Protection from herpes simplex virus (HSV)-2 infection with replication-defective HSV-2 or glycoprotein D2 vaccines in HSV-1-seropositive and HSV-1-seronegative guinea pigs

ICP8-vhs- HSV-2 Vaccine Expressing B7 Costimulation Molecules Optimizes Safety and Efficacy against HSV-2 Infection in Mice

Herpes simplex virus 2 (HSV-2) causes most sexually transmitted genital ulcerative disease. No effective prophylactic vaccine is currently available. Replication-defective (ICP8-) HSV stimulates immune responses in animals without producing progeny virus, making it potentially useful as a safe form of a live vaccine against HSV. We previously demonstrated that mice generate a stronger response to ICP8- virus encoding B7-2 costimulation molecules than to the parental replication-defective virus. We have also demonstrated enhanced immunogenicity of an ICP8-, virion host shutoff (vhs)- virus which can no longer destabilize viral and host mRNAs. Here, we constructed a triple mutant, ICP8-vhs-B7-2+ strain, and compared it to both double mutant viruses. Immunization of mice with a single dose of ICP8-B7-2+ or ICP8-vhs-B7-2+ virus decreased challenge virus replication in the vaginal mucosa, genital disease, and mortality more effectively than immunization with the ICP8-vhs- virus. Immunization with ICP8-B7-2+ or ICP8-vhs-B7-2+ virus also effectively suppressed subsequent HSV-2 infection of the nervous system compared to immunization with the ICP8-vhs- virus. ICP8-B7-2+ and ICP8-vhs-B7-2+ strains induced more IFN gamma-producing CD8 T cells and memory CD8 T cells than did ICP8-vhs- virus, potentially explaining the enhanced protective effects. Thus, B7 costimulation molecules expressed from a replication-defective vaccine can enhance vaccine efficacy, even in an immunocompetent host.

Nonclinical safety evaluation of two vaccine candidates for herpes simplex virus type 2 to support combined administration in humans

Herpes simplex virus type 2 (HSV-2) is the most common cause of genital disease worldwide. The development of an effective HSV-2 vaccine would significantly impact global health based on the psychological distress caused by genital herpes for some individuals, the risk transmitting the infection from mother to infant, and the elevated risk of acquiring HIV-1. Five nonclinical safety studies were conducted with the replication defective HSV529 vaccine, alone or adjuvanted with GLA-SE, and the G103 subunit vaccine containing GLA-SE. A biodistribution study was conducted in guinea pigs to evaluate distribution, persistence, and shedding of HSV529. A preliminary immunogenicity study was conducted in rabbits to demonstrate HSV529-specific humoral response and its enhancement by GLA-SE. Three repeated-dose toxicity studies, one in guinea pigs and two in rabbits, were conducted to assess systemic toxicity and local tolerance of HSV529, alone or adjuvanted with GLA-SE, or G103 containing GLA-SE. Data from these studies show that both vaccines are safe and well tolerated and support the ongoing HSV-2 clinical trial in which the two vaccine candidates will be given either sequentially or concomitantly to explore their potential synergistic and incremental effects.

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.

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.

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.

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.

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.

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.

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.

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

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

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

CLINICAL TRIALS REGISTRATION

NCT01915212.

Duration of protection from live attenuated vs. sub unit HSV-2 vaccines in the guinea pig model of genital herpes: Reassessing efficacy using endpoints from clinical trials

BACKGROUND

Although herpes simplex viruses (HSV) are a major target for vaccine development no vaccine is currently licensed.

METHODS

A live attenuated HSV virus vaccine, VC2 was compared to a subunit HSV vaccine, glycoprotein D (gD2) administered with the adjuvant, MPL/Alum using the guinea pig model of genital herpes. Three doses of intramuscular (IM) vaccine were provided followed by intravaginal challenge with HSV-2 at either 3 weeks or six months after the last vaccination.

RESULTS

Both VC2 and gD2 vaccines reduced acute genital disease. VC2 was somewhat more effective in reducing acute vaginal replication, the amount of virus in neural tissue, subsequent recurrent disease and recurrent virus shedding following challenge at 3 weeks post vaccination. Both vaccines continued to provide protection at 6 months after vaccination but the differences between the vaccines became more pronounced in favor of the live attenuated vaccine, VC2. Significant differences in acute disease, acute vaginal virus replication, recurrent disease and recurrent virus shedding (P<0.05 for each) was observed comparing the vaccines. Re-examination of protection for this study using criteria similar to those used in recent clinical trials (inclusion of recurrent disease) showed that efficacy may not be as high in this model as previously thought prompting a need to assess the best predictive outcomes for protection in humans.

CONCLUSION

While both the live attenuated vaccine, VC2, and the gD2 subunit vaccine provided protection, the duration of protection appeared to be greater for VC2. Using the same evaluation criteria as used in human trials provided unique insights into the utility of the guinea pig model.

Evolution of rational vaccine designs for genital herpes immunotherapy

Immunotherapeutic vaccines have emerged as a novel treatment modality for genital herpes, a sexually transmitted disease mainly caused by herpes simplex virus type 2. The approaches to identify potential vaccine antigens have evolved from classic virus attenuation and characterization of antibody and T cell responses in exposed, but seronegative individuals, to systematic screens for novel T cell antigens. Combined with implementation of novel vaccine concepts revolving around immune evasion and local recruitment of immune effectors, the development of a safe and effective therapeutic vaccine is within reach. Here, we describe the vaccine approaches that currently show promise at clinical and pre-clinical stages and link them to the evolving scientific strategies that led to their identification.

