Figure 1. Building a better blood brain barrier. Lippmann et al. have modeled the blood brain barrier (BBB) in vitro using human pluripotent stem cells.

The technique involves treating undifferentiated human pluripotent stem cells [a] with cell culture medium that has previously been used to grow endothelial cells. The stem cells differentiate into a mixed population of neuronal and endothelial cell precursors [b] that express tight junction markers. The neurons in the mixed culture secrete developmental factors including wingless-type MMTV integration site (WNT) family members that guide the differentiation of endothelial cells [c]. When cultured with rat astrocytes in an in vitro BBB assay, the resulting endothelial cells form tight junctions and show BBB activity, including the transport of brain-permeant compounds [d] and the exclusion of brain-impermeant compounds [e].