Central nervous system cell transplantation: a novel therapy for storage diseases?

Many methods of gene transfer to the brain are under study. One employs a neural stem cell based strategy. Transplanting neural progenitor cells that intrinsically secrete missing or therapeutic gene products, or are genetically engineered ex vivo to do so, may provide a strategy for long-term treatment of central nervous system manifestations of a number of neurogenetic diseases. Multipotent neural progenitors or stem cells (or cells that mimic their behavior) are capable of differentiating along multiple central nervous system cell-type lineages. They can engraft as integral members of normal structures throughout the host central nervous system without disturbing other neurobiological processes. They can also be easily genetically manipulated ex vivo. By exploiting their basic biological properties, these cells may be able to deliver therapeutic gene products in a sustained, direct, and perhaps regulated fashion throughout the central nervous system. Furthermore, although they may disseminate these gene products throughout the brain, they nevertheless restrict that distribution to only the central nervous system. Thus, these vehicles may overcome many of the limitations of viral and non-neural cellular vectors, as well as pharmacologic and genetic interventions. The feasibility of this neural stem cell-based strategy has been demonstrated by correcting the widespread central nervous system pathology of a murine model of a prototypical inherited neurodegenerative disease, mucopolysaccharidosis type VII. These studies have helped to establish the use of such cells as a paradigm for transferring other molecules of therapeutic or developmental interest throughout the central nervous system at many ages.