Enablers of continuous processing of biotherapeutic products

The benefits of continuous processing over batch manufacturing are widely acknowledged across the biopharmaceutical industry, primary of which are higher productivity and greater consistency in product quality. Furthermore, the reduced equipment and facility footprint lead to significantly lower capital costs. Technology enablers have a major role in this migration from batch to continuous processing. In this review, we highlight the various enablers that are facilitating adoption of continuous upstream and downstream bioprocessing. This includes new bioreactors and cell retention devices for upstream operations, and on-column and continuous flow refolding, novel continuous chromatography, and single-pass filtration systems for downstream processes. We also elucidate the significant roles of process integration and control as well as of data analytics in these processes.

Downstream Processing of Therapeutic Peptides by Means of Preparative Liquid Chromatography

The market of biomolecules with therapeutic scopes, including peptides, is continuously expanding. The interest towards this class of pharmaceuticals is stimulated by the broad range of bioactivities that peptides can trigger in the human body. The main production methods to obtain peptides are enzymatic hydrolysis, microbial fermentation, recombinant approach and, especially, chemical synthesis. None of these methods, however, produce exclusively the target product. Other species represent impurities that, for safety and pharmaceutical quality reasons, must be removed. The remarkable production volumes of peptide mixtures have generated a strong interest towards the purification procedures, particularly due to their relevant impact on the manufacturing costs. The purification method of choice is mainly preparative liquid chromatography, because of its flexibility, which allows one to choose case-by-case the experimental conditions that most suitably fit that particular purification problem. Different modes of chromatography that can cover almost every separation case are reviewed in this article. Additionally, an outlook to a very recent continuous chromatographic process (namely Multicolumn Countercurrent Solvent Gradient Purification, MCSGP) and future perspectives regarding purification strategies will be considered at the end of this review.

A novel twin-column continuous chromatography approach for separation and enrichment of monoclonal antibody charge variants

Downstream processing of mAb charge variants is difficult owing to their similar molecular structures and surface charge properties. This study aimed to apply a novel twin-column continuous chromatography (called N-rich mode) to separate and enrich acidic variants of an IgG1 mAb. Besides, a comparison study with traditional scaled-up batch-mode cation exchange (CEX) chromatography was conducted. For the N-rich process, two 3.93 mL columns were used, and the buffer system, flow rate and elution gradient slope were optimized. The results showed that 1.33 mg acidic variants with nearly 100% purity could be attained after a 22-cycle accumulation. The yield was 86.21% with the productivity of 7.82 mg/L/h. On the other hand, for the batch CEX process, 4.15 mL column was first used to optimize the separation conditions, and then a scaled-up column of 88.20 mL was used to separate 1.19 mg acidic variants with the purity of nearly 100%. The yield was 59.18% with the productivity of 7.78 mg/L/h. By comparing between the N-rich and scaled-up CEX processes, the results indicated that the N-rich method displays a remarkable advantage on the product yield, i.e. 1.46-fold increment without the loss of productivity and purity. Generally, twin-column N-rich continuous chromatography displays a high potential to enrich minor compounds with a higher yield, more flexibility and lower resin cost.

Oncolytic virus purification with periodic counter-current chromatography

Virus-based biologicals are one of the most promising biopharmaceuticals of the 21st century medicine and play a significant role in the development of innovative therapeutic, prophylactic, and clinical applications. Oncolytic virus manufacturing scale can range from 5 L in research and development up to 50 L for clinical studies and reach hundreds of liters for commercial scale. The inherent productivity and high integration potential of periodic counter-current chromatography (PCC) offer a transversal solution to decrease equipment footprint and the reduction of several non-value-added unit operations. We report on the design of an efficient PCC process applied to the intermediate purification of oncolytic adenovirus. The developed ion-exchange chromatographic purification method was carried out using a four-column setup for three different scenarios: (i) variation in the feedstock, (ii) potential use of a post-load washing step to improve virus recovery, and (iii) stability during extended operation. Obtained virus recoveries (57%-86%) and impurity reductions (>80% DNA, and >70% total protein) match or overcome batch purification. Regarding process stability and automation, our results show that not only the dynamic control strategy used is able to suppress perturbations in the sample inlet but also allows for unattended operation in the case of ion exchange capture.

