion exchange chromatography or selective precipitation in polyethylene glycol (PEG) solutions. In this study, we have developed a coupled process, in which advantages of simplicity and ease in realization of PEG-aided precipitation and high separation selectivity of anion exchange chromatography (AEX) were exploited. The design of AEX was supported by the kinetic-dispersive model, which was supplemented with the colloidal particle adsorption isotherm, whereas the precipitation process and its coupling with AEX was quantified by simple mass balance equations and underlying thermodynamic dependencies. The model was used to assess the performance of the coupling of AEX and precipitation under different operating conditions. The advantage of the coupled process over the stand-alone AEX depended on the demand for the av reduction as well as the initial variant composition of the mAb pool, e.g., the improvement in the throughput provided by the optimized sequence of AEX and PREC varied from 70 to 600% for the initial av content changed from 35 to 50% w/w, and the reduction demand changed from 30 to 60%.

A Highly Efficient Workflow for Detecting and Identifying Sequence Variants in Therapeutic Proteins with a High Resolution LC-MS/MS Method

Large molecule protein therapeutics have steadily grown and now represent a significant portion of the overall pharmaceutical market. These complex therapies are commonly manufactured using cell culture technology. Sequence variants (SVs) are undesired minor variants that may arise from the cell culture biomanufacturing process that can potentially affect the safety and efficacy of a protein therapeutic. SVs have unintended amino acid substitutions and can come from genetic mutations or translation errors. These SVs can either be detected using genetic screening methods or by mass spectrometry (MS). Recent advances in Next-generation Sequencing (NGS) technology have made genetic testing cheaper, faster, and more convenient compared to time-consuming low-resolution tandem MS and Mascot Error Tolerant Search (ETS)-based workflows which often require ~6 to 8 weeks data turnaround time. However, NGS still cannot detect non-genetic derived SVs while MS analysis can do both. Here, we report a highly efficient Sequence Variant Analysis (SVA) workflow using high-resolution MS and tandem mass spectrometry combined with improved software to greatly reduce the time and resource cost associated with MS SVA workflows. Method development was performed to optimize the high-resolution tandem MS and software score cutoff for both SV identification and quantitation. We discovered that a feature of the Fusion Lumos caused significant relative under-quantitation of low-level peptides and turned it off. A comparison of common Orbitrap platforms showed that similar quantitation values were obtained on a spiked-in sample. With this new workflow, the amount of false positive SVs was decreased by up to 93%, and SVA turnaround time by LC-MS/MS was shortened to 2 weeks, comparable to NGS analysis speed and making LC-MS/MS the top choice for SVA workflow.

Protein Stability After Administration: A Physiologic Consideration

Regulatory authorities and the scientific community have identified the need to monitor the in vivo stability of therapeutic proteins (TPs). Due to the unique physiologic conditions in patients, the stability of TPs after administration can deviate largely from their stability under drug product (DP) conditions. TPs can degrade at substantial rates once immersed in the in vivo milieu. Changes in protein stability upon administration to patients are critical as they can have implications on patient safety and clinical effectiveness of DPs. Physiologic conditions are challenging to simulate and require dedicated in vitro models for specific routes of administration. Advancements of in vitro models enable to simulate the exposure to physiologic conditions prior to resource demanding pre-clinical and clinical studies. This enables to evaluate the in vivo stability and thus may allow to improve the safety/efficacy profile of DPs. While in vitro-in vivo correlations are challenging, benchmarking DP candidates enables to identify liabilities and optimize molecules. The in vivo stability should be an integral part of holistic stability assessments during early development. Such assessments can accelerate development timelines and lead to more stable DPs for patients.

Preferential precipitation of acidic variants from monoclonal antibody pools

Microheterogeneity of monoclonal antibodies (mAbs) can impact their activity and stability. Formation of charge variants is considered as the most important source of the microheterogeneity. In particular, controlling the content of the acidic species is often of major importance for the production process and regulatory approval of therapeutic proteins. In this study, the preferential precipitation process was developed for reducing the content of acidic variants in mAb downstream pools. The process design was preceded by the determination of phase behavior of mAb variants in the presence of different precipitants. It was shown that the presence of polyethylene glycol (PEG) in protein solutions favored precipitation of acidic variants of mAbs. Precipitation yield was influenced by the variant composition in the mAb feed solutions, the concentration of the precipitant and the protein, and the ionic strength of the solutions. To improve yield, multistage precipitation was employed, where the precipitate was recycled to the precipitation process. The final product was a mixture of supernatants pooled together from the recycling steps. Such an approach can be potentially used either instead or in a combination with chromatography for adjusting the acidic variant content of mAbs, which can benefit in improvement in throughput and reduction in manufacturing costs.

Developability assessment at early-stage discovery to enable development of antibody-derived therapeutics

Developability refers to the likelihood that an antibody candidate will become a manufacturable, safe and efficacious drug. Although the safety and efficacy of a drug candidate will be well considered by sponsors and regulatory agencies, developability in the narrow sense can be defined as the likelihood that an antibody candidate will go smoothly through the chemistry, manufacturing and control (CMC) process at a reasonable cost and within a reasonable timeline. Developability in this sense is the focus of this review. To lower the risk that an antibody candidate with poor developability will move to the CMC stage, the candidate's developability-related properties should be screened, assessed and optimized as early as possible. Assessment of developability at the early discovery stage should be performed in a rapid and high-throughput manner while consuming small amounts of testing materials. In addition to monoclonal antibodies, bispecific antibodies, multispecific antibodies and antibody-drug conjugates, as the derivatives of monoclonal antibodies, should also be assessed for developability. Moreover, we propose that the criterion of developability is relative: expected clinical indication, and the dosage and administration route of the antibody could affect this criterion. We also recommend a general screening process during the early discovery stage of antibody-derived therapeutics. With the advance of artificial intelligence-aided prediction of protein structures and features, computational tools can be used to predict, screen and optimize the developability of antibody candidates and greatly reduce the risk of moving a suboptimal candidate to the development stage.

