FDA-approved fulvestrant-induced CAR phase separation enables precise control of CAR T antitumor function.

Chimeric antigen receptor (CAR) T cell therapy faces challenges, such as tumor relapse due to antigen loss and poor CAR T cell expansion in vivo. Optimal tonic signaling (spontaneous CAR signaling) is crucial for CAR T cell fitness and antitumor function, requiring precise calibration to avoid dysfunction or exhaustion. Although CAR phase separation can enhance CAR clustering and tonic signaling to improve cytotoxicity and antigen sensitivity, constitutively high signaling could lead to potential side effects, including cytokine storm and neuronal toxicity. To overcome this limitation, we developed a drug-inducible phase-separation CAR (iPhase-CAR) system utilizing FDA-approved fulvestrant and an engineered estrogen receptor α (ERα) mutant as the drug-inducible phase-separation (DiPS) module. Incorporating the DiPS module into CARs enables drug-inducible clustering of CARs on T cell membranes. iPhase-CAR T cells demonstrate superior antitumor function. This system provides quantitative, reversible promotion of CAR T effector functions, enabling precise control over therapeutic efficacy only upon administration of the FDA-approved drug.