Better neutralization of herpes simplex virus type 1 (HSV-1) than HSV-2 by antibody from recipients of GlaxoSmithKline HSV-2 glycoprotein D2 subunit vaccine

Human Antibodies against Herpes Simplex Virus 2 Glycoprotein G Do Not Neutralize but Mediate Antibody-Dependent Cellular Cytotoxicity

Herpes simplex virus 2 (HSV-2) is a sexually transmitted infection affecting 491 million individuals globally. Consequently, there is a great need for both prophylactic and therapeutic vaccines. Unfortunately, several vaccine clinical trials, primarily employing the glycoprotein D of HSV-2 (gD-2), have failed. The immune protection conferred by human anti-HSV-2 antibodies in genital infection and disease remains elusive. It is well-known that gD-2 elicits cross-reactive neutralizing antibodies, i.e., anti-gD-2 antibodies recognize gD in HSV-1 (gD-1). In contrast, anti-glycoprotein G in HSV-2 (mgG-2) antibodies are exclusively type-specific for HSV-2. In this study, truncated versions of gD-2 and mgG-2 were recombinantly produced in mammalian cells and used for the purification of anti-gD-2 and anti-mgG-2 antibodies from the serum of five HSV-2-infected subjects, creating a pool of purified antibodies. These antibody pools were utilized as standards together with purified mgG-2 and gD-2 antigens in ELISA to quantitatively estimate and compare the levels of cross-reactive anti-gD-1 and anti-gD-2 antibodies, as well as anti-mgG-2 antibodies in sera from HSV-1+2-, HSV-2-, and HSV-1-infected subjects. The median concentration of anti-mgG-2 antibodies was five times lower in HSV-1+2-infected subjects as compared with cross-reactive anti-gD-1 and anti-gD-2 antibodies, and three times lower in HSV-2 infected subjects as compared with anti-gD-2 antibodies. The pool of purified anti-gD-2 antibodies presented neutralization activity at low concentrations, while the pool of purified anti-mgG-2 antibodies did not. Instead, these anti-mgG-2 antibodies mediated antibody-dependent cellular cytotoxicity (ADCC) by human granulocytes, monocytes, and NK-cells, but displayed no complement-dependent cytotoxicity. These findings indicate that antibodies to mgG-2 in HSV-2-infected subjects are present at low concentrations but mediate the killing of infected cells via ADCC rather than by neutralizing free viral particles. We, and others, speculate that Fc-receptor mediated antibody functions such as ADCC following HSV-2 vaccination may serve as a better marker of protection correlate instead of neutralizing activity. In an mgG-2 therapeutic vaccine, our findings of low levels of anti-mgG-2 antibodies in HSV-2-infected subjects may suggest an opportunity to enhance the immune responses against mgG-2. In a prophylactic HSV-2 mgG-2 vaccine, a possible interference in cross-reactive immune responses in already infected HSV-1 subjects can be circumvented.

Summary of the Centers for Disease Control and Prevention/National Institute of Allergy and Infectious Diseases Joint Workshop on Genital Herpes: 3-4 November 2022

Genital herpes is caused by infection with herpes simplex virus types 1 and 2 (HSV-1 and HSV-2) and currently has no cure. The disease is the second-most common sexually transmitted infection in the United States, with an estimated 18.6 million prevalent genital infections caused by HSV-2 alone. Genital herpes diagnostics and treatments are not optimal, and no vaccine is currently available. The Centers for Disease Control and Prevention and the National Institute of Allergy and Infectious Diseases convened a workshop entitled "CDC/NIAID Joint Workshop on Genital Herpes." This report summarizes 8 sessions on the epidemiology of genital herpes, neonatal HSV, HSV diagnostics, vaccines, treatments, cures, prevention, and patient advocacy perspective intended to identify opportunities in herpes research and foster the development of strategies to diagnose, treat, cure, and prevent genital herpes.

Effector functions are required for broad and potent protection of neonatal mice with antibodies targeting HSV glycoprotein D

Multiple failed herpes simplex virus (HSV) vaccine candidates induce robust neutralizing antibody (Ab) responses in clinical trials, raising the hypothesis that Fc-domain-dependent effector functions may be critical for protection. While neonatal HSV (nHSV) infection results in mortality and lifelong neurological morbidity in humans, it is uncommon among neonates with a seropositive birthing parent, supporting the hypothesis that Ab-based therapeutics could protect neonates from HSV. We therefore investigated the mechanisms of monoclonal Ab (mAb)-mediated protection in a mouse model of nHSV infection. For a panel of glycoprotein D (gD)-specific mAbs, neutralization and effector functions contributed to nHSV-1 protection. In contrast, effector functions alone were sufficient to protect against nHSV-2, exposing a functional dichotomy between virus types consistent with vaccine trial results. Effector functions are therefore crucial for protection by these gD-specific mAbs, informing effective Ab and vaccine design and demonstrating the potential of polyfunctional Abs as therapeutics for nHSV infections.

The current landscape of the antimicrobial peptide melittin and its therapeutic potential

Melittin, a main component of bee venom, is a cationic amphiphilic peptide with a linear α-helix structure. It has been reported that melittin can exert pharmacological effects, such as antitumor, antiviral and anti-inflammatory effects in vitro and in vivo. In particular, melittin may be beneficial for the treatment of diseases for which no specific clinical therapeutic agents exist. Melittin can effectively enhance the therapeutic properties of some first-line drugs. Elucidating the mechanism underlying melittin-mediated biological function can provide valuable insights for the application of melittin in disease intervention. However, in melittin, the positively charged amino acids enables it to directly punching holes in cell membranes. The hemolysis in red cells and the cytotoxicity triggered by melittin limit its applications. Melittin-based nanomodification, immuno-conjugation, structural regulation and gene technology strategies have been demonstrated to enhance the specificity, reduce the cytotoxicity and limit the off-target cytolysis of melittin, which suggests the potential of melittin to be used clinically. This article summarizes research progress on antiviral, antitumor and anti-inflammatory properties of melittin, and discusses the strategies of melittin-modification for its future potential clinical applications in preventing drug resistance, enhancing the selectivity to target cells and alleviating cytotoxic effects to normal cells.

Dual impacts of a glycan shield on the envelope glycoprotein B of HSV-1: evasion from human antibodies in vivo and neurovirulence

Identification of the mechanisms of viral evasion from human antibodies is crucial both for understanding viral pathogenesis and for designing effective vaccines. Here we show in cell cultures that an N-glycan shield on the herpes simplex virus 1 (HSV-1) envelope glycoprotein B (gB) mediated evasion from neutralization and antibody-dependent cellular cytotoxicity due to pooled γ-globulins derived from human blood. We also demonstrated that the presence of human γ-globulins in mice and immunity to HSV-1 induced by viral infection in mice significantly reduced replication in their eyes of a mutant virus lacking the glycosylation site but had little effect on the replication of its repaired virus. These results suggest that an N-glycan shield on a specific site of HSV-1 envelope gB mediated evasion from human antibodies in vivo and from HSV-1 immunity induced by viral infection in vivo. Notably, we also found that an N-glycan shield on a specific site of HSV-1 gB was significant for HSV-1 neurovirulence and replication in the central nervous system of naïve mice. Thus, we have identified a critical N-glycan shield on HSV-1 gB that has dual impacts, namely evasion from human antibodies in vivo and viral neurovirulence. IMPORTANCE Herpes simplex virus 1 (HSV-1) establishes lifelong latent and recurrent infections in humans. To produce recurrent infections that contribute to transmission of the virus to new human host(s), the virus must be able to evade the antibodies persisting in latently infected individuals. Here, we show that an N-glycan shield on the specific site of the envelope glycoprotein B (gB) of HSV-1 mediates evasion from pooled γ-globulins derived from human blood both in cell cultures and mice. Notably, the N-glycan shield on the specific site of gB was also significant for HSV-1 neurovirulence in naïve mice. Considering the clinical features of HSV-1 infection, these results suggest that the glycan shield not only facilitates recurrent HSV-1 infections in latently infected humans by evading antibodies but is also important for HSV-1 pathogenesis during the initial infection.

Greater Durability and Protection against Herpes Simplex Viral Disease following Immunization of Mice with Single-Cycle ΔgD-2 Compared to an Adjuvanted Glycoprotein D Protein Vaccine

Herpes simplex viruses (HSV) cause chronic infections with significant morbidity. Prior vaccines, designed to generate neutralizing antibodies (nAbs) targeting glycoprotein D (gD), failed to provide durable protection. We adopted a different strategy and evaluated a single-cycle virus deleted in gD (ΔgD-2). ΔgD-2elicits antibodies that primarily mediate antibody-dependent cell mediated cytolysis (ADCC) and provides complete protection against clinical isolates of HSV in multiple lethal mouse models. To assess durability, we vaccinated mice (2 doses administered intramuscularly) with ΔgD-2, adjuvanted recombinant gD-2 (rgD-2/Alum-MPL), or uninfected cells as a control, and quantified antibody responses over one year. Mice (n = 5/group) were lethally challenged at 2, 4, 6, 8, and 10-months post-boost. ΔgD-2-vaccinated mice elicited a durable ADCC-mediating response, which provided complete protection against challenge at all timepoints. In contrast, rgD-2/Alum-MPL elicited only nAbs, which declined significantly within 6 months, provided only partial protection at early timepoints, and no protection after 6 months. Serum sampling after viral challenge showed that infection elicited low levels of ADCC-mediating antibodies in rgD-2/Alum-MPL-vaccinated mice and boosted the nAb response, but only after 6 months. Conversely, infection significantly and consistently boosted both the ADCC and nAbs responses in ΔgD-2-vaccinated mice. Results recapitulate clinical trial outcomes with gD vaccines, highlight the importance of ADCC, and predict that ΔgD-2 will elicit durable responses in humans.

