Antiviral activity of herpes simplex virus vectors expressing murine alpha 1-interferon

Mutant herpes simplex virus type I (HSV-1) vectors were engineered to express murine alpha 1 interferon (IFN) and assessed for their ability to inhibit the replication of challenge viruses in infection of monolayer cell cultures. The alpha 1 IFN gene was placed under control of the Rous sarcoma virus (RSV) long terminal repeat (LTR) region in the thymidine kinase (tk) locus of both the wild-type HSV-1 strain KOS and the replication-defective KOS mutant dl20, in which both copies of the ICP4 immediate-early (IE) gene are deleted. To evaluate IFN expression, vector-infected cell culture media from epithelial, fibroblast and neuronal cells were assayed for alpha IFN release. These cells did not secrete detectable levels of alpha IFN when infected with control KOS or d120-based viruses. Cells infected at a multiplicity of infection (MOI) of 10 with either RSV-LTR-IFN vector produced from approximately 12 to 100 U of alpha 1-IFN per millilitre of culture fluid in 24 h, as determined by a standard vesicular stomatitis virus (VSV) replication inhibition assay. Vector-derived alpha 1-IFN expression did not inhibit the growth of the KOS-RSV-IFN virus in IFN sensitive cell lines. However, pretreatment of murine L cells with IFN produced from the RSV-IFN vectors blocked the replication of HSV-1. Additionally, L cells infected with d120-RSV-IFN (at an MOI of 0.5 to 0.06) were protected from superinfection with VSV. Thus, pre-infection of a small percentage of cells with a nonreplicating HSV-IFN expression vector provided complete protection of tissue culture cell monolayers from the cytopathic effect of a challenge virus infection. These vectors should be useful for in vivo analysis of the antiviral potential of IFN expression from within the nervous system.