CD7 is a special protein found on most cancer cells in T-cell acute lymphoblastic leukemia (T-ALL) and T-cell lymphoma. This makes CD7 a very good target for CAR-T cell therapy, which uses the patient’s own immune T cells to fight cancer. However, because CD7 is also on many normal T cells, scientists must carefully change the CAR-T cells to stop them from attacking themselves. This careful change is called gene deletion or blocking CD7 on the CAR-T cells to keep them safe.