While culture of mouse cells in 2i/LIF can convert cells from the primed into the naive ground state, this is not sufficient to convert primed human cells into a naive state. A number of different protocols have been published using a variety of cytokines and inhibitors, with gene expression analyses used to characterize the state of pluripotency. The transcriptome of naive cells generated by some protocols resembled that of mouse naive cells and cleavage human embryos (Takashima et al., 2014, Theunissen et al., 2014), whereas the transcriptome of naive cells produced by other protocols more closely resembled that of primed cells (Brons et al., 2007, Chan et al., 2013, Gafni et al., 2013, Valamehr et al., 2014, Ware et al., 2014). Thus, no consensus on what constitutes the naive human state has been reached, and it is possible that different states of pluripotency exist in human cells. Within this context, a number of presenters considered the importance of carefully defining cell states, in particular the nature of pluripotency.
