MF59, an oil-in-water nanoemulsion, has been used in licensed seasonal influenza vaccines for many years. Administration of such vaccines by injection is associated with pain and safety issues. Here, we evaluated the potential of administering MF59 via a transcutaneous route with antigen
loading (either encapsulated into or mixed with MF59) to intact or microneedle-pretreated skin. In addition to commercial MF59, we also prepared a nanoemulsion to encapsulate hydrophilic antigens by mimicking the formulation and preparation technique of MF59. The nanoemulsion was prepared
using a water-in-oil-in-water emulsion method, and was similar to MF59 in composition, particle size, and morphology. Compared with the intact skin group, the microneedle-pretreated group showed significant enhanced antigen penetration. In vivo transcutaneous immunization analysis showed
that the MF59-adjuvant influenza vaccine elicited approximately 3–5 times higher hemagglutination inhibition titers than the influenza solution alone in BALB/c mice after microneedle pretreatment. The intact skin group showed negative immune results at the same dose, suggesting that
microneedle pretreatment was critical for efficient delivery of antigens, to obtain strong immune responses. Furthermore, the loading method (encapsulation or mixing with the vehicle) did not affect the dermal penetration or transcutaneous immunization of antigens on microneedle-pretreated
skin. Moreover, in vitro cellular assays showed that MF59 facilitated the maturation of dendritic cells and enhanced antigen uptake by antigen-presenting cells. In conclusion, the combination of microneedle pretreatment and mixing of MF59 with antigen provides a simple approach to enhance
transcutaneous immunization.