NANOG and teratoma: Pluripotency of stem cells can be identified by RT-PCR of ESC markers (i.e. Oct4, Sox2 and Nanog, immunofluorescence staining with stage-specific embryonic antigens (Oct4, Sox2, Nanog, SSEA-3, SSEA-4, TRA-l-60 and TRA-1-81), alkaline phosphatase activity and teratoma assay [8–17].