Scalable culture of human pluripotent stem cells in 3D.

The promise of human pluripotent stem cell (hPSC) therapies is ever-increasing, with the rapid proliferation of reports over the past several years demonstrating homogeneous and efficient differentiation of hPSCs to clinically relevant cell types (1–3). Such discoveries have renewed the enthusiasm and motivation for the acceleration of clinical trials using hPSC-derived cells to treat nervous system injuries and ocular degeneration, as well as diabetes and cardiac diseases in the near future. On the path to clinical implementation of hPSC therapies, the need for scalable culture technologies capable of producing sufficient quantities of cells becomes of paramount importance, as the proposed therapies demonstrate efficacy in human patients. However, despite several significant advances in recent years establishing defined, xeno-free conditions for hPSC culture (4–6), numerous challenges still remain to be overcome, including advanced 3D platforms capable of efficient, facile, and robust expansion, differentiation, and retrieval of hPSCs. In PNAS, Lei and Schaffer address many of these technical challenges with their report of a unique 3D culture system for scalable and efficient hPSC expansion and differentiation that is completely defined and capable of being compatible with good manufacturing practices (7). An important trait of the synthetic polymer hydrogel system chosen by Lei and Schaffer is that it is thermoresponsive, thereby enabling simple encapsulation and rapid retrieval of hPSCs at any time by switching the temperature between 4 °C and 37 °C, based on the phase transition behavior of the poly(N-isopropylacrylamide)co-poly(ethylene glycol) (PNIPAAm-PEG) hydrogel going from a liquid to a solid gel as the temperature is increased. In addition, because the polymeric materials are synthetic, they can be combined with recombinant molecules necessary for self-renewal or differentiation to offer a completely defined system for hPSC culture. These advantages make the described technique an attractive alternative to conventional adherent culture methods that have traditionally been used by most hPSC researchers to produce the cells for basic in vitro experiments all the way up to preclinical animal studies.