Efficacy results of a trial of a herpes simplex vaccine

Sexually transmitted infections and female reproductive health

Women are disproportionately affected by sexually transmitted infections (STIs) throughout life. In addition to their high prevalence in women, STIs have debilitating effects on female reproductive health due to female urogenital anatomy, socio-cultural and economic factors. In this Review, we discuss the prevalence and impact of non-HIV bacterial, viral and parasitic STIs on the reproductive and sexual health of cisgender women worldwide. We analyse factors affecting STI prevalence among transgender women and women in low-income settings, and describe the specific challenges and barriers to improved sexual health faced by these population groups. We also synthesize the latest advances in diagnosis, treatment and prevention of STIs.

Women are more affected by sexually transmitted infections than men. This Review examines the impact of non-HIV STIs on women’s health, and discusses recent advances and current challenges in the treatment and prevention of STIs.

Combinatorial Herpes Simplex Vaccine Strategies: From Bedside to Bench and Back

The development of vaccines against herpes simplex virus type 1 and type 2 (HSV1 and HSV-2) is an important goal for global health. In this review we reexamined (i) the status of ocular herpes vaccines in clinical trials; and (ii) discusses the recent scientific advances in the understanding of differential immune response between HSV infected asymptomatic and symptomatic individuals that form the basis for the new combinatorial vaccine strategies targeting HSV; and (iii) shed light on our novel "asymptomatic" herpes approach based on protective immune mechanisms in seropositive asymptomatic individuals who are "naturally" protected from recurrent herpetic diseases. We previously reported that phenotypically and functionally distinct HSV-specific memory CD8+ T cell subsets in asymptomatic and symptomatic HSV-infected individuals. Moreover, a better protection induced following a prime/pull vaccine approach that consists of first priming anti-viral effector memory T cells systemically and then pulling them to the sites of virus reactivation (e.g., sensory ganglia) and replication (e.g., eyes and vaginal mucosa), following mucosal administration of vectors expressing T cell-attracting chemokines. In addition, we reported that a combination of prime/pull vaccine approach with approaches to reverse T cell exhaustion led to even better protection against herpes infection and disease. Blocking PD-1, LAG-3, TIGIT and/or TIM-3 immune checkpoint pathways helped in restoring the function of antiviral HSV-specific CD8+ T cells in latently infected ganglia and increased efficacy and longevity of the prime/pull herpes vaccine. We discussed that a prime/pull vaccine strategy that use of asymptomatic epitopes, combined with immune checkpoint blockade would prove to be a successful herpes vaccine approach.

Efficacy of an HSV-1 Neuro-Attenuated Vaccine in Mice Is Reduced by Preventing Viral DNA Replication

We previously isolated an HSV-1 mutant, KOS-NA, that contains two non-synonymous mutations in UL39. One of the mutations, resulting in an R950H amino acid substitution in ICP6, renders KOS-NA severely neuro-attenuated and significantly reduces HSV-1 latency. Vaccination of mice with KOS-NA prior to corneal challenge provides significant protection against HSV-1-mediated eye diseases even at a very low immunizing dose, indicating its utility as a vaccine scaffold. Because KOS-NA contains a neuro-attenuating mutation in a single gene, we sought to improve its safety by deleting a portion of the UL29 gene whose protein product, ICP8, is essential for viral DNA replication. Whereas KOS-NA reduced replication of HSV-1 challenge virus in the corneal epithelium and protected mice against blepharitis and keratitis induced by the challenge virus, KOS-NA/8- and an ICP8- virus were significantly less efficacious except at higher doses. Our results suggest that the capacity to replicate, even at significantly reduced levels compared with wild-type HSV-1, may be an important feature of an effective vaccine. Means to improve safety of attenuated viruses as vaccines without compromising efficacy should be sought.

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.

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

Antigen-specific TRM 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+ TRM persisting at sites of healed human HSV-2 lesions have an activated phenotype but it is unclear if TRM can be cultivated in vitro. We recovered HSV-specific TRM 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 TRM 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 TRM 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 TRM 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.

A potent neutralizing and protective antibody against a conserved continuous epitope on HSV glycoprotein D

Infections caused by herpes simplex virus type 1 (HSV-1) and type 2 (HSV-2) remain a serious global health issue, and the medical countermeasures available thus far are limited. Virus-neutralizing monoclonal antibodies (NAbs) are crucial tools for studying host-virus interactions and designing effective vaccines, and the discovery and development of these NAbs could be one approach to treat or prevent HSV infection. Here, we report the isolation of five HSV NAbs from mice immunized with both HSV-1 and HSV-2. Among these were two antibodies that potently cross-neutralized both HSV-1 and HSV-2 with the 50% virus-inhibitory concentrations (IC₅₀) below 200 ng/ml, one of which (4A3) exhibited high potency against HSV-2, with an IC₅₀ of 59.88 ng/ml. 4A3 neutralized HSV at the prebinding stage and prevented HSV infection and cell-to-cell spread. Significantly, administration of 4A3 completely prevented weight loss and improved survival of mice challenged with a lethal dose of HSV-2. Using structure-guided molecular modeling combined with alanine-scanning mutagenesis, we observed that 4A3 bound to a highly conserved continuous epitope (residues 216 to 220) within the receptor-binding domain of glycoprotein D (gD) that is essential for viral infection and the triggering of membrane fusion. Our results provide guidance for developing NAb drugs and vaccines against HSV.

40 Years after the Registration of Acyclovir: Do We Need New Anti-Herpetic Drugs?

Herpes simplex virus types 1 and 2 HSV1 and 2, namely varicella-zoster VZV and cytomegalovirus CMV, are among the most common pathogens worldwide. They remain in the host body for life. The course of infection with these viruses is often asymptomatic or mild and self-limiting, but in immunocompromised patients, such as solid organ or bone marrow transplant recipients, the course can be very severe or even life-threatening. Unfortunately, in the latter group, the highest percentage of infections with strains resistant to routinely used drugs is observed. On the other hand, frequent recurrences of genital herpes can be a problem even in people with normal immunity. Genital herpes also increases the risk of acquiring sexually transmitted diseases, including HIV infection and, if present in pregnant women, poses a risk to the fetus and newborn. Even more frequently than herpes simplex, congenital infections can be caused by cytomegalovirus. We present the most important anti-herpesviral agents, the mechanisms of resistance to these drugs, and the associated mutations in the viral genome. Special emphasis was placed on newly introduced drugs such as maribavir and brincidofovir. We also briefly discuss the most promising substances in preclinical testing as well as immunotherapy options and vaccines currently in use and under investigation.

