Suppression of CAR T-cell cytotoxicity through TCR signaling inhibition. (A) Schematic of the TCR signaling reporter system is shown on the left. Scatter plot comparing drug-mediated inhibition of CAR T-cell cytotoxicity and average inhibition of NFAT, AP-1, and NF-κB reporter activity quantified by the DSS is shown on the right. Data are from screens with CD28 costimulation. Enlarged points indicate drugs with T-cell reporter DSS >15 or CAR T-cell cytotoxicity DSS below −25, with selected drugs labeled, and drugs with high inhibition of both cytotoxicity and TCR signaling circled. (B) Dose-response curves of NFAT, NF-κB, and AP-1 reporter activity for selected drugs. Data are from screens with CD28 costimulation. (C) Dose-response curves of CAR T-cell cytotoxicity for selected drugs. (D) Schematic of proposed mechanisms of CAR T-cell cytotoxicity and TCR signaling inhibition by selected drugs of 50 most potent CAR T-cell cytotoxicity inhibitors. Average DSSs of AP-1 (blue), NF-kB (green), and NFAT (red) inhibition for the listed drugs in the CD28 costimulation screens are shown as bar plots.