An HSV-1 gD mutant virus as an entry-impaired live virus vaccine

Reducing Viral Inhibition of Host Cellular Apoptosis Strengthens the Immunogenicity and Protective Efficacy of an Attenuated HSV-1 Strain

Herpes simplex virus 1 (HSV-1), a member of α herpesviruses, shows a high infectivity rate of 30%-60% in populations of various ages. Some herpes simplex (HSV) vaccine candidates evaluated during the past 20 years have not shown protective efficacy against viral infection. An improved understanding of the immune profile of infected individuals and the associated mechanism is needed. HSV uses an immune evasion strategy during viral replication, and various virus-encoded proteins, such as ICP47 and Vhs, participate in this process through limiting the ability of CD8⁺ cytotoxic T lymphocytes to recognize target cells. Other proteins, e.g., Us3 and Us5, also play a role in viral immune evasion via interfering with cellular apoptosis. In this work, to study the mechanism by which HSV-1 strain attenuation interferes with the viral immune evasion strategy, we constructed a mutant strain, M5, with deletions in the Us3 and Us5 genes. M5 was shown to induce higher neutralizing antibody titers and a stronger cellular immune response than our previously reported M3 strain, and to prevent virus infection more effectively than the M3 strain in an in vivo mouse challenge test.

Attenuated phenotypes and analysis of a herpes simplex virus 1 strain with partial deletion of the UL7, UL41 and LAT genes

We previously constructed a herpes simplex virus 1 (HSV-1) UL7 mutant virus (M1) and showed that a partial deletion mutation of the UL7 gene led to a lower proliferative rate and an attenuated phenotype. Using the M1 mutant, we further modified the UL41 gene, which encodes another tegument protein, and the latency-associated transcript (LAT) gene. Observations of the resulting mutants with modified UL7 and UL41 (M2) or UL7, UL41 and LAT (M3) genes indicated attenuated phenotypes, with lower proliferative ratios in various cells, non-lethal infections in mice and lower viral loads in nervous tissues compared with the wild-type strain. Furthermore, no LAT stable intron could be detected in the trigeminal ganglion of M3-infected animals. The results obtained with the three HSV-1 mutants indicate that the M3 mutant is an attenuated strain with low pathogenicity during both acute and latent infections. Together, the results support the use of the M3 mutant as a candidate for the development of an HSV-1 vaccine.

Viral genes and cellular markers associated with neurological complications during herpesvirus infections

Despite the importance of neurological disorders associated with herpesviruses, the mechanism by which these viruses influence the central nervous system (CNS) has not been definitively established. Owing to the limitations of studying neuropathogenicity of human herpesviruses in their natural host, many aspects of their pathogenicity and immune response are studied in animal models. Here, we present an important model system that enables studying neuropathogenicity of herpesviruses in the natural host. Equine herpesvirus type 1 (EHV-1) is an alphaherpesvirus that causes a devastating neurological disease (EHV-1 myeloencephalopathy; EHM) in horses. Like other alphaherpesviruses, our understanding of virus neuropathogenicity in the natural host beyond the essential role of viraemia is limited. In particular, information on the role of different viral proteins for virus transfer to the spinal cord endothelium in vivo is lacking. In this study, the contribution of two viral proteins, DNA polymerase (ORF30) and glycoprotein D (gD), to the pathogenicity of EHM was addressed. Furthermore, different cellular immune markers, including alpha-interferon (IFN-α), gamma-interferon (IFN-γ), interleukin-10 (IL-10) and interleukin-1 beta (IL-1β), were identified to play a role during the course of the disease.

