Illustration of CAR (chimeric antigen receptor) T cell immunotherapy, a process that is being developed to treat cancer. T cells (one at centre), part of the body's immune system, are taken from the patient and have their DNA (deoxyribonucleic acid) modified by viruses (spiky spheres) so that they produce chimeric antigen receptor (CAR) proteins. These proteins will be specific to the patient's cancer. The modified T cells are then multiplied in the laboratory before being reintroduced to the patient.