Transient gene transfer to neurons and glia: Analysis of adenoviral vector performance in the CNS and PNS

In this paper a detailed protocol is presented for neuroscientists planning to start work on first generation recombinant adenoviral vectors as gene transfer agents for the nervous system. The performance of a prototype adenoviral vector encoding the bacterial lacZ gene as a reporter was studied, following direct injection in several regions of the central and peripheral nervous system. The distribution of the cells expressing the transgene appears to be determined by natural anatomical boundaries and possibly by the degree of myelinization of a particular brain region. In highly myelinated areas with a compact cellular structure (e.g. the cortex and olfactory bulb) the spread of the viral vector is limited to the region close to the injection needle, while in areas with a laminar structure (e.g. the hippocampus and the eye) more widespread transgene expression is observed. Retrograde transport of the viral vector may serve as an attractive alternative route of transgene delivery. A time course of expression of P-galactosidase in neural cells in the facial nucleus revealed high expression during the first week after AdLacZ injection. However, a significant decline in transgene expression during the second and third week was observed. This may be caused by an immune response against the transduced cells or by silencing of the cytomegalovirus promoter used to drive transgene expression. Taken together, the data underscore that for each application of adenoviral vectors as gene transfer agents in the nervous system it is important to examine vector spread in and infectability of the neural structure that is subject to genetic modification.