Analysis and optimal design of batch and two-column continuous chromatographic frontal processes for monoclonal antibody purification

The increasing demand for efficient and robust processes in the purification of monoclonal antibodies (mAbs) has recently brought frontal chromatography to the forefront. Applied during the polishing step, it enables the removal of high molecular weight aggregates from the target product, achieving high purities. Typically, this process is operated in batch using a single column, which makes it intrinsically subjected to a purity-yield tradeoff. This means that high purities can only be achieved at the cost of lowering the product yield and vice versa. Recently, a two-column continuous implementation of frontal chromatography, referred to as Flow2, was developed. Despite being able of alleviating the purity-yield tradeoff typical of batch operations, the increase in the number of process parameters complicates its optimal design, with the risk of not exploiting its full potential. In this study, we developed an ad hoc design procedure (DP) suitable for the optimization of both batch frontal chromatography and Flow2 in terms of purity, yield, and productivity. This procedure provided similar results as a multiobjective optimization based on genetic algorithm but with lower computational effort. Then, batch and Flow2 operated at their optimal conditions were compared. Besides showing a more favorable Pareto front of yield and productivity at a specified purity, the Flow2 process demonstrated improved robustness compared to the batch process with respect to modifications in the loading linear velocity, washing buffer ionic strength and loading time, thus providing an appealing operation for integrated processes.

Process development and optimization of continuous capture with three-column periodic counter-current chromatography

Continuous capture with affinity chromatography is one of the most important units for continuous manufacturing of monoclonal antibody (mAb). Due to the complexity of three-column periodic counter-current chromatography (3C-PCC), three approaches (experimental, model-based, and simplified approaches) were studied for process development and optimization. The effects of residence time for interconnected load (RT _C ), breakthrough percentage of the first column for interconnected load (s) and feed protein concentration (c ₀ ) on productivity and capacity utilization were focused. The model-based approach was found superior to the experimental approach in process optimization and evaluation. Two phases of productivity were observed and the optimal RT _C for the maximum productivity was located at the boundary of the two phases. The comprehensive effects of the operating parameters (RT _C , s, and c ₀ ) were evaluated by the model-based approach, and the operation space was predicted. The best performance of 34.5 g/L/h productivity and 97.6% capacity utilization were attained for MabSelect SuRe LX resin under 5 g/L concentration at RT _C  = 2.8 min and s = 87.5%. Moreover, a simplified approach was suggested to obtain the optimal RT _C for the maximum productivity. The results demonstrated that model-assisted tools are useful to determine the optimum conditions for 3C-PCC continuous capture with high productivity and capacity utilization.

Linear flow-velocity gradient chromatography-An efficient method for increasing the process efficiency of batch and continuous capture chromatography of proteins

A new method was proposed for increasing the capture chromatography process efficiency, linear flow-velocity gradient (LFG). The method uses a linear decreasing flow-velocity gradient with time during the sample loading. The initial flow velocity, the final flow velocity and the gradient time are the parameters to be tuned. We have developed a method for determining these parameters by using the total column capacity and the total loaded amount as a function of time. The capacity can be calculated by using the relationships between dynamic binding capacity (DBC) and residence time. By leveraging the capacity, loading amount, and the required conditions, the optimum LFG can be designed. The method was verified by ion-exchange and protein A chromatography of monoclonal antibodies (mAbs). A two-fold increase in the productivity during the sample loading was possible by LFG compared with the constant flow-velocity (CF) operation. LFG was also applied to a 4-column continuous process. The simulation showed that the cost of resin per unit amount of processed mAbs can be reduced by 13% while 1.4 times enhancement in productivity was preserved after optimization by LFG compared to CF. The process efficiency improvement is more pronounced when the isotherm is highly favorable and the loading volume is large.

