Effective strategies for host cell protein clearance in downstream processing of monoclonal antibodies and Fc-fusion proteins

Host cell protein-mediated adjuvanticity and immunogenicity risks of biotherapeutics

Host cell proteins (HCPs) are process-related impurities of biotherapeutic production that might affect product quality and/or patient safety. In a few cases, adverse events were attributed to HCPs present in the administered biotherapeutic. HCP-associated immune risks include adjuvanticity and immunogenicity with potential cross-reactivity. Based on the published data, some HCPs can act as adjuvants increasing the immunogenicity of the biotherapeutic as a bystander effect. HCPs may also induce immunogenicity against themselves, resulting in anti-HCP T cell responses and anti-HCP antibody formation. Depending on sequence similarities, these anti-HCP immune responses might theoretically be cross-reactive to the biotherapeutic or human endogenous proteins. In this review, we examine HCP-associated immune-related risks reported from non-clinical and clinical studies. We also discuss the potential and limitations of in vitro and in silico methods to evaluate the adjuvanticity and immunogenicity potential of HCPs. A risk-based assessment of the safety impact of HCPs may include the identity of the HCP and similarity to the biotherapeutic and human proteins, as well as product, treatment-, and patient-related factors.

Assessing the Adjuvant Potential of Chinese Hamster Ovary Host Cell Proteins Using an In Vitro Dendritic Cell Assay

Host cell proteins (HCPs) are process-related impurities of therapeutic protein production and may affect product quality or patient safety. In clinical trials, certain HCPs (e.g., PLBL2 or CCL2) that co-purify with the therapeutic protein have been associated with immune reactions in patients. In this study, we examined the adjuvant potential of six commonly detected HCPs from CHO cells (PRDX1, S100A4, PLBL2, CCL2, CLU, and YWHAE) using an in vitro dendritic cell (DC) maturation assay. Recombinant HCPs were expressed in CHO cells to mimic manufacturing conditions. PRDX1, S100A4, and PLBL2 caused a slight increase in the expression of maturation markers on DCs, while YWHAE, CLU, and CCL2 did not. Interestingly, CLU and CCL2 reduced the DC maturation induced by rituximab. In addition, we observed that process parameters such as elution conditions during chromatographic purification can influence HCP aggregation, which in turn can mask or enhance the intrinsic adjuvant potential of an HCP. These findings not only provide initial insights into the adjuvant potential of individual HCPs but also indicate that the quantity as well as the degree of aggregation of HCPs might influence adjuvanticity.

General strategies for IgG-like bispecific antibody purification

Bispecific antibodies (bsAbs) can simultaneously bind two different antigens or epitopes. Their dual-targeting capability enables novel mechanisms of action, gaining therapeutic advantages over conventional monospecific mAbs. In recent years, the number of bsAbs grows rapidly and bsAbs under development are available in diverse formats. In particular, Fc-containing IgG-like bsAbs, which represent the major group, can be constructed in asymmetric or symmetric format. For asymmetric ones, whose assembly requires multiple distinct chains, although numerous strategies have been developed to promote desired chain pairing, product-related variants such as free chains, half molecules and mispaired species are usually present at various levels. For symmetric ones, increased level of aggregates and truncating variants is often associated with their production. In general, bsAbs pose greater challenges to the downstream team than regular mAbs. In the past few years, our team successfully developed the downstream process for over 70 bsAbs in greater than 30 different formats and accumulated substantial experience. This review introduces general strategies that we have used while purifying these challenging molecules.

Polysorbates degrading enzymes in biotherapeutics - a current status and future perspectives

Polysorbates, in particular polysorbate (PS) 20 and 80, are the most commonly used surfactants for stabilising biotherapeutics produced by biotechnological processes. PSs are derived from ethoxylated sorbitan (a derivative of sorbitol) esterified with fatty acids of varying chain length and degree of saturation. In the past, these surfactants have been reported to have specific liabilities. Chemical (oxidations and hydrolyses) and enzymatic degradations have been reported to affect the stability of PS in drug products. Specifically, the presence of trace amounts (sub-ppm) of certain host cell proteins (HCPs) can induce enzymatic PS degradation, which can lead to the release of free fatty acids during storage over time. Enzymatic polysorbate degradation may impair the functionality of the surfactant in stabilising therapeutic proteins, leading to the formation of visible and/or sub-visible particles in biopharmaceutical drug products. This review summarises the enzymes currently known to be involved in the degradation of polysorbate in mammalian biotechnological processes for therapeutic proteins. In recent years, advanced analytical methods have been developed to qualify and quantify the PS-degrading enzymes. Most of these assays are based on mass spectrometry with a preceding HCP enrichment approach. Efforts were made to measure the enzyme activity and correlate it with observed PS degradation. The impact on drug product quality attributes, including fatty acid solubility and phase separation, up to the formation of visible particles, and the potential induction of protein and protein/fatty acid mixed particles as well as the sensitivity of specific PS quality towards enzymatic degradation, was considered. Various drug substance (DS) mitigation strategies related to the occurrence of PS degrading enzymes are discussed as amongst them the generation of stable HCP knockout cell lines, which are also carefully analysed. The underlying opinion article reflects the undergoing discussions related to PS degrading enzymes and focusses on (i) impact on drug product, (ii) analytics for identification/quantification (characterisation) of the PS degrading enzymes, (iii) enzyme activity (iv) currently identified enzymes, and (v) potential mitigation strategies to avoid enzymatic PS degradation during DS manufacturing.

