The ability of the central nervous system to replace its damaged or diseased tissue is limited and cell-based therapies will be required for replacement strategies in the central nervous system. Most neurons are born during prenatal gestation and early postnatal periods.1,2
However, cell-specific neurogenesis persists in the adult dentate gyrus of the hippocampus and the subventricular zone (SVZ) of the lateral ventricles in a number of mammalian species including humans.3–5
The existence of postnatal and adult neural stem cells offers a potential source for production of new neurons and glia in damaged or diseased neural tissue6–8
The endogenous nature of these stem cells is particularly attractive as they may eliminate the use of exogenous embryonic stem cells, and potentially bypass problems associated with transplanted cells and tissues.9,10
However, restricted differentiation potential of adult neural stem cells to generate multiple types of neurons in vivo11–13
must be overcome before their utilization in cell-based therapies. For example, only subsets of interneurons in the olfactory bulb (OB) and glial cell types in the white matter are generated in the adult SVZ.3
It is now clear that genetic/epigenetic manipulation for reprogramming the adult neural stem cells will be essential for generation and differentiation of distinct neuronal and glial cell types at the site of injury or disease. Thus, methods for cell-specific gene transfer are critical for utilization of adult stem cells in cell-based therapies.
Currently methods for cell-specific gene transfer primarily depend on promoter activity in target cells. However, utilization of promoters is technically difficult, and can be limiting for adult stem cells, which are a heterogeneous population with presumably distinct sets of active promoters. Thus, development of tools that specifically target adult neural stem cells while sparing their progeny during the initial transduction event will be highly valuable for both basic science and future therapeutic applications.
Viral vectors have proven to be the most effective tools for in vivo
and recently electroporation techniques have also been established in embryonic and adult mice.16,17
The caveat with electroporation is the transient nature of gene expression inherent to this method, with mostly acute results in the targeted cells and subsequent ‘dilution’ of the transferred gene in the long run. Moreover, current methodologies involving electroporation in mice are unlikely to translate into larger mammalian species or humans owing to technical difficulties that arise with electroporation of large brains. A number of viral vectors have been used to study gene function and lineage tracing in postnatal and adult neurogenesis;18–22
however, a comprehensive analysis of their transduction targets is not clear. Moreover, target specificity of many of the vectors is thought to be based on their origin (for example, adeno- or lenti-based vectors) and pseudotyping. Of the tested viral vectors, lentiviruses have an efficient capacity to induce long-term changes, as their retroviral capacity dictates an efficient integration of carried genetic material into host chromosomal DNA.14
Here, we show that a replication-incompetent vector based on the Equine Infectious Anemia Virus (EIAV), expressing Enhanced Green Fluorescent Protein (EGFP) is highly specific for gene transfer to adult neural stem cells. We chose EIAV because of its high transduction capacity,23
the limited adverse effects of its viral particles after transduction in vivo
as well as its earlier use in neural tissue.25
The vector was pseudotyped with the vesicular stomatitis virus G-protein, and we show that it preferentially transduces adult neural stem cells in the SVZ. The specific targeting of adult stem cells allowed for assessment of proliferation, migration and differentiation of their progeny in the postnatal brain.