Precise Control of Switchable Chimeric Antigen Receptor T Cells Allows Enhanced Safety and Less T Cell Exhaustion

Background Chimeric antigen receptor (CAR)-T cell therapies have achieved remarkable success in hematologic malignancies, yet their clinical utility remains limited by safety concerns, limited persistence, and T-cell exhaustion driven by continuous receptor signaling. While switchable CAR designs provide external control, many reported systems are irreversible, strictly binary, or compromise CAR-T potency. Methods We engineered an optimized chemically switchable CAR platform (CSN CAR) that pharmacologically regulates antigen engagement by controlling the surface expression of the full-length CAR. An NS3 protease module was embedded within the CAR construct to enable drug-dependent stabilization of intact CAR on T cells. Using engineered CAR-T cells, we quantified drug-controlled activation, cytotoxicity, and cytokine release against CD19 + tumor cells by flow cytometry and ELISA in vitro . We further screened clinically approved NS3/4A inhibitors in CAR-HEK and CAR-T cells to identify optimal small-molecule controllers. A chronic stimulation model was established to assess CAR-T persistence and exhaustion-associated phenotypes in vitro . Results CSN CAR-T cells enabled precise, dose-dependent regulation of CAR surface density, cytokine production, and cytotoxicity. In the OFF state, switchable CAR-T cells showed minimal basal activity, consistent with reduced antigen-driven activation and cytokine release in the absence of drug in the experimental conditions. Upon drug addition, intact surface CAR was detectable within 1 hour, reaching ∼80% of peak observed CAR expression by 4 hours. Reversible suppression of CAR expression enabled attenuation of cytotoxicity toward normal CD19 + B cells in vitro after target-cell reduction, supporting a potential strategy to mitigate prolonged on-target/off-tumor activity. Under chronic stimulation, switchable CAR-T cells exhibited reduced exhaustion-associated markers, more stable CAR expression, and preferential differentiation toward a central memory phenotype. Conclusion Together, these findings establish CSN CAR as a reversible and tunable switchable CAR-T platform enabled by clinically approved NS3/4A inhibitors, supporting controllable modulation of CAR activity with potential applications for improving the precision and safety of CAR-T cell therapy.