Herpes simplex virus type 2 ICP47 inhibits human TAP but not mouse TAP

The expression and function of HSV ICP47 and its promoter in mice

IMPORTANCE

Immune evasion and latency are key mechanisms that underlie the success of herpesviruses. In each case, interactions between viral and host proteins are required and due to co-evolution, not all mechanisms are preserved across host species, even if infection is possible. This is highlighted by the herpes simplex virus (HSV) protein immediate early-infected cell protein (ICP)47, which inhibits the detection of infected cells by killer T cells and acts with high efficiency in humans, but poorly, if at all in mouse cells. Here, we show that ICP47 retains modest but detectable function in mouse cells, but in an in vivo model we found no role during acute infection or latency. We also explored the activity of the ICP47 promoter, finding that it could be active during latency, but this was dependent on genome location. These results are important to interpret HSV pathogenesis work done in mice.

Enhancing the immune effect of oHSV-1 therapy through TLR3 signaling in uveal melanoma

PURPOSE

Uveal melanoma (UM) is the most common primary intraocular malignant tumor in adults, with patients having a low overall survival rate. Oncolytic viruses (OVs) have been shown effective as monotherapy or combined with immunotherapy in the treatment of UM. Oncolytic herpes simplex type I virus (oHSV-1) was found to alter gene expression and immune function in UMs. We investigated whether a combination treatment would be more effective in treating UM and reactive immune cells.

METHODS

RNA sequencing analysis were used to identify the effect of oHSV-1 infection in UM cells and protein changes were validated by western blot. Cell viability assays were performed through UM cell lines (MUM2B, 92.1, and MP41) and retinal pigment epithelial cell line (ARPE-19) to identify the efficacy and safety of the combination treatment. Western blot, qRT-PCR, cell viability assay and immunocytochemistry were performed to discover the reactivation of immune cells (U937 and HMC3).

RESULTS

Through RNA sequencing analysis and in vitro molecular biology assays, this study tested the ability of oHSV-1 combined with the TLR3 agonist poly(I:C) to re-activate the TLR3 meditated NF-ƙB signaling pathway and further increase the anti-tumor activity of UM cells and macrophages, including the stimulation of macrophage polarization and proliferation.

CONCLUSIONS

These findings indicate that the treatment of UM with a combination of oHSV-1 and poly(I:C) generates immune responses and enhances anti-tumoral activity, suggesting the need for further investigations and clinical trials of this combination.

Nanotechnology-Based Nucleic Acid Vaccines for Treatment of Ovarian Cancer

Anticancer vaccines represent a promising approach for effective treatment of cancer and along with recent advantages of nucleic acid-based vaccines for other diseases form a prospective and potentially efficacious direction of the research, development and clinical applications. Despite the ongoing several clinical trials of mRNA vaccines for the treatment of various types of cancer, to-date no cancer vaccines were approved by the US Food and Drug Administration. The present review analyzes and summarizes major approaches for treating of different forms of ovarian cancer including mRNA-based vaccines as well as nanotechnology-based approaches for their delivery.

Simplexviruses successfully adapt to their host by fine-tuning immune responses

Primate herpes simplex viruses are species-specific and relatively harmless to their natural hosts. However, cross-species transmission is often associated with severe disease, as exemplified by the virulence of macacine herpesvirus 1 (B virus) in humans. We performed a genome-wide scan for signals of adaptation of simplexviruses to their hominin hosts. Among core genes, we found evidence of episodic positive selection in three glycoproteins, with several selected sites located in antigenic determinants. Positively selected noncore genes were found to be involved in different immune-escape mechanisms. The herpes simplex virus (HSV)-1/HSV-2 encoded product (ICP47) of one of these genes is known to down-modulate major histocompatibility complex class I expression. This feature is not shared with B virus, which instead up-regulates Human Leukocyte Antigen (HLA)-G, an immunomodulatory molecule. By in vitro expression of different ICP47 mutants, we functionally characterized the selection signals. Results indicated that the selected sites do not represent the sole determinants of binding to the transporter associated with antigen processing (TAP). Conversely, the amino acid status at these sites was sufficient to determine HLA-G up-regulation. In fact, both HSV-1 and HSV-2 ICP47 induced HLA-G when mutated to recapitulate residues in B virus, whereas the mutated version of B virus ICP47 failed to determine HLA-G expression. These differences might contribute to the severity of B virus infection in humans. Importantly, they indicate that the evolution of ICP47 in HSV-1/HSV-2 led to the loss of an immunosuppressive effect. Thus, related simplexviruses finely tune the balance between immunosuppressive and immunostimulatory pathways to promote successful co-existence with their primate hosts.

