Fabrication of influenza virus-like particles using M2 fusion proteins for imaging single viruses and designing vaccines.

Influenza virus-like particles (VLPs) are noninfectious and the assembly of influenza VLPs depends on the interactions of M1 proteins and/or other viral surface proteins, such as HA, NA, and M2, with the cellular lipid membranes. In this study we propose that M2 protein can be used as a molecular fabricator without disrupting the assembly of VLPs and while retaining the native structures of HA and NA envelope protein oligomers on the particle surfaces. First, we demonstrated that influenza VLPs can be fabricated by the M2 fusion of enhanced green fluorescent protein for imaging single virus entering A549 cells. Second, we engineered two molecular adjuvants (flagellin and profilin) fused to M2 protein to generate molecular adjuvanted VLPs. Theses molecular adjuvanted VLPs had stimulatory functions, including increasing TNF-α production and promoting the maturation of dendritic cells. Immunization of mice with molecular adjuvanted VLPs also enhanced the response of the neutralizing antibodies against homologous and heterologous H5N1 viruses. The results can provide useful information for imaging single viruses and designing novel vaccines against influenza virus infection.