A non-neutralizing glycoprotein B monoclonal antibody protects against herpes simplex virus disease in mice

Structure of the Kaposi's sarcoma-associated herpesvirus gB in post-fusion conformation

Discovered in 1994 in lesions of an AIDS patient, Kaposi's sarcoma-associated herpesvirus (KSHV) is a member of the gammaherpesvirus subfamily of the Herpesviridae family, which contains a total of nine that infect humans. These viruses all contain a large envelope glycoprotein, glycoprotein B (gB), that is required for viral fusion with host cell membrane to initial infection. Although the atomic structures of five other human herpesviruses in their postfusion conformation and one in its prefusion conformation are known, the atomic structure of KSHV gB has not been reported. Here, we report the first structure of the KSHV gB ectodomain determined by single-particle cryogenic electron microscopy (cryoEM). Despite a similar global fold between herpesvirus gB, KSHV gB possesses local differences not shared by its relatives in other herpesviruses. The glycosylation sites of gB are arranged in belts down the symmetry axis with distinct localization compared to that of other herpesviruses, which occludes certain antibody binding sites. An extended glycan chain observed in domain I (DI), located proximal to the host membrane, may suggest its possible role in host cell attachment. Local flexibility of domain IV (DIV) governed by molecular hinges at its interdomain junctions identifies a means for enabling conformational change. A mutation in the domain III (DIII) central helix disrupts incorporation of gB into KSHV virions despite adoption of a canonical fold in vitro. Taken together, this study reveals mechanisms of structural variability of herpesvirus fusion protein gB and informs its folding and immunogenicity.IMPORTANCEIn 1994, a cancer-causing virus was discovered in lesions of AIDS patients, which was later named Kaposi's sarcoma-associated herpesvirus (KSHV). As the latest discovered human herpesvirus, KSHV has been classified into the gammaherpesvirus subfamily of the Herpesviridae. In this study, we have expressed KSHV gB and employed cryogenic electron microscopy (cryoEM) to determine its first structure. Importantly, our structure resolves some glycans beyond the first sugar moiety. These glycans are arranged in a pattern unique to KSHV, which impacts the antigenicity of KSHV gB. Our structure also reveals conformational flexibility caused by molecular hinges between domains that provide clues into the mechanism behind the drastic change between prefusion and postfusion states.

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

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

A replication-incompetent adenoviral vector encoding for HSV-2 gD2 is immunogenic and protective against HSV-2 intravaginal challenge in mice

Herpes Simplex virus (HSV) is the cause of genital herpes and no prophylactic treatment is currently available. Replication-incompetent adenoviral vectors are potent inducers of humoral and cellular immune responses in humans. We have designed an adenoviral vector type 35 (Ad35)-based vaccine encoding the HSV-2 major surface antigen gD2 (Ad35.HSV.gD2). Immunization of mice with Ad35.HSV.gD2 elicited virus neutralizing antibody titers (VNT) and cellular responses against HSV-2 and HSV-1. While immunity was lower than for CJ2-gD2, both vaccines showed 100% survival against intravaginal challenge with HSV-2 G strain and a strong inverse correlation was observed between HSV-2 infection (as measured by viral shedding) and VNT. A combination of Ad35.HSV.gD2 with Ad35 encoding for gB2 (Ad35.HSV.gB2) resulted in increased VNT and lower infection, compared with Ad35.HSV.gD2 alone. Transfer of immune serum into naïve BALB/c mice before intravaginal challenge confirmed the role of antibodies in the protection of mice against infection although other immune factors may play a role as well.

