Disposables historically have been used in biotechnology processes for the past three decades, initiated with the use of single-use plastic support for cell culture (e.g., vials, shakers, T-flasks, and roller bottles). Another step was made more recently by the implementation of plastic bags into these processes, either used in the process itself or in supportive steps, such as media and buffer preparation and storage.
One of the key trends for biotech manufacturing is the development of disposable bioreactors. This trend was initiated by the introduction of the Wave system. The implementation of this technology was in line with the use of disposable plastic bags. The Wave bag technology quickly captured the interest of the biotech community. These systems mainly are used for cell expansion to replace shake flasks or intermediate small- and pilot-scale bioreactors, simplifying the process. Despite many advantages, this technology presents some limitations for its use as a final production-scale bioreactor, such as scalability, specificity of the agitation, and the bioreactor geometry.
Because of these limitations, an industrial need drove the development of more conventional and scalable disposable bioreactors. One of the first systems introduced on the market was the Single-Use Bioreactor (SUB) from Hyclone. The SUB opened a new range of applications because of its potential use either as seed vessels or as production vessels for cell-based processes.
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Today, single-use bioreactors are used extensively for the production of monoclonal antibodies (MAbs) and recombinant proteins. Based on this market trend, vaccine manufacturers such as GSK Biologicals decided to investigate the potential use of this emerging technology for vaccine manufacturing. The focus of this article will be on the use of disposable bioreactors in the context of viral vaccine production.
Viral Vaccines Specificity
Viral vaccine manufacturing processes present some specific constraints as compared to other biotech products linked to the cell substrate used and to the viral production. These specificities are:
- Multiple cell lines are used for these productions such as VERO, MDCK, MRC5, BHK, and CHO cells, making it more challenging to develop a platform process.
- Cell substrates for viral production often are cell-anchored cell lines, such as VERO cells, requiring the use of micro-carriers for bioreactor process steps.
- Viral production must be handled in the right biosafety containment, i.e., biosafety level 2 or 3 environments.
- Production scales generally are smaller compared to MAb processes (ranging from 500 to 2,000 L).
Main Drivers for Implementing Disposable Bioreactors in Vaccine Production
There are many benefits of using disposable systems in biotech processes. Two of these benefits justify the evaluation of disposable bioreactors for viral production processes.
- Maximizing facility output because of the fast turnover of disposable systems (no clean-in-place and steam-in-place operations in production vessels).
- The reduction of capital investments linked to the reduction and simplification of the facility design and to the reduction of equipment investment.
In addition to these points, other drivers specific to vaccine manufacturing were considered.
- Simplified biosafety level 2 and 3 production areas (because of the smaller footprint, lower ceiling height, and removal of water-for-injection and steam utilities).
- Minimizing the harvest size to reduce the size of purification equipment and suites.
As previously mentioned, generic processes are difficult to define in the context of viral vaccine production. Therefore, a worst-case process that would cover all other company viral vaccine processes was defined. The disposable bioreactor technology selection based on this process will then be recommended as a standard single-use bioreactor platform for viral vaccine applications.
The following set of parameters was used to define the worst-case process:
- animal-free media to decrease shear protection and nutritive support from serum containing formulations
- cell cultures using micro-carriers (at a high concentration) because cells grown in this condition are more sensitive to shear stress compared to suspension cultures
- VERO-adherent cell lines
- medium renewal by sedimentation
- lytic virus.
The combination of these process criteria made this process challenging enough to cover a large range of current and future in-house processes.
Figure 1. Disposable bioreactors from four companies were evaluated
Single-Use Bioreactor Selection
Based on market availability, system maturity, available scale, and mixing systems, four disposable bioreactors were selected (Figure 1).
- Cultibag STR from Sartorius Stedim Biotech
- Nucleo from ATMI—Pierre Guerin
- Hyclone SUB from ThermoFisher
- XDR from Xcellerex.
Criteria for Selection
To evaluate these four disposable bioreactor technologies, several criteria were selected. These criteria can be divided in two sections:
Process criteria such as cell culture and viral production performances, mixing and aeration characteristics, and scale-up predictability.
General criteria such as film type, biosafety, procurement, assurance of supply, and price.
Mixing and aeration performance evaluation remains mandatory to ensure robust scale-up of cell culture processes, especially for adherent cell line applications (microcarrier use). In this study, these performances were evaluated for the four bioreactor technologies that were identified.