Depending on the resin, loading conditions and charge variant profile of the antibody product, the amount of product loaded can reach one hundred grams per liter of resin without compromising product quality. A lower level of impurity in the product will result in a higher amount of product loaded. Bind-and-elute mode. Anion exchange chromatography in bind-and-elute mode has also been implemented in the manufacturing of mAbs.
The antibody product pool is first loaded onto an anion exchange column and the product of interest is then eluted with a higher salt concentration in a step or linear gradient, leaving the majority of impurities bound to the column.
The impurities are eluted from the column during the cleaning or regeneration step. In the development and optimization of an anion exchange chromatography in bind-and-elute mode, the operating pH should be above or close to the pI of the product in order to obtain a net negative charge or higher negative charge number on the surface of the antibody molecules, and hence to achieve a higher binding capacity during the chromatography step.
Similarly, to reach a high binding capacity, the ionic strength for the load should be in the low range and the pH should be less than pH 9. Manufacturing issues around the need to achieve lower ionic strength in the load will come into play, including the capability or need for diafiltration, product holding vessel volumes if the load will be diluted manually, and operational lower limits of buffer pumps when running a gradient if the sample is to be diluted in-line.
Optimal elution conditions can be achieved using either a linear gradient or step elution. Step elution can deliver smaller product pool volumes and higher product concentration, while linear gradient elution can provide better process control, process monitoring and reproducibility. Even if a quick or short linear gradient program is performed, the same principal should be applied as used to develop a step elution program in selecting an initial salt concentration and the conductivity of the elution buffer.
Weak partitioning chromatography. Recently, a mode of anion exchange chromatography termed weak partitioning chromatography WPC has been developed. This can enable a two chromatography recovery process comprising Protein A and anion exchange for many antibodies. This takes advantage of the fact that the impurities to be removed are more acidic than the product. Both antibody and impurities bind to the anion exchange resin, but the impurities are much more tightly bound than in flow-through mode, which can lead to an increase in impurity removal Fig.
Thus, weaker binding impurities that are not removed efficiently in flow-through mode can be removed to a greater degree under conditions where their partition coefficient Kp has been increased. High load capacity runs of monoclonal antibody. Under chromatographic conditions at selected optimal Kp 0. Due to the increased clearance of virus, host cell protein and product related species compared to anion exchange chromatography in flow-through mode, weak partitioning chromatography can enable a two column recovery process for many products.
One challenge is less efficient removal of high molecular weight species compared to recovery processes employing a third chromatographic step such as cation exchange, so it may not be applicable to all products. One aspect of weak partitioning chromatography is that the pH and counterion conditions need to be optimized for each product. This is in contrast to some platform chromatography processes that are able to use standardized conditions on an anion exchange matrix resin or membrane for most products.
In order to rapidly define the optimal operating conditions for WPC, high throughput screening HTS methods have been developed. This can be refined subsequently through column chromatography or if HTS capability is not available, optimization can be carried out in entirety using columns.
Flow-through chromatography conditions can be used as a starting point for determining the optimal mobile phase composition. Cation exchange chromatography uses a resin modified with negatively charged functional groups. They can be strong acidic ligands such as sulphopropyl, sulfoethyl and sulfoisobutyl groups or weak acidic ligand such as carboxyl group.
Cation exchange chromatography has been applied for purification processes for many mAbs with pI values ranging from neutral to basic. Most humanized IgG1 and IgG2 subclasses are perfect candidates for cation exchange chromatography, in which the antibody is bound onto the resin during the loading step and eluted through either increasing conductivity or increasing pH in the elution buffer. The most negatively charged process-related impurities such as DNA, some host cell protein, leached Protein A and endotoxin are removed in the load and wash fraction.
Cation exchange chromatography can also provide separation power to reduce antibody variants from the target antibody product such as deamidated products, oxidized species and N-terminal truncated forms, as well as high molecular weight species.
The dynamic binding capacity of mAbs on cation exchange resins depends on pH and conductivity. Confocal scanning laser microscopy indicated that under the conditions studied proteins are unable to penetrate deeply into the porous chromatography beads. It is possible that protein molecules adsorbed at pore channels near the external surface of the media hinder other molecules from entering the pores and such exclusion is reduced at high conductivity, leading to a direct relationship between net protein charge and the solution conductivity yielding optimal dynamic capacity.
