Detailed characterization of T cell responses to herpes simplex virus-2 in immune seronegative persons

Characterization of Nasal Mucosal T Cells in Horses and Their Response to Equine Herpesvirus Type 1

Equine herpesvirus type 1 (EHV-1) enters through the upper respiratory tract (URT). Mucosal immunity at the URT is crucial in limiting viral infection and morbidity. Here, intranasal immune cells were collected from horses (n = 15) during an experimental EHV-1 infection. CD4+ and CD8+ T cells were the major intranasal cell populations before infection and increased significantly by day six and fourteen post-infection, respectively. Nasal mucosal T cells were further characterized in healthy horses. Compared to peripheral blood mononuclear cells (PBMC), mucosal CD8+ T-cell percentages were elevated, while CD4+ T-cell percentages were similar. A small population of CD4+CD8+ T cells was also recovered from mucosal samples. Within the URT tissue, CD4+ cells predominantly accumulated in the epithelial layer, while most CD8+ cells resided deeper in the mucosa or the submucosa below the basement membrane. In vitro stimulation of mucosal cells from healthy horses with (n = 5) or without (n = 5) peripheral T-cell immunity against EHV-1 induced IFN-γ production in nasal T cells upon polyclonal stimulation. However, after EHV-1 re-stimulation, mucosal T cells failed to respond with IFN-γ. This work provided the first characterization of mucosal T-cell phenotypes and functions in the URT of healthy horses and during EHV-1 infection.

Therapeutic vaccines for herpesviruses

Herpesviruses establish latent infections, and most reactivate frequently, resulting in symptoms and virus shedding in healthy individuals. In immunocompromised patients, reactivating virus can cause severe disease. Persistent EBV has been associated with several malignancies in both immunocompromised and nonimmunocompromised persons. Reactivation and shedding occur with most herpesviruses, despite potent virus-specific antibodies and T cell immunity as measured in the blood. The licensure of therapeutic vaccines to reduce zoster indicates that effective therapeutic vaccines for other herpesviruses should be feasible. However, varicella-zoster virus is different from other human herpesviruses in that it is generally only shed during varicella and zoster. Unlike prophylactic vaccines, in which the correlate of immunity is antibody function, T cell immunity is the correlate of immunity for the only effective therapeutic herpesvirus vaccine-zoster vaccine. While most studies of therapeutic vaccines have measured immunity in the blood, cellular immunity at the site of reactivation is likely critical for an effective therapeutic vaccine for certain viruses. This Review summarizes the status of therapeutic vaccines for herpes simplex virus, cytomegalovirus, and Epstein-Barr virus and proposes approaches for future development.

Cytometry profiling of ex vivo recall responses to Coxiella burnetii in previously naturally exposed individuals reveals long-term changes in both adaptive and innate immune cellular compartments

Introduction

Q fever, caused by the intracellular bacterium Coxiella burnetii, is considered an occupational and biodefense hazard and can result in debilitating long-term complications. While natural infection and vaccination induce humoral and cellular immune responses, the exact nature of cellular immune responses to C. burnetii is incompletely understood. The current study seeks to investigate more deeply the nature of long-term cellular recall responses in naturally exposed individuals by both cytokine release assessment and cytometry profiling.

Methods

Individuals exposed during the 2007-2010 Dutch Q fever outbreak were grouped in 2015, based on a C. burnetii-specific IFNγ release assay (IGRA), serological status, and self-reported clinical symptoms during initial infection, into asymptomatic IGRA-negative/seronegative controls, and three IGRA-positive groups (seronegative/asymptomatic; seropositive/asymptomatic and seropositive/symptomatic). Recall responses following in vitro re-stimulation with heat-inactivated C. burnetii in whole blood, were assessed in 2016/2017 by cytokine release assays (n=55) and flow cytometry (n=36), and in blood mononuclear cells by mass cytometry (n=36).

Results

Cytokine release analysis showed significantly elevated IL-2 responses in all seropositive individuals and elevated IL-1β responses in those recovered from symptomatic infection. Comparative flow cytometry analysis revealed significantly increased IFNγ, TNFα and IL-2 recall responses by CD4 T cells and higher IL-6 production by monocytes from symptomatic, IGRA-positive/seropositive individuals compared to controls. Mass cytometry profiling and unsupervised clustering analysis confirmed recall responses in seropositive individuals by two activated CD4 T cell subsets, one characterized by a strong Th1 cytokine profile (IFNγ+IL-2+TNFα+), and identified C. burnetii-specific activation of CD8 T cells in all IGRA-positive groups. Remarkably, increased C. burnetii-specific responses in IGRA-positive individuals were also observed in three innate cell subpopulations: one characterized by an IFNγ+IL-2+TNFα+ Th1 cytokine profile and lack of canonical marker expression, and two IL-1β-, IL-6- and IL-8-producing CD14+ monocyte subsets that could be the drivers of elevated secretion of innate cytokines in pre-exposed individuals.

Discussion

These data highlight that there are long-term increased responses to C. burnetii in both adaptive and innate cellular compartments, the latter being indicative of trained immunity. These findings warrant future studies into the protective role of these innate responses and may inform future Q fever vaccine design.

Can T Cells Abort SARS-CoV-2 and Other Viral Infections?

Despite the highly infectious nature of the SARS-CoV-2 virus, it is clear that some individuals with potential exposure, or even experimental challenge with the virus, resist developing a detectable infection. While a proportion of seronegative individuals will have completely avoided exposure to the virus, a growing body of evidence suggests a subset of individuals are exposed, but mediate rapid viral clearance before the infection is detected by PCR or seroconversion. This type of "abortive" infection likely represents a dead-end in transmission and precludes the possibility for development of disease. It is, therefore, a desirable outcome on exposure and a setting in which highly effective immunity can be studied. Here, we describe how early sampling of a new pandemic virus using sensitive immunoassays and a novel transcriptomic signature can identify abortive infections. Despite the challenges in identifying abortive infections, we highlight diverse lines of evidence supporting their occurrence. In particular, expansion of virus-specific T cells in seronegative individuals suggests abortive infections occur not only after exposure to SARS-CoV-2, but for other coronaviridae, and diverse viral infections of global health importance (e.g., HIV, HCV, HBV). We discuss unanswered questions related to abortive infection, such as: 'Are we just missing antibodies? Are T cells an epiphenomenon? What is the influence of the dose of viral inoculum?' Finally, we argue for a refinement of the current paradigm that T cells are only involved in clearing established infection; instead, we emphasise the importance of considering their role in terminating early viral replication by studying abortive infections.

