Enhanced reporter gene expression in the rat brain from helper virus-free HSV-1 vectors packaged in the presence of specific mutated HSV-1 proteins that affect the virion

Herpes simplex virus (HSV-1) gene expression is hypothesized to shut off pr omoters in HSV-1 vectors, but in a helper virus-free HSV-1 vector system, a number of promoters support only short-term expression. Thus, recombinant gene expression remains short-term in the absence of similar to 99% of the HSV-1 genome. To resolve this paradox, we hypothesized that specific HSV-1 proteins that affect the virion can shut off recombinant gene expression. T his study evaluated expression from HSV-1 vectors, containing neuronal-spec ific promoters, that were packaged in the presence of specific mutated HSV- 1 proteins that affect the virion. The mutated HSV-1 proteins that were exa mined included two protein kinases (U(L)13 and U(S)3), the virion host shut -off factor (vhs), the transactivator of immediate early promoters (VP16), and a virion protein that affects RNA metabolism (U(S)11). Helper virus-fre e packaging could occur in the presence of each mutated protein alone or sp ecific combinations of two or three mutated proteins. In BHK and PC12 cells , vectors packaged in the presence of each mutated protein increased (simil ar to2-fold) the level of expression per cell, and vectors packaged in the presence of specific combinations of mutated proteins supported larger (4-7 -fold) increases. In the rat striatum, Vectors packaged in the presence of a mutated U(S)3 displayed enhanced gene transfer (13-18-fold increases in t he number of cells at 4 days), and vectors packaged in the presence of muta ted U(L)13 or VP16 enhanced long-term expression (2 months). Vectors packag ed in the presence of mutated vhs or U(S)11 displayed minimal changes in ex pression. (C) 2001 Elsevier Science B.V. All rights reserved.