Development of an insect cell-based adeno-associated virus packaging cell line employing advanced Rep gene expression control system

The insect cell-based baculovirus expression vector (BEV) sys-tem is a leading platform for scalable production of adeno-associated viruses (AAVs). The previously described One-Bac system consists of an insect packaging cell line harboring the AAV Rep and Cap genes and a BEV carrying the transgene and AAV inverted terminal repeats. Here we describe a new sys-tem where we successfully translated the molecular design of a double AAV Rep expression cassette to inducible plasmid vectors. These optimized plasmid vectors employ non -canoni-cal late promoters and alternative start codons that alleviate promoter-promoter competition. Because too much Rep expression can be toxic to the host cells, tighter regulation of AAV Rep expression is warranted. This has been achieved by adopting alternate baculovirus homologous region enhancers. Inoculation of the resultant stable insect Rep packaging cell line by a recombinant BEV produced high-titer recombinant AAV (rAAV) preparations (1 x 1011 genome copies/mL). Sequential batch reactor experiments indicate that this system is amenable to large-scale AAV production. We generated an insect packaging cell line that employs an optimized Rep gene control system, ensuring stable and appropriate Rep expres-sion. This platform produces potent and high-yield AAV particles and demonstrates potential for scale up.