Chimeric virus-like particles of nodavirus displaying M2e of human and avian influenza A viruses as a potential dual-use vaccine: Inducing a broader immune response and protecting mice against viral infections.

The haemagglutinin (HA) and neuraminidase (NA) of influenza A viruses (IAVs) mutate rapidly, necessitating yearly updates to seasonal influenza vaccines. The highly conserved matrix 2 ectodomain protein (M2e) of IAVs presents a promising candidate for developing a universal influenza vaccine. However, variations in the M2e amino acid sequences, particularly in host-restriction specificity regions between human and avian IAVs, pose significant challenges. To broaden the M2e immunogenicity, we previously fused M2e from human and avian IAVs at the C-terminal end of Macrobrachium rosenbergii nodavirus capsid protein (NvC). The chimeric protein self-assembled into virus-like particles (VLPs), stimulating IgY antibodies and cell-mediated immune responses to human and avian M2e in chickens. In this study, we investigated the breadth and cross-subtype immunity of these chimeric VLPs in BALB/c mice to assess their potential for human use. The chimeric protein purified with immobilised metal affinity chromatography exhibited significant antigenicity to anti-H1N1 and anti-H9N2 M2e antibodies. Immunisation of BALB/c mice subcutaneously with the chimeric VLPs led to the development of anti-H1N1 and anti-H9N2 M2e-specific IgG antibodies that cross-reacted with M2e of H5N1 and H5N2 IAVs. The chimeric VLPs also elicited a strong cell-mediated immune response, characterised by a balanced Th1 and Th2 cytokine profile. Additionally, a significant increase in the CD8+/CD4+ cell ratio in splenocytes suggests enhanced cytotoxic T lymphocyte (CTL) activity. The chimeric VLPs, with or without adjuvant, conferred 100 % protection against challenges with four times median lethal dose (4xLD) of mouse-adapted H1N1 and H3N2 IAVs, reducing morbidity, pathology, and viral load in their lungs. Collectively, our data showed that the chimeric VLPs that induce potent immunogenicity in chickens hold potential for human application as demonstrated in BALB/c mice study, where anti-IAV immunity was broadened, protecting the mice from H1N1 and H3N2 IAV infections.