Chimeric antigen receptor (CAR) T cells first entered US clinics in 2017 (1), and this therapeutic modality holds tremendous potential as one of the most effective forms of personalized cancer care ever to reach patients. The revolutionary impact of CAR T-cell therapy comes from its ability to rewire our own immune defenses to kill cancer cells: It essentially modifies a patient’s naturally existing immune cells to boost their recognition and attack of cancer cells so that the person’s own immune system…