Structural and Functional Analysis of CEX Fractions Collected from a Novel Avastin® Biosimilar Candidate and Its Innovator: A Comparative Study

Avastin^® is a humanized recombinant monoclonal antibody used to treat cancer by targeting VEGF-A to inhibit angiogenesis. SIMAB054, an Avastin^® biosimilar candidate developed in this study, showed a different charge variant profile than its innovator. Thus, it is fractionated into acidic, main, and basic isoforms and collected physically by Cation Exchange Chromatography (CEX) for a comprehensive structural and functional analysis. The innovator product, fractionated into the same species and collected by the same method, is used as a reference for comparative analysis. Ultra-Performance Liquid Chromatography (UPLC) ESI-QToF was used to analyze the modifications leading to charge heterogeneities at intact protein and peptide levels. The C-terminal lysine clipping and glycosylation profiles of the samples were monitored by intact mAb analysis. The post-translational modifications, including oxidation, deamidation, and N-terminal pyroglutamic acid formation, were determined by peptide mapping analysis in the selected signal peptides. The relative binding affinities of the fractionated charge isoforms against the antigen, VEGF-A, and the neonatal receptor, FcRn, were revealed by Surface Plasmon Resonance (SPR) studies. The results show that all CEX fractions from the innovator product and the SIMAB054 shared the same structural variants, albeit in different ratios. Common glycoforms and post-translational modifications were the same, but at different percentages for some samples. The dissimilarities were mostly originating from the presence of extra C-term Lysin residues, which are prone to enzymatic degradation in the body, and thus they were previously assessed as clinically irrelevant. Another critical finding was the presence of different glyco proteoforms in different charge species, such as increased galactosylation in the acidic and afucosylation in the basic species. SPR characterization of the isolated charge variants further confirmed that basic species found in the CEX analyses of the biosimilar candidate were also present in the innovator product, although at lower amounts. The charge variants’ in vitro antigen- and neonatal receptor-binding activities varied amongst the samples, which could be further investigated in vivo with a larger sample set to reveal the impact on the pharmacokinetics of drug candidates. Minor structural differences may explain antigen-binding differences in the isolated charge variants, which is a key parameter in a comparability exercise. Consequently, such a biosimilar candidate may not comply with high regulatory standards unless the binding differences observed are justified and demonstrated not to have any clinical impact.

Optimized Methods for Analytical and Functional Comparison of Biosimilar mAb Drugs: A Case Study for Avastin, Mvasi, and Zirabev

Bevacizumab is a humanized therapeutic monoclonal antibody used to reduce angiogenesis, a hallmark of cancer, by binding to VEGF-A. Many pharmaceutical companies have developed biosimilars of Bevacizumab in the last decade. The official reports provided by the FDA and EMA summarize the analytical performance of biosimilars as compared to the originators without giving detailed analytical procedures. In the current study, several key methods were optimized and reported for analytical and functional comparison of bevacizumab originators (Avastin, Altuzan) and approved commercial biosimilars (Zirabev and Mvasi). This case study presents a comparative analysis of a set of biosimilars under optimized analytical conditions for the first time in the literature. The chemical structure of all products was analyzed at intact protein and peptide levels by high-resolution mass spectrometry; the major glycoforms and posttranslational modifications, including oxidation, deamidation, N-terminal PyroGlu addition, and C-terminal Lys clipping, were compared. The SPR technique was used to reveal antigen and some receptor binding kinetics of all products, and the ELISA technique was used for C1q binding affinity analysis. Finally, the inhibition performance of the samples was evaluated by an MTS-based proliferation assay in vitro. Major glycoforms were similar, with minor differences among the samples. Posttranslational modifications, except C-terminal Lys, were determined similarly, while unclipped Lys percentage was higher in Zirabev. The binding kinetics for VEGF, FcRn, FcγRIa, and C1q were similar or in the value range of originators. The anti-proliferative effect of Zirabev was slightly higher than the originators and Mvasi. The analysis of biosimilars under the same conditions could provide a new aspect to the literature in terms of the applied analytical techniques. Further studies in this field would be helpful to better understand the inter-comparability of the biosimilars.

Antibody charge variant modulation by in vitro enzymatic treatment in different CHO cell cultures

Charge variants represent a critical quality attribute that must be controlled during the development and manufacturing of monoclonal antibodies (mAb). Previously, we reported the development of a cost-effective enzymatic treatment capable of removing the C-terminal lysine from a mAb produced by a Chinese hamster ovary (CHO) GS cell line. This treatment resulted in a significant decrease in basic charge variants and a corresponding improvement in the main peak, enabling a longer cell culture production duration for titer improvement. Here, we describe this enzymatic treatment protocol in detail and demonstrate its applicability to two additional mAbs produced by distinct industrial cell lines. The simple addition of carboxypeptidase B (CpB) at a ratio of 1:10,000 (w/w) to whole cell cultures significantly improved the main peaks for both mAbs without affecting other critical quality attributes, including size exclusion chromatography impurities and N-glycans. Our results demonstrate that this in vitro CpB treatment protocol can be used as a platform strategy to improve main peak for mAbs that exhibit high levels of basic variants attributable to C-terminal lysines. An in vitro enzymatic treatment in general may be another good addition to existing in vivo CHO cell culture strategies for titer improvement and control of critical quality attributes. This article is protected by copyright. All rights reserved.

