Novel strategies using DNA for the induction of mucosal immunity

The mucosal surfaces are the primary sites for transmission of most infectious diseases. However, most conventional vaccines are administered parenterally [e.g., by intramuscular (IM) or intradermal (ID) injection] and induce systemic but rarely mucosal immunity. Novel vaccination strategies capable of inducing both systemic and mucosal immune responses could greatly reduce infection and morbidity worldwide. One of the most exciting advances in vaccine technology in recent years has been the development of DNA vaccines, through which the antigen is synthesized in vivo after direct introduction of its encoding sequences. The vast majority of DNA vaccines have been delivered parenterally; however, in recent years a number of studies have reported successful mucosal immunization with DNA vaccines. The induction of strong immune responses following the introduction of DNA appears to be partly due to the potent adjuvant effect of unmethylated immunostimulatory CpG motifs present in the DNA backbone. Synthetic oligodeoxynucleotides (ODN) containing such immunostimulatory CpG motifs are potent adjuvants systemically and mucosally in mice, and have synergistic action with other adjuvants, such as alum and cholera toxin (CT). This article highlights the recent advances in vaccination strategies using DNA delivered to mucosal surfaces either as an antigen-encoding plasmid or as an adjuvant.