Enhancing aggregate reduction using anion exchange hybrid filter in an immunocytokine diabody fusion protein purification process

Significant aggregation challenges were encountered during the manufacturing processing of an immunocytokine diabody fusion protein. To mitigate this issue and reduce aggregates in the purification process, a variety of depth filters were evaluated for harvest clarification and post-Protein A intermediate filtration. Emphaze™ AEX Hybrid Purifier, a fully synthetic quaternary amine functionalized anion exchange (AEX) nonwoven filter, was found to be particularly effective in removing aggregates during both harvest clarification and post-Protein A intermediate filtration steps. Pre-filters were identified to improve Emphaze filter throughput and further enhance aggregate reduction during the harvest clarification. The effect of operating pH and feed stream aggregate level were evaluated for Emphaze filter for the post-Protein A intermediate filtration, and the aggregate binding capacity of the Emphaze filter was assessed to optimize the aggregate removal. The study also elucidated the aggregate binding mechanism, which was primarily attributed to electrostatic interaction. Overall, the implementation of Emphaze filter resulted in greater than 20 % aggregates reduction, which significantly reduced the impurity clearance workload on the downstream chromatography steps, enabling process simplification while achieving desirable product quality for the diabody fusion protein.

The downstream purification of bispecific antibodies

Bispecific antibodies, a class of therapeutic antibodies, can simultaneously bind to two distinct targets. Compared with monospecific antibodies, bispecific antibodies offer advantages, including superior efficacy and reduced side effects. However, because of their structural complexity, the purification of bispecific antibodies is highly challenging. The purification process must strike a delicate balance between purity and productivity, eliminating a broad spectrum of contaminants, including product-related and process-related impurities, while also maximizing the yield wherever feasible. This review systematically describes the strategies for bispecific antibody capture, the elimination of product-related impurities, and the mitigation of the formation of process-related impurities, thereby, providing guidance for the development of downstream purification processes for bispecific antibodies.

Clear insight into complex multimodal resins and impurities to overcome recombinant protein purification challenges: A review

Increasing attention has been paid to the purity of therapeutic proteins imposing extensive costs and challenges to the downstream processing of biopharmaceuticals. One of the efforts, that has been exerted to overcome such limitations, was developing multimodal or mixed-mode chromatography (MMC) resins for launching selective, orthogonal, non-affinity purification platforms. Despite relatively extensive usage of MMC resins, their real potential and fulfillment have not been extensively reviewed yet. In this work, the explanation of practical and key aspects of downstream processing of recombinant proteins with or without MMC resins was debated, as being useful for further purification process development. This review has been written as a step-by-step guide to deconvolute both inherent protein purification and MMC complexities. Here, after complete elucidation of the potential of MMC resins, the effects of frequently used additives (mobile phase modifiers) and their possible interactions during the purification process, the critical characteristics of common product-related impurities (e.g., aggregates, charge variants, fragments), host-related impurities (e.g., host cell protein and DNA) and process related impurities (e.g., endotoxin, and viruses) with solved or unsolved challenges of traditional and MMC resins have been discussed. Such collective experiences which are reported in this study could be considered as an applied guide for developing successful downstream processing in challenging conditions by providing a clear insight into complex MMC resins and impurities.

Integrated strategy for deep profiling of host cell proteins in downstream processing of therapeutic monoclonal antibodies: Novel approach to isolate and digest host cell proteins

Host cell proteins (HCPs) are process-related impurities generated during the production of biopharmaceuticals, which may contaminate the final product unless they are efficiently removed. Due to their potential impact on product safety, quality and efficacy, regulatory authorities require removal of HCPs during processing down to trace amounts in final manufactured biopharmaceuticals. The current standard method for detecting HCPs is enzyme-linked immunosorbent assay (ELISA), which should reveal the total amount of HCPs. A necessary orthogonal technique to get more granular information on HCPs is obtained by application of liquid chromatography-mass spectrometry (LC-MS) techniques that permit identification and quantification of individual HCPs. However, differences in sample preparation methods and MS acquisition techniques have led to discrepancies in detected HCPs between studies, which may compromise product safety, quality and efficacy. To address this issue, we have developed a novel and reproducible workflow for isolation, digestion, and mass spectrometry detection of HCPs that is applicable to downstream process characterization of therapeutic monoclonal antibodies (mAbs). This article describes a rapid and efficient workflow for the isolation, digestion and identification of HCPs. For the first time, Fc-receptor (FcγRIIIa) affinity chromatography is employed to isolate the HCP fraction from the mAb. Next, the HCPs are precipitated with acetone and digested using a newly developed "single-pot" method that improves digestion performance and prevents sample loss of problematic low-abundant HCPs. The new HCP isolation method outperforms protein A affinity chromatography for monitoring problematic HCPs.

Host cell proteins in monoclonal antibody processing: Control, detection, and removal

Host cell proteins (HCPs) are process-related impurities in a therapeutic protein expressed using cell culture technology. This review presents biopharmaceutical industry trends in terms of both HCPs in the bioprocessing of monoclonal antibodies (mAbs) and the capabilities for HCP clearance by downstream unit operations. A comprehensive assessment of currently implemented and emerging technologies in the manufacturing processes with extensive references was performed. Meta-analyses of published downstream data were conducted to identify trends. Improved analytical methods and understanding of "high-risk" HCPs lead to more robust manufacturing processes and higher-quality therapeutics. The trend of higher cell density cultures leads to both higher mAb expression and higher HCP levels. However, HCP levels can be significantly reduced with improvements in operations, resulting in similar concentrations of approx. 10 ppm HCPs. There are no differences in the performance of HCP clearance between recent enhanced downstream operations and traditional batch processing. This review includes best practices for developing improved processes.

