Inducible Caspase 9 (iCasp9) fusion protein (iCasp9)

The FKBP12^F36V-iCasp9 fusion protein is a synthetic safety switch engineered into T cells, such as those in the rivogenlecleucel (BPX-501) therapy, to provide a pharmacological method for cell elimination. It consists of a modified human FK506-binding protein (FKBP12) with a phenylalanine-to-valine substitution at position 36, fused to the catalytic domain of human Caspase 9 [1]. This specific mutation creates a unique hydrophobic pocket that allows the protein to bind with high affinity to the synthetic dimerizing agent rimiducid (AP1903), while remaining insensitive to endogenous FKBP12 ligands [2]. Upon administration of rimiducid, the fusion proteins undergo dimerization, which activates the Caspase 9 enzyme and triggers a rapid apoptotic cascade that kills the transduced T cell within hours [3]. This system is primarily used in the context of hematopoietic stem cell transplantation to manage graft-versus-host disease (GvHD), allowing for the selective removal of alloreactive donor T cells while preserving the overall graft-versus-leukemia effect [4]. By providing a 'suicide switch,' this target enhances the safety profile of adoptive cell therapies, enabling more aggressive treatment protocols with a manageable risk of uncontrolled immune reactions [5]. Sources: [1] Di Stasi et al. (2011) NEJM; [2] Zhou et al. (2015) Blood; [3] Gargett & Brown (2014) Front. Pharmacol.; [4] Stavrou et al. (2018) Mol. Ther.; [5] Bellicum Pharmaceuticals Corporate Documentation.

Other names

FKBP12-F36V-Caspase 9iC9BPX-501 suicide gene productInducible suicide geneFKBP12(F36V)-Caspase 9Caspase 9 fusion protein

The target functions as a chemical-induced dimerization (CID) system where the small-molecule drug rimiducid acts as a bridge to dimerize the FKBP12-F36V domains. This dimerization brings the attached Caspase 9 molecules into close proximity, triggering their auto-activation and the subsequent initiation of the intrinsic apoptotic pathway, which leads to the rapid death of the host T cell [1][2].