CAR T cell cancer immunotherapy. Illustration of the membrane of a cell involved in CAR (chimeric antigen receptor) T cell immunotherapy, a process that is being developed to treat cancer. In this process, T cells (part of the immune system) are treated with a virus in a form of genetic engineering, resulting in them producing chimeric antigen receptor (CAR) proteins. These proteins will be specific to the patient's cancer. Here, these engineered receptors (light blue, one at upper right) bind specifically to CD19-antigen molecules (purple), in this case on a leukaemia cell. This activates a signal cascade in the T-cell leading to the segregation of vesicles that contain perforin and granzyme (yellow) molecules. The perforins build channels for the granzymes which enter the leukaemia cell and trigger the apoptosis (cell death) of the cancer cell.