Failure of Herpes Simplex Virus Glycoprotein D Antibodies to Elicit Antibody-Dependent Cell-Mediated Cytotoxicity: Implications for Future Vaccines

BACKGROUND

The glycoprotein D (gD)/AS04 vaccine failed to prevent herpes simplex virus (HSV) 2 in clinical trials. Failure was recapitulated in mice, in which the vaccine elicited neutralizing antibody but not antibody-dependent cell-mediated cytotoxicity (ADCC) responses. Preclinical findings suggest that ADCC is important for protection, but the clinical data are limited. We hypothesized that gD/AS04 and acute HSV-2 infection elicit primarily neutralizing antibodies, whereas ADCC emerges over time.

METHODS

HSV-specific immunoglobulin G, subclass, function (neutralization, C1q binding and ADCC), and antigenic targets were compared (paired t test or Mann-Whitney U test) at enrollment and after gD/AS04 vaccination, before and after HSV-2 acquisition in vaccine controls, and in an independent cohort with chronic HSV-2 infection.

RESULTS

Vaccination elicited only a neutralizing antibody response, whereas acute infection elicited neutralizing and C1q-binding antibodies but not a significant ADCC response. Antibodies to gD were exclusively immunoglobulin G1 and only neutralizing. In contrast, women with chronic HSV-2 infection had significantly greater ADCC responses and targeted a broader range of viral antigens compared with acutely infected or gD/AS04 vaccine recipients (P < .001).

CONCLUSIONS

Results from gD/AS04 vaccinated or acutely infected women recapitulate murine findings of limited functional antibody responses, supporting the speculation that vaccines that generate polyfunctional and specifically ADCC responses may be required to prevent HSV-2 acquisition and limit recurrences.

HSV-2-Specific Human Female Reproductive Tract Tissue Resident Memory T Cells Recognize Diverse HSV Antigens

Antigen-specific T_RM persist and protect against skin or female reproductive tract (FRT) HSV infection. As the pathogenesis of HSV differs between humans and model organisms, we focus on humans with well-characterized recurrent genital HSV-2 infection. Human CD8+ T_RM persisting at sites of healed human HSV-2 lesions have an activated phenotype but it is unclear if T_RM can be cultivated in vitro. We recovered HSV-specific T_RM from genital skin and ectocervix biopsies, obtained after recovery from recurrent genital HSV-2, using ex vivo activation by viral antigen. Up to several percent of local T cells were HSV-reactive ex vivo. CD4 and CD8 T cell lines were up to 50% HSV-2-specific after sorting-based enrichment. CD8 T_RM displayed HLA-restricted reactivity to specific HSV-2 peptides with high functional avidities. Reactivity to defined peptides persisted locally over several month and was quite subject-specific. CD4 T_RM derived from biopsies, and from an extended set of cervical cytobrush specimens, also recognized diverse HSV-2 antigens and peptides. Overall we found that HSV-2-specific T_RM are abundant in the FRT between episodes of recurrent genital herpes and maintain competency for expansion. Mucosal sites are accessible for clinical monitoring during immune interventions such as therapeutic vaccination.

An mRNA vaccine to prevent genital herpes

The rapid development of two nucleoside-modified mRNA vaccines that are safe and highly effective against coronavirus disease 2019 has transformed the vaccine field. The mRNA technology has the advantage of accelerated immunogen discovery, induction of robust immune responses, and rapid scale up of manufacturing. Efforts to develop genital herpes vaccines have been ongoing for 8 decades without success. The advent of mRNA technology has the potential to change that narrative. Developing a genital herpes vaccine is a high public health priority. A prophylactic genital herpes vaccine should prevent HSV-1 and HSV-2 genital lesions and infection of dorsal root ganglia, the site of latency. Vaccine immunity should be durable for decades, perhaps with the assistance of booster doses. While these goals have been elusive, new efforts with nucleoside-modified mRNA-lipid nanoparticle vaccines show great promise. We review past approaches to vaccine development that were unsuccessful or partially successful in large phase 3 trials, and describe lessons learned from these trials. We discuss our trivalent mRNA-lipid nanoparticle approach for a prophylactic genital herpes vaccine and the ability of the vaccine to induce higher titers of neutralizing antibodies and more durable CD4+ T follicular helper cell and memory B cell responses than protein-adjuvanted vaccines.

Neutralizing Antibody Kinetics and Immune Protection Against Herpes Simplex Virus 1 Genital Disease in Vaccinated Women

BACKGROUND

Previously, our group conducted the Herpevac Trial for Women, a randomized efficacy field trial of type 2 glycoprotein D (gD2) herpes simplex virus (HSV) vaccine adjuvanted with ASO4 in 8323 women. Study participants were selected to be seronegative for HSV-1 and HSV-2. We found that the vaccine was 82% protective against culture-positive HSV-1 genital disease but offered no significant protection against HSV-2 genital disease. Efficacy against HSV-1 was associated with higher levels of antibody to gD2 at enzyme-linked immunosorbent assay (ELISA).

METHODS

To better understand the results of the efficacy study, we measured postvaccination concentrations of neutralizing antibody (nAb) to either HSV-1 and HSV-2 from HSV-infected study participants and matched uninfected controls. Statistical modeling was used to determine whether these responses were correlated with protection against HSV.

RESULTS

nAbs to either HSV-1 or HSV-2 were correlated with ELISA binding antibodies to gD2. HSV-1 or HSV-2 nAb findings support the observation of protection by higher levels of antibody against HSV-1 infection, but the lack of protection against HSV-2 remains unexplained.

CONCLUSIONS

The protection against HSV-1 infection observed in the Herpevac Trial for Women was associated with nAbs directed against the virus, although the power to assess this was lower in the nAb study compared with the ELISA results owing to smaller sample size.

CLINICAL TRIALS REGISTRATION

NCT00057330.

Developments in Vaccination for Herpes Simplex Virus

Herpes simplex virus (HSV) is an alpha herpes virus, with two subtypes: HSV-1 and HSV-2. HSV is one of the most prevalent sexually transmitted infections. It is the cause of severe neonatal infections and a leading cause of infectious blindness in the Western world. As of 2016, 13.2% of the global population ages 15-49 were existing with HSV-2 infection and 66.6% with HSV-1. This high prevalence of disease and the fact that resistance to current therapies is on the rise makes it imperative to develop and discover new methods of HSV prevention and management. Among the arsenal of therapies/treatments for this virus has been the development of a prophylactic or therapeutic vaccine to prevent the complications of HSV reactivation. Our current understanding of the immune responses involved in latency and reactivation provides a unique challenge to the development of vaccines. There are no approved vaccines currently available for either prophylaxis or therapy. However, there are various promising candidates in the pre-clinical and clinical phases of study. Vaccines are being developed with two broad focuses: preventative and therapeutic, some with a dual use as both immunotherapeutic and prophylactic. Within this article, we will review the current guidelines for the treatment of herpes simplex infections, our understanding of the immunological pathways involved, and novel vaccine candidates in development.

A truncated glycoprotein G vaccine formulated with Advax-CpG adjuvant provides protection of mice against genital herpes simplex virus 2 infection

Herpes simplex virus type 2 (HSV-2) is a common sexually transmitted disease that affects approximately 500 million individuals globally. There is currently no approved vaccine to prevent HSV-2 infection. EXCT4 is a truncated form of the mature glycoprotein G-2 (mgG-2) that unlike full mature form is secreted by expressing cells enabling it to be rapidly scaled up for production. The current study examined whether EXCT4 immunity in mice could be further enhanced through use of adjuvants. EXCT4 formulated with Advax-CpG adjuvant induced a strong Th1-type immune response characterized by interferon gamma (IFN-γ) and protected animals against a lethal genital challenge with HSV-2. This response was associated with reduced viral load in vaginal washes, spinal cord, and dorsal root ganglia. Together the results provide proof of concept that EXCT4 formulated with Advax-CpG adjuvant is a promising HSV-2 vaccine candidate warranting further investigation.

The Role of Tissue Resident Memory CD4 T Cells in Herpes Simplex Viral and HIV Infection

Tissue-resident memory T cells (TRM) were first described in 2009. While initially the major focus was on CD8⁺ TRM, there has recently been increased interest in defining the phenotype and the role of CD4⁺ TRM in diseases. Circulating CD4⁺ T cells seed CD4⁺ TRM, but there also appears to be an equilibrium between CD4⁺ TRM and blood CD4⁺ T cells. CD4⁺ TRM are more mobile than CD8⁺ TRM, usually localized deeper within the dermis/lamina propria and yet may exhibit synergy with CD8⁺ TRM in disease control. This has been demonstrated in herpes simplex infections in mice. In human recurrent herpes infections, both CD4⁺ and CD8⁺ TRM persisting between lesions may control asymptomatic shedding through interferon-gamma secretion, although this has been more clearly shown for CD8⁺ T cells. The exact role of the CD4⁺/CD8⁺ TRM axis in the trigeminal ganglia and/or cornea in controlling recurrent herpetic keratitis is unknown. In HIV, CD4⁺ TRM have now been shown to be a major target for productive and latent infection in the cervix. In HSV and HIV co-infections, CD4⁺ TRM persisting in the dermis support HIV replication. Further understanding of the role of CD4⁺ TRM and their induction by vaccines may help control sexual transmission by both viruses.

