Engineering programmable CAR-T cells with tunable controls as fail-safe mechanisms during cancer immunotherapy

Chimeric antigen receptor (CAR) T-cell therapies have demonstrated remarkable efficacy in treating various cancers, but significant risks of severe adverse effects remain. In this study, we present a synthetic biology toolbox for engineering CAR-T cells with tunable and controllable features to mitigate these risks. Using this toolbox, we programmed cytotoxic CAR-T cells to be turned on and off using synthetic genes with tetracycline response elements, referred to as iOnCAR and iOffCAR. We achieved temporal regulation of CAR expression using the synthetic Notch receptor system and "AND-gate" programs, which allow for additional control using doxycycline. We also engineered cooperation among T cells through CD4 help to CD8 T cells in targeting cancer cells via synthetic Notch receptors controlled by doxycycline treatment. Additionally, we developed a T cell fratricide system by triggering a genetic "Battle Royale" mechanism that enables CAR-T cells to eliminate each other. In this system, surviving T cells become activated, proliferate, and display high cytotoxicity to target cells. In conclusion, our synthetic biology toolbox provides targeted fail-safe solutions for improving the safety and potency of CAR-T cell therapies by integrating different genetic circuits with a commonly used antibiotic.