The profound neuro-attenuation of KOS-NA suggested its utility as a vaccine, and indeed, it elicited higher titer antibody and IFNγ-producing CD4 and CD8 T cell responses than ICP8- or ICP0- viruses and was efficacious in protecting against HSV-1-induced keratitis and blepharitis in mice [25]. This evidence concerns the gene XK and keratitis.