Illustration showing chimeric antigen receptor (CAR) T cells (blue) being used to treat a melanoma (orange). Melanoma is a form of skin cancer arising from melanocytes, the cells that produce the pigment melanin. CAR-T cells are a patient's 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.