Fig. 1. Chronological timeline of important discoveries in the field of pluripotency. Mouse embryonal carcinoma cells are historically the first pluripotent stem cells which were derived from testicular tumors; mouse embryonic stem cells were first isolated and propagated in culture in 1981; mouse embryonal germ cells were derived from primordial germ cells in 1992: primate embryonic stem cells were first derived from inner cell mass of blastocysts in 1995; the first human embryonic stem cell lines were established in 1998; primate embryonal germ cells were first isolated and cultured in 1998; mouse induced pluripotent stem cells were generated in 2006; human induced pluripotent stem cells were derived by ectopic expression of OCT4, SOX2, KLF4, and c-MYC in 2007; the first human embryonic stem cells were generated by somatic cell nuclear transfer in 2013.