Modeling scalability of impurity precipitation in downstream biomanufacturing

Precipitation during the viral inactivation, neutralization and depth filtration step of a monoclonal antibody (mAb) purification process can provide quantifiable and potentially significant impurity reduction. However, robust commercial implementation of this unit operation is limited due to the lack of a representative scale-down model to characterize the removal of impurities. The objective of this work is to compare isoelectric impurity precipitation behavior for a monoclonal antibody product across scales, from benchtop to pilot manufacturing. Scaling parameters such as agitation and vessel geometry were investigated, with the precipitate amount and particle size distribution (PSD) characterized via turbidity and flow imaging microscopy. Qualitative analysis of the data shows that maintaining a consistent energy dissipation rate (EDR) could be used for approximate scaling of vessel geometry and agitator speeds in the absence of more detailed simulation. For a more rigorous approach, however, agitation was simulated via computational fluid dynamics (CFD) and these results were applied alongside a population balance model to simulate the trajectory of the size distribution of precipitate. CFD results were analyzed within a framework of a two-compartment mixing model comprising regions of high- and low-energy agitation, with material exchange between the two. Rate terms accounting for particle formation, growth and breakage within each region were defined, accounting for dependence on turbulence. This bifurcated model was successful in capturing the variability in particle sizes over time across scales. Such an approach enhances the mechanistic understanding of impurity precipitation and provides additional tools for model-assisted prediction for process scaling.

Host cell protein networks as a novel co-elution mechanism during protein A chromatography

Host cell proteins (HCPs) are process-related impurities of therapeutic proteins produced in for example, Chinese hamster ovary (CHO) cells. Protein A affinity chromatography is the initial capture step to purify monoclonal antibodies or Fc-based proteins and is most effective for HCP removal. Previously proposed mechanisms that contribute to co-purification of HCPs with the therapeutic protein are either HCP-drug association or leaching from chromatin heteroaggregates. In this study, we analyzed protein A eluates of 23 Fc-based proteins by LC-MS/MS to determine their HCP content. The analysis revealed a high degree of heterogeneity in the number of HCPs identified in the different protein A eluates. Among all identified HCPs, the majority co-eluted with less than three Fc-based proteins indicating a drug-specific co-purification for most HCPs. Only ten HCPs co-purified with over 50% of the 23 Fc-based proteins. A correlation analysis of HCPs identified across multiple protein A eluates revealed their co-elution as HCP groups. Functional annotation and protein interaction analysis confirmed that some HCP groups are associated with protein-protein interaction networks. Here, we propose an additional mechanism for HCP co-elution involving protein-protein interactions within functional networks. Our findings may help to guide cell line development and to refine downstream purification strategies.

Understanding virus retention mechanisms on protein a chromatography based on using different wash buffers - Evaluating the possibility for a generic wash buffer toolbox to improve virus clearance capacity

During manufacturing of mammalian-cell derived monoclonal antibodies (mAbs) virus clearance capacity of the downstream process has to be demonstrated. The protein A chromatography step typically achieves less than 4 log10 and is not considered as a major contributing step. Having been successfully applied to host cell protein removal before, we used different wash buffers for three mAbs with two model viruses (Minute virus of mice and Murine leukemia virus) in series as well as separately to further understand major contributing interactions for virus retention and potentially design a generic toolbox of stringent wash buffers to be applied to various mAbs. Results indicate a major relevance of hydrophobic interaction for Murine leukemia virus (xMuLV) and mAb A, based on improved clearance for buffers additionally containing increased levels of hydrophobic compounds. This effect was less pronounced for Minute virus of mice (MVM), whereby hydrogen-bonds were expected to play a stronger role for this model virus. Additionally, electrostatic interactions presumably are more relevant for MVM retention compared to xMuLV under the conditions evaluated. A generic mAb and virus-independent stringent wash buffer toolbox could not be identified. However, based on our results a customized mAb and virus wash buffer design with improved virus clearance is possible, with here demonstrated log reduction increase by 1.3 log10 for MVM and 2.2 log10 for xMuLV for the protein A step compared to equilibration buffer alone.

Development of continuous processing platform utilizing aqueous two-phase extraction for purification of monoclonal antibodies

Monoclonal antibody downstream processing typically entails chromatography-based purification processes beginning with Protein A chromatography, accounting for 50 % of the total manufacturing expense. Alternatives to protein A chromatography have been explored by several researchers. In this paper, aqueous two-phase extraction (ATPE) has been proposed for continuous processing of monoclonal antibodies (mAbs) as an alternative to the traditional protein A chromatography. The PEG-sulfate system has been employed for phase formation in ATPE, and the mAb is separated in the salt phase, while impurities like high molecular weight (HMW) and host cell proteins (HCPs) are separated in the PEG phase. Following ATPE of clarified cell culture harvest, yield of ≥ 80 % and purity of ≥ 97 % were achieved in the salt phase. Considerable (28 %) reduction in consumable cost has been estimated when comparing the proposed platform to the traditional protein A based platform. The outcomes demonstrate that ATPE can be a potentially effective substitute for the traditional Protein A chromatography for purification of mAbs. The proposed platform offers easy implementation, delivers comparative results, and offers significantly better economics for manufacturing mAb-based biotherapeutics.

