Prolonged Biologically Active Transgene Expression Driven by HSV LAP2 in Brain in Vivo

Herpes simplex virus (HSV) naturally establishes a life-long latent state in neurons, characterized by the expression of latency-associated transcripts (LATs) in the absence of viral lytic functions, and the latency-associated promoter (LAP2) has been identified as a moveable element responsible for the expression of LATs from latent HSV genomes. Prolonged transgene expression will be required for the treatment of chronic diseases of the CNS using HSV vectors. We therefore examined the ability of LAP2 to drive prolonged expression of a biologically active transgene from latent HSV vector genomes in brain in vivo using the 6-hydroxydopamine (6-OHDA) and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) models of Parkinson disease. A replication-incompetent HSV vector containing the glial cell-derived neurotrophic factor (GDNF) under the control of LAP2 was injected into the substantia nigra and 5 and a half months later 6-OHDA was injected into the striatum. GDNF expression from the vector preserved dopaminergic function measured by histology and behavior 6 months after vector inoculation. Mice inoculated with the LAP2-GDNF replication-incompetent HSV vector followed by 3 months of daily low-dose MPTP injections were substantially protected against the consequences of that treatment measured by weekly behavioral testing and histologic measures at the conclusion of the experiment. These studies using subacute and chronic models of neurodegeneration demonstrate that the HSV LAP2 promoter element provides prolonged expression of relevant amounts of a transgene to produce significant biological effects in brain in vivo over the course of many months.