January 15, 2008 (Vol. 28, No. 2)
ReadyToProcess™ Products Can Play a Key Role in This Increasingly Important Therapeutic Area
All steps in vaccine production need to be robust, reproducible, and safe, as pathogens or pathogenic antigens are frequently involved. There are currently many products ranging from advanced analytical systems to modular, ready-to-use products to help vaccine manufacturers achieve those objectives. Some of the products from GE Healthcare (www.gehealthcare.com) that optimize vaccine development and manufacture are reviewed in this article.
Viral Production: Eggs or Cells?
Cell-based viral production has several advantages over the use of eggs. Cells can be frozen and quickly expanded, capacity can be increased in a modular fashion by adding fermentation equipment, and processing takes place in closed systems. Cell-based vaccines are also suitable for people who are allergic to eggs and thus unable to receive currently licensed vaccines. In addition, egg-based production cannot easily be scaled up during an emergency.
Cross-linked dextran beads such as Cytodex™ microcarriers from GE Healthcare provide an extended surface and stable environment for optimal cell growth. Virus titers obtained from adherent cell lines are frequently superior to those obtained from cells in suspension.
Process Development Strategies for Separation and Chromatography
Pressure to increase throughput of candidates in development at ever lower operating costs has created demand for statistical and high-throughput tools. In process development for chromatography, this approach is used to select resins and to optimize purification; about 400 conditions for two chromatographic steps may be tested in one day. These conditions have been confirmed in laboratory-scale columns.
Bottlenecks in process development may be eliminated by using tried-and-true technology platforms and a standard set of conditions and methods applied to all molecules of a given class.
Membrane separations can improve the efficacy of bioprocessing by concentrating and washing the feedstream prior to chromatography. The more open porosity rating of hollow-fiber technology, for example, enables the use of ultrafiltration membranes in the virus purification process. Their open-flow path design reduces potentially harmful shear forces; viral recovery rates are thus improved.
In cross-flow setups, in contrast to normal flow filtration, the membrane surface is continually swept by the circulating feedstream, minimizing blinding and allowing units to be cleaned and re-used. As the feedstream circulates, retentate continues to circulate, while permeate is transported through the membrane.
Viruses, viral vectors, and plasmids are considerably larger than most other biopharmaceuticals and cannot easily enter the pores of microporous resins. Thus, the means to create larger surface areas, e.g., by reducing the bead size of chromatography media, should be sought.
Adsorptive technologies such as, affinity chromatography, can be used to purify adeno-associated virus or influenza virus for clinical trials, thereby replacing previously used density gradient centrifugation. Anion exchange media like Capto™ ViralQ can be used to polish viruses such as adenovirus. Group separation on agarose-based gels is a commonly used technology to separate viruses from host-cell protein and small DNA molecules.
Label-free interaction analysis based on surface plasmon resonance rapidly provides kinetic data, i.e., association and dissociation rates, on interactions to support critical decisions at every step of the vaccine development and manufacturing process. Binding events are monitored in real-time, providing insight into protein function beyond any that can be inferred from end point assays such as ELISA.
Biacore systems from GE Healthcare have been applied, for example, to show how the kinetic profiles of antibodies induced by a potential vaccine change throughout the response period. By measuring both association and dissociation rates, it is possible to differentiate between potential interaction partners, which despite similar affinities, may have radically different kinetic profiles.
Although concerns have been raised over the necessity to immobilize one interaction partner on a sensor surface, it should be noted that immobilization occurs on chemically active groups at the ends of long flexible carbohydrate polymers so that the tethered interaction partner retains its mobility.
Plug-and-play products may help address the need for operational efficiencies in the industry. Self contained, fast to implement process setups extensively based on disposable solutions are already in reach for most unit operations. Tanks can be replaced with bags, hard piping can be replaced with flexible tubing, disposable pump heads and detection cells can be used, and both cleaning and validation efforts can be reduced.
A significant challenge resides in the integration of such unit operations and in finding the right connectivity among, what is today, still a rather uncoordinated offering. ReadyToProcess™ products include both complete solutions engineered for flexibility as well as single-use devices and components. With minimal installation times and mobile hardware, the flexible and modular nature of ReadyToProcess enables a quick capacity deployment in the event of an emergency such as a pandemic outbreak.
This suite of products embraces single-use cell culture technology and includes Wave bioreactor systems and mixers, fluid handling, filtration, and chromatography solutions. ReadyToProcess filters include cleanroom-to-cleanroom, single-use cartridges and assemblies for both aseptic cross flow and sterile normal flow filtration (NFF) operations.
ReadyToProcess NFF devices are produced according to the medical devices standard (ISO 13485), provided sterile and gamma irradiated. Both filtration solutions come fully certified, either as stand-alone units or as part of full assemblies.
ReadyToProcess chromatography products include cleanroom-to-cleanroom columns, available in several sizes from 2.5 L to 20 L bed volumes. This range of modular columns is packed with resins designed to meet the demands of modern chromatography. The portfolio currently includes high-flow Capto™ Q (strong anion exchanger), Capto S (strong cation exchanger), or Phenyl Sepharose™ 6 Fast Flow for hydrophobic interaction chromatography.
These columns are fully certified and tested high-performance modules, available for developmental work and clinical-scale manufacturing, enabling smooth scale up, rapid project changes, free from the risk of cross-contamination and packing failures.
Although quality suppliers with a broad range of products and services can help vaccine producers minimize their dependency on alternative providers for manufacturing processes, concern is occasionally raised about the capacity of contractors to maintain services in times of stress, such as a pandemic. Vaccine producers should thus perform rigorous audits of supplier quality systems as well as contingency plans.
Pitfalls associated with dependence on external vendors under stressed circumstances may include delays in validation, delays in the start-up of manufacturing facilities especially when several outside contractors are involved, and a failure to secure vaccine production. In most cases, the worst possible outcome can be avoided by reasonable forward planning and common sense such as seeking reliable and qualified advice and evaluating options for alternative supplies before a crisis arises.
Many opportunities to optimize vaccine development and manufacture can be found in the analytical and processing technologies employed by commercial producers of other types of biopharmaceuticals. Industrial suppliers of these technologies also possess a considerable body of practical and regulatory know-how, from which vaccine manufacturers can derive much support. This overall expertise should help meet the overriding goals of safe and economic production capable of meeting the diverse worldwide market needs for vaccine products.
Silke Fetzer is head of product
management cell culture & vaccine operational marketing at GE Healthcare. Web: www.gehealthcare.com.