Protection from genital herpes disease, seroconversion and latent infection in a non-lethal murine genital infection model by immunization with an HSV-2 replication-defective mutant virus

Viral vaccines have traditionally protected against disease, but for viruses that establish latent infection, it is desirable for the vaccine to reduce infection to reduce latent infection and reactivation. While seroconversion has been used in clinical trials of herpes simplex virus (HSV) vaccines to measure protection from infection, this has not been modeled in animal infection systems. To measure the ability of a genital herpes vaccine candidate to protect against various aspects of infection, we established a non-lethal murine model of genital HSV-2 infection, an ELISA assay to measure antibodies specific for infected cell protein 8 (ICP8), and a very sensitive qPCR assay. Using these assays, we observed that immunization with HSV-2 dl5-29 virus reduced disease, viral shedding, seroconversion, and latent infection by the HSV-2 challenge virus. Therefore, it may be feasible to obtain protection against genital disease, seroconversion and latent infection by immunization, even if sterilizing immunity is not achieved.

Global Diversity within and between Human Herpesvirus 1 and 2 Glycoproteins

Human herpes simplex viruses 1 and 2 (HSV-1 and HSV-2) are large-genome DNA viruses that establish a persistent infection in sensory neurons and commonly manifest with recurring oral or genital erosions that transmit virus. HSV encodes 12 predicted glycoproteins that serve various functions, including cellular attachment, entry, and egress. Glycoprotein G is currently the target of an antibody test to differentiate HSV-1 from HSV-2; however, this test has shown reduced capacity to differentiate HSV strains in East Africa. Until the recent availability of 26 full-length HSV-1 and 36 full-length HSV-2 sequences, minimal comparative information was available for these viruses. In this study, we use a variety of sequence analysis methods to compare all available sequence data for HSV-1 and HSV-2 glycoproteins, using viruses isolated in Europe, Asia, North America, the Republic of South Africa, and East Africa. We found numerous differences in diversity, nonsynonymous/synonymous substitution rates, and recombination rates between HSV-1 glycoproteins and their HSV-2 counterparts. Phylogenetic analysis revealed that while most global HSV-2 glycoprotein G sequences did not form clusters within or between continents, one clade (supported at 60.5%) contained 37% of the African sequences analyzed. Accordingly, sequences from this African subset contained unique amino acid signatures, not only in glycoprotein G, but also in glycoproteins I and E, which may account for the failure of sensitive antibody tests to distinguish HSV-1 from HSV-2 in some African individuals. Consensus sequences generated in the study can be used to improve diagnostic assays that differentiate HSV-1 from HSV-2 in global populations.

IMPORTANCE

Human herpes simplex viruses 1 and 2 (HSV-1 and HSV-2) are large DNA viruses associated with recurring oral or genital erosions that transmit virus. Up to 12 HSV-1 and HSV-2 glycoproteins are involved in HSV cell entry or are required for viral spread in animals, albeit some are dispensable for replication in vitro. The recent availability of comparable numbers of full-length HSV-1 and HSV-2 sequences enabled comparative analysis of gene diversity of glycoproteins within and between HSV types. Overall, we found less glycoprotein sequence diversity within HSV-2 than within the HSV-1 strains studied, while at the same time, several HSV-2 glycoproteins were evolving under less selective pressure. Because HSV glycoproteins are the focus of antibody tests to detect and differentiate between infections with the two strains and are constituents of vaccines in clinical-stage development, these findings will aid in refining the targets for diagnostic tests and vaccines.

Immunogenicity, protective efficacy, and non-replicative status of the HSV-2 vaccine candidate HSV529 in mice and guinea pigs

HSV-2 vaccine is needed to prevent genital disease, latent infection, and virus transmission. A replication-deficient mutant virus (dl5-29) has demonstrated promising efficacy in animal models of genital herpes. However, the immunogenicity, protective efficacy, and non-replicative status of the highly purified clinical vaccine candidate (HSV529) derived from dl5-29 have not been evaluated. Humoral and cellular immune responses were measured in mice and guinea pigs immunized with HSV529. Protection against acute and recurrent genital herpes, mortality, latent infection, and viral shedding after vaginal HSV-2 infection was determined in mice or in naïve and HSV-1 seropositive guinea pigs. HSV529 replication and pathogenicity were investigated in three sensitive models of virus replication: severe combined immunodeficient (SCID/Beige) mice inoculated by the intramuscular route, suckling mice inoculated by the intracranial route, and vaginally-inoculated guinea pigs. HSV529 immunization induced HSV-2-neutralizing antibody production in mice and guinea pigs. In mice, it induced production of specific HSV-2 antibodies and splenocytes secreting IFNγ or IL-5. Immunization effectively prevented HSV-2 infection in all three animal models by reducing mortality, acute genital disease severity and frequency, and viral shedding. It also reduced ganglionic viral latency and recurrent disease in naïve and HSV-1 seropositive guinea pigs. HSV529 replication/propagation was not detected in the muscles of SCID/Beige mice, in the brains of suckling mice, or in vaginal secretions of inoculated guinea pigs. These results confirm the non-replicative status, as well as its immunogenicity and efficacy in mice and guinea pigs, including HSV-1 seropositive guinea pigs. In mice, HSV529 produced Th1/Th2 characteristic immune response thought to be necessary for an effective vaccine. These results further support the clinical investigation of HSV529 in human subjects as a prophylactic vaccine.