A Herpes Simplex Virus 2 (HSV-2) gD Mutant Impaired for Neural Tropism Is Superior to an HSV-2 gD Subunit Vaccine To Protect Animals from Challenge with HSV-2

A recent phase 3 trial with soluble herpes simplex virus 2 (HSV-2) glycoprotein D (gD2t) in adjuvant failed to show protection against genital herpes. We postulated that live attenuated HSV-2 would provide more HSV antigens for induction of virus-specific antibodies and cellular immunity than would gD2t. We previously reported an HSV-2 mutant, HSV2-gD27, in which the nectin-1 binding domain of gD2 is altered so that the virus is impaired for infecting neural cells, but not epithelial cells, in vitro and is impaired for infecting dorsal root ganglia in mice (K. Wang, J. D. Kappel, C. Canders, W. F. Davila, D. Sayre, M. Chavez, L. Pesnicak, and J. I. Cohen, J Virol 86:12891-12902, 2012, doi:10.1128/JVI.01055-12). Here we report that the mutations in HSV2-gD27 were stable when the virus was passaged in cell culture and during acute infection of mice. HSV2-gD27 was attenuated in mice when it was inoculated onto the cornea, intramuscularly (i.m.), intravaginally, and intracranially. Vaccination of mice i.m. with HSV2-gD27 provided better inhibition of challenge virus replication in the vagina than when the virus was used to vaccinate mice intranasally or subcutaneously. Comparison of i.m. vaccinations with HSV2-gD27 versus gD2t in adjuvant showed that HSV2-gD27 induced larger reductions of challenge virus replication in the vagina and reduced latent viral loads in dorsal root ganglia but induced lower serum neutralizing antibody titers than those obtained with gD2t in adjuvant. Taken together, our data indicate that a live attenuated HSV-2 vaccine impaired for infection of neurons provides better protection from vaginal challenge with HSV-2 than that obtained with a subunit vaccine, despite inducing lower titers of HSV-2 neutralizing antibodies in the serum.

IMPORTANCE

Genital herpes simplex is one of the most prevalent sexually transmitted diseases. Though HSV-2 disease is usually mild, it can be life threatening in neonates and immunocompromised persons. In addition, genital herpes increases the frequency of HIV infection and transmission. HSV-2 maintains a latent infection in sensory neurons and cannot be cleared with antiviral drugs. The virus frequently reactivates, resulting in virus shedding in the genital area, which serves as a source for transmission. A prophylactic vaccine is needed to prevent disease and to control the spread of the virus. Previous human trials of subunit vaccines have been unsuccessful. Here we report the results of vaccinating mice with a new type of live attenuated HSV-2 vaccine that is impaired for infection of neurons and provides better protection of mice than that obtained with a subunit vaccine. The strategy of altering the cell tropism of a virus is a new approach for a live attenuated vaccine.

Antigenic breadth: a missing ingredient in HSV-2 subunit vaccines?

The successful human papillomavirus and hepatitis B virus subunit vaccines contain single viral proteins that represent 22 and 12%, respectively, of the antigens encoded by these tiny viruses. The herpes simplex virus 2 (HSV-2) genome is >20 times larger. Thus, a single protein subunit represents 1% of HSV-2's total antigenic breadth. Antigenic breadth may explain why HSV-2 glycoprotein subunit vaccines have failed in clinical trials, and why live HSV-2 vaccines that express 99% of HSV-2's proteome may be more effective. I review the mounting evidence that live HSV-2 vaccines offer a greater opportunity to stop the spread of genital herpes, and I consider the unfounded 'safety concerns' that have kept live HSV-2 vaccines out of U.S. clinical trials for 25 years.

An attenuated herpes simplex virus type 1 (HSV1) encoding the HIV-1 Tat protein protects mice from a deadly mucosal HSV1 challenge