Dynamic binding capacity of a monoclonal antibody as a function of pH and conductivity displays two regions. In the first domain positively sloped capacity trend , the capacity increases with increasing conductivity.
In the second region negatively sloped capacity trend , the capacity decreases with increasing conductivity. High loading on the resin normally results in higher levels of impurities in the elution pool, although different ligands and resin bead sizes can have significant effects on the resolution of impurities. Therefore, a resin screening study should be performed to select the best resin, i. The resin screening study is also linked with the elution condition development.
The same principles described for anion exchange chromatography regarding development of the elution program apply to cation exchange chromatography as well.
The development of elution conditions is linked to impurity removal and characteristics of the product pool that can be processed easily in the subsequent unit operation.
Generally, a linear salt or pH gradient elution program can be conducted to determine the best elution condition. Aggregate removal was comparable with both resins and both linear gradient programs. Final selection of a weak or strong cation exchanger should take into consideration other factors such as binding capacity, removal of other impurities and the product pool profile. Typically, a smaller pool volume with higher product concentration and lower conductivity is desired if subsequent anion exchange chromatography is to be employed.
Elution condition development for a monoclonal antibody. C and D the same linear pH and salt elution programs applied on a strong anion exchange column Fractogel SO- resin , respectively. Hydrophobic interaction chromatography HIC is a useful tool for separating proteins based on their hydrophobicity, and is complementary to other techniques that separate proteins based on charge, size or affinity.
The sample is typically loaded on the HIC column in a high salt buffer. The salt in the buffer interacts with water molecules to reduce solvation of the protein molecules in solution, thereby exposing hydrophobic regions in the sample protein molecules that consequently bind to the HIC resin.
The more hydrophobic the molecule, the less salt is needed to promote binding. A gradient of decreasing salt concentration is usually used to elute samples from the column. As the ionic strength decreases, the exposure of the hydrophilic regions of the molecules increases and molecules elute from the column in order of increasing hydrophobicity.
HIC is a versatile liquid chromatography technique that is frequently used in a rational purification strategy. HIC resins containing phenyl or butyl ligands are often found in mAb purification processes; 60 — 63 however, due to the high efficiency of Protein A affinity chromatography, HIC is mostly used as an intermediate purification step after Protein A chromatography or as a polishing step after ion exchange chromatography.
HIC in flow-through mode is efficient in removing a large percentage of aggregates with a relatively high yield.
HIC in bind-and-elute mode normally provides effective separation of process-related and product-related impurities from antibody product. The majority of host cell protein, DNA and aggregates can be removed from the antibody product through selection of a suitable salt concentration in the elution buffer or use of a gradient elution method. Hydrophobic charge induction chromatography HCIC is based on the pH-dependent behavior of ligands that ionize at low pH.
To overcome the problem of harsh elution conditions, which are typically used with very hydrophobic resins, desorption in HCIC is facilitated by lowering the pH to produce charge repulsion between the ionizable ligand and the bound protein. It is a cellulose-based media with 4-mercaptoethyl pyridine as the functional group.
The ligand is a hydrophobic moiety with an N-heterocyclic ring that acquires a positive charge at low pH. Due to the high cost of Protein A resins and their somewhat lower resistance to extreme conditions, HCIC resin has been suggested as a potential alternative to Protein A resins for the initial capture and purification of IgG antibodies.
Salt-independent antibody binding and successful elution at a somewhat higher pH range than is possible with Protein A chromatography has been demonstrated; 56 , 66 , 67 however, one critical drawback of HCIC is that it has stronger non-specific binding and can be less efficient than Protein A chromatography in reducing impurities such as host cell protein.
Consequently, use of HCIC in an antibody purification process can be challenging. Continued evaluation of HCIC in combination with other orthogonal purification steps that can provide sufficient removal of residual impurities, such as ion exchange chromatography, precipitation and crystallization, will determine whether it will play a prominent role in antibody purification process development in the future.
Ceramic hydroxyapatite Ca 5 PO4 3 OH 2 is a form of calcium phosphate that can be used for the separation and purification of proteins, enzymes, nucleic acids, viruses and other macromolecules. Hydroxyapatite has unique separation properties and unparalleled selectivity and resolution. It often separates proteins that appear to be homogeneous by other chromatographic and electrophoretic techniques.
Ceramic hydroxyapatite CHT chromatography with a sodium phosphate gradient elution has been used as a robust polishing step in mAb purification process to remove dimers, aggregates and leached Protein A. These multimodal resins combine different types of interactions such as ionic interaction, hydrogen bonding and hydrophobic interaction.
