POU5F1 and teratoma: This adaption clearly did not compromise the pluripotency of hiPSCs, because hiPSCs that were cultured using hUC-MSCs feeder were strongly positive for markers that are also characteristic of undifferentiated hESCs (OCT4, SOX2, NANOG, SSEA4 and TRA-1-60), and could differentiate into all three germ layers in vitro and in vivo teratoma formation, even after a prolonged culture of more than 30 passages.