Multi-Antigen Elephant Endotheliotropic Herpesvirus (EEHV) mRNA Vaccine Induces Humoral and Cell-Mediated Responses in Mice

Background/Objectives: Elephant endotheliotropic herpesvirus (EEHV) causes lethal hemorrhagic disease (HD) in Asian and African elephants in human care and the wild. It is the leading cause of death for young Asian elephants in North American and European zoos despite sensitive diagnostic tests and improved treatments. Thus, there is a critical need to develop an effective vaccine to prevent severe illness and reduce mortality from EEHV-HD. We generated a multi-antigenic EEHV mRNA vaccine to address this need that encodes the EEHV1A-subtype glycoproteins gB, gH, gL, and gO. These conserved proteins are the entry machinery for several herpesviruses in the betaherpesvirus subfamily and elicit humoral and cellular immunity in naturally infected elephants. Methods: Outbred CD-1 mice were vaccinated with two doses of an mRNA vaccine comprising modified EEHV1A gB, gH, gL, and gO mRNAs encapsulated into lipid nanoparticles. Humoral and T-cell immunity was assessed three weeks after the first dose or three weeks after the booster dose using luciferase immunoprecipitation system assays and flow cytometry, respectively. Results: The CD-1 mice vaccinated once had detectable antibody titers against gB, gH, and gL that increased significantly three weeks after a booster dose. Activated CD4+ and CD8+ T cells secreting cytokines associated with a TH1 response were induced against all four glycoproteins. No adverse effects were observed following one or two doses of the vaccine. Conclusions: We found that gB, gH, gL, and gO as a multivalent vaccine stimulated robust humoral and cell-mediated immunity. This is a critical step for moving this candidate EEHV1A mRNA vaccine into clinical trials in Asian elephants.

Immune Response Elicited by Recombinant Adenovirus-Delivered Glycoprotein B and Nucleocapsid Protein UL18 and UL25 of HSV-1 in Mice

Due to the complex pathogenic and immune escape mechanisms of herpes simplex virus type 1 (HSV-1), especially the failure of induced immune responses to block the initial cell-to-cell transmission of the virus from skin cells to neurons, the body struggles to establish effective prevention and control methods, resulting in the failure of currently developed vaccines. Previous studies have highlighted the crucial roles of surface glycoproteins and nucleocapsid proteins in activating the body's immune defense system against HSV-1 infection. In this study, recombinant adenoviruses were used as vectors to generate adenoviruses carrying the nucleocapsid protein genes UL18 and UL25, as well as the surface glycoprotein gene gB. This approach aimed to mimic the protein expression process that occurs following viral infection of the host and to investigate the immune response characteristics induced by UL18, UL25, and gB proteins. The findings revealed that UL18, UL25, and gB proteins could all trigger the expression of genes associated with innate immune responses; however, the specific genes induced varied in type and level. Furthermore, all three proteins were capable of promoting the proliferation of CD8+ T cells in the lymph nodes. Notably, only UL18 and gB could elicit a Th1 cell immune response. Interestingly, among these proteins, only UL18 could also induce a relatively higher IL-4 level, indicating a Th2 cell immune response. In addition to cellular immunity, all three proteins stimulated the production of specific IgG antibodies. Notably, UL18 induced higher and more sustained levels of specific IgG antibodies in mice. By contrast, only glycoprotein gB induced lower levels of neutralizing antibodies in mice. Moreover, when these mice were challenged with HSV-1, the co-immunization with UL18 and gB provided better protection than gB alone. In conclusion, HSV-1 surface glycoproteins and nucleocapsid proteins exhibit differences in their ability to induce innate and adaptive immunity in the body, suggesting potential avenues for vaccine design by leveraging their complementary advantages.

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

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

Improving antibody-mediated protection against HSV infection by eliminating interactions with the viral Fc receptor gE/gI