Evaluation of mild pH elution protein A resins for antibodies and Fc-fusion proteins

Protein A affinity chromatography is widely used as a capture step for monoclonal antibodies (mAb) and molecules that possess an Fc-domain, such as fusion proteins and bispecific antibodies. However, the use of low pH (3.0-4.0) to elute the molecule and achieve acceptable yield (>85 %) can lead to product degradation (e.g. fragmentation, aggregation) for molecules sensitive to low pH. In this paper, we describe a comprehensive evaluation of two protein A resins with ligands designed to elute at a milder pH as a result of modified sequences in their Fc and VH3 binding regions. One of the evaluated resins has been made commercially available by Purolite and named Praesto Jetted A50 HipH. Results demonstrated that Jetted A50 HipH could elute the Fc-fusion protein and most mAbs evaluated with an elution pH at or above 4.6. Elution and wash optimization determined run conditions for high recovery (>90 % monomer yield), reduction of high molecular weight (HMW) species (>50 %), and significant host cell protein (HCP) clearance at the mildest elution pH possible. For a pH-stable mAb and a pH-sensitive fusion protein, cell culture material was purified with optimized conditions and demonstrated the mild elution pH resins' ability to purify product with acceptable yield, comparable or better impurity clearance, and significantly milder native eluate pH compared to traditional resins. The benefits of the mild elution pH resins were clearly exemplified for the pH-sensitive protein, where a milder elution buffer and native eluate pH resulted in only 2 % HMW in the eluate that remained stable over 48 h. In contrast, a traditional protein A resin requiring low pH elution led to eluate HMW levels of 8 %, which increased to 16 % over the same hold time. Additionally, these resins have high dynamic binding capacity and allow the use of traditional HCP washes. Therefore, Jetted A50 HipH is an ideal candidate for a platform protein A resin and provides flexibility for pH-sensitive proteins and stable mAbs, while preserving product quality, recovery, and seamless integration into a downstream process.

Illuminating a biologics development challenge: systematic characterization of CHO cell-derived hydrolases identified in monoclonal antibody formulations

Monoclonal antibodies (mAb) and other biological drugs are affected by enzymatic polysorbate (PS) degradation that reduces product stability and jeopardizes the supply of innovative medicines. PS represents a critical surfactant stabilizing the active pharmaceutical ingredients, which are produced by recombinant Chinese hamster ovary (CHO) cell lines. While the list of potential PS-degrading CHO host cell proteins (HCPs) has grown over the years, tangible data on industrially relevant HCPs are still scarce. By means of a highly sensitive liquid chromatography-tandem mass spectrometry method, we investigated seven different mAb products, resulting in the identification of 12 potentially PS-degrading hydrolases, including the strongly PS-degrading lipoprotein lipase (LPL). Using an LPL knockout CHO host cell line, we were able to stably overexpress and purify the remaining candidate hydrolases through orthogonal affinity chromatography methods, enabling their detailed functional characterization. Applying a PS degradation assay, we found nine mostly secreted, PS-active hydrolases with varying hydrolytic activity. All active hydrolases showed a serine-histidine-aspartate/glutamate catalytical triad. Further, we subjected the active hydrolases to pH-screenings and revealed a diverse range of activity optima, which can facilitate the identification of residual hydrolases during bioprocess development. Ultimately, we compiled our dataset in a risk matrix identifying PAF-AH, LIPA, PPT1, and LPLA2 as highly critical hydrolases based on their cellular expression, detection in purified antibodies, active secretion, and PS degradation activity. With this work, we pave the way toward a comprehensive functional characterization of PS-degrading hydrolases and provide a basis for a future reduction of PS degradation in biopharmaceutical drug products.

Purification and Quality Control of Recombinant Proteins Expressed in Mammalian Cells: A Practical Review

In the recent years, there has been a rapid development of new technologies and strategies when it comes to protein purification and quality control (QC), but the basic technologies for these processes go back a long way, with many improvements over the past few decades. The purpose of this chapter is to review these approaches, as well as some other topics such as the advantages and disadvantages of various purification methods for intracellular or extracellular proteins, the most effective and widely used genetically engineered affinity tags, solubility-enhancing tags, and specific proteases for removal of nontarget sequences. Affinity chromatography (AC), like Protein A or G resins for the recovery of antibodies or Fc fusion proteins or immobilized metals for the recovery of histidine-tagged proteins, will be discussed along with other conventional chromatography techniques: ion exchange (IEC), hydrophobic exchange (HEC), mixed mode (MMC), size exclusion (SEC), and ultrafiltration (UF) systems. How to select and combine these different technologies for the purification of any given protein and the minimal criteria for QC characterization of the purity, homogeneity, identity, and integrity of the final product will be presented.

Effect of Host Cell Protein on Chinese Hamster Ovary Recombinant Protein Production and its Removal Strategies: A Mini Review

Chinese hamster ovary cells are the main expression system for recombinant therapeutic proteins. During the production of these proteins, certain host cell proteins are secreted, broken down, and released by host cells in the culture along with the proteins of interest. These host cell proteins are often difficult to remove during the downstream purification process, and thus affect the quality, safety, and effectiveness of recombinant protein biopharmaceutical products and increase the production cost of recombinant therapeutic proteins. Therefore, host cell protein production must be reduced as much as possible during the production process and eliminated during purification. This article reviews the harm caused by host cell proteins in the production of recombinant protein drugs using Chinese hamster ovary cell, factors affecting host cell proteins, the monitoring and identification of these proteins, and methods to reduce their type and quantity in the final product.

