LONG-TERM EXPRESSION OF A FOREIGN GENE FROM A UNIQUE POSITION IN THE LATENT HERPES-SIMPLEX VIRUS GENOME

As a result of its capacity to establish and maintain a life-long late nt infection in the nervous system, herpes simplex virus (HSV) has bee n promoted as an ideal vector for introducing DNA into mature, differe ntiated, post-mitotic neurons. Although delivery of foreign genes into neurons using HSV vectors has been well established, the potential of these vectors for scientific inquiry or therapeutic use has been hamp ered by the lack of efficient long-term expression of these foreign ge nes. In the few instances where expression from the latent genome has been reported, expression appears to be minimal and levels of mRNA pre sent have not been established. Here we describe HSV viral vectors tha t express a foreign gene during latency in dorsal root ganglia (DRG). More particularly, we have constructed a vector that, by histochemical assays for the protein, expresses the beta-galactosidase (beta-Gal) g ene for at least 18 months post infection. We have further characteriz ed the expression of beta-Gal transcripts by quantitative reverse tran scription polymerase chain reaction (RT-PCR) and determined that there are 32,000 copies of beta-Gal transcripts per 0.5 mu g of total RNA a t 18 months post infection. The vector makes use of the mouse Moloney leukemia virus (MMLV) long terminal repeat (LTR) promoter located dire ctly upstream from the latency-associated transcripts (LAT) promoter r egion and expresses mRNA from the DNA strand opposite to that expressi ng the LAT. Finally, the vector was constructed using a system that al lows other promoter/gene constructs to be easily inserted into the vir al genome. It may have utility in studying the effects of cellular or viral gene expression on establishment, maintenance or reactivation fr om latency or for the delivery and expression of therapeutic proteins employed in gene therapy of the nervous system.