Topical vaccination: The skin as a unique portal to adaptive immune responses

Skin is an ideal tissue for vaccine administration, as it is comprised of immunocompetent cells such as keratinocytes and Langerhans cells and elicits both innate and adaptive immune responses. In this paper, we summarize the immune responses induced by topical vaccination of the skin and review the effects of adjuvants on skin vaccination. We also summarize the existing techniques for skin vaccination. New techniques such as the use of lasers to enhance skin permeability are also discussed, as well as the role of the stratum corneum in skin vaccination. A recent study demonstrating enhanced skin vaccination by using surfactants to extract partial lamellar lipids of the stratum corneum will also be introduced in this review.