Alphaherpesvirus Vaccines

Prophylactic and therapeutic vaccines for the alphaherpesviruses including varicella zoster virus (VZV) and herpes simplex virus types 1 and 2 have been the focus of enormous preclinical and clinical research. A live viral vaccine for prevention of chickenpox and a subunit therapeutic vaccine to prevent zoster are highly successful. In contrast, progress towards the development of effective prophylactic or therapeutic vaccines against HSV-1 and HSV-2 has met with limited success. This review provides an overview of the successes and failures, the different types of immune responses elicited by various vaccine modalities, and the need to reconsider the preclinical models and immune correlates of protection against HSV.

Herpes Simplex Virus Type 2 Is More Difficult to Neutralize by Antibodies Than Herpes Simplex Virus Type 1

Infections with herpes simplex virus type 1 (HSV-1) and type 2 (HSV-2) are a global health burden. Besides painful oral or genital lesions in otherwise healthy subjects, both viruses can cause devastating morbidity and mortality in immune-compromised and immune-immature individuals. The latter are particularly susceptible to a disseminated, life-threatening disease. Neutralizing antibodies (NAb) constitute a correlate of protection from disease, and are promising candidates for the prophylactic or therapeutic treatment of severe HSV infections. However, a clinical vaccine trial suggested that HSV-2 might be more resistant to NAbs than HSV-1. In the present study, we investigated the antiviral efficacy of the well-characterized humanized monoclonal antibody (mAb) hu2c against HSV-2, in a NOD/SCID immunodeficiency mouse model. Despite the fact that hu2c recognizes a fully conserved epitope and binds HSV-1 and HSV-2 glycoprotein B with equal affinity, it was much less effective against HSV-2 in vitro and in NOD/SCID mice. Although intravenous antibody treatment prolonged the survival of HSV-2-infected mice, complete protection from death was not achieved. Our data demonstrate that HSV-2 is more resistant to NAbs than HSV-1, even if the same antibody and antigen are concerned, making the development of a vaccine or therapeutic antibodies more challenging.

Epidemiological Impact of Novel Preventive and Therapeutic HSV-2 Vaccination in the United States: Mathematical Modeling Analyses

This study aims to inform herpes simplex virus type 2 (HSV-2) vaccine development, licensure, and implementation by delineating the population-level impact of vaccination. Mathematical models were constructed to describe the transmission dynamics in presence of prophylactic or therapeutic vaccines assuming 50% efficacy, with application to the United States. Catch-up prophylactic vaccination will reduce, by 2050, annual number of new infections by 58%, incidence rate by 60%, seroprevalence by 21%, and avert yearly as much as 350,000 infections. Number of vaccinations needed to avert one infection was only 50 by 2050, 34 by prioritizing those aged 15-19 years, 4 by prioritizing the highest sexual risk group, 43 by prioritizing women, and 47 by prioritizing men. Therapeutic vaccination of infected adults with symptomatic disease will reduce, by 2050, annual number of new infections by 12%, incidence rate by 13%, seroprevalence by 4%, and avert yearly as much as 76,000 infections. Number of vaccinations needed to avert one infection was eight by 2050, two by prioritizing those aged 15-19 years, three by prioritizing the highest sexual risk group, seven by prioritizing men, and ten by prioritizing women. HSV-2 vaccination offers an impactful and cost-effective intervention to prevent genital herpes medical and psychosexual disease burden.

An HSV-2 nucleoside-modified mRNA genital herpes vaccine containing glycoproteins gC, gD, and gE protects mice against HSV-1 genital lesions and latent infection

HSV-1 causes 50% of first-time genital herpes infections in resource-rich countries and affects 190 million people worldwide. A prophylactic herpes vaccine is needed to protect against genital infections by both HSV-1 and HSV-2. Previously our laboratory developed a trivalent vaccine that targets glycoproteins C, D, and E present on the HSV-2 virion. We reported that this vaccine protects animals from genital disease and recurrent virus shedding following lethal HSV-2 challenge. Importantly the vaccine also generates cross-reactive antibodies that neutralize HSV-1, suggesting it may provide protection against HSV-1 infection. Here we compared the efficacy of this vaccine delivered as protein or nucleoside-modified mRNA immunogens against vaginal HSV-1 infection in mice. Both the protein and mRNA vaccines protected mice from HSV-1 disease; however, the mRNA vaccine provided better protection as measured by lower vaginal virus titers post-infection. In a second experiment, we compared protection provided by the mRNA vaccine against intravaginal challenge with HSV-1 or HSV-2. Vaccinated mice were totally protected against death, genital disease and infection of dorsal root ganglia caused by both viruses, but somewhat better protected against vaginal titers after HSV-2 infection. Overall, in the two experiments, the mRNA vaccine prevented death and genital disease in 54/54 (100%) mice infected with HSV-1 and 20/20 (100%) with HSV-2, and prevented HSV DNA from reaching the dorsal root ganglia, the site of virus latency, in 29/30 (97%) mice infected with HSV-1 and 10/10 (100%) with HSV-2. We consider the HSV-2 trivalent mRNA vaccine to be a promising candidate for clinical trials for prevention of both HSV-1 and HSV-2 genital herpes.

Immune Response to Herpes Simplex Virus Infection and Vaccine Development

Herpes simplex virus (HSV) infections are among the most common viral infections and usually last for a lifetime. The virus can potentially be controlled with vaccines since humans are the only known host. However, despite the development and trial of many vaccines, this has not yet been possible. This is normally attributed to the high latency potential of the virus. Numerous immune cells, particularly the natural killer cells and interferon gamma and pathways that are used by the body to fight HSV infections have been identified. On the other hand, the virus has developed different mechanisms, including using different microRNAs to inhibit apoptosis and autophagy to avoid clearance and aid latency induction. Both traditional and new methods of vaccine development, including the use of live attenuated vaccines, replication incompetent vaccines, subunit vaccines and recombinant DNA vaccines are now being employed to develop an effective vaccine against the virus. We conclude that this review has contributed to a better understanding of the interplay between the immune system and the virus, which is necessary for the development of an effective vaccine against HSV.

Vaccines to prevent genital herpes

Genital herpes increases the risk of acquiring and transmitting Human Immunodeficiency Virus (HIV), is a source of anxiety for many about transmitting infection to intimate partners, and is life-threatening to newborns. A vaccine that prevents genital herpes infection is a high public health priority. An ideal vaccine will prevent both genital lesions and asymptomatic subclinical infection to reduce the risk of inadvertent transmission to partners, will be effective against genital herpes caused by herpes simplex virus types 1 and 2 (HSV-1, HSV-2), and will protect against neonatal herpes. Three phase 3 human trials were performed over the past 20 years that used HSV-2 glycoproteins essential for virus entry as immunogens. None achieved its primary endpoint, although each was partially successful in either delaying onset of infection or protecting a subset of female subjects that were HSV-1 and HSV-2 uninfected against HSV-1 genital infection. The success of future vaccine candidates may depend on improving the predictive value of animal models by requiring vaccines to achieve near-perfect protection in these models and by using the models to better define immune correlates of protection. Many vaccine candidates are under development, including DNA, modified mRNA, protein subunit, killed virus, and attenuated live virus vaccines. Lessons learned from prior vaccine studies and select candidate vaccines are discussed, including a trivalent nucleoside-modified mRNA vaccine that our laboratory is pursuing. We are optimistic that an effective vaccine for prevention of genital herpes will emerge in this decade.

Herpes simplex virus type 2 trivalent protein vaccine containing glycoproteins C, D and E protects guinea pigs against HSV-1 genital infection

A vaccine to prevent genital herpes is an unmet public health need. We previously reported that a trivalent vaccine containing herpes simplex virus type 2 (HSV-2) glycoproteins C, D, and E (gC2, gD2, gE2) produced in baculovirus and administered with CpG/alum as adjuvants blocks immune evasion mediated by gC2 and gE2 and virus entry by gD2. The vaccine protected guinea pigs against HSV-2 vaginal infection. We evaluated whether the HSV-2 vaccine cross-protects against HSV-1 because many first-time genital herpes infections are now caused by HSV-1. Guinea pigs were mock immunized or immunized with the trivalent vaccine and challenged intravaginally with a different HSV-1 isolate in two experiments. Guinea pigs immunized with the trivalent vaccine developed genital lesions on fewer days than the mock group: 2/477 (0.4%) days compared to 15/424 (3.5%) in experiment one, and 0/135 days compared to 17/135 (12.6%) in experiment two (both P < .001). No animal in the trivalent group had HSV-2 DNA detected in vaginal secretions: 0/180 days for trivalent compared to 4/160 (2.5%) for mock (P < .05) in experiment one, and 0/65 days for trivalent compared to 4/65 (6%) for mock in experiment two. Therefore, a vaccine designed to prevent HSV-2 also protects against HSV-1 genital infection.