Displacement to separate host-cell proteins and aggregates in cation-exchange chromatography of monoclonal antibodies

An efficient and consistent method of monoclonal antibody (mAb) purification can improve process productivity and product consistency. Although protein A chromatography removes most host-cell proteins (HCPs), mAb aggregates and the remaining HCPs are challenging to remove in a typical bind-and-elute cation-exchange chromatography (CEX) polishing step. A variant of the bind-and-elute mode is the displacement mode, which allows strongly binding impurities to be preferentially retained and significantly improves resin utilization. Improved resin utilization renders displacement chromatography particularly suitable in continuous chromatography operations. In this study we demonstrate and exploit sample displacement between a mAb and impurities present at low prevalence (0.002%-1.4%) using different multicolumn designs and recycling. Aggregate displacement depends on the residence time, sample concentration, and solution environment, the latter by enhancing the differences between the binding affinities of the product and the impurities. Displacement among the mAb and low-prevalence HCPs resulted in an effectively bimodal-like distribution of HCPs along the length of a multi-column system, with the mAb separating the relatively more basic group of HCPs from those that are more acidic. Our findings demonstrate that displacement of low-prevalence impurities along multiple CEX columns allows for selective separation of mAb aggregates and HCPs that persist through protein A chromatography.

Oligonucleotides: Current Trends and Innovative Applications in the Synthesis, Characterization, and Purification

Oligonucleotides (ONs) are gaining increasing importance as a promising novel class of biopharmaceuticals. Thanks to their fundamental role in gene regulation, they can be used to develop custom-made drugs (also called N-to-1) able to act on the gene expression at pre-translational level. With recent approvals of ON-based therapeutics by the Food and Drug Administration (FDA), a growing demand for high-quality chemically modified ONs is emerging and their market is expected to impressively prosper in the near future. To satisfy this growing market demand, a scalable and economically sustainable ON production is needed. In this paper, the state of the art of the whole ON production process is illustrated with the aim of highlighting the most promising routes toward the auspicated market-size production. In particular, the most recent advancements in both the upstream stage, mainly based on solid-phase synthesis and recombinant technology, and the downstream one, focusing on chromatographic techniques, are reviewed. Since ON production is projected to expand to the large scale, automatized multicolumn countercurrent technologies will reasonably be required soon to replace the current ones based on batch single-column operations. This consideration is supported by a recent cutting-edge application of continuous chromatography for the ON purification.

Recent Developments in Bioprocessing of Recombinant Proteins: Expression Hosts and Process Development

Infectious diseases, along with cancers, are among the main causes of death among humans worldwide. The production of therapeutic proteins for treating diseases at large scale for millions of individuals is one of the essential needs of mankind. Recent progress in the area of recombinant DNA technologies has paved the way to producing recombinant proteins that can be used as therapeutics, vaccines, and diagnostic reagents. Recombinant proteins for these applications are mainly produced using prokaryotic and eukaryotic expression host systems such as mammalian cells, bacteria, yeast, insect cells, and transgenic plants at laboratory scale as well as in large-scale settings. The development of efficient bioprocessing strategies is crucial for industrial production of recombinant proteins of therapeutic and prophylactic importance. Recently, advances have been made in the various areas of bioprocessing and are being utilized to develop effective processes for producing recombinant proteins. These include the use of high-throughput devices for effective bioprocess optimization and of disposable systems, continuous upstream processing, continuous chromatography, integrated continuous bioprocessing, Quality by Design, and process analytical technologies to achieve quality product with higher yield. This review summarizes recent developments in the bioprocessing of recombinant proteins, including in various expression systems, bioprocess development, and the upstream and downstream processing of recombinant proteins.