OrienX010, an oncolytic virus, in patients with unresectable stage IIIC-IV melanoma: a phase Ib study

BACKGROUND

Melanoma in people of Asian descent presents primarily in non-sun-exposed areas, such as acral and mucosal melanoma. Compared with the predominant sun-exposed area melanomas in Caucasians, acral and mucosal melanomas do not respond as well to immunotherapy and are associated with a worse prognosis. Hence, there is an urgent need for improved treatment for melanoma in Asians. This phase Ib trial evaluated the safety and efficacy of the modified herpes simplex virus-1 oncolytic virus OrienX010 in Chinese patients with unresectable stage IIIC-IV melanoma.

METHODS

Patients were treated in two different cohorts. In cohort 08 (n=12), patients received up to 5 mL of 8×10⁷ pfu/mL OrienX010 intratumoral injections every 2 weeks until disease progression and responses were evaluated every 6 weeks. In cohort 09 (n=14), patients received up to 10 mL of 8×10⁷ pfu/mL OrienX010 intratumoral injections and responses were evaluated every 8 weeks.

RESULTS

Between June 2014 and May 2017, 26 patients were enrolled, including 18 (69.2%) patients with acral melanoma. Fever and injection site reaction were the most frequent adverse events. Only one patient experienced a grade ≥3 adverse event and no dose-limiting toxicities were observed. The objective response rate was 19.2% and the disease control rate was 53.8%. The median duration of response was 6.0 months. Antitumor effects were observed in 54.6% of injected lesions and 48.8% of non-injected lesions, including one (16.7%) of six evaluable distant lung metastases. The median progression-free survival was 2.9 months and overall survival was 19.2 months. Compared with patients treated in cohort 08, patients treated in cohort 09 had an improved objective response rate (28.6% vs 8.3%) and a median progression-free survival of 3.0 months vs 2.8 months.

CONCLUSIONS

OrienX010 oncolytic virotherapy has a tolerable safety profile with antitumor effects in both injected and non-injected metastases and warrants further evaluation in patients with melanoma. Based on these results, the higher cohort 09 dose (up to 10 mL of 8×10⁷ pfu/mL every 2 weeks) was selected as the recommended phase II dose for ongoing trials.

TRIAL REGISTRATION NUMBER

CTR20140631 (cohort 08), CTR20150881 (cohort 09).

Overcoming innate immune barriers that impede AAV gene therapy vectors

The field of gene therapy has made considerable progress over the past several years. Adeno-associated virus (AAV) vectors have emerged as promising and attractive tools for in vivo gene therapy. Despite the recent clinical successes achieved with recombinant AAVs (rAAVs) for therapeutics, host immune responses against the vector and transgene product have been observed in numerous preclinical and clinical studies. These outcomes have hampered the advancement of AAV gene therapies, preventing them from becoming fully viable and safe medicines. The human immune system is multidimensional and complex. Both the innate and adaptive arms of the immune system seem to play a concerted role in the response against rAAVs. While most efforts have been focused on the role of adaptive immunity and developing ways to overcome it, the innate immune system has also been found to have a critical function. Innate immunity not only mediates the initial response to the vector, but also primes the adaptive immune system to launch a more deleterious attack against the foreign vector. This Review highlights what is known about innate immune responses against rAAVs and discusses potential strategies to circumvent these pathways.

A review on the advances and challenges of immunotherapy for head and neck cancer

Head and neck cancer (HNC), which includes lip and oral cavity, larynx, nasopharynx, oropharynx, and hypopharynx malignancies, is one of the most common cancers worldwide. Due to the interaction of tumor cells with immune cells in the tumor microenvironment, immunotherapy of HNCs, along with traditional treatments such as chemotherapy, radiotherapy, and surgery, has attracted much attention. Four main immunotherapy strategies in HNCs have been developed, including oncolytic viruses, monoclonal antibodies, chimeric antigen receptor T cells (CAR-T cells), and therapeutic vaccines. Oncorine (H101), an approved oncolytic adenovirus in China, is the pioneer of immunotherapy for the treatment of HNCs. Pembrolizumab and nivolumab are mAbs against PD-L1 that have been approved for recurrent and metastatic HNC patients. To date, several clinical trials using immunotherapy agents and their combination are under investigation. In this review, we summarize current the interaction of tumor cells with immune cells in the tumor microenvironment of HNCs, the main strategies that have been applied for immunotherapy of HNCs, obstacles that hinder the success of immunotherapies in patients with HNCs, as well as solutions for overcoming the challenges to enhance the response of HNCs to immunotherapies.

