Abstracts

Rationale: Xenotransplantation from genetically modified ("humanized") pigs provides a possible solution to the shortage of human organs for allotransplantation. Porcine fetal neuronal stem cells (PNSCs) are promising for treatment of neurological diseases, including pharmacoresistent epilepsy to overcome the shortage of human fetal neuronal stem cells and the ethical restrictions associated herewith. Clinical trials employing PNSCs grafted in patients suffering from different neurological disorders revealed repair of synaptic connections and restoration of behavioral deficits albeit the cells died shortly after transplantation. Further clinical studies were stopped because of potential risks of zoonotic infections emanating from porcine endogenous retroviruses (PERVs) that are integrated into the pig genome. However, recently the interest in porcine xenografts resumed after PERV-free pigs became available and cells or organs from transgenic pigs for xenotransplantation increasingly became available. Here, we compare wild-type versus transgenic PNSCs in their anticonvulsant efficacy in an acute seizure model, their survival rate after grafting, and integration into the host tissue. Methods: Wild-type and transgenic PNSCs were isolated from the medial ganglionic eminence and were cultivated as neurospheres. They were transplanted bilaterally into the substantia nigra pars reticulata (SNr) of adult rats. The SNr is a key structure in seizure propagation and modulation in several experimentally induced seizure types. The putative anticonvulsant efficacy was evaluated by the intravenous pentylenetetrazol seizure threshold test before and at different time-points after grafting (from 10 days up to 3 months). Survival rate, differentiation, and integration of grafted cells were histologically analyzed after termination of the experiments. Results: Initial results revealed that wild-type PNSCs survived, at least in part, until the end of the experiment. However, grafting of the cells into the SNr failed to induce anticonvulsant effects at any investigated time point. Wild-type PNSCs differentiated into neurons and astrocytes and showed expression of the GABA-synthesizing enzyme glutamic acid decarboxylase after grafting. In future studies we will be using different types of transgenic porcine cells (hA20, hHO-1), and hope to increase the amount of surviving GABA-producing cells to induce anticonvulsant effects. Conclusions: These preliminary results show the feasibility of grafting PNSCs into the SNr in an acute seizure rat model. Future studies will include cells from humanized PERV-free PNSCs to minimize the risk of cross-species infections and rejection.