Exposed seronegative: Cellular immune responses to SARS-CoV-2 in the absence of seroconversion

The factors determining whether infection will occur following exposure to SARS-CoV-2 remain elusive. Certain SARS-CoV-2-exposed individuals mount a specific T-cell response but fail to seroconvert, representing a population that may provide further clarity on the nature of infection susceptibility and correlates of protection against SARS-CoV-2. Exposed seronegative individuals have been reported in patients exposed to the blood-borne pathogens Human Immunodeficiency virus and Hepatitis C virus and the sexually transmitted viruses Hepatitis B virus and Herpes Simplex virus. By comparing the quality of seronegative T-cell responses to SARS-CoV-2 with seronegative cellular immunity to these highly divergent viruses, common patterns emerge that offer insights on the role of cellular immunity against infection. For both SARS-CoV-2 and Hepatitis C, T-cell responses in exposed seronegatives are consistently higher than in unexposed individuals, but lower than in infected, seropositive patients. Durability of T-cell responses to Hepatitis C is dependent upon repeated exposure to antigen - single exposures do not generate long-lived memory T-cells. Finally, exposure to SARS-CoV-2 induces varying degrees of immune activation, suggesting that exposed seronegative individuals represent points on a spectrum rather than a discrete group. Together, these findings paint a complex landscape of the nature of infection but provide clues as to what may be protective early on in SARS-CoV-2 disease course. Further research on this phenomenon, particularly through cohort studies, is warranted.

Antiviral T-Cell Frequencies in a Healthy Population: Reference Values for Evaluating Antiviral Immune Cell Profiles in Immunocompromised Patients

Viral infections and reactivations are major causes of morbidity and mortality after hematopoietic stem cell (HSCT) and solid organ transplantation (SOT) as well as in patients with immunodeficiencies. Latent herpesviruses (e.g., cytomegalovirus, Epstein-Barr virus, and human herpesvirus 6), lytic viruses (e.g., adenovirus), and polyomaviruses (e.g., BK virus, JC virus) can cause severe complications. Antiviral drugs form the mainstay of treatment for viral infections and reactivations after transplantation, but they have side effects and cannot achieve complete viral clearance without prior reconstitution of functional antiviral T-cell immunity. The aim of this study was to establish normal ranges for virus-specific T-cell (VST) frequencies in healthy donors. Such data are needed for better interpretation of VST frequencies observed in immunocompromised patients. Therefore, we measured the frequencies of VSTs against 23 viral protein-derived peptide pools from 11 clinically relevant human viruses in blood from healthy donors (n = 151). Specifically, we determined the VST frequencies by interferon-gamma enzyme-linked immunospot assay and classified their distribution according to age and gender to allow for a more specific evaluation and prediction of antiviral immune responses. The reference values established here provide an invaluable tool for immune response evaluation, intensity of therapeutic drugs and treatment decision-making in immunosuppressed patients. This data should make an important contribution to improving the assessment of immune responses in immunocompromised patients.

Herpes Labialis, Chlamydophila pneumoniae, Helicobacter pylori, and Cytomegalovirus Infections and Risk of Dementia: The Framingham Heart Study

BACKGROUND

An association between chronic infectious diseases and development of dementia has been suspected for decades, based on the finding of pathogens in postmortem brain tissue and on serological evidence. However, questions remain regarding confounders, reverse causality, and how accurate, reproducible and generalizable those findings are.

OBJECTIVE

Investigate whether exposure to Herpes simplex (manifested as herpes labialis), Chlamydophila pneumoniae (C. pneumoniae), Helicobacter pylori (H. pylori), and cytomegalovirus (CMV) modifies the risk of dementia in a populational cohort.

METHODS

Questionnaires regarding incidence of herpes infections were administered to Original Framingham Study participants (n = 2,632). Serologies for C. pneumoniae, H. pylori, and CMV were obtained in Original (n = 2,351) and Offspring cohort (n = 3,687) participants. Participants are under continuous dementia surveillance. Brain MRI and neuropsychological batteries were administered to Offspring participants from 1999-2005. The association between each infection and incident dementia was tested with Cox models. Linear models were used to investigate associations between MRI or neuropsychological parameters and serologies.

RESULTS

There was no association between infection serologies and dementia incidence, total brain volume, and white matter hyperintensities. Herpes labialis was associated with reduced 10-year dementia risk (HR 0.66, CI 0.46-0.97), but not for the duration of follow-up. H. pylori antibodies were associated with worse global cognition (β -0.14, CI -0.22, -0.05).

CONCLUSION

We found no association between measures of chronic infection and incident dementia, except for a reduction in 10-year dementia risk for patients with herpes labialis. This unexpected result requires confirmation and further characterization, concerning antiviral treatment effects and capture of episodes.

SARS-CoV-2-specific T cells are rapidly expanded for therapeutic use and target conserved regions of the membrane protein

T-cell responses to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) have been described in recovered patients, and may be important for immunity following infection and vaccination as well as for the development of an adoptive immunotherapy for the treatment of immunocompromised individuals. In this report, we demonstrate that SARS-CoV-2-specific T cells can be expanded from convalescent donors and recognize immunodominant viral epitopes in conserved regions of membrane, spike, and nucleocapsid. Following in vitro expansion using a good manufacturing practice-compliant methodology (designed to allow the rapid translation of this novel SARS-CoV-2 T-cell therapy to the clinic), membrane, spike, and nucleocapsid peptides elicited interferon-γ production, in 27 (59%), 12 (26%), and 10 (22%) convalescent donors (respectively), as well as in 2 of 15 unexposed controls. We identified multiple polyfunctional CD4-restricted T-cell epitopes within a highly conserved region of membrane protein, which induced polyfunctional T-cell responses, which may be critical for the development of effective vaccine and T-cell therapies. Hence, our study shows that SARS-CoV-2 directed T-cell immunotherapy targeting structural proteins, most importantly membrane protein, should be feasible for the prevention or early treatment of SARS-CoV-2 infection in immunocompromised patients with blood disorders or after bone marrow transplantation to achieve antiviral control while mitigating uncontrolled inflammation.

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.