Herpes simplex virus types 1 and 2 (HSV1 and HSV2) are common infectious agents in both industrialized and developing countries. They cause recurrent asymptomatic and/or symptomatic infections, and life-threatening diseases and death in newborns and immunocompromised patients. Current treatment for HSV relies on antiviral medications, which can halt the symptomatic diseases but cannot prevent the shedding that occurs in asymptomatic patients or, consequently, the spread of the viruses. Therefore, prevention rather than treatment of HSV infections has long been an area of intense research, but thus far effective anti-HSV vaccines still remain elusive. One of the key hurdles to overcome in anti-HSV vaccine development is the identification and effective use of strategies that promote the emergence of Th1-type immune responses against a wide range of epitopes involved in the control of viral replication. Since the HIV1 Tat protein has several immunomodulatory activities and increases CTL recognition of dominant and subdominant epitopes of heterologous antigens, we generated and assayed a recombinant attenuated replication-competent HSV1 vector containing the tat gene (HSV1-Tat). In this proof-of-concept study we show that immunization with this vector conferred protection in 100% of mice challenged intravaginally with a lethal dose of wild-type HSV1. We demonstrate that the presence of Tat within the recombinant virus increased and broadened Th1-like and CTL responses against HSV-derived T-cell epitopes and elicited in most immunized mice detectable IgG responses. In sharp contrast, a similarly attenuated HSV1 recombinant vector without Tat (HSV1-LacZ), induced low and different T cell responses, no measurable antibody responses and did not protect mice against the wild-type HSV1 challenge. These findings strongly suggest that recombinant HSV1 vectors expressing Tat merit further investigation for their potential to prevent and/or contain HSV1 infection and dissemination.

DNAVaxDB: the first web-based DNA vaccine database and its data analysis

Since the first DNA vaccine studies were done in the 1990s, thousands more studies have followed. Here we report the development and analysis of DNAVaxDB (http://www.violinet.org/dnavaxdb), the first publically available web-based DNA vaccine database that curates, stores, and analyzes experimentally verified DNA vaccines, DNA vaccine plasmid vectors, and protective antigens used in DNA vaccines. All data in DNAVaxDB are annotated from reliable resources, particularly peer-reviewed articles. Among over 140 DNA vaccine plasmids, some plasmids were more frequently used in one type of pathogen than others; for example, pCMVi-UB for G- bacterial DNA vaccines, and pCAGGS for viral DNA vaccines. Presently, over 400 DNA vaccines containing over 370 protective antigens from over 90 infectious and non-infectious diseases have been curated in DNAVaxDB. While extracellular and bacterial cell surface proteins and adhesin proteins were frequently used for DNA vaccine development, the majority of protective antigens used in Chlamydophila DNA vaccines are localized to the inner portion of the cell. The DNA vaccine priming, other vaccine boosting vaccination regimen has been widely used to induce protection against infection of different pathogens such as HIV. Parasitic and cancer DNA vaccines were also systematically analyzed. User-friendly web query and visualization interfaces are available in DNAVaxDB for interactive data search. To support data exchange, the information of DNA vaccines, plasmids, and protective antigens is stored in the Vaccine Ontology (VO). DNAVaxDB is targeted to become a timely and vital source of DNA vaccines and related data and facilitate advanced DNA vaccine research and development.

The challenge of developing a herpes simplex virus 2 vaccine

HSV infections are prevalent worldwide. A vaccine to prevent genital herpes would have a significant impact on this disease. Several vaccines have shown promise in animal models; however, so far these have not been successful in human clinical studies. Prophylactic HSV vaccines to prevent HSV infection or disease have focused primarily on eliciting antibody responses. Potent antibody responses are needed to result in sufficiently high levels of virus-specific antibody in the genital tract. Therapeutic vaccines that reduce recurrences need to induce potent T-cell responses at the site of infection. With the increasing incidence of HSV-1 genital herpes, an effective herpes vaccine should protect against both HSV-1 and HSV-2. Novel HSV vaccines, such as replication-defective or attenuated viruses, have elicited humoral and cellular immune responses in preclinical studies. These vaccines and others hold promise in future clinical studies.

Live attenuated herpes simplex virus 2 glycoprotein E deletion mutant as a vaccine candidate defective in neuronal spread