Murine Model of Maternal Immunization Demonstrates Protective Role for Antibodies That Mediate Antibody-Dependent Cellular Cytotoxicity in Protecting Neonates From Herpes Simplex Virus Type 1 and Type 2

BACKGROUND

Neonatal herpes simplex virus (HSV) disease results in unacceptable morbidity and mortality. The primary humoral immune response to natural infection is neutralizing antibodies (Abs). However, Abs that activate Fc gama receptors (FcγRs) and mediate antibody-dependent cell-mediated cytotoxicity (ADCC) may play a dominant role in protection. In adult mice, a single-cycle HSV candidate vaccine deleted in glycoprotein-D (ΔgD-2) that induces ADCC provided complete protection against HSV disease and prevented the establishment of latency. Passive transfer studies showed that Abs were sufficient for protection. The current study tested the hypothesis that maternal immunization with ΔgD-2 would protect neonates.

METHODS

C57BL/6 female mice were vaccinated 3 weeks apart with ΔgD-2, and pups were challenged at different times postnatally with lethal doses of HSV-1 or HSV-2. Concentration and functionality of Abs and immune cells were assessed.

RESULTS

Maternal ΔgD-2 immunization provided significant protection and reduced viral dissemination after lethal challenge with HSV-1 or HSV-2. Protection correlated with Abs acquired transplacentally or from breastmilk that mediated ADCC. Protection was reduced when pups were challenged on Day 1 of life, and this was associated with decreased ability of newborn cells to mediate Ab-dependent cell killing.

CONCLUSIONS

Antibodies mediating ADCC provide significant protection against neonatal HSV.

Intramuscular vaccination of mice with the human herpes simplex virus type-1(HSV-1) VC2 vaccine, but not its parental strain HSV-1(F) confers full protection against lethal ocular HSV-1 (McKrae) pathogenesis

Herpes simplex virus type-1 (HSV-1) can cause severe ocular infection and blindness. We have previously shown that the HSV-1 VC2 vaccine strain is protective in mice and guinea pigs against genital herpes infection following vaginal challenge with HSV-1 or HSV-2. In this study, we evaluated the efficacy of VC2 intramuscular vaccination in mice against herpetic keratitis following ocular challenge with lethal human clinical strain HSV-1(McKrae). VC2 vaccination in mice produced superior protection and morbidity control in comparison to its parental strain HSV-1(F). Specifically, after HSV-1(McKrae) ocular challenge, all VC2 vaccinated- mice survived, while 30% of the HSV-1(F)- vaccinated and 100% of the mock-vaccinated mice died post challenge. VC2-vaccinated mice did not exhibit any symptoms of ocular infection and completely recovered from initial conjunctivitis. In contrast, HSV-1(F)-vaccinated mice developed time-dependent progressive keratitis characterized by corneal opacification, while mock-vaccinated animals exhibited more severe stromal keratitis characterized by immune cell infiltration and neovascularization in corneal stroma with corneal opacification. Cornea in VC2-immunized mice exhibited significantly increased infiltration of CD3⁺ T lymphocytes and decreased infiltration of Iba1+ macrophages in comparison to mock- or HSV-1(F)-vaccinated groups. VC2 immunization produced higher virus neutralization titers than HSV-1(F) post challenge. Furthermore, VC-vaccination significantly increased the CD4 T central memory (TCM) subsets and CD8 T effector memory (TEM) subsets in the draining lymph nodes following ocular HSV-1 (McKrae) challenge, then mock- or HSV-1(F)-vaccination. These results indicate that VC2 vaccination produces a protective immune response at the site of challenge to protect against HSV-1-induced ocular pathogenesis.

Biologic interactions between HSV-2 and HIV-1 and possible implications for HSV vaccine development

Development of a safe and effective vaccine against herpes simplex virus type 2 (HSV-2) has the potential to limit the global burden of HSV-2 infection and disease, including genital ulcer disease and neonatal herpes, and is a global sexual and reproductive health priority. Another important potential benefit of an HSV-2 vaccine would be to decrease HIV infections, as HSV-2 increases the risk of HIV-1 acquisition several-fold. Acute and chronic HSV-2 infection creates ulcerations and draws dendritic cells and activated CD4+ T cells into genital mucosa. These cells are targets for HIV entry and replication. Prophylactic HSV-2 vaccines (to prevent infection) and therapeutic vaccines (to modify or treat existing infections) are currently under development. By preventing or modifying infection, an effective HSV-2 vaccine could limit HSV-associated genital mucosal inflammation and thus HIV risk. However, a vaccine might have competing effects on HIV risk depending on its mechanism of action and cell populations generated in the genital mucosa. In this article, we review biologic interactions between HSV-2 and HIV-1, consider HSV-2 vaccine development in the context of HIV risk, and discuss implications and research needs for future HSV vaccine development.

A vaccine containing highly purified virus particles in adjuvant provides high level protection against genital infection and disease in guinea pigs challenged intravaginally with homologous and heterologous strains of herpes simplex virus type 2

Infection with Herpes Simplex Viruses (HSVs) represents a significant health burden worldwide with HSV-1 and HSV-2 causing genital disease and HSV-2 contributing to human immunodeficiency virus acquisition. Despite great need, there is currently no licensed vaccine against HSV. In this report, we evaluated the protective efficacy of a vaccine containing highly purified, inactivated HSV-2 particles (with and without additional recombinant glycoprotein D) formulated with a monophosphoryl lipid A/Alhydrogel adjuvant in a guinea pig HSV genital model. The key results from 3 independent studies were: (1) vaccination consistently provided significant 3-3.5 Log10 reductions in vaginal HSV-2 titers on day 2 postchallenge; (2) following homologous or heterologous challenge with two U.S. isolates, all vaccine groups showed complete protection against lesion formation, significant 3 Log10 reductions in day 2 virus shedding, enhanced virus clearance, significant reductions in HSV-2 DNA within ganglia, and no detectable shedding (<2 PFU) or latent viral DNA in some immunized animals; (3) following challenge with a third heterologous strain, vaccination provided complete protection against primary and recurrent lesions, significant reductions in primary virus shedding, a 50% reduction in recurrent shedding days, and undetectable latent virus in the ganglia and spinal cords of most animals; and (4) adding glycoprotein D provided no enhanced protection relative to that elicited by the inactivated HSV-2 particles alone. Together, these data provide strong support for further development of this exceedingly protective and highly feasible vaccine candidate for human trials.

The Roles of Host and Viral Antibody Fc Receptors in Herpes Simplex Virus (HSV) and Human Cytomegalovirus (HCMV) Infections and Immunity

Herpesvirus infections are a leading cause of neurodevelopmental delay in newborns and end-organ disease in immunocompromised patients. One leading strategy to reduce the disease burden of herpesvirus infections such as herpes simplex virus (HSV) and human cytomegalovirus (HCMV) is to prevent primary acquisition by vaccination, yet vaccine development remains hampered by limited understanding of immune correlates of protection against infection. Traditionally, vaccine development has aimed to increase antibody titers with neutralizing function, which involves the direct binding of antibodies to viral particles. However, recent research has explored the numerous other responses that can be mediated by engagement of the antibody constant region (Fc) with Fc receptors (FcR) present on immune cells or with complement molecules. These functions include antiviral responses such as antibody-dependent cell-mediated cytotoxicity (ADCC) and antibody-dependent cellular phagocytosis (ADCP). Uniquely, herpesviruses encode FcR that can act as distractor receptors for host antiviral IgG, thus enabling viral evasion of host defenses. This review focuses on the relative roles of neutralizing and non-neutralizing functions antibodies that target herpesvirus antigens for HSV and HCMV, as well as the roles of Fc-FcR interactions for both host defenses and viral escape.

A Randomized, Double-Blinded, Placebo-Controlled, Phase 1 Study of a Replication-Defective Herpes Simplex Virus (HSV) Type 2 Vaccine, HSV529, in Adults With or Without HSV Infection

BACKGROUND

Herpes simplex virus 2 (HSV2) causes genital herpes in >400 million persons worldwide.

METHODS

We conducted a randomized, double-blinded, placebo-controlled trial of a replication-defective HSV2 vaccine, HSV529. Twenty adults were enrolled in each of 3 serogroups of individuals: those negative for both HSV1 and HSV2 (HSV1-/HSV2-), those positive or negative for HSV1 and positive for HSV2 (HSV1±/HSV2+), and those positive for HSV1 and negative for HSV2 (HSV1+/HSV2-). Sixty participants received vaccine or placebo at 0, 1, and 6 months. The primary end point was the frequency of solicited local and systemic reactions to vaccination.

RESULTS

Eighty-nine percent of vaccinees experienced mild-to-moderate solicited injection site reactions, compared with 47% of placebo recipients (95% confidence interval [CI], 12.9%-67.6%; P = .006). Sixty-four percent of vaccinees experienced systemic reactions, compared with 53% of placebo recipients (95% CI, -17.9% to 40.2%; P = .44). Seventy-eight percent of HSV1-/HSV2- vaccine recipients had a ≥4-fold increase in neutralizing antibody titer after 3 doses of vaccine, whereas none of the participants in the other serogroups had such responses. HSV2-specific CD4+ T-cell responses were detected in 36%, 46%, and 27% of HSV1-/HSV2-, HSV1±/HSV2+, and HSV1+/HSV2- participants, respectively, 1 month after the third dose of vaccine, and CD8+ T-cell responses were detected in 14%, 8%, and 18% of participants, respectively.

