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

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.