Illustration of the immune response caused by an mRNA (messenger ribonucleic acid) vaccine. The mRNA 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.