Chimeric virus-like particles of nodavirus displaying human and avian influenza A M2e induce conserved anamnestic protective immunity against human and avian influenza A viruses.

The conserved matrix 2 ectodomain (M2e) peptides of influenza A viruses (IAVs) have been employed in developing universal vaccines. However, interspecies M2e variations between human and avian strains, including those associated with host adaptation during zoonotic and reverse-zoonotic transmission, result in notable antigenic and immunogenic differences. Therefore, we fused two copies each of M2e peptides from human and avian IAVs at the C-terminus of Macrobrachium rosenbergii nodavirus capsid protein (NvC), which self-assembled into virus-like particles (VLPs). This chimeric VLP provided 100% protection against lethal H1N1 and H3N2 infections in mice and promoted viral clearance against H9N2 and H5N2 infections in chickens. In this study, a comparative immunoprofile induced by the chimeric VLPs in BALB/c mice before and upon the viral infections was performed to identify the immune determinant of chimeric VLPs-mediated protection. The mice immunized with the chimeric VLPs produced both IgG1 and IgG2a isotypes of anti-H1N1 and anti-H9N2 M2e-specific antibodies, indicating the activation of both Th1 and Th2 responses. Antibody-secreting cell analysis of the splenocytes demonstrated memory B cell activation. Moreover, the chimeric VLPs stimulated memory T cell response upon recall with H1N1- or H9N2-derived M2e peptide. An increase in the CD8+:CD4+ ratio, and reduced percentage of macrophage and natural killer (NK) cells were detected at day 5 post-infection with H1N1 or H3N2 IAV. Furthermore, distinct cytokine profiles were observed in the circulating and pulmonary compartments, with both Th1 and Th2 responses. Notably, lower IL-6 and IL-10 levels were identified in the immunized mice's lungs. Overall, this study revealed that the chimeric VLPs induced robust protective immunity in BALB/c mice, demonstrating their potential as a bivalent M2e-based vaccine targeting IAVs of both human and avian origins.