Intranasally administered protein coated chitosan nanoparticles encapsulating influenza H9N2 HA2 and M2e mRNA molecules elicit protective immunity against avian influenza viruses in chickens.

Chitosan nanoparticles (CNPs) represent an efficient vaccination tool to deliver immunogenic antigens to the antigen-presenting cells (APCs), which subsequently stimulate protective immune responses against infectious diseases. Herein, we prepared CNPs encapsulating mRNA molecules followed by surface coating with conserved H9N2 HA2 and M2e influenza proteins. We demonstrated that CNPs efficiently delivered mRNA molecules into APCs and had effectively penetrated the mucosal barrier to reach to the immune initiation sites. To investigate the potential of CNPs delivering influenza antigens to stimulate protective immunity, we intranasally vaccinated chickens with empty CNPs, CNPs delivering HA2 and M2e in both mRNA and protein formats (CNPs + RNA + Pr) or CNPs delivering antigens in protein format only (CNPs + Pr). Our results demonstrated that chickens vaccinated with CNPs + RNA + Pr elicited significantly (p < 0.05) higher systemic IgG, mucosal IgA antibody responses and cellular immune responses compared to the CNPs + Pr vaccinated group. Consequently, upon challenge with either H7N9 or H9N2 avian influenza viruses (AIVs), efficient protection, in the context of viral load and lung pathology, was observed in chickens vaccinated with CNPs + RNA + Pr than CNPs + Pr vaccinated group. In conclusion, we show that HA2 and M2e antigens elicited a broad spectrum of protection against AIVs and incorporation of mRNAs in vaccine formulation is an effective strategy to induce superior immune responses.