The multimodal functionality of the resin provides selectivity that is different from standard ion exchange ligands, which makes them suitable for solving purification problems at both high and low conductivity or pH. A strong anionic multimodal resin, Capto Adhere, has been evaluated as a second antibody purification step after Protein A chromatography to remove aggregate, host cell protein and leached Protein A.
As for other chromatography resins, one needs to take into account factors such as resin lifetime, lot-to-lot variability, effective cleaning and regeneration, viral clearance, platform suitability and the probability of identifying an alternate resin for second sourcing efforts.
High throughput screening HTS in robotic format is being used to quickly optimize chromatographic separations.
Resin selection, binding capacities, binding and elution conditions, impact of intermediate wash steps, yield, as well as resolution of impurities can be determined in automated fashion.
Screening can be carried out in batch mode in well plates and well filterplates Whatman, Innovative Microplate, GE Healthcare , and also in mini-columns in well column formats Atoll-Bio. For instance, gradient elution can be more easily implemented for the mini-column format in which multiple step-wise gradient can be used to simulate the linear gradient. In batch mode, a defined quantity of resin is aliquoted into the well, washed and equilibrated with the appropriate buffer, the protein-containing sample is added and the plate is mixed for an appropriate time and then unbound material is removed either by centrifugation or the use of a vacuum manifold.
The resin can subsequently be washed and eluted as appropriate, and all of the various fractions analyzed. Examples of HTS in batch binding mode applied to HIC, 74 hydroxyapatite 75 and ion exchange chromatography have been published recently. Kelley et al. Advantages of HTS include the ability to rapidly screen a very large number of conditions, reduced sample requirements and the potential for realizing economic benefits.
Since only a single theoretical plate is obtained, this method is not appropriate for evaluation of methods such as SEC that rely on many plates for separation. A consequence of HTS is the generation of a large numbers of samples to be analyzed, generating a substantially increased analytical burden.
Without the availability of appropriate analytical methods of sufficient throughput and sensitivity for the quantity and volume of the samples, sample and data analysis will become a bottleneck. Parallel analysis methods are highly preferred. Reduced sample volumes affect the sensitivity and often the time, required for analysis. Dynamic binding capacity and other parameters such as yield and purity may differ in separations in a packed bed column at full bed height under actual operating conditions.
For this reason, HTS process development is frequently followed by confirmation and final optimization using standard packed bed chromatography, with the advantage that the operating range is already well defined.
HTS is likely to gain in prominence in the future as the methodology evolves and economic pressures increase. Membrane and filtration technologies are used extensively in the isolation and purification of mAb and other recombinant DNA products, from the initial clarification of cell culture broth to the final sterile filtration of purified bulk solutions.
This section focuses on several of these technologies used for the purification of mAb products or removal of contaminants and impurities, including depth filtration, membrane chromatography, ultrafiltration, high performance tangential flow filtration using neutral or charged membranes and virus filtration.
Membrane chromatography or membrane adsorbers, function similarly to packed chromatography columns, but in the format of conventional filtration modules.
The benefit of membrane chromatography over conventional bead chromatography is the elimination of diffusive pores. For membrane chromatography, binding sites are located along the through pores rather than nestled within long diffusive pores.
In membrane chromatography, membranes consist of a polymeric substrate to which a functional ligand is chemically coupled. The polymer substrate is composed of multilayers of polyethersulfone, polyvinylidene fluoride and regenerated cellulose membrane.
The most widely used functional ligands are the same as those used in chromatography resins, including ion exchange, e. Among the adsorptive membranes commercially available, the Q membrane adsorber has attracted a lot of industry interest, especially in mAb purification processes. Similar to conventional bed chromatography, Q membranes are normally exploited as polishing steps in flow-through mode to remove trace amounts of impurities. Around neutral to slightly basic pH and at low conductivities, viruses, DNA, endotoxin, a large population of host cell proteins and leached Protein A bind to the Q membrane, whereas the typically basic antibody molecules flow through the membrane matrix without being bound.
Membrane chromatography is potentially useful for protein purification at laboratory and pilot scale; however, it has limitations that need to be overcome before it can be successfully employed in process-scale production. Major limitations are uneven flow distribution, non-identical membrane size distribution, uneven membrane thickness, the availability of appropriate scale-down devices and low binding capacities.