Structural Characterization of RC28-E, a Recombinant Fusion Protein With Dual Targets on VEGF and FGF2

Vascular endothelial growth factor (VEGF) and fibroblast growthfactor (FGF) play important roles in angiogenesis-related diseases. RC28-E is a soluble fusion protein composed of the human VEGF receptor 1 (VEGFR1) extracellular domain 2 (ECD 2), VEGFR2 ECD 3, FGFR1 ECDs 2 and 3, and the Fc regions of human immunoglobulin G1. By targeting both VEGF and FGF2, RC28-E may represent a useful antiangiogenetic agent, but structural and functional characterizations of this fusion protein are needed. Liquid chromatography–tandem mass spectrometry, size exclusion high-performance liquid chromatography, capillary electrophoresis-sodium dodecyl sulfate, imaged capillary isoelectric focusing, and bio-layer interferometry were used to characterize the properties of RC28-E. The purity of RC28-E was confirmed to be 98% or greater. The glycosylation modification of RC28-E was found to be very complicated, with 11 potential N-linked glycosylation points and 23 types of N-glycans, causing high heterogeneity of the protein. The primary modifications of the amino acid sequence of RC28-E protein included C-terminal K truncation, N-deamidation, and M-oxidation modification. Notably, RC28-E demonstrated a higher affinity for both VEGF and FGF2 than VEGF trap or FGF trap for their respective targets.

Low pKa of Lys promotes glycation at one complementarity-determining region of a bispecific antibody

Protein glycation is a common, normally innocuous, post-translational modification in therapeutic monoclonal antibodies. However, when glycation occurs on complementarity-determining regions (CDRs) of a therapeutic monoclonal antibody, its biological activities (e.g., potency) may be impacted. Here, we present a comprehensive approach to understanding the mechanism of protein glycation using a bispecific antibody. Cation exchange chromatography and liquid chromatography-mass spectrometry were used to characterize glycation at a lysine residue within a heavy chain (HC) CDR (HC-CDR3-Lys98) of a bispecific antibody. Thermodynamic analysis revealed that this reaction is reversible and can occur under physiological conditions with an apparent affinity of 8-10 mM for a glucose binding to HC-CDR3-Lys98. Results from kinetic analysis demonstrated that this reaction follows Arrhenius behavior in the temperature range of 5°C-45°C and can be well predicted in vitro and in a non-human primate. In addition, this glycation reaction was found to be driven by an unusually low pK_a on the ε-amino group of HC-CDR3-Lys98. Van't Hoff analysis and homology modeling suggested that this reaction is enthalpically driven, with this lysine residue surrounded by a microenvironment with low polarity. This study provides, to our knowledge, new insights toward a mechanistic understanding of protein glycation and strategies to mitigate the impact of protein glycation during pharmaceutical development.

Characterization of N-Terminal Glutamate Cyclization in Monoclonal Antibody and Bispecific Antibody Using Charge Heterogeneity Assays and Hydrophobic Interaction Chromatography

N-terminal glutamate (E) cyclization to form pyroglutamate (pE) generates charge heterogeneities for mAbs and proteins. Thus far, pE formation rate in lyophilized formulation as compared to in liquid formulation has not been reported. Impact of pE on antibody biological activity has only been predicted or assessed using stressed samples that may contain other confounding degradations besides pE. Additionally, application of hydrophobic interaction chromatography (HIC) to separate pE has not been reported. In our study, N-terminal E cyclization was identified as the major degradation pathway in lyophilized formulation at elevated temperature for both monoclonal antibody (mAb-A) and IgG-like bispecific antibody (bsAb-A). pE was enriched in salt-gradient ion exchange chromatography (IEC) as pre-peak and in HIC as post-peak for both mAb-A and bsAb-A. Structure-function studies with pE-enriched IEC and HIC fractions confirmed that pE did not affect binding activities for mAb-A and bsAb-A. In vitro incubation of bsAb-A in serum and PBS revealed that the serum matrix may play a role in pE conversion in human serum, in contrast to the chemical reaction mechanism reported. These techniques can help in characterization of N-terminal E-to-pE cyclization and quality attribute severity assessment during therapeutic protein product development.

Productivity improvement and charge variant modulation for intensified cell culture processes by adding a carboxypeptidase B (CpB) treatment step

The goal of cell culture process intensification is to improve productivity while maintaining acceptable quality attributes. In this report, four processes, namely a conventional manufacturing Process A, and processes intensified by enriched N-1 seed (Process B), by perfusion N-1 seed (Process C), and by perfusion production (Process D) were developed for the production of a monoclonal antibody. The three intensified processes substantially improved productivity, however, the product either failed to meet the specification for charge variant species (main peak) for Process D or the production process required early harvest to meet the specification for charge variant species, Day 10 or Day 6 for Processes B and C, respectively. The lower main peak for the intensified processes was due to higher basic species resulting from higher C-terminal lysine. To resolve this product quality issue, we developed an enzyme treatment method by introducing carboxypeptidase B (CpB) to clip the C-terminal lysine, leading to significantly increased main peak and an acceptable and more homogenous product quality for all the intensified processes. Additionally, Processes B and C with CpB treatment extended bioreactor durations to Day 14 increasing titer by 38% and 108%, respectively. This simple yet effective enzyme treatment strategy could be applicable to other processes that have similar product quality issues.