Frequent Recurrences of Genital Herpes Are Associated with Enhanced Systemic HSV-Specific T Cell Response

Objectives

Genital herpes simplex virus (HSV) infection is controlled by HSV-specific T cells in the genital tract, and the role of systemic T cell responses is not fully understood. Thus, we analysed T cell responses in patients with recurrent genital herpes (GH).

Methods

T cell responses to HSV-1 and HSV-2 native antigens and the expression of HLA-DR and CD38 molecules on circulating CD8+ T cells were analysed in adults with high frequency of GH recurrences (19 patients) and low frequency of GH recurrences (7 patients) and 12 HSV-2 seronegative healthy controls. The study utilized the interferon-γ Elispot assay for measurement of spot-forming cells (SFC) after ex vivo stimulation with HSV antigens and flow cytometry for analysis of the expression of activation markers in unstimulated T cells.

Results

The patients with high frequency of GH recurrences (mean number of recurrences of 13.3 per year) had significantly enhanced HSV-specific T cell responses than the HSV-2 seronegative healthy controls. Moreover, a trend of higher numbers of SFC was observed in these patients when compared with those with low frequency of GH recurrences (mean number of recurrences of 3.3 per year). Additionally, no differences in CD38 and HLA-DR expression on circulating CD8+ T cells were found among the study groups.

Conclusions

Frequency of GH recurrences positively correlates with high numbers of systemic HSV-specific T cells.

The controversial natural history of oral herpes simplex virus type 1 infection

The natural history of oral herpes simplex virus type 1 (HSV-1) infection in the immunocompetent host is complex and rich in controversial phenomena, namely the role of unapparent transmission in primary infection acquisition, the high frequency of asymptomatic primary and recurrent infections, the lack of immunogenicity of HSV-1 internalized in the soma (cell body) of the sensory neurons of the trigeminal ganglion, the lytic activity of HSV-1 in the soma of neurons that is inhibited in the sensory neurons of the trigeminal ganglion and often uncontrolled in the other neurons, the role of keratin in promoting the development of recurrence episodes in immunocompetent hosts, the virus-host Nash equilibrium, the paradoxical HSV-1-seronegative individuals who shed HSV-1 through saliva, the limited efficacy of anti-HSV vaccines, and why the oral route of infection is the least likely to produce severe complications. The natural history of oral HSV-1 infection is also a history of symbiosis between humans and virus that may switch from mutualism to parasitism and vice versa. This balance is typical of microorganisms that are highly coevolved with humans, and its knowledge is essential to oral healthcare providers to perform adequate diagnosis and provide proper individual-based HSV-1 infection therapy.

Herpes simplex virus type 1 and Alzheimer's disease: link and potential impact on treatment

Introduction: Alzheimer's disease (AD), the most common form of dementia worldwide, is a multifactorial disease with a still unknown etiology. Herpes simplex virus 1 (HSV-1) has long been suspected to be one of the factors involved in the pathogenesis of the disease. Areas covered: We review the literature focusing on viral characteristics of HSV-1, the mechanisms this virus uses to infect neural cells, its interaction with the host immune system and genetic background and summarizes results and research that support the hypothesis of an association between AD and HSV-1. The possible usefulness of virus-directed pharmaceutical approaches as potential treatments for AD will be discussed as well. Expert opinion: We highlight crucial aspects that must be addressed to clarify the possible role of HSV-1 in the pathogenesis of the disease, and to allow the design of new therapeutical approaches for AD.

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.

Enrichment of herpes simplex virus type 2 (HSV-2) reactive mucosal T cells in the human female genital tract

Local mucosal cellular immunity is critical in providing protection from HSV-2. To characterize and quantify HSV-2-reactive mucosal T cells, lymphocytes were isolated from endocervical cytobrush and biopsy specimens from 17 HSV-2-infected women and examined ex vivo for the expression of markers associated with maturation and tissue residency and for functional T-cell responses to HSV-2. Compared with their circulating counterparts, cervix-derived CD4+ and CD8+ T cells were predominantly effector memory T cells (CCR7-/CD45RA-) and the majority expressed CD69, a marker of tissue residency. Co-expression of CD103, another marker of tissue residency, was highest on cervix-derived CD8+ T cells. Functional HSV-2 reactive CD4+ and CD8+ T-cell responses were detected in cervical samples and a median of 17% co-expressed CD103. HSV-2-reactive CD4+ T cells co-expressed IL-2 and were significantly enriched in the cervix compared with blood. This first direct ex vivo documentation of local enrichment of HSV-2-reactive T cells in the human female genital mucosa is consistent with the presence of antigen-specific tissue-resident memory T cells. Ex vivo analysis of these T cells may uncover tissue-specific mechanisms of local control of HSV-2 to assist the development of vaccine strategies that target protective T cells to sites of HSV-2 infection.

An Interleukin 12 Adjuvanted Herpes Simplex Virus 2 DNA Vaccine Is More Protective Than a Glycoprotein D Subunit Vaccine in a High-Dose Murine Challenge Model

Vaccination is a proven intervention against human viral diseases; however, success against Herpes Simplex Virus 2 (HSV-2) remains elusive. Most HSV-2 vaccines tested in humans to date contained just one or two immunogens, such as the virion attachment receptor glycoprotein D (gD) and/or the envelope fusion protein, glycoprotein B (gB). At least three factors may have contributed to the failures of subunit-based HSV-2 vaccines. First, immune responses directed against one or two viral antigens may lack sufficient antigenic breadth for efficacy. Second, the antibody responses elicited by these vaccines may have lacked necessary Fc-mediated effector functions. Third, these subunit vaccines may not have generated necessary protective cellular immune responses. We hypothesized that a polyvalent combination of HSV-2 antigens expressed from a DNA vaccine with an adjuvant that polarizes immune responses toward a T helper 1 (Th1) phenotype would compose a more effective vaccine. We demonstrate that delivery of DNA expressing full-length HSV-2 glycoprotein immunogens by electroporation with the adjuvant interleukin 12 (IL-12) generates substantially greater protection against a high-dose HSV-2 vaginal challenge than a recombinant gD subunit vaccine adjuvanted with alum and monophosphoryl lipid A (MPL). Our results further show that DNA vaccines targeting optimal combinations of surface glycoproteins provide better protection than gD alone and provide similar survival benefits and disease symptom reductions compared with a potent live attenuated HSV-2 0ΔNLS vaccine, but that mice vaccinated with HSV-2 0ΔNLS clear the virus much faster. Together, our data indicate that adjuvanted multivalent DNA vaccines hold promise for an effective HSV-2 vaccine, but that further improvements may be required.

