Replication-defective herpes simplex virus vectors for neurotrophic factor gene transfer in vitro and in vivo

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Abstract
We report here the construction and the use of two replication-defective herpes simplex virus vectors, SH FGF-2 and TH FGF-2, which efficiently transfer and express the cDNA for fibroblast-growth-factor-2 (FGF-2) in vitro and in vivo. One mutant was deleted in the immediate–early gene encoding ICP4; the other was deleted in ICP4, ICP22 and ICP27. FGF-2 – or the control gene lacZ – were inserted in tk, under control of the human cytomegalovirus immediate–early promoter. Infection of Vero cells with SH FGF-2 induced a dramatic increase in FGF-2 protein levels in the first 2 days after infection, with a rapid return to baseline levels within day 4. In contrast, infection of Vero cells with TH FGF-2 displayed FGF-2 levels progressively increasing up to days 4–5, and slowly returning to baseline. Protein extracts of cells infected with TH FGF-2 induced neuronal differentiation of PC12 cells, indicating that the newly synthesized FGF-2 was biologically active. Robust transient transgene expression was also observed in the rat hippocampus after stereotaxical inoculation of TH FGF-2, but not of TH lacZ or of SH vectors. Enhanced gene expression both in vitro and in vivo by the triple immediate–early gene deletion mutant might be attributed to reduced vector cytotoxicity. The present data suggest that TH FGF-2 is suitable for studies of FGF-2 involvement in neurological disorders.