LC-MS based case-by-case analysis of the impact of acidic and basic charge variants of bevacizumab on stability and biological activity

The present study investigates the impact of charge variants on bevacizumab's structure, stability, and biological activity. Five basic and one acidic charge variants were separated using semi-preparative cation exchange chromatography using linear pH gradient elution with purity > 85%. Based on the commercial biosimilar product's composition, two basic variants, one acidic and the main bevacizumab product, were chosen for further investigation. Intact mass analysis and tryptic peptide mapping established the basic variants' identity as those originating from an incomplete clipping of either one or both C-terminal lysine residues in the heavy chain of bevacizumab. Based on peptide mapping data, the acidic variant formation was attributed to deamidation of asparagine residue (N84), oxidation of M258, and preservation of C-terminal lysine residue, located on the heavy chain of bevacizumab. None of the observed charge heterogeneities in bevacizumab were due to differences in glycosylation among the variants. The basic (lysine) variants exhibited similar structural, functional, and stability profiles as the bevacizumab main product. But it was also noted that both the variants did not improve bevacizumab's therapeutic utility when pooled in different proportions with the main product. The acidic variant was found to have an equivalent secondary structure with subtle differences in the tertiary structure. The conformational difference also translated into a ~ 62% decrease in biological activity. Based on these data, it can be concluded that different charge variants behave differently with respect to their structure and bioactivity. Hence, biopharmaceutical manufacturers need to incorporate this understanding into their process and product development guidelines to maintain consistency in product quality.

Mass spectrometric analysis of core fucosylation and sequence variation in a human-camelid monoclonal antibody

Electrospray mass spectrometry (ESI-MS) was used to measure the masses of an intact dimeric monoclonal antibody (Mab) and assess the fucosylation level. The Mab under study was EG2-hFc, a chimeric human-camelid antibody of about 80 kDa (A. Bell et al., Cancer Lett., 2010, 289(1), 81-90). It was obtained from cell culture with and without a fucosylation inhibitor, and treated with EndoS which cleaves between the two core N-acetyl glucosamine (GlcNAc) residues. It is the first time that this combined approach with a unique mass spectrometer was used to measure 146 Da differences as part of a large intact dimeric antibody. Results showed that in the dimer, both heavy chains were fucosylated on the core GlcNAc of the Fc Asn site equivalent to Asn297. In the presence of the fucosylation inhibitor, fucosylation was lost on both subunits. Following reduction, monomers were analyzed and the masses obtained corroborated the dimer results. Dimeric EG2-hFc Mab treated with PNGase F, to deglycosylate the protein, was also measured by MS for mass comparison. In spite of the success of fucosylation level measurements, the experimental masses of deglycosylated dimers and GlcNAc-Fuc bearing dimers did not correspond to masses of our sequence of reference (A. Bell et al., Cancer Lett., 2010, 289(1), 81-90; ; ), which prompted experiments to determine the protein backbone sequence. Digest mixtures from trypsin, GluC, as well as trypsin + GluC proteolysis were analyzed by matrix-assisted laser desorption/ionization (MALDI) MS and MS/MS. A few variations were found relative to the reference sequence, which are discussed in detail herein. These measurements allowed us to build a new "experimental" sequence for the EG2-hFc samples investigated in this work, although there are still ambiguities to be resolved in this new sequence. MALDI-MS/MS also confirmed the fucosylation pattern in the Fc tryptic peptide EEQYNSTYR.

Reduction of charge variants by CHO cell culture process optimization

Over the past decade, global interest in the development of therapeutic monoclonal antibodies (mAbs) has risen rapidly. As therapeutic agents, antibodies have shown marked efficacy in combatting a range of cancers and immune diseases with high target specificity and low toxicity (Carla Lucia et al. in PLoS ONE 6:e24071, 2011; Donaghy in MAbs 8:659-671, 2016; Nasiri et al. in J Cell Physiol 9:6441-6457, 2018; Teo et al. in Cancer Immunol Immunother 61:2295-2309, 2012). Recent advances in cell culture technology, such as high-throughput clone screening, have facilitated antibody production at concentrations exceeding 10 g/L (Chen et al. in BMC Immunol 19:35, 2018; Huang et al. in Biotechnol Prog 26:1400-1410, 2010; Lu et al. in Biotechnol Bioeng 110:191-205, 2013; Singh et al. in Biotechnol Bioeng 113:698-716, 2016). As titers have improved, the industry has begun to focus on the adjustment of target antibody quality profiles to improve efficacy. Cell lines, culture media, and culture conditions impact protein quality (Van Beers and Bardor in Biotechnol J 7:1473-1484, 2012). Optimization of critical quality attributes (CQAs), such as charge variants, can be achieved through bioprocess development and is the preferred approach as changes to the cell line or growth media used is considered unfavorable by regulatory bodies (Gawlitzek et al. in Biotechnol Bioeng 103:1164-1175, 2009; Jordan et al. in Cytotechnology 65:31-40, 2013; Pan et al. in Cytotechnology 69:39-56, 2016). In this study, the effect of process control and ion supplementation on charge variants of mAbs produced by Chinese hamster ovary (CHO) cells was investigated. Results of this study demonstrated that the concentration of Zn²⁺, duration of culturing, and temperature affect charge variants of a given mAb. Under the optimum conditions of 3L bioreactors, the most significant was that Zn^{2 +} and temperature shift could further improve the quality of antibody. The main peak increased by 12%, and the acid peak decreased by 16%. At the same time, there was no significant loss of titer. This study provided supporting evidence for methods to improve charge variants arising during mAb production.