Macrophage polarization contributes to the efficacy of an oncolytic HSV-1 targeting human uveal melanoma in a murine xenograft model

Uveal melanoma (UM), the most common primary malignant tumor of the eye in adults, is difficult-to-treat. UM has a relatively high mortality secondary to distant metastasis and poor overall survival with existing therapies. The oncolytic virus herpes simplex virus type-1 (HSV-1) has been approved for clinical use in melanoma. This double-stranded DNA virus was suspected to directly activate lysis specifically in neoplastic cells. We tested the antitumor efficacy of recombinant oncolytic HSV-1-EGFP (oHSV-EGFP) in UM and characterized the local and systemic antitumor innate immune response in a murine xenograft model. We first determined the efficacy of the oncolytic virus in 92.1, MUM2B and MP41 cell lines. In murine xenograft models, oHSV-EGFP reduced intraocular tumors as well as systemic subcutaneous tumors. A significant change in cytokines was observed in viral infected cells, especially a rise in IFNγ. In vivo analyses showed increased anti-tumorigenic M1 macrophages and decreased pro-tumorigenic M2 macrophages in peripheral blood, and intraocular and distant tumors after intravitreal viral treatment. Increased infiltration of natural killer cells and mature dendritic cells was also detected after viral treatment. In addition, no virus was detected in major organs after the treatment. Our data support that oHSV-EGFP is effective, neoplasm specific, immune active and safe, providing possible clinical translatable options to treat ocular and metastatic UM.

Crosstalk between oncolytic viruses and autophagy in cancer therapy

Oncolytic viruses have attracted attention as a promising strategy in cancer therapy owing to their ability to selectively infect and kill tumor cells, without affecting healthy cells. They also exert their anti-tumor effects by releasing immunostimulatory molecules from dying cancer cells. Several regulatory mechanisms, such as autophagy, contribute to the anti-tumor properties of oncolytic viruses. Autophagy is a conserved catabolic process in responses to various stresses, such as nutrient deprivation, hypoxia, and infection that produces energy by lysosomal degradation of intracellular contents. Autophagy can support infectivity and replication of the oncolytic virus and enhance their anti-tumor effects via mediating oncolysis, autophagic cell death, and immunogenic cell death. On the other hand, autophagy can reduce the cytotoxicity of oncolytic viruses by providing survival nutrients for tumor cells. In his review, we summarize various types of oncolytic viruses in clinical trials, their mechanism of action, and autophagy machinery. Furthermore, we precisely discuss the interaction between oncolytic viruses and autophagy in cancer therapy and their combinational effects on tumor cells.

"Non-Essential" Proteins of HSV-1 with Essential Roles In Vivo: A Comprehensive Review

Viruses encode for structural proteins that participate in virion formation and include capsid and envelope proteins. In addition, viruses encode for an array of non-structural accessory proteins important for replication, spread, and immune evasion in the host and are often linked to virus pathogenesis. Most virus accessory proteins are non-essential for growth in cell culture because of the simplicity of the infection barriers or because they have roles only during a state of the infection that does not exist in cell cultures (i.e., tissue-specific functions), or finally because host factors in cell culture can complement their absence. For these reasons, the study of most nonessential viral factors is more complex and requires development of suitable cell culture systems and in vivo models. Approximately half of the proteins encoded by the herpes simplex virus 1 (HSV-1) genome have been classified as non-essential. These proteins have essential roles in vivo in counteracting antiviral responses, facilitating the spread of the virus from the sites of initial infection to the peripheral nervous system, where it establishes lifelong reservoirs, virus pathogenesis, and other regulatory roles during infection. Understanding the functions of the non-essential proteins of herpesviruses is important to understand mechanisms of viral pathogenesis but also to harness properties of these viruses for therapeutic purposes. Here, we have provided a comprehensive summary of the functions of HSV-1 non-essential proteins.

