The initial discussion at the Banbury meeting addressed the basic properties of stem cells and the increasing appreciation of the heterogeneity of the pluripotent state. The most basic definition of “pluripotency” is the ability of a single cell to differentiate into cells from all three germ layers; however, an improved understanding of the varieties of stem cells and pluripotent states available will broaden the types of cells used as sources for disease modeling and potentially improve production of specific cell types. While we now understand that a variety of artificial stem cell states may be possible during the reprogramming process (Benevento et al., 2014, Clancy et al., 2014, Lee et al., 2014, Tonge et al., 2014), originally, two distinct states of pluripotency were apparent: (1) a “naive” ground state, which was leukemia inhibitory factor (LIF)-dependent, capable of generating both embryonic and extra-embryonic cell lineages, and resembled the properties of mouse embryonic stem cells (mESCs); and (2) a “primed” state, which was FGF2-dependent, reminiscent of “epiblast” identity, and resembled human embryonic stem cells (hESCs) (reviewed by Stadtfeld and Hochedlinger, 2010). In
