- The antigenic and immunogenic potential was examined of human adenovirus type 5 (Ad) recombinants carrying and expressing from one to four tandem repeats of a linear neutralizing epitope from the gD protein of herpes simplex virus type 1 (HSV-1) as a fusion with the beta-galactosidase protein. The fusion proteins produced by these Ad vectors in infected cell culture reacted with a herpes simplex virus (HSV) epitope-specific monoclonal antibody to a degree dependent on the number of epitope repeats in the protein. Mice immunized by intraperitoneal injection of the Ad vectors developed an anti-HSV immune response as measured by ELISA and by HSV-1 neutralization assays. The mean antibody titre induced by a single injection of the Ad vector increased with the number of epitope repeats expressed by the recombinant. Any animal that had developed a serum-neutralizing titre of at least 1:80 survived challenge with a normally lethal dose of HSV-2 administered by the intraperitoneal route. Recombinant vectors expressing four repeats of the HSV epitope were as effective in antibody induction and protection as an adenovirus vector carrying and expressing the entire HSV gD protein. These results suggest that the expression of tandem repeats of appropriate epitopic sequences by adenovirus vectors may provide a safe and effective method of immunizing against HSV infection.