Development of adsorptive hybrid filters to enable two-step purification of biologics

Advances in high-throughput, high-capacity nonwoven membranes for chromatography in downstream processing: A review

Nonwoven membranes are highly engineered fibrous materials that can be manufactured on a large scale from a wide range of different polymers, and their surfaces can be modified using a large variety of different chemistries and ligands. The fiber diameters, surface areas, pore sizes, total porosities, and thicknesses of the nonwoven mats can be carefully controlled, providing many opportunities for creative approaches for the development of novel membranes with unique properties to meet the needs of the future of downstream processing. Fibrous membranes are already finding use in ultrafiltration, microfiltration, depth filtration, and, more recently, in membrane chromatography for product capture and impurity removal. This article summarizes the various methods of manufacturing nonwoven fabrics, and the many methods available for the modification of the fiber surfaces. It also reviews recent studies focused on the use of nonwoven fabric devices in membrane chromatography and provides some perspectives on the challenges that need to be overcome to increase binding capacities, decrease residence times, and reduce pressure drops so that eventually they can replace resin column chromatography in downstream process operations.

Primary clarification of mammalian cell culture fluid using enhanced sedimentation on inclined surfaces inside the single-use disposable Sudhin BioSettler150

The first downstream processing step in the purification of a biopharmaceutical protein secreted into mammalian cell culture fluid is the primary clarification of the culture fluid. As cell densities in the fed-batch and increasingly more common perfusion bioreactors have increased over last two decades through intensified upstream bioreactor production processes, the traditional primary clarification unit operations of centrifugation and/or microfiltration become more challenging with issues like frequent desludging, cell disruption due to shear damage and quick fouling of membranes. We have developed a novel compact cell settler device exploiting the enhanced sedimentation on inclined surfaces and demonstrated that this settler device can be adapted easily to remove and contain cells or cell clumps from the clarified supernatant collected via the top effluent of the settler. In this work, we present high product recovery results during primary clarification of mammalian cell culture supernatant using our novel single-use disposable BioSettler150 while processing about 10 L of cell culture broth within short processing times of about 4 h.

Fiber chromatographic enabled process intensification increases monoclonal antibody product yield

The most straightforward method to increase monoclonal antibody (mAb) product yield is to complete the purification process in less steps. Here, three different fiber chromatographic devices were implemented using a holistic approach to intensify the mAb purification process and increase yield. Fiber protein A (proA) chromatography was first investigated, but traditional depth filtration was not sufficient in reducing the contaminant load as the fiber proA device prematurely fouled. Further experimentation revealed that chromatin aggregates were the most likely reason for the fiber fouling. To reduce levels of chromatin aggregates, a chromatographic clarification device (CCD) was incorporated into the process, resulting in single-stage clarification of harvested cell culture fluid and reduction of DNA levels. The CCD clarified pool was then successfully processed through the fiber proA device, fully realizing the productivity gains that the fiber technology offers. After the proA and viral inactivation neutralization (VIN) hold step, the purification process was further intensified using a novel single-use fiber-based polishing anion exchange (AEX) material that is capable of binding both soluble and insoluble contaminants. The three-stage fiber chromatographic purification process was compared to a legacy five-step process of dual-stage depth filtration, bead-based proA chromatography, post-VIN depth filtration, and bead-based AEX chromatography. The overall yield from the five-step process was 60%, while the fiber chromatographic-enabled intensified process had an overall yield of 70%. The impurity clearance of DNA and host cell protein (HCP) for both processes were within the regulatory specification (<100 ppm HCP, <1 ppb DNA). For the harvest of a 2000 L cell culture, the intensified process is expected to increase productivity by 2.5-fold at clarification, 50-fold at the proA step, and 1.6-fold in polishing. Relative to the legacy process, the intensified process would reduce buffer use by 1088 L and decrease overall process product mass intensity by 12.6%.

