Prolonged in vivo gene expression driven by a tyrosine hydroxylase promoter in a defective herpes simplex virus amplicon vector

A 9.0-kb fragment of the tyrosine hydroxylase (TH) promoter, previously shown to direct tissue-specific expression in transgenic mice, was fused to an Escherichia coli LacZ reporter gene in a defective herpes simplex virus type-1 (HSV-1) amplicon vector (THlac), The HSV immediate early (1E) 4/5 promoter (HSVlac) was used as a control, LacZ gene expression was visualized by X-Gal histochemical and TH immunocytochemical analysis, Two days and 10 weeks after THlac injection into rat caudate nucleus (CN), X-Gal-stained cells were observed in the substantia nigra (SN) and locus ceruleus (LC) ipsilateral to the injection site, These blue cells were TH-positive neurons as evidenced by double labeling with immunocytochemistry, Moreover, the number of X-Gal(+), TH+ (double-positive) neurons in the SN is increased at 10 weeks as compared to that seen 2 days after THlac injection, In marked contrast, few double-positive nigral neurons were observed either 2 days or 10 weeks after direct injection of THlac into SN, However, neither nigral nor striatal injection of HSVlac resulted in prolonged gene expression, These results suggest that a neuronal, but not a viral, promoter in an HSV vector can produce cell-type-specific, prolonged, and stable gene expression following retrograde transport, In addition, THlac produced infrequent gene expression in TH-negative cells (CN and dorsal to SN) after THlac injection into CN and SN, respectively, Overall, these results suggest that in some in vivo contexts cell-type-preferred expression can be achieved by a cellular promoter in an amplicon vector, Moreover, they underscore the need for the careful and systematic study of neuronal promoters in HSV vectors.