Antitumor Efficacy of Oncolytic Herpes Virus Type 1 Armed with GM-CSF in Murine Uveal Melanoma Xenografts

Background

Uveal melanoma (UM) is the most common primary intraocular tumor in adults with a high incidence of metastasis. Standard care therapies for UM include enucleation and radiation, which are minimally effective in prolonging patient survival. Oncolytic virus treatment has become a new trend in cancer field. Of which, oncolytic herpes simplex virus type 1 (HSV-1) therapy is one of the most effective antitumor treatments. Here, we established an oncolytic HSV-1 encoding granulocyte-macrophage colony-stimulating factor (GM-CSF), tested its efficacy in UM therapy, and investigated the innate immune response induced by this virus.

Methods

Oncolytic HSV-1 expressing GM-CSF (HSV-GM-CSF) was constructed, then verified using qPCR and Western blot assays. Cell viability assays and transmission electron microscopy were conducted on three UM cell lines, MUM2B, 92.1, and MP41, to assess the cell-killing ability and virus infection of this virus. For in vivo experiments, BALB/c-nude mice in situ UM xenografts were established to testify the efficacy of the oncolytic virus, oncolytic HSV-1, and HSV-GM-CSF groups, respectively. IVIS images, ocular volumes, mice weights, and survivals were tracked to see the efficacy of the virus. Hematoxylin and eosin staining, immunohistochemistry, and flow cytometry analyses were conducted to demonstrate the immune activity after virus treatment.

Results

All three tested UM cell lines were sensitive to infection by HSV-GM-CSF. In vivo xenograft experiments revealed that oncolytic virus HSV-1 reduced UM tumor volume and that oncolytic virus HSV-1 armed with GM-CSF enhanced the antitumor effect compared with unmodified HSV-1. The bodyweights of untreated control group mice were significantly lower than those of mice in either virus-treated group (HSV-1 or HSV-GM-CSF). Follow-up survivals were prolonged in the virus-treated groups compared with the control group and were prolonged to a greater extent in the HSV-GM-CSF group than in the HSV-1 group. Macrophage stimulation was observed following HSV-GM-CSF treatment.

Conclusion

Our results indicate that the recombinant oncolytic virus HSV-GM-CSF is a potential therapeutic treatment for UM.

Clinical CAR-T Cell and Oncolytic Virotherapy for Cancer Treatment

Immunotherapy has recently garnered success with the induction of clinical responses in tumors, which are traditionally associated with poor outcomes. Chimeric antigen receptor T (CAR-T) cells and oncolytic viruses (OVs) have emerged as promising cancer immunotherapy agents. Herein, we provide an overview of the current clinical status of CAR-T cell and OV therapies. While preclinical studies have demonstrated curative potential, the benefit of CAR-T cells and OVs as single-agent treatments remains limited to a subset of patients. Combinations of different targeted therapies may be required to achieve efficient, durable responses against heterogeneous tumors, as well as the microenvironment. Using a combinatorial approach to take advantage of the unique features of CAR-T cells and OVs with other treatments can produce additive therapeutic effects. This review also discusses ongoing clinical evaluations of these combination strategies for improved outcomes in treatment of resistant malignancies.

Antitumor efficacy of oncolytic HSV-1 expressing cytosine deaminase is synergistically enhanced by DPD down-regulation and EMT inhibition in uveal melanoma xenograft

Uveal melanoma (UM) is the most common intraocular tumor in adults and has a high incidence of metastases. Possible treatments remain limited in UM with enucleation and radiation, leading to poor prognosis in this chemo-resistant carcinoma. Thus, urging demand for novel treatment is needed. We examined the antitumor efficacy of a new recombinant oncolytic herpes simplex virus type 1 (oHSV-1) armed with E.coli cytosine deaminase (CD). We determined the efficacy of the oncolytic virus in UM cell lines. In vivo experiments showed that oHSV-CD/5-fluorocytosine (5-FC) treatment reduce tumor volume and prolonged survival. We further demonstrated the molecular mechanisms of oHSV-CD/5-FC treatment. The oncolytic virus down-regulated IL-6 expression and thereby reversed the epithelial-mesenchymal transition (EMT) phenotype. Dihydropyrimidine dehydrogenase (DPD), the rate-limiting enzyme in 5-fluorouracil (5-FU) metabolism, was also down-regulated. Therefore, the efficacy of oHSV-CD/5-FC was synergistically enhanced by DPD down-regulation and EMT inhibition. This study provides solid evidence for the antitumor efficacy of oHSV-CD/5-FC treatment in vitro and in vivo. The molecular mechanisms of this treatment may bring a new therapeutic approach for future treatment of UM.