Improved binding capacities and flow distribution have been achieved by optimizing pore size, membrane chemistry, membrane thickness or the number of membrane layers and employment of tentacle ligands. Ultrafiltration is a pressure-driven membrane process that is widely used for protein concentration and buffer exchange.
Ultrafiltration is a size-based separation, where species larger than the membrane pores are retained and smaller species pass through freely. Separation in ultrafiltration is achieved through differences in the filtration rates of different components across the membrane under a given pressure driving force. Ultrafiltration with membrane pores ranging from 1 to 20 nm can provide separation of species ranging in molecular weight from daltons to 1, kilodaltons.
Membrane selectivity is controlled by a thin skin layer that is approximately 0. Ultrafiltration membranes can be cast from a wide variety of polymers, including polysulfone, polyethersulfone, polyvinylidene fluoride and regenerated cellulose. The synthetic polymers exhibit strong resistance to acids, bases, alcohols and higher temperatures, allowing for effective membrane cleaning. In this manner, ultrafiltration membranes can be reused without deterioration of flow rates and cross contamination.
In contrast, cellulose membranes have low protein binding but can be damaged by harsh cleaning methods. New composite regenerated cellulose membranes have significantly less protein fouling, are more easily cleaned, and have excellent mechanical strength.
Due to these favorable properties, cellulose membranes are superior to other membranes in process permeability and retention characteristics for protein ultrafiltration and diafiltration. Ultrafiltration is normally carried out in tangential flow filtration TFF mode, in which fluid passes across the filter cross-flow , tangential to the plane of the filter surface. The primary advantage of TFF is that the cross-flow continuously sweeps the filter surface, reducing the extent to which materials accumulate on the filter surface, and increasing filtration throughput.
Ultrafiltration systems can be operated with different control strategies. Ultrafiltration and diafiltration processes are typically developed using constant retentate pressure, constant trans-membrane pressure or constant filtrate flux. As these control methods do not factor in the effects of the protein gel layer at the membrane surface, a method of maintaining constant protein concentration at the membrane surface was introduced.
Delivery of therapeutic mAbs by subcutaneous administration is convenient for patients, but a high concentration formulation must be used in order to keep the injection volume low. With high concentration ultrafiltration processes, solutions often become very viscous and this limits the final concentration. Recent work has demonstrated use of elevated temperature as an approach to safely manage the rheological properties of high concentration formulations, as well as to enhance overall mass transfer.
Processing at the higher temperature did not impact the product quality. An important process development aspect of a final UFDF formulation step includes the final sterile filtration or bulk filtration of the product. In general, sterile filtration is an important concern for all intermediate purification pools, but considerably more so at the end of the process where the highest protein concentrations are present and greatest value has been imparted onto the product.
Proper scale-up techniques using equipment representative to manufacturing is critical. Ultrafiltration has the inherent nature of high throughput and low resolution. Recent studies have shown that ultrafiltration systems can be used for the separation of proteins of similar and moderately different sizes based on differences in protein charge.
The emerging technique of high performance tangential flow filtration HPTFF is a two-dimensional unit operation in which both size and charge differences are utilized for the purpose of purification and separation.
Charged proteins in electrolyte solutions are surrounded by a diffuse ion cloud or electrical double layer due to electrostatic interactions with the counter-ions and co-ions.
The hydrodynamic size increases with charges and decreases with ionic strength since higher conductivities shield charges on proteins. In addition, membrane charge could further enhance the resolution between charged and neutral molecules. A positively charged membrane could provide much greater retention of a positively charged protein than a negatively charged or neutral membrane. In HPTFF, membrane pore size distribution affects selectivity by altering solute sieving coefficients and filtrate flow distribution.
Eliminating large defects and controlling the pore size distribution can significantly improve the performance of the HPTFF membrane. As in conventional ultrafiltration processes, the successful implementation of HPTFF processes relies on optimizing operational fluxes, transmembrane pressure, module and flow path design to enhance selectivity and reduce protein fouling on membrane surfaces to reach an optimal performance.
One example resulted in the reduction of Chinese hamster ovary proteins CHOP from ppm parts per million, i. Mammalian cells used in the manufacture of mAbs and other therapeutic recombinant proteins produce endogenous retroviruses and are occasionally infected with adventitious viruses during processing. This typically translates to approximately 12—18 log 10 clearance of endogenous retroviruses and 6 log 10 clearance for adventitious viruses.
