Chapter 3 - HSV Amplicon Vectors for Gene Delivery to the Nervous System

Abstract

This chapter discusses the characteristics of herpes simplex virus type 1 (HSV-1) along with its uses in the nervous system. The HSV amplicon vector incorporates features of HSV-1, including a 150 kb transgene capacity, a viral origin of DNA replication and packaging signal, and virion proteins. The large transgene capacity is one of the most distinguishing features of this vector system, which allows incorporation of multiple transgenes and large genomic fragments, as well as informational elements from other virus vectors, including AAV, EBV, and retrovirus. Vectors have been modified to include elements, which increase infection of specific cell types and allow retention of transgene sequences, either as replicating episomal elements or through site-specific integration into the cell genome, and provide the ability to control transgene expression. The virion itself includes proteins that can be used to track the infection and deliver fusion proteins to the cells. HSV amplicon vectors have a broad tropism for many cell types through a basic binding mechanism to heparan sulfate on the cell surface and entry through at least four different receptors. HSV amplicon vectors provide an ideal vehicle to explore neuronal functions based on their efficient gene delivery to neurons, minimal impact on cellular physiology, and ease of generation. Within the nervous system, these vectors are especially useful due to the natural neurotropism of the virus, with a strong retrograde component, and minimal perturbation of neuronal physiology. HSV seems particularly suited to the peripheral nervous system expression in both the dorsal and the ventral spinal ganglia. Vectors have been used to deliver proteins to facilitate fluorescence, bioluminescent, and magnetic resonance imaging, as well as to monitor neuronal functions in animal models involving learning/memory and addiction paradigms. Amplicon vectors are considered compatible with clinical trials due to their intrinsic lack of toxicity, but methods of production need to be improved to generate high titers and clinically compatible vector stocks.