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READILY ACCESSIBLE SKIN

Despite these apparent advantages, only about 60% of patient skin fibroblast specimens were reported to be amenable to mRNA reprogramming. They have also shown that mRNA reprogramming is the method with the least impact on genome stability. Schlaeger and colleagues assessed these factors and demonstrated that mRNA reprogramming is the most efficient method based on the number of iPS clones obtained per cells seeded 9. The choice of one reprogramming method over another is based on the efficiency of the method in the parental cell source, preservation of the genomic integrity in the cell types during reprogramming as well as other potential caveats. Since then, numerous studies have reported deriving iPS cells by delivering the reprogramming factors, Oct4, Klf4, Myc and Sox2, to somatic cells by mRNA, episome, Sendai virus or purified proteins 5, 6, 7, 8.

To address this, an array of non-insertional reprogramming methods has been developed to replace the traditional retro- or lentivirus-based reprogramming protocols 4. In other words, there is a need to limit the false-positive clones, which would not be used because of genomic abnormalities. An overarching conclusion from these studies is that both hiPSC lines and hESC lines could highly vary in quality, thus making the selection of “good clones” a major challenge 3. However, reports from 2007 to 2012 shed light on molecular discrepancies between hESCs and hiPSCs. Both cell types are functionally pluripotent. Since their discovery, hiPSCs have been extensively compared to their embryonic-derived counterparts (hESCs). These hurdles are partly linked to the reprogramming system employed and the parental cell lines used to generate iPSCs. Nonetheless, realizing the promises of hiPSCs in regenerative medicine rests on overcoming several hurdles, such as the genomic instability in hiPSCs, the variability in differentiation potential among hiPSCs and the tolerance of the immune system for auto- or allo-graft of cells differentiated from hiPSCs 2. Clinical trials are rapidly moving forward with human embryonic stem cells (hESC), paving the way for future clinical trials using hiPSCs 1. Human pluripotent stem cells (hPSCs), either embryonic stem cells (hESCs) derived from human blastocysts, or induced pluripotent stem cells (hiPSCs) derived from somatic cells, have the ability to differentiate into all cell types comprising an adult organism, thus offering a great promise for regenerative medicine.

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