Delivery of an inactivated avian influenza virus vaccine adjuvanted with poly(D,L-lactic-co-glycolic acid) encapsulated CpG ODN induces protective immune responses in chickens

In poultry, systemic administration of commercial vaccines consisting of inactivated avian influenza virus (AIV) requires the simultaneous delivery of an adjuvant (water-in-oil emulsion). These vaccines are often limited in their ability to induce quantitatively better local (mucosal) antibody responses capable of curtailing virus shedding. Therefore, more efficacious adjuvants with the ability to provide enhanced immunogenicity and protective anti-AIV immunity in chickens are needed. While the Toll-like receptor (TLR) 21 agonist, CpG oligodeoxynucleotides (ODNs) has been recognized as a potential vaccine adjuvant in chickens, poly(D,L-lactic-co-glycolic acid) (PLGA) nanoparticles, successfully tested as vaccine delivery systems in other species, have not been extensively explored. The present study, therefore, assessed both systemic and mucosal antibody-mediated responses following intramuscular vaccination (administered at 7 and 21 days post-hatch) of chickens with PLGA encapsulated H9N2 AIV plus encapsulated CpG ODN 2007 (CpG 2007), and nonencapsulated AIV plus PLGA encapsulated CpG 2007 vaccine formulations. Virus challenge was performed at 2 weeks post-secondary vaccination using the oculo-nasal route. Our results showed that chickens vaccinated with the nonencapsulated AIV vaccine plus PLGA encapsulated CpG 2007 developed significantly higher systemic IgY and local (mucosal) IgY antibodies as well as haemagglutination inhibition antibody titres compared to PLGA encapsulated AIV plus encapsulated CpG 2007 vaccinated chickens. Furthermore, chickens that received CpG 2007 as an adjuvant in the vaccine formulation had antibodies exhibiting higher avidity indicating that the TLR21-mediated pathway may enhance antibody affinity maturation qualitatively. Collectively, our data indicate that vaccination of chickens with nonencapsulated AIV plus PLGA encapsulated CpG 2007 results in qualitatively and quantitatively augmented antibody responses leading to a reduction in virus shedding compared to the encapsulated AIV plus PLGA encapsulated CpG 2007 formulation.