Abstract
With an increasing demand for efficacious, safe, and affordable vaccines for human and animal use, process intensification in cell culture-based viral vaccine production demands advanced process strategies to overcome the limitations of conventional batch cultivations. However, the use of fed-batch, perfusion, or continuous modes to drive processes at high cell density (HCD) and overextended operating times has so far been little explored in large-scale viral vaccine manufacturing. Also, possible reductions in cell-specific virus yields for HCD cultivations have been reported frequently. Taking into account that vaccine production is one of the most heavily regulated industries in the pharmaceutical sector with tough margins to meet, it is understandable that process intensification is being considered by both academia and industry as a next step toward more efficient viral vaccine production processes only recently. Compared to conventional batch processes, fed-batch and perfusion strategies could result in ten to a hundred times higher product yields. Both cultivation strategies can be implemented to achieve cell concentrations exceeding 107 cells/mL or even 108 cells/mL, while keeping low levels of metabolites that potentially inhibit cell growth and virus replication. The trend towards HCD processes is supported by development of GMP-compliant cultivation platforms, i.e., acoustic settlers, hollow fiber bioreactors, and hollow fiber-based perfusion systems including tangential flow filtration (TFF) or alternating tangential flow (ATF) technologies. In this review, these process modes are discussed in detail and compared with conventional batch processes based on productivity indicators such as space-time yield, cell concentration, and product titers. In addition, options for the production of viral vaccines in continuous multi-stage bioreactors such as two- and three-stage systems are addressed. While such systems have shown similar virus titers compared to batch cultivations, keeping high yields for extended production times is still a challenge. Overall, we demonstrate that process intensification of cell culture-based viral vaccine production can be realized by the consequent application of fed-batch, perfusion, and continuous systems with a significant increase in productivity. The potential for even further improvements is high, considering recent developments in establishment of new (designer) cell lines, better characterization of host cell metabolism, advances in media design, and the use of mathematical models as a tool for process optimization and control.
Highlights
Most biologicals produced in animal cell culture are continuously synthesized during the cell proliferation phase
We demonstrate that process intensification of cell culture-based viral vaccine production can be realized by the consequent application of fedbatch, perfusion, and continuous systems with a significant increase in productivity
The production of viral vaccines typically requires a cell growth phase followed by a virus replication phase as most viruses propagate in a complex process that requires the internalization of their genetic material into the host cell, the synthesis of viral RNA/DNA and viral proteins as well as the release of progeny virus particles (Aunins 2003)
Summary
Most biologicals produced in animal cell culture are continuously synthesized during the cell proliferation phase. The production of viral vaccines typically requires a cell growth phase followed by a virus replication phase (both typically operated in batch mode) as most viruses propagate in a complex process that requires the internalization of their genetic material into the host cell, the synthesis of viral RNA/DNA and viral proteins as well as the release of progeny virus particles (Aunins 2003). The main problem with the use of true continuous cultivation strategies in viral vaccine production is, that it is not clear whether vaccines produced would be acceptable for regulatory agencies such as FDA and EMA as several open questions remain to be answered regarding the long-term genetic stability of cell substrates and virus strains (Gallo-Ramirez et al 2015) It has to be investigated in detail, whether undesired viral mutations can accumulate overproduction time that can negatively influence potency and safety of vaccines. As very few studies deal with HCD cultivations or continuous production systems in large-scale virus vaccine manufacturing, mainly, results obtained at laboratory scale will be presented for illustration of process options
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