Herpes simplex virus (HSV) encodes surface glycoproteins that are host defense evasion molecules, allowing the virus to escape immune clearance. In addition to their role in neuropathogenesis and cell-cell spread, glycoproteins E and I (gE/gI) form a viral Fc receptor (vFcR) for most subclasses and allotypes of human IgG and promote evasion of humoral immune responses. While monoclonal antibodies (mAbs) protect mice from neonatal HSV (nHSV) infections, the impact of the vFcR on mAb-mediated protection by binding to IgG is unknown. Using HSV-1 with intact and ablated gE-mediated IgG Fc binding, and Fc-engineered antibodies with modified ability to interact with gE/gI, we investigated the role of the vFcR in viral pathogenesis and mAb-mediated protection from nHSV. The gD-specific human mAb HSV8 modified to lack binding to gE exhibited enhanced neutralization and in vivo protection compared to its native IgG1 form. This improved protection by the engineered mAbs was dependent on the presence of the vFcR. Human IgG3 allotypes lacking vFcR binding also exhibited enhanced antiviral activity in vivo, suggesting that vaccines that robustly induce IgG3 responses could show enhanced protection. suggesting the value of vaccination strategies that robustly induce this subclass. Lastly, analysis of longitudinal responses to acute primary genital infection in humans raised the possibility that unlike most viruses, HSV may exhibited slow induction of IgG3. In summary, this study demonstrates that mAbs lacking the ability to interact with the vFcR can exhibit improved protection from HSV-offering new prospects for antibody-based interventions.

Therapeutic glycan-specific antibody binding mediates protection during primary amoebic meningoencephalitis

Naegleria fowleri (N. fowleri) infection via the upper respiratory tract causes a fatal CNS disease known as primary amoebic meningoencephalitis (PAM). The robust in vivo immune response to N. fowleri infection underlies the immunopathology that characterizes the disease. However, little is known about why this pathogen evades immune control. Infections occur in seemingly healthy individuals and effective clinical options are lacking, thus a nearly 98% fatality rate. It is unclear how or if host factors may contribute to susceptibility or disease exacerbation, yet mechanistic studies of the in vivo immune response and disease progression are hampered by a lack of tools. In this study, we have generated monoclonal antibodies to N. fowleri surface antigens and shown them to be excellent tools for studying the in vivo immune response. We also identified one monoclonal, 2B6, with potent inherent anti-amoebastatic activity in vitro. This antibody is also able to therapeutically prolong host survival in vivo and furthermore, recombinant antibodies with an isotype more capable of directing immune effector activity further improved survival when given therapeutically. Thus, we report the generation of a novel monoclonal antibody to N. fowleri that can enhance beneficial immune functions, even when given therapeutically during disease. We believe this provides evidence for the potential of therapeutic antibody treatments in PAM.IMPORTANCENaegleria fowleri (N. fowleri) is a free-living amoeba that is found ubiquitously in warm freshwater. While human exposure is common, it rarely results in pathogenesis. However, when N. fowleri gains access to the upper airway, specifically the olfactory mucosa, infection leads to a lethal disease known as primary amoebic meningoencephalitis (PAM). As a free-living amoeba, N. fowleri does not need a mammalian host; indeed, it can be accurately described as an accidental opportunistic pathogen. While most opportunistic infections occur in humans who are immunocompromised, there are no reported immune dysfunctions associated with N. fowleri infection. Therefore, the basis for N. fowleri opportunism is not known, and the reasons why some humans develop PAM while others do not are simply not well understood. It is reasonable to speculate that local or acute immune failures, potentially even a lack of prior adaptive immunity, are related to disease susceptibility. Careful immune profiling and characterization of the in vivo immune response to N. fowleri in a mammalian host are desperately needed to understand which host factors are critical to defense, and how these responses might be compromised in a way that results in lethal infection. To identify genes and pathways that provide resistance against in vivo N. fowleri infection, we generated surface reactive monoclonal antibodies (Abs) that provide rapid amoeba detection and quantification in vivo. Interestingly, N. fowleri binding Abs have been readily detected in the serum and saliva of humans and animals suggesting that non-lethal exposure drives a humoral immune response against the amoeba. Yet, how Abs might interact with Naegleria in vivo or contribute to preventing lethal infection is not well understood. In this study, we have generated and characterized a monoclonal antibody (Ab), Clone 2B6, that recognizes a glycosylated surface antigen present in cultured in vitro N. fowleri as well as mouse passaged N. fowleri. When clone 2B6 binds to N. fowleri, it inhibits amoeba motility and feeding behavior, leading to strong growth inhibition. Mice treated systemically and intracerebrally with Ab displayed a delayed disease onset and prolonged survival. In addition, we found that enhancing immune-directed effector activity via antibody isotype could further enhance survival without obvious immunopathogenic side effects. These findings show the potential for antibody treatment as an additional therapeutic to those used currently in PAM.

