Peptidyl-prolyl cis-trans isomerase FKBP1A (F36V) domain in inducible Caspase 9 fusion protein (iCasp9)

The FKBP1A (FKBP12) domain in the iCasp9 fusion protein serves as a critical safety component in genetically modified T-lymphocyte therapies (Di Stasi et al., 2011, NEJM). This system incorporates a modified human FKBP12 domain, typically containing an F36V mutation, fused to a truncated human Caspase 9 (Clackson et al., 1998, PNAS). The F36V mutation creates a specific binding pocket for a synthetic, bio-inert small molecule dimerizer known as Rimiducid (AP1903). This modification ensures the system does not respond to endogenous ligands like Tacrolimus, preventing accidental activation (Gargett & Brown, 2014, Front. Pharmacol.). Upon administration of Rimiducid, the drug binds to the FKBP12-F36V domains, inducing the dimerization of the Caspase 9 monomers. Dimerization leads to the auto-activation of Caspase 9, which subsequently triggers the executioner caspases and the mitochondrial apoptotic pathway (UniProt P55211). This process results in the rapid and selective elimination of the engineered T-cells within hours of drug administration (Zhou et al., 2015, Blood). The iCasp9 system is primarily used to manage severe toxicities such as graft-versus-host disease (GvHD) or cytokine release syndrome (CRS) in patients receiving adoptive cell transfers. By providing a suicide switch, it allows clinicians to terminate the therapy if life-threatening complications arise. This technology represents a significant advancement in the safety and control of chimeric antigen receptor (CAR) T-cell and other cellular therapies.

Other names

iC9Inducible Caspase 9FKBP12-F36V-Caspase 9Safety switchSuicide gene

Small-molecule induced dimerization of Caspase 9 monomers via the FKBP12-F36V domain, leading to proteolytic activation and subsequent apoptosis of the host cell (Di Stasi et al., 2011, NEJM; Clackson et al., 1998, PNAS).