Nature Immunology, Published online: 22 June 2026; doi:10.1038/s41590-026-02559-7 Asymmetric cell division can result in functionally distinct CAR-T cells. Data now indicate that this asymmetry is an early ‘program selector’ that can explain why 4-1BBζ CAR-T cells preferentially generate durable memory progeny whereas CD28ζ CAR-T cells skew toward short-lived effector fates.