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

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

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

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

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

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

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

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

Novel rat models to study primary genital herpes simplex virus-2 infection

In this study we describe that six rat models (SD, WIST, LEW, BN, F344 and DA) are susceptible to intravaginal herpes simplex virus-2 (HSV-2) infection after pre-treatment with progesterone. At a virus dose of 5 × 10(6) PFU of HSV-2, all rat models were infected presenting anti-HSV-2 antibodies, infectious virus in vaginal washes, and HSV-2 DNA genome copies in lumbosacral dorsal root ganglia and the spinal cord. Most of the LEW, BN, F344, and DA rats succumbed in systemic progressive symptoms at day 8-14 post infection, but presented no or mild genital inflammation while SD and WIST rats were mostly infected asymptomatically. Infected SD rats did not reactivate HSV-2 spontaneously or after cortisone treatment. In an HSV-2 virus dose reduction study, F344 rats were shown to be most susceptible. We also investigated whether an attenuated HSV-1 strain (KOS321) given intravaginally, could protect from a subsequent HSV-2 infection. All LEW, BN, and F344 rats survived a primary HSV-1 infection and no neuronal infection was established. In BN and F344 rats, anti-HSV-1 antibodies were readily detected while LEW rats were seronegative. In contrast to naïve LEW, BN, and F344 rats where only 3 of 18 animals survived 5 × 10(6) PFU of HSV-2, 23 of 25 previously HSV-1 infected rats survived a challenge with HSV-2. The described models provide a new approach to investigate protective effects of anti-viral microbicides and vaccine candidates, as well as to study asymptomatic primary genital HSV-2 infection.

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

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

IMPORTANCE

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

Prospects and perspectives for development of a vaccine against herpes simplex virus infections

Herpes simplex viruses 1 and 2 are human pathogens that lead to significant morbidity and mortality in certain clinical settings. The development of effective antiviral medications, however, has had little discernible impact on the epidemiology of these pathogens, largely because the majority of infections are clinically silent. Decades of work have gone into various candidate HSV vaccines, but to date none has demonstrated sufficient efficacy to warrant licensure. This review examines developments in HSV immunology and vaccine development published since 2010, and assesses the prospects for improved immunization strategies that may result in an effective, licensed vaccine in the near future.

A herpes simplex virus 2 (HSV-2) glycoprotein D-expressing nonreplicating dominant-negative HSV-2 virus vaccine is superior to a gD2 subunit vaccine against HSV-2 genital infection in guinea pigs

We recently constructed a novel non-replicating dominant-negative HSV-2 recombinant viral vaccine (CJ2-gD2) capable of expressing various HSV-2 antigens that are dominant targets of HSV-2-specific CD8 T-cell response. Importantly, CJ2-gD2 expresses gD2, the HSV-2 major antigen glycoprotein D, as efficiently as wild-type HSV-2 infection and can lead to a nearly 500-fold reduction in wild-type HSV-2 viral replication in cells co-infected with CJ2-gD2 and wild-type HSV-2. In this report, we show that CJ2-gD2 elicits a strong antibody response to various HSV-2 antigens and is highly effective in the prevention of primary and recurrent HSV-2 genital infection and disease in the immunized guinea pigs. The direct comparison study between CJ2-gD2 and a gD2 subunit vaccine (gD2-alum/MPL) with a formulation akin to a vaccine tested in phase III clinical trials shows that CJ2-gD2 is 8 times more effective than the gD2-alum/MPL subunit vaccine in eliciting an anti-HSV-2 specific neutralizing antibody response and offers significantly superior protection against primary and recurrent HSV-2 genital infections. Importantly, no challenge wild-type HSV-2 viral DNA was detectable in dorsal root ganglia DNA isolated from CJ2-gD2-immunized guinea pigs on day 60 post-challenge. CJ2-gD2 should be an excellent HSV-2 vaccine candidate for protection against HSV-2 genital infection and disease in humans.

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

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

IMPORTANCE

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

Protection provided by a herpes simplex virus 2 (HSV-2) glycoprotein C and D subunit antigen vaccine against genital HSV-2 infection in HSV-1-seropositive guinea pigs

A prophylactic vaccine for genital herpes disease remains an elusive goal. We report the results of two studies performed collaboratively in different laboratories that assessed immunogenicity and vaccine efficacy in herpes simplex virus 1 (HSV-1)-seropositive guinea pigs immunized and subsequently challenged intravaginally with HSV-2. In study 1, HSV-2 glycoproteins C (gC2) and D (gD2) were produced in baculovirus and administered intramuscularly as monovalent or bivalent vaccines with CpG and alum. In study 2, gD2 was produced in CHO cells and given intramuscularly with monophosphoryl lipid A (MPL) and alum, or gC2 and gD2 were produced in glycoengineered Pichia pastoris and administered intramuscularly as a bivalent vaccine with Iscomatrix and alum to HSV-1-naive or -seropositive guinea pigs. In both studies, immunization boosted neutralizing antibody responses to HSV-1 and HSV-2. In study 1, immunization with gC2, gD2, or both immunogens significantly reduced the frequency of genital lesions, with the bivalent vaccine showing the greatest protection. In study 2, both vaccines were highly protective against genital disease in naive and HSV-1-seropositive animals. Comparisons between gD2 and gC2/gD2 in study 2 must be interpreted cautiously, because different adjuvants, gD2 doses, and antigen production methods were used; however, significant differences invariably favored the bivalent vaccine. Immunization of naive animals with gC2/gD2 significantly reduced the number of days of vaginal shedding of HSV-2 DNA compared with that for mock-immunized animals. Surprisingly, in both studies, immunization of HSV-1-seropositive animals had little effect on recurrent vaginal shedding of HSV-2 DNA, despite significantly reducing genital disease.