Virus-Receptor Interactions and Virus Neutralization: Insights for Oncolytic Virus Development

Oncolytic viruses (OVs) are replication competent agents that selectively target cancer cells. After penetrating the tumor cell, viruses replicate and eventually trigger cell lysis, releasing the new viral progeny, which at their turn will attack and kill neighbouring cells. The ability of OVs to self-amplify within the tumor while sparing normal cells can provide several advantages including the capacity to encode and locally produce therapeutic protein payloads, and to prime the host immune system. OVs targeting of cancer cells is mediated by host factors that are differentially expressed between normal tissue and tumors, including viral receptors and internalization factors. In this review article, we will discuss the evolution of oncolytic viruses that have reached the stage of clinical trials, their mechanisms of oncolysis, cellular receptors, strategies for targeting cancers, viral neutralization and developments to bypass virus neutralization.

Recent advances of oncolytic virus in cancer therapy

Oncolytic viruses have been taking the front stage in biological therapy for cancer recently. The first and most potent virus to be used in oncolytic virotherapy is human adenovirus. Recently, ongoing extensive research has suggested that other viruses like herpes simplex virus (HSV) and measles virus can also be considered as potential candidates in cancer therapy. An HSV-based oncolytic virus, T-VEC, has completed phase Ш clinical trial and has been approved by the U.S. Food and Drug Administration (FDA) for use in biological cancer therapy. Moreover, the vaccine strain of the measles virus has shown impressive results in pre-clinical and clinical trials. Considering their therapeutic efficacy, safety, and reduced side effects, the use of such engineered viruses in biological cancer therapy has the potential to establish a milestone in cancer research. In this review, we summarize the recent clinical advances in the use of oncolytic viruses in biological therapy for cancer. Additionally, this review evaluates the potential viral candidates for their benefits and shortcomings and sheds light on the future prospects.

Herpes Simplex Virus Evasion of Early Host Antiviral Responses

Herpes simplex viruses type 1 (HSV-1) and type 2 (HSV-2) have co-evolved with humans for thousands of years and are present at a high prevalence in the population worldwide. HSV infections are responsible for several illnesses including skin and mucosal lesions, blindness and even life-threatening encephalitis in both, immunocompetent and immunocompromised individuals of all ages. Therefore, diseases caused by HSVs represent significant public health burdens. Similar to other herpesviruses, HSV-1 and HSV-2 produce lifelong infections in the host by establishing latency in neurons and sporadically reactivating from these cells, eliciting recurrences that are accompanied by viral shedding in both, symptomatic and asymptomatic individuals. The ability of HSVs to persist and recur in otherwise healthy individuals is likely given by the numerous virulence factors that these viruses have evolved to evade host antiviral responses. Here, we review and discuss molecular mechanisms used by HSVs to evade early innate antiviral responses, which are the first lines of defense against these viruses. A comprehensive understanding of how HSVs evade host early antiviral responses could contribute to the development of novel therapies and vaccines to counteract these viruses.

Inhibition of antigen presentation during AAV gene therapy using virus peptides

The clinical trial using adeno-associated virus (AAV) vector delivery of mini-dystrophin in patients with Duchenne Muscular Dystrophy (DMD) demonstrated a cytotoxic lymphocyte (CTL) response targeting the transgene product. These mini-dystrophin-specific T-cells have the potential to clear all transduced muscle, presenting the general gene therapy concern of overcoming the CTL response to foreign proteins that provide therapeutic benefit. In this study, we exploited a natural immunosuppression strategy employed by some viruses that results in CTL evasion only in transduced cells. After transfection of the plasmids encoding viral peptides and ovalbumin, which includes the immune-domain epitope SIINFEKL, several viral small peptides (ICP47 and US6) inhibited the SIINFEKL peptide presentation. A single AAV vector genome that consisted of either transgene AAT fused with SIINFEKL epitope and, separately, ICP47 expressed from different promoters or a single fusion protein with ICP47 linked by a furin cleavage peptide (AATOVA-ICP47) decreased antigen presentation. Compared with AAV/AATOVA in which decreased AAT expression was observed at late time points, persistent transgene expression was obtained after systemic administration of AAV/AATOVA-ICP47 vectors in mice. We extended this strategy to DMD gene therapy. After administration of AAV vector encoding human mini-dystrophin fusion protein with ICP47 into mdx mice, a lower mini-dystrophin-specific CTL response was induced. Importantly, the ICP47 fusion to mini-dystrophin inhibited CTLs mediated cytotoxicity. Although demonstrated herein using AAT and mini-dystrophin transgenes in an AAV context, the collective results have implications for all gene therapy applications resulting in foreign peptides by immune suppression in only genetically modified cells.

