Disruption of Virion Host Shutoff Activity Improves the Immunogenicity and Protective Capacity of a Replication-Incompetent Herpes Simplex Virus Type 1 Vaccine Strain

Abstract

The virion host shutoff (vhs) protein encoded by herpes simplex virus type 1 (HSV-1) destabilizes both viral and host mRNAs. An HSV-1 strain with a mutation in vhs is attenuated in virulence and induces immune responses in mice that are protective against corneal infection with virulent HSV-1, but it has the capacity to establish latency. Similarly, a replication-incompetent HSV-1 strain with a mutation in ICP8 elicits an immune response protective against corneal challenge, but it may be limited in viral antigen production. We hypothesized therefore that inactivation of vhs in an ICP8؊ virus would yield a replication-incompetent mutant with enhanced immunogenicity and protective capacity. ؊ mutant virus. The data indicate that inactivation of vhs in a replicationincompetent virus significantly enhances its protective efficacy while retaining its safety for potential human vaccination. Possible mechanisms of enhanced immunogenicity are discussed.Herpes simplex virus type 1 (HSV-1) is a common human pathogen, infecting approximately 80% of individuals by adulthood (49). The virus typically enters the body at epithelial and mucosal surfaces, where lytic infection of epithelial cells and fibroblasts leads to infection of sensory neurons innervating the mucosa and to the rapid establishment of latent infection in the neuronal cell bodies. In this latent reservoir, HSV infection is maintained for the life of the host. Either initial infection or reactivation can result in serious human disease, including rare but devastating encephalitis and keratitis, which is the second most common cause of nontraumatic corneal blindness (49). A vaccine to obviate or therapeutically alleviate these HSV-1-mediated diseases is a desirable goal.Development of an antiviral vaccine requires consideration of both safety and immunogenicity. An effective balance between these can be difficult to achieve, especially when faced with HSV that has a complex and persistent lifestyle. Immunization with live attenuated virus has the potential advantages of generating immune responses to a broad spectrum of viral proteins and induction of type 1 T-cell as well as humoral responses. In the development of prototypic live virus vaccines, several viral proteins that regulate host cell and viral synthetic processes have been manipulated to advantage. During infection, one of the earliest viral activities is that mediated by the virion host shutoff (vhs) protein, a product of the UL41 gene. This viral tegument component exerts its effects immediately upon entry into the cell, prior to viral gene expression (13,39). The vhs protein is associated with degradation of both cellular and viral mRNAs (24-26, 36, 39, 43) and endoribonucleolytic activity (9, 52), and the destabilization of viral messages mediated by vhs has been theorized to promote the switch from transcription of one kinetic class of viral genes to the next (43). We have previously shown that mice immunized with an HSV-1 strain that is deficient in vhs activity, UL41NHB, are significantly pro...

A Proautophagic Antiviral Role for the Cellular Prion Protein Identified by Infection with a Herpes Simplex Virus 1 ICP34.5 Mutant

“…and homogenized for determination of virus titers by standard plaque assay. For corneal infection, 2 ϫ 10 5 or 2 ϫ 10 6 PFU of virus in a 5-l volume was applied to each lightly scarified cornea of anesthetized mice (62,63). Virus replication in the corneal epithelium was assessed at 4 h and days 1 through 4 p.i.…”

CD8+ T cells control corneal disease following ocular infection with herpes simplex virus type 1

“…Serum was collected from mice at weekly intervals following infection and examined for HSV-specific antibody content as described previously (Geiss et al, 2000). Briefly, for ELISA, serial fourfold dilutions of mouse serum were incubated for 2 h in duplicate wells of a 96-well plate coated with purified HSV-1 glycoprotein.…”

“…Briefly, for ELISA, serial fourfold dilutions of mouse serum were incubated for 2 h in duplicate wells of a 96-well plate coated with purified HSV-1 glycoprotein. Biotinylated goat anti-mouse IgG was subsequently used in a colorimetric assay to determine specific IgG levels based on comparison with a standard curve generated as described previously (Geiss et al, 2000).…”

The Virion Host Shutoff Protein of Herpes Simplex Virus 1 Blocks the Replication-Independent Activation of NF-κB in Dendritic Cells in the Absence of Type I Interferon Signaling

“…In contrast, in vivo infections with a vhs mutant virus are severely attenuated (26,57,58). There is much interest in employing vhs-null viruses as live, attenuated vaccines for HSV due in large part to this replication defect (15,22,23,64). Interestingly, this growth defect is partially overcome when IFN signaling is absent, suggesting that the vhs block of the pathway is important for virus replication and pathogenesis (36).…”