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.

Extensive CD4 and CD8 T Cell Cross-Reactivity between Alphaherpesviruses

The Alphaherpesvirinae subfamily includes HSV types 1 and 2 and the sequence-divergent pathogen varicella zoster virus (VZV). T cells, controlled by TCR and HLA molecules that tolerate limited epitope amino acid variation, might cross-react between these microbes. We show that memory PBMC expansion with either HSV or VZV enriches for CD4 T cell lines that recognize the other agent at the whole-virus, protein, and peptide levels, consistent with bidirectional cross-reactivity. HSV-specific CD4 T cells recovered from HSV-seronegative persons can be explained, in part, by such VZV cross-reactivity. HSV-1-reactive CD8 T cells also cross-react with VZV-infected cells, full-length VZV proteins, and VZV peptides, as well as kill VZV-infected dermal fibroblasts. Mono- and cross-reactive CD8 T cells use distinct TCRB CDR3 sequences. Cross-reactivity to VZV is reconstituted by cloning and expressing TCRA/TCRB receptors from T cells that are initially isolated using HSV reagents. Overall, we define 13 novel CD4 and CD8 HSV-VZV cross-reactive epitopes and strongly imply additional cross-reactive peptide sets. Viral proteins can harbor both CD4 and CD8 HSV/VZV cross-reactive epitopes. Quantitative estimates of HSV/VZV cross-reactivity for both CD4 and CD8 T cells vary from 10 to 50%. Based on these findings, we hypothesize that host herpesvirus immune history may influence the pathogenesis and clinical outcome of subsequent infections or vaccinations for related pathogens and that cross-reactive epitopes and TCRs may be useful for multi-alphaherpesvirus vaccine design and adoptive cellular therapy.

Herpes Simplex Vaccines: Prospects of Live-attenuated HSV Vaccines to Combat Genital and Ocular infections

Herpes simplex virus type-1 (HSV-1) and its closely related type-2 (HSV-2) viruses cause important clinical manifestations in humans including acute ocular disease and genital infections. These viruses establish latency in the trigeminal ganglionic and dorsal root neurons, respectively. Both viruses are widespread among humans and can frequently reactivate from latency causing disease. Currently, there are no vaccines available against herpes simplex viral infections. However, a number of promising vaccine approaches are being explored in pre-clinical investigations with few progressing to early phase clinical trials. Consensus research findings suggest that robust humoral and cellular immune responses may partially control the frequency of reactivation episodes and reduce clinical symptoms. Live-attenuated viral vaccines have long been considered as a viable option for generating robust and protective immune responses against viral pathogens. Varicella zoster virus (VZV) belongs to the same alphaherpesvirus subfamily with herpes simplex viruses. A live-attenuated VZV vaccine has been extensively used in a prophylactic and therapeutic approach to combat primary and recurrent VZV infection indicating that a similar vaccine approach may be feasible for HSVs. In this review, we summarize pre-clinical approaches to HSV vaccine development and current efforts to test certain vaccine approaches in human clinical trials. Also, we discuss the potential advantages of using a safe, live-attenuated HSV-1 vaccine strain to protect against both HSV-1 and HSV-2 infections.

A Dual-Modality Herpes Simplex Virus 2 Vaccine for Preventing Genital Herpes by Using Glycoprotein C and D Subunit Antigens To Induce Potent Antibody Responses and Adenovirus Vectors Containing Capsid and Tegument Proteins as T Cell Immunogens

We evaluated a genital herpes prophylactic vaccine containing herpes simplex virus 2 (HSV-2) glycoproteins C (gC2) and D (gD2) to stimulate humoral immunity and UL19 (capsid protein VP5) and UL47 (tegument protein VP13/14) as T cell immunogens. The HSV-2 gC2 and gD2 proteins were expressed in baculovirus, while the UL19 and UL47 genes were expressed from replication-defective adenovirus vectors. Adenovirus vectors containing UL19 and UL47 stimulated human and murine CD4(+) and CD8(+) T cell responses. Guinea pigs were either (i) mock immunized; (ii) immunized with gC2/gD2, with CpG and alum as adjuvants; (iii) immunized with the UL19/UL47 adenovirus vectors; or (iv) immunized with the combination of gC2/gD2-CpG/alum and the UL19/UL47 adenovirus vectors. Immunization with gC2/gD2 produced potent neutralizing antibodies, while UL19 and UL47 also stimulated antibody responses. After intravaginal HSV-2 challenge, the mock and UL19/UL47 adenovirus groups developed severe acute disease, while 2/8 animals in the gC2/gD2-only group and none in the combined group developed acute disease. No animals in the gC2/gD2 or combined group developed recurrent disease; however, 5/8 animals in each group had subclinical shedding of HSV-2 DNA, on 15/168 days for the gC2/gD2 group and 13/168 days for the combined group. Lumbosacral dorsal root ganglia were positive for HSV-2 DNA and latency-associated transcripts for 5/8 animals in the gC2/gD2 group and 2/8 animals in the combined group. None of the differences comparing the gC2/gD2-only group and the combined group were statistically significant. Therefore, adding the T cell immunogens UL19 and UL47 to the gC2/gD2 vaccine did not significantly reduce genital disease and vaginal HSV-2 DNA shedding compared with the excellent protection provided by gC2/gD2 in the guinea pig model.

IMPORTANCE

HSV-2 infection is a common cause of genital ulcer disease and a significant public health concern. Genital herpes increases the risk of transmission and acquisition of HIV-1 infection 3- to 4-fold. A herpes vaccine that prevents genital lesions and asymptomatic genital shedding will have a substantial impact on two epidemics, i.e., both the HSV-2 and HIV-1 epidemics. We previously reported that a vaccine containing HSV-2 glycoprotein C (gC2) and glycoprotein D (gD2) reduced genital lesions and asymptomatic HSV-2 genital shedding in guinea pigs, yet the protection was not complete. We evaluated whether adding the T cell immunogens UL19 (capsid protein VP5) and UL47 (tegument protein VP13/14) would enhance the protection provided by the gC2/gD2 vaccine, which produces potent antibody responses. Here we report the efficacy of a combination vaccine containing gC2/gD2 and UL19/UL47 for prevention of genital disease, vaginal shedding of HSV-2 DNA, and latent infection of dorsal root ganglia in guinea pigs.

