Antigen-loaded APCs travel to the draining lymph nodes, where they present peptide antigens to naïve T cells, thereby eliciting both humoral and cellular immune responses. Although plasmid DNA vaccines vectors can induce antibody and CD4 + T cell helper responses, they are particularly suited to induce CD8 + T cell responses because they express antigens intracellularly, introducing them directly into the MHC I antigen processing and presentation pathway [31] .