In the gene therapy group our main interest is to develop systems for sufficient and sustained expression of transgenes in the CNS. We are using gene transfer to express trophic factors or neurotransmitter-producing enzymes in animal models of neurodegenerative disease. We are currently working with three different vector systems: adeno-associated viral, retroviral and lentiviral. These vectors can be used both for direct injection (in vivo gene transfer) or transduction of cells in culture for subsequent transplantation (ex vivo gene transfer). To address the problem of sustained expression in vivo (a major limitation of many gene transfer methods as of now) we are investigating the use of different promoters, post-transcriptional regulating elements and vectors.