Gamma-irradiated influenza A virus provides adjuvant activity to a co-administered poorly immunogenic SFV vaccine in mice

Many currently available inactivated vaccines require "adjuvants" to maximize the protective immune responses generated against the antigens of interest. Recent studies in mice with gamma-irradiated influenza A virus (gamma-FLU) have shown its superior efficacy compared to other forms of inactivated FLU vaccines and its ability to induce both potent interferon type-I (IFN-I) responses and the IFN-I-associated partial lymphocyte activation. Commonly, IFN-I responses induced by adjuvants, combined in vaccine preparations, have been shown to effectively enhance the immunogenicity of the antigens of interest.Therefore, we investigated the potential adjuvant activity of gamma-FLU and the possible effect on antibody responses against co-administrated antigens, using gamma-irradiated Semliki Forest virus (gamma-SFV) as the experimental vaccine in mice. Our data show that co-vaccination with gamma-FLU and gamma-SFV resulted in enhanced SFV-specific antibody responses in terms of increased titers by sixfold and greater neutralization efficacy, when compared to vaccination with gamma-SFV alone. This study provides promising evidence related to the possible use of gamma-FLU as an adjuvant to poorly immunogenic vaccines without compromising the vaccine efficacy of gamma-FLU.