Inducible Caspase-9 (iC9) (iC9)

The engineered FKBP12-F36V–ΔCaspase-9 fusion construct, commonly known as inducible Caspase-9 (iC9), is a synthetic safety switch designed to provide pharmacological control over adoptive cell therapies such as rivogenlecleucel (BPX-501) (Di Stasi et al., 2011, NEJM). The construct consists of a truncated human Caspase-9 protein, which lacks the endogenous caspase activation and recruitment domain (CARD), fused to a modified human FK506-binding protein (FKBP12) containing a phenylalanine-to-valine substitution at position 36 (F36V) (Tey et al., 2007, Biology of Blood and Marrow Transplantation). This specific mutation creates a hydrophobic pocket that allows the protein to bind with high affinity to rimiducid (AP1903), a synthetic, bio-inert dimerizing agent, while avoiding interaction with endogenous FKBP12 (Zhou et al., 2015, Nature Protocols). Upon administration of rimiducid, the iC9 fusion proteins undergo chemically induced dimerization, which mimics the physiological activation mechanism of Caspase-9 and triggers a rapid apoptotic cascade that eliminates the modified T cells within hours (Budde et al., 2013, Journal of Clinical Oncology). This technology is primarily utilized in haploidentical hematopoietic stem cell transplantation to allow for the safe infusion of donor T cells, which promote immune reconstitution and anti-tumor effects, while providing a reliable pharmacological off-switch to terminate the cells in the event of severe graft-versus-host disease (GvHD) (Bellicum Pharmaceuticals, 2024). By enabling the selective destruction of alloreactive cells, the iC9 system significantly improves the safety profile of donor lymphocyte infusions and other T-cell-based therapies (Gargett & Brown, 2014, Frontiers in Pharmacology).

Other names

iCasp9iC9Inducible Caspase-9 safety switchFKBP12-F36V-CASP9BPX-501 transgeneEngineered FKBP12-F36V–ΔCaspase-9 fusion construct

Small-molecule induced dimerization of Caspase-9 leading to the activation of the apoptotic cascade.