Discordant humoral and cellular immune responses to Cytomegalovirus (CMV) in glioblastoma patients whose tumors are positive for CMV

Background. Glioblastoma (GBM) is the most common malignant brain tumor in adults and is nearly always fatal. Emerging evidence suggests that human Cytomegalovirus (HCMV) is present in 90-100% of GBMs and that add-on antiviral treatment for HCMV show promise to improve survival. Methods. In a randomized, placebo-controlled trial of valganciclovir in 42 GBM patients, blood samples were collected for analyses of HCMV DNA, RNA, reactivity against HCMV peptides, IgG, and IgM at baseline and at 3, 12, and 24 weeks of treatment. Results. All 42 tumors were positive for HCMV protein. All patients examined had at least one blood sample positive for HCMV DNA, 63% were HCMV RNA positive, and 21% were IgM positive. However, 29% of GBM patients were IgG negative for HCMV. Five of these samples were positive in an enzyme-linked immunosorbent assay (ELISA) that used antigens derived from a clinical isolate. Blood T cells from 11 of 13 (85%) HCMV IgG-negative GBM patients reacted against HCMV peptides. Valganciclovir did not affect IgG titers, DNA, or RNA levels of the HCMV immediate early (HCMV IE) gene in blood. Conclusion. In GBM patients, HCMV activity is higher than in healthy controls and serology is a poor test to define previous or active HCMV infection in these patients.

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.

Herpes simplex virus 2 (HSV-2) infected cell proteins are among the most dominant antigens of a live-attenuated HSV-2 vaccine

Virion glycoproteins such as glycoprotein D (gD) are believed to be the dominant antigens of herpes simplex virus 2 (HSV-2). We have observed that mice immunized with a live HSV-2 ICP0^- mutant virus, HSV-2 0ΔNLS, are 10 to 100 times better protected against genital herpes than mice immunized with a HSV-2 gD subunit vaccine (PLoS ONE 6:e17748). In light of these results, we sought to determine which viral proteins were the dominant antibody-generators (antigens) of the live HSV-2 0ΔNLS vaccine. Western blot analyses indicated the live HSV-2 0ΔNLS vaccine elicited an IgG antibody response against 9 or more viral proteins. Many antibodies were directed against infected-cell proteins of >100 kDa in size, and only 10 ± 5% of antibodies were directed against gD. Immunoprecipitation (IP) of total HSV-2 antigen with 0ΔNLS antiserum pulled down 19 viral proteins. Mass spectrometry suggested 44% of immunoprecipitated viral peptides were derived from two HSV-2 infected cells proteins, RR-1 and ICP8, whereas only 14% of immunoprecipitated peptides were derived from HSV-2’s thirteen glycoproteins. Collectively, the results suggest the immune response to the live HSV-2 0ΔNLS vaccine includes antibodies specific for infected cell proteins, capsid proteins, tegument proteins, and glycoproteins. This increased breadth of antibody-generating proteins may contribute to the live HSV-2 vaccine’s capacity to elicit superior protection against genital herpes relative to a gD subunit vaccine.

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

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

Persistence of mucosal T-cell responses to herpes simplex virus type 2 in the female genital tract

Relatively little is known about the human T-cell response to herpes simplex virus type 2 (HSV-2) in the female genital tract, a major site of heterosexual HSV-2 acquisition, transmission, and reactivation. In order to understand the role of local mucosal immunity in HSV-2 infection, T-cell lines were expanded from serial cervical cytobrush samples from 30 HSV-2-infected women and examined for reactivity to HSV-2. Approximately 3% of the CD3+ T cells isolated from the cervix were HSV-2 specific and of these, a median of 91.3% were CD4+, whereas a median of 3.9% were CD8+. HSV-2-specific CD4+ T cells expanded from the cervix were not only more frequent than CD8+ T cells but also exhibited greater breadth in terms of antigenic reactivity. T cells directed at the same HSV-2 protein were often detected in serial cervical cytobrush samples and in blood. Thus, broad and persistent mucosal T-cell responses to HSV-2 were detected in the female genital tract of HSV-2+ women suggesting that these cells are resident at the site of HSV-2 infection. Understanding the role of these T cells at this biologically relevant site will be central to the elucidation of adaptive immune mechanisms involved in controlling HSV-2 disease.

The challenges and opportunities for the development of a T-cell epitope-based herpes simplex vaccine

Herpes simplex virus type 1 and type 2 (HSV-1 & HSV-2) infections have been prevalent since the ancient Greek times. To this day, they still affect a staggering number of over a billion individuals worldwide. HSV-1 infections are predominant than HSV-2 infections and cause potentially blinding ocular herpes, oro-facial herpes and encephalitis. HSV-2 infections cause painful genital herpes, encephalitis, and death in newborns. While prophylactic and therapeutic HSV vaccines remain urgently needed for centuries, their development has been difficult. During the most recent National Institute of Health (NIH) workshop titled "Next Generation Herpes Simplex Virus Vaccines: The Challenges and Opportunities", basic researchers, funding agencies, and pharmaceutical representatives gathered: (i) to assess the status of herpes vaccine research; and (ii) to identify the gaps and propose alternative approaches in developing a safe and efficient herpes vaccine. One "common denominator" among previously failed clinical herpes vaccine trials is that they either used a whole virus or a whole viral protein, which contain both "pathogenic symptomatic" and "protective asymptomatic" antigens and epitopes. In this report, we continue to advocate developing "asymptomatic" epitope-based sub-unit vaccine strategies that selectively incorporate "protective asymptomatic" epitopes which: (i) are exclusively recognized by effector memory CD4(+) and CD8(+) T cells (TEM cells) from "naturally" protected seropositive asymptomatic individuals; and (ii) protect human leukocyte antigen (HLA) transgenic animal models of ocular and genital herpes. We review the role of animal models in herpes vaccine development and discuss their current status, challenges, and prospects.

