Mechanism of action of DNA vaccine after intra muscular (i.m.) plasmid delivery. Transfected muscle cells produce the antigen expressed on the plasmid. This antigen is expressed to cell surface with MHC I and presented to cytotoxic CD8+ T cells (Cell mediated Immunity). Antigen is also excreted by the muscle, which is phagocytosed by the professional Antigen Presenting Cells (APC), usually Dendritic cells. A small proportion of DNA vaccine is also taken up directly by APC and the encoded antigen can then be processed and presented endogenously (Humoural Immunity).