Immunogenicity of an adeno-vector vaccine expressing the F protein of a respiratory syncytial virus manufactured from serum-free suspension culture

We have developed an efficient cell culture process to scale up the production of a recombinant adenovirus that expresses the membrane-trunked fusion protein of respiratory syncytial virus (RSV; Ad-F0ΔTM). Adherent cells of human embryonic kidney (HEK) 293-derived cell, 293A, which supports the production of E1/E3-deleted Ad-F0ΔTM when cultured in the presence of fetal bovine serum (FBS), were adapted to suspension growth under serum-free medium. In doing so, we studied the immunogenicity of Ad-F0ΔTM_sus, which propagated in a bioreactor that was cultured with serum-free suspension of 293A, in comparison with Ad-F0ΔTM_adh, which was produced from parental 293A cells that were adherently cultured in medium containing FBS. The size and morphology of Ad-F0ΔTM_sus and Ad-F0ΔTM_adh virions were identical upon inspection with electron microscopy. The results showed that anti-F IgG and RSV-neutralizing titer were raised in the serum of both mice that were intranasally immunized twice with Ad-F0ΔTM_sus or Ad-F0ΔTM_adh at two-week injection intervals. Furthermore, the immune responses persisted for six months after vaccination. Activation of F protein-specific CD8⁺ T cell's epitope associated IFN-γ and IL-4 was induced in both Ad-F0ΔTM_sus- and Ad-F0ΔTM_adh, but not in Ad-LacZ_sus, -immunized mouse splenocytes. No vaccine-enhanced lung inflammation, airway mucus occlusion or eosinophils infiltration were observed in Ad-immunized mice followed by RSV challenge; however, these symptoms were observed following immunization with formalin-inactivated RSV vaccine. These results indicate that the safety and potency of Ad-F0ΔTM produced from either adherent cells or suspension and serum-free cells are the same.