Efficacy of an Experimental Chitosan-Based Influenza Nanovaccine in Combination with TIR-TLR7

Background:H9N2 is the most common subtype of influenza viruses in chickens and causes great economic loss for the poultry industry. The virus spreads into vast majority regions nationwide and has become endemic in Iran. Candidate H9N2 subtype as a potential next pandemic agent has raised a concern about new controlling strategies.Nanoparticles are served recently for mucosal antigen delivery system for induction of protective immunity. In this study, the efficacy of chitosan nanoparticle-based H9N2 influenza vaccine with Toll/interleukin-1 receptor (TIR) domain of TLR7 as a molecular adjuvant to induce protective immunity against the virus was examined. Methods:The influenza H9N2 virus antigen was prepared in SPF egg and inactivated with beta propiolactone. The inactivated antigen alone and in combination with TIR-TLR7 was encapsulated into chitosan nanoparticles by gelatinization method. Groups of SPF chickens received chitosan nanoparticle-based H9N2 antigen alone or in combination with TIR-TLR7 in a prime/boost platform via intraconjactival route. Blood samples were taken up to 8 weeks post inoculation at defined intervals. The efficacy of the adjuvanted-nanovaccine candidate was evaluated by estimating theinfluenza virus antigen-specific antibody titers using ELISA assay.Results: Serological analysis indicated that SPF chickens receiving the TIR-TLR7/H9N2 nanoparticles formulation induced higher antibody titers that were sustained until the end of experiment. The chitosan nanoparticle-based H9N2 antigenwithout TIR-TLR7 was also induced humoral immunity in SPF chickens against H9N2 antigen, while loading H9N2 antigen and TIR-TLR7 onto the nanoparticles coated with chitosan carrier developed improved immune responses. Conclusion: The data demonstrate the eye-drop vaccination of TIR-TLR7/H9N2nanopaticles is an effective and safe tool to enhance protective immunity against influenza.The improvement is dependent on the reversible interaction of chitosan with both TIR-TLR7 and H9N2 that allows antigen uptake and enhance antigenic trans-mucosal delivery.

Keywords:

Avian influenza virus , H9N2 subtype , Chitosan nanoparticles , TIR-TLR7 , Immune response