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

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

Identification of novel virus-specific antigens by CD4⁺ and CD8⁺ T cells from asymptomatic HSV-2 seropositive and seronegative donors

Reactivation of latent herpes simplex virus 2 (HSV-2) infections can be characterized by episodic recurrent genital lesions and/or viral shedding. We hypothesize that infected (HSV-2(pos)) asymptomatic individuals have acquired T cell responses to specific HSV-2 antigen(s) that may be an important factor in controlling their recurrent disease symptoms. Our proteomic screening technology, ATLAS, was used to characterize the antigenic repertoire of T cell responses in infected (HSV-2(pos)) and virus-exposed seronegative (HSV-2(neg)) subjects. T cell responses, determined by IFN-γ secretion, were generated to gL, UL2, UL11, UL21, ICP4, ICP0, ICP47 and UL40 with greater magnitude and/or frequency among cohorts of exposed HSV-2(neg) or asymptomatic HSV-2(pos) individuals, compared to symptomatic recurrent HSV-2(pos) subjects. T cell antigens recognized preferentially among individuals who are resistant to infection or who are infected and have mild or no clinical disease may provide new targets for the design of vaccines aimed at treating and/or preventing HSV-2 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.

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

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

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.

Heterogeneity and breadth of host antibody response to KSHV infection demonstrated by systematic analysis of the KSHV proteome

The Kaposi sarcoma associated herpesvirus (KSHV) genome encodes more than 85 open reading frames (ORFs). Serological evaluation of KSHV infection now generally relies on reactivity to just one latent and/or one lytic protein (commonly ORF73 and K8.1). Most of the other polypeptides encoded by the virus have unknown antigenic profiles. We have systematically expressed and purified products from 72 KSHV ORFs in recombinant systems and analyzed seroreactivity in US patients with KSHV-associated malignancies, and US blood donors (low KSHV seroprevalence population). We identified several KSHV proteins (ORF38, ORF61, ORF59 and K5) that elicited significant responses in individuals with KSHV-associated diseases. In these patients, patterns of reactivity were heterogeneous; however, HIV infection appeared to be associated with breadth and intensity of serological responses. Improved antigenic characterization of additional ORFs may increase the sensitivity of serologic assays, lead to more rapid progresses in understanding immune responses to KSHV, and allow for better comprehension of the natural history of KSHV infection. To this end, we have developed a bead-based multiplex assay detecting antibodies to six KSHV antigens.

Enhanced and efficient detection of virus-driven cytokine expression by human NK and T cells

Cutting edge immune monitoring techniques increasingly measure multiple functional outputs for various cell types, such as intracellular cytokine staining (ICS) assays that measure cytokines expressed by T cells. To date, however, there is no precise method to measure virus-specific cytokine production by both T cells as well as NK cells in the same well, which is important to a greater extent given recent identification of NK cells expressing a memory phenotype. This study describes an adaptable and efficient ICS assay platform that can be used to detect antigen-driven cytokine production by human T cells and NK cells, termed "viral ICS". Importantly, this assay uses limited amount of cryopreserved PBMCs along with autologous heat-inactivated serum, thereby allowing for this assay to be performed when sample is scarce as well as geographically distant from the laboratory. Compared to a standard ICS assay that detects antigen-specific T cell cytokine expression alone, the viral ICS assay is comparable in terms of both HIV-specific CD4 and CD8T cell cytokine response rates and magnitude of response, with the added advantage of ability to detect virus-specific NK cell responses.

Pan-HSV-2 IgG antibody in vaccinated mice and guinea pigs correlates with protection against herpes simplex virus 2

We lack a correlate of immunity to herpes simplex virus 2 (HSV-2) that may be used to differentiate whether a HSV-2 vaccine elicits robust or anemic protection against genital herpes. This gap in knowledge is often attributed to a failure to measure the correct component of the adaptive immune response to HSV-2. However, efforts to identify a correlate of immunity have focused on subunit vaccines that contain less than 3% of HSV-2's 40,000-amino-acid proteome. We were interested to determine if a correlate of immunity might be more readily identified if 1. animals were immunized with a polyvalent immunogen such as a live virus and/or 2. the magnitude of the vaccine-induced immune response was gauged in terms of the IgG antibody response to all of HSV-2's antigens (pan-HSV-2 IgG). Pre-challenge pan-HSV-2 IgG levels and protection against HSV-2 were compared in mice and/or guinea pigs immunized with a gD-2 subunit vaccine, wild-type HSV-2, or one of several attenuated HSV-2 ICP0⁻ viruses (0Δ254, 0Δ810, 0ΔRING, or 0ΔNLS). These six HSV-2 immunogens elicited a wide range of pan-HSV-2 IgG levels spanning an ∼500-fold range. For 5 of the 6 immunogens tested, pre-challenge levels of pan-HSV-2 IgG quantitatively correlated with reductions in HSV-2 challenge virus shedding and increased survival frequency following HSV-2 challenge. Collectively, the results suggest that pan-HSV-2 IgG levels may provide a simple and useful screening tool for evaluating the potential of a HSV-2 vaccine candidate to elicit protection against HSV-2 genital herpes.

Varicella zoster vaccines and their implications for development of HSV vaccines

Live attenuated vaccines to prevent varicella and zoster have been available in the US for the past 17 years, with a resultant dramatic decrease in varicella incidence and a predicted future decrease in the incidence of zoster. The pathogenesis and immune responses to varicella zoster virus (VZV) as well as the safety and effectiveness of VZV vaccines are reviewed. The lack of sterilizing immunity provided by VZV vaccines has not prevented them from being safe and effective. Virological and pathological information concerning parallels and differences between VZV and herpes simplex virus (HSV) are highlighted. Although VZV and HSV are distinct pathogens, they appear to have similarities in target organs and immunity that provide an expectation of a high likelihood for the success of vaccination against HSV, and predicted to be similar to that of VZV.

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.

CD8+ T Lymphocyte Epitopes From The Herpes Simplex Virus Type 2 ICP27, VP22 and VP13/14 Proteins To Facilitate Vaccine Design And Characterization

CD8+ T cells have the potential to control HSV-2 infection. However, limited information has been available on CD8+ T cell epitopes or the functionality of antigen specific T cells during infection or following immunization with experimental vaccines. Peptide panels from HSV-2 proteins ICP27, VP22 and VP13/14 were selected from in silico predictions of binding to human HLA-A*0201 and mouse H-2Kd, Ld and Dd molecules. Nine previously uncharacterized CD8+ T cell epitopes were identified from HSV-2 infected BALB/c mice. HSV-2 specific peptide sequences stabilized HLA-A*02 surface expression with intermediate or high affinity binding. Peptide specific CD8+ human T cell lines from peripheral blood lymphocytes were generated from a HLA-A*02+ donor. High frequencies of peptide specific CD8+ T cell responses were elicited in mice by DNA vaccination with ICP27, VP22 and VP13/14, as demonstrated by CD107a mobilization. Vaccine driven T cell responses displayed a more focused immune response than those induced by viral infection. Furthermore, vaccination with ICP27 reduced viral shedding and reduced the clinical impact of disease. In conclusion, this study describes novel HSV-2 epitopes eliciting strong CD8+ T cell responses that may facilitate epitope based vaccine design and aid immunomonitoring of antigen specific T cell frequencies in preclinical and clinical settings.

