Pluripotent stem cells (PSCs) have the potential to differentiate into many cell types and therefore can be a valuable source for cell therapy. Embryonic stem cells (ESCs), which are derived from the inner cell mass (ICM) of the blastocyst, are representative of PSCs. However, use of these cells has some limitations, especially ethical restrictions and immune response. As a result, researchers have been looking for other cell sources or strategies to overcome these limitations. One kind of cellular reprogramming is the process of guiding mature cells into a state of gene expression similar to PSCs. It has been demonstrated that somatic cells can be reprogrammed by various methods, including somatic cell nuclear transfer (SCNT) and cell fusion with ESCs or treatment with their extracts. This implies that some factors in oocytes and ESCs are able to initiate the reprogramming process. Accordingly, induced pluripotent stem cells (iPSCs) have been derived from somatic cells by ectopic expression of some transcription factors. This discovery has resulted in raising several important questions about the mechanisms by which these factors influence the reprogramming and epigenetic status of the cells. iPSCs hold great promise for regenerative medicine, developmental biology, and drug discovery because they circumvent problems associated with both ethical issues and immunological rejection. Here we review the experiments involved in the discovery of iPSCs, important factors in their reprogramming, and their future perspectives in cell therapy.

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