A cutting-edge therapy using base-edited immune cells is offering a major breakthrough for patients with one of the toughest forms of blood cancer, T-cell acute lymphoblastic leukaemia. By precisely rewriting tiny sections of DNA, scientists at UCL and Great Ormond Street Hospital created universal CAR T-cells capable of targeting the cancer without harming themselves—a long-standing challenge in T-cell–based therapies. Early trial results show deep, long-lasting remissions, including in patients who had exhausted standard treatment options.