VLPs containing stalk domain and ectodomain of matrix protein 2 of influenza induce protection in mice

BACKGROUND: As a result of antigenic drift, current influenza vaccines provide limited protection against circulating influenza viruses, and vaccines with broad cross protection are urgently needed. Hemagglutinin stalk domain and ectodomain of matrix protein 2 are highly conserved among influenza viruses and have great potential for use as a universal vaccine. METHODS: In this study, we co-expressed the stalk domain and M2e on the surface of cell membranes and generated chimeric and standard virus-like particles of influenza to improve antigen immunogenicity. We subsequently immunized BALB/c mice through intranasal and intramuscular routes. RESULTS: Data obtained demonstrated that vaccination with VLPs elicited high levels of serum-specific IgG (approximately 30-fold higher than that obtained with soluble protein), induced increased ADCC activity to the influenza virus, and enhanced T cell as well as mucosal immune responses. Furthermore, mice immunized by VLP had elevated level of mucosal HA and 4M2e specific IgA titers and cytokine production as compared to mice immunized with soluble protein. Additionally, the VLP-immunized group exhibited long-lasting humoral antibody responses and effectively reduced lung viral titers after the challenge. Compared to the 4M2e-VLP and mHA-VLP groups, the chimeric VLP group experienced cross-protection against the lethal challenge with homologous and heterologous viruses. The stalk domain specific antibody conferred better protection than the 4M2e specific antibody. CONCLUSION: Our findings demonstrated that the chimeric VLPs anchored with the stalk domain and M2e showed efficacy in reducing viral loads after the influenza virus challenge in the mice model. This antibody can be used in humans to broadly protect against a variety of influenza virus subtypes. The chimeric VLPs represent a novel approach to increase antigen immunogenicity and are promising candidates for a universal influenza vaccine.