Manufacturing of recombinant adeno-associated viruses using mammalian expression platforms

Manufacturing practices for recombinant adeno-associated viruses (AAV) have improved in the last decade through the development of new platforms in conjunction with better production and purification methods. In this review, we discuss the advantages and limitations of the most popular systems and methods employed with mammalian cell platforms. Methods and systems such as transient transfection, packaging and producer cells and adenovirus and herpes simplex virus are described. In terms of best production yields, they are comparable with about 10⁴ -10⁵ vector genomes produced per cell but transient transfection of HEK293 cells is by far the most commonly used. For small-scale productions, AAV can be directly purified from the producing cell lysate by ultracentrifugation on a CsCl or iodixanol-step gradient whereas large-scale purification requires a combination of multiple steps. Micro/macrofiltration (i.e. including tangential flow filtration and/or dead-end filtration) and chromatography based-methods are used for large-scale purification. Purified AAV products must then be quantified and characterized to ensure quality. Recent purification methods and current analytical techniques are reviewed here. Finally, AAV technology is very promising, but manufacturing improvements are still required to meet the needs of affordable, safe and effective AAV vectors essential for licensing of gene therapy clinical protocols.