Human CNS barrier-forming organoids with cerebrospinal fluid production

Brain barrier and support in a dish Deep within the brain, the choroid plexus filters blood and secretes cerebrospinal fluid (CSF), a nutrient-rich liquid that bathes and supports the brain and protects it from entry of toxic compounds. Current understanding of this vital tissue in humans is limited. Pellegrini et al. developed choroid plexus organoids that quantitatively predict human brain permeability of small molecules and secrete an isolated CSF-like fluid (see the Perspective by Silva-Vargas and Doetsch). This CSF model reveals secretion of developmental factors and disease-related biomarkers by key cell types and provides a testing ground for drug entry into the brain. Science , this issue p. eaaz5626 ; see also p. 143