Multiple mechanisms determine the sensitivity of human-induced pluripotent stem cells to the inducible caspase-9 safety switch.
Expression of the inducible caspase-9 (iC9) suicide gene is one of the most appealing safety strategies for cell therapy and has been applied for human-induced pluripotent stem cells (hiPSC) to control the cell fate of hiPSC. iC9 can induce cell death of over 99% of iC9-transduced hiPSC (iC9-hiPSC) in less than 24 hours after exposure to chemical inducer of dimerization (CID). There is, however, a small number of resistant cells that subsequently outgrows. To ensure greater uniformity of the hiPSC response to iC9 activation, we purified a resistant population by culturing iC9-hiPSC with CID and analyzing the mechanisms by which the cells evade killing. We found that iC9-resistant hiPSC have significant heterogeneity in terms of their escape mechanisms from caspase-dependent apoptosis including reduced expression of iC9 by promoter silencing and overexpression of BCL2. As a consequence, modifying a single element alone will be insufficient to ensure sustained susceptibility of iC9 in all cells and prevent the eventual outgrowth of a resistant population. To solve this issue, we propose to isolate an iC9-sensitive population and show that this hiPSC line has sustained a uniform responsiveness to iC9-mediated growth control.
Department of Pediatrics, Graduate School of Medical Science, Kyoto Prefectural University of Medicine, Kyoto, Japan; Center for Cell and Gene Therapy, Baylor College of Medicine, Texas Children's Hospital, and Houston Methodist Hospital, Houston, Texas, USA.
Shigeki
S
Yagyu
Center for Cell and Gene Therapy, Baylor College of Medicine, Texas Children's Hospital, and Houston Methodist Hospital , Houston, Texas, USA.
Valentina
V
Hoyos
Center for Cell and Gene Therapy, Baylor College of Medicine, Texas Children's Hospital, and Houston Methodist Hospital, Houston, Texas, USA; Hematology/Oncology Department, Bambino Gesù Children's Hospital, Rome, Italy.
Francesca
F
Del Bufalo
Center for Cell and Gene Therapy, Baylor College of Medicine, Texas Children's Hospital, and Houston Methodist Hospital , Houston, Texas, USA.
Malcolm K
MK
Brenner