CD4 T-cell memory responses to viral infections of humans show pronounced immunodominance independent of duration or viral persistence

Little is known concerning immunodominance within the CD4 T-cell response to viral infections and its persistence into long-term memory. We tested CD4 T-cell reactivity against each viral protein in persons immunized with vaccinia virus (VV), either recently or more than 40 years ago, as a model self-limited viral infection. Similar tests were done with persons with herpes simplex virus 1 (HSV-1) infection as a model chronic infection. We used an indirect method capable of counting the CD4 T cells in blood reactive with each individual viral protein. Each person had a clear CD4 T-cell dominance hierarchy. The top four open reading frames accounted for about 40% of CD4 virus-specific T cells. Early and long-term memory CD4 T-cell responses to vaccinia virus were mathematically indistinguishable for antigen breadth and immunodominance. Despite the chronic intermittent presence of HSV-1 antigen, the CD4 T-cell dominance and diversity patterns for HSV-1 were identical to those observed for vaccinia virus. The immunodominant CD4 T-cell antigens included both long proteins abundantly present in virions and shorter, nonstructural proteins. Limited epitope level and direct ex vivo data were also consistent with pronounced CD4 T-cell immunodominance. We conclude that human memory CD4 T-cell responses show a pattern of pronounced immunodominance for both chronic and self-limited viral infections and that this pattern can persist over several decades in the absence of antigen.

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.

The efficacy of HSV-2 vaccines based on gD and gB is enhanced by the addition of ICP27

DNA vaccines expressing HSV-2 gD, gB, ICP27, VP22 and VP13/14 were shown to be immunogenic in mice; gD and gB elicited neutralising antibody, and all five antigens induced T cell responses measured by IFNγ ELISPOT. In murine HSV-2 challenge studies, gD and gB provided moderate to high levels of protection while ICP27 provided a lower level of protection depending on the model (intravaginal or intranasal) and the challenge dose. Combining vaccines expressing gB or gD with vaccines expressing ICP27 provided greater protection than any antigen alone. We conclude that the addition of ICP27 to enhance the anti-viral T cell response can improve the efficacy of gD- and gB-based vaccines.

Immunology in the Clinic Review Series; focus on host responses: T cell responses to herpes simplex viruses

Herpes virus infections are chronic and co-exist with acquired immune responses that generally prevent severe damage to the host, while allowing periodic shedding of virus and maintenance of its transmission in the community. Herpes simplex viruses type 1 and 2 (HSV-1, HSV-2) are typical in this regard and are representative of the viral subfamily Alphaherpesvirinae, which has a tropism for neuronal and epithelial cells. This review will emphasize recent progress in decoding the physiologically important CD8(+) and CD4(+) T cell responses to HSV in humans. The expanding data set is discussed in the context of the search for an effective HSV vaccine as therapy for existing infections and to prevent new infections.

Preventing sexually transmitted infections: back to basics

Sexually transmitted infections (STIs) have plagued humans for millennia and can result in chronic disease, pregnancy complications, infertility, and even death. Recent technological advances have led to a better understanding of the causative agents for these infections as well as aspects of their pathogenesis that might represent novel therapeutic targets. The articles in this Review Series provide excellent updates on the recent advances in understanding of the pathogenesis of some very important and persistent STIs and discuss the importance of considering each pathogen in the broader context of the environment of the individual who it infects.

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.

T-helper cell-mediated proliferation and cytokine responses against recombinant Merkel cell polyomavirus-like particles

The newly discovered Merkel Cell Polyomavirus (MCPyV) resides in approximately 80% of Merkel cell carcinomas (MCC). Causal role of MCPyV for this rare and aggressive skin cancer is suggested by monoclonal integration and truncation of large T (LT) viral antigen in MCC cells. The mutated MCPyV has recently been found in highly purified leukemic cells from patients with chronic lymphocytic leukemia (CLL), suggesting a pathogenic role also in CLL. About 50-80% of adults display MCPyV-specific antibodies. The humoral immunity does not protect against the development of MCC, as neutralizing MCPyV antibodies occur in higher levels among MCC patients than healthy controls. Impaired T-cell immunity has been linked with aggressive MCC behavior. Therefore, cellular immunity appears to be important in MCPyV infection surveillance. In order to elucidate the role of MCPyV-specific Th-cell immunity, peripheral blood mononuclear cells (PBMC) of healthy adults were stimulated with MCPyV VP1 virus-like particles (VLPs), using human bocavirus (HBoV) VLPs and Candida albicans antigen as positive controls. Proliferation, IFN-γ, IL-13 and IL-10 responses were examined in 15 MCPyV-seropositive and 15 seronegative volunteers. With the MCPyV antigen, significantly stronger Th-cell responses were found in MCPyV-seropositive than MCPyV-seronegative subjects, whereas with the control antigens, the responses were statistically similar. The most readily detectable cytokine was IFN-γ. The MCPyV antigen tended to induce stronger IFN-γ responses than HBoV VLP antigen. Taken together, MCPyV-specific Th-cells elicit vigorous IFN-γ responses. IFN-γ being a cytokine with major antiviral and tumor suppressing functions, Th-cells are suggested to be important mediators of MCPyV-specific immune surveillance.