Depth filter material process interaction in the harvest of mammalian cells

Upstream advances have led to increased mAb titers above 5 g/L in 14-day fed-batch cultures. This is accompanied by higher cell densities and process-related impurities such as DNA and Host Cell Protein (HCP), which have caused challenges for downstream operations. Depth filtration remains a popular choice for harvesting CHO cell culture, and there is interest in utilizing these to remove process-related impurities at the harvest stage. Operation of the harvest stage has also been shown to affect the performance of the Protein A chromatography step. In addition, manufacturers are looking to move away from natural materials such as cellulose and Diatomaceous Earth (DE) for better filter consistency and security of supply. Therefore, there is an increased need for further understanding and knowledge of depth filtration. This study investigates the effect of depth filter material and loading on the Protein A resin lifetime with an industrially relevant high cell density feed material (40 million cells/ml). It focuses on the retention of process-related impurities such as DNA and HCP through breakthrough studies and a novel confocal microscopy method for imaging foulant in-situ. An increase in loading of the primary-synthetic filter by a third, led to earlier DNA breakthrough in the secondary filter, with DNA concentration at a throughput of 50 L/m2 being more than double. Confocal imaging of the depth filters showed that the foulant was pushed forward into the filter structure with higher loading. The additional two layers in the primary-synthetic filter led to better pressure profiles in both primary and secondary filters but did not help to retain HCP or DNA. Reduced filtrate clarity, as measured by OD600, was 1.6 fold lower in the final filtrate where a synthetic filter train was used. This was also associated with precipitation in the Protein A column feed. Confocal imaging of resin after 100 cycles showed that DNA build-up around the outside of the bead was associated with synthetic filter trains, leading to potential mass transfer problems.

Analysis of fouling and breakthrough of process related impurities during depth filtration using confocal microscopy

Titer improvement has driven process intensification in mAb manufacture. However, this has come with the drawback of high cell densities and associated process related impurities such as cell debris, host cell protein (HCP), and DNA. This affects the capacity of depth filters and can lead to carryover of impurities to protein A chromatography leading to early resin fouling. New depth filter materials provide the opportunity to remove more process related impurities at this early stage in the process. Hence, there is a need to understand the mechanism of impurity removal within these filters. In this work, the secondary depth filter Millistak+ X0HC (cellulose and diatomaceous earth) is compared with the X0SP (synthetic), by examining the breakthrough of DNA and HCP. Additionally, a novel method was developed to image the location of key impurities within the depth filter structure under a confocal microscope. Flux, tested at 75, 100, and 250 LMH was found to affect the maximal throughput based on the max pressure of 30 psi, but no significant changes were seen in the HCP and DNA breakthrough. However, a drop in cell culture viability, from 87% to 37%, lead to the DNA breakthrough at 10% decreasing from 81 to 55 L/m² for X0HC and from 105 to 47 L/m² for X0SP. The HCP breakthrough was not affected by cell culture viability or filter type. The X0SP filter has a 30%-50% higher max throughput depending on viability, which can be explained by the confocal imaging where the debris and DNA are distributed differently in the layers of the filter pods, with more of the second tighter layer being utilized in the X0SP.

Virus filtration: A Review of Current and Future Practices in Bioprocessing

For drug products manufactured in mammalian cells, safety assurance practices are needed during production to assure that the final medicinal product is safe from the potential risk of viral contamination. Virus filters provide viral retention for a range of viruses through robust, largely size-based retention mechanism. Therefore, a virus filtration step is commonly utilized in a well-designed recombinant therapeutic protein purification process and is a key component in an overall strategy to minimize the risks of adventitious and endogenous viral particles during the manufacturing of biotechnology products. This review summarizes the history of virus filtration, currently available virus filters and prefilters, and virus filtration integrity test methods and study models. There is also discussion of current understanding and gaps with an eye toward future trends and emerging filtration technologies. This article is protected by copyright. All rights reserved.

Chromatographic capture of cells to achieve single stage clarification in recombinant protein purification

Recent advancements in cell culture engineering have allowed drug manufacturers to achieve higher productivity by driving higher product titers through cell line engineering and high‐cell densities. However, these advancements have shifted the burden to clarification and downstream processing where the difficulties now revolve around removing higher levels of process‐ and product‐related impurities. As a result, a lot of research efforts have turned to developing new approaches and technologies or process optimization to still deliver high quality biological products while controlling cost of goods. Here, we explored the impact of a novel single use technology employing chromatographic principle‐based clarification for a process‐intensified cell line technology. In this study, a 16% economic benefit ($/g) was observed using a single‐use chromatographic clarification compared to traditional single‐use clarification technology by improving the overall product cost through decreased operational complexity, higher loading capacity, increased product recovery, and higher impurity clearance. In the end, the described novel chromatographic approach significantly simplified and enhanced the cell culture fluid harvest unit operation by combining the reduction of insoluble and key soluble contaminants of the harvest fluid into a single stage.

