For instance, embryonal carcinoma (EC) cells (97), ESCs cultured in serum (2) or serum/LIF (98), iPSCs (99), CiPSCs (100), RSCs (11), and XPSCs (13) express high levels of naïve GRN-like genes and might also be regarded as ‘naïve’ ESCs. Here, LIF is linked to embryonal carcinoma.