LONG-TERM PERSISTENCE OF DEFECTIVE HSV-1 VECTORS IN THE RAT-BRAIN IS DEMONSTRATED BY REACTIVATION OF VECTOR GENE-EXPRESSION

Wild-type HSV-1 is known to persist indefinitely in neurons in the lat ent state; however, defective HSV-1 vectors, or amplicons, contain onl y approximately 1% of the HSV-I genome and persistence of these HSV-1 vectors has not been studied even semiquantitatively in the adult rat brain. Defective HSV-1 vectors contain bath an HSV-1 origin of replica tion and a packaging site, and in the presence of helper virus can und ergo DNA replication and packaging into HSV-1 particles. Our prototype defective HSV-1 vector, pHSVlac, uses the HSV-1 immediate-early (IE) promoter to regulate expression of the Escherichia coli lacZ gene. Usi ng cultured neuronal cells, we have previously shown that expression f rom pHSVlac can be augmented by superinfection with a helper virus. In this study, pHSVlac was delivered into the adult rat striatum or hipp ocampus, and 2-3 months after gene transfer we utilized superinfection with several replication-incompetent HSV-1 mutants to reactivate expr ession from pHSVlac approximately 30% of the number of cells observed at 4 days after gene transfer. Thus, HSV-1 plasmid vectors can persist for at least 2-3 months in at least approximately 30% of the cells wh ich are initially infected.