Novel Mouse Model of Recurrent Sublethal Herpes Simplex Virus Infection Recapitulates Human Antibody Responses to Primary and Chronic Infection

Background: Herpes simplex virus (HSV) vaccine development has been impeded by the absence of predictive preclinical models and defined correlates of immune protection. Prior candidates elicited neutralizing responses greater than natural infection but no antibody-dependent cellular cytotoxicity (ADCC) and failed to protect in clinical trials. Primary HSV infection also elicits only neutralizing responses, but ADCC and an expanded antigenic repertoire emerge over time. This evolution may contribute to the decreased frequency and severity of recurrences. To test this notion, we developed a recurrent HSV infection mouse model and evaluated changes in humoral immunity with repeated challenges. Methods: Mice were repeatedly infected intranasally with clinical isolates of HSV-1 or HSV-2 for four months. HSV binding IgG, neutralizing (with or without complement) and ADCC-mediating antibodies were quantified prior to each round of infection. Viral targets were assessed by western blotting. Pooled immune serum (750 μg IgG per mouse) was passively transferred into naïve wild-type or Hvem knockout mice 24 h prior to lethal skin challenge. Results: Repeated exposure to HSV-1 or HSV-2 induced an increase in total HSV-binding IgG but did not boost neutralizing titers. In contrast, ADCC-mediating responses increased significantly from the first to the fourth viral exposure (p < 0.01). The increase was associated with an expanded antigenic repertoire. Passive transfer of fourth round immune serum provided significant protection whereas first round serum failed to protect (p < 0.01). However, protection was lost when serum was transferred into Hvem knockout mice, which are impaired in mediating ADCC killing. Conclusion: This novel model recapitulates clinical responses, highlights the importance of ADCC in protecting against recurrent infection, and provides a strategy for evaluating therapeutic vaccines.

Development of a highly effective combination monoclonal antibody therapy against Herpes simplex virus

BACKGROUND

Infections with Herpes simplex virus (HSV)-1 or -2 usually present as mild chronic recurrent disease, however in rare cases can result in life-threatening conditions with a large spectrum of pathology. Monoclonal antibody therapy has great potential especially to treat infections with virus resistant to standard therapies. HDIT101, a humanized IgG targeting HSV-1/2 gB was previously investigated in phase 2 clinical trials. The aim of this study was to develop a next-generation therapy by combining different antiviral monoclonal antibodies.

METHODS

A lymph-node derived phage display library (LYNDAL) was screened against recombinant gB from Herpes simplex virus (HSV) -1 and HDIT102 scFv was selected for its binding characteristics using bio-layer interferometry. HDIT102 was further developed as fully human IgG and tested alone or in combination with HDIT101, a clinically tested humanized anti-HSV IgG, in vitro and in vivo. T-cell stimulating activities by antigen-presenting cells treated with IgG-HSV immune complexes were analyzed using primary human cells. To determine the epitopes, the cryo-EM structures of HDIT101 or HDIT102 Fab bound to HSV-1F as well as HSV-2G gB protein were solved at resolutions < 3.5 Å.

