Development of a vaccination scheme to stimulate both B and T cell dependent heterosubtypic protection against influenza A virus

Abstract

Introduction: The frequent transmission of animal influenza viruses to human poses a serious threat to public health. However, the current vaccine strategy only provides a very limited protection, which necessitates the development of novel vaccine approaches. To achieve a better heterosubtypic protection against influenza, we explore the use of sequential vaccination by using different viral antigens in different orders. Method: The vaccine scheme used in this study included inactivated H1N1 virus(08), inactivated H5N1 virus(09) and a vaccinia virus-based H5N1 virus(V). BALB/c mice were sequentially immunized intramuscularly 3 weeks apart, with 2 doses of H1N1 vaccines followed by 2 doses of inactivated H5N1(Group 08-09) or vaccinia virus-based live-attenuated H5N1(Group 08-V) vaccines. After vaccination, a lethal dose of heterosubtypic influenza virus(H1N1/PR/8 or H3N2/HK/68,10LD50) was given. Morbidity and weight loss were monitored daily. Lung viral loads and total protein concentration in bronchoalveolar lavage(BAL) of infected mice were measured using TCID50 and Bicinchoninic Acid(BCA) assay respectively. Influenza virus-IgG antibody levels before and after the challenge were studied by ELISA and neutralization assay. T cell recall responses were determined by intracellular cytokine staining(ICS) assay. Results: Sequential vaccinations were 80-100% protective against heterologous influenza virus. However, different vaccination regimes resulted in different recovery rates and vaccine-induced immune profiles. Anti-NP antibody level of Group 08-V was found to be higher than the one of Group 08-09 before challenge. Furthermore, Tc1 CD8+ T cells recalled to the spleen played a dominant role both before and after challenge, along with significantly higher IFN-γ and TNF-α generation in “08V”(P<0.05). At 7-day post-infection, lung viral titer and BAL protein level of Group 08-V were significantly lower than those of Group 08-09(P<0.01). Significance: Sequential vaccination using viral antigens of different subtypes can induce heterosubtypic protection. The use of vaccinia-based live-attenuated vaccine in the studied sequential vaccination can induce heterosubtypic protections that are better that those induced by inactivated vaccines.