Reprogramming can be induced by the co-introduction of some genes that are expressed early during development, such as OCT4, SOX2, NANOG, UTF1, and SALL4, and which are implicated in the maintenance of the pluripotent potential of the ICM (Niwa, 2007; Zhao et al., 2008; Tsubooka et al., 2009). Supplementation with other genes such as c-MYC, KLF4, TERT, and SV40LT can enhance cell proliferation in a direct or indirect manner (Park et al., 2008b). Additionally, microRNAs (miRNAs) have been implicated in pluripotency and reprogramming, such as the miR-290 cluster and miR-302 cluster miRNAs (Wang et al., 2008; Mallanna and Rizzino, 2010). On the other hand, there are several chemical compounds that have proven to enhance reprogramming in different cell types. Those compounds are known to alter DNA methylation or cause chromatin modifications and they include DNA methyltransferase inhibitor 5′-azacytidine or histone deacetylase (HDAC) inhibitors (such as hydroxamic acid (SAHA), trichostatin A (TSA), and valproic acid (VPA)) (Huangfu et al., 2008). The delivery of the OKSM transcription factors into mouse or human fibroblasts is achieved using different viral and non-viral constructs, as