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.

Evaluation of HSV-2 gE Binding to IgG-Fc and Application for Vaccine Development

Glycoprotein E (gE) and glycoprotein I (gI) are expressed as a heterodimer on the surface of Herpes simplex virus (HSV). Glycoprotein E binds Fc domain of immunoglobulin G (IgG) and inhibits activities mediated by the IgG Fc domain, contributing to immune evasion by HSV. It has been reported that HSV type 1 gE (gE-1) is capable of binding IgG Fc as a monomer and in a heterodimeric complex with gI, with the heterodimer having 50- to100-fold greater affinity for Fc than gE alone. We report the production of both a soluble form of HSV type 2 gE (gE-2) and a soluble HSV-2 gE/gI heterodimer (gE-2/gI-2). Characterization of soluble gE-2 by surface plasmon resonance (SPR) demonstrates that it is incapable of binding human IgG or the IgG Fc domain. Co-expression with HSV-2 gI (gI-2) and purification of the gE-2/gI-2 heterodimer enable gE-2 to bind human IgG through its Fc domain. We hypothesize that functional epitopes of wildtype gE-2 may be masked by plasma IgG Fc and affect the immunogenicity of the gE-2/gI-2 heterodimer as a vaccine antigen. A series of gE-2 mutations within the surface-exposed Fc:gE-2 interface was designed, and gE-2 mutants were co-expressed with gI-2. Evaluation of twelve gE-2 mutant heterodimers by SPR assay identified nine gE-2 mutations which abrogated or reduced Fc binding while maintaining heterodimer formation with gI. Vaccinating rabbits with the four most Fc-binding deficient gE-2/gI-2 heterodimers elicited comparable anti-heterodimer binding antibody titers and statistically significantly higher serum neutralization antibody levels than wildtype heterodimers. Taken together, these data support the concept of rational antigen design for improved vaccine candidates.

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.

Trivalent nucleoside-modified mRNA vaccine yields durable memory B cell protection against genital herpes in preclinical models

Nucleoside-modified mRNA vaccines have gained global attention because of COVID-19. We evaluated a similar vaccine approach for preventing a chronic, latent genital infection rather than an acute respiratory infection. We used animal models to compare an HSV-2 trivalent nucleoside-modified mRNA vaccine with the same antigens prepared as proteins, with an emphasis on antigen-specific memory B cell responses and immune correlates of protection. In guinea pigs, serum neutralizing-antibody titers were higher at 1 month and declined far less by 8 months in mRNA- compared with protein-immunized animals. Both vaccines protected against death and genital lesions when infected 1 month after immunization; however, protection was more durable in the mRNA group compared with the protein group when infected after 8 months, an interval representing greater than 15% of the animal's lifespan. Serum and vaginal neutralizing-antibody titers correlated with protection against infection, as measured by genital lesions and vaginal virus titers 2 days after infection. In mice, the mRNA vaccine generated more antigen-specific memory B cells than the protein vaccine at early times after immunization that persisted for up to 1 year. High neutralizing titers and robust B cell immune memory likely explain the more durable protection by the HSV-2 mRNA vaccine.

A Live Olfactory Mouse Cytomegalovirus Vaccine, Attenuated for Systemic Spread, Protects against Superinfection

Vaccination against the betaherpesvirus, human cytomegalovirus (HCMV) is a public health goal. However, HCMV has proved difficult to vaccinate against. Vaccination against single HCMV determinants has not worked, suggesting that immunity to a wider antigenic profile may be required. Live attenuated vaccines provide the best prospects for protection, but the question remains as to how to balance vaccine virulence with safety. Animal models of HCMV infection provide insights into identifying targets for virus attenuation and understanding how host immunity blocks natural, mucosal infection. Here, we evaluated the vaccine potential of a mouse cytomegalovirus (MCMV) vaccine deleted of a viral G protein-coupled receptor (GPCR), designated M33, that renders it attenuated for systemic spread. A single noninvasive olfactory ΔM33 MCMV vaccine replicated locally, but as a result of the loss of the M33 GPCR, it failed to spread systemically and was attenuated for latent infection. Vaccination did not prevent host entry of a superinfecting MCMV but spread from the mucosa was blocked. This approach to vaccine design may provide a viable alternative for a safe and effective betaherpesvirus vaccine. IMPORTANCE Human cytomegalovirus (HCMV) is the most common cause of congenital infection for which a vaccine is not yet available. Subunit vaccine candidates have failed to achieve licensure. A live HCMV vaccine may prove more efficacious, but it faces safety hurdles which include its propensity to persist and to establish latency. Understanding how pathogens infect guide rational vaccine design. However, HCMV infections are asymptomatic and thus difficult to capture. Animal models of experimental infection provide insight. Here, we investigated the vaccine potential of a mouse cytomegalovirus (MCMV) attenuated for systemic spread and latency. We used olfactory vaccination and virus challenge to mimic its natural acquisition. We provide proof of concept that a single olfactory MCMV that is deficient in systemic spread can protect against wild-type MCMV superinfection and dissemination. This approach of deleting functional counterpart genes in HCMV may provide safe and effective vaccination against congenital HCMV disease.

