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

A QS21 + CpG-Adjuvanted Trivalent HSV-2 Vaccine and Trivalent HSV-2 mRNA Vaccine Induce a Strong Immune Response, Protect Against HSV-2 Infection, and Cross-Protect Against HSV-1 Infection in Mice

BACKGROUND

HSV-2 infection continues to be a significant global health concern, as there are no approved vaccines despite numerous attempts at development.

METHODS

This study explored the immunogenicity and protective efficacy of aluminum- or QS21 + CpG-adjuvanted trivalent HSV-2 vaccines and a trivalent HSV-2 mRNA vaccine incorporating the gC2, gD2, and gE2 antigens.

RESULTS

Our results demonstrated that the QS21 + CpG-adjuvanted subunit vaccine and mRNA vaccines successfully induced robust antigen-specific humoral and cellular immune responses and provided significant protection against both HSV-2 and HSV-1 infection. These vaccines showed remarkable efficiency in reducing the viral load and preventing clinical symptoms in mice, highlighting their potential for clinical application. Conversely, the aluminum-adjuvanted vaccine exhibited limited effectiveness, emphasizing the superiority of the QS21 + CpG-adjuvanted and mRNA vaccines.

CONCLUSIONS

These findings provide valuable insights for the continued development of effective HSV vaccines and suggest promising strategies for preventing both HSV-2 and HSV-1 infection.

Animal models of human herpesvirus infection

Human herpesvirus, a specific group within the herpesvirus family, is responsible for a variety of human diseases. These viruses can infect humans and other vertebrates, primarily targeting the skin, mucous membranes, and neural tissues, thereby significantly impacting the health of both humans and animals. Animal models are crucial for studying virus pathogenesis, vaccine development, and drug testing. Despite several vaccine candidates being in preclinical and clinical stages, no vaccines are current available to prevent lifelong infections caused by these human herpesviruses, except for varicella-zoster virus (VZV) vaccine. However, the strict host tropism of herpesviruses and other limitations mean that no single animal model can fully replicate all key features of human herpesvirus-associated diseases. This makes it challenging to evaluate vaccines and antivirals against human herpesvirus comprehensively. Herein, we summarize the current animal models used to study the human herpesviruses including α-herpesviruses (herpes simplex virus type 1(HSV-1), HSV-2, VZV), β-herpesviruses (human cytomegalovirus (HCMV), γ-herpesviruses (Epstein-Barr virus (EBV)) and Kaposi's sarcoma herpesvirus (KSHV)). By providing concise information and detailed analysis of the potential, limitations and applications of various models, such as non-human primates, mice, rabbits, guinea pigs, and tree shrews, this summary aims to help researchers efficiently select the most appropriate animal model, offering practical guidance for studying human herpesvirus.

Tackling cutaneous herpes simplex virus disease with topical immunomodulators-a call to action

SUMMARYAntivirals play important roles in restricting viral diseases. Nevertheless, they act on a relatively limited number of viruses and occasionally display partial effectiveness in some tissues or against escape variants. Although vaccination remains the most cost-effective approach for preventing microbial diseases, developing prophylactic or therapeutic solutions for pathogens, such as herpes simplex viruses (HSVs), that effectively reduce their clinical manifestations in the skin has proven exceptionally challenging despite extensive research. Alternatively, a less explored approach for tackling HSV skin infection involves using topical immunomodulatory molecules to potentiate the host's innate antiviral immune responses. When applied directly to herpetic skin lesions where viral antigen is present, this strategy has the potential to elicit virus-specific adaptive immunity. Based on currently available data, we foresee substantial potential for this approach in addressing HSV skin infections, along with additional prospects to advance understanding of skin biology and apply relevant new findings to other dermatological conditions. However, due to the limited number of case studies evaluating this method and its safety profile, particularly in immunocompromised individuals and pregnant women, further research is crucial, especially to assess the effects of immunomodulators in these vulnerable populations. Here, we revisit and discuss the use of immunomodulatory molecules for potentiating the host immune response against HSV skin infection and call for action for increased research and clinical trials regarding the possible benefits of this latter strategy for treating HSV cutaneous disease and recurrences. We also revisit and discuss antivirals and vaccine candidates against HSVs.

An updated review of HSV-1 infection-associated diseases and treatment, vaccine development, and vector therapy application

Herpes simplex virus type 1 (HSV-1) is a globally widespread virus that causes and associates with a wide range of diseases, including herpes simplex encephalitis, herpes simplex keratitis, and herpes labialis. The interaction between HSV-1 and the host involves complex immune response mechanisms, including recognition of viral invasion, maintenance of latent infection, and triggering of reactivation. Antiviral therapy is the core treatment for HSV-1 infections. Meanwhile, vaccine development employs different strategies and methods, and several promising vaccine types have emerged, such as live attenuated, protein subunit, and nucleic acid vaccines, offering new possibilities for the prevention of HSV-1 infection. Moreover, HSV-1 can be modified into a therapeutic vector for gene therapy and tumour immunotherapy. This review provides an in-depth summary of HSV-1 infection-associated innate and adaptive immune responses, disease pathogenesis, current therapeutic approaches, recent advances in vaccine development, and vector therapy applications for cancer treatment. Through a systematic review of multiple aspects of HSV-1, this study aims to provide a comprehensive and detailed reference for the public on the prevention, control, and treatment of HSV-1.

