Cholera toxin B subunit fusion enhances the immunogenicity of the H5 stem domain against the H5N2 avian influenza virus.

PURPOSE: The development of a universal avian influenza vaccine remains a critical issue for both the global public health and poultry industries. The hemagglutinin (H) stem/stalk region of highly pathogenic avian influenza viruses (HPAIVs) is capable of inducing broadly neutralizing antibodies but is limited by its poor immunogenicity. MATERIALS AND METHODS: To increase the immunogenicity of the stem domain, we engineered a recombinant fusion construct consisting of the stem domain of the H5 subtype and the nontoxic cholera toxin B subunit (CTB), a well-characterized mucosal adjuvant and immunomodulator. C57BL/6 mice were immunized intraperitoneally with the CTB-H5 stem fusion protein. Humoral immune responses and virus-neutralizing activities were subsequently assessed. RESULTS: Mice immunized with CTB-H5 stem fusion protein developed significantly higher serum immunoglobulin G titers and increased binding affinity to the native trimeric H5 antigen. Sera from the CTB-H5 stem group demonstrated enhanced virus-neutralizing activity in plaque reduction assays against the H5N2 virus. These results suggest that CTB fusion significantly enhances the immunogenicity and protective potential of the conserved H5 stem domain against the H5N2 virus. CONCLUSION: These findings support the use of CTB as an effective adjuvant platform for the development of stem-based influenza vaccines targeting HPAIVs.