Process for Continuous Fab Production by Digestion of IgG

Intensified processing and end-to-end integrated continuous manufacturing are increasingly being considered in bioprocessing as an alternative to the current batch-based technologies. Similar approaches can also be used at later stages of the production chain, such as in the post-translational modifications that are often considered for therapeutic proteins. In this work, a process to intensify the enzymatic digestion of immunoglobulin G (IgG) and the purification of the resulting Fab fragment is developed. The process consists of the integration of a continuous packed-bed reactor into a multicolumn chromatographic process. The integration is realized through the development of a novel multicolumn countercurrent solvent gradient purification (MCSGP) process, which, by adding a third column to the classical two-column MCSGP process, allows for continuous loading and then straight-through processing of the mixture leaving the reactor.

Experimental Evaluation of the Impact of Intrinsic Process Parameters on the Performance of a Continuous Chromatographic Polishing Unit (MCSGP)

The semicontinuous twin-column multicolumn countercurrent solvent gradient purification (MCSGP) process improves the trade-off between purity and yield encountered in traditional batch chromatography, while its complexity, in terms of hardware requirements and process design, is reduced in comparison to process variants using more columns. In this study, the MCSGP process is experimentally characterized, specifically with respect to its unique degrees of freedom, i.e., the four switching times, which alternate the columns between interconnected and batch states. By means of isolation of the main charge isoform of an antibody, it is shown that purity is determined by the selection of the product collection window with negligible influence from the recycle phases. In addition, the amount of weak and strong impurities can be specifically attributed to the start and end of the collection, respectively. Due to higher abundance of weakly adsorbing impurities, the start of product collection influences productivity and yield more than the other switching times. Furthermore, most of the encountered tendencies scale between different loadings. The found trends can be rationalized from the corresponding batch chromatogram and therefore used during process design to obtain desirable process performances without extensive trial-and-error experimentation or complete model development and calibration.

Progression of continuous downstream processing of monoclonal antibodies: Current trends and challenges

Rapid advances in intensifying upstream processes for biologics production have left downstream processing as a bottleneck in the manufacturing scheme. Biomanufacturers are pursuing continuous downstream process development to increase efficiency and flexibility, reduce footprint and cost of goods, and improve product consistency and quality. Even after successful laboratory trials, the implementation of a continuous process at manufacturing scale is not easy to achieve. This paper reviews specific challenges in converting each downstream unit operation to a continuous mode. Key elements of developing practical strategies for overcoming these challenges are detailed. These include equipment valve complexity, favorable column aspect ratio, protein-A resin selection, quantitative assessment of chromatogram peak size and shape, holistic process characterization approach, and a customized process economic evaluation. Overall, this study provides a comprehensive review of current trends and the path forward for implementing continuous downstream processing at the manufacturing scale.

Evaluation of Continuous Membrane Chromatography Concepts with an Enhanced Process Simulation Approach

Modern biopharmaceutical products strive for small-scale, low-cost production. Continuous chromatography has shown to be a promising technology because it assures high-capacity utilization, purity and yield increases, and lower facility footprint. Membrane chromatography is a fully disposable low-cost alternative to bead-based chromatography with minor drawbacks in terms of capacity. Hence, continuous membrane chromatography should have a high potential. The evaluation of continuous processes goes often along with process modeling. Only few experiments with small feed demand need to be conducted to estimate the model parameters. Afterwards, a variety of different process setups and working points can be analyzed in a very short time, making the approach very efficient. Since the available modeling approaches for membrane chromatography modules did not fit the used design, a new modeling approach is shown. This combines the general rate model with an advanced fluid dynamic distribution. Model parameter determination and model validation were done with industrial cell cultures containing Immunoglobulin G (IgG). The validated model was used to evaluate the feasibility of the integrated Counter Current Chromatography (iCCC) concept and the sequential chromatography concept for membrane adsorber modules, starting with a laboratory-type module used for sample preparation. A case study representing a fed-batch reactor with a capacity from 20 to 2000 L was performed. Compared to batch runs, a 71% higher capacity, 48.5% higher productivity, and 38% lower eluent consumption could be achieved.