Harnessing ceramic hydroxyapatite as an effective polishing strategy to remove product- and process-related impurities in bispecific antibody purification

Bispecific antibody (bsAb), a novel therapeutic modality, provides excellent treatment efficacy, yet poses numerous challenges to downstream process development, which are mainly due to the intricate diversity of bsAb structures and impurity profiles. Ceramic hydroxyapatite (CHT), a mixed-mode medium, allows proteins to interact with its calcium sites (C-sites) through metal affinity and/or its phosphate sites (P-sites) through cation exchange interactions. This dual-binding capability potentially offers unique bind and elute behaviours for different proteins of interest, resulting in optimal product purity when suitable elution conditions are employed. In this study, the effectiveness of CHT as a polishing step for bsAb purification was investigated across three model molecules and benchmarked against the traditional cation exchange chromatography (CEX). For both asymmetric and symmetric IgG-like bsAb post Protein A eluates, at least 97% product purity was achieved after CHT polishing. CHT delivered a superior aggregate clearance to CEX, resulting in low high molecular weight (HMW) impurities (0.5%) and low process-related impurities in the product pools. Moreover, CHT significantly mitigated "chromatography-induced aggregation" whereas eightfold more HMW was generated by CEX. This study illustrated the developability of CHT in effectively eliminating low molecular weight (LMW) impurities through post-load-wash (PLW) optimization, resulting in an additional reduction of up to 48% in LMW impurities. A mechanistic explanation regarding the performance of impurity removal and mitigation of the chromatography-induced aggregation by CHT was proposed, illustrating unique CHT capability is potentially driven by C-site cooperation, of which effectiveness could depend on the bsAb composition and size.

High-performance countercurrent membrane purification for host cell protein removal from monoclonal antibody products

The transition to continuous biomanufacturing has led to renewed interest in alternative approaches for downstream processing of monoclonal antibody (mAb) products. In this study, we examined the potential of using high-performance countercurrent membrane purification (HPCMP) for the removal of host cell proteins (HCPs) derived from Chinese Hamster Ovary cells in the purification of a mAb. Initial studies used several model proteins to identify appropriate operating conditions for the hollow fiber membrane modules. HPCMP was then used for mAb purification, with mAb yield >95% and more than 100-fold reduction in HCP. Stable operation was maintained for 48 h for feeds that were first prefiltered through the 3MTM Harvest RC chromatographic clarifier to remove DNA and other foulants. In addition, the Process Mass Intensity for HPCMP can be much less than that for alternative HCP separation processes. These results highlight the potential of using HPCMP as part of a fully continuous mAb production process.

Application of Formulation Principles to Stability Issues Encountered During Processing, Manufacturing, and Storage of Drug Substance and Drug Product Protein Therapeutics

The field of formulation and stabilization of protein therapeutics has become rather extensive. However, most of the focus has been on stabilization of the final drug product. Yet, proteins experience stress and degradation through the manufacturing process, starting with fermentaition. This review describes how formulation principles can be applied to stabilize biopharmaceutical proteins during bioprocessing and manufacturing, considering each unit operation involved in prepration of the drug substance. In addition, the impact of the container on stabilty is discussed as well.

A custom-made time-resolved fluoroimmunoassay for the quantitation of the host cell protein of Vero in rabies vaccine

Host cell proteins (HCPs) are the process-specific and inevitable impurities during the manufacture via a host cell, which affect the safety or efficacy of the bio-product. However, the commercial HCP enzyme-linked immunosorbent assay (ELISA) kits may not apply to specific products such as rabies vaccine from Vero cells. More advanced and process-specific assay methods are needed in the quality control of rabies vaccine throughout the whole manufacturing process. Therefore, a novel time-resolved fluoroimmunoassay (TRFIA) for the detection of process-specific HCP of Vero cells in rabies vaccine was established in this study. Liquid chromatography coupled tandem mass spectrometry (LC-MS/MS) was used during the preparation of HCP antigen. Based on a sandwich-type immunoassay format, analytes in samples were captured by one antibody coating in the wells and "sandwiched" by another antibody labeled with europium chelates. Due to the complex composition of HCP, both the capture and detected antibodies are polyclonal antibodies from the same anti-HCP antibodies pool. Multiple experiments have identified the optimal conditions to allow the valid and reliable detection of HCP in rabies vaccine. The TRFIA had a satisfactory limit of detection value (0.011 μg/ml) under optimal conditions, with the linear range from 0.0375 to 2.4 μg/ml of HCP. The coefficient variations (CVs) were all < 10%, and the recoveries were in the range of 97.00-102.42%. All the test results of Vero cell protein reference substance were included in the expected concentration, which demonstrated that the present method was available for the test of HCP in rabies vaccine. Based on these results, the novel TRFIA to detect HCP appears to be important for application in modern vaccine quality control during the whole manufacturing process.

Effectively removing the homodimer in bispecific antibodies by weak partitioning mode of anion exchange chromatography

Small amounts of by-products are nevertheless created during the recombinant production of IgG-like bispecific antibodies due to imbalanced chain expression and improper chain pairing, despite the employment of molecular strategy techniques to promote accurate pairing. Among them, homodimers represent the species that are more difficult to remove due to their physical and chemical properties being similar to the target antibody. Homodimer by-products are always produced even though various technologies can significantly increase the expression of heterodimers, so a robust purification process to recover high-purity heterodimers is required. Most of the chromatography methods commonly adopt the bind-and-elute mode or two-step to separate homodimers, which has numerous drawbacks such as prolonged process times and limited dynamic binding capacity. Flow-through mode of anion exchange is a frequently-used polishing step for antibodies, but it is typically regarded as being more effective for host-cell protein or host-cell DNA removal rather than other product-related impurities such as homodimers and aggregates. This paper demonstrated that single-step anion exchange chromatography allows high capacity and effective clearance of the homodimer byproduct to be simultaneously achieved, suggesting that weak partitioning was a better polishing strategy for achieving a high level of heterodimer purity. And robust operation range of anion exchange chromatography steps for homodimer removal was also developed by leveraging the design of experiments.