Eczema herpeticum in atopic dermatitis

Atopic dermatitis (AD) is one of the most common chronic inflammatory skin diseases leading to pruritic skin lesions. A subset of AD patients exhibits a disseminated severe HSV infection called eczema herpeticum (EH) that can cause life-threatening complications. This review gives an overview of the clinical picture, and characteristics of the patients as well as the diagnosis and therapy of EH. A special focus lies on the pathophysiological hallmarks identified so far that predispose for EH. This aspect covers genetic aberrations, immunological changes, and environmental influences displaying a complex multifactorial situation, which is not completely understood. Type 2 skewing of virus-specific T cells in ADEH⁺ patients has been implicated in immune profile abnormalities, along with impaired functions of dendritic cells and natural killer cells. Furthermore, aberrations in interferon pathway-related genes such as IFNG and IFNGR1 have been identified to increase the risk of EH. IL-4, IL-25, and thymic stromal lymphopoietin (TSLP) are overexpressed in EH, whereas antimicrobial peptides like human β-defensins and LL-37 are reduced. Concerning the epidermal barrier, single nucleotide polymorphisms (SNPs) in skin barrier proteins such as filaggrin were identified in ADEH⁺ patients. A dysbalance of the skin microbiome also contributes to EH due to an increase of Staphylococcus aureus, which provides a supporting role to the viral infection via secreted toxins such as α-toxin. The risk of EH is reduced in AD patients treated with dupilumab. Further research is needed to identify and specifically target risk factors for EH in AD patients.

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.

Development of a microneutralization assay for HSV-2

BACKGROUND

Plaque Reduction Neutralization Test (PRNT) is the standard assay used for measuring neutralizing antibody responses to Herpes simplex virus type-2 (HSV-2). The PRNT is a cumbersome, time-consuming and laborious assay. The development of a faster, high throughput microneutralization assay (MNA) for HSV-2 viruses carried out in a 96-well format will allow for rapid testing of large numbers of samples for drug and vaccine development.

METHODS

We describe the generation of a MNA that utilizes a pair of anti-HSV human monoclonal antibodies (mAbs) for virus detection in HSV-2 infected Vero cells. Antibodies were generated by B-cell cloning from PBMC's isolated from HSV-1 negative/HSV-2 positive donors. We describe the selection and characterization of the antibodies used for virus detection by ELISA with purified, recombinant anti-HSV glycoproteins, antibody binding in infected cells, and Western Blot. We determine the anti-HSV-2 neutralizing titers of immune sera from mice by MNA and PRNT and compare these results by linear regression analysis.

RESULTS

We show that neutralization titers for HSV-2, determined by the 96-well MNA correlate with titers determined by a PRNT completed in 24-well plates in both the absence (R² = 0.8250) and presence (R² = 0.7075) of complement.

CONCLUSIONS

We have successfully developed an MNA that can be used in place of the burdensome PRNT to determine anti-HSV-2 neutralizing activity in serum. This MNA has much greater throughput than the PRNT, allowing many more samples to be processed in a shorter time saving ∼90 % of the time required by the laboratory scientist to complete the task as compared to the traditional PRNT.

Immunoregulatory Functions of Interferons During Genital HSV-2 Infection

Herpes simplex virus type 2 (HSV-2) infection is one of the most prevalent sexually transmitted infections that disproportionately impacts women worldwide. Currently, there are no vaccines or curative treatments, resulting in life-long infection. The mucosal environment of the female reproductive tract (FRT) is home to a complex array of local immune defenses that must be carefully coordinated to protect against genital HSV-2 infection, while preventing excessive inflammation to prevent disease symptoms. Crucial to the defense against HSV-2 infection in the FRT are three classes of highly related and integrated cytokines, type I, II, and III interferons (IFN). These three classes of cytokines control HSV-2 infection and reduce tissue damage through a combination of directly inhibiting viral replication, as well as regulating the function of resident immune cells. In this review, we will examine how interferons are induced and their critical role in how they shape the local immune response to HSV-2 infection in the FRT.

Antibodies Elicited in Response to a Single Cycle Glycoprotein D Deletion Viral Vaccine Candidate Bind C1q and Activate Complement Mediated Neutralization and Cytolysis

Herpes simplex virus (HSV) prevention is a global health priority but, despite decades of research, there is no effective vaccine. Prior efforts focused on generating glycoprotein D (gD) neutralizing antibodies, but clinical trial outcomes were disappointing. The deletion of gD yields a single-cycle candidate vaccine (∆gD-2) that elicits high titer polyantigenic non-gD antibodies that exhibit little complement-independent neutralization but mediate antibody-dependent cellular cytotoxicity (ADCC) and phagocytosis (ADCP). Active or passive immunization with DgD-2 completely protects mice from lethal disease and latency following challenge with clinical isolates of either serotype. The current studies evaluated the role of complement in vaccine-elicited protection. The immune serum from the DgD-2 vaccinated mice exhibited significantly greater C1q binding compared to the serum from the gD protein vaccinated mice with infected cell lysates from either serotype as capture antigens. The C1q-binding antibodies recognized glycoprotein B. This resulted in significantly greater antibody-mediated complement-dependent cytolysis and neutralization. Notably, complete protection was preserved when the DgD-2 immune serum was passively transferred into C1q knockout mice, suggesting that ADCC and ADCP are sufficient in mice. We speculate that the polyfunctional responses elicited by DgD-2 may prove more effective in preventing HSV, compared to the more restrictive responses elicited by adjuvanted gD protein vaccines.

Immunological Identification and Characterization of the Capsid Scaffold Protein Encoded by UL26.5 of Herpes Simplex Virus Type 2

Herpes simplex virus type 2 (HSV2), a pathogen that causes genital herpes lesions, interferes with the host immune system via various known and unknown mechanisms. This virus has been used to study viral antigenic composition. Convalescent serum from HSV2-infected patients was used to identify viral antigens via 2-D protein electrophoresis and immunoblotting. The serum predominantly recognized several capsid scaffold proteins encoded by gene UL26.5, mainly ICP35. This protein has been primarily reported to function temporarily in viral assembly but is not expressed in mature virus particles. Further immunological studies suggested that this protein elicits specific antibody and cytotoxic T lymphocyte (CTL) responses in mice, but these responses do not result in a clinical protective effect in response to HSV2 challenge. The data suggested that immunodominance of ICP35 might be used to design an integrated antigen with other viral glycoproteins.

