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

Chimeric antigen receptor (CAR)-T cell therapies have achieved remarkable success in treating hematologic malignancies, yet their clinical utility remains limited by safety concerns, poor persistence, and T-cell exhaustion driven by continuous receptor signaling. Although switchable CAR systems offer external control, most existing designs are irreversible, binary, or compromising CAR-T potency. Here, we introduce a chemically switchable CAR platform that enables graded, reversible regulation of CAR-T activity while retaining full therapeutic capacity. Using engineered CAR-T cells, we evaluate drug-controlled activation, cytotoxicity, and cytokine release against CD19⁺ tumor cells and screened clinically approved NS3/4A inhibitors to identify optimal small-molecule controllers. Compared with conventional CAR-T cells, switchable CAR-T cells exhibited minimal background activity in the OFF state, preventing antigen-driven activation and cytokine release in the absence of drug. Upon drug addition, CAR expression was rapidly restored, with full-length CAR detectable within 1 hour and ~80% of maximal expression achieved by 4 hours. Reversible suppression of CAR expression protected normal CD19⁺ B cells once malignant cells were eliminated, addressing the clinical challenge of persistent CD19 CAR-T activity that can lead to B-cell aplasia, hypogammaglobulinemia, and recurrent infections. Furthermore, switchable CAR-T cells displayed reduced exhaustion, enhanced persistence, stable CAR expression, and preferential central memory differentiation following tumor clearance. Together, these findings establish the switchable CAR-T system as a next-generation, reversible, and clinically compatible CAR-T platform.