Unambiguous Identification of Pyroglutamate in Full-Length Biopharmaceutical Monoclonal Antibodies by NMR Spectroscopy

Biotherapeutic proteins are an indispensable class of pharmaceuticals that present a high degree of structural complexity and are prone to chemical modifications during production, processing, and storage, which have to be tightly controlled. Pyroglutamate (pGlu), a cyclization product of N-terminal Gln or Glu residues, is a widespread post-translational modification in proteins, including monoclonal antibodies (mAbs). The unambiguous identification and quantification of this modification in proteins is challenging, since the mass difference of -17 Da or -18 Da, when formed from Gln or Glu, respectively, is not unique. Moreover, deamidation and dehydration occur not only during cyclization to pGlu, but also during other reactions leading to different types of modifications, like succinimide or isopeptide bond moieties due to cross-linking between Asn or Gln and Lys side chains. Here we report the unambiguous identification and quantification of pGlu in intact mAbs with natural isotope distribution by NMR spectroscopy. The assignment of all ¹H, ¹³C and ¹⁵N random coil chemical shifts of pGlu in short reference peptides led to the identification of unique chemical shift pairs that are distinct from the random coil chemical shifts of the natural amino-acid residues. These characteristic correlations are suited for the detection of pGlu in denatured proteins. We achieved complete denaturation of mAbs using a straightforward protocol, and could detect and quantify pGlu, in agreement with available mass spectrometric data. The application to the mAbs rituximab and adalimumab illustrates the potential of our approach for the characterization of biotherapeutics containing isotopes at natural abundance.

Proteoform-Resolved FcɤRIIIa Binding Assay for Fab Glycosylated Monoclonal Antibodies Achieved by Affinity Chromatography Mass Spectrometry of Fc Moieties

Fcɤ receptors (FcɤR) mediate key functions in immunological responses. For instance, FcɤRIIIa is involved in antibody-dependent cell-mediated cytotoxicity (ADCC). FcɤRIIIa interacts with the fragment crystallizable (Fc) of immunoglobulin G (IgG). This interaction is known to be highly dependent on IgG Fc glycosylation. Thus, the impact of glycosylation features on this interaction has been investigated in several studies by numerous analytical and biochemical techniques. FcɤRIIIa affinity chromatography (AC) hyphenated to mass spectrometry (MS) is a powerful tool to address co-occurring Fc glycosylation heterogeneity of monoclonal antibodies (mAbs). However, MS analysis of mAbs at the intact level may provide limited proteoform resolution, for example, when additional heterogeneity is present, such as antigen-binding fragment (Fab) glycosylation. Therefore, we investigated middle-up approaches to remove the Fab and performed AC-MS on the IgG Fc to evaluate its utility for FcɤRIIIa affinity assessment compared to intact IgG analysis. We found the protease Kgp to be particularly suitable for a middle-up FcɤRIIIa AC-MS workflow as demonstrated for the Fab glycosylated cetuximab. The complexity of the mass spectra of Kgp digested cetuximab was significantly reduced compared to the intact level while affinity was fully retained. This enabled a reliable assignment and relative quantitation of Fc glycoforms in FcɤRIIIa AC-MS. In conclusion, our workflow allows a functional separation of differentially glycosylated IgG Fc. Consequently, applicability of FcɤRIIIa AC-MS is extended to Fab glycosylated IgG, i.e., cetuximab, by significantly reducing ambiguities in glycoform assignment vs. intact analysis.

Subunit mass analysis for monitoring multiple attributes of monoclonal antibodies

RATIONALE

Multi-Attribute Methods (MAMs) are appealing due to their ability to provide data on multiple molecular attributes from a single assay. If fully realized, such tests could reduce the number of assays required to support a product control strategy while providing equivalent or greater product understanding relative to the conventional approach. In doing so, MAMs have the potential to decrease development and manufacturing costs by reducing the number of tests in a release panel.

METHODS

In this work, we report a MAM which is based on subunit mass analysis.

RESULTS

The MAM assay is shown to be suitable for use as a combined method for identity testing, glycan profiling, and protein ratio determination for co-formulated monoclonal antibody (mAb) drugs. This is achieved by taking advantage of the high mass accuracy and relative quantification capabilities of intact mass analysis using quadrupole time-of-flight mass spectrometry (Q-TOF MS). Protein identification is achieved by comparing the measured masses of light chain (LC) and heavy chain (HC) mAbs against their theoretical values. Specificity is based on instrument mass accuracy. Glycan profiling and relative protein ratios are determined by the relative peak intensities of the protein HC glycoforms and LC glycoforms, respectively. Results for these relative quantifications agree well with those obtained by the conventional hydrophilic interaction liquid chromatography (HILIC) and reversed-phase LC methods.

CONCLUSIONS

The suitability of this MAM for use in a quality control setting is demonstrated through assessment specificity for mAb identity, and accuracy, precision, linearity and robustness for glycan profiling and ratio determination. Results from this study indicate that a MAM with subunit mass analysis has the potential to replace three conventional methods widely used for mAb release testing including identification assay, glycosylation profiling, and ratio determination for co-formulated mAbs.

