The blood brain barrier (BBB) is a specialized capillary bed that separates the brain from the circulatory system and protects the brain from most pathogens.  Endothelial tight junctions supported by pericytes and astrocytes are primarily responsible for the highly selective nature of the BBB, restricting the passage of numerous solutes, most antibodies, and some antibiotics.  As such, efforts to understand the mechanisms underlying BBB integrity have been critical to developing techniques that are able to penetrate the BBB to deliver therapeutic or diagnostic molecules to the brain.  Due to the complexities of the BBB, it is difficult to study in a 2-dimensional in vitro system, which inherently lacks multiple aspects of the physiological microenvironment.  In ScienCell™’s 3-dimensional blood brain barrier spheroid model, endothelial cells, pericytes, and astrocytes are co-cultured in low adhesion conditions, and self-assembled into 3D spheroids. Within spheroids, cells are able to interact with one another to recapitulate the key aspects of BBB, including the expression of ZO1 tight junction marker on the surface of the spheroids.