Toward the Eradication of Herpes Simplex Virus: Vaccination and Beyond

Herpes simplex virus (HSV) has coevolved with Homo sapiens for over 100,000 years, maintaining a tenacious presence by establishing lifelong, incurable infections in over half the human population. As of 2024, an effective prophylactic or therapeutic vaccine for HSV remains elusive. In this review, we independently screened PubMed, EMBASE, Medline, and Google Scholar for clinically relevant articles on HSV vaccines. We identified 12 vaccines from our literature review and found promising candidates across various classes, including subunit vaccines, live vaccines, DNA vaccines, and mRNA vaccines. Notably, several vaccines-SL-V20, HF10, VC2, and mRNA-1608-have shown promising preclinical results, suggesting that an effective HSV vaccine may be within reach. Additionally, several other vaccines such as GEN-003 (a subunit vaccine from Genocea), HerpV (a subunit vaccine from Agenus), 0ΔNLS/RVx201 (a live-attenuated replication-competent vaccine from Rational Vaccines), HSV 529 (a replication-defective vaccine from Sanofi Pasteur), and COR-1 (a DNA-based vaccine from Anteris Technologies) have demonstrated potential in clinical trials. However, GEN-003 and HerpV have not advanced further despite promising results. Continued progress with these candidates brings us closer to a significant breakthrough in preventing and treating HSV infections.

A review of HSV pathogenesis, vaccine development, and advanced applications

Herpes simplex virus (HSV), an epidemic human pathogen threatening global public health, gains notoriety for its complex pathogenesis that encompasses lytic infection of mucosal cells, latent infection within neurons, and periodic reactivation. This intricate interplay, coupled with HSV's sophisticated immune evasion strategies, gives rise to various diseases, including genital lesions, neonatal encephalitis, and cancer. Despite more than 70 years of relentless research, an effective preventive or therapeutic vaccine against HSV has yet to emerge, primarily due to the limited understanding of virus-host interactions, which in turn impedes the identification of effective vaccine targets. However, HSV's unique pathological features, including its substantial genetic load capacity, high replicability, transmissibility, and neurotropism, render it a promising candidate for various applications, spanning oncolytic virotherapy, gene and immune therapies, and even as an imaging tracer in neuroscience. In this review, we comprehensively update recent breakthroughs in HSV pathogenesis and immune evasion, critically summarize the progress made in vaccine candidate development, and discuss the multifaceted applications of HSV as a biological tool. Importantly, we highlight both success and challenges, emphasizing the critical need for intensified research into HSV, with the aim of providing deeper insights that can not only advance HSV treatment strategies but also broaden its application horizons.

Immunopathology of herpes simplex virus-associated neuroinflammation: Unveiling the mysteries

The immunopathology of herpes simplex virus (HSV)-associated neuroinflammation is a captivating and intricate field of study within the scientific community. HSV, renowned for its latent infection capability, gives rise to a spectrum of neurological expressions, ranging from mild symptoms to severe encephalitis. The enigmatic interplay between the virus and the host's immune responses profoundly shapes the outcome of these infections. This review delves into the multifaceted immune reactions triggered by HSV within neural tissues, intricately encompassing the interplay between innate and adaptive immunity. Furthermore, this analysis delves into the delicate equilibrium between immune defence and the potential for immunopathology-induced neural damage. It meticulously dissects the roles of diverse immune cells, cytokines, and chemokines, unravelling the intricacies of neuroinflammation modulation and its subsequent effects. By exploring HSV's immune manipulation and exploitation mechanisms, this review endeavours to unveil the enigmas surrounding the immunopathology of HSV-associated neuroinflammation. This comprehensive understanding enhances our grasp of viral pathogenesis and holds promise for pioneering therapeutic strategies designed to mitigate the neurological ramifications of HSV infections.

Unique Attributes of Guinea Pigs as New Models to Study Ocular Herpes Pathophysiology and Recurrence

Purpose

The objective of this study was to explore the ocular and systemic outcomes of herpes simplex virus type 1 (HSV-1) infection in guinea pigs, to monitor the spontaneous reactivation of the virus, and to assess the effectiveness of various treatments, drawing comparisons to conventional rabbit models.

