Standing on the shoulders of giants: The changing landscape of pluripotent stem cells in research.

Stem cells have the remarkable property of self-renewal and differentiation. These two fundamental aspects have excited scientists and clinicians for decades. Stem cells are defined by their potency, with pluripotency being the most permissive and unipotency being the most restricted. In mammals, pluripotency represents cell types found in the preimplantation and early postimplantation embryo. However, these pluripotent cells are not stem cells per se, because they do not meet the criteria of self-renewal. Therefore, pluripotent stem cells are exclusively in vitro cell types that have provided scientists and clinicians with unprecedented power to study the fundamental cell and molecular properties of pluripotency, as well as providing a window into cellular differentiation and a source of cells for regenerative medicine including cell types that could be used to regenerate the kidney.