Illustration showing a chimeric antigen receptor (CAR) T cell (blue) being used to treat acute lymphoblastic lymphoma (ALL, pink, irregular). Healthy red blood cells (red discs) and white blood cells (purple) are seen in the surrounding blood. ALL is a rare cancer in which excess white blood cell progenitor cells called lymphoblasts are produced in the bone marrow. CAR-T cells are a patients own T cells, a form of white blood cell, that have been genetically modified to recognise and destroy certain cancer or autoimmune cells that might otherwise be tolerated by the immune system.