B cells join T cell clusters in the host response to recurrent herpes simplex virus 2 infection

Recurrent genital herpes lesions are infiltrated by various leukocytes, yet the role of B cell subsets in this process is unknown. In this issue of the JCI, Ford et al. describe the presence and antibody-secreting role of local B cell populations in herpes simplex virus 2 (HSV-2) recurrent lesions. The authors analyzed a comprehensive array of sequential skin biopsy specimens from HSV-2-infected patients over time and at various stages of infection. Using immunofluorescence and in situ hybridization, the authors show the presence of rare IgD+ naive B cells and IgG-expressing antibody-secreting cells (ASCs) in recurrent HSV-2 lesions embedded in CD4+ T cell-rich dermal immune infiltrates, levels of which transiently increase during lesion reactivation and healing. Notably, local increases in HSV-2-specific antibodies in recurrent lesions were detected, whereas serum HSV-2 antibody levels remained stable. Future research is needed to understand the precise role of these tissue-visiting B cells in disease resolution.

CCL19 and CCL28 Assist Herpes Simplex Virus 2 Glycoprotein D To Induce Protective Systemic Immunity against Genital Viral Challenge

An effective HSV-2 vaccine should induce antigen (Ag)-specific immune responses against viral mucosal infection. This study reveals that chemokine CCL19 or CCL28 enhanced HSV-2 glycoprotein D ectodomain (gD-306aa)-induced immune responses against vaginal virus challenge.

Potent systemic immunity is important for recalled mucosal immune responses, but in the defense against mucosal viral infections, it usually remains low at mucosal sites. Based on our previous findings that enhanced immune responses can be achieved by immunization with an immunogen in combination with a molecular adjuvant, here we designed chemokine-antigen (Ag) fusion constructs (CCL19- or CCL28-herpes simplex virus 2 glycoprotein D [HSV-2 gD]). After intramuscular (i.m.) immunization with different DNA vaccines in a prime and boost strategy, BALB/c mice were challenged with a lethal dose of HSV-2 through the genital tract. Ag-specific immune responses and chemokine receptor-specific lymphocytes were analyzed to determine the effects of CCL19 and CCL28 in strengthening humoral and cellular immunity. Both CCL19 and CCL28 were efficient in inducing long-lasting HSV-2 gD-specific systemic immunity. Compared to CCL19, less CCL28 was required to elicit HSV-2 gD-specific serum IgA responses, Th1- and Th2-like responses of immunoglobulin (Ig) subclasses and cytokines, and CCR3⁺ T cell enrichment (>8.5-fold) in spleens. These findings together demonstrate that CCL28 tends to assist an immunogen to induce more potently protective immunity than CCL19. This work provides information for the application potential of a promising vaccination strategy against mucosal infections caused by HSV-2 and other sexually transmitted viruses.

IMPORTANCE An effective HSV-2 vaccine should induce antigen (Ag)-specific immune responses against viral mucosal infection. This study reveals that chemokine CCL19 or CCL28 enhanced HSV-2 glycoprotein D ectodomain (gD-306aa)-induced immune responses against vaginal virus challenge. In addition to eliciting robust humoral immune responses, the chemokine-Ag fusion construct also induced Th1- and Th2-like immune responses characterized by the secretion of multiple Ig subclasses and cytokines that were able to be recalled after HSV-2 challenge, while CCL28 appeared to be more effective than CCL19 in promoting gD-elicited immune responses as well as the migration of T cells to secondary lymph tissues. Of importance, both CCL19 and CCL28 significantly facilitated gD to induce protective mucosal immune responses in the genital tract. The above-described findings together highlight the potential of CCL19 or CCL28 in combination with gD as a vaccination strategy to control HSV-2 infection.

Assessment of Two Novel Live-Attenuated Vaccine Candidates for Herpes Simplex Virus 2 (HSV-2) in Guinea Pigs

Treatment to ameliorate the symptoms of infection with herpes simplex virus 2 (HSV-2) and to suppress reactivation has been available for decades. However, a safe and effective preventative or therapeutic vaccine has eluded development. Two novel live-attenuated HSV-2 vaccine candidates (RVx201 and RVx202) have been tested preclinically for safety. Hartley guinea pigs were inoculated vaginally (n = 3) or intradermally (n = 16) with either vaccine candidate (2 × 10⁷ PFU) and observed for disease for 28 days. All animals survived to study end without developing HSV-2-associated disease. Neither vaccine candidate established latency in dorsal root or sacral sympathetic ganglia, as determined by viral DNA quantification, LAT expression, or explant reactivation. Infectious virus was shed in vaginal secretions for three days following vaginal inoculation with RVx202, but not RVx201, although active or latent HSV-2 was not detected at study end. In contrast, guinea pigs inoculated with wild-type HSV-2 MS (2 × 10⁵ PFU) vaginally (n = 5) or intradermally (n = 16) developed acute disease, neurological signs, shed virus in vaginal secretions, experienced periodic recurrences throughout the study period, and had latent HSV-2 in their dorsal root and sacral sympathetic ganglia at study end. Both vaccine candidates generated neutralizing antibody. Taken together, these findings suggest that these novel vaccine candidates are safe in guinea pigs and should be tested for efficacy as preventative and/or therapeutic anti-HSV-2 vaccines.

20 years since the Herpetic Eye Disease Study: Lessons, developments and applications to clinical practice

Herpes Simplex Virus (HSV) is the most common virus that causes eye disease. Although around 60% of the world's population are seropositive for HSV antigens, fortunately, it is estimated that only 1% of seropositive individuals develop eye disease. The most common ocular manifestation of HSV is keratitis, while uveitis and retinal necrosis occur in a small number of cases. HSV keratitis is a debilitating disease, for several reasons: pain , photophobia, and vision loss in acute disease, latency of the virus which leads to infection reactivation from various triggers, scarring, and neovascularisation, leading to permanent vision loss with poor visual rehabilitation prospects. The Herpetic Eye Disease Study (HEDS) was a landmark series of randomised controlled trials in the 1990s that set the benchmark for evidence-based treatment guidelines for anterior eye herpetic disease. Since this time, there has been a change in the distribution of seroprevalence of herpes in the community, a simplified diagnostic classification, advances in treatment options, an emergence of new and a better understanding of risk factors, and discoveries in science that show promise for vaccine and novel future treatments. However, many of the principles of the HEDS study remain rightly entrenched in clinical practice. In this article, the HEDS study is revisited 20 years on through the lens of published literature, to determine current best practise and look towards the future.

Dissociation of DNA damage sensing by endoglycosidase HPSE

Balance between cell proliferation and elimination is critical in handling threats both exogenous and of internal dysfunction. Recent work has implicated a conserved but poorly understood endoglycosidase heparanase (HPSE) in the restriction of innate defense responses, yet biochemical mediators of these key functions remained unclear. Here, an unbiased immunopurification proteomics strategy is employed to identify and rank uncharacterized interactions between HPSE and mediators of canonical signaling pathways linking cell cycle and stress responses. We demonstrate with models of genotoxic stress including herpes simplex virus infection and chemotherapeutic treatment that HPSE dampens innate responses to double-stranded DNA breakage by interfering with signal transduction between initial sensors and downstream mediators. Given the long-standing recognition of HPSE in driving late-stage inflammatory disease exemplified by tissue destruction and cancer metastasis, modulation of this protein with control over the DNA damage response imparts a unique strategy in the development of unconventional multivalent therapy.

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HPSE binds key proteins at interface of DNA damage signaling and IFN responses

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Nuclear translocation of DNA damage transducer ATM is enhanced in absence of HPSE

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Cells lacking HPSE display enhanced sensitivity to DNA damage-induced death

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HPSE interfaces with regulators of DNA damage response to influence cell fate

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.

On the irrationality of rational design of an HIV vaccine in light of protein intrinsic disorder

The lack of progress in finding an efficient vaccine for a human immunodeficiency virus (HIV) is daunting. In fact, this search has spanned nearly four decades without much success. There are several objective reasons for such a failure, which include the highly glycosylated nature of HIV-1, the presence of neotopes, and high mutation rates. This article argues that the presence of highly flexible and intrinsically disordered regions in both human anti-HIV-1 antibodies and the major HIV-1immunogen, its surface glycoprotein gp120, represent one of the major causes for the lack of success in utilization of structure-based reverse vaccinology.

Herpes Simplex Virus Cell Entry Mechanisms: An Update

Herpes simplex virus (HSV) can infect a broad host range and cause mild to life threating infections in humans. The surface glycoproteins of HSV are evolutionarily conserved and show an extraordinary ability to bind more than one receptor on the host cell surface. Following attachment, the virus fuses its lipid envelope with the host cell membrane and releases its nucleocapsid along with tegument proteins into the cytosol. With the help of tegument proteins and host cell factors, the nucleocapsid is then docked into the nuclear pore. The viral double stranded DNA is then released into the host cell’s nucleus. Released viral DNA either replicates rapidly (more commonly in non-neuronal cells) or stays latent inside the nucleus (in sensory neurons). The fusion of the viral envelope with host cell membrane is a key step. Blocking this step can prevent entry of HSV into the host cell and the subsequent interactions that ultimately lead to production of viral progeny and cell death or latency. In this review, we have discussed viral entry mechanisms including the pH-independent as well as pH-dependent endocytic entry, cell to cell spread of HSV and use of viral glycoproteins as an antiviral target.

Shell disorder and the HIV vaccine mystery: lessons from the legendary Oswald Avery

The search for a human immunodeficiency virus (HIV) vaccine has spanned nearly four decades without much success. A much needed paradigm shift can be found in the abnormally high levels of intrinsic disorder in the outer shells of HIVs, the hepatitis C virus (HCV), and herpes simplex viruses (HSVs), for which successful vaccines have not been established. On the other hand, this feature (high levels of intrinsic disorder in the outer shells) is completely absent in classic viruses for which effective vaccines are found, such as the rabies virus. The motions arising from the disordered outer shell result in the inability of antibodies to bind tightly to the polysaccharides on the viral surface proteins, and, therefore, induce inadequate immune response. Experiments conducted by the legendary Avery Oswald in the 1920s form the theoretical underpinning of this new model. Failures of the vaccines based on the HIV glycoprotein Gp120 and other vaccines can be traced back to the lack of understanding of the important roles of shell disorder in a "Trojan-horse" immune evasion mechanism utilized by the virus.Communicated by Ramaswamy H. Sarma.

Vaccines for Perinatal and Congenital Infections-How Close Are We?

Congenital and perinatal infections are transmitted from mother to infant during pregnancy across the placenta or during delivery. These infections not only cause pregnancy complications and still birth, but also result in an array of pediatric morbidities caused by physical deformities, neurodevelopmental delays, and impaired vision, mobility and hearing. Due to the burden of these conditions, congenital and perinatal infections may result in lifelong disability and profoundly impact an individual's ability to live to their fullest capacity. While there are vaccines to prevent congenital and perinatal rubella, varicella, and hepatitis B infections, many more are currently in development at various stages of progress. The spectrum of our efforts to understand and address these infections includes observational studies of natural history of disease, epidemiological evaluation of risk factors, immunogen design, preclinical research of protective immunity in animal models, and evaluation of promising candidates in vaccine trials. In this review we summarize this progress in vaccine development research for Cytomegalovirus, Group B Streptococcus, Herpes simplex virus, Human Immunodeficiency Virus, Toxoplasma, Syphilis, and Zika virus congenital and perinatal infections. We then synthesize this evidence to examine how close we are to developing a vaccine for these infections, and highlight areas where research is still needed.

The R2 non-neuroinvasive HSV-1 vaccine affords protection from genital HSV-2 infections in a guinea pig model

Herpes simplex virus (HSV) infections are common and can cause severe illness but no vaccine is currently available. The recent failure of subunit HSV vaccines has highlighted the need for vaccines that present a diverse array of antigens, including the development of next-generation live-attenuated vaccines. However, most attenuated HSV strains propagate poorly, limiting their ability to elicit protective immune responses. A live-attenuated vaccine that replicates in non-neural tissue but is ablated for transmission into the nervous system may elicit protective immune responses without evoking neurologic complications or establishing life-long infections. Initial studies of R2, a live-attenuated vaccine that is engineered to be unable to invade the nervous system, used the guinea pig genital HSV model to evaluate the ability of R2 to replicate at the site of inoculation, cause disease and infect neural tissues. R2 was then evaluated as a vaccine using three routes of inoculation: intramuscular (IM), intradermal (ID) and intravaginal (IVag) and compared to IM administered gD2+MPL/Alum vaccine in the same model. R2 replicated in the genital tract but did not produce acute or recurrent disease and did not infect the neural tissue. The R2 vaccine-induced neutralizing antibody and decreased the severity of acute and recurrent HSV-2 disease as well as recurrent shedding. The ID route was the most effective. ID administered R2 was more effective than gD2+MPL/Alum at inducing neutralizing antibody, suppressing acute disease, and acute vaginal virus replication. R2 was especially more effective at reducing recurrent virus shedding, the most common source of HSV transmission. The live-attenuated prophylactic HSV vaccine, R2, was effective in the guinea pig model of genital HSV-2 especially when administered by the ID route. The use of live-attenuated HSV vaccines that robustly replicate in mucosal tissues but are ablated for neuroinvasion offers a promising approach for HSV vaccines.

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.

HVEM signaling promotes protective antibody-dependent cellular cytotoxicity (ADCC) vaccine responses to herpes simplex viruses

Herpes simplex virus (HSV) glycoprotein D (gD) not only is required for virus entry and cell-to-cell spread but also binds the host immunomodulatory molecule, HVEM, blocking interactions with its ligands. Natural infection primarily elicits neutralizing antibodies targeting gD, but subunit protein vaccines designed to induce this response have failed clinically. In contrast, preclinical studies demonstrate that an HSV-2 single-cycle strain deleted in gD, ΔgD-2, induces primarily non-neutralizing antibodies that activate Fcγ receptors (FcγRs) to mediate antibody-dependent cellular cytotoxicity (ADCC). These studies were designed to test the hypothesis that gD interferes with ADCC through engagement of HVEM. Immunization of Hvem-/- mice with ΔgD-2 resulted in significant reduction in HSV-specific IgG2 antibodies, the subclass associated with FcγR activation and ADCC, compared with wild-type controls. This translated into a parallel reduction in active and passive vaccine protection. A similar decrease in ADCC titers was observed in Hvem-/- mice vaccinated with an alternative HSV vaccine candidate (dl5-29) or an unrelated vesicular stomatitis virus-vectored vaccine. Unexpectedly, not only did passive transfer of immune serum from ΔgD-2-vaccinated Hvem-/- mice fail to protect wild-type mice but transfer of immune serum from ΔgD-2-vaccinated wild-type mice failed to protect Hvem-/- mice. Immune cells isolated from Hvem-/- mice were impaired in FcγR activation, and, conversely, addition of gD protein or anti-HVEM antibodies to in vitro murine or human FcγR activation assays inhibited the response. These findings uncover a previously unrecognized role for HVEM signaling in generating and mediating ADCC and an additional HSV immune evasion strategy.

A HSV1 mutant leads to an attenuated phenotype and induces immunity with a protective effect

Herpes simplex virus type 1 (HSV1) is a complicated structural agent with a sophisticated transcription process and a high infection rate. A vaccine against HSV1 is urgently needed. As multiple viral-encoded proteins, including structural and nonstructural proteins, contribute to immune response stimulation, an attenuated or deficient HSV1 vaccine may be relatively reliable. Advances in genomic modification technologies provide reliable means of constructing various HSV vaccine candidates. Based on our previous work, an M6 mutant with mutations in the UL7, UL41, LAT, Us3, Us11 and Us12 genes was established. The mutant exhibited low proliferation in cells and an attenuated phenotype in an animal model. Furthermore, in mice and rhesus monkeys, the mutant can induce remarkable serum neutralizing antibody titers and T cell activation and protect against HSV1 challenge by impeding viral replication, dissemination and pathogenesis.

Use of the Guinea pig model of genital herpes to evaluate vaccines and antivirals: Review

Herpes simplex virus (HSV) infections type 1 (HSV-1) and type 2 (HSV-2) are common throughout the world. Infections are lifelong and may produce both acute and recurrent vesiculoulcerative disease as well as more severe diseases. Despite disappointing results from recent HSV vaccine trials new vaccines and more potent antiviral therapies continue to be developed. These newer approaches require initial evaluations in animal models. In this review I have briefly described some of the models available and then more thoroughly describe the guinea pig model of acute and recurrent genital herpes infections. As discussed, the guinea pig model most closely mimics human disease and provides several important endpoints for evaluating vaccines and antivirals.

Vaccines against Genital Herpes: Where Are We?

Genital herpes is a venereal disease caused by herpes simplex virus (HSV). Although HSV symptoms can be reduced with antiviral drugs, there is no cure. Moreover, because HSV infected individuals are often unaware of their infection, it is highly likely that they will transmit HSV to their sexual partner. Once infected, an individual has to live with HSV for their entire life, and HSV infection can lead to meningitis, encephalitis, and neonatal herpes as a result of vertical transmission. In addition, HSV infection increases the rates of human immunodeficiency virus (HIV) infection and transmission. Because of the high burden of genital herpes, HSV vaccines have been developed, but none have been very successful. In this review, we discuss the current status of genital herpes vaccine development.

Herpes Simplex Virus Type 1 Interactions with the Interferon System

The interferon (IFN) system is one of the first lines of defense activated against invading viral pathogens. Upon secretion, IFNs activate a signaling cascade resulting in the production of several interferon stimulated genes (ISGs), which work to limit viral replication and establish an overall anti-viral state. Herpes simplex virus type 1 is a ubiquitous human pathogen that has evolved to downregulate the IFN response and establish lifelong latent infection in sensory neurons of the host. This review will focus on the mechanisms by which the host innate immune system detects invading HSV-1 virions, the subsequent IFN response generated to limit viral infection, and the evasion strategies developed by HSV-1 to evade the immune system and establish latency in the host.

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.

A Single-Cycle Glycoprotein D Deletion Viral Vaccine Candidate, ΔgD-2, Elicits Polyfunctional Antibodies That Protect against Ocular Herpes Simplex Virus

Herpes simplex virus 1 (HSV-1) is a leading cause of infectious blindness, highlighting the need for effective vaccines. A single-cycle HSV-2 strain with the deletion of glycoprotein D, ΔgD-2, completely protected mice from HSV-1 and HSV-2 skin or vaginal disease and prevented latency following active or passive immunization in preclinical studies. The antibodies functioned primarily by activating Fc receptors to mediate antibody-dependent cellular cytotoxicity (ADCC). The ability of ADCC to protect the immune-privileged eye, however, may differ from skin or vaginal infections. Thus, the current studies were designed to compare active and passive immunization with ΔgD-2 versus an adjuvanted gD subunit vaccine (rgD-2) in a primary lethal ocular murine model. ΔgD-2 provided significantly greater protection than rgD-2 following a two-dose vaccine regimen, although both vaccines were protective compared to an uninfected cell lysate. However, only immune serum from ΔgD-2-vaccinated, but not rgD-2-vaccinated, mice provided significant protection against lethality in passive transfer studies. The significantly greater passive protection afforded by ΔgD-2 persisted after controlling for the total amount of HSV-specific IgG in the transferred serum. The antibodies elicited by rgD-2 had significantly higher neutralizing titers, whereas those elicited by ΔgD-2 had significantly more C1q binding and Fc gamma receptor activation, a surrogate for ADCC function. Together, the findings suggest ADCC is protective in the eye and that nonneutralizing antibodies elicited by ΔgD-2 provide greater protection than neutralizing antibodies elicited by rgD-2 against primary ocular HSV disease. The findings support advancement of vaccines, including ΔgD-2, that elicit polyfunctional antibody responses.IMPORTANCE Herpes simplex virus 1 is the leading cause of infectious corneal blindness in the United States and Europe. Developing vaccines to prevent ocular disease is challenging because the eye is a relatively immune-privileged site. In this study, we compared a single-cycle viral vaccine candidate, which is unique in that it elicits predominantly nonneutralizing antibodies that activate Fc receptors and bind complement, and a glycoprotein D subunit vaccine that elicits neutralizing but not Fc receptor-activating or complement-binding responses. Only the single-cycle vaccine provided both active and passive protection against a lethal ocular challenge. These findings greatly expand our understanding of the types of immune responses needed to protect the eye and will inform future prophylactic and therapeutic strategies.

Vaccination Route as a Determinant of Protective Antibody Responses against Herpes Simplex Virus

Herpes simplex viruses (HSV) are significant global health problems associated with mucosal and neurologic disease. Prior experimental vaccines primarily elicited neutralizing antibodies targeting glycoprotein D (gD), but those that advanced to clinical efficacy trials have failed. Preclinical studies with an HSV-2 strain deleted in gD (ΔgD-2) administered subcutaneously demonstrated that it elicited a high titer, weakly neutralizing antibodies that activated Fcg receptors to mediate antibody-dependent cellular cytotoxicity (ADCC), and completely protected mice against lethal disease and latency following vaginal or skin challenge with HSV-1 or HSV-2. Vaccine efficacy, however, may be impacted by dose and route of immunization. Thus, the current studies were designed to compare immunogenicity and efficacy following different routes of vaccination with escalating doses of ΔgD-2. We compared ΔgD-2 with two other candidates: recombinant gD protein combined with aluminum hydroxide and monophosphoryl lipid A adjuvants and a replication-defective virus deleted in two proteins involved in viral replication, dl5-29. Compared to the subcutaneous route, intramuscular and/or intradermal immunization resulted in increased total HSV antibody responses for all three vaccines and boosted the ADCC, but not the neutralizing response to ΔgD and dl5-29. The adjuvanted gD protein vaccine provided only partial protection and failed to elicit ADCC independent of route of administration. In contrast, the increased ADCC following intramuscular or intradermal administration of DgD-2 or dl5-29 translated into significantly increased protection. The DgD-2 vaccine provided 100% protection at doses as low as 5 × 104 pfu when administered intramuscularly or intradermally, but not subcutaneously. However, administration of a combination of low dose subcutaneous DgD-2 and adjuvanted gD protein resulted in greater protection than low dose DgD-2 alone indicating that gD neutralizing antibodies may contribute to protection. Taken together, these results demonstrate that ADCC provides a more predictive correlate of protection against HSV challenge in mice and support intramuscular or intradermal routes of vaccination.

Nucleoside-modified mRNA encoding HSV-2 glycoproteins C, D, and E prevents clinical and subclinical genital herpes

The goals of a genital herpes vaccine are to prevent painful genital lesions and reduce or eliminate subclinical infection that risks transmission to partners and newborns. We evaluated a trivalent glycoprotein vaccine containing herpes simplex virus type 2 (HSV-2) entry molecule glycoprotein D (gD2) and two immune evasion molecules: glycoprotein C (gC2), which binds complement C3b, and glycoprotein E (gE2), which blocks immunoglobulin G (IgG) Fc activities. The trivalent vaccine was administered as baculovirus proteins with CpG and alum, or the identical amino acids were expressed using nucleoside-modified mRNA in lipid nanoparticles (LNPs). Both formulations completely prevented genital lesions in mice and guinea pigs. Differences emerged when evaluating subclinical infection. The trivalent protein vaccine prevented dorsal root ganglia infection, and day 2 and 4 vaginal cultures were negative in 23 of 30 (73%) mice compared with 63 of 64 (98%) in the mRNA group (P = 0.0012). In guinea pigs, 5 of 10 (50%) animals in the trivalent subunit protein group had vaginal shedding of HSV-2 DNA on 19 of 210 (9%) days compared with 2 of 10 (20%) animals in the mRNA group that shed HSV-2 DNA on 5 of 210 (2%) days (P = 0.0052). The trivalent mRNA vaccine was superior to trivalent proteins in stimulating ELISA IgG antibodies, neutralizing antibodies, antibodies that bind to crucial gD2 epitopes involved in entry and cell-to-cell spread, CD4⁺ T cell responses, and T follicular helper and germinal center B cell responses. The trivalent nucleoside-modified mRNA-LNP vaccine is a promising candidate for human trials.

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.

Trivalent Glycoprotein Subunit Vaccine Prevents Neonatal Herpes Simplex Virus Mortality and Morbidity

Herpes simplex virus (HSV) can cause severe infection in neonates leading to mortality and lifelong morbidity. Prophylactic approaches, such as maternal immunization, could prevent neonatal HSV (nHSV) infection by providing protective immunity and preventing perinatal transmission. We previously showed that maternal immunization with a replication-defective HSV vaccine candidate, dl5-29, leads to transfer of virus-specific antibodies into the neonatal circulation and protects against nHSV neurological sequela and mortality (C. D. Patel, I. M. Backes, S. A. Taylor, Y. Jiang, et al., Sci Transl Med, 11:eaau6039, 2019, https://doi.org/10.1126/scitranslmed.aau6039). In this study, we evaluated the efficacy of maternal immunization with an experimental trivalent (gC2, gD2, and gE2) subunit vaccine to protect against nHSV. Using a murine model of nHSV, we demonstrated that maternal immunization with the trivalent vaccine protected offspring against nHSV-disseminated disease and mortality. In addition, offspring of immunized dams were substantially protected from behavioral pathology following HSV infection. This study supports the idea that maternal immunization is a viable strategy for the prevention of neonatal infections.IMPORTANCE Herpes simplex virus is among the most serious infections of newborns. Current antiviral therapies can prevent mortality if infection is recognized early and treated promptly. Most children who survive nHSV develop lifelong neurological and behavioral deficits, despite aggressive antiviral treatment. We propose that maternal immunization could provide protection against HSV for both mother and baby. To this end, we used a trivalent glycoprotein vaccine candidate to demonstrate that offspring are protected from nHSV following maternal immunization. Significantly, this approach protected offspring from long-term behavioral morbidity. Our results emphasize the importance of providing protective immunity to neonates during this window of vulnerability.

Model of vaccine efficacy against HSV-2 superinfection of HSV-1 seropositive mice demonstrates protection by antibodies mediating cellular cytotoxicity

A majority of the world’s population is infected with HSV-1, highlighting the need for vaccines that are effective in HSV-1-seropositive hosts. We established a superinfection model by infecting mice intranasally with a sublethal dose of HSV-1, which results in high rates of seropositive, latently infected mice susceptible to HSV-2 superinfection. Sublethal HSV-1 induced a predominantly neutralizing antibody response. Vaccination of HSV-1-seropositive mice with recombinant adjuvanted glycoprotein D (rgD-2) failed to significantly boost HSV total or neutralizing antibody responses and provided no significant increased protection against HSV-2 superinfection compared to control-vaccinated HSV-1-seropositive mice. In contrast, immunization with a single-cycle virus deleted in gD (ΔgD-2) significantly boosted total HSV-specific antibody titers and elicited new antibody-dependent cell-mediated cytotoxicity responses, providing complete protection from death following HSV-2 superinfection. This model recapitulates clinical responses to natural infection and the rgD-2 vaccine trial outcomes and suggests that ΔgD-2 may prove protective in HSV-1-seropositive hosts.

Maternal immunization confers protection against neonatal herpes simplex mortality and behavioral morbidity

Neonatal herpes simplex virus (nHSV) infections cause devastating morbidity and mortality in infants. Most nHSV cases are associated with primary maternal infection, consistent with the hypothesis that maternal immunity is protective. In humans, we found HSV-specific neutralizing antibodies in newborns of immune mothers, indicating that placentally transferred HSV-specific antibody is protective. Using a murine model, we showed that passive administration of HSV-specific antibody to dams prevented disseminated infection and mortality in pups. Maternal immunization with an HSV-2 replication-defective vaccine candidate, dl5-29, led to transfer of HSV-specific antibodies into neonatal circulation that protected against nHSV neurological disease and death. Furthermore, we observed considerable anxiety-like behavior in adult mice that had been infected with low doses of HSV as neonates, despite a notable lack of signs of infection. This phenotype suggests that nHSV infection can have an unsuspected and permanent impact on behavior. These behavioral sequelae of nHSV were prevented by maternal immunization with dl5-29, demonstrating an unexpected benefit of immunization. These findings also support the general concept that maternal immunization can prevent neurotropic neonatal infections and associated morbidity and mortality.

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.

A Pentavalent Epstein-Barr Virus-Like Particle Vaccine Elicits High Titers of Neutralizing Antibodies against Epstein-Barr Virus Infection in Immunized Rabbits

Primary infection with Epstein-Barr virus (EBV) is associated with acute infectious mononucleosis, whereas persistent infection is associated with chronic diseases such as autoimmune diseases and various types of cancer. Indeed, approximately 2% of all new cancer cases occurring annually worldwide are EBV-associated. Currently, there is no licensed EBV prophylactic vaccine. Selection of appropriate viral protein subunits is critical for development of an effective vaccine. Although the major EBV surface glycoprotein gp350/220 (gp350) has been proposed as an important prophylactic vaccine target, attempts to develop a potent vaccine based on gp350 alone have shown limited success in the clinic. We provide data showing that five EBV glycoproteins (gp350, gB, gp42, gH, and gL) involved in viral entry and infection can successfully be incorporated on the surface of EBV-like particles (EBV-LPs). These EBV-LPs, when administered together with aluminum hydroxide and monophosphoryl lipid A as adjuvants to New Zealand white rabbits, elicited EBV glycoprotein-specific antibodies capable of neutralizing viral infection in vitro in both B cells and epithelial cells, better than soluble gp350 ectodomain. Our findings suggest that a pentavalent EBV-LP formulation might be an ideal candidate for development as a safe and immunogenic EBV vaccine.