Supplementation of Influenza Split Vaccines with Conserved M2 Ectodomains Overcomes Strain Specificity and Provides Long-term Cross Protection

Abstract

Current influenza vaccines do not provide good protection against antigenically different influenza A viruses. As an approach to overcome strain specificity of protection, this study demonstrates significantly improved long-term cross protection by supplementing split vaccines with a conserved molecular target, a repeat of the influenza M2 ectodomain (M2e) expressed on virus-like particles (M2e5x VLPs) in a membrane-anchored form. Intramuscular immunization with H1N1 split vaccine (A/California/07/2009) supplemented with M2e5x VLPs induced M2e-specific humoral and cellular immune responses, and shaped the host responses to the vaccine in the direction of T-helper type 1 responses inducing dominant IgG2a isotype antibodies as well as interferon-γ (IFN-γ) producing cells in systemic and mucosal sites. Upon lethal challenge, M2e5x VLP-supplemented vaccination lowered lung viral loads and induced long-term cross protection against H3N2 or H5N1 subtype influenza viruses over 12 months. M2e antibodies, CD4 T cells, and CD8 T cells were found to contribute to improving heterosubtypic cross protection. In addition, improved cross protection by supplemented vaccination with M2e5x VLPs was mediated via Fc receptors. The results support evidence that supplementation with M2e5x VLPs is a promising approach for overcoming the limitation of strain-specific protection by current influenza vaccination.

Influenza M2 virus-like particles confer a broader range of cross protection to the strain-specific pre-existing immunity

“…A possible mechanism by which M2 antibodies provide protection is that influenza viruses bound to non-neutralizing antibodies are likely to be recognized and removed by opsonophagocytosis via Fc receptors [12, 23–27]. In this study, M2e specific antibody after M2e5x VLP immunization was reactive to M2-expressing MDCK cell or MDCK cells infected with influenza viruses, which suggests that binding antibody to infected cell can mediate opsonophagocytosis.…”

“…2). Also, in line with this result, co-immunization with mix of M2e5x VLP and split vaccines was shown to induce high levels of IgG2a antibody and improved cross protection [27]. Thus, shifting immunoglobulin isotypes to IgG2a antibodies as a result of M2e5x VLP immunization later might have contributed to improving cross protection in addition to the induction of M2e specific antibodies.…”

A Novel Vaccination Strategy Mediating the Induction of Lung-Resident Memory CD8 T Cells Confers Heterosubtypic Immunity against Future Pandemic Influenza Virus

“…Thus, as shown herein, it is highly significant that a universal vaccination strategy can provide superior cross protection to current vaccines in the scenario of when a first infecting virus is antigenically different from a vaccine strain. Protective mechanisms by M2e immunity include anti-M2e specific IgG antibodies, Fc γ receptors, natural killer cells, CD4 + and CD8 + T cells, alveolar macrophages, and dendritic cells (34, 37, 44-45). …”

Roles of antibodies to influenza A virus hemagglutinin, neuraminidase, and M2e in conferring cross protection

“…It is unclear what differences are in the protective mechanisms between NA protein and M2e5x VLP vaccines. T cells induced by M2e5x VLP vaccination were shown to play a role in conferring cross protection [17]. It is possible that in addition to M2e antibodies, T cells induced by M2e5x VLP vaccination contribute to more effective cross protection than NA protein immunization since we observed that N2 NA protein and M2e5x VLP immune sera conferred a similar level of protection against A/Phil H3N2 virus.…”

“…Supplementation of inactivated influenza vaccines with M2e-based antigens resulted in inducing significantly improved cross protection in BALB/c mice [17]. It was reported that addition of NA and M2e vaccines to recombinant HA vaccines confers long-lasting cross protection against primary and secondary influenza virus infections in BALB/c mice [22].…”