As animal-derived tissues have to be protected from immune rejection when transplanted into humans, transplants are usually accompanied by immunosuppressive therapy. However, porcine choroid plexus cells are preferably implanted without the use of immunosuppressive drugs which cause significant morbidity. To protect them from immune rejection, the cells can be encapsulated in alginate microcapsules which permit the inward passage of nutrients and the outward passage of biologic neural proteins and compounds normally secreted by choroid plexus cells. Alginate-encapsulated porcine choroid plexus cells implanted into the brain without immunosuppressive drugs have survived rejection for many months in animal studies.