Chimeric antigen receptors (CARs) are antibody fragments linked to activation molecules, that recognise molecules specifically present on the surface of cancer cells. These CAR complexes are genetically engineered into the immune cell (T cell or NK cell) genome and expressed on their surface. When the antibody fragment engages with the cancer cell, the activation molecules signal the immune cell to kill the cancer cell by releasing toxic granules or cytokines that cause death of the cancer cell. They keep killing cancer cells until exhausted. We multiply these aggressive immune cells and we also help them avoid messages from the tumour environment to be disabled.