Ocular and neural distribution of feline herpesvirus-1 during active and latent experimental infection in cats

BACKGROUND

Herpes simplex virus 1 (HSV-1) and varicella zoster virus (VZV) cause extensive intra-ocular and neural infections in humans and are closely related to Felid herpes virus 1 (FeHV-1). We report the extent of intra-ocular replication and the extent and morphological aspects of neural replication during the acute and latent phases of FeHV-1 infection. Juvenile, SPF cats were inoculated with FeHV-1. Additional cats were used as negative controls. Cats were euthanized on days 6, 10, and 30 post-inoculation.

RESULTS

FeHV-1 was isolated from the conjunctiva, cornea, uveal tract, retina, optic nerve, ciliary ganglion (CG), pterygopalatine ganglion (PTPG), trigeminal ganglion (TG), brainstem, visual cortex, cerebellum, and olfactory bulb of infected cats during the acute phase, but not the cranial cervical ganglion (CCG) and optic chiasm. Viral DNA was detected in all tissues during acute infection by a real-time quantitative PCR assay. On day 30, viral DNA was detected in all TG, all CCG, and 2 PTPG. Histologically mild inflammation and ganglion cell loss were noted within the TG during acute, but not latent infection. Using linear regression, a strong correlation existed between clinical score and day 30 viral DNA copy number within the TG.

CONCLUSIONS

The correlation between clinical score and day 30 viral DNA copy number suggests the severity of the acute clinical infection is related to the quantity of latent viral DNA. The histologic response was similar to that seen during HSV-1 or VZV infection. To the author's knowledge this is the first report of FeHV-1 infection involving intraocular structures and autonomic ganglia.

Current status and prospects for development of an HSV vaccine

Herpes simplex virus type 2 (HSV-2) infects 530million people, is the leading cause of genital ulcer disease, and increases the risk of HIV-1 acquisition. Although several candidate vaccines have been promising in animal models, prophylactic and therapeutic vaccines have not been effective in clinical trials thus far. Null results from the most recent prophylactic glycoprotein D2 subunit vaccine trial suggest that we must reevaluate our approach to HSV-2 vaccine development. We discuss HSV-2 pathogenesis, immunity, and vaccine efforts to date, as well as the current pipeline of candidate vaccines and design of trials to evaluate new vaccine constructs.

Generating protective immunity against genital herpes

Genital herpes is an incurable, chronic disease that affects millions of people worldwide. Not only does genital herpes cause painful, recurrent symptoms, it is also a significant risk factor for the acquisition of other sexually transmitted infections such as HIV-1. Antiviral drugs are used to treat herpes simplex virus (HSV) infection, but they cannot stop viral shedding and transmission. Thus, developing a vaccine that can prevent or clear infection will be crucial in limiting the spread of disease. In this review we outline recent studies that improve our understanding of host responses against HSV infection, discuss past clinical vaccine trials, and highlight new strategies for vaccine design against genital herpes.

High-purity preparation of HSV-2 vaccine candidate ACAM529 is immunogenic and efficacious in vivo

Genital herpes is a sexually transmitted infection (STI) caused by herpes simplex virus 2 (HSV-2) and to a lesser extent herpes simplex virus 1 (HSV-1). Infection by HSV-2 is life-long and is associated with significant cost to healthcare systems and social stigma despite the highly prevalent nature of the disease. For instance, the proportion of HSV-2 seropositive to seronegative adults is approximately 1 in 5 in the US and greater than 4 in 5 in some areas of sub-Saharan Africa. The replication-defective vaccine strain virus dl5-29 was re-derived using cells appropriate for GMP manufacturing and renamed ACAM529. Immunization with dl5-29 was previously reported to be protective both in mice and in guinea pigs, however these studies were performed with vaccine that was purified using methods that cannot be scaled for manufacturing of clinical material. Here we describe methods which serve as a major step towards preparation of ACAM529 which may be suitable for testing in humans. ACAM529 can be harvested from infected cell culture of the trans-complementing cell line AV529 clone 19 (AV529-19) without mechanical cell disruption. ACAM529 may then be purified with respect to host cell DNA and proteins by a novel purification scheme, which includes a combination of endonuclease treatment, depth filtration, anion-exchange chromatography and ultrafiltration/diafiltration (UF/DF). The resultant virus retains infectivity and is ∼ 200-fold more pure with respect to host cell DNA and proteins than is ACAM529 purified by ultracentrifugation. Additionally, we describe a side-by-side comparison of chromatography-purified ACAM529 with sucrose cushion-purified ACAM529, which shows that both preparations are equally immunogenic and protective when tested in vivo.