Risk-Based Comparability Assessment for Monoclonal Antibodies During Drug Development: A Clinical Pharmacology Perspective

Due to complexities in the structure, function, and manufacturing process of antibody-based therapeutic proteins, comparability assessment for supporting manufacturing changes can sometimes be a challenging task. Regulatory guidance recommends a hierarchical risk-based approach, starting with Chemistry, Manufacturing, and Controls (CMC) analytical characterizations, followed by non-clinical and/or clinical studies to ensure that any potential changes in quality attributes have no adverse impact on efficacy and safety of the product. This review focuses on the changes in quality attributes which may potentially affect the pharmacokinetics (PK), pharmacodynamics (PD), and immunogenicity of a monoclonal antibody (mAb) product, and provides general guidelines in designing non-clinical and clinical PK/PD studies to help support comparability assessments. A decision tree for comparability assessment is proposed depending on the nature of the changes in quality attributes, the potential impact of such changes, and the timing of the manufacturing change relative to the development process. Ideally, the optimization of manufacturing process should take place in the early stage of drug development (i.e., preclinical to phase 2a) as more stringent comparability criteria would have to be met if manufacturing changes occur in the late stage of drug development (i.e., phase 2b and after), and consequently, major changes in manufacturing process should be avoided during confirmatory phase 3 studies and post-approval of drug products.

Discovery, characterization, and remediation of a C-terminal Fc-extension in proteins expressed in CHO cells

Protein-based biotherapeutics are produced in engineered cells through complex processes and may contain a wide variety of variants and post-translational modifications that must be monitored or controlled to ensure product quality. Recently, a low level (~1-5%) impurity was observed in a number of proteins derived from stably transfected Chinese hamster ovary (CHO) cells using mass spectrometry. These molecules include antibodies and Fc fusion proteins where Fc is on the C-terminus of the construct. By liquid chromatography-mass spectrometry (LC-MS), the impurity was found to be ~1177 Da larger than the expected mass. After tryptic digestion and analysis by LC-MS/MS, the impurity was localized to the C-terminus of Fc in the form of an Fc sequence extension. Targeted higher-energy collision dissociation was performed using various normalized collision energies (NCE) on two charge states of the extended peptide, resulting in nearly complete fragment ion coverage. The amino acid sequence, SLSLSPEAEAASASELFQ, obtained by the de novo sequencing effort matches a portion of the vector sequence used in the transfection of the CHO cells, specifically in the promoter region of the selection cassette downstream of the protein coding sequence. The modification was the result of an unexpected splicing event, caused by the resemblance of the commonly used GGU codon of the C-terminal glycine to a consensus splicing donor. Three alternative codons for glycine were tested to alleviate the modification, and all were found to completely eliminate the undesirable C-terminal extension, thus improving product quality.

Native mass spectrometry combined with enzymatic dissection unravels glycoform heterogeneity of biopharmaceuticals

Robust manufacturing processes resulting in consistent glycosylation are critical for the efficacy and safety of biopharmaceuticals. Information on glycosylation can be obtained by conventional bottom–up methods but is often limited to the glycan or glycopeptide level. Here, we apply high-resolution native mass spectrometry (MS) for the characterization of the therapeutic fusion protein Etanercept to unravel glycoform heterogeneity in conditions of hitherto unmatched mass spectral complexity. Higher spatial resolution at lower charge states, an inherent characteristic of native MS, represents a key component for the successful revelation of glycan heterogeneity. Combined with enzymatic dissection using a set of proteases and glycosidases, assignment of specific glycoforms is achieved by transferring information from subunit to whole protein level. The application of native mass spectrometric analysis of intact Etanercept as a fingerprinting tool for the assessment of batch-to-batch variability is exemplified and may be extended to demonstrate comparability after changes in the biologic manufacturing process.

The specific glycosylation patterns of biological drugs often impact the efficacy and safety of the therapeutic product. Here the authors describe a native mass spectrometry approach that allows the resolution of highly complex glycosylation patterns on large proteins, which they apply to the therapeutic Fc-fusion protein Etanercept.

Analytical techniques for the characterization of Antibody Drug Conjugates: Challenges and prospects

Antibody drug conjugates are increasingly being researched for the treatment of cancer. Accurate and reliable characterization of ADCs is inevitable for their development as potential therapeutic agent. Different analytical techniques have been used in order to decipher heterogeneous nature of antibody drug conjugates, enabling successful characterization. This review will summarize specially three major analytical tools i.e. UV-Vis spectroscopy, liquid chromatography, and mass spectrometry used in characterization of antibody drug conjugates. In this review, major challenges during analysis due to the inherent features of analytical techniques and antibody drug conjugates are summarized along with the modifications intended to address each challenge.

Identification and quantification of signal peptide variants in an IgG1 monoclonal antibody produced in mammalian cell lines

Sequence variants of a monoclonal antibody resulting from incomplete processing of signal peptide were identified and characterized using multiple mass spectrometry platforms and reverse phase chromatography. Detection and quantification of these variants by three LC/MS platforms were assessed. Quantification was also performed by mass spectrometric analysis of the subunits of the antibody generated by reduction and IdeS proteolysis. Peptide mapping with LC/MS/MS detection was used to quantify and confirm the identities of signal peptide sequence variants. Although quantification of the signal peptide variants thru mass spectrometry approaches is system dependent, our data revealed the results are close to the values determined by chromatographic separation with UV detection. Each of the methods have proven effective in demonstrating the consistency of signal peptide variants levels across the manufacture history of the antibody.

