Production of Recombinant Adeno-Associated Viral Vectors Using a Baculovirus/Insect Cell Suspension Culture System: From Shake Flasks to a 20-L Bioreactor

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Abstract
Production of recombinant adeno‐associated viral vectors using a baculovirus/insect cell system at various scales is presented. Shake flask studies were conducted to assess conditions to be used in bioreactors. Two insect cell lines, Trichoplusia ni (H5) and Spodoptera frugiperda (Sf9), were compared for their ability to produce rAAV‐2 after infection with recombinant baculoviruses coding for the essential components of the vector. The effect of varying the ratio between individual baculoviruses and the effect of the overall multiplicity of infection (MOI), as well as the cell density at infection, were also examined. Infectious rAAV‐2 particles were proportionally produced when increasing the individual MOI of BacRep virus up to 1.6. When equal amounts of each virus were used, a leveling effect occurred beyond an overall MOI of 5 and a maximum titer was obtained. Increasing the cell density at infection resulted in higher yields when infecting the cells in fresh medium; however, for the production of bioactive particles, an optimal peak cell density of ∼1 × 106 cells/mL was observed without medium exchange. Infection in 3‐ and 20‐L bioreactors was done at an overall MOI of 5 with a ratio of the three baculoviruses equal to 1:1:1. Under these conditions and infecting the cells in fresh medium, a total of ∼2.2 × 1012 infectious viral particles (bioactive particles) or 2.6 × 1015 viral particles were produced in a 3‐L bioreactor. Without replacing the medium at infection, similar titers were produced in 20 L. Our data demonstrates the feasibility of rAAV‐2 production by BEVS at various scales in bioreactors and indicates that further optimization is required for production at high cell densities.