Development and optimization of an adenovirus production process

Adenoviral vectors have a number of advantages such as their ability to infect post-mitotic tissues. They are produced at high titers and are currently used in 28% of clinical protocols targeting mainly cancer diseases through different strategies. The major disadvantages of the first generation of recombinant adenoviruses are addressed by developing new recombinant adenovirus vectors with improved capacity and safety and reduced inflammatory response. To meet increasing needs of adenovirus vectors for gene therapy programs, parallel development of efficient, scalable and reproducible production processes is required. HEK-293 complementing cell line physiology, metabolism and viral infection kinetics were studied at small scale to identify optimal culture conditions. Batch, fed-batch and perfusion culture modes were evaluated. Development of new monitoring tools (in situ GFP probe) and quantification techniques (HPLC determination of total viral particles) contributed to acceleration of process development. On-line monitoring of physiological parameters such as respiration and biovolume of the culture allowed real-time supervision and control of critical phases of the process. Use of column chromatographic steps instead of CsCl gradient purification greatly eased process scale-up. The implementation of the findings at large scale led to the development of an optimized and robust integrated process for adenovirus production using HEK-293 cells cultured in suspension and serum-free medium. The two-step column-chromatography purification was optimized targeting compliance with clinical material specifications. The complete process is routinely operated at a 20-L scale and has been scaled-up to 100 L. Scale-up of adenoviral vector production in suspension and serum-free medium, and purification according to regulatory requirements, are achievable. To overcome metabolic limitations at high cell densities, use of perfusion mode with low-shear cell retention devices is now a common trend in adenovirus manufacturing. Further process improvements will rely on better understanding of the mechanisms of virus replication and maturation in complementing host cells.