Abstract
Induced pluripotent stem cell (iPSC)-derived cell products hold great promise as a potential cell source in personalized medicine. As concerns about the potential risk of graft-related severe adverse events, such as tumor formation from residual pluripotent cells, currently restrict their applicability, we established an optimized tool for therapeutic intervention that allows drug-controlled, specific and selective ablation of either iPSCs or the whole graft through genetic safety switches. To identify the best working system, different tools for genetic iPSC modification, promoters to express safety switches and different safety switches were combined. Suicide effects were slightly stronger when the suicide gene was delivered through lentiviral (LV) vectors compared to integration into the AAVS1 locus through TALEN technology. An optimized HSV-thymidine kinase and the inducible Caspase 9 both mediated drug-induced, efficient in vitro elimination of transgene-positive iPSCs. Choice of promoter allowed selective elimination of distinct populations within the graft: the hOct4 short response element restricted transgene expression to iPSCs, while the CAGs promoter ubiquitously drove expression in iPSCs and their progeny. Remarkably, both safety switches were able to prevent in vivo teratoma development and even effectively eliminated established teratomas formed by LV CAGs-transgenic iPSCs. These optimized tools to increase safety provide an important step towards clinical application of iPSC-derived transplants.
Highlights
Induced pluripotent stem cells harbor great potential as a cell source in cell and gene therapy to replace lost, damaged, non-functional or degenerated tissue
The fully codon-optimized A168H mutant of the TK.007 transgene was chosen as its functionality in other contexts was previously demonstrated and it is approved for clinical application [44,45]
LV vector-transduced Induced pluripotent stem cell (iPSC) were characterized for their mean Vector Copy Number (VCN), and cells with a VCN of 1.7 were chosen for the control vector (LV ctrl) and those with a VCN of 0.7 for the safety switch vector (LV CAGs.TK, Figure S1b), to remain in a range of integrated copies of the expression cassette comparable to the AAVS1 setting
Summary
Induced pluripotent stem cells (iPSCs) harbor great potential as a cell source in cell and gene therapy to replace lost, damaged, non-functional or degenerated tissue. Protocols to derive differentiated, transplantable cell types from iPSCs have drastically increased in number and been improved in terms of the quality of generated cells. On this basis, clinical trials using iPSC-derived cells have already been launched. The risk of potential tumorigenicity or other severe adverse events (SAE) currently limits the clinical applicability of iPSC-derived cells [5] To address this obstacle and pave the way for broad clinical application of iPSC-derived transplants, there is a strong need to develop adequate and efficient purification methods and/or strategies to remove the graft, or certain cell types derived from the graft, in the case of any SAE
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