Herpesviruses: Harmonious Pathogens but Relevant Cofactors in Other Diseases?

Most vertebrates are infected with one or more herpesviruses and remain so for the rest of their lives. The relationship of immunocompetent healthy host with herpesviruses may sometime be considered as harmonious. However, clinically severe diseases can occur when host immunity is compromised due to aging, during some stress response, co-infections or during neoplastic disease conditions. Discord can also occur during iatrogenic immunosuppression used for controlling graft rejection, in some primary genetic immunodeficiencies as well as when the virus infects a non-native host. In this review, we discuss such issues and their influence on host-herpesvirus interaction.

Increasing antigen presentation on HSV-1-infected cells increases lesion size but does not alter neural infection or latency

CD8⁺ T cells have a role in the control of acute herpes simplex virus (HSV) infection and may also be important in the maintenance of latency. In this study we have explored the consequences of boosting the efficacy of CD8⁺ T cells against HSV by increasing the amount of an MHC I-presented epitope on the surface of infected cells. To do this we used HSVs engineered to express an extra copy of the immunodominant CD8⁺ T cell epitope in C57Bl/6 mice, namely gB₄₉₈ (SSIEFARL). Despite greater presentation of gB₄₉₈ on infected cells, CD8⁺ T cell responses to these viruses in mice were similar to those elicited by a control virus. Further, the expression of extra gB₄₉₈ did not significantly alter the extent or stability of latency in our mouse model, and virus loads in skin and sensory ganglia of infected mice were not affected. Surprisingly, mice infected with these viruses developed significantly larger skin lesions than those infected with control viruses and notably, this phenotype was dependent on MHC haplotype. Therefore increasing the visibility of HSV-infected cells to CD8⁺ T cell attack did not impact neural infection or latency, but rather enhanced pathology in the skin.

Talimogene laherparepvec: First in class oncolytic virotherapy

Oncolytic viruses represent a novel drug class in which native or modified viruses mediate tumor regression through selective replication within and lysis of tumor cells as well as induction of systemic antitumor immunity capable of eradicating tumor at distant, uninjected sites. Talimogene laherparepvec (TVEC) is a type I herpes simplex virus genetically modified to preferentially replicate in tumor cells, enhance antigen loading of MHC class I molecules and express granulocyte-macrophage colony-stimulating factor to increase tumor-antigen presentation by dendritic cells. It is presently the only oncolytic virus approved by the FDA with an indication for advanced melanoma based upon improved durable response rate in a randomized, phase III trial. Clinical trials are underway in melanoma investigating TVEC as neoadjuvant monotherapy and in combination with checkpoint inhibitors for unresectable disease as well as in an array of other malignancies. It is appropriate to review TVEC's biology mechanism of action, clinical indication and future directions as a prototype of the burgeoning class of oncolytic viruses.

Molecular Basis for the Recognition of Herpes Simplex Virus Type 1 Infection by Human Natural Killer Cells

Primary infection with Herpes simplex virus type 1 (HSV1) is subclinical or only mildly symptomatic in normal individuals, yet the reason for the body's effective immune defense against this pathogen in the absence of antigen-specific immunity has not been well understood. It is clear that human natural killer (NK) cells recognize and kill HSV1-infected cells, and those individuals who either lack or have functionally impaired NK cells can suffer severe, recurrent, and sometimes fatal HSV1 infection. In this article, we review what is known about the recognition of HSV1 by NK cells, and describe a novel mechanism of innate immune surveillance against certain viral pathogens by NK cells called Fc-bridged cell-mediated cytotoxicity.

