Chimeric antigen receptor, illustration. CAR T cells are currently developed with the hope they may eventually transform immunotherapy of cancer patients. They are produced by taking immune cells (T cells) from a patients blood and genetically engineering them to specifically attack the tumour cells. This includes genetically inserting into these patient derived cells the instructions for a chimeric antigen receptor (CAR), a protein that binds to a specific antigen on the surface of cancer cells. The CAR contains a section of the T cell receptor (blue) and fuses it to the variable section of an antibody (green), which recognises the known tumour antigen. The CAR mediates the interaction of the CAR T cell with the tumour and binds to the specific antigen exposed on the tumour, upon engagement of antigen and CAR, it provides an activating signal to the T cell to kill the cancer cell.