CONCLUSIONS

HSV529 vaccine was safe and elicited neutralizing antibody and modest CD4+ T-cell responses in HSV-seronegative vaccinees.

CLINICAL TRIALS REGISTRATION

NCT01915212.

Cell-to-Cell Spread Blocking Activity Is Extremely Limited in the Sera of Herpes Simplex Virus 1 (HSV-1)- and HSV-2-Infected Subjects

Herpes simplex virus 1 (HSV-1) and HSV-2 can evade serum antibody-mediated neutralization through cell-to-cell transmission mechanisms, which represent one of the central steps in disease reactivation. To address the role of humoral immunity in controlling HSV-1 and HSV-2 replication, we analyzed serum samples from 44 HSV-1 and HSV-2 seropositive subjects by evaluating (i) their efficiency in binding both the purified viral particles and recombinant gD and gB viral glycoproteins, (ii) their neutralizing activity, and (iii) their capacity to inhibit the cell-to-cell virus passage in vitro All of the sera were capable of binding gD, gB, and whole virions, and all sera significantly neutralized cell-free virus. However, neither whole sera nor purified serum IgG fraction was able to inhibit significantly cell-to-cell virus spreading in in vitro post-virus-entry infectious assays. Conversely, when spiked with an already described anti-gD human monoclonal neutralizing antibody capable of inhibiting HSV-1 and -2 cell-to-cell transmission, each serum boosted both its neutralizing and post-virus-entry inhibitory activity, with no interference exerted by serum antibody subpopulations.IMPORTANCE Despite its importance in the physiopathology of HSV-1 and -2 infections, the cell-to-cell spreading mechanism is still poorly understood. The data shown here suggest that infection-elicited neutralizing antibodies capable of inhibiting cell-to-cell virus spread can be underrepresented in most infected subjects. These observations can be of great help in better understanding the role of humoral immunity in controlling virus reactivation and in the perspective of developing novel therapeutic strategies, studying novel correlates of protection, and designing effective vaccines.

Vaccine-induced antibodies target sequestered viral antigens to prevent ocular HSV-1 pathogenesis, preserve vision, and preempt productive neuronal infection

The cornea is essential for vision yet highly sensitive to immune-mediated damage following infection. Generating vaccines that provide sterile immunity against ocular surface pathogens without evoking vision loss is therefore clinically challenging. Here, we tested a prophylactic live-attenuated vaccine against herpes simplex virus type 1 (HSV-1), a widespread human pathogen that can cause corneal blindness. Parenteral vaccination of mice resulted in sterile immunity to subsequent HSV-1 challenge in the cornea and suppressed productive infection of the nervous system. This protection was unmatched by a relevant glycoprotein subunit vaccine. Efficacy of the live-attenuated vaccine involved a T-dependent humoral immune response and complement C3 but not Fcγ-receptor 3 or interferon-α/β signaling. Proteomic analysis of viral proteins recognized by antiserum revealed an unexpected repertoire dominated by sequestered antigens rather than surface-exposed envelope glycoproteins. Ocular HSV-1 challenge in naive and subunit-vaccinated mice triggered vision loss and severe ocular pathologies including corneal opacification, scar formation, neovascularization, and sensation loss. However, corneal pathology was absent in mice receiving the live-attenuated vaccine concomitant with complete preservation of visual acuity. Collectively, this is the first comprehensive report of a prophylactic vaccine candidate that elicits resistance to ocular HSV-1 infection while fully preserving the cornea and visual acuity.

Correlation between herpes simplex virus neutralizing antibody titers determined by ELVIS cell and traditional plaque reduction assays

Preventive viral vaccine efficacy trials require large-scale sample analysis to quantitate immune responses and their correlation with infection outcomes. Traditional plaque reduction assays measure a functionally important form of humoral immunity, neutralizing antibody titer. These assays, however, are time-consuming and laborious. We previously developed a higher throughput assay of neutralizing antibody to herpes simplex viruses 1 and 2 (Blevins et al., PLOS ONE, 10(12), e0144738) using the enzyme-linked virus inducible system (ELVIS) cell line; this cell line produces β-galactosidase in response to HSV infection. Here, serum samples from recipients of an investigational vaccine in the Herpevac Trial for Women were used to compare the ELVIS cell assay with the lower throughput, traditional plaque reduction assay. We demonstrate that neutralizing antibody titers to HSV-1 or HSV-2 determined using ELVIS cells positively correlate with neutralizing antibody titers determined by traditional plaque reduction assay, thus validating a higher throughput alternative for large-scale sample analysis.

A new era in cytomegalovirus vaccinology: considerations for rational design of next-generation vaccines to prevent congenital cytomegalovirus infection

Human cytomegalovirus (HCMV), a member of the beta-herpesvirus family, is the most common cause of congenital infection worldwide as well as an important cause of morbidity in transplant recipients and immunosuppressed individuals. An estimated 1 in 150 infants are infected with HCMV at birth, which can result in lifelong, debilitating neurologic sequelae including microcephaly, sensorineural hearing loss, and cognitive impairment. Natural maternal immunity to HCMV decreases the frequency of reinfection and reduces risk of congenital transmission but does not completely protect against neonatal disease. Thus, a vaccine to reduce the incidence and severity of infant infection is a public health priority. A variety of candidate HCMV vaccine approaches have been tried previously, including live-attenuated viruses, glycoprotein subunit formulations, viral vectors, and single/bivalent DNA plasmids, but all have failed to reach target endpoints in clinical trials. Nevertheless, there is a great deal to be learned from the successes and failures of the HCMV vaccine field (both congenital and transplant-associated), as well as from vaccine development efforts for other herpesvirus pathogens including herpes simplex virus 1 and 2, varicella zoster virus, and Epstein-Barr virus. Here, we review those successes and failures, evaluating recent cutting-edge discoveries that have shaped the HCMV vaccine field and identifying topics of critical importance for future investigation. These considerations will inform rational design and evaluation of next-generation vaccines to prevent HCMV-associated congenital infection and disease.

Vaccine-induced antibodies to herpes simplex virus glycoprotein D epitopes involved in virus entry and cell-to-cell spread correlate with protection against genital disease in guinea pigs

Herpes simplex virus type 2 (HSV-2) glycoprotein D (gD2) subunit antigen is included in many preclinical candidate vaccines. The rationale for including gD2 is to produce antibodies that block crucial gD2 epitopes involved in virus entry and cell-to-cell spread. HSV-2 gD2 was the only antigen in the Herpevac Trial for Women that protected against HSV-1 genital infection but not HSV-2. In that trial, a correlation was detected between gD2 ELISA titers and protection against HSV-1, supporting the importance of antibodies. A possible explanation for the lack of protection against HSV-2 was that HSV-2 neutralization titers were low, four-fold lower than to HSV-1. Here, we evaluated neutralization titers and epitope-specific antibody responses to crucial gD2 epitopes involved in virus entry and cell-to-cell spread as correlates of immune protection against genital lesions in immunized guinea pigs. We detected a strong correlation between neutralizing antibodies and protection against genital disease. We used a high throughput biosensor competition assay to measure epitope-specific responses to seven crucial gD2 linear and conformational epitopes involved in virus entry and spread. Some animals produced antibodies to most crucial epitopes while others produced antibodies to few. The number of epitopes recognized by guinea pig immune serum correlated with protection against genital lesions. We confirmed the importance of antibodies to each crucial epitope using monoclonal antibody passive transfer that improved survival and reduced genital disease in mice after HSV-2 genital challenge. We re-evaluated our prior study of epitope-specific antibody responses in women in the Herpevac Trial. Humans produced antibodies that blocked significantly fewer crucial gD2 epitopes than guinea pigs, and antibody responses in humans to some linear epitopes were virtually absent. Neutralizing antibody titers and epitope-specific antibody responses are important immune parameters to evaluate in future Phase I/II prophylactic human vaccine trials that contain gD2 antigen.

Meeting report: Initial World Health Organization consultation on herpes simplex virus (HSV) vaccine preferred product characteristics, March 2017

The development of vaccines against herpes simplex virus (HSV) is an important global goal for sexual and reproductive health. A key priority to advance development of HSV vaccines is the definition of preferred product characteristics (PPCs), which provide strategic guidance on World Health Organization (WHO) preferences for new vaccines, specifically from a low- and middle-income country (LMIC) perspective. To start the PPC process for HSV vaccines, the WHO convened a global stakeholder consultation in March 2017, to define the priority public health needs that should be addressed by HSV vaccines and discuss the key considerations for HSV vaccine PPCs, particularly for LMICs. Meeting participants outlined an initial set of overarching public health goals for HSV vaccines in LMICs, which are: to reduce the acquisition of HIV associated with HSV-2 infection in high HIV-prevalence populations and to reduce the burden of HSV-associated disease, including mortality and morbidity due to neonatal herpes and impacts on sexual and reproductive health. Participants also considered the role of prophylactic versus therapeutic vaccines, whether both HSV-2 and HSV-1 should be targeted, important target populations, and infection and disease endpoints for clinical trials. This article summarizes the main discussions from the consultation.

