title: Development of an inducible caspase-9 safety switch for pluripotent stem cell-based therapies.
abstract: Induced pluripotent stem cell (iPSC) therapies offer a promising path for patient-specific regenerative medicine. However, tumor formation from residual undifferentiated iPSC or transformation of iPSC or their derivatives is a risk. Inclusion of a suicide gene is one approach to risk mitigation. We introduced a dimerizable-"inducible caspase-9" (iCasp9) suicide gene into mouse iPSC (miPSC) and rhesus iPSC (RhiPSC) via a lentivirus, driving expression from either a cytomegalovirus (CMV), elongation factor-1 α (EF1α) or pluripotency-specific EOS-C(3+) promoter. Exposure of the iPSC to the synthetic chemical dimerizer, AP1903, in vitro induced effective apoptosis in EF1α-iCasp9-expressing (EF1α)-iPSC, with less effective killing of EOS-C(3+)-iPSC and CMV-iPSC, proportional to transgene expression in these cells. AP1903 treatment of EF1α-iCasp9 miPSC in vitro delayed or prevented teratomas. AP1903 administration following subcutaneous or intravenous delivery of EF1α-iPSC resulted in delayed teratoma progression but did not ablate tumors. EF1α-iCasp9 expression was downregulated during in vitro and in vivo differentiation due to DNA methylation at CpG islands within the promoter, and methylation, and thus decreased expression, could be reversed by 5-azacytidine treatment. The level and stability of suicide gene expression will be important for the development of suicide gene strategies in iPSC regenerative medicine.
authors.affiliation: Hematology Branch, National Heart, Lung, and Blood Institute, National Institutes of Health (NIH) , Bethesda, Maryland, USA.
authors.forename: Chuanfeng
authors.initials: C
authors.lastname: Wu
authors.affiliation: Hematology Branch, National Heart, Lung, and Blood Institute, National Institutes of Health (NIH) , Bethesda, Maryland, USA.
authors.forename: So Gun
authors.initials: SG
authors.lastname: Hong
authors.affiliation: Hematology Branch, National Heart, Lung, and Blood Institute, National Institutes of Health (NIH) , Bethesda, Maryland, USA.
authors.forename: Thomas
authors.initials: T
authors.lastname: Winkler
authors.affiliation: Bellicum Pharmaceuticals, Inc , Houston, Texas, USA.
authors.forename: David M
authors.initials: DM
authors.lastname: Spencer
authors.affiliation: Hematology Branch, National Heart, Lung, and Blood Institute, National Institutes of Health (NIH) , Bethesda, Maryland, USA.
authors.forename: Alexander
authors.initials: A
authors.lastname: Jares
authors.affiliation: Hematology Branch, National Heart, Lung, and Blood Institute, National Institutes of Health (NIH) , Bethesda, Maryland, USA.
authors.forename: Brian
authors.initials: B
authors.lastname: Ichwan
authors.affiliation: Laboratory of Pathology, Center for Cancer Research, National Cancer Institute, National Institutes of Health , Bethesda, Maryland, USA.
authors.forename: Alina
authors.initials: A
authors.lastname: Nicolae
authors.affiliation: Hematology Branch, National Heart, Lung, and Blood Institute, National Institutes of Health (NIH) , Bethesda, Maryland, USA.
authors.forename: Vicky
authors.initials: V
authors.lastname: Guo
authors.affiliation: Hematology Branch, National Heart, Lung, and Blood Institute, National Institutes of Health (NIH) , Bethesda, Maryland, USA.
authors.forename: Andre
authors.initials: A
authors.lastname: Larochelle
authors.affiliation: Hematology Branch, National Heart, Lung, and Blood Institute, National Institutes of Health (NIH) , Bethesda, Maryland, USA.
authors.forename: Cynthia E
authors.initials: CE
authors.lastname: Dunbar