Superiority of the ear pinna over muscle tissue as site for DNA vaccination

Three different vaccination sites were compared for efficiency of immunization with naked DNA. Using the bacterial lacZ gene as a model, all three sites of the mouse (skeletal muscle, dermis of abdominal skin or of the ear pinna) could express the gene product beta-gal but varied in expression time with muscle tissue showing the longest expression. Expression time, however, did not correlate with immune response intensity. The ear pinna was by far the most effective and muscle the least effective priming site for specific humoral and cytotoxic T cell-mediated immune responses. Following intra-pinna DNA inoculation, beta-gal expressing cells were detectable around the injection site and in the major draining lymph node. Efficiency of immunization was also dependent on the promoter and expression vector used. The cytomegalus virus promoter driven pCMV beta vector was superior to the Moloney murine leukemia virus LTR driven BAG vector. LacZ DNA immunization was also compared with cell-based vaccination with lacZ-transfected tumor cells, in which case again the pinna was the best site for inducing strong immune responses. Tumor-specific T cell responses could also be well induced in the pinna, leading to cytotoxic T lymphocyte induction and protective antitumor immunity. Thus, the pinna was found to be a privileged site for induction of antitumor responses and for genetic immunization, an important finding of immediate practical and potential future clinical implications.