Illustration of the immune response caused by a DNA (deoxyribonucleic acid) vaccine. The DNA vaccine firstly enters the dendritic cell (purple), which leads to the expression of antigen peptides and proteins. The antigen peptide is presented to T cells (blue), turning some of them into cytotoxic T cells (green). The antigen proteins activate B cells (pink), and the B cells can differentiate into memory B cells and plasma cells (orange) that can generate antibodies in response to an antigen.