Immunogenicity and protective efficacy of the norovirus P particle-M2e chimeric vaccine in chickens.

The ectodomain of the influenza matrix protein 2 (M2e) is highly conserved across strains and has been shown to be a promising candidate for universal influenza vaccine in the mouse model. In this study, we tested immune response and protective efficacy of a chimeric norovirus P particle containing the avian M2e protein against challenges with three avian influenza (AI) viruses (H5N2, H6N2, H7N2) in chickens. Two-week-old specific pathogen free chickens were vaccinated 3 times with an M2e-P particle (M2e-PP) vaccine via the subcutaneous (SQ) route with oil adjuvant, and transmucosal routes (intranasal, IN; eye drop, ED; microspray, MS) without adjuvant. M2e-PP vaccination via the SQ route induced significant IgG antibody responses which were increased by each booster vaccination. In groups vaccinated via IN, ED or MS, neither IgG nor IgA responses were detected from sera or nasal washes of immunized birds. The M2e-PP vaccination via the SQ route significantly reduced the virus shedding in the trachea and the cloaca for all three challenge viruses. Despite the absence of detectable IgG and IgA responses in birds vaccinated with the M2e-PP via intranasal routes, a similar level of reduction in virus shedding was observed in the IN group compared to the SQ group. Our results supports that the universal vaccine approach using M2e-based vaccine can provide cross-protection against challenge viruses among different HA subtypes although the efficacy of the vaccine should be enhanced further to be practical. Better understanding of the protective immune mechanism will be critical for the development of an M2e-based vaccine in chickens.