An adjuvanted herpes simplex virus 2 subunit vaccine elicits a T cell response in mice and is an effective therapeutic vaccine in Guinea pigs

Immunotherapeutic herpes simplex virus 2 (HSV-2) vaccine efficacy depends upon the promotion of antigen-specific immune responses that inhibit reactivation or reactivated virus, thus controlling both recurrent lesions and viral shedding. In the present study, a candidate subunit vaccine, GEN-003/MM-2, was evaluated for its ability to induce a broad-spectrum immune response in mice and therapeutic efficacy in HSV-2-infected guinea pigs. GEN-003 is comprised of HSV-2 glycoprotein D2 (gD2ΔTMR340-363) and a truncated form of infected cell polypeptide 4 (ICP4383-766), formulated with Matrix M-2 (MM-2) adjuvant (GEN-003/MM-2). In addition to eliciting humoral immune responses, CD4(+) and CD8(+) T cells characterized by the secretion of multiple cytokines and cytolytic antigen-specific T cell responses that were able to be recalled at least 44 days after the last immunization were induced in immunized mice. Furthermore, vaccination with either GEN-003 or GEN-003/MM-2 led to significant reductions in both the prevalence and severity of lesions in HSV-2-infected guinea pigs compared to those of phosphate-buffered saline (PBS) control-vaccinated animals. While vaccination with MM-2 adjuvant alone decreased recurrent disease symptoms compared to the PBS control group, the difference was not statistically significant. Importantly, the frequency of recurrent viral shedding was considerably reduced in GEN-003/MM-2-vaccinated animals but not in GEN-003- or MM-2-vaccinated animals. These findings suggest a possible role for immunotherapeutic GEN-003/MM-2 vaccination as a viable alternative to chronic antiviral drugs in the treatment and control of genital herpes disease.

The challenge of developing a herpes simplex virus 2 vaccine

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

HSV-2 vaccine: current state and insights into development of a vaccine that targets genital mucosal protection

HSV-2 is one of the most prevalent sexually transmitted infections that result in significant morbidity and financial burden on health systems around the world. Recurrent and asymptomatic re-activation accompanied by viral shedding is common among sero-positive individuals, leading to relatively high efficiency of transmission. Prophylactic HSV-2 vaccines are the best and cheapest option to address the problems associated with HSV-2 infections globally. However, despite persistent efforts, the search for an efficacious vaccine for HSV-2 remains elusive. In this review, the current state of HSV-2 vaccines and the outcome of past human trials are examined. Furthermore, we discuss the evidence and strategies from experimental mouse models that have been successful in inducing protective immunity in the genital tract against HSV-2, following immunization. Future vaccination strategies that focus on induction of robust mucosal immunity in the genital tract may hold the key for a successful vaccine against HSV-2.

Immunogenicity and efficacy of intramuscular replication-defective and subunit vaccines against herpes simplex virus type 2 in the mouse genital model

Herpes simplex virus type 2 (HSV-2) is a sexually transmitted virus that is highly prevalent worldwide, causing a range of symptoms that result in significant healthcare costs and human suffering. ACAM529 is a replication-defective vaccine candidate prepared by growing the previously described dl5-29 on a cell line appropriate for GMP manufacturing. This vaccine, when administered subcutaneously, was previously shown to protect mice from a lethal vaginal HSV-2 challenge and to afford better protection than adjuvanted glycoprotein D (gD) in guinea pigs. Here we show that ACAM529 given via the intramuscular route affords significantly greater immunogenicity and protection in comparison with subcutaneous administration in the mouse vaginal HSV-2 challenge model. Further, we describe a side-by-side comparison of intramuscular ACAM529 with a gD vaccine across a range of challenge virus doses. While differences in protection against death are not significant, ACAM529 protects significantly better against mucosal infection, reducing peak challenge virus shedding at the highest challenge dose by over 500-fold versus 5-fold for gD. Over 27% (11/40) of ACAM529-immunized animals were protected from viral shedding while 2.5% (1/40) were protected by the gD vaccine. Similarly, 35% (7/20) of mice vaccinated with ACAM529 were protected from infection of their dorsal root ganglia while none of the gD-vaccinated mice were protected. These results indicate that measuring infection of the vaginal mucosa and of dorsal root ganglia over a range of challenge doses is more sensitive than evaluating survival at a single challenge dose as a means of directly comparing vaccine efficacy in the mouse vaginal challenge model. The data also support further investigation of ACAM529 for prophylaxis in human subjects.

Inactivated HSV-2 in MPL/alum adjuvant provides nearly complete protection against genital infection and shedding following long term challenge and rechallenge

Herpes Simplex Virus Type 2 (HSV-2) infection can result in life-long recurrent genital disease, asymptomatic virus shedding, and transmission. No vaccine to date has shown significant protection clinically. Here, we used a mouse model of genital HSV-2 infection to test the efficacy of a vaccine consisting of whole, formalin-inactivated HSV-2 (FI-HSV2) formulated with monophosphoryl lipid A (MPL) and alum adjuvants. Vaccine components were administered alone or as a prime-boost immunization together with DNA vaccines encoding a truncated glycoprotein D2 (gD2t) and two conserved HSV-2 genes necessary for virus replication, UL5 (DNA helicase) and UL30 (DNA polymerase). Our results show: (1) compared with mock immunized controls, mice immunized with FI-HSV2 plus MPL/alum consistently showed protection against disease burden and total viral shedding while the mice immunized with gD2t protein with MPL/alum did not; (2) protection against genital disease and viral replication correlated with the type of boost in a prime-boost immunization with little advantage afforded by a DNA prime; (3) intramuscular (i.m.) immunization with FI-HSV2 in MPL/Alhydrogel adjuvant provided nearly complete protection against vaginal HSV-2 shedding after a lethal intravaginal (i.vag.) short-term challenge and long-term rechallenge; (4) single formulation immunization with DNA vaccines, FI-HSV2, and MPL in an aluminum phosphate (Adju-Phos) adjuvant did not increase protection relative to FI-HSV2/MPL/Adju-Phos alone; and (5) addition of MPL/alum to the FI-HSV2 was required for optimal protection against disease, viral replication, and latent virus load in the dorsal root ganglia (DRG). Most notably, an optimized vaccine formulation of FI-HSV2 MPL/Alhydrogel given i.m. completely protected against detectable vaginal HSV-2 shedding in the majority of animals and HSV-2 latent DNA in the DRG of all animals.