RESULTS

HDIT102 Fab showed strong binding to HSV-1F gB with Kd of 8.95 × 10-11 M and to HSV-2G gB with Kd of 3.29 × 10-11 M. Neutralization of cell-free virus and inhibition of cell-to-cell spread were comparable between HDIT101 and HDIT102. Both antibodies induced internalization of gB from the cell surface into acidic endosomes by binding distinct epitopes in domain I of gB and compete for binding. CryoEM analyses revealed the ability to form heterogenic immune complexes consisting of two HDIT102 and one HDIT101 Fab bound to one gB trimeric molecule. Both antibodies mediated antibody-dependent phagocytosis by antigen presenting cells which stimulated autologous T-cell activation. In vivo, the combination of HDIT101 and HDIT102 demonstrated synergistic effects on survival and clinical outcome in immunocompetent BALB/cOlaHsd mice.

CONCLUSION

This biochemical and immunological study showcases the potential of an effective combination therapy with two monoclonal anti-gB IgGs for the treatment of HSV-1/2 induced disease conditions.

Protective human antibodies against a conserved epitope in pre- and postfusion influenza hemagglutinin

Phylogenetically and antigenically distinct influenza A and B viruses (IAV and IBV) circulate in human populations, causing widespread morbidity. Antibodies (Abs) that bind epitopes conserved in both IAV and IBV hemagglutinins (HAs) could protect against disease by diverse virus subtypes. Only one reported HA Ab, isolated from a combinatorial display library, protects against both IAV and IBV. Thus, there has been so far no information on the likelihood of finding naturally occurring human Abs that bind HAs of diverse IAV subtypes and IBV lineages. We have now recovered from several unrelated human donors five clonal Abs that bind a conserved epitope preferentially exposed in the postfusion conformation of IAV and IVB HA2. These Abs lack neutralizing activity in vitro but in mice provide strong, IgG subtype-dependent protection against lethal IAV and IBV infections. Strategies to elicit similar Abs routinely might contribute to more effective influenza vaccines.

Antibody attributes, Fc receptor expression, gestation and maternal SARS-CoV-2 infection modulate HSV IgG placental transfer

Antibody-dependent cellular cytotoxicity (ADCC) is associated with protection against neonatal herpes. We hypothesized that placental transfer of ADCC-mediating herpes simplex virus (HSV) immunoglobulin G (IgG) is influenced by antigenic target, function, glycans, gestational age, and maternal severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. Maternal and cord blood were collected from HSV-seropositive (HSV+) mothers pre-COVID and HSV+/SARS-CoV-2+ mothers during the pandemic. Transfer of HSV neutralizing IgG was significantly lower in preterm versus term dyads (transfer ratio [TR] 0.84 vs. 2.44) whereas the TR of ADCC-mediating IgG was <1.0 in both term and preterm pre-COVID dyads. Anti-glycoprotein D IgG, which had only neutralizing activity, and anti-glycoprotein B (gB) IgG, which displayed neutralizing and ADCC activity, exhibited different relative affinities for the neonatal Fc receptor (FcRn) and expressed different glycans. The transfer of ADCC-mediating IgG increased significantly in term SARS-CoV-2+ dyads. This was associated with greater placental colocalization of FcRn with FcγRIIIa. These findings have implications for strategies to prevent neonatal herpes.

Antibody effector functions are required for broad and potent protection of neonates from herpes simplex virus infection

The failure of multiple herpes simplex virus (HSV) vaccine candidates that induce neutralizing antibody responses raises the hypothesis that other activities, such as Fc domain-dependent effector functions, may be critical for protection. While neonatal HSV (nHSV) infection result in mortality and lifelong neurological morbidity in humans, it is uncommon among neonates with a seropositive birthing parent, suggesting the potential efficacy of antibody-based therapeutics to protect neonates. We therefore investigated the mechanisms of monoclonal antibody (mAb)-mediated protection in a mouse model of nHSV infection. Both neutralization and effector functions contributed to robust protection against nHSV-1. In contrast, effector functions alone were sufficient to protect against nHSV-2, exposing a functional dichotomy between virus types that is consistent with vaccine trial results. Together, these results emphasize that effector functions are crucial for optimal mAb-mediated protection, informing effective Ab and vaccine design, and demonstrating the potential of polyfunctional Abs as potent therapeutics for nHSV infections.

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

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