Virus filtration can provide a size-based viral clearance mechanism that complements other virus clearance steps. Since the presence of only a small number of abnormally large pores will permit excessive virus leakage, virus filters must be manufactured so as to eliminate these large porous defects.
Current virus-retentive filters are ultrafilters or microfilters with very small pores. According to the size distribution of viruses that are removed, virus filters can be categorized into retrovirus filters and parvovirus filters.
Commercially available virus filters, their construction materials and virus retention are summarized in Table 1. Parvoviruses have a diameter of 18—26 nm, and a typical mAb has a hydrodynamic diameter of 8—12 nm.
To achieve efficient retention of the viruses and passage of the mAb, parvovirus filters are required to have a very narrow pore size distribution. During virus filtration, fouling is typically caused by the presence of protein aggregate, DNA, partially denatured product and other debris. Fouling can be significantly reduced using appropriate prefilters, and prefiltration of the feed solution can have a dramatic impact on virus filtration performance.
Prefiltration through adsorptive depth filters and charged membranes have been observed to provide significant protection to the virus filters. The lack of any significant change suggests the levels of HMWS as parvovirus filter foulants in the feedstream are low. Viresolve Pro filter throughput improvement through coupling Mustang S membrane as a pre-filter. Different lots of viral filters and feed solutions used in viral filtration processes can give different filtration throughputs, whereas manufacturing variability of filter membrane permeability can be controlled with an acceptable range.
The impurity content in feed streams from different manufacturing lots is often variable and freshness and storage conditions for feed solutions can also significantly affect throughput. This can be more pronounced if an in-process product pool from an earlier purification step is used as feed solution for viral filtration.
The difference of filtration throughput of an in-process pool on a VPro viral filter is shown in Figure 9. The lower throughput of the third lot was due to slightly higher percentage of HMW impurities present in the pool.
Filtration throughput variation of a mAb in-process purification pool on Viresolve Pro filter. It results a lower filtration throughput with the Lot 3 in-process pool. As a routine practice, virus filters are integrity tested pre- and post-use to ensure that the filter achieves the required level of performance. Both the bubble point test and the forward flow test evaluate a wet membrane as a barrier to the free flow of a gas.
The gold particle test, the post-use integrity test used with Planova Asahi-Kasei filters, is a destructive integrity test. Generally, nondestructive tests are preferred for end-users due to the option of retesting filter integrity if the initial test fails. In practice, if the post-use integrity tests and retests fail, refiltration is a common practice for virus filtration steps.
The use of a platform for cell culture and purification processes allows rapid development of a suitable process for generation of early phase clinical supplies. A platform process incorporates experience gained from working with a number of antibodies and thus includes defined purification steps and resins or membrane with operating conditions chosen to work with the majority of new products.
Table 2 provides a reference list for selecting primary recovery and purification unit operations that can be used to build a platform process. Platforms are designed to allow rapid development of a process generating a final product with the purity required for use in humans with use of minimal resources. Centrifugation and filtration parameters are chosen that can cover the expected range conservatively to maximize the probability of success for this step.
The choice of chromatography resins may be limited or fixed in a platform process. Likewise, buffer compositions for wash and elution buffers and even the final formulation buffer, may be predefined or only require optimization within a defined range. In an ideal case, downstream process development for a new molecule entails verifying process fit, establishing dynamic binding capacities and loading parameters for the chromatography steps, defining the pH and conductivity of the buffers involved and verifying impurity clearance and product quality.
In practice, this is often successful, but pipelines may include molecules that aren't fully compatible with the platform for one or more steps, and in those instances additional development will be required. Downstream processing practices and platform technologies will need to advance to keep pace with increases in cell culture titers, increasing regulatory requirements, changes in the market and the need to control costs.
In the near term, downstream processes must be adapted to cope with higher titer cell culture processes in existing plant infrastructure. Future plants will need to take into account current and anticipated advances in expression systems, cell culture and downstream processes. An excellent perspective on future directions in mAb purification has recently been published.
As titers have increased, the need to recover an entire batch using existing infrastructure has presented new challenges. Constraints include working with existing chromatography column dimensions, buffer and hold tank volumes and skid capabilities in the manufacturing plant.
The use of high capacity resins can allow the use of existing chromatography columns to process a greater mass of material. Opportunities for minimizing pool volumes to use existing hold tanks include optimizing elution conditions and taking a close look at step order and load conditioning requirements.
