Instability of WT AAV2 genome and AAV promoter activities in the Baculovirus/Sf9 cells system. Spodoptera frugiperda

The human Adeno-Associated Virus serotype 2 (WT AAV2) is a common non-pathological virus and its recombinant form (rAAV) is widely used as gene therapy vector. However, it has been shown that WT AAV2 and recombinant AAV display significantly different characteristics, especially regarding infection rate, with a near perfect infectivity and better encapsidation rate of WT AAV2. Even though rAAVs are routinely produced in the Baculovirus/Sf9 cell system, WT AAV2 has never been produced in this context. To understand the infectivity and encapsidation rate differences between WT AAV2 and rAAV, we tried to produce WT AAV2 in baculovirus/Sf9 cells system hypothesizing that the WT AAV2 may be considered as a normal recombinant AAV transgene. Through our attempts to produce WT AAV2 in Baculovirus/Sf9, we found that WT AAV2 p5 promoter, which controls the expression of large Rep proteins in mammalian cells, was active in this system. p5 promoter activity in the baculovirus/Sf9 cell system led to the expression of Rep78 that finally excises WT AAV2 genome from the baculovirus genome during the earliest phase of baculovirus stock production. The p5 promoter expression kinetics and the specific strand RNA-Seq analysis of the WT AAV2, rAAV Rep2/Cap2 cassettes in the baculovirus context was performed. We demonstrate that the WT AAV2 native promoters, p5, p19 and p40 are all active and lead to the expression of different proteins and peptides. In addition, this study demonstrates that the baculovirus brings at least some of the helper functions needed in the AAV replication/life cycle. Overall design: RNA-Seq analysis of the expression of WT AAV2, rAAV Rep2/Cap2 cassettes in the baculovirus system