Blueprint for antibody biologics developability

Large-molecule antibody biologics have revolutionized medicine owing to their superior target specificity, pharmacokinetic and pharmacodynamic properties, safety and toxicity profiles, and amenability to versatile engineering. In this review, we focus on preclinical antibody developability, including its definition, scope, and key activities from hit to lead optimization and selection. This includes generation, computational and in silico approaches, molecular engineering, production, analytical and biophysical characterization, stability and forced degradation studies, and process and formulation assessments. More recently, it is apparent these activities not only affect lead selection and manufacturability, but ultimately correlate with clinical progression and success. Emerging developability workflows and strategies are explored as part of a blueprint for developability success that includes an overview of the four major molecular properties that affect all developability outcomes: 1) conformational, 2) chemical, 3) colloidal, and 4) other interactions. We also examine risk assessment and mitigation strategies that increase the likelihood of success for moving the right candidate into the clinic.

Product-safety considerations in allogeneic chimeric antigen-receptor T-cell process flows

Allogeneic chimeric antigen-receptor T-cell process flows comprise large-scale primary cultures incorporating traditional biologics processing steps such as cell expansion, with novel processing steps such as electroporation. In addition, these process flows begin with donor-derived peripheral blood mononuclear cells and generate single batches of product, which may be used to treat hundreds of patients. The corresponding unit operation-process safety considerations are individually diverse, and in combination are currently unique and rapidly evolving. The use of available regulations and the principles of quality by design are useful in designing appropriate control strategies into the process during development to ensure process safety.

Quality by Design in Downstream Process Development of Romiplostim

Background

Background: Downstream processing of therapeutic recombinant proteins expressed as the inclusion bodies (IBs) in E. coli is quite challenging. This study aimed to use the quality by design approach for developing the multi-step downstream process of a structurally complex therapeutic Fc-Peptide fusion protein, romiplostim.

Methods

Methods: For development of a successful downstream process, risk analysis and experimental designs were used to characterize the most critical quality attributes (CQAs) and effects of process parameters on these quality attributes.

Results

Results: The solubilization of IBs was optimized by design of experiment on three parameters with a focus on solubility yield, which resulted in >75% increase of the target protein solubilization. The pH of sample was identified as CQA in anion exchange chromatography that might have an impact on achieving >85% host cell proteins removal and >90% host cell DNA reduction. In the refolding step, process parameters were screened. Cystine/cysteine ratio, pH, and incubation time identified as CPPs were further optimized using Box-Behnken analysis, which >85% of the target protein was refolded. The design space for further purification step by HIC was mapped with a focus on high molecular weight impurities. After polishing by gel filtration, the final product's biological activity showed no statistically significant differences among the groups received romiplostim and Nplate®, as the reference product.

Conclusions

Conclusion: This research presents a precise and exhaustive model for mapping the design space in order to describe and anticipate the link between the yield and quality of romiplostim and its downstream process parameters.

Integrated continuous biomanufacturing on pilot scale for acid-sensitive monoclonal antibodies

In this study, we demonstrated the first, to our knowledge, integrated continuous bioprocess (ICB) designed for the production of acid-sensitive monoclonal antibodies, prone to aggregate at low pH, on pilot scale. A high cell density perfusion culture, stably maintained at 100 x 10⁶ cells/mL, was integrated with the downstream process, consisting of a capture step with the recently developed Protein A ligand, Z_Ca ; a solvent/detergent-based virus inactivation; and two ion exchange chromatography steps. The use of a mild pH in the downstream process makes this ICB suitable for the purification of acid-sensitive monoclonal antibodies. Integration and automation of the downstream process were achieved using the Orbit software, and the same equipment and control system were used in initial small-scale trials and the pilot-scale downstream process. High recovery yields of around 90% and a productivity close to 1 g purified antibody/L/day were achieved, with a stable glycosylation pattern and efficient removal of impurities, such as host cell proteins and DNA. Finally, negligible levels of antibody aggregates were detected owing to the mild conditions used throughout the process. The present work paves the way for future industrial-scale integrated continuous biomanufacturing of all types of antibodies, regardless of acid stability. This article is protected by copyright. All rights reserved.

Identification of the specific causes of polysorbate 20 degradation in monoclonal antibody formulations containing multiple lipases

PURPOSE

Polysorbates (PS) are excipients used in the biotech industry to stabilize monoclonal antibody (mAb) protein products. However, PS in drug product formulations can be degraded during storage and lead to particle formation because of the limited solubility of the free fatty acids released through the enzymatic hydrolysis of PS-a process driven by residual host cell proteins, especially lipases, that are co-purified with the drugs. When multiple lipases are present, it is very difficult to know the cause for PS degradation. In this study, we aim to determine the cause of PS degradation from two lipases, lysosomal acid lipase (LAL) and lipoprotein lipase (LPL).

METHODS

PS degradation pattern of the drug product was compared with those induced by recombinant lipases. Correlations between the concentration of LPL or LAL and PS20 loss were compared. Specific inhibitors, LAL inhibitor lalistat2 and LPL inhibitor GSK264220A, were used to differentiate their degradation of PS in the drug products.

RESULTS

The complete inhibition of PS20 degradation by lalistat2 suggested that LAL, rather than LPL, was responsible for the PS20 degradation. In addition, LAL was more strongly correlated than LPL with the percentage of PS20 degradation. No PS20 degradation was observed for several mAbs containing similar levels of LPL (0.5-1.5 ppm) in the absence of LAL, suggesting that LPL concentrations below 1.5 ppm does not degrade PS20 in drug products.

CONCLUSIONS

LAL was determined to be the cause of the PS20 degradation. This study provides a practical strategy to determine the root cause of PS degradation.