Methods

Guinea pigs and rabbits were infected in the right corneas with differing doses and strains of HSV-1. Observations were made over a 71-day period, focusing on comparing ocular lesions, viral shedding patterns, and weight loss between the two animal models. Postinfection, the effectiveness of trifluridine ophthalmic drops, oral acyclovir, and valacyclovir was evaluated. The confirmation of viral infection was done through virus titer assay, fluorescein staining, and corneal imaging.

Results

Guinea pigs and rabbits manifested symptoms akin to human herpes stromal keratitis (HSK) when exposed to varying titers of viral suspension. Regardless of the initial viral load, all guinea pig groups demonstrated comparable ocular pathology, witnessing conditions like blepharitis and conjunctivitis within 3 days, progressing to severe conditions, including total corneal opacification and necrotizing keratitis. Tear film collection revealed nonsignificant differences in viral plaques between all groups. Notably, guinea pigs in the low-infection group experienced the most weight loss, although without significant differences. The replication of the same experiment on rabbits yielded consistent results in disease pathology across different groups, with occurrences of blepharitis and conjunctivitis. Interestingly, after initial resolution, guinea pigs presented a more frequent and broadly observed increase in disease score and corneal opacity, a phenomenon rarely seen in rabbits within the same timeframe. The effectiveness of 1% trifluridine was observed in mitigating ocular HSV-1 disease in both species, whereas oral acyclovir and valacyclovir were found to be detrimental and ineffective in guinea pigs but not in rabbits.

Conclusions

This study demonstrates the potential suitability of guinea pigs as new models for ocular HSV-1 investigations, filling a critical preclinical void of models capable of showcasing spontaneous HSV reactivation in the eye. The observed similarities and differences in the reactions of guinea pigs and rabbits to HSV-1 infection and treatments provide crucial insights, laying the foundation for future studies on ocular HSV pathogenesis, latency, and improved treatment options.

Rapid and accurate detection of herpes simplex virus type 2 using a low-cost electrochemical biosensor

Herpes simplex virus type 2 (HSV-2) infection, which is almost exclusively sexually transmitted, causes genital herpes. Although this lifelong and incurable infection is extremely widespread, currently there is no readily available diagnostic device that accurately detects HSV-2 antigens to a satisfactory degree. Here, we report an ultrasensitive electrochemical device that detects HSV-2 antigens within 9 min and costs just $1 (USD) to manufacture. The electrochemical biosensor is biofunctionalized with the human cellular receptor nectin-1 and detects the glycoprotein gD2, which is present within the HSV-2 viral envelope. The performance of the device is tested in a guinea pig model that mimics human biofluids, yielding 88.9% sensitivity, 100.0% specificity, and 95.0% accuracy under these conditions, with a limit of detection of 0.019 fg mL-1 for gD2 protein and 0.057 PFU mL-1 for titered viral samples. Importantly, no cross-reactions with other viruses were detected, indicating the adequate robustness and selectivity of the sensor. Our low-cost technology could facilitate more frequent testing for HSV-2.

Advances in mRNA vaccines for viral diseases

Since the onset of the pandemic caused by severe acute respiratory syndrome coronavirus 2, messenger RNA (mRNA) vaccines have demonstrated outstanding performance. mRNA vaccines offer significant advantages over conventional vaccines in production speed and cost-effectiveness, making them an attractive option against other viral diseases. This article reviewed recent advances in viral mRNA vaccines and their delivery systems to provide references and guidance for developing mRNA vaccines for new viral diseases.

An Insight into Current Treatment Strategies, Their Limitations, and Ongoing Developments in Vaccine Technologies against Herpes Simplex Infections

Herpes simplex virus (HSV) infection, the most prevalent viral infection that typically lasts for a lifetime, is associated with frequent outbreaks of oral and genital lesions. Oral herpes infection is mainly associated with HSV-1 through oral contact, while genital herpes originates due to HSV-2 and is categorized under sexually transmitted diseases. Immunocompromised patients and children are more prone to HSV infection. Over the years, various attempts have been made to find potential targets for the prevention of HSV infection. Despite the global distress caused by HSV infections, there are no licensed prophylactic and therapeutic vaccines available on the market against HSV. Nevertheless, there are numerous promising candidates in the pre-clinical and clinical stages of study. The present review gives an overview of two herpes viruses, their history, and life cycle, and different treatments adopted presently against HSV infections and their associated limitations. Majorly, the review covers the recent investigations being carried out globally regarding various vaccine strategies against oral and genital herpes virus infections, together with the recent and advanced nanotechnological approaches for vaccine development. Consequently, it gives an insight to researchers as well as people from the health sector about the challenges and upcoming solutions associated with treatment and vaccine development against HSV infections.

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.

