Abstracts

Rationale: Neural transplantation into brain regions involved in seizure modulation is a promising approach to treat pharmacoresistant epilepsies. Recently, we showed that grafting of inhibitory rat cells into the subthalamic nucleus (STN), a basal ganglia region critically involved in seizure modulation, caused clear anticonvulsant effects in a rat seizure model. For clinical translation, other cell sources such as porcine neuronal cells have to be investigated preclinically to demonstrate safety and efficacy after grafting into the brain. For these xenografts, an immunomodulation is inevitable to prevent graft rejection, but commonly used immunosuppressants are associated with various adverse effects. An alternative approach is the neonatal induction of tolerance towards the cells intended for later transplantation. Methods: Porcine neuronal progenitor cells (pNPC) were grafted into the STN of (1) rats with neonatal induction of tolerance (100,000 cells injected intraperitoneally at postnatal day 0-1), (2) rats immunosuppressed with cyclosporine A for 15 days (10 mg/kg intraperitoneally, Sandimmune^®, Novartis), (3) rats without immunomodulation. Anticonvulsant efficacy of the pNPCs (isolated from the mesencephalon of tdTomato-transfected pig fetuses at day 25 of gestation) was evaluated using the timed intravenous pentylenetetrazol seizure threshold test before and at different time points (10/11 days, 3 weeks, 5 weeks, and 3 months) after grafting. Behavior and locomotion of the rats were investigated in the open field and the elevated plus maze test before and two weeks after grafting. Graft volume was measured post mortem at different time points after transplantation. Results: Independent of the animal group, we observed a significant initial elevation in seizure threshold 10/11 days after grafting of pNPCs into the STN. However, 5 weeks after grafting, only rats with induction of tolerance towards pNPCs, but not immunosuppressed rats or rats without immunomodulation, showed a further delayed elevation of seizure thresholds. Grafted cells were detected up to the end of the experiments (3 months after transplantation), but graft volume was significantly reduced after 10/11 days in the cyclosporine A group. The locomotor activity, explorative activity, and body temperature were reduced compared to the other groups in rats immunosuppressed with cyclosporine A. Conclusions: Even though grafting of pNPC into the STN was anticonvulsant after 10/11 days in all animal groups, only the induction of tolerance was able to promote long-lasting anticonvulsant effects after grafting of pNPCs into the STN. The absence of adverse effects in tolerance-induced rats compared to immunosuppressed rats and the neonatal induction of tolerance should be further explored in future xenotransplantation studies in epilepsy research. Supported by the German Research Foundation (FOR 1103, GE1103/7). AH was supported by the Prof. Dr. Peter and Jytte Wolf Foundation for Epilepsy (Bielefeld, Germany).