The Neonatal Fc Receptor and Complement Fixation Facilitate Prophylactic Vaccine-Mediated Humoral Protection against Viral Infection in the Ocular Mucosa

The capacity of licensed vaccines to protect the ocular surface against infection is limited. Common ocular pathogens, such as HSV-1, are increasingly recognized as major contributors to visual morbidity worldwide. Humoral immunity is an essential correlate of protection against HSV-1 pathogenesis and ocular pathology, yet the ability of Ab to protect against HSV-1 is deemed limited due to the slow IgG diffusion rate in the healthy cornea. We show that a live-attenuated HSV-1 vaccine elicits humoral immune responses that are unparalleled by a glycoprotein subunit vaccine vis-à-vis Ab persistence and host protection. The live-attenuated vaccine was used to assess the impact of the immunization route on vaccine efficacy. The hierarchical rankings of primary immunization route with respect to efficacy were s.c. ≥ mucosal > i.m. Prime-boost vaccination via sequential s.c. and i.m. administration yielded greater efficacy than any other primary immunization route alone. Moreover, our data support a role for complement in prophylactic protection, as evidenced by intracellular deposition of C3d in the corneal epithelium of vaccinated animals following challenge and delayed viral clearance in C3-deficient mice. We also identify that the neonatal Fc receptor (FcRn) is upregulated in the cornea following infection or injury concomitant with increased Ab perfusion. Lastly, selective small interfering RNA-mediated knockdown of FcRn in the cornea impeded protection against ocular HSV-1 challenge in vaccinated mice. Collectively, these findings establish a novel mechanism of humoral protection in the eye involving FcRn and may facilitate vaccine and therapeutic development for other ocular surface diseases.

Global sensing of the antigenic structure of herpes simplex virus gD using high-throughput array-based SPR imaging

While HSV-2 typically causes genital lesions, HSV-1 is increasingly the cause of genital herpes. In addition, neonatal HSV infections are associated with a high rate of mortality and HSV-2 may increase the risk for HIV or Zika infections, reinforcing the need to develop an effective vaccine. In the GSK Herpevac trial, doubly sero-negative women were vaccinated with a truncated form of gD2 [gD2(284t)], then examined for anti-gD serum titers and clinical manifestations of disease. Surprisingly, few vaccinees were protected against genital HSV-2 but 86% were protected from genital HSV-1. These observations suggest that subtle differences in gD structure might influence a protective response. To better understand the antigenic structure of gD and how it impacts a protective response, we previously utilized several key anti-gD monoclonal antibodies (mAbs) to dissect epitopes in vaccinee sera. Several correlations were observed but the methodology limited the number of sera and mAbs that could be tested. Here, we used array-based surface plasmon imaging (SPRi) to simultaneously measure a larger number of protein-protein interactions. We carried out cross-competition or “epitope binning” studies with 39 anti-gD mAbs and four soluble forms of gD, including a form [gD2(285t)] that resembles the Herpevac antigen. The results from these experiments allowed us to organize the mAbs into four epitope communities. Notably, relationships within and between communities differed depending on the form of gD, and off-rate analysis suggested differences in mAb-gD avidity depending on the gD serotype and length. Together, these results show that gD1 and gD2 differ in their structural topography. Consistent with the Herpevac results, several mAbs that bind both gD1 and gD2 neutralize only HSV-1. Thus, this technology provides new insights into the antigenic structure of gD and provides a rationale as to how vaccination with a gD2 subunit may lead to protection from HSV-1 infection.

Understanding the complex steps of herpes simplex virus (HSV) entry into susceptible cells is key for developing an effective vaccine to prevent clinical disease and control recurrences of this important human pathogen. For either serotype (HSV-1 or HSV-2), it is the interaction of glycoprotein D (gD) with receptor that initiates the cascade of events to begin infection. Importantly, gD stimulates high titers of virus-neutralizing antibodies that predict its importance in a protective response. Many HSV vaccines under development center around gD. In one recent clinical trial, subjects vaccinated with gD2 were protected against HSV-1 genital infection but not HSV-2, leading us to address how type specificity affects the antigenic topography of gD. Using a large panel of monoclonal antibodies (mAbs), we employed a new high-throughput, array-based approach to organize the mAbs into communities. Relationships within and between communities differed depending on the isotype and length of gD, suggesting significant differences in the epitope topography. We found that a subset of mAbs bound both gD1 and gD2 yet only neutralized HSV-1, possibly accounting for the anomalous results of the clinical trial. This new technology has proven to yield significant insights about how different regions of gD contribute to immune responses.

An HSV-2 Trivalent Vaccine Is Immunogenic in Rhesus Macaques and Highly Efficacious in Guinea Pigs

A genital herpes vaccine is urgently needed to prevent pain and suffering, reduce the incidence of neonatal herpes, and decrease the risk of HIV acquisition and transmission that accompanies genital infection. We evaluated a trivalent HSV-2 subunit antigen vaccine administered with CpG and alum in rhesus macaques and guinea pigs. The vaccine contains glycoproteins C, D and E (gC2, gD2, gE2) to block virus entry by gD2 and immune evasion by gC2 and gE2. In rhesus macaques, the trivalent vaccine induced plasma and mucosa neutralizing antibodies, antibodies that block gC2 and gE2 immune evasion activities, and stimulated CD4 T cell responses. After intravaginal challenge, a self-limited vaginal infection of brief duration was detected by histopathology and immunohistochemistry in naïve, but not in trivalent immunized macaques. Vaccine efficacy was evaluated in female guinea pigs. Animals were mock immunized, or immunized with gD2, the trivalent vaccine or the trivalent vaccine followed by a booster dose of gD2 (trivalent + gD2). The trivalent and trivalent + gD2 groups were 97% and 99% efficacious, respectively in preventing genital lesions and both outperformed gD2 alone. As a marker of transmission risk, vaginal swabs were evaluated daily for HSV-2 DNA and replication competent virus between five and seven weeks after challenge. HSV-2 DNA shedding was reduced in all groups compared with mock. Shedding of replication competent virus occurred on fewer days in the trivalent than gD2 immunized animals while the trivalent + gD2 group had no shedding of replication competent virus. Overall, the trivalent group had genital lesions on < 1% days and shedding of replication competent virus on 0.2% days. The vaccine has outstanding potential for prevention of genital herpes in humans.

Approximately a half-billion people worldwide are infected with herpes simplex virus type 2 (HSV-2), the virus that causes genital herpes. In some individuals, infection results in painful, recurrent genital ulcers, while in others, the infection remains quiescent. In both settings, infected individuals may transmit virus to their intimate partners. Genital herpes increases the risk that an infected person will acquire HIV if exposed during sexual intercourse. A vaccine for the prevention of genital herpes is a high priority. We describe a vaccine that induces antibodies that block the ability of the virus to enter cells and that prevents the virus from escaping immune attack mediated by antibody and complement. The vaccine contains HSV-2 glycoproteins C, D and E and is immunogenic in non-human primates. The vaccine protects immunized non-human primates against a mild vaginal infection that develops in naïve animals after intravaginal inoculation of virus. Naïve guinea pigs develop severe genital disease, while immunized animals are almost 100% protected after intravaginal infection. The vaccine greatly reduces the number of days during the recurrent phase of infection that animals shed virus in genital secretions, thereby reducing the risk of transmission. We consider this novel vaccine a leading candidate for clinical trials aimed at preventing genital herpes infection in humans.

A Highly Efficacious Herpes Simplex Virus 1 Vaccine Blocks Viral Pathogenesis and Prevents Corneal Immunopathology via Humoral Immunity

Correlates of immunologic protection requisite for an efficacious herpes simplex virus 1 (HSV-1) vaccine remain unclear with respect to viral pathogenesis and clinical disease. In the present study, mice were vaccinated with a novel avirulent, live attenuated virus (0ΔNLS) or an adjuvanted glycoprotein D subunit (gD-2) similar to that used in several human clinical trials. Mice vaccinated with 0ΔNLS showed superior protection against early viral replication, neuroinvasion, latency, and mortality compared to that of gD-2-vaccinated or naive mice following ocular challenge with a neurovirulent clinical isolate of HSV-1. Moreover, 0ΔNLS-vaccinated mice exhibited protection against ocular immunopathology and maintained corneal mechanosensory function. Vaccinated mice also showed suppressed T cell activation in the draining lymph nodes following challenge. Vaccine efficacy correlated with serum neutralizing antibody titers. Humoral immunity was identified as the correlate of protection against corneal neovascularization, HSV-1 shedding, and latency through passive immunization. Overall, 0ΔNLS affords remarkable protection against HSV-1-associated ocular sequelae by impeding viral replication, dissemination, and establishment of latency.

IMPORTANCE

HSV-1 manifests in a variety of clinical presentations ranging from a rather benign "cold sore" to more severe forms of infection, including necrotizing stromal keratitis and herpes simplex encephalitis. The present study was undertaken to evaluate a novel vaccine to ocular HSV-1 infection not only for resistance to viral replication and spread but also for maintenance of the visual axis. The results underscore the necessity to reconsider strategies that utilize attenuated live virus as opposed to subunit vaccines against ocular HSV-1 infection.

