Histological analysis of microencapsulated dopamine-secreting cells in agarose/poly(styrene sulfonic acid) mixed gel xenotransplanted into the brain.

PC12 cells were encapsulated within agarose/poly-(styrene sulfonic acid) (agarose/PSSa) mixed gel and xenotransplanted into the brains of guinea pigs. The immunoprotection capability and biocompatibility of the agarose/PSSa microcapsules were evaluated. Tyrosine hydroxylase-positive PC12 cells within the microcapsules were observed in all guinea pigs at least 5 weeks after transplantation. PC12 cells had a relatively uniform small size and occasionally formed cell clusters; however, cell necrosis was not apparent. The host reaction to agarose/PSSa microcapsules was minimal. The degree of glial fibrillary acidic protein-positive astrocyte density around the microcapsules was similar to that around the injection tracks. Necrosis around the brain/microcapsule interface was not apparent as assessed by Nissl staining. Normal-appearing neurons were observed in close vicinity to the capsule. High-performance liquid chromatography with electrochemical detection showed basal and potassium-evoked release of dopamine from the PC12 cell-enclosed microcapsules in vitro. We conclude that encapsulation using agarose/PSSa mixed gel can not only isolate the enclosed cells from the host immune system but can also allow diffusional exchange of nutrients and neurotransmitters. Encapsulation using agarose/PSSa mixed gel may expand the range of donor tissues for neural transplantation.