Construction, phenotypic analysis, and immunogenicity of a UL5/UL29 doubledeletion mutant of herpes simplex virus 2

A number of studies have shown that replication-defective mutant strains of herpes simplex virus (HSV) can induce protective immunity in animal system s against wild-type HSV challenge. However, all of those studies used virus es with single mutations. Because multiple, stable mutations provide optima l levels of safety for live vaccines, we felt that additional mutations nee ded to be engineered into a candidate vaccine strain for HSV-2 and genital herpes. We therefore isolated an HSV-2 strain with deletion mutations in tw o viral DNA replication protein genes, UL5 and UL29. The resulting double d eletion mutant virus strain, dl5-29, fails to form plaques or to give any d etectable single cycle yields in normal monkey or human cells. Nevertheless , dl5-29 expresses nearly the same pattern of gene products as the wild-typ e virus or the single mutant viruses and induces antibody titers in mice th at are equivalent to those induced by single deletion mutant viruses. There fore, it is feasible to isolate a mutant HSV strain with two mutations in e ssential genes and with an increased level of safety but which is still hig hly immunogenic.