Vaccination with the Secreted Glycoprotein G of Herpes Simplex Virus 2 Induces Protective Immunity after Genital Infection

Herpes simplex virus 2 (HSV-2) infects the genital mucosa and establishes a life-long infection in sensory ganglia. After primary infection HSV-2 may reactivate causing recurrent genital ulcerations. HSV-2 infection is prevalent, and globally more than 400 million individuals are infected. As clinical trials have failed to show protection against HSV-2 infection, new vaccine candidates are warranted. The secreted glycoprotein G (sgG-2) of HSV-2 was evaluated as a prophylactic vaccine in mice using two different immunization and adjuvant protocols. The protocol with three intramuscular immunizations combining sgG-2 with cytosine-phosphate-guanine dinucleotide (CpG) motifs and alum induced almost complete protection from genital and systemic disease after intra-vaginal challenge with HSV-2. Robust immunoglobulin G (IgG) antibody titers were detected with no neutralization activity. Purified splenic CD4+ T cells proliferated and produced interferon-γ (IFN-γ) when re-stimulated with the antigen in vitro. sgG-2 + adjuvant intra-muscularly immunized mice showed a significant reduction of infectious HSV-2 and increased IFN-γ levels in vaginal washes. The HSV-2 DNA copy numbers were significantly reduced in dorsal root ganglia, spinal cord, and in serum at day six or day 21 post challenge. We show that a sgG-2 based vaccine is highly effective and can be considered as a novel candidate in the development of a prophylactic vaccine against HSV-2 infection.

Higher Throughput Quantification of Neutralizing Antibody to Herpes Simplex Viruses

We report a rapid, higher throughput method for measuring neutralizing antibody to herpes simplex virus (HSV) in human sera. Clinical isolates and sera from the Herpevac Trial for Women were used in a colorimetric assay in which infection of tissue culture (lack of neutralization) was indicated by substrate metabolism by beta-galactosidase induced in the ELVIS cell line. The neutralization assay was optimized by addition of guinea pig complement, which particularly enhanced neutralizing antibody titers to HSV-2. Higher neutralizing antibody titers were also achieved using virus particles isolated from the supernatant of infected cells rather than lysate of infected cells as the source of virus. The effect of assay incubation time and incubation time with substrate were also optimized. We found that incubating with substrate until a standard optical density of 1.0 was reached permitted a better comparison among virus isolates, and achieved reliable measurement of neutralizing antibody activity. Interestingly, in contrast to results in the absence of complement, addition of complement allowed sera from HSV-2 gD-vaccinated subjects to neutralize HSV-1 and HSV-2 clinical and laboratory isolates with equal potency.

A novel HSV-2 subunit vaccine induces GLA-dependent CD4 and CD8 T cell responses and protective immunity in mice and guinea pigs

BACKGROUND/OBJECTIVES

There is currently no licensed prophylactic or therapeutic vaccine for HSV-2 infection.

METHODS

We developed a novel preclinical vaccine candidate, G103, consisting of three recombinantly expressed HSV-2 proteins (gD and the UL19 and UL25 gene products) adjuvanted with the potent synthetic TLR4 agonist glucopyranosyl lipid A (GLA) formulated in stable emulsion. The vaccine was tested for immunogenicity and efficacy in pre-clinical models for preventative and therapeutic vaccination.

RESULTS

Vaccination of mice with G103 elicited antigen-specific binding and neutralizing antibody responses, as well as robust CD4 and CD8 effector and memory T cells. The T cell responses were further boosted by subsequent challenge with live virus. Prophylactic immunization completely protected against lethal intravaginal HSV-2 infection in mice, with only transient replication of virus in the genital mucosa and sterilizing immunity in dorsal root ganglia. Supporting the use of G103 therapeutically, the vaccine expanded both CD4 and CD8 T cells induced in mice by previous infection with HSV-2. In the guinea pig model of recurrent HSV-2 infection, therapeutic immunization with G103 was approximately 50% effective in reducing the number of lesions per animal as well as the overall lesions score.

CONCLUSIONS

Taken together, the data show that G103 is a viable candidate for development of a novel prophylactic and therapeutic HSV-2 vaccine.

Patient-Specific Neutralizing Antibody Responses to Herpes Simplex Virus Are Attributed to Epitopes on gD, gB, or Both and Can Be Type Specific

Herpes simplex virus 1 (HSV-1) and HSV-2 infect many humans and establish a latent infection in sensory ganglia. Although some infected people suffer periodic recurrences, others do not. Infected people mount both cell-mediated and humoral responses, including the production of virus-neutralizing antibodies (Abs) directed at viral entry glycoproteins. Previously, we examined IgGs from 10 HSV-seropositive individuals; all neutralized virus and were directed primarily against gD or gD+gB. Here, we expand our studies and examine 32 additional sera from HSV-infected individuals, 23 of whom had no recurrent disease. Using an Octet RED96 system, we screened all 32 serum samples directly for both glycoprotein binding and competition with known neutralizing anti-gD and -gB monoclonal Abs (MAbs). On average, the recurrent cohort exhibited higher binding to gD and gB and had higher neutralization titers. There were similar trends in the blocking of MAbs to critical gD and gB epitopes. When we depleted six sera of Abs to specific glycoproteins, we found different types of responses, but always directed primarily at gD and/or gB. Interestingly, in one dual-infected person, the neutralizing response to HSV-2 was due to gD2 and gB2, whereas HSV-1 neutralization was due to gD1 and gB1. In another case, virus neutralization was HSV-1 specific, with the Ab response directed entirely at gB1, despite this serum blocking type-common anti-gD and -gB neutralizing MAbs. These data are pertinent in the design of future HSV vaccines since they demonstrate the importance of both serotypes of gD and gB as immunogens.

IMPORTANCE

We previously showed that people infected with HSV produce neutralizing Abs directed against gD or a combination of gD+gB (and in one case, gD+gB+gC, which was HSV-1 specific). In this more extensive study, we again found that gD or gD+gB can account for the virus neutralizing response and critical epitopes of one or both of these proteins are represented in sera of naturally infected humans. However, we also found that some individuals produced a strong response against gB alone. In addition, we identified type-specific contributions to HSV neutralization from both gD and gB. Contributions from the other entry glycoproteins, gC and gH/gL, were minimal and limited to HSV-1 neutralization. Knowing the variations in how humans see and mount a response to HSV will be important to vaccine development.

Herpes simplex type 2 virus deleted in glycoprotein D protects against vaginal, skin and neural disease

Subunit vaccines comprised of glycoprotein D (gD-2) failed to prevent HSV-2 highlighting need for novel strategies. To test the hypothesis that deletion of gD-2 unmasks protective antigens, we evaluated the efficacy and safety of an HSV-2 virus deleted in gD-2 and complemented allowing a single round of replication on cells expressing HSV-1 gD (ΔgD^−/+gD−1). Subcutaneous immunization of C57BL/6 or BALB/c mice with ΔgD^−/+gD1 provided 100% protection against lethal intravaginal or skin challenges and prevented latency. ΔgD^−/+gD1 elicited no disease in SCID mice, whereas 1000-fold lower doses of wild-type virus were lethal. HSV-specific antibodies were detected in serum (titer 1:800,000) following immunization and in vaginal washes after intravaginal challenge. The antibodies elicited cell-mediated cytotoxicity, but little neutralizing activity. Passive transfer of immune serum completely protected wild-type, but not Fcγ-receptor or neonatal Fc-receptor knock-out mice. These studies demonstrate that non-neutralizing Fc-mediated humoral responses confer protection and support advancement of this attenuated vaccine.

DOI:http://dx.doi.org/10.7554/eLife.06054.001

Herpes simplex virus 2 (or HSV-2) infects millions of people worldwide and is the leading cause of genital diseases. The virus initially infects skin cells, but then spreads to nerve cells where it persists for life. Often, the virus remains in a dormant state for long periods of time and does not cause any symptoms. However, HSV-2 can periodically re-activate, leading to repeated infections; this can be life-threatening in patients who suffer from a weak immune system. There is no cure for Herpes simplex virus infection, and there are currently no vaccines that would prevent the virus from infecting humans.

HSV-2 contains a protein on its surface known as ‘glycoprotein D’ which it needs to enter host cells. The interaction between glycoprotein D and the host is also essential for cell-to-cell spread of the virus. Vaccines that contain glycoprotein D trigger the production of antibodies that bind to this viral protein. These vaccines have been tested in several large clinical trials, but the results have so far been disappointing. As such, new vaccines that provide effective protection against HSV-2 are urgently needed.

Live attenuated vaccines are commonly used to prevent diseases such as measles mumps and chicken pox or shingles. These vaccines contain a harmless or weakened version of the disease-causing virus. Petro, González et al. have now developed a new potential vaccine that contains live attenuated HSV-2, which completely lacks glycoprotein D and thus cannot spread from cell-to-cell. When this weakened virus was administered to mice that have a poor immune system, the mice remained healthy. On the other hand, when Petro, González et al. treated similar mice with the wild-type HSV-2 virus instead, many mice died within a few days.

