To insure TH gene expression only in the nigral-striatal tract of brain, a cDNA encoding human preproGDNF (P39905) was engineered with 8 kb of the rat TH gene promoter (pro), and this THpro-preproGDNF expression plasmid was encapsulated in THLs targeted with the rat OX26 TfRMAb, and administered IV to rats with toxin-induced experimental PD (246). This evidence concerns the gene TH and Parkinson disease.