Microheterogeneity of Recombinant Antibodies: Analytics and Functional Impact

Antibodies are typical examples of biopharmaceuticals which are composed of numerous, almost infinite numbers of potential molecular entities called variants or isoforms, which constitute the microheterogeneity of these molecules. These variants are generated during biosynthesis by so-called posttranslational modification, during purification or upon storage. The variants differ in biological properties such as pharmacodynamic properties, for example, Antibody Dependent Cellular Cytotoxicity, complement activation, and pharmacokinetic properties, for example, serum half-life and safety. Recent progress in analytical technologies such as various modes of liquid chromatography and mass spectrometry has helped to elucidate the structure of a lot of these variants and their biological properties. In this review the most important modifications (glycosylation, terminal modifications, amino acid side chain modifications, glycation, disulfide bond variants and aggregation) are reviewed and an attempt is made to give an overview on the biological properties, for which the reports are often contradictory. Even though there is a deep understanding of cellular and molecular mechanism of antibody modification and their consequences, the clinical proof of the effects observed in vitro and in vivo is still not fully rendered. For some modifications such as core-fucosylation of the N-glycan and aggregation the effects are clear and should be monitored, but with others such as C-terminal lysine clipping the reports are contradictory. As a consequence it seems too early to tell if any modification can be safely ignored.

Resolving the micro-heterogeneity and structural integrity of monoclonal antibodies by hybrid mass spectrometric approaches

For therapeutic monoclonal antibodies (mAbs), detailed analysis of the structural integrity and heterogeneity, which results from multiple types of post-translational modifications (PTMs), is relevant to various processes, including product characterization, storage stability and quality control. Despite the recent rapid development of new bioanalytical techniques, it is still challenging to completely characterize the proteoform profile of a mAb. As a nearly indispensable tool in mAb analysis, mass spectrometry (MS) provides unique structural information at multiple levels. Here, we tested a hybrid strategy for the comprehensive characterization of micro-heterogeneity by integrating 2 state-of-the-art MS-based approaches, high-resolution native MS and targeted glycan profiling, to perform complementary analysis at the intact protein level and released glycan level, respectively. We compared the performance of these methods using samples of engineered half-body IgG4s and a panel of mAbs approved for human use. The glycosylation characterization data derived from these approaches were found to be mutually consistent in composition profiling, and complementary in identification and relative-quantitation of low-abundant uncommon glycoforms. In addition, multiple other sources of micro-heterogeneity, such as glycation, lack of glycosylation, and loss of light chains, could be detected by this approach, and the contribution of multiple types of modifications to the overall micro-heterogeneity could be assessed using our superposition algorithm. Our data demonstrate that the hybrid strategy allows reliable and thorough characterization of mAbs, revealing product characteristics that would easily be missed if only a single approach were used.

Microheterogeneity of therapeutic monoclonal antibodies is governed by changes in the surface charge of the protein

It has previously been shown for individual antibodies, that the microheterogenity pattern can have a significant impact on various key characteristics of the product. The aim of this study to get a more generalized understanding of the importance of microheterogeneity. For that purpose, the charge variant pattern of various different commercially available therapeutic mAb products was compared using Cation-Exchange Chromatography with linear pH gradient antigen affinity, Fc-receptor affinity, antibody dependent cellular cytotoxicity (ADCC) and conformational stability. For three of the investigated antibodies, the basic charge variants showed a stronger binding affinity towards FcγRIIIa as well as an increased ADCC response. Differences in the conformational stability of antibody charge variants and the corresponding reference samples could not be detected by differential scanning calorimetry. The different biological properties of the mAb variants are therefore governed by changes in the surface charge of the protein and not by an altered structure. This can help to identify aspects of microheterogeneity that are critical for product quality and can lead to further improvements in the development and production of therapeutic antibody products.

Charge heterogeneity: Basic antibody charge variants with increased binding to Fc receptors

We identified active isoforms of the chimeric anti-GD2 antibody, ch14.18, a recombinant antibody produced in Chinese hamster ovary cells, which is already used in clinical trials.^1,2,3 We separated the antibody by high resolution ion-exchange chromatography with linear pH gradient elution into acidic, main and basic charge variants on a preparative scale yielding enough material for an in-depth study of the sources and the effects of microheterogeneity. The binding affinity of the charge variants toward the antigen and various cell surface receptors was studied by Biacore. Effector functions were evaluated using cellular assays for antibody-dependent cell-mediated cytotoxicity and complement-dependent cytotoxicity. Basic charge variants showed increased binding to cell surface receptor FcγRIIIa, which plays a major role in regulating effector functions. Furthermore, increased binding of the basic fractions to the neonatal receptor was observed. As this receptor mediates the prolonged half-life of IgG in human serum, this data may well hint at an increased serum half-life of these basic variants compared to their more acidic counterparts. Different glycoform patterns, C-terminal lysine clipping and N-terminal pyroglutamate formation were identified as the main structural sources for the observed isoform pattern. Potential differences in structural stability between individual charge variant fractions by nano differential scanning calorimetry could not been detected. Our in-vitro data suggests that the connection between microheterogeneity and the biological activity of recombinant antibody therapeutics deserves more attention than commonly accepted.

Evaluation of Heavy-Chain C-Terminal Deletion on Product Quality and Pharmacokinetics of Monoclonal Antibodies

Due to their potential influence on stability, pharmacokinetics, and product consistency, antibody charge variants have attracted considerable attention in the biotechnology industry. Subtle to significant differences in the level of charge variants and new charge variants under various cell culture conditions are often observed during routine manufacturing or process changes and pose a challenge when demonstrating product comparability. To explore potential solutions to control charge heterogeneity, monoclonal antibodies (mAbs) with native, wild-type C-termini, and mutants with C-terminal deletions of either lysine or lysine and glycine were constructed, expressed, purified, and characterized in vitro and in vivo. Analytical and physiological characterization demonstrated that the mAb mutants had greatly reduced levels of basic variants without decreasing antibody biologic activity, structural stability, pharmacokinetics, or subcutaneous bioavailability in rats. This study provides a possible solution to mitigate mAb heterogeneity in C-terminal processing, improve batch-to-batch consistency, and facilitate the comparability study during process changes.

