T-cells and breast cancer cell. Composite conceptual coloured scanning electron micrograph (SEM) of T-cells and a breast cancer cell (pink). CAR T-cell therapy involves producing large quantities of specialised T-cells on an individual basis for each patient. T-cells are extracted from a patient’s blood sample and reprogrammed to recognise a specific target protein on the patient’s tumour cells. To achieve this, the T-cells are infected with a harmless virus, which inserts a gene into the T-cell’s DNA that causes the T-cell to produce a receptor on its surface that recognises a specific tumour protein. Large quantities of the reprogrammed T-cells are grown in the lab before being injected back into the patient where they seek out the target protein on breast cancer cells and attack them.