A DNA vaccine against an H1N1 avian influenza virus induced humoral and cell-mediated immunity in SPF chickens

The development of cost-effective avian influenza (AI) vaccine is a priority to prevent pandemic flu outbreaks. DNA-based immunization offers a promising strategy to prevent viral diseases. In this study, immunological response induced by an experimental DNA vaccine against AIV in specific pathogen-free chickens was investigated. The vaccine consisted of the entire HA gene of an AIV H1N1 subtype Alabama strain (A/blue-winged teal/ AL/167/2007) cloned into the pcDNA6.2 DNA eukaryotic expression vector. The in vitro expression of the DNA vector was confirmed in COS-7 cells by indirect immunofluorescence. The in vivo expression of the cloned gene was confirmed in intramuscularly (IM) vaccinated chicken breast muscles by immunohistological analysis. Results indicated that pcDNA6.2 vector was as effective as a commercial inactivated H1N1 AIV vaccine given IM in inducing hemagglutination inhibition (HI) antibody. This vector produced lower neutralization antibody than the commercial vaccine. The Th1 (IFN-γ, IL-2) and Th2 (IL-4, IL-6, IL-10) cytokine profiles in vaccinated birds were analyzed by reverse transcriptase and quantitative real-time PCR (qRT-PCR). The Th1-like immune response of the experimental vaccinated birds was high as shown by levels of interferon gamma (INF-γ) and interleukin-2 (IL-2), but not IL-4, IL-6 or IL10. Our results suggest that the experimental DNA vaccine produced measurable humoral and cellular immune responses in chickens.