Assessing the polysorbate degradation fingerprints and kinetics of lipases - how the activity of polysorbate degrading hydrolases is influenced by the assay and assay conditions

Two of the most widely used surfactants to stabilize biologicals against e.g. interfacial stresses are polysorbate 20 (PS20) and polysorbate 80 (PS80). In recent years, numerous cases of hydrolytic polysorbate (PS) degradation in liquid formulations of biopharmaceuticals have been observed. Concomitant with the degradation of PSs, formulated proteins become inherently instable and more susceptible to aggregation. Furthermore, poorly soluble fatty acids (FA) are released from the PSs, which might lead to FA precipitation and the formation of visible and subvisible particles. Therefore, possible particle inducing factors have to be monitored closely. The major root cause of hydrolytic PS degradation in biologicals is the presence of enzymatic active host cell proteins (HCP), like lipases and esterases, which are co-purified with the active pharmaceutical ingredient. Such contaminants can be detected via their hydrolytic activity, either using ester-based substrates or PS itself. However, each approach has its up- and downsides, which makes the comparison of the results from other publications difficult. It was therefore the aim of the present study to investigate the impact of lipase specificities on the assay readouts. This study evaluates three different surrogate (model) lipases with distinctively different degradation kinetics and substrate specificities using specific analytical methods. The analytical panel contains on one hand two lipase activity assays with ester-based substrates, either detecting the release of para-nitrophenol or 4-methylumbelliferone, and on the other hand two PS-based monitoring analyses (fluorescence micelle assay and reverse phase high performance liquid chromatography - charged aerosol detection), which detect hydrolytic "activity" directly in the target substrate. Thereby, strengths and weaknesses of each assay are discussed, and recommendations are made for the respective use cases. Our results show that the determined lipase activities vary not only from assay to assay, but also significantly for the lipase tested, thus showing a different degradation fingerprint in the RP-HPLC-CAD chromatogram. This demonstrates that a comprehensive monitoring approach is essential to assess potential HCP contaminations.

Purification of Modified Therapeutic Proteins Available on the Market: An Analysis of Chromatography-Based Strategies

Proteins, which have inherent biorecognition properties, have long been used as therapeutic agents for the treatment of a wide variety of clinical indications. Protein modification through covalent attachment to different moieties improves the therapeutic's pharmacokinetic properties, affinity, stability, confers protection against proteolytic degradation, and increases circulation half-life. Nowadays, several modified therapeutic proteins, including PEGylated, Fc-fused, lipidated, albumin-fused, and glycosylated proteins have obtained regulatory approval for commercialization. During its manufacturing, the purification steps of the therapeutic agent are decisive to ensure the quality, effectiveness, potency, and safety of the final product. Due to the robustness, selectivity, and high resolution of chromatographic methods, these are recognized as the gold standard in the downstream processing of therapeutic proteins. Moreover, depending on the modification strategy, the protein will suffer different physicochemical changes, which must be considered to define a purification approach. This review aims to deeply analyze the purification methods employed for modified therapeutic proteins that are currently available on the market, to understand why the selected strategies were successful. Emphasis is placed on chromatographic methods since they govern the purification processes within the pharmaceutical industry. Furthermore, to discuss how the modification type strongly influences the purification strategy, the purification processes of three different modified versions of coagulation factor IX are contrasted.

Influence of excipients in Protein A chromatography and virus inactivation

The purification of monoclonal antibodies and Fc fusion proteins consist of several unit operations operated commonly as a platform approach, starting with Protein A chromatography. The first capture step, the following low pH virus inactivation, and subsequent ion exchange chromatography steps are mostly able to remove any impurities, like host cell proteins, aggregates, and viruses. The changes in pH and conductivity during these steps can lead to additional unwanted product species like aggregates. In this study, excipients with stabilizing abilities, like polyols, were used as buffer system additives to study their impact on several aspects during Protein A chromatography, low pH virus inactivation, and cation exchange chromatography. The results show that excipients, like PEG4000, influence antibody elution behavior, as well as host-cell protein elution behavior in a pH-gradient setup. Sugar excipients, like Sucrose, stabilize the antibody during low pH virus inactivation. All excipients tested show no negative impact on virus inactivation and dynamic binding capacity in a subsequent cation exchange chromatography step. This study indicates that excipients and, possibly excipient combinations, can have a beneficial effect on purification without harming subsequent downstream processing steps.

Polysorbate Degradation and Particle Formation in a High Concentration mAb: Formulation Strategies to Minimize Effect of Enzymatic Polysorbate Degradation

Polysorbate (PS) 20 and 80 are the most common surfactants in monoclonal antibody (mAb) drug product (DP) formulations. Residual host cell proteins (HCP) present at extremely low concentrations in DP formulations can maintain enough enzymatic activity to degrade PS surfactants. Over time, the hydrolysis of surfactant causes the accumulation of minimally soluble free fatty acids resulting in precipitation and formation of subvisible and visible particulates. This manuscript summarizes the investigation of a batch of high concentration (>100 mg/mL) mAb DP where subvisible particles formed abruptly after prolonged storage at 5C°. The work also summarizes the effectiveness of different strategies for managing host cell proteins and fatty acid particles. The concentration and fatty acid composition of polysorbates were found to be significant factors in particle development. Solubilizers and alternative surfactants were all shown to be effective means of preventing particle formation. Lipase inhibitors proved to be a simple means to identify the problem but are more difficult to utilize as a solution.

