A phase I/II, dose escalation, DNA vaccination trial with plasmid DNA, which carries prostate-specific membrane antigen (PSMA), fused to a domain (DOM1) of Fragment C of tetanus toxin, delivered either by i.m. or by i.m. followed by EP, was performed in patients with recurrent prostate cancer. The epitope used in this study, PSMA 27 is a short stretch of 9 amino acids tumor-derived epitope belonging to the PSMA. Preliminary analysis of CD8 + Tcell reactivity against the prostate-specific membrane antigen target peptide indicated significant responses in 3 out of 3 patients and CD4 + T-cell responses against the DOM1. These data validated EP as a potent method for stimulating humoral responses induced by DNA vaccination in humans [46, 47, 64] .