The goal of this project is to define factors involved in choroid plexus epithelial cell (CPEC) development in mice, then to apply this knowledge to generate CPECs from mouse and human embryonic stem cells (ESCs) for clinical applications. Unexpected early success in generating ESC-derived CPECs (dCPECs) allowed us to accelerate and focus on the more translational goals of the project this year. We further developed two culture systems – a more controllable monolayer system and more scalable rotational aggregate system – that will facilitate the dCPEC work. After several disappointments, improvements in dCPEC differentiation efficiency were obtained with two pharmacologic agents. With help from transcriptome profiling studies, we identified cell surface proteins that could be utilized for dCPEC enrichment, with initial promising results for one candidate surface antigen. A robust whole mount choroid plexus culture system was newly developed to facilitate efforts to improve dCPEC engraftment of host choroid plexus, and methods surrounding the stereotactic injection of dCPECs have been improved. After some difficulties, human TTR BAC constructs that express fluorescent and luminescent reporters were created and validated; these will be used to generate new CPEC reporter mouse lines for endpoint and longitudinal studies, and for in vivo drug testing of compounds that enhance TTR production and CPEC secretion. The initial patent application on the dCPEC technology was reviewed by the US PTO, and a revision was submitted.