Induction Of Heterologous Protection By Combined Use Of Sequential Influenza Vaccination Strategy In Balb/c Mouse

Abstract

Background: Influenza remains a most common and significant public health concern worldwide. Annual vaccination is recommended as the most important step against influenza and its potentially serious complications. However, current vaccines leave the public exposed to the emerging influenza viruses from antigenic drift or shift. Therefore, it is a high priority to develop tools that can induce broader immunity to control the escaped divergent viruses. Method: BALB/c mice were treated intramuscularly with 2 or 4 doses of inactivated (seasonal H1N1/A/Brisbane/59/07, pandemic H1N1/A/California/09/2009, and highly pathogenic H5N1/A/VN/1203/04; plus adjuvant) and vaccinia virus-based H5N1 live-attenuated (Wyeth/IL-15/5Flu) vaccines in different combinations (3 weeks interval). Wyeth/IL-15/5Flu is a novel pentavalent vaccine, expressing HA, NA and NP proteins from H5N1/A/Vietnam/1203/2004, M1 and M2 proteins from H5N1/A/CK/Indonesia/PA/2003 virus, and human IL-15 as a molecular adjuvant. 3 weeks post-vaccination, H9N2/Y280 was given intranasally, and weight loss were monitored daily. Lung viral titers were measured by TCID50 assay at day 3. T cell recall responses from BAL at day 7 were determined by intracellular cytokine staining assay. Protective NP-specific Ab measurement in sera was conducted using ELISA at day 7. Results: All studied sequential 4-dose vaccinations could induce higher degrees of heterosubtypic immune response in mice. Significantly different kinetics in regaining weight was seen (P<0.01). Furthermore, the lung viral load represented a faster clearance of virus after challenge (P<0.01). Meanwhile, recovery was partially associated with higher CD8+ T cell responses in the BAL (IFN-γ and TNF-α, P<0.05) and higher levels of NP-specific IgG1 Ab in sera, which depended on vaccination regimens. Conclusion: These vaccine methodologies may lead to the development of universal vaccine strategy for future influenza prophylactics.