Selective Expression of CCR10 and CXCR3 by Circulating Human Herpes Simplex Virus-Specific CD8 T Cells

Herpes simplex virus (HSV) infection is restricted to epithelial cells and neurons and is controlled by CD8 T cells. These cells both traffic to epithelial sites of recurrent lytic infection and to ganglia and persist at the dermal-epidermal junction for up to 12 weeks after lesion resolution. We previously showed that cutaneous lymphocyte-associated antigen (CLA), a functional E-selectin ligand (ESL), is selectively expressed on circulating HSV-2-specific CD8 T cells. CLA/ESL mediates adhesion of T cells to inflamed vascular endothelium. Later stages in T-cell homing involve chemokines (Ch) and lymphocyte chemokine receptors (ChR) for vascular wall arrest and diapedesis. Several candidate ChR have been implicated in skin homing. We measured cell surface ChR on HSV-specific human peripheral blood CD8 T cells and extended our studies to HSV-1. We observed preferential cell surface expression of CCR10 and CXCR3 by HSV-specific CD8 T cells compared to CD8 T cells specific for control viruses, Epstein-Barr virus (EBV) and cytomegalovirus (CMV), and compared to bulk memory CD8 T cells. CXCR3 ligand mRNA levels were selectively increased in skin biopsy specimens from persons with recurrent HSV-2, while the mRNA levels of the CCR10 ligand CCL27 were equivalent in lesion and control skin. Our data are consistent with a model in which CCL27 drives baseline recruitment of HSV-specific CD8 T cells expressing CCR10, while interferon-responsive CXCR3 ligands recruit additional cells in response to virus-driven inflammation.IMPORTANCE HSV-2 causes very localized recurrent infections in the skin and genital mucosa. Virus-specific CD8 T cells home to the site of recurrent infection and participate in viral clearance. The exit of T cells from the blood involves the use of chemokine receptors on the T-cell surface and chemokines that are present in infected tissue. In this study, circulating HSV-2-specific CD8 T cells were identified using specific fluorescent tetramer reagents, and their expression of several candidate skin-homing-associated chemokine receptors was measured using flow cytometry. We found that two chemokine receptors, CXCR3 and CCR10, are upregulated on HSV-specific CD8 T cells in blood. The chemokines corresponding to these receptors are also expressed in infected tissues. Vaccine strategies to prime CD8 T cells to home to HSV lesions should elicit these chemokine receptors if possible to increase the homing of vaccine-primed cells to sites of infection.

Oncolytic Viral Therapy for Mesothelioma

The limited effectiveness of conventional therapy for malignant pleural mesothelioma demands innovative approaches to this difficult disease. Even with aggressive multimodality treatment of surgery, radiation, and/or chemotherapy, the median survival is only 1–2 years depending on stage and histology. Oncolytic viral therapy has emerged in the last several decades as a rapidly advancing field of immunotherapy studied in a wide spectrum of malignancies. Mesothelioma makes an ideal candidate for studying oncolysis given the frequently localized pattern of growth and pleural location providing access to direct intratumoral injection of virus. Therefore, despite being a relatively uncommon disease, the multitude of viral studies for mesothelioma can provide insight for applying such therapy to other malignancies. This article will begin with a review of the general principles of oncolytic therapy focusing on antitumor efficacy, tumor selectivity, and immune system activation. The second half of this review will detail results of preclinical models and human studies for oncolytic virotherapy in mesothelioma.

Modulation of the Intratumoral Immune Landscape by Oncolytic Herpes Simplex Virus Virotherapy

Vaccines and immunotherapeutic approaches to cancers with the advent of immune checkpoint inhibitors and chimeric antigen receptor-modified T cells have recently demonstrated preclinical success and entered clinical trials. Despite advances in these approaches and combinatorial therapeutic regimens, depending on the nature of the cancer and the immune and metabolic landscape within the tumor microenvironment, current immunotherapeutic modalities remain inadequate. Recent clinical trials have demonstrated clear evidence of significant, and sometimes dramatic, antitumor activity, and long-term survival effects of a variety of oncolytic viruses (OVs), particularly oncolytic herpes simplex virus (oHSV). Acting as a multifaceted gene therapy vector and potential adjuvant-like regimens, oHSV can carry genes encoding immunostimulatory molecules in its genome. The oncolytic effect of oHSV and the inflammatory response that the virus stimulates provide a one-two punch at attacking tumors. However, mechanisms underlying oHSV-induced restoration of intratumoral immunosuppression demand extensive research in order to further improve its therapeutic efficacy. In this review, we discuss the current OV-based therapy, with a focus on the unique aspects of oHSV-initiated antiviral and antitumor immune responses, arising from virus-mediated immunological cell death to intratumoral innate and adaptive immunity.

Improved Transgenic Mouse Model for Studying HLA Class I Antigen Presentation

HLA class I (