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Feliza Mirasol is the science editor for BioPharm International.
Downstream process equipment for mAbs manufacturing must be designed to fit technology developments in upstream processes.
Downstream separation and purification remains challenging in the manufacture of monoclonal antibodies (mAb). One way that suppliers are tackling this challenge is through the development of innovative membrane technology. BioPharm International discussed past and current innovations in membrane technology with Gabriel Tkacik, the director of Filtration R&D at MilliporeSigma.
BioPharm: What currently are the key challenges in the downstream separation and purification process for mAbs?
Tkacik: After 20-plus years of a standard manufacturing template for mAbs, we are seeing an evolution towards more intensified processes, which means that current templates can range from standard batch to fully flow-through continuous processing. Fluid streams from intensified processes may be more concentrated than batch streams, which can result in higher viscosity and impact the efficiency of processing. The range of operating conditions and processing times of continuous processes are likely to be different from those of batch processes for which current technologies were designed. Maintaining efficiency while controlling costs under these different processing conditions is a challenge for every operation.
From a device perspective, one clear challenge for many operations is the loss of process fluid in a device, which is referred to as ‘dead’ or ‘hold-up’ volumes. This is especially important for higher concentration fluids, where high holdup volumes have a greater impact on yield and process economics. Another challenge is maintaining the integrity of the material, through connected operations, in a ‘closed’ flowpath. Closed processing offers manufacturers greater flexibility, minimizes changeover cleaning requirements, and reduces the risk of product contamination by limiting microbial ingress.
Considering individual unit operations for separation, reducing impurities and particulates from fluid streams remains a challenge. These can come from the cell culture process or they can be high-molecular-weight aggregated forms of the target protein, which tend to form at higher protein concentrations. As target molecules have been engineered with more complexity, separating the desired molecule from variants that may have been produced in the cell culture process can be challenging.
The limited availability of single-use membrane chromatography technologies currently constrains many manufacturers to traditional resin purification technologies, which require regeneration and sanitization after use. Finding solutions to these different separation and purification challenges should increase flexibility and operational efficiency for all production processes.
BioPharm: Innovations in membrane technology have been one way to tackle these challenges. What are some current examples of innovative membrane technology?
Tkacik: Separation technologies have seen many recent improvements as we have moved away from a one-size-fits-all membrane filter to more specialized membranes for specific operations. For efficient processing of feed streams with higher particulate concentrations, high-area filters have been developed that contain prefilters and sterilizing-grade membranes packed in a single device and are designed to maximize membrane area in a smaller filter footprint than standard filters.
For tangential flow filtration, the challenges of product loss in device dead volume accelerated development of more efficient membranes that enable higher flux processing for a given cross-flow in single-use devices with limited dead volume. These devices result in more consistent, reliable performance. Similarly, processing efficiency of virus retentive membrane filters has been improved by the development of specialized membrane prefilters that operate under specific pH and conductivity conditions to separate protein aggregates from monomers, thus improving filterability.
In terms of biosafety, the focus on risk analysis has highlighted needs of differentiated separation technologies for microorganism retention at different process steps. Where once sterilizing-grade membranes might have been used throughout upstream and downstream processes, specialized virus-retentive membranes have been developed for processing cell culture media to reduce the risk of adventitious virus and more challenging microorganisms contaminating bioreactors and cell-culture processes.
For downstream operations, where many steps are considered ‘low bioburden,’ rather than truly aseptic, membrane filters that offer bioburden reduction rather than sterilizing-grade performance have been developed as a cost-effective alternative to reduce microbial risk.
Major technical advances have been made in purification technologies to meet the desire of manufacturers to move to more flexible single-use templates. Development of single-use membrane technologies, which can be run in flow-through mode or rapidly cycled, offer opportunities to replace traditional resin-based purification operations. These newer membrane technologies offer both flexibility and operational efficiency and increase options for manufacturers.
BioPharm: What challenges does continuous processing pose to the way membranes must be used or how they need to perform?
Tkacik: Continuous processing conditions can be quite different to batch operations and generally are of longer duration, perhaps weeks as compared to hours for typical batch processes. This extended duration heightens the need for tight bioburden control; gamma pre-sterilized devices are needed, as are tools for sterile sampling and collection. The separation and purification technologies should also maintain performance during flow or process interruptions that are likely to occur during long-duration processes. Devices for use in continuous processes should be designed to enable sample collection without compromising the sterility of the fluid flowpath and should be easily integrated into single-use systems. As with many major shifts in technology, continuous processing presents another challenge: should we reconsider how we validate filter performance during these operations?
BioPharm: What objectives or performance criteria should newer membrane technologies strive for?
Tkacik: Newer membrane technologies need to be ready for tomorrow’s processes, which are likely to increase in diversity as manufacturers fit processes to meet the needs of their facility, scale, and the API being produced. Manufacturers are developing processes for more complex and diverse molecules than ever before and need efficient separation and purification for fluid streams of both high and low concentrations, in batch and continuous operations, with closed processing options and flexibility for rapid setup and changeover. These options will ideally reduce risk of product and operator contamination, be easy to use, and be reasonably priced to work in the cost framework of manufacturing operations. For mAb operations, the portfolio of product offerings is extensive, but for novel therapies, there is opportunity for novel or improved membrane technologies to simplify production and increase accessibility to these novel therapies.
BioPharm: In what aspect(s) is current membrane technology still lacking (i.e., where is there still need for improvement)?
Tkacik: For mAb separation and purification technologies, the development of ‘SMART’ membrane technology that could provide real-time processing information and potentially alert operators in the event of excursions would add a level of control not available today. Ideally, data would be automatically collected into the batch records.
For both separation and purification membranes, the availability of more accurate scaling tools that can better predict the sizes or area requirements of the full-scale process would prevent oversizing or under-sizing devices and the resultant product loss or increased risk that would incur.
For novel therapies, there is a real need for innovative meßmbrane technologies to enable efficient processing: viral vector production processes are challenging separations as the vectors themselves are similar in size to the microorganisms they are being separated from. For novel cell therapy and viral vector processes, membranes that can efficiently filter all cell culture media components might add a level of safety assurance to processes with limited options for viral clearance during downstream purification. Purification technologies that could effectively partition the target therapeutic from impurities could streamline production. Understanding the specific needs of these new applications offers suppliers new opportunities for technology development and offers manufacturers the opportunity to work closely with suppliers to design or modify products to meet these needs.
Vol. 32, No. 3
When referring to this article, please cite it as F. Mirasol, “Membrane Technology for Enhancing Separation and Purification,"BioPharm International 32 (3) 2019.