Intensified Downstream Processing of Monoclonal Antibodies Using Membrane Technology

The need to intensify downstream processing of monoclonal antibodies to complement the advances in upstream productivity has led to increased attention toward implementing membrane technologies. With the industry moving toward continuous operations and single use processes, membrane technologies show promise in fulfilling the industry needs due to their operational flexibility and ease of implementation. Recently, the applicability of membrane-based unit operations in integrating the downstream process has been explored. In this article, the major developments in the application of membrane-based technologies in the bioprocessing of monoclonal antibodies are reviewed. The recent progress toward developing intensified end-to-end bioprocesses and the critical role membrane technology will play in achieving this goal are focused upon.

Glass Leachables as a Nucleation Factor for Free Fatty Acid Particle Formation in Biopharmaceutical Formulations

Surfactants are essential components in protein formulations protecting them against interfacial stress. One of the current industry-wide challenges is enzymatic degradation of parenteral surfactants such as polysorbate 20 (PS20) and polysorbate 80, which leads to the accumulation of free fatty acids (FFAs) potentially forming visible particles over the drug product shelf-life. While the concentration of FFAs can be quantified, the time point of particle formation remains unpredictable. In this work, we studied the influence of glass leachables as nucleation factors for FFA particle formation. We demonstrate the feasibility of nucleation of FFA particles in the presence of inorganic salts like NaAlO₂ and CaCl₂ simulating relevant glass leachables. We further demonstrate FFA particle formation depending on relevant aluminum concentrations. FFA particle formation was subsequently confirmed with lauric/myristic acid in the presence of different quantities and compositions of glass leachables obtained by several sterilization cycles using different types of glass vials. We further verified the formation of particles in aged protein formulation containing degraded PS20 through the spiking of glass leachables. Particles were characterized as a complex of glass leachables, such as aluminum and FFAs. Based on our findings, we propose a likely pathway for FFA particle formation that considers specific nucleation factors.

Effectiveness of host cell protein removal using depth filtration with a filter containing diatomaceous earth

The increased cell density and product titer in biomanufacturing have led to greater use of depth filtration as part of the initial clarification of cell culture fluid, either as a stand-alone unit operation or after centrifugation. Several recent studies have shown that depth filters can also reduce the concentration of smaller impurities like host cell proteins (HCP) and DNA, decreasing the burden on subsequent chromatographic operations. The objective of this study was to evaluate the HCP removal properties of the Pall PDH4 depth filter media, a model depth filter containing diatomaceous earth, cellulose fibers, and a binder. Experiments were performed with both cell culture fluid (CCF) and a series of model proteins with defined pI, molecular weight, and hydrophobicity chosen to match the range of typical HCP. The location of adsorbed (fluorescently labeled) proteins within the depth filters was determined using confocal scanning laser microscopy. Protein binding was greater for proteins that were positively charged and more hydrophobic, consistent with adsorption to the negatively charged diatomaceous earth. The lowest degree of binding was seen with proteins near their pI, which were poorly removed by this filter. These results provide new mechanistic insights into the factors governing the filter capacity and performance characteristics of depth filters containing diatomaceous earth that are widely used in the clarification of CCF.

The uniqueness of flow in probing the aggregation behavior of clinically relevant antibodies

The development of therapeutic monoclonal antibodies (mAbs) can be hindered by their tendency to aggregate throughout their lifetime, which can illicit immunogenic responses and render mAb manufacturing unfeasible. Consequently, there is a need to identify mAbs with desirable thermodynamic stability, solubility, and lack of self-association. These behaviors are assessed using an array of in silico and in vitro assays, as no single assay can predict aggregation and developability. We have developed an extensional and shear flow device (EFD), which subjects proteins to defined hydrodynamic forces which mimic those experienced in bioprocessing. Here, we utilize the EFD to explore the aggregation propensity of 33 IgG1 mAbs, whose variable domains are derived from clinical antibodies. Using submilligram quantities of material per replicate, wide-ranging EFD-induced aggregation (9-81% protein in pellet) was observed for these mAbs, highlighting the EFD as a sensitive method to assess aggregation propensity. By comparing the EFD-induced aggregation data to those obtained previously from 12 other biophysical assays, we show that the EFD provides distinct information compared with current measures of adverse biophysical behavior. Assessing a candidate's liability to hydrodynamic force thus adds novel insight into the rational selection of developable mAbs that complements other assays.

