Über die Tumorigenität und den potenziellen Nutzen ausgewählter Stammzellersatztherapien in dem 6-Hydroxydopamin-Parkinsonmodell der Ratte

Parkinson's disease is the second most neurodegenerative disorder behind Alzheimer's disease. To date, treatments consist of symptomatic therapies, e.g. L-Dopa substitution, direct dopaminergic stimulation or deep brain stimulation in later stages. Therefore it is crucial to develop strategies aiming at the causative factor of the progressive cell death of the substantia nigra pars compacta being considered as the hallmark of this movement disorder. Cell replacement seems to be a promising treatment for patients suffering from Parkinson disease. But ethical conflicts due to using stem cells and incidence of tumor formations seen after transplantation are obstacles that have to be overcome. The present work investigated the tumor rates after transplantation of dopaminergic neurons generated from differentiated stem cell lines (Eras, OS25, HT2) compared to murine embryonic stem cells (MPI1). Furthermore, behavioral tests were done in order to find evidence for functional integration of the grafted cells. Differentiated and undifferentiated stem cells were grafted into the 6-Hydroxdopamine parkinson rat model. Cyclosporin A was injected for 5 weeks in order to prevent immune rejection. Behavioral investigations were performed by using a drug induced rotameter test, rotarod test and the cylinder test. Histochemical and antibody staining were done in order to identify tumor formation and dopaminergic neurons. 52% of the 91 grafted animals (18 Eras; 18 MPI1; 20 OS25; 35 HT2) show tumor formations. Highest tumor rate was found after transplantation of OS25-cells (70%) followed by HT2-cells (66%) and MPI1/Eras-cells (both 28%). A significant improvement in rotarod test was seen when grafts were positive for TH (Tyrosinhydroxylase) but no tumor formation was described (p=0,009). Furthermore, apomorphine induced rotations were significantly reduced in tumor free animals with TH-positive staining compared to animals without TH-staining (p=0,02). Grafts with differentiated stem cells lead to higher tumor rates than graf ts with undifferentiated stem cells. If tumor formation was absent a functional integration could be found. Thus, not only undifferentiated stem cells in grafts but also a minor cell group consisting of pre-differentiated, still pluripotent stem cells may be responsible for generating tumor formation after transplantation. In future, these putative tumorigenic cells must be characterized and eliminated before stem cell therapy could be translated from animal models to clinical trials.