The ongoing pursuit of a prophylactic HSV vaccine

HSV is among the most common human pathogens in the world. It is known to cause painful, persistent skin lesions, while also being the most common cause of fatal non-epidemic encephalitis as well as the leading cause of corneal blindness. The development of prophylactic vaccines could substantially reduce global health problems associated with HSV. So far, HSV vaccine strategies have shown noticeable efficacy in early development during preclinical phases but remained unsuccessful or unproven in human trials. New understanding of how the immune system mounts a defence against HSV offers practical strategies for vaccine development. A number of promising vaccine candidates are currently awaiting clinical development or already undergoing clinical testing. Therefore, this is a suitable time to assess the progress of HSV vaccine development and consider existing challenges and future improvements needed to achieve an effective prophylactic HSV vaccine.

Herpes simplex virus-2 in the genital mucosa: insights into the mucosal host response and vaccine development

PURPOSE OF REVIEW

Herpes simplex virus (HSV)-2 is the predominant cause of genital herpes and has been implicated in HIV infection and transmission. Thus far, vaccines developed against HSV-2 have been clinically ineffective in preventing infection. This review aims to summarize the innate and adaptive immune responses against HSV-2 and examines the current status of vaccine development.

RECENT FINDINGS

Both innate and adaptive immune responses are essential for an effective primary immune response and the generation of immunity. The innate response involves Toll-like receptors, natural killer cells, plasmacytoid dendritic cells, and type I, II, and III interferons. The adaptive response requires a balance between CD4+ and CD8+ T-cells for optimal viral clearance. T-regulatory cells may be involved, although their exact function has yet to be determined. Current vaccine development involves the use of HSV-2 peptides or attenuated/replication-defective HSV-2 to generate adaptive anti-HSV-2 immune responses, however the generation of innate responses may also be an important consideration.

SUMMARY

Although vaccine development has primarily focused on the adaptive response, arguments for innate involvement are emerging. A greater understanding of the innate and adaptive processes underlying the response to HSV-2 infection will provide the foundation for the development of an effective vaccine.

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

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

HSV-2: in pursuit of a vaccine

Herpes simplex virus type 2 (HSV-2) is one of the most prevalent sexually transmitted infections worldwide. In addition to recurrent genital ulcers, HSV-2 causes neonatal herpes, and it is associated with a 3-fold increased risk for HIV acquisition. Although many HSV-2 vaccines have been studied in animal models, few have reached clinical trials, and those that have been tested in humans were not consistently effective. Here, we review HSV-2 pathogenesis, with a focus on novel understanding of mucosal immunobiology of HSV-2, and vaccine efforts to date, in an attempt to stimulate thinking about future directions for development of effective prophylactic and therapeutic HSV-2 vaccines.

Immunization with a vaccine combining herpes simplex virus 2 (HSV-2) glycoprotein C (gC) and gD subunits improves the protection of dorsal root ganglia in mice and reduces the frequency of recurrent vaginal shedding of HSV-2 DNA in guinea pigs compared to immunization with gD alone

Attempts to develop a vaccine to prevent genital herpes simplex virus 2 (HSV-2) disease have been only marginally successful, suggesting that novel strategies are needed. Immunization with HSV-2 glycoprotein C (gC-2) and gD-2 was evaluated in mice and guinea pigs to determine whether adding gC-2 to a gD-2 subunit vaccine would improve protection by producing antibodies that block gC-2 immune evasion from complement. Antibodies produced by gC-2 immunization blocked the interaction between gC-2 and complement C3b, and passive transfer of gC-2 antibody protected complement-intact mice but not C3 knockout mice against HSV-2 challenge, indicating that gC-2 antibody is effective, at least in part, because it prevents HSV-2 evasion from complement. Immunization with gC-2 also produced neutralizing antibodies that were active in the absence of complement; however, the neutralizing titers were higher when complement was present, with the highest titers in animals immunized with both antigens. Animals immunized with the gC-2-plus-gD-2 combination had robust CD4+ T-cell responses to each immunogen. Multiple disease parameters were evaluated in mice and guinea pigs immunized with gC-2 alone, gD-2 alone, or both antigens. In general, gD-2 outperformed gC-2; however, the gC-2-plus-gD-2 combination outperformed gD-2 alone, particularly in protecting dorsal root ganglia in mice and reducing recurrent vaginal shedding of HSV-2 DNA in guinea pigs. Therefore, the gC-2 subunit antigen enhances a gD-2 subunit vaccine by stimulating a CD4+ T-cell response, by producing neutralizing antibodies that are effective in the absence and presence of complement, and by blocking immune evasion domains that inhibit complement activation.