A herpes simplex virus 2 (HSV-2) glycoprotein E deletion mutant (gE2-del virus) was evaluated as a replication-competent, attenuated live virus vaccine candidate. The gE2-del virus is defective in epithelial cell-to-axon spread and in anterograde transport from the neuron cell body to the axon terminus. In BALB/c and SCID mice, the gE2-del virus caused no death or disease after vaginal, intravascular, or intramuscular inoculation and was 5 orders of magnitude less virulent than wild-type virus when inoculated directly into the brain. No infectious gE2-del virus was recovered from dorsal root ganglia (DRG) after multiple routes of inoculation; however, gE2-del DNA was detected by PCR in lumbosacral DRG at a low copy number in some mice. Importantly, no recurrent vaginal shedding of gE2-del DNA was detected in immunized guinea pigs. Intramuscular immunization outperformed subcutaneous immunization in all parameters evaluated, although individual differences were not significant, and two intramuscular immunizations were more protective than one. Immunized animals had reduced vaginal disease, vaginal titers, DRG infection, recurrent genital lesions, and recurrent vaginal shedding of HSV-2 DNA; however, protection was incomplete. A combined modality immunization using live virus and HSV-2 glycoprotein C and D subunit antigens in guinea pigs did not totally eliminate recurrent lesions or recurrent vaginal shedding of HSV-2 DNA. The gE2-del virus used as an immunotherapeutic vaccine in previously HSV-2-infected guinea pigs greatly reduced the frequency of recurrent genital lesions. Therefore, the gE2-del virus is safe, other than when injected at high titer into the brain, and is efficacious as a prophylactic and immunotherapeutic vaccine.

A wide extent of inter-strain diversity in virulent and vaccine strains of alphaherpesviruses

Alphaherpesviruses are widespread in the human population, and include herpes simplex virus 1 (HSV-1) and 2, and varicella zoster virus (VZV). These viral pathogens cause epithelial lesions, and then infect the nervous system to cause lifelong latency, reactivation, and spread. A related veterinary herpesvirus, pseudorabies (PRV), causes similar disease in livestock that result in significant economic losses. Vaccines developed for VZV and PRV serve as useful models for the development of an HSV-1 vaccine. We present full genome sequence comparisons of the PRV vaccine strain Bartha, and two virulent PRV isolates, Kaplan and Becker. These genome sequences were determined by high-throughput sequencing and assembly, and present new insights into the attenuation of a mammalian alphaherpesvirus vaccine strain. We find many previously unknown coding differences between PRV Bartha and the virulent strains, including changes to the fusion proteins gH and gB, and over forty other viral proteins. Inter-strain variation in PRV protein sequences is much closer to levels previously observed for HSV-1 than for the highly stable VZV proteome. Almost 20% of the PRV genome contains tandem short sequence repeats (SSRs), a class of nucleic acids motifs whose length-variation has been associated with changes in DNA binding site efficiency, transcriptional regulation, and protein interactions. We find SSRs throughout the herpesvirus family, and provide the first global characterization of SSRs in viruses, both within and between strains. We find SSR length variation between different isolates of PRV and HSV-1, which may provide a new mechanism for phenotypic variation between strains. Finally, we detected a small number of polymorphic bases within each plaque-purified PRV strain, and we characterize the effect of passage and plaque-purification on these polymorphisms. These data add to growing evidence that even plaque-purified stocks of stable DNA viruses exhibit limited sequence heterogeneity, which likely seeds future strain evolution.

Alphaherpesviruses such as herpes simplex virus (HSV) are ubiquitous in the human population. HSV causes oral and genital lesions, and has co-morbidities in acquisition and spread of human immunodeficiency virus (HIV). The lack of a vaccine for HSV hinders medical progress for both of these infections. A related veterinary alphaherpesvirus, pseudorabies virus (PRV), has long served as a model for HSV vaccine development, because of their similar pathogenesis, neuronal spread, and infectious cycle. We present here the first full genome characterization of a live PRV vaccine strain, Bartha, and reveal a spectrum of unique mutations that are absent from two divergent wild-type PRV strains. These mutations can now be examined individually for their contribution to vaccine strain attenuation and for potential use in HSV vaccine development. These inter-strain comparisons also revealed an abundance of short repetitive elements in the PRV genome, a pattern which is repeated in other herpesvirus genomes and even the unrelated Mimivirus. We provide the first global characterization of repeats in viruses, comparing both their presence and their variation among different viral strains and species. Repetitive elements such as these have been shown to serve as hotspots of variation between individuals or strains of other organisms, generating adaptations or even disease states through changes in length of DNA-binding sites, protein folding motifs, and other structural elements. These data suggest for the first time that similar mechanisms could be widely distributed in viral biology as well.

