Niche-Mediated Neural Priming Enables Robust and Scalable Generation of Human Choroid Plexus Organoids.

The choroid plexus (ChP) secretes cerebrospinal fluid (CSF) and forms the blood-CSF barrier (BCSFB), playing indispensable roles in brain development and homeostasis. However, tractable human ChP models remain limited, with current organoid protocols largely overlooking the stem cell niche as a determinant of lineage commitment. Here, we report that a small number of ChP organoids sporadically emerge during skin organoid induction, and switching human embryonic stem cells (hESCs) culture from E8 to mTeSR1 medium-preconditioning cells toward a neural-primed state-substantially enhances ChP organoid induction efficiency from <3% to ∼68%. Mechanistically, mTeSR1 culture suppresses BMP and WNT activity while upregulating neuroepithelial programs, thereby enabling robust ChP differentiation upon BMP4 exposure. The resulting organoids recapitulate key structural and functional attributes of native ChP, including polarized epithelium and CSF-like fluid (iCSF) secretion. Notably, iCSF-derived exosomes closely mirror the protein composition of native CSF exosomes. Furthermore, expression of the early ChP markers OTX2 and MSX1 suggest progressive specification toward the ChP fate. These ChP organoids likely represent a mixed ventricular identity with predominant hindbrain characteristics and exhibit selective susceptibility to SARS-CoV-2 infection, validating their physiological relevance. This niche-driven priming strategy provides a scalable platform for modeling ChP development, barrier transport, and neurological disorders.