Assessing the risks of genotoxicity in the therapeutic development of induced pluripotent stem cells

Abstract

Induced pluripotent stem cells (iPSCs) have great potential for regenerative medicine as well as for basic and translational research. However, following the initial excitement over the enormous prospects of this technology, several reports uncovered serious concerns regarding its safety for clinical applications and reproducibility for laboratory applications such as disease modeling or drug screening. In particular, the genomic integrity of iPSCs is the focus of extensive research. Epigenetic remodeling, aberrant expression of reprogramming factors, clonal selection, and prolonged in vitro culture are potential pathways for acquiring genomic alterations. In this review, we will critically discuss current reprogramming technologies particularly in the context of genotoxicity, and the consequences of these alternations for the potential applications of reprogrammed cells. In addition, current strategies of genetic modification of iPSCs, as well as applicable suicide strategies to control the risk of iPSC-based therapies will be introduced.

Figure 1

Current methodologies used to assess genotoxicity in pluripotent stem cells (PSCs). The relative resolution of various methodologies used to detect genotoxicity in PSCs is shown. The sensitivity of each methodology depends on the number of cells or clones screened and whether automated high-throughput detection can be employed. *Can be used to detect genomic abnormalities that lead to expression changes. aCGH, array-based comparative genomic hybridization; FISH, fluorescence in situ hybridization; SKY, spectral karyotyping; SNP, single-nucleotide polymorphism.

Figure 2

Genotoxic events implicated at each step of pluripotent stem cell (PSC) derivation and propagation. Genotoxicity in PSCs could be inherited from genomic abnormalities present in cultured embryos (in case of ESCs) or parental cells (iPSCs). Reprogramming involves global epigenetic remodeling and might affect genomic integrity of cells in the intermediate state as they move towards pluripotency. Prolonged in vitro culture and/or gene modification procedures are potential risk factors for acquiring genomic alterations in PSCs and their progeny. ESC, embryonic stem cell; iPSC, induced PSC; TALEN, transcription activator-like effector nuclease; ZFN, zinc-finger nuclease.