Enhanced Influenza VLP vaccines comprising matrix-2 ectodomain and nucleoprotein epitopes protects mice from lethal challenge.

The matrix protein 2ectodomain (M2e) of the influenza A virus is a rational target antigen candidate for the development of a universal influenza virus-like particle (VLP) vaccine. In this study, a recombinant M2 protein with three tandem copies of M2e (3M2e), nucleoprotein (NP) epitopes and hepatitis B virus core (HBc), were expressed in Escherichia coli and purified by column chromatography. Mice immunized with 3M2e-NP-HBc in combination with an oil-in-water SP01 adjuvant produced robust M2e specific antibodies and cellular immune responses. Most importantly, the 3M2e-NP-HBc VLP vaccine provided enhanced protection against a lethal challenge with pandemic 2009 H1N1 and HPAI H5N1 virus through increased survival rates, a significant decrease in viral replication, and obvious alleviation of histopathological lung changes in challenged mice. Our results imply that a cellular immune response to NP is a plausible mechanism mediating this enhanced protection. These findings suggest that 3M2e-NP-HBc VLP has great potential as the basis development of a broadly protective influenza vaccine.