The use of inline dilution or conditioning to achieve the target pH, conductivity and buffer composition may be employed. Likewise, using inline dilution and buffer concentrates can allow existing buffer tanks to be employed.
Advances in purification technology that may be considered for incorporation in future recovery processes include use of high-flow high capacity chromatography resins, non-chromatographic processes such as membrane adsorbers, precipitation, flocculation and crystallization, as well as streamlined processes and methods development. Another possible development in mAb production is the possibility of using expression systems other than CHO, which is the predominant cell line for expressing mAbs.
One reason is their capacity for glycosylation, which is critical for antibodies that require effector function to be efficacious. NS0 cells are used to a lesser extent. Engineered yeast cells are capable of producing antibodies with desired glycosylation and may have advantages in both cell line development and engineering the expression of particular glycoforms. Lastly, transgenic animals and plants have been extensively explored as alternatives to mammalian cell culture.
Recovery of mAbs from different expression systems can be quite variable, e. Initial harvest from transgenic plants may involve homogenization and the removal of a large quantity of solids, oils and other substances; in the case of transgenic expression in milk, removal of milk fat and casein is necessary.
Even when the product may be secreted, e. Due to the long timelines associated with transgenic expression, the current high titers being achieved in CHO and the fact that the capacity crunch in biologics manufacturing has eased, at present there is less of a drive towards transgenic expression. Expression systems such as yeast Pichia pastoris and microbes E. Flocculation is a method that has been widely used in other fields and is gathering interest in the recovery of proteins from mammalian cell culture.
One of its most tangible advantages is the reduction of membrane surface area in harvest depth filtration. It is also possible that flocculation could provide substantial impurity clearance, opening the door to alternative or streamlined processes downstream. Since Protein A chromatography is the most expensive chromatographic step in the downstream process, lower cost alternatives are being sought.
It is possible to achieve the desired clearance of host cell proteins using only ion exchange and hydrophobic interaction chromatography, 56 or even cation and anion exchange chromatography followed by HPTFF. Crystallization is a method that has been used for protein purification since the s. It is possible that an entirely chromatography-free process that can provide adequate impurity clearance might be available at some point.
One factor that needs to be considered is viral clearance—replacing chromatographic steps that provide a high degree of viral clearance with steps that may or may not provide a similar degree of viral clearance may entail the use of new modes of viral filtration and inactivation.
Newer alternatives being developed include inactivating viruses with UV or broad spectrum light, — gamma irradiation, , heat , and caprylic acid. Streamlined processes with fewer conventional steps are also gaining prominence.
As a counterpoint to the perceived need for alternatives to chromatography at high titers, Kelley also concludes that it is entirely feasible for a single plant to produce 10 tons of a mAb per year using conventional methods and highlights potential issues that may arise from the adoption of non-conventional methods.
Over the short term, the primary changes compared to today are likely to be in the adoption of chromatography resins with improved properties and the use of HTS for optimizing chromatographic operations. Time will tell if Q membrane adsorbers gain a significant foothold in replacing a conventional anion exchange chromatography step. The adoption of non-chromatographic recovery schemes will require additional data on viral clearance, ability to be applied to a wide range of antibodies, impact on development time and economic benefit and likely some plant redesign as well.
Previously published online: www. National Center for Biotechnology Information , U. Journal List MAbs v. Author information Article notes Copyright and License information Disclaimer. Corresponding author. Correspondence to: Hui F.
Liu; E-mail: moc. Received Apr 23; Accepted Jun This article has been cited by other articles in PMC. Abstract Hundreds of therapeutic monoclonal antibodies mAbs are currently in development, and many companies have multiple antibodies in their pipelines. Key words: monoclonal antibody, recovery, purification, chromatography, membrane, filtration, platform process.
Introduction Hundreds of monoclonal antibodies mAbs are either currently on the market or under development. Open in a separate window. Figure 1. Primary Recovery Process The first unit operation in a downstream process is the removal of cells and cell debris from the culture broth and clarification of the cell culture supernatant that contains the antibody product. Figure 2. Depth filtration.
Depth filters are usually given a nominal pore-size rating, but these filters are far from absolute with regard to their particle size retention For harvesting applications, depth filters can be applied directly with the whole cell broth or in conjunction with a primary separator such as TFF or centrifugation.