Safety and immunogenicity of long HSV-2 peptides complexed with rhHsc70 in HSV-2 seropositive persons

HSV-2, the primary causative agent of genital herpes, establishes latency in sensory ganglia and reactivates causing recurrent lesions and viral shedding. Induction or expansion of CD4(+) and CD8(+) T cell responses are expected to be important for a successful therapeutic vaccine against HSV-2. A candidate vaccine consisting of 32 synthetic 35mer HSV-2 peptides non-covalently complexed with recombinant human Hsc70 protein (named HerpV, formerly AG-707) was tested for safety and immunogenicity in a Phase I study. These peptides are derived from 22 HSV-2 proteins representative of all phases of viral replication. Thirty-five HSV-2 infected participants were randomized and treated in one of four groups: HerpV+QS-21 (saponin adjuvant), HerpV, QS-21, or vehicle. The vaccine was well tolerated and safe. All seven participants with evaluable samples who were administered HerpV with QS-21 demonstrated a statistically significant CD4(+) T cell response to HSV-2 antigens, and the majority of such participants demonstrated a statistically significant CD8(+) T cell response as well. To our knowledge, this is the first candidate vaccine against HSV-2 to demonstrate a broad CD4(+) and CD8(+) T cell response in HSV-2(+) participants, and the first HSP-based vaccine to show immune responses against viral antigens in humans.

Single and combination herpes simplex virus type 2 glycoprotein vaccines adjuvanted with CpG oligodeoxynucleotides or monophosphoryl lipid A exhibit differential immunity that is not correlated to protection in animal models

Despite several attempts to develop an effective prophylactic vaccine for HSV-2, all have failed to show efficacy in the clinic. The most recent of these failures was the GlaxoSmithKline (GSK) subunit vaccine based on the glycoprotein gD with the adjuvant monophosphoryl lipid A (MPL). In a phase 3 clinical trial, this vaccine failed to protect from HSV-2 disease, even though good neutralizing antibody responses were elicited. We aimed to develop a superior, novel HSV-2 vaccine containing either gD or gB alone or in combination, together with the potent adjuvant CpG oligodeoxynucleotides (CPG). The immunogenic properties of these vaccines were compared in mice. We show that gB/CPG/alum elicited a neutralizing antibody response similar to that elicited by gD/CPG/alum vaccine but a significantly greater gamma interferon (IFN-γ) T cell response. Furthermore, the combined gB-gD/CPG/alum vaccine elicited significantly greater neutralizing antibody and T cell responses than gD/MPL/alum. The efficacies of these candidate vaccines were compared in the mouse and guinea pig disease models, including a novel male guinea pig genital disease model. These studies demonstrated that increased immune response did not correlate to improved protection. First, despite a lower IFN-γ T cell response, the gD/CPG/alum vaccine was more effective than gB/CPG/alum in mice. Furthermore, the gB-gD/CPG/alum vaccine was no more effective than gD/MPL/alum in mice or male guinea pigs. We conclude that difficulties in correlating immune responses to efficacy in animal models will act as a deterrent to researchers attempting to develop effective HSV vaccines.

Development of an interferon-gamma ELISPOT assay to detect human T cell responses to HSV-2

BACKGROUND

The need for an HSV-2 vaccine is great considering the increasing prevalence of HSV-2 despite the widespread use of antiviral drugs. Human clinical trials of HSV-2 vaccines that elicit neutralizing antibodies have proven to be only partially effective suggesting that induction of effective T cell responses to HSV-2 is also a critical component to an efficacious vaccine. A sensitive and specific assay to measure HSV-specific T cell responses is a necessary part of vaccine development and thus we undertook the development of an interferon-γ (IFN-γ) ELISPOT assay to measure T cell responses to HSV-2.

METHODS

PBMC from HSV-seronegative (HSVneg) (n=35), HSV-1-seropositive (HSV-1+/2-) (n=20) and HSV-2-seropositive (HSV-2+) subjects (n=26) were screened by IFN-γ ELISPOT for T cell responses using 34 peptide pools representing 16 HSV-2 proteins including mostly virion and immediate-early (IE) proteins.

RESULTS

Overall, 85% of HSV-2+ subjects had a positive response to the HSV-2 peptide pools and on average, HSV-2+ subjects responded to 3 peptide pools (range 1-10). The most frequent responses were to gD-2, UL39, UL46, ICP0, UL49, gB-2, and ICP4. In contrast, only 2 of 35 (6%) HSVneg subjects had detectable T cell responses and in both cases, responses were of low magnitude relative to responses in HSV-2+ subjects and were directed at a single peptide pool. The response rate to the HSV-2 peptide pools in HSV-1+/2- subjects was 40% suggesting that the HSV-2 peptide pools contain a significant number of type-common T cell epitopes. The IFN-γ ELISPOT assay detected CD4 and CD8 T cells directed at HSV-2 peptides as confirmed by intracellular cytokine staining and flow cytometry.

CONCLUSION

We have developed a quantitative IFN-γ ELISPOT assay that detects both CD4 and CD8 T cells to HSV-2 peptides. This assay does not require large quantities of PBMC to generate dendritic cells for T cell stimulation, making it an ideal assay for monitoring the immunogenicity of candidate HSV-2 vaccines designed to elicit T cell responses to HSV-2 specific epitopes.

A heat shock protein based polyvalent vaccine targeting HSV-2: CD4(+) and CD8(+) cellular immunity and protective efficacy

Efforts to develop a subunit vaccine against genital herpes have been hampered by lack of knowledge of the protective antigens of HSV-2, the causative agent of the disease. Vaccines based either on selected antigens or attenuated live virus approaches have not demonstrated meaningful clinical activity. We present here results of a therapeutic vaccine candidate, HerpV (formerly called AG-707), consisting of 32 HSV-2 peptides derived from 22 HSV-2 proteins, complexed non-covalently to the HSP70 chaperone and formulated with QS-21 saponin adjuvant. HerpV is observed to be immunogenic, generating CD4(+) and CD8(+) T cell responses in three mouse strains including HLA-A2 transgenic mice. Optimal T cell stimulation was dependent on the synergistic adjuvant properties of QS-21 with hsp70. The vaccine provided significant protection from viral challenge in a mouse prophylaxis model and showed signals of activity in a guinea pig therapeutic model of existing infection. Peripheral blood mononuclear cells from human HSV-2(+) subjects also showed reactivity in vitro to a subset of individual peptides and to the pool of all 32 peptides. Recombinant human Hsc70 complexed with the 32 peptides also stimulated the expansion of CD8(+) T cells from HSV-2(+) subjects in vitro. These studies demonstrate that HerpV is a promising immunotherapy candidate for genital herpes, and provide a foundation for evaluating HerpV in human HSV-2(+) subjects with the intent of eliciting CD4(+) and CD8(+) T cell responses to a broad array of viral antigens.