Intradermal vaccination with influenza virus-like particles by using microneedles induces protection superior to that with intramuscular immunization.

Influenza virus-like particles (VLPs) are a promising cell culture-based vaccine, and the skin is considered an attractive immunization site. In this study, we examined the immunogenicity and protective efficacy of influenza VLPs (H1N1 A/PR/8/34) after skin vaccination using vaccine dried on solid microneedle arrays. Coating of microneedles with influenza VLPs using an unstabilized formulation was found to decrease hemagglutinin (HA) activity, whereas inclusion of trehalose disaccharide preserved the HA activity of influenza VLP vaccines after microneedles were coated. Microneedle vaccination of mice in the skin with a single dose of stabilized influenza VLPs induced 100% protection against challenge infection with a high lethal dose. In contrast, unstabilized influenza VLPs, as well as intramuscularly injected vaccines, provided inferior immunity and only partial protection (</=40%). The stabilized microneedle vaccination group showed IgG2a levels that were 1 order of magnitude higher than those of other groups and had the lowest lung viral titers after challenge. Also, levels of recall immune responses, including hemagglutination inhibition titers, neutralizing antibodies, and antibody-secreting plasma cells, were significantly higher after skin vaccination with stabilized formulations. Therefore, our results indicate that HA stabilization, combined with vaccination via the skin using a vaccine formulated as a solid microneedle patch, confers protection superior to that with intramuscular injection and enables potential dose-sparing effects which are reflected by pronounced increases in rapid recall immune responses against influenza virus.