Needle-free, non-adjuvanted skin immunization by electroporation-enhanced transdermal delivery of diphtheria toxoid and a candidate peptide vaccine against hepatitis B virus.

To explore the feasibility of non-adjuvanted, needle-free skin immunization, we examined the immune responses of mice immunized by three routes with two antigens (Ag) differing in molecular size and lipophilicity. Diphtheria toxoid (DT) or a myristylated peptide (MYR) administered either by transdermal electroporation (EP) or intradermally (i.d.) with a needle elicited markedly different responses. The EP route elicited higher responses to MYR than i.d. immunization, but lower responses to DT. Intraperitoneal (i.p.) immunization evoked responses against MYR that were higher than those evoked by EP. It was inferred that EP is a promising technique for non-adjuvanted skin immunization, specially with low molecular weight, weakly immunogenic Ag.