Petro, González et al. then went on to show that mice that had been treated with the weakened virus as a vaccine were completely protected from a later infection with wild-type HSV-2 and did not develop any symptoms of the disease. Furthermore, no virus was detected in the nerve cells of these mice—which is where the virus would normally persist in its dormant state. Finally, Petro, González et al. showed that blood serum from immunized mice could be used to completely protect other mice from exposure to wild-type virus. These results demonstrate that a live attenuated HSV-2 virus that lacks glycoprotein D (the main component of other failed vaccines) elicits a different type of immune response and is a safe and effective vaccine in mouse models of virus infection. With further work, these findings may eventually lead to a preventative treatment to combat HSV-2 infections in humans.

DOI:http://dx.doi.org/10.7554/eLife.06054.002

Antiviral activity of a single-domain antibody immunotoxin binding to glycoprotein D of herpes simplex virus 2

Despite years of research dedicated to preventing the sexual transmission of herpes simplex virus 2 (HSV-2), there is still no protective vaccine or microbicide against one of the most common sexually transmitted infections in the world. Using a phage display library constructed from a llama immunized with recombinant HSV-2 glycoprotein D, we identified a single-domain antibody VHH, R33, which binds to the viral surface glycoprotein D. Although R33 does not demonstrate any HSV-2 neutralization activity in vitro, when expressed with the cytotoxic domain of exotoxin A, the resulting immunotoxin (R33ExoA) specifically and potently kills HSV-2-infected cells, with a 50% neutralizing dilution (IC50) of 6.7 nM. We propose that R33ExoA could be used clinically to prevent transmission of HSV-2 through killing of virus-producing epithelial cells during virus reactivation. R33 could also potentially be used to deliver other cytotoxic effectors to HSV-2-infected cells.

Anti-glycoprotein g antibodies of herpes simplex virus 2 contribute to complete protection after vaccination in mice and induce antibody-dependent cellular cytotoxicity and complement-mediated cytolysis

We investigated the role of antibodies against the mature portion of glycoprotein G (mgG-2) of herpes simplex virus 2 (HSV-2) in protective immunity after vaccination. Mice were immunized intramuscularly with mgG-2 and oligodeoxynucleotides containing two CpG motifs plus alum as adjuvant. All C57BL/6 mice survived and presented no genital or systemic disease. High levels of immunoglobulin G subclass 1 (IgG1) and IgG2 antibodies were detected and re-stimulated splenic CD4+ T cells proliferated and produced IFN-γ. None of the sera from immunized mice exhibited neutralization, while all sera exerted antibody-dependent cellular cytotoxicity (ADCC) and complement-mediated cytolysis (ACMC) activity. Passive transfer of anti-mgG-2 monoclonal antibodies, or immune serum, to naive C57BL/6 mice did not limit disease progression. Immunized B‑cell KO mice presented lower survival rate and higher vaginal viral titers, as compared with vaccinated B-cell KO mice after passive transfer of immune serum and vaccinated C57BL/6 mice. Sera from mice that were vaccinated subcutaneously and intranasally with mgG-2 presented significantly lower titers of IgG antibodies and lower ADCC and ACMC activity. We conclude that anti-mgG-2 antibodies were of importance to limit genital HSV‑2 infection. ADCC and ACMC activity are potentially important mechanisms in protective immunity, and could tentatively be evaluated in future animal vaccine studies and in clinical trials.

Topical herpes simplex virus 2 (HSV-2) vaccination with human papillomavirus vectors expressing gB/gD ectodomains induces genital-tissue-resident memory CD8+ T cells and reduces genital disease and viral shedding after HSV-2 challenge

No herpes simplex virus 2 (HSV-2) vaccine has been licensed for use in humans. HSV-2 glycoproteins B (gB) and D (gD) are targets of neutralizing antibodies and T cells, but clinical trials involving intramuscular (i.m.) injection of HSV-2 gB and gD in adjuvants have not been effective. Here we evaluated intravaginal (ivag) genetic immunization of C57BL/6 mice with a replication-defective human papillomavirus pseudovirus (HPV PsV) expressing HSV-2 gB (HPV-gB) or gD (HPV-gD) constructs to target different subcellular compartments. HPV PsV expressing a secreted ectodomain of gB (gBsec) or gD (gDsec), but not PsV expressing a cytoplasmic or membrane-bound form, induced circulating and intravaginal-tissue-resident memory CD8(+) T cells that were able to secrete gamma interferon (IFN-γ) and tumor necrosis factor alpha (TNF-α) as well as moderate levels of serum HSV neutralizing antibodies. Combined immunization with HPV-gBsec and HPV-gDsec (HPV-gBsec/gDsec) vaccines conferred longer survival after vaginal challenge with HSV-2 than immunization with HPV-gBsec or HPV-gDsec alone. HPV-gBsec/gDsec ivag vaccination was associated with a reduced severity of genital lesions and lower levels of viral shedding in the genital tract after HSV-2 challenge. In contrast, intramuscular vaccination with a soluble truncated gD protein (gD2t) in alum and monophosphoryl lipid A (MPL) elicited high neutralizing antibody titers and improved survival but did not reduce genital lesions and viral shedding. Vaccination combining ivag HPV-gBsec/gDsec and i.m. gD2t-alum-MPL improved survival and reduced genital lesions and viral shedding. Finally, high levels of circulating HSV-2-specific CD8(+) T cells, but not serum antibodies, correlated with reduced viral shedding. Taken together, our data underscore the potential of HPV PsV as a platform for a topical mucosal vaccine to control local manifestations of primary HSV-2 infection.

IMPORTANCE

Genital herpes is a highly prevalent chronic disease caused by HSV infection. To date, there is no licensed vaccine against HSV infection. This study describes intravaginal vaccination with a nonreplicating HPV-based vector expressing HSV glycoprotein antigens. The data presented in this study underscore the potential of HPV-based vectors as a platform for the induction of genital-tissue-resident memory T cell responses and the control of local manifestations of primary HSV infection.

Improving immunogenicity and efficacy of vaccines for genital herpes containing herpes simplex virus glycoprotein D

No vaccines are approved for prevention or treatment of genital herpes. The focus of genital herpes vaccine trials has been on prevention using herpes simplex virus type 2 (HSV-2) glycoprotein D (gD2) alone or combined with glycoprotein B. These prevention trials did not achieve their primary end points. However, subset analyses reported some positive outcomes in each study. The most recent trial was the Herpevac Trial for Women that used gD2 with monophosphoryl lipid A and alum as adjuvants in herpes simplex virus type 1 (HSV-1) and HSV-2 seronegative women. Unexpectedly, the vaccine prevented genital disease by HSV-1 but not HSV-2. Currently, HSV-1 causes more first episodes of genital herpes than HSV-2, highlighting the importance of protecting against HSV-1. The scientific community is conflicted between abandoning vaccine efforts that include gD2 and building upon the partial successes of previous trials. We favor building upon success and present approaches to improve outcomes of gD2-based subunit antigen vaccines.

Blocking herpes simplex virus 2 glycoprotein E immune evasion as an approach to enhance efficacy of a trivalent subunit antigen vaccine for genital herpes

Herpes simplex virus 2 (HSV-2) subunit antigen vaccines targeting virus entry molecules have failed to prevent genital herpes in human trials. Our approach is to include a virus entry molecule and add antigens that block HSV-2 immune evasion. HSV-2 glycoprotein C (gC2) is an immune evasion molecule that inhibits complement. We previously reported that adding gC2 to gD2 improved vaccine efficacy compared to the efficacy of either antigen alone in mice and guinea pigs. Here we demonstrate that HSV-2 glycoprotein E (gE2) functions as an immune evasion molecule by binding the IgG Fc domain. HSV-2 gE2 is synergistic with gC2 in protecting the virus from antibody and complement neutralization. Antibodies produced by immunization with gE2 blocked gE2-mediated IgG Fc binding and cell-to-cell spread. Mice immunized with gE2 were only partially protected against HSV-2 vaginal challenge in mice; however, when gE2 was added to gC2/gD2 to form a trivalent vaccine, neutralizing antibody titers with and without complement were significantly higher than those produced by gD2 alone. Importantly, the trivalent vaccine protected the dorsal root ganglia (DRG) of 32/33 (97%) mice between days 2 and 7 postchallenge, compared with 27/33 (82%) in the gD2 group. The HSV-2 DNA copy number was significantly lower in mice immunized with the trivalent vaccine than in those immunized with gD2 alone. The extent of DRG protection using the trivalent vaccine was better than what we previously reported for gC2/gD2 immunization. Therefore, gE2 is a candidate antigen for inclusion in a multivalent subunit vaccine that attempts to block HSV-2 immune evasion.

IMPORTANCE

Herpes simplex virus is the most common cause of genital ulcer disease worldwide. Infection results in emotional distress for infected individuals and their partners, is life threatening for infants exposed to herpes during childbirth, and greatly increases the risk of individuals acquiring and transmitting HIV infection. A vaccine that prevents genital herpes infection will have major public health benefits. Our vaccine approach includes strategies to prevent the virus from evading immune attack. Mice were immunized with a trivalent vaccine containing an antigen that induces antibodies to block virus entry and two antigens that induce antibodies that block immune evasion from antibody and complement. Immunized mice demonstrated no genital disease, and 32/33 (97%) animals had no evidence of infection of dorsal root ganglia, suggesting that the vaccine may prevent the establishment of latency and recurrent infections.