Adsorptive filtration: A case study for early impurity reduction in an Escherichia coli production process

Primary recovery of intracellular products from Escherichia coli requires cell disruption which leads to a massive release of process-related impurities burdening subsequent downstream process (DSP) unit operations. Especially, DNA and endotoxins challenge purification operations due to their size and concentrations. Consequently, an early reduction in impurities will not only simplify the production process but also increase robustness while alleviating the workload afterward. In the present work, we studied the proof of concept whether a nonwoven anion exchange filter material decreases soluble impurities immediately at the clarification step of E. coli DSP. In a first attempt, endotoxin burden was reduced by 4.6-fold and the DNA concentration by 3.6-fold compared to conventional depth filtration. A design of experiment for the adsorptive filtration approach was carried out to analyze the influence of different critical process parameters (CPPs) on impurity reduction. We showed that depending on the CPPs chosen, a DNA lowering of more than 3 log values, an endotoxin decrease of approximately 7 logs, and a minor HCP clearance of at least 0.3 logs could be achieved. Thus, we further revealed a chromatography column protecting effect when using adsorptive filtration beforehand.

Emerging biomaterials for downstream manufacturing of therapeutic proteins

Downstream processing is considered one of the most challenging phases of industrial manufacturing of therapeutic proteins, accounting for a large portion of the total production costs. The growing demand for therapeutic proteins in the biopharmaceutical market in addition to a significant rise in upstream titers have placed an increasing burden on the downstream purification process, which is often limited by high cost and insufficient capacities. To achieve efficient production and reduced costs, a variety of biomaterials have been exploited to improve the current techniques and also to develop superior alternatives. In this work, we discuss the significance of utilizing traditional biomaterials in downstream processing and review the recent progress in the development of new biomaterials for use in protein separation and purification. Several representative methods will be highlighted and discussed in detail, including affinity chromatography, non-affinity chromatography, membrane separations, magnetic separations, and precipitation/phase separations. STATEMENT OF SIGNIFICANCE: Nowadays, downstream processing of therapeutic proteins is facing great challenges created by the rapid increase of the market size and upstream titers, starving for significant improvements or innovations in current downstream unit operations. Biomaterials have been widely used in downstream manufacturing of proteins and efforts have been continuously devoted to developing more advanced biomaterials for the implementation of more efficient and economical purification methods. This review covers recent advances in the development and application of biomaterials specifically exploited for various chromatographic and non-chromatographic techniques, highlighting several promising alternative strategies.

DNA RETENTION ON DEPTH FILTERS

Depth filtration is a commonly-used bioprocessing unit operation for harvest clarification that reduces the levels of process- and product-related impurities such as cell debris, host-cell proteins, nucleic acids and protein aggregates. Since depth filters comprise multiple components, different functionalities may contribute to such retention, making the mechanisms by which different impurities are removed difficult to decouple. Here we probe the mechanisms by which double-stranded DNA (dsDNA) is retained on depth filter media by visualizing the distribution of fluorescently-labeled retained DNA on spent depth filter discs using confocal fluorescence microscopy. The extent of DNA displacement into the depth filter was found to increase with decreasing DNA length with increasing operational parameters such as wash volume and buffer ionic strength. Finally, using 5ethynyl-2'-deoxyuridine (EdU) to label DNA in dividing CHO cells, we showed that Chinese hamster ovary (CHO) cellular DNA in the lysate supernatant migrates deeper into the depth filter than the lysate re-suspended pellet, elucidating the role of the size of the DNA in its form as an impurity. Apart from aiding DNA purification and removal, our experimental approaches and findings can be leveraged in studying the transport and retention of nucleic acids and other impurities on depth filters at a small scale.