Evidence for differences in immunologic and pathogenesis properties of herpes simplex virus 2 strains from the United States and South Africa

BACKGROUND

Genital infection with herpes simplex virus 2 (HSV-2) is linked to an increased risk of infection with human immunodeficiency virus (HIV) in areas such as Sub-Saharan Africa. Thus, an effective genital herpes vaccine would be an important weapon in the fight against HIV/AIDS.

METHODS

To test whether a current vaccine candidate can protect against HSV-2 from Sub-Saharan Africa, we examined the ability of an HSV-2 vaccine strain, dl5-29, and other HSV-2 replication-defective mutant strains to protect against genital challenge with US or South African strains in a murine model.

RESULTS

Immunization with dl5-29 reduces infection by both viruses but is significantly more efficacious against the US virus than against the African virus. Furthermore, another US vaccine strain was more efficacious against US than against African viruses, and the converse was observed for the parallel African vaccine strain. Nevertheless, protection against the African viruses was significantly less with all vaccines used in this study.

CONCLUSIONS

We conclude that there may be differences in protective epitopes and pathogenesis between the US and African strains that raise the need for increased doses of the existing vaccine candidate or an HSV-2 vaccine strain based on viruses from that region.

A live-attenuated HSV-2 ICP0 virus elicits 10 to 100 times greater protection against genital herpes than a glycoprotein D subunit vaccine

Glycoprotein D (gD-2) is the entry receptor of herpes simplex virus 2 (HSV-2), and is the immunogen in the pharmaceutical industry's lead HSV-2 vaccine candidate. Efforts to prevent genital herpes using gD-2 subunit vaccines have been ongoing for 20 years at a cost in excess of $100 million. To date, gD-2 vaccines have yielded equivocal protection in clinical trials. Therefore, using a small animal model, we sought to determine if a live-attenuated HSV-2 ICP0⁻ virus would elicit better protection against genital herpes than a gD-2 subunit vaccine. Mice immunized with gD-2 and a potent adjuvant (alum+monophosphoryl lipid A) produced high titers of gD-2 antibody. While gD-2-immunized mice possessed significant resistance to HSV-2, only 3 of 45 gD-2-immunized mice survived an overwhelming challenge of the vagina or eyes with wild-type HSV-2 (MS strain). In contrast, 114 of 115 mice immunized with a live HSV-2 ICP0⁻ virus, 0ΔNLS, survived the same HSV-2 MS challenges. Likewise, 0ΔNLS-immunized mice shed an average 125-fold less HSV-2 MS challenge virus per vagina relative to gD-2-immunized mice. In vivo imaging demonstrated that a luciferase-expressing HSV-2 challenge virus failed to establish a detectable infection in 0ΔNLS-immunized mice, whereas the same virus readily infected naïve and gD-2-immunized mice. Collectively, these results suggest that a HSV-2 vaccine might be more likely to prevent genital herpes if it contained a live-attenuated HSV-2 virus rather than a single HSV-2 protein.

Immunization with herpes simplex virus 2 (HSV-2) genes plus inactivated HSV-2 is highly protective against acute and recurrent HSV-2 disease

To date, no vaccine that is safe and effective against herpes simplex virus 2 (HSV-2) disease has been licensed. In this study, we evaluated a DNA prime-formalin-inactivated-HSV-2 (FI-HSV2) boost vaccine approach in the guinea pig model of acute and recurrent HSV-2 genital disease. Five groups of guinea pigs were immunized and intravaginally challenged with HSV-2. Two groups were primed with plasmid DNAs encoding the secreted form of glycoprotein D2 (gD2t) together with two genes required for viral replication, either the helicase (UL5) and DNA polymerase (UL30) genes or the single-stranded DNA binding protein (UL29) and primase (UL52) genes. Both DNA-primed groups were boosted with FI-HSV2 formulated with monophosphoryl lipid A (MPL) and alum adjuvants. Two additional groups were primed with the empty backbone plasmid DNA (pVAX). These two groups were boosted with MPL and alum (MPL-alum) together with either formalin-inactivated mock HSV-2 (FI-Mock) or with FI-HSV2. The final group was immunized with gD2t protein in MPL-alum. After challenge, 0/9 animals in the group primed with UL5, UL30, and gD2t DNAs and all 10 animals in the mock-immunized control group (pVAX-FI-Mock) developed primary lesions. All mock controls developed recurrent lesions through day 100 postchallenge. Only 1 guinea pig in the group primed with pVAX DNA and boosted with FI-HSV2 (pVAX-FI-HSV2 group) and 2 guinea pigs in the group primed with UL5, UL30, and gD2t DNAs and boosted with FI-HSV2 (UL5, UL30, gD2t DNA-FI-HSV2 group) developed recurrent lesions. Strikingly, the UL5, UL30, gD2t DNA-FI-HSV2 group showed a 97% reduction in recurrent lesion days compared with the mock controls, had the highest reduction in days with recurrent disease, and contained the lowest mean HSV-2 DNA load in the dorsal root ganglia.