Guinea Pig and Mouse Models for Genital Herpes Infection

This article describes procedures for two preclinical animal models for genital herpes infection. The guinea pig model shares many features of genital herpes in humans, including a natural route of inoculation, self-limiting primary vulvovaginitis, spontaneous recurrences, symptomatic and subclinical shedding of HSV-2, and latent infection of the associated sensory ganglia (lumbosacral dorsal root ganglia, DRG). Many humoral and cytokine responses to HSV-2 infection in the guinea pig have been characterized; however, due to the limited availability of immunological reagents, assessments of cellular immune responses are lacking. In contrast, the mouse model has been important in assessing cellular immune responses to herpes infection. Both the mouse and guinea pig models have been extremely useful for evaluating preventative and immunotherapeutic approaches for controlling HSV infection and recurrent disease. In this article, we describe procedures for infecting guinea pigs and mice with HSV-2, scoring subsequent genital disease, and measuring replicating virus to confirm infection. We also provide detailed protocols for dissecting and isolating DRG (the site of HSV-2 latency), quantifying HSV-2 genomic copies in DRG, and assessing symptomatic and subclinical shedding of HSV-2 in the vagina. © 2021 Wiley Periodicals LLC. Basic Protocol 1: Primary and recurrent genital herpes infection in the guinea pig model Support Protocol 1: Blood collection via lateral saphenous vein or by cardiac puncture after euthanasia Support Protocol 2: Dissection and isolation of dorsal root ganglia from guinea pigs Support Protocol 3: PCR amplification and quantification of HSV-2 genomic DNA from samples Basic Protocol 2: Primary genital herpes infection in the mouse model Alternate Protocol: Flank infection with HSV-2 in the mouse model Support Protocol 4: Dissection and isolation of mouse dorsal root ganglia.

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.

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.

Current vaccine approaches and emerging strategies against herpes simplex virus (HSV)

Introduction: Vaccine development for the disease caused by the herpes simplex virus (HSV) has been challenging over the years and is always in dire need of novel approaches for prevention and cure. To date, the HSV disease remains incurable and challenging to prevent. The disease is extremely widespread due to its high infection rate, resulting in millions of infection cases worldwide.Areas covered: This review first explains the diverse forms of HSV-related disease presentations and reports past vaccine history for the disease. Next, this review examines current and novel HSV vaccine approaches being studied and tested for efficacy and safety as well as vaccines in clinical trial phases I to III. Modern approaches to vaccine design using bioinformatics are described. Finally, we discuss measures to enhance new vaccine development pipelines for HSV.Expert opinion: Modernized approaches using in silico analysis and bioinformatics are emerging methods that exhibit potential for producing vaccines with enhanced targets and formulations. Although not yet fully established for HSV disease, we describe current studies using these approaches for HSV vaccine design to shed light on these methods. In addition, we provide up-to-date requirements of immunogenicity, adjuvant selection, and routes of administration.

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.

Protection against herpes simplex virus type 2 infection in a neonatal murine model using a trivalent nucleoside-modified mRNA in lipid nanoparticle vaccine

Neonatal herpes is a dreaded complication of genital herpes infection in pregnancy. We recently compared two vaccine platforms for preventing genital herpes in female mice and guinea pigs and determined that HSV-2 glycoproteins C, D and E expressed using nucleoside-modified mRNA in lipid nanoparticles provided better protection than the same antigens produced as baculovirus proteins and administered with CpG and alum. Here we evaluated mRNA and protein immunization for protection against neonatal herpes. Female mice were immunized prior to mating and newborns were infected intranasally with HSV-2. IgG binding and neutralizing antibody levels in mothers and newborns were comparable using the mRNA or protein vaccines. Both vaccines protected first and second litter newborns against disseminated infection based on virus titers in multiple organs. We conclude that both vaccines are efficacious at preventing neonatal herpes, which leaves the mRNA vaccine as our preferred candidate based on better protection against genital herpes.

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.

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.

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.

Systematic Profiling of Full-Length Ig and TCR Repertoire Diversity in Rhesus Macaque through Long Read Transcriptome Sequencing

The diversity of Ig and TCR repertoires is a focal point of immunological studies. Rhesus macaques (Macaca mulatta) are key for modeling human immune responses, placing critical importance on the accurate annotation and quantification of their Ig and TCR repertoires. However, because of incomplete reference resources, the coverage and accuracy of the traditional targeted amplification strategies for profiling rhesus Ig and TCR repertoires are largely unknown. In this study, using long read sequencing, we sequenced four Indian-origin rhesus macaque tissues and obtained high-quality, full-length sequences for over 6000 unique Ig and TCR transcripts, without the need for sequence assembly. We constructed, to our knowledge, the first complete reference set for the constant regions of all known isotypes and chain types of rhesus Ig and TCR repertoires. We show that sequence diversity exists across the entire variable regions of rhesus Ig and TCR transcripts. Consequently, existing strategies using targeted amplification of rearranged variable regions comprised of V(D)J gene segments miss a significant fraction (27-53% and 42-49%) of rhesus Ig/TCR diversity. To overcome these limitations, we designed new rhesus-specific assays that remove the need for primers conventionally targeting variable regions and allow single cell level Ig and TCR repertoire analysis. Our improved approach will enable future studies to fully capture rhesus Ig and TCR repertoire diversity and is applicable for improving annotations in any model organism.

