In today's medical industry, the range of vaccines that exist for administration in humans represents an eclectic variety of forms and immunologic mechanisms. Namely, these are the live attenuated viruses, inactivated viruses, subunit proteins, and virus-like particles for treating virus-caused diseases, as well as the bacterial-based polysaccharide, protein, and conjugated vaccines. Currently, a new approach to vaccination is being investigated with the concept of DNA vaccines. As an alternative delivery route to enhance the vaccination efficacy, microneedles have been devised to target the rich network of immunologic antigen-presenting cells in the dermis and epidermis layers under the skin. Numerous studies have outlined the parameters of microneedle delivery of a wide range of vaccines, revealing comparable or higher immunogenicity to conventional intramuscular routes, overall level of stability, and dose-sparing advantages. Furthermore, recent mechanism studies have begun to successfully elucidate the biological mechanisms behind microneedle vaccination. This paper describes the current status of microneedle vaccine research.

Microneedles were initially developed as pretreatment tools for the delivery of therapeutic drugs to intradermal locales in the human skin. Over time, variations in microneedle forms and functions burgeoned through the works of many researchers worldwide. The four major types of microneedles in use today are solid, dissolving, coating, and hollow microneedles. The emergence of different types of microneedles also paved the way for a flourishing diversification of microneedle applications, one of the most remarkable of which deals with the transcutaneous delivery of prophylactic vaccines. Here, we describe fabrication methods of microneedles and DNA vaccine loading methods on the microneedle surface. Furthermore, in the latter part of this chapter, in vivo test protocols for assessing the efficacy of gene delivery using microneedles are described.