Inducible caspase 9 (iCasp9) suicide switch (iCasp9)

The Engineered FKBP12–iCasp9 suicide switch is a synthetic safety system integrated into cell-based therapies to provide a controlled method for cell elimination (Di Stasi et al., 2011, NEJM). It comprises a human pro-caspase 9 protein fused to a modified FK506-binding protein (FKBP12) that carries an F36V mutation (Gargett & Brown, 2014, Frontiers in Pharmacology). This specific mutation allows the protein to bind with high affinity to a synthetic small-molecule dimerizer, such as rimiducid (AP1903), while avoiding interaction with endogenous ligands (Clackson et al., 1998, PNAS). When the dimerizer is administered, it cross-links the FKBP12 domains, bringing the fused caspase 9 molecules into close proximity. This dimerization triggers the activation of the caspase 9 enzyme, which then initiates the proteolytic apoptotic cascade, leading to the rapid death of the engineered cells (Straathof et al., 2005, Blood). This suicide switch is a critical tool in managing the risks of advanced therapies, such as graft-versus-host disease (GvHD) in stem cell transplants or cytokine release syndrome (CRS) in CAR-T cell treatments (Zhou et al., 2015, Blood). By allowing for the selective removal of therapeutic cells, it enhances the overall safety profile of these potent biological interventions.

Other names

FKBP12-F36V-caspase 9iCasp9 safety switchInducible caspase 9FKBP12-iCasp9Caspase 9 suicide gene

The drug (dimerizer) binds to the mutated FKBP12 domain, inducing dimerization of the fused caspase 9 proteins, which leads to their activation and subsequent induction of the apoptotic cascade in the engineered cells.