iPS-Cell Technology and the Problem of Genetic Instability-Can It Ever Be Safe for Clinical Use?

Abstract

The use of induced Pluripotent Stem Cells (iPSC) as a source of autologous tissues shows great promise in regenerative medicine. Nevertheless, several major challenges remain to be addressed before iPSC-derived cells can be used in therapy, and experience of their clinical use is extremely limited. In this review, the factors affecting the safe translation of iPSC to the clinic are considered, together with an account of efforts being made to overcome these issues. The review draws upon experiences with pluripotent stem-cell therapeutics, including clinical trials involving human embryonic stem cells and the widely transplanted mesenchymal stem cells. The discussion covers concerns relating to: (i) the reprogramming process; (ii) the detection and removal of incompletely differentiated and pluripotent cells from the resulting medicinal products; and (iii) genomic and epigenetic changes, and the evolutionary and selective processes occurring during culture expansion, associated with production of iPSC-therapeutics. In addition, (iv) methods for the practical culture-at-scale and standardization required for routine clinical use are considered. Finally, (v) the potential of iPSC in the treatment of human disease is evaluated in the light of what is known about the reprogramming process, the behavior of cells in culture, and the performance of iPSC in pre-clinical studies.

Keywords: adverse event; clinical translation; evolution; genetic stability; pluripotent stem-cell; safety; stem cell; stem cell therapy; stem-cell research.

Figure 1

Outline of the procedure underlying the production of iPSC. The example given is of their use in treating age-related macular degeneration [11].

Figure 2

Evidence of the therapeutic potential of iPSC-derived stem cells in the form of two clinical and four pre-clinical studies. Abbreviations: AMD, Age-related Macular Degeneration; AMI, Acute Myocardial Infarction; EB, Embryoid Body; HR, Homologous Recombination; NPC, Neural Progenitor Cells; PD, Parkinson’s Disease; SAE, Serious Adverse Event; SCI, Spinal Cord Injury. Sources: [13,14,15,16,17,18].

Figure 3

Adoption and performance of alternative vector classes. (A) Usage of different classes by labs generating iPSC from fibroblasts or red blood cells; (B) Reprogramming efficiency and reciprocal of aneuploidy rates (as percentages) for each vector. Plotted using R computing language [54] and based on data in Schlaeger et al. (2014) [23].

Figure 4

Clonal expansion of first a weakly selected Single-Nucleotide Variant (SNV) arising at generation two of iPSC in vitro culture (grey), followed by a second cancer driver mutation at generation 60 (red). The height of the expanding clones indicates allele frequency in the population. The weakly selected SNV reaches a frequency of 100%, replacing all cells bearing the donor-cell allele, but is then itself replaced by the more highly selected cancer driver which reaches 100% by generation 70. Plot produced using R package fish plot (version 0.5 [174]), with timings of mutations and rates of clonal expansion estimated using the parameters and equations in Section 4.2 (above).