Human IgG is produced in a pro-form that requires clipping of C-terminal lysines for maximal complement activation

Human IgG is produced with C-terminal lysines that are cleaved off in circulation. The function of this modification was unknown and generally thought not to affect antibody function. We recently reported that efficient C1q binding and complement-dependent cytotoxicity (CDC) requires IgG hexamerization at the cell surface. Here we demonstrate that C-terminal lysines may interfere with this process, leading to suboptimal C1q binding and CDC of cells opsonized with C-terminal lysine-containing IgG. After we removed these lysines with a carboxypeptidase, maximal complement activation was observed. Interestingly, IgG1 mutants containing either a negative C-terminal charge or multiple positive charges lost CDC almost completely; however, CDC was fully restored by mixing C-terminal mutants of opposite charge. Our data indicate a novel post-translational control mechanism of human IgG: human IgG molecules are produced in a pro-form in which charged C-termini interfere with IgG hexamer formation, C1q binding and CDC. To allow maximal complement activation, C-terminal lysine processing is required to release the antibody's full cytotoxic potential.

Advances in recombinant antibody manufacturing

Since the first use of Chinese hamster ovary (CHO) cells for recombinant protein expression, production processes have steadily improved through numerous advances. In this review, we have highlighted several key milestones that have contributed to the success of CHO cells from the beginning of their use for monoclonal antibody (mAb) expression until today. The main factors influencing the yield of a production process are the time to accumulate a desired amount of biomass, the process duration, and the specific productivity. By comparing maximum cell densities and specific growth rates of various expression systems, we have emphasized the limiting parameters of different cellular systems and comprehensively described scientific approaches and techniques to improve host cell lines. Besides the quantitative evaluation of current systems, the quality-determining properties of a host cell line, namely post-translational modifications, were analyzed and compared to naturally occurring polyclonal immunoglobulin fractions from human plasma. In summary, numerous different expression systems for mAbs are available and also under scientific investigation. However, CHO cells are the most frequently investigated cell lines and remain the workhorse for mAb production until today.

Multi-Angle Effector Function Analysis of Human Monoclonal IgG Glycovariants

Therapeutic performance of recombinant antibodies relies on two independent mechanisms: antigen recognition and Fc-mediated antibody effector functions. Interaction of Fc-fragment with different FcR triggers antibody-dependent cellular cytotoxicity and complement-dependent cytotoxicity and determines longevity of the antibody in serum. In context of therapeutic antibodies FcγRs play the most important role. It has been demonstrated that the Fc-attached sugar moiety is essential for IgG effector functionality, dictates its affinity to individual FcγRs and determines binding to different receptor classes: activating or inhibitory. In this study, we systematically analyze effector functions of monoclonal IgG1 and its eight enzymatically engineered glycosylation variants. The analysis of interaction of glycovariants with FcRs was performed for single, as well as for antigen-bound antibodies and IgGs in a form of immune complex. In addition to functional properties we addressed impact of glycosylation on the structural properties of the tested glycovariants. We demonstrate a clear impact of glycosylation pattern on antibody stability and interaction with different FcγRs. Consistent with previous reports, deglycosylated antibodies failed to bind all Fcγ-receptors, with the exception of high affinity FcγRI. The FcγRII and FcγRIIIa binding activity of IgG1 was observed to depend on the galactosylation level, and hypergalactosylated antibodies demonstrated increased receptor interaction. Sialylation did not decrease the FcγR binding of the tested IgGs; in contrast, sialylation of antibodies improved binding to FcγRIIa and IIb. We demonstrate that glycosylation influences to some extent IgG1 interaction with FcRn. However, independent of glycosylation pattern the interaction of IgG1 with a soluble monomeric target surprisingly resulted in an impaired receptor binding. Here, we demonstrate, that immune complexes (IC), induced by multimeric ligand, compensated for the decreased affinity of target bound antibody towards FcRs, showing the importance of the IC-formation for the FcR- mediated effector functions.

Biochemical Characterization of Human Anti-Hepatitis B Monoclonal Antibody Produced in the Microalgae Phaeodactylum tricornutum

Monoclonal antibodies (mAbs) represent actually the major class of biopharmaceuticals. They are produced recombinantly using living cells as biofactories. Among the different expression systems currently available, microalgae represent an emerging alternative which displays several biotechnological advantages. Indeed, microalgae are classified as generally recognized as safe organisms and can be grown easily in bioreactors with high growth rates similarly to CHO cells. Moreover, microalgae exhibit a phototrophic lifestyle involving low production costs as protein expression is fueled by photosynthesis. However, questions remain to be solved before any industrial production of algae-made biopharmaceuticals. Among them, protein heterogeneity as well as protein post-translational modifications need to be evaluated. Especially, N-glycosylation acquired by the secreted recombinant proteins is of major concern since most of the biopharmaceuticals including mAbs are N-glycosylated and it is well recognized that glycosylation represent one of their critical quality attribute. In this paper, we assess the quality of the first recombinant algae-made mAbs produced in the diatom, Phaeodactylum tricornutum. We are focusing on the characterization of their C- and N-terminal extremities, their signal peptide cleavage and their post-translational modifications including N-glycosylation macro- and microheterogeneity. This study brings understanding on diatom cellular biology, especially secretion and intracellular trafficking of proteins. Overall, it reinforces the positioning of P. tricornutum as an emerging host for the production of biopharmaceuticals and prove that P. tricornutum is suitable for producing recombinant proteins bearing high mannose-type N-glycans.