Hydrolytic polysorbate 20 degradation - Sensitive detection of free fatty acids in biopharmaceuticals via UPLC-QDa analytics with isolator column

The enzymatic hydrolysis of polysorbates, e.g. induced by specific host cell proteins in biologics, is a known risk factor regarding the potential particle formation in the product over time. One of the root causes for this observation is an increase in free fatty acids (FA) within the formulation, which indicates the need for convenient monitoring of FA release. This study presents a novel UPLC-QDa based method to evaluate the content of the FAs esterified to polysorbate 20 (PS20) after hydrolysis. The presented method is label-free, i.e. independent of elaborate fluorophore-labeling and able to directly measure the ionized FAs. Furthermore, the method allows the determination of released FAs as percentage of ester bond hydrolysis and as absolute concentration expressed in ng/mL. Additionally, we describe for the first time in FA analytics the application of an isolator column, to remove trace levels of FAs present in the eluents to improve the sensitivity of the method. Lastly, the capabilities of the newly developed method are proven in case studies with three different monoclonal antibodies, which display characteristic FA release patterns in PS20-containing formulations. In summary, we developed a reliable, sensitive method for FA quantification in biologics, which could also be used as a predictive tool, considering FA solubility, regarding the formation of particles.

High-capacity multimodal anion-exchange membranes for polishing of therapeutic proteins

This contribution reports on a study using Purexa™-MQ multimodal anion-exchange (AEX) membranes for protein polishing at elevated solution conductivities. Dynamic binding capacities (DBC₁₀ ) of bovine serum albumin (BSA), human immunoglobulins, and salmon sperm DNA (ss-DNA) are reported for various salt types, salt concentrations, flowrates, and pH. Using 1 mg/ml BSA, DBC₁₀ values for Purexa™-MQ were >90 mg/ml at conductivities up to 15 mS/cm. The membranes maintained a high, salt-tolerant BSA DBC₁₀ of 89.8 ± 2.7 (SD) over the course of 100 bind-elute cycles. Polishing studies with acidic and basic monoclonal antibodies at >2 kg/L loads showed that Purexa™-MQ had higher clearance of host cell proteins and aggregate species at high conductivity (13 mS/cm) and in the presence of phosphate than other commercial AEX media. Purexa™-MQ also had a high ss-DNA DBC₁₀ of 50 mg/ml at conductivities up to 15 mS/cm, markedly outperforming other commercial products. In addition to the effectiveness of Purexa™-MQ for protein polishing at elevated solution conductivities, its unusually high binding capacity for ss-DNA indicates potential applications for plasmid DNA purification.

Discovery and characterization of CHO host cell protease-induced fragmentation of a recombinant monoclonal antibody during production process development

Monoclonal antibody (mAb) fragmentation is a widespread issue of protein stability that needs to be carefully monitored for critical mAb quality control during the production process development. This study describes here the discovery and characterization of CHO host cell protease-induced fragmentation of a therapeutic mAb-X in the formulation samples from an early production process. The fragmentation was observed in the sodium dodecyl sulfate capillary electrophoresis (CE-SDS) analysis of mAb-X formulation samples incubated at elevated temperature. Size exclusion liquid chromatography (SEC-HPLC) was used to analyze and collect these cleaved fragments derived from mAb-X. Reversed phase liquid chromatography mass spectrometry (RP-LC-MS) and tandem mass (MS/MS) analysis demonstrated that the fragment was generated mainly due to the hinge region cleavage of mAb-X. The fragmentation rate was characterized in the mAb-X formulation samples at pH from 4.0 to 6.0 using CE-SDS and SDS-PAGE analysis. The percentage of the main fragment increased dramatically from 2.8% to 31.2% as pH decreased from 6.0 to 4.0 at 40 °C for 28 days, which indicated the fragmentation was highly pH-dependent. The SDS-PAGE analysis further verified the pH-dependent property of the framentation of mAb-X. Moreover, the fragmentation was characterized in the presence and absence of pepstatin A, an inhibitor of acidic proteases. Significant inhibition of mAb-X fragmentation was observed with the addition of pepstatin A to mAb-X formulation samples. These results suggested residual acidic host cell protease(s) in the formulation samples from an early production process caused the fragmentation of mAb-X. To prove evidence, we developed an optimized protein A chromatography to enhance the residual host cell protease(s) removal capability of mAb-X purification process and consequently eliminate the above described cleaved fragment of mAb-X, which further supported the hypothesis that the fragmentation of mAb-X was catalyzed by the residual host cell protease(s) in the formulation samples from the early production process. This case study reiterated that residual host cell protease is a critical quality attribute (CQA) that should be carefully controlled and evaluated to guarantee successful manufacture processes for mAb products.

Recent advancements, challenges, and practical considerations in the mass spectrometry-based analytics of protein biotherapeutics: A viewpoint from the biosimilar industry

The extensive analytical characterization of protein biotherapeutics, especially of biosimilars, is a critical part of the product development and registration. High-resolution mass spectrometry became the primary analytical tool used for the structural characterization of biotherapeutics. Its high instrumental sensitivity and methodological versatility made it possible to use this technique to characterize both the primary and higher-order structure of these proteins. However, even by using high-end instrumentation, analysts face several challenges with regard to how to cope with industrial and regulatory requirements, that is, how to obtain accurate and reliable analytical data in a time- and cost-efficient way. New sample preparation approaches, measurement techniques and data evaluation strategies are available to meet those requirements. The practical considerations of these methods are discussed in the present review article focusing on hot topics, such as reliable and efficient sequencing strategies, minimization of artefact formation during sample preparation, quantitative peptide mapping, the potential of multi-attribute methodology, the increasing role of mass spectrometry in higher-order structure characterization and the challenges of MS-based identification of host cell proteins. On the basis of the opportunities in new instrumental techniques, methodological advancements and software-driven data evaluation approaches, for the future one can envision an even wider application area for mass spectrometry in the biopharmaceutical industry.