Protective immunity against influenza H5N1 virus challenge in chickens by oral administration of recombinant Lactococcus lactis expressing neuraminidase

Background: Highly pathogenic H5N1 avian influenza viruses pose a debilitating pandemic threat in poultry. Current influenza vaccines predominantly focus on hemagglutinin (HA) which anti-HA antibodies are often neutralizing, and are used routinely to assess vaccine immunogenicity. However, Neuraminidase (NA), the other major glycoprotein on the surface of the influenza virus, has historically served as the target for antiviral drug therapy and is much less studied in the context of humoral immunity. The aim of this study was to evaluate the protective immunity of NA based on Lactococcus lactis (L.lactis) expression system against homologous H5N1 virus challenge in a chicken model. Results: L.lactis/pNZ2103-NA which NA is derived from A/Vietnam/1203/2004 (H5N1) (VN/1203/04) was constructed based on L.lactis constitutive expression system in this study. Chickens vaccinated orally with 10(12) colony-forming unit (CFU) of L.lactis/pNZ2103-NA could elicit significant NA-specific serum IgG and mucosa IgA antibodies, as well as neuraminidase inhibition (NI) titer compared with chickens administered orally with saline or L.lactis/pNZ2103 control. Most importantly, the results revealed that chickens administered orally with L.lactis/pNZ2103-NA were completely protected from a lethal H5N1 virus challenge. Conclusions: The data obtained in the present study indicate that recombinant L.lactis/pNZ2103-NA in the absence of adjuvant can be considered an effective mucosal vaccine against H5N1 infection in chickens via oral administration. Further, these findings support that recombinant L.lactis/pNZ2103-NA can be used to perform mass vaccination in poultry during A/H5N1 pandemic.