Illustration of the DNA (deoxyribonucleic acid) and mRNA (messenger ribonucleic acid) vaccine mechanisms of action. For DNA vaccines, the plasmid DNA needs to pass through both the plasma membrane and nuclear membrane for transcription into mRNA, and then the subsequent translation into the antigen protein. For mRNA vaccines, the mRNA is translated into the antigen protein after passing through the plasma membrane. For both DNA and mRNA vaccines, the antigen protein is then processed into antigen peptides, and presented by MHC I, or the antigen protein is expressed on the cell surface. For a labelled version of this image see F042/5621.