Engineered cells: a promising therapeutic approach for neural disease.

The transplantation technique has been invaluable for studying the CNS. Recently, the use of genetically modified cells for CNS grafting has further increased the utility of this technique. Studies conducted during the past 10 years have shown that a variety of genes can be successfully expressed in both neural and non-neural populations. Depending on the cell type used for gene transfer, engineered cells survive well within the CNS and continue to synthesize engineered products. In addition to providing insights into CNS development and plasticity, genetically modified cells have revealed the therapeutic role of different factors in neural disease. Cells engineered to produce growth factors have been shown to prevent and/or minimize neural degeneration following an experimental damage while the intracerebral transplantation of cells genetically modified to produce neurotransmit-ters have successfully reversed behavioral impairments of animals with experimental Parkinson's disease or Alzheimer's disease. Recent results with engineered cells transplanted into the brain of non-human primates suggest the potential of engineered cells for human therapy. Work with encapsulation techniques to isolate engineered cells from a host brain offers one of several approaches for ensuring the safety of genetically modified cells grafted into the CNS. Identifying factors that influence the survival and gene expression of engineered cells following transplantation will enhance the usefulness of these cells for studying and repairing the CNS.