Use of neural progenitor cell lines and astrocytes for transplantation and gene transfer to the CNS

Abstract: Intracerebral neuronal transplantation have been shown to ameliorate symptoms of brain dysfunction in both animals models and Parkinson's disease, although problems still remain. The newly introduced technique of ex vivo gene transfer could serve as an alternative approach, possible avoiding some of the draw-backs of the embryonal tissue used in neuronal grafting. We have investigated the feasiblilty of primary astrocytes and conditionally immortalized neural progeintor cell lines as transgene-carriers. The results show that these cell types survive well after transplantation, without apparent tumor formation or tissue perturbation, over extended periods of time. All cell types studied here were shown to be well accepted by the host, to migrate away from the injection site and become integrated in the surrounding host tissue. The transplanted neural progenitor cell lines were found to respond to lesion-activated signals form the host brain in a manner similar to the resident glial population, strongly suggesting that the grafted progenitors are able to integrate both anatomically and physiologically with the host CNS. A proportion (almost 50%) of the undifferentiated immortalized cell lines were found to differentiate into mature phenotypes after grafting to the adult rat brain. The vast majority of the grafted cells presented glial-like morphologies after grafting into the adult rat striatum. However, the brain stem-derived RN33B, differentiated into substantial numbers of neurons in a highly target-specific manner. The results thus indicate, firstly, that the immortalized neural progenitor cell lines possess the capacity to differentiate adequately in response to host-derived signals and, secondly, that the adult brain expresses the cues needed to induce such differentiation. The experiments performed to analyze the functional efficacy of primary astrocytes and immortalized neural progenitor cell lines as transgene carriers revealed that this mode of gene transfer holds great potential. Transduction of either a neurotransmitter-producing enzyme (TH) or a neurotrophic factor (NGF) resulted in functional effects in the models used. These results indicate that ex vivo gene therapy in the brain is possible and that neural cells, used a vehicles for the transgenes, would be feasible in this context. The results of the present thesis serve as a good basis for the design of future experiments regarding the search of differentiating signals retained by the adult brain, as well as further development of ex vivo gene transfer to the brain towards clinical applications.