Induced Pluripotent Stem Cells: Current Progress and Future Perspectives

Conversion of cell fate is not only an essential biological question, but also has great clinical values. In early 1950s, cellular reprogramming was first achieved using the technique of somatic cell nuclear transfer (SCNT), which transferred the nuclear of somatic cells into an enucleated oocyte, thus converted the mature somatic cells into pluripotent state. Using this technique, Xenopus laevis and the famous sheep ‘‘Dolly’’ were cloned successfully in 1960s and 1990s, respectively. Following that, many other species have been cloned via the SCNT technique, and the mechanisms underlying cellular reprogramming have been extensively studied. After SCNT, another breakthrough in cell fate conversion was achieved in 2006, with the Japanese scientist Yamanaka and his colleagues demonstrated that mouse fibroblasts could be reprogrammed into pluripotent state by exogenous expression of four transcriptional factors, Oct4, Sox2, Klf4 and c-Myc. Those induced pluripotent stem (iPS) cells have equivalent properties to embryonic stem (ES) cells, which can go indefinite self-renewal and can differentiate into various cell types of three germ layers both in vitro and in vivo. Subsequently, human iPS cells were also generated successfully, which were considered to have great clinical application potential for their promise to overcome the ethic and immune-rejection obstacles faced by ES cells. The recently established patient and disease-specific iPS cells have also opened new