Effects of herpes simplex virus type 2 glycoprotein vaccines and CLDC adjuvant on genital herpes infection in the guinea pig

Genital herpes simplex virus (HSV) infections are common but results from vaccine trials with HSV-2 glycoprotein D (gD) have been disappointing. We therefore compared a similar HSV gD2 vaccine, to a further truncated gD2 vaccine, to a vaccine with gD2 plus gB2 and gH2/gL2 and to a vaccine with only gB2 and gH2/gL2 in a guinea pig model of genital herpes. All vaccines were administered with cationic liposome-DNA complexes (CLDC) as an adjuvant. All vaccines significantly decreased the severity of acute genital disease and vaginal virus replication compared to the placebo group. The majority of animals in all groups developed at least one episode of recurrent disease but the frequency of recurrent disease was significantly reduced by each vaccine compared to placebo. No vaccine was significantly more protective than gD2 alone for any of the parameters described above. No vaccine decreased recurrent virus shedding. When protection against acute infection of dorsal root ganglia and the spinal cord was evaluated all vaccines decreased the per cent of animal with detectable virus and the quantity of virus but again no vaccine was significantly more protective than another. Improvements in HSV-2 vaccines may require inclusion of more T cell targets, more potent adjuvants or live virus vaccines.

Antibody-profiling technologies for studying humoral responses to infectious agents

Analyses of humoral responses against different infectious agents are critical for infectious disease diagnostics, understanding pathogenic mechanisms, and the development and monitoring of vaccines. While ELISAs are often used to measure antibody responses to one or several targets, new antibody-profiling technologies, such as protein microarrays, can now evaluate antibody responses to hundreds, or even thousands, of recombinant antigens at one time. These large-scale studies have uncovered new antigenic targets, provided new insights into vaccine research and yielded an overview of immunoreactivity against almost the entire proteome of certain pathogens. However, solid-phase antigen arrays also have drawbacks that limit the type of information obtained, including suboptimal detection of conformational epitopes, high backgrounds due to impure antigens and a narrow dynamic range of detection. We have developed a solution-phase antibody-profiling technology, luciferase immunoprecipitation systems (LIPS), which harnesses light-emitting recombinant antigen fusion proteins to quantitatively measure patient antibody titers. Owing to the highly linear light output of the luciferase reporter, some antibodies can be detected without serum dilution in a dynamic range of detection often spanning seven orders of magnitude. When LIPS is applied iteratively with multiple target antigens, a high-definition antibody profile is obtained. Here, we discuss the application of these different antibody-profiling technologies and their associated limitations with particular emphasis on protein microarrays. We also describe LIPS in detail and discuss several clinically relevant uses of the technology. Together, these new technologies offer new tools for understanding humoral responses to known and emerging infectious agents.

Host responses to herpes simplex virus and herpes simplex virus vectors

Herpes simplex virus (HSV) is a well-known, ubiquitous pathogen of humans. Engineered mutants of HSV can also be exploited as vectors in gene therapy or for virotherapy of tumors. HSV has multiple abilities to evade and modulate the innate and adaptive responses of the host. The increasing knowledge on the mutual interactions of the invading HSV with the host defenses will contribute to our deeper understanding of the relationship between HSV and the host, and thereby lead to future development of more effective and specific HSV vectors for treatment of human diseases. The future advances of HSV vaccines and vaccine vectors are based on the knowlegde of the complex interplay between HSV and the host defenses.

HSV Recombinant Vectors for Gene Therapy

The very deep knowledge acquired on the genetics and molecular biology of herpes simplex virus (HSV), has allowed the development of potential replication-competent and replication-defective vectors for several applications in human healthcare. These include delivery and expression of human genes to cells of the nervous systems, selective destruction of cancer cells, prophylaxis against infection with HSV or other infectious diseases, and targeted infection to specific tissues or organs. Replication-defective recombinant vectors are non-toxic gene transfer tools that preserve most of the neurotropic features of wild type HSV-1, particularly the ability to express genes after having established latent infections, and are thus proficient candidates for therapeutic gene transfer settings in neurons. A replication-defective HSV vector for the treatment of pain has recently entered in phase 1 clinical trial. Replication-competent (oncolytic) vectors are becoming a suitable and powerful tool to eradicate brain tumours due to their ability to replicate and spread only within the tumour mass, and have reached phase II/III clinical trials in some cases. The progress in understanding the host immune response induced by the vector is also improving the use of HSV as a vaccine vector against both HSV infection and other pathogens. This review briefly summarizes the obstacle encountered in the delivery of HSV vectors and examines the various strategies developed or proposed to overcome such challenges.

HSV Recombinant Vectors for Gene Therapy

The very deep knowledge acquired on the genetics and molecular biology of herpes simplex virus (HSV), has allowed the development of potential replication-competent and replication-defective vectors for several applications in human healthcare. These include delivery and expression of human genes to cells of the nervous systems, selective destruction of cancer cells, prophylaxis against infection with HSV or other infectious diseases, and targeted infection to specific tissues or organs. Replication-defective recombinant vectors are non-toxic gene transfer tools that preserve most of the neurotropic features of wild type HSV-1, particularly the ability to express genes after having established latent infections, and are thus proficient candidates for therapeutic gene transfer settings in neurons. A replication-defective HSV vector for the treatment of pain has recently entered in phase 1 clinical trial. Replication-competent (oncolytic) vectors are becoming a suitable and powerful tool to eradicate brain tumours due to their ability to replicate and spread only within the tumour mass, and have reached phase II/III clinical trials in some cases. The progress in understanding the host immune response induced by the vector is also improving the use of HSV as a vaccine vector against both HSV infection and other pathogens. This review briefly summarizes the obstacle encountered in the delivery of HSV vectors and examines the various strategies developed or proposed to overcome such challenges.