M2e-Derived Peptidyl and Peptide Amphiphile Micelles as Novel Influenza Vaccines

Background: A significant problem with current influenza vaccines is their reliance on predictions of the most prevalent strains for the upcoming season, with inaccurate forecasts greatly reducing the overall efficacy of the immunization campaign. A universal influenza vaccine, which leverages epitopes conserved across many, if not all, strains of influenza, could reduce the need for extremely accurate forecasting. The highly conserved ectodomain of the influenza M2 protein contains a B cell epitope in the M2_2-16 region, making it a promising candidate as a universal influenza vaccine. Unfortunately, free peptide antigens alone are limited as vaccines due to their poor stability and weak immunogenicity in vivo. To improve the potential of peptide vaccines, immunostimulatory micellar nanoparticles can be generated from them by lipid conjugation (i.e., peptide amphiphiles-PAs). Methods: M2_2-16 peptides and Palm₂K-M2_2-16-(KE)₄ PAs were synthesized and characterized. BALB/c mice were subcutaneously vaccinated with these formulations, and ELISAs were conducted on serum collected from the vaccinated mice to evaluate induced antibody responses. Results: Unlike other peptide antigens previously studied, the unmodified M2_2-16 peptide micellized without any peptidyl or lipid modifications. M2_2-16 peptidyl micelles (PMs) were spherical with largely undefined secondary structure somewhat different from the cylindrical, β-sheet-containing Palm₂K-M2_2-16-(KE)₄ peptide amphiphile micelles (PAMs). Differences in physical properties were found to correlate with slightly different immune responses with PAMs eliciting higher antibody titers after the initial immunization, whereas both micelle types elicited strong IgG titers after a prime-boost regimen. Conclusions: These results suggest the viability of PAMs as single-dose vaccines, while both PMs and PAMs show potential using a multi-dose immunization approach.