B7 costimulation molecules encoded by replication-defective, vhs-deficient HSV-1 improve vaccine-induced protection against corneal disease

Herpes simplex virus 1 (HSV-1) causes herpes stromal keratitis (HSK), a sight-threatening disease of the cornea for which no vaccine exists. A replication-defective, HSV-1 prototype vaccine bearing deletions in the genes encoding ICP8 and the virion host shutoff (vhs) protein reduces HSV-1 replication and disease in a mouse model of HSK. Here we demonstrate that combining deletion of ICP8 and vhs with virus-based expression of B7 costimulation molecules created a vaccine strain that enhanced T cell responses to HSV-1 compared with the ICP8⁻vhs⁻ parental strain, and reduced the incidence of keratitis and acute infection of the nervous system after corneal challenge. Post-challenge T cell infiltration of the trigeminal ganglia and antigen-specific recall responses in local lymph nodes correlated with protection. Thus, B7 costimulation molecules expressed from the genome of a replication-defective, ICP8⁻vhs⁻ virus enhance vaccine efficacy by further reducing HSK.

Immunization with HSV-1 glycoprotein C prevents immune evasion from complement and enhances the efficacy of an HSV-1 glycoprotein D subunit vaccine

Herpes simplex virus type 1 (HSV-1) glycoprotein C (gC-1) binds complement component C3b and inhibits complement-mediated immunity. HSV-1 glycoprotein D (gD-1) is a potent immunogen and a candidate antigen for a subunit vaccine. We evaluated whether combined immunization with gD-1 and gC-1 provides better protection against challenge than gD-1 alone based on antibodies to gC-1 preventing HSV-1-mediated immune evasion. IgG purified from mice immunized with gC-1 blocked C3b binding to gC-1 and greatly increased neutralization by gD-1 IgG in the presence of complement. Passive transfer of gC-1 IgG protected complement intact mice against HSV-1 challenge but not C3 knockout mice, indicating that gC-1 antibody activity in vivo is complement-dependent. Immunizing mice with gD-1 and gC-1 provided better protection than gD-1 alone in preventing zosteriform disease and infection of dorsal root ganglia. Therefore, gC-1 immunization prevents HSV-1 evasion from complement and enhances the protection provided by gD-1 immunization.

A replication-competent, neuronal spread-defective, live attenuated herpes simplex virus type 1 vaccine

Herpes simplex virus type 1 (HSV-1) produces oral lesions, encephalitis, keratitis, and severe infections in the immunocompromised host. HSV-1 is almost as common as HSV-2 in causing first episodes of genital herpes, a disease that is associated with an increased risk of human immunodeficiency virus acquisition and transmission. No approved vaccines are currently available to protect against HSV-1 or HSV-2 infection. We developed a novel HSV vaccine strategy that uses a replication-competent strain of HSV-1, NS-gEnull, which has a defect in anterograde and retrograde directional spread and cell-to-cell spread. Following scratch inoculation on the mouse flank, NS-gEnull replicated at the site of inoculation without causing disease. Importantly, the vaccine strain was not isolated from dorsal root ganglia (DRG). We used the flank model to challenge vaccinated mice and demonstrated that NS-gEnull was highly protective against wild-type HSV-1. The challenge virus replicated to low titers at the site of inoculation; therefore, the vaccine strain did not provide sterilizing immunity. Nevertheless, challenge by HSV-1 or HSV-2 resulted in less-severe disease at the inoculation site, and vaccinated mice were totally protected against zosteriform disease and death. After HSV-1 challenge, latent virus was recovered by DRG explant cocultures from <10% of vaccinated mice compared with 100% of mock-vaccinated mice. The vaccine provided protection against disease and death after intravaginal challenge and markedly lowered the titers of the challenge virus in the vagina. Therefore, the HSV-1 gEnull strain is an excellent candidate for further vaccine development.