Figure 3. Chromatographic Processes For more than a decade the workhorse of commercial mAb purification has been Protein A chromatography, followed by two or three subsequent chromatographic polishing steps. Affinity chromatography. Ion exchange chromatography. Anion exchange chromatography. Figure 4. Cation exchange chromatography.
Figure 5. Figure 6. Hydrophobic interaction chromatography. Hydrophobic charge induction chromatography. Ceramic hydroxyapatite chromatography.
Multimodal chromatography. Use of high throughput screening to optimize separations. Membrane and Filtration Technology Membrane and filtration technologies are used extensively in the isolation and purification of mAb and other recombinant DNA products, from the initial clarification of cell culture broth to the final sterile filtration of purified bulk solutions.
Membrane chromatography. High performance tangential flow filtration. Virus filtration. Figure 7. Figure 8. Figure 9. Platform Purification Processes The use of a platform for cell culture and purification processes allows rapid development of a suitable process for generation of early phase clinical supplies. Table 2 Unit operations that can be used in mAb purification process. High cost. Multiple cycles on smaller column may reduce cost and risk.
Reduce process-related impurities and product-related impurities Enables building a process without protein A affinity chromatography BE Mab binding capacity, cost or plant constraints may require multi-cycles to processing a single batch.
Dirty feed streams may limit regeneration and reuse. May require pre-dilution of the load pool. Mab binding capacity constraint in BE mode may require multiple cycles to process a single batch. Higher impurity level in load can limit throughput and increase process cost 2 nd chromatography step low 3 rd chromatography step medium Hydrophobic interaction chromatography Resin Used as a polishing step to remove unwanted product variants and aggregates, viruses, residual HCP, DNA and other unwanted impurities BE, FT Mab binding capacity, cost or manufacturing plant constraints may require multiple cycles to process a single batch.
Not compatible with citrate salt and EDTA chelating agent. Resin lifetime needs to be evaluated. Limited Mab binding capacity 1 st or 2 nd or 3 rd chromatography step low Viral filtration Membrane Removes a broad size of viruses depending on pore size of filter FT High cost.
Often prone to fouling, limiting throughput After 2 nd or 3 rd chromatography step high TFF—Microfiltration Membrane Used as a primary cell culture harvest step Size exclusion Prone to fouling with cell culture fluid containing high solid contents Prone to higher shear and cell lysis Harvest step medium TFF—Ultrafiltration Membrane Concentrate and buffer exchange of intermediate pools and purified bulk Size exclusion Diligent system design required for complete buffer exchange, high product recovery and high concentration formulation Various intermediate pools and final formulation high TFF—High performance TFF Membrane Two-dimensional unit operation in which both size and charge differences are utilized for the purpose of purification and separation Size exclusion Highly complex.
Not commercially available yet Used for both purification and concentration and buffer exchange low Sterile filtration Membrane Bioburden reduction, particulate removal. Effective in providing a sterile barrier for intermediate hold steps or final storage Size exclusion Typically not suitable for handling large particulate loads.
Prone to pore plugging. All points in the purification process High. Perspectives on the Future Downstream processing practices and platform technologies will need to advance to keep pace with increases in cell culture titers, increasing regulatory requirements, changes in the market and the need to control costs.
Footnotes Previously published online: www. References 1. Development trends for monoclonal antibody cancer therapeutics. Nat Rev Drug Discov. Industrial purification of pharmaceutical antibodies: development, operation and validation of chromatography processes. Biotechnol Genet Eng Rev. Antibody production. Adv Drug Delivery Rev. Assessment of a disc stack centrifuge for use in mammalian cell separation.
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Impact of cell density and viability on primary clarification of mammalian cell broth. Bioprocess Int. Laird M. Schmidt M. In: Charge-modified filter media. Filtration in the biopharmaceutical industry. Retrovirus and parvovirus clearance from an affinity column product using adsorptive depth filtration.
BioPharm Int. Gerba CP, Hou K. Endotoxin removal by charge-modified filters. Appl Environ Microbiol. Capture of latex beads, bacteria, endotoxin and viruses by charge-modified filters. Evaluation of depth filtration to remove prion challenge from an immunoglobulin preparation. Vox Sang. The role of charge in the retention of DNA by charged cellulose-based depth filters.
