Illustration of chimeric antigen receptor (CAR) T cells (blue) attacking a cancerous white blood cell precursors (purple) in a case of acute myeloid leukaemia (AML). Healthy red blood cells (discs) are seen in the surrounding blood. AML is a cancer affecting the bone marrow (myeloid tissue) causing the overproduction of white blood cell precursors called myeloblasts. The excess cells can stop other blood cells from developing correctly, and can enter the bloodstream, spreading to other parts of the body. CAR-T therapy is a type of immunotherapy that genetically modifies a patients own T cells, a form of white blood cell, to recognise and destroy cancer cells.