HSV-1-derived recombinant and amplicon vectors for gene transfer and gene therapy

Herpes simplex virus type 1 (HSV-1) is a major human pathogen whose lifestyle is based on a long-term dual interaction with the infected host characterized by the existence of lytic and latent infections. Although in most cell types infection with HSV-1 will induce toxic effects ending in the death of the infected cells, the very deep knowledge we possess on the genetics and molecular biology of HSV-1 has permitted the deletion of most toxic genes and the development of non-pathogenic HSV-1-based vectors for gene transfer. Several unique features of HSV-1 make vectors derived from this virus very appealing for preventive or therapeutic gene transfer. These include (i) the very high transgenic capacity of the virus particle, authorizing to convey very large pieces of foreign DNA to the nucleus of mammalian cells, (ii) the genetic complexity of the virus genome, allowing to generate many different types of attenuated vectors possessing oncolytic activity, and (iii) the ability of HSV-1 vectors to invade and establish lifelong non-toxic latent infections in neurons from sensory ganglia and probably in other neurons as well, from where transgenes can be strongly and long-term expressed. Three different classes of vectors can be derived from HSV-1: replication-competent attenuated vectors, replication-incompetent recombinant vectors, and defective helper-dependent vectors known as amplicons. Each of these different vectors attempts to exploit one or more of the above-mentioned features of HSV-1. In this review we will update the current know-how concerning design, construction, and recent applications, as well as the potential and current limitations of the three different classes of HSV-1-based vectors.