Auxin-Activated Caspase 9 System (AuxiCasp9), a Suicide Switch for Engineered Cells

Abstract Engineered cells incorporating synthetic gene circuits have been developed for therapeutic and diagnostic applications. However, cell proliferation and long-term engraftment may pose a risk of unpredictable toxicities. To address this issue, a suicide switch that can be selectively activated by exogenous stimuli has been developed as a regulatory system for engineered cells. However, the variety of reliable suicide switches is limited and insufficient for the orthogonal integration of multiple functions in engineered cells. This study developed auxin-activated caspase 9 (AuxiCasp9), a novel auxin-based suicide switch, by fusing the auxin receptor protein transport inhibitor response 1 (TIR1) carrying E7K/E10K/F74A mutations and auxin protein (Aux) to caspase 9. AuxiCasp9 exhibited cell death-inducing activity comparable to that of the established systems, inducible caspase 9 (iCasp9) and rapamycin-activated caspase 9 (RapaCasp9). Finally, we confirmed the orthogonality of AuxiCasp9 and iCasp9, suggesting the feasibility of multiplexed control of engineered cells.