Transdermal protein delivery and immunization by a solid-in-oil nanodispersion technique

Transcutaneous vaccination is an attractive strategy that delivers antigen molecules topically into the skin to induce protective or therapeutic immune responses. In the last two decades, the skin has been regarded as a potential administration site for vaccines due to the abundant antigen presenting cells in the skin such as Langerhans cells and dermal dendritic cells, which are found in the epidermis or dermis. To create an efficient transcutaneous vaccine, the antigen needs to be penetrated across the stratum corneum, which is the outermost layer of the skin and possesses a high barrier function. To overcome this issue, various types of drug delivery systems have been proposed such as ultrasound, jet immunization and microneedles as physical methods, and penetration peptides, liposomes and nanoparticles as chemical methods. In this review, a solid-in-oil (S/O) nanodispersion, which is an oil-based drug carrier for proteins and peptides, and its application for transcutaneous protein delivery and vaccination are summarized. Along with comparing the S/O nanodispersion with the other oil-based drug carriers, the transdermal delivery of proteins such as insulin is introduced. Finally, basic immunological responses via transcutaneous administration with the S/O nanodispersion containing a model antigen, and researches on protect and therapeutic applications are summarized.