Characterisation of a generic monoclonal antibody harvesting system for adsorption of DNA by depth filters and various membranes. Exploitation of the adsorptive properties of depth filters for host cell protein removal during monoclonal antibody purification. Biotechnology Progress. Induced flocculation of animal cells in suspension culture. Selective flocculation of cellular contaminants from soluble proteins using polyethyleneimine: a study of several organisms and polymer molecular weights.
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Instead, enhanced binding of the UM5. Maximum neutralization was ob- UM8. Clones which showed no neutraliza- UM8. In the reciprocal assays, enhanced binding was tion of the avirulent strain of SFV also did not neutralize the also observed Fig. The CBA data indicated that virulent strain. Neutralization titers were in each case higher each anti-E1-specific MA recognized a separate Ela to Elf for the virulent strain than for the avirulent strain.
The antigenic determinant six in total Table 2. In vivo protection was not concordant with in MAs recognized the same antigenic determinant. Two exam- vitro neutralization plaque reduction. For the E1l determi- ples are shown in Fig. In reversed assays, similar results were obtained. Four MAs were specific for there was no plaque reduction at all.
MA UM8. CBAs see legend to Fig. We found one more antigenic determinant on Fig. The number of epitopes on El against vesicular stomatitis virus 15 and La Crosse virus involved in neutralization of SFV exceeded by two the 11 and might be related to an advantageous allosteric known number found on El of Sindbis virus 23 and alteration of the antigenic glycoprotein after binding with the Venezuelan equine encephalomyelitis virus Another explanation of this enhancement phe- immunization procedure.
Mice were immunized with live nomenon might be the formation of a multicomponent com- avirulent SFV without addition of an adjuvant and were plex 6. This is in agreement with other data for MAs against could be distinguished. Each of the anti-E1 MAs was unique Sindbis virus 23 and Venezuelan equine encephalomyelitis when tested for a number of biological parameters like virus The MA UM8.
This might be due to sequence for both alphaviruses. Analysis of biochemical parameters of the MAs coupling. These MAs will be used in future search project no. Boere, W. Benaissa-Trouw, M. Harmsen, C. None of KraaiJeveld, and H. Neutralizing and non-neutral- our MAs exhibited both functions neutralization and HAI , izing monoclonal antibodies to the E2 glycoprotein of Semliki which is in contrast to the findings of Chanas et al.
Sindbis virus. On the other hand, three MAs UM8. Bradish, C. Allner, and H. The virulence UM8. Carter, M. Wilicocks, S. Loffler, and V. Ter Meulen. Although virus neutralization might be related Relationships between monoclonal antibody-binding sites to IgG isotypes none of our IgGl isotypes showed protec- on the measles virus haemagglutinin. Chanas, A.
Gould, J. Clegg, and M. Monoclonal antibodies to Sindbis virus glycoprotein El MA. Our results Fig. Clarke, D. Techniques for hemaggluti- tion. Ehrlich, P. Moyle, Z. Moustafa, and R. The two MAs which were the most effective in in Mixing two monoclonal antibodies yields enhanced affini- vivo protection UM8.
Ey, P. Prowse, and C. Immunochemistry Fazekas de St. Groth, S. Production during the purification procedure by the cesium chloride of monoclonal antibodies: strategy and tactics. Garoff, H. Kondor-Koch, and H. Structure and assembly of alphaviruses. Schmaljohn et al. Henderson, B. Metselaar, G. Kirya, and G. They Investigations into yellow fever virus and other arbovi- found five distinct epitopes on E1 and only one epitope on ruses in the northern regions of Kenya.
The E1 glycoproteins of Kingsford, L. Ishizawa, and D. Biological protective epitopes on the glycoproteins of Venezuelan equine activities of monoclonal antibodies reactive with antigenic sites encephalomyelitis virus by passive transfer of monoclonal anti- mapped on the G, glycoprotein of La Crosse virus. Virology bodies. Nakane, P. Peroxidase-labeled anti- Kohler, G. Howe, and C. Fusion between body: a new method of conjugation.
Rabinowitz, S. Host defenses during Kraaijeveld, C. Harmsen, and B. Khader Boutahar- primary Venezuelan equine encephalomyelitis virus infection in Trouw. Cellular immunity against Semliki Forest virus in mice. Passive transfer of protection with immune serum and mice. Khader Boutahar- Rector, J. Lausch, and J. Identification Trouw. Delayed-type hypersensitivity against Semliki of infected cell-specific monoclonal antibodies and their role in Forest virus in mice.
Lefrancois, L.
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