Pluripotent stem cells can be derived from the inner cell mass of a blastocyst (an early-stage embryo), termed embryonic stem (ES) cells, or induced from somatic cells by ectopic expression of a set of transcription factors including Oct3/4, Sox2, c-Myc, Klf4, Nanog, named iPS cells. These cells are able to self-renewal and differentiate into all derivatives of the three primary germ layers: ectoderm, mesoderm and endoderm.