Integrated continuous bioprocessing: Economic, operational, and environmental feasibility for clinical and commercial antibody manufacture

This paper presents a systems approach to evaluating the potential of integrated continuous bioprocessing for monoclonal antibody (mAb) manufacture across a product's lifecycle from preclinical to commercial manufacture. The economic, operational, and environmental feasibility of alternative continuous manufacturing strategies were evaluated holistically using a prototype UCL decisional tool that integrated process economics, discrete-event simulation, environmental impact analysis, operational risk analysis, and multiattribute decision-making. The case study focused on comparing whole bioprocesses that used either batch, continuous or a hybrid combination of batch and continuous technologies for cell culture, capture chromatography, and polishing chromatography steps. The cost of goods per gram (COG/g), E-factor, and operational risk scores of each strategy were established across a matrix of scenarios with differing combinations of clinical development phase and company portfolio size. The tool outputs predict that the optimal strategy for early phase production and small/medium-sized companies is the integrated continuous strategy (alternating tangential flow filtration (ATF) perfusion, continuous capture, continuous polishing). However, the top ranking strategy changes for commercial production and companies with large portfolios to the hybrid strategy with fed-batch culture, continuous capture and batch polishing from a COG/g perspective. The multiattribute decision-making analysis highlighted that if the operational feasibility was considered more important than the economic benefits, the hybrid strategy would be preferred for all company scales. Further considerations outside the scope of this work include the process development costs required to adopt continuous processing. © 2017 The Authors Biotechnology Progress published by Wiley Periodicals, Inc. on behalf of American Institute of Chemical Engineers Biotechnol. Prog., 33:854-866, 2017.

Performance optimization of continuous countercurrent tangential chromatography for antibody capture

Recent studies have demonstrated that continuous countercurrent tangential chromatography (CCTC) can effectively purify monoclonal antibodies from clarified cell culture fluid. CCTC has the potential to overcome many of the limitations of conventional packed bed protein A chromatography. This paper explores the optimization of CCTC in terms of product yield, impurity removal, overall productivity, and buffer usage. Modeling was based on data from bench-scale process development and CCTC experiments for protein A capture of two clarified Chinese Hamster Ovary cell culture feedstocks containing monoclonal antibodies provided by industrial partners. The impact of resin binding capacity and kinetics, as well as staging strategy and buffer recycling, was assessed. It was found that optimal staging in the binding step provides better yield and increases overall system productivity by 8-16%. Utilization of higher number of stages in the wash and elution steps can lead to significant decreases in buffer usage (∼40% reduction) as well as increased removal of impurities (∼2 log greater removal). Further reductions in buffer usage can be obtained by recycling of buffer in the wash and regeneration steps (∼35%). Preliminary results with smaller particle size resins show that the productivity of the CCTC system can be increased by 2.5-fold up to 190 g of mAb/L of resin/hr due to the reduction in mass transfer limitations in the binding step. These results provide a solid framework for designing and optimizing CCTC technology for capture applications. © 2016 American Institute of Chemical Engineers Biotechnol. Prog., 32:430-439, 2016.

Continuous bioprocessing: the real thing this time? 10(th) Annual bioProcessUK Conference, December 3-4, 2013, London, UK

The Annual bioProcessUK Conference has acted as the key networking event for bioprocess scientists and engineers in the UK for the past 10 years. The following article is a report from the sessions that focused on continuous bioprocessing during the 10^th Annual bioProcessUK Conference (London, December 2013). These sessions were organized by the ‘EPSRC Centre for Innovative Manufacturing in Emergent Macromolecular Therapies’ hosted at University College London. A plenary lecture and workshop provided a forum for participants to debate topical issues in roundtable discussions with industry and academic experts from institutions such as Genzyme, Janssen, Novo Nordisk, Pfizer, Merck, GE Healthcare and University College London. The aim of these particular sessions was to understand better the challenges and opportunities for continuous bioprocessing in the bioprocessing sector.