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.

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.

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.

Vaccines for Herpes Simplex: Recent Progress Driven by Viral and Adjuvant Immunology

Herpes simplex viruses (HSV) types 1 and 2 are ubiquitous. They both cause genital herpes, occasionally severe disease in the immunocompromised, and facilitate much HIV acquisition globally. Despite more than 60 years of research, there is no licensed prophylactic HSV vaccine and some doubt as to whether this can be achieved. Nevertheless, a previous HSV vaccine candidate did have partial success in preventing genital herpes and HSV acquisition and another immunotherapeutic candidate reduced viral shedding and recurrent lesions, inspiring further research. However, the entry pathway of HSV into the anogenital mucosa and the subsequent cascade of immune responses need further elucidation so that these responses could be mimicked or improved by a vaccine, to prevent viral entry and colonization of the neuronal ganglia. For an effective novel vaccine against genital herpes the choice of antigen and adjuvant may be critical. The incorporation of adjuvants of the vaccine candidates in the past, may account for their partial efficacy. It is likely that they can be improved by understanding the mechanisms of immune responses elicited by different adjuvants and comparing these to natural immune responses. Here we review the history of vaccines for HSV, those in development and compare them to successful vaccines for chicken pox or herpes zoster. We also review what is known of the natural immune control of herpes lesions, via interacting innate immunity and CD4 and CD8 T cells and the lessons they provide for development of new, more effective vaccines.

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.

Successful application of prime and pull strategy for a therapeutic HSV vaccine

One promising approach for a herpes simplex virus vaccine uses a vaccine to prime and a chemoattractant to pull immune cells into the genital tract. We evaluated subunit vaccines (prime) and imiquimod (pull) in the guinea pig (gp) model of recurrent Herpes simplex virus type-2 (HSV-2). Following vaginal HSV-2 infection, gps were vaccinated with various combination of glycoproteins and adjuvant with or without subcutaneous or local applications of imiquimod after infection. Animals were examined daily for recurrent lesions and vaginal swabs collected for recurrent shedding. Although both the vaccines alone and imiquimod alone reduced recurrent HSV disease, the combination of local imiquimod and vaccine (Prime and Pull) was the most effective. In the first study, immunization with the trivalent vaccine alone or imiquimod alone decreased recurrent disease. However, the largest decrease was with the combination of vaccine and local imiquimod (P < 0.001 vs. placebo or vaccine alone). No effect on recurrent shedding was observed. In the second study, recurrent disease scores were similar in the PBS control group and the trivalent-immunized group treated with subcutaneous imiquimod however, significant reductions with glycoprotein vaccines and local imiquimod (p < 0.01 vs. placebo) were noted. The number of qPCR-positive recurrent swabs, ranged from 5 to 11% in the vaccinated+local imiquimod groups compared 29% in the PBS control group (P < 0.05). No recurrent swab samples from vaccinated groups were culture positive. We conclude that the strategy of prime (subunit HSV vaccine) and topical pull (intravaginal/topical imiquimod) decreased recurrent HSV more effectively than vaccine alone.

“Prime and pull” vaccination strategies involve an initial vaccination followed by the local application of a stimulant such as chemokines to recruit immune cells to infection target areas such as the mucosa. David Bernstein and colleagues investigate the efficacy of a prime and pull approach in a guinea pig model of recurrent genital Herpes simplex virus 2 (HSV-2) infection. Animals were vaccinated with HSV-2 glycoproteins in adjuvant with or without subcutaneous or topical (vaginal) exposure to the immune stimulant imiquimod to act as the “pull”. Animals with topical imiquimod show superior control of HSV-2 infection and improved recruitment of CD8⁺ T cells to the vaginal epithelium. Topical application of imiquimod demonstrates better control than subcutaneous imiquimod suggesting that “pulling” might be a useful approach in HSV vaccination.

Antibody responses to crucial functional epitopes as a novel approach to assess immunogenicity of vaccine adjuvants

We are interested in developing a vaccine that prevents genital herpes. Adjuvants have a major impact on vaccine immunogenicity. We compared two adjuvants, an experimental Merck Sharp & Dohme lipid nanoparticle (LNP) adjuvant, LNP-2, with CpG oligonucleotide combined with alum for immunogenicity in mice when administered with herpes simplex virus type 2 (HSV-2) glycoproteins C, D and E (gC2, gD2, gE2). The immunogens are intended to produce neutralizing antibodies to gC2 and gD2, antibodies to gD2 and gE2 that block cell-to-cell spread, and antibodies to gE2 and gC2 that block immune evasion from antibody and complement, respectively. Overall, CpG/alum was better at producing serum and vaginal IgG binding antibodies, neutralizing antibodies, antibodies that block virus spread from cell-to-cell, and antibodies that block immune evasion domains on gC2. We used a novel high throughput biosensor assay to further assess differences in immunogenicity by mapping antibody responses to seven crucial epitopes on gD2 involved in virus entry or cell-to-cell spread. We found striking differences between CpG/alum and LNP-2. Mice immunized with gD2 CpG/alum produced higher titers of antibodies than LNP-2 to six of seven crucial epitopes and produced antibodies to more crucial epitopes than LNP-2. Measuring epitope-specific antibodies helped to define mechanisms by which CpG/alum outperformed LNP-2 and is a valuable technique to compare adjuvants.

Mechanisms of Immune Control of Mucosal HSV Infection: A Guide to Rational Vaccine Design

Herpes Simplex Virus (HSV) is a highly prevalent sexually transmitted infection that aside from causing cold sores and genital lesions, causes complications in the immunocompromised and has facilitated a large proportion of HIV acquisition globally. Despite decades of research, there is no prophylactic HSV vaccine ready for use in humans, leaving many questioning whether a prophylactic vaccine is an achievable goal. A previous HSV vaccine trial did have partial success in decreasing acquisition of HSV2–promising evidence that vaccines can prevent acquisition. However, there is still an incomplete understanding of the immune response pathways elicited by HSV after initial mucosal infection and how best to replicate these responses with a vaccine, such that acquisition and colonization of the dorsal root ganglia could be prevented. Another factor to consider in the rational design of an HSV vaccine is adjuvant choice. Understanding the immune responses elicited by different adjuvants and whether lasting humoral and cell-mediated responses are induced is important, especially when studies of past trial vaccines found that a sufficiently protective cell-mediated response was lacking. In this review, we discuss what is known of the immune control involved in initial herpes lesions and reactivation, including the importance of CD4 and CD8 T cells, and the interplay between innate and adaptive immunity in response to primary infection, specifically focusing on the viral relay involved. Additionally, a summary of previous and current vaccine trials, including the components used, immune responses elicited and the feasibility of prophylactic vaccines looking forward, will also be discussed.

Herpes Simplex Virus Type 2 Immediate Early Protein ICP27 Inhibits IFN-β Production in Mucosal Epithelial Cells by Antagonizing IRF3 Activation

Herpes simplex virus type 2 (HSV-2) is the main cause of genital herpes and infections are common in the lower genital tract. Although neuronal and immune cells can be infected, epithelial cells, and keratinocytes are the primary HSV-2 target cells. HSV-2 establishes latency by evading the host immune system and its infection can also increase the risk of HIV-1 sexual transmission. Our pervious study found that HSV-2 immediate early protein ICP22, inhibited IFN-β production by interfering with the IRF3 pathway. However, ICP22-null HSV-2 did not completely lose the capability of suppressing IFN-β induction, suggesting the involvement of other viral components in the process. In this study, by using an ex vivo cervical explant model, we first demonstrated that HSV-2 can indeed inhibit IFN-β induction in human mucosal tissues. We further identified HSV-2 immediate early protein ICP27 as a potent IFN-β antagonist. ICP27 significantly suppresses the Sendai virus or polyinosinic-polycytidylic acid-induced IFN-β production in human mucosal epithelial cells, showing that ICP27 inhibits the IFN-β promoter activation, and IFN-β production at both mRNA and protein levels. Additional studies revealed that ICP27 directly associates with IRF3 and inhibits its phosphorylation and nuclear translocation, resulting in the inhibition of IFN-β induction. Our findings provide insights into the molecular mechanism underlying HSV-2 mucosal immune evasion, and information for the design of HSV-2 mucosal vaccines.

A trivalent gC2/gD2/gE2 vaccine for herpes simplex virus generates antibody responses that block immune evasion domains on gC2 better than natural infection

Vaccines for prevention and treatment of genital herpes are high public health priorities. Our approach towards vaccine development is to focus on blocking virus entry mediated by herpes simplex virus type 2 (HSV-2) glycoprotein D (gD2) and to prevent the virus from evading complement and antibody attack by blocking the immune evasion domains on HSV-2 glycoproteins C (gC2) and E (gE2), respectively. HSV-2 gC2 and gE2 are expressed on the virion envelope and infected cell surface where they are potential targets of antibodies that bind and block their immune evasion activities. We demonstrate that antibodies produced during natural infection in humans or intravaginal inoculation in guinea pigs bind to gC2 but generally fail to block the immune evasion domains on this glycoprotein. In contrast, immunization of naïve or previously HSV-2-infected guinea pigs with gC2 subunit antigen administered with CpG and alum as adjuvants produces antibodies that block domains involved in immune evasion. These results indicate that immune evasion domains on gC2 are weak antigens during infection, yet when used as vaccine immunogens with adjuvants the antigens produce antibodies that block immune evasion domains.

Clinical management of herpes simplex virus infections: past, present, and future

Infection with herpes simplex virus (HSV) types 1 and 2 is ubiquitous in the human population. Most commonly, virus replication is limited to the epithelia and establishes latency in enervating sensory neurons, reactivating periodically to produce localized recurrent lesions. However, these viruses can also cause severe disease such as recurrent keratitis leading potentially to blindness, as well as encephalitis, and systemic disease in neonates and immunocompromised patients. Although antiviral therapy has allowed continual and substantial improvement in the management of both primary and recurrent infections, resistance to currently available drugs and long-term toxicity pose a current and future threat that should be addressed through the development of new antiviral compounds directed against new targets. The development of several promising HSV vaccines has been terminated recently because of modest or controversial therapeutic effects in humans. Nevertheless, several exciting vaccine candidates remain in the pipeline and are effective in animal models; these must also be tested in humans for sufficient therapeutic effects to warrant continued development. Approaches using compounds that modulate the chromatin state of the viral genome to suppress infection and reactivation or induce enhanced antiviral immunity have potential. In addition, technologies such as CRISPR/Cas9 have the potential to edit latent viral DNA in sensory neurons, potentially curing the neuron and patient of latent infection. It is hoped that development on all three fronts—antivirals, vaccines, and gene editing—will lead to substantially less HSV morbidity in the future.

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.

Attenuated Phenotype and Immunogenic Characteristics of a Mutated Herpes Simplex Virus 1 Strain in the Rhesus Macaque

Herpes simplex virus type 1(HSV-1) presents a conundrum to public health worldwide because of its specific pathogenicity and clinical features. Some experimental vaccines, such as the recombinant viral glycoproteins, exhibit the viral immunogenicity of a host-specific immune response, but none of these has achieved a valid epidemiological protective efficacy in the human population. In the present study, we constructed an attenuated HSV-1 strain M3 through the partial deletion of UL7, UL41, and the latency-associated transcript (LAT) using the CRISPR/Cas9 system. The mutant strain exhibited lowered infectivity and virulence in macaques. Neutralization testing and ELISpot detection of the specific T-cell responses confirmed the specific immunity induced by M3 immunization and this immunity defended against the challenges of the wild-type strain and restricted the entry of the wild-type strain into the trigeminal ganglion. These results in rhesus macaques demonstrated the potential of the attenuated vaccine for the prevention of HSV-1 in humans.

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.

Chronic wasting disease management in ranched elk using rectal biopsy testing

Chronic wasting disease (CWD) is a transmissible spongiform encephalopathy (TSE) affecting members of the cervid species, and is one of the few TSEs with an expanding geographic range. Diagnostic limitations, efficient transmission, and the movement of infected animals are important contributing factors in the ongoing spread of disease. Managing CWD in affected populations has proven difficult, relying on population reduction in the case of wild deer and elk, or quarantine and depopulation in farmed cervids. In the present study, we evaluated the effectiveness of managing endemic CWD in a closed elk herd using antemortem sampling combined with both conventional and experimental diagnostic testing, and selective, targeted culling of infected animals. We hypothesized that the real-time quaking-induced conversion (RT-QuIC) assay, a developing amplification assay, would offer greater detection capabilities over immunohistochemistry (IHC) in the identification of infected animals using recto-anal mucosa associated lymphoid tissue (RAMALT). We further sought to develop a better understanding of CWD epidemiology in elk with various PRNP alleles, and predicted that CWD prevalence would decrease with targeted culling. We found that RT-QuIC identified significantly more CWD-positive animals than IHC using RAMALT tissues (121 vs. 86, respectively, out of 553 unique animals), and that longstanding disease presence was associated with an increasing frequency of less susceptible PRNP alleles. Prevalence of CWD increased significantly over the first two years of the study, implying that refinements in our management strategy are necessary to reduce the prevalence of CWD in this herd.

Experimental Oral Herpes Simplex Virus-1 (HSV-1) Co-infection in Simian Immunodeficiency Virus (SIV)-Infected Rhesus Macaques

Herpes simplex virus 1 and 2 (HSV-1/2) similarly initiate infection in mucosal epithelia and establish lifelong neuronal latency. Anogenital HSV-2 infection augments the risk for sexual human immunodeficiency virus (HIV) transmission and is associated with higher HIV viral loads. However, whether oral HSV-1 infection contributes to oral HIV susceptibility, viremia, or oral complications of HIV infection is unknown. Appropriate non-human primate (NHP) models would facilitate this investigation, yet there are no published studies of HSV-1/SIV co-infection in NHPs. Thus, we performed a pilot study for an oral HSV-1 infection model in SIV-infected rhesus macaques to describe the feasibility of the modeling and resultant immunological changes. Three SIV-infected, clinically healthy macaques became HSV-1-infected by inoculation with 4 × 108 pfu HSV-1 McKrae on buccal, tongue, gingiva, and tonsils after gentle abrasion. HSV-1 DNA was shed in oral swabs for up to 21 days, and shedding recurred in association with intra-oral lesions after periods of no shedding during 56 days of follow up. HSV-1 DNA was detected in explant cultures of trigeminal ganglia collected at euthanasia on day 56. In the macaque with lowest baseline SIV viremia, SIV plasma RNA increased following HSV-1 infection. One macaque exhibited an acute pro-inflammatory response, and all three animals experienced T cell activation and mobilization in blood. However, T cell and antibody responses to HSV-1 were low and atypical. Through rigorous assessesments, this study finds that the virulent HSV-1 strain McKrae resulted in a low level HSV-1 infection that elicited modest immune responses and transiently modulated SIV infection.

Maternal Antiviral Immunoglobulin Accumulates in Neural Tissue of Neonates To Prevent HSV Neurological Disease

While antibody responses to neurovirulent pathogens are critical for clearance, the extent to which antibodies access the nervous system to ameliorate infection is poorly understood. In this study on herpes simplex virus 1 (HSV-1), we demonstrate that HSV-specific antibodies are present during HSV-1 latency in the nervous systems of both mice and humans. We show that antibody-secreting cells entered the trigeminal ganglion (TG), a key site of HSV infection, and persisted long after the establishment of latent infection. We also demonstrate the ability of passively administered IgG to enter the TG independently of infection, showing that the naive TG is accessible to antibodies. The translational implication of this finding is that human fetal neural tissue could contain HSV-specific maternally derived antibodies. Exploring this possibility, we observed HSV-specific IgG in HSV DNA-negative human fetal TG, suggesting passive transfer of maternal immunity into the prenatal nervous system. To further investigate the role of maternal antibodies in the neonatal nervous system, we established a murine model to demonstrate that maternal IgG can access and persist in neonatal TG. This maternal antibody not only prevented disseminated infection but also completely protected the neonate from neurological disease and death following HSV challenge. Maternal antibodies therefore have a potent protective role in the neonatal nervous system against HSV infection. These findings strongly support the concept that prevention of prenatal and neonatal neurotropic infections can be achieved through maternal immunization.

Herpes simplex virus 1 is a common infection of the nervous system that causes devastating neonatal disease. Using mouse and human tissue, we discovered that antiviral antibodies accumulate in neural tissue after HSV-1 infection in adults. Similarly, these antibodies pass to the offspring during pregnancy. We found that antiviral maternal antibodies can readily access neural tissue of the fetus and neonate. These maternal antibodies then protect neonatal mice against HSV-1 neurological infection and death. These results underscore the previously unappreciated role of maternal antibodies in protecting fetal and newborn nervous systems against infection. These data suggest that maternal immunization would be efficacious at preventing fetal/neonatal neurological infections.

A trivalent subunit antigen glycoprotein vaccine as immunotherapy for genital herpes in the guinea pig genital infection model

An estimated 417 million people worldwide ages 15 to 49 are infected with herpes simplex virus type 2 (HSV-2), the most common cause of genital ulcer disease. Some individuals experience frequent recurrences of genital lesions, while others only have subclinical infection, yet all risk transmitting infection to their intimate partners. A vaccine was developed that prevents shingles, which is a recurrent infection caused by varicella-zoster virus (VZV), a closely related member of the Herpesviridae family. The success of the VZV vaccine has stimulated renewed interest in a therapeutic vaccine for genital herpes. We have been evaluating a trivalent subunit antigen vaccine for prevention of genital herpes. Here, we assess the trivalent vaccine as immunotherapy in guinea pigs that were previously infected intravaginally with HSV-2. The trivalent vaccine contains HSV-2 glycoproteins C, D, and E (gC2, gD2, gE2) subunit antigens administered with CpG and alum as adjuvants. We previously demonstrated that antibodies to gD2 neutralize the virus while antibodies to gC2 and gE2 block their immune evasion activities, including evading complement attack and inhibiting activities mediated by the IgG Fc domain, respectively. Here, we demonstrate that the trivalent vaccine significantly boosts ELISA titers and neutralizing antibody titers. The trivalent vaccine reduces the frequency of recurrent genital lesions and vaginal shedding of HSV-2 DNA by approximately 50% and almost totally eliminates vaginal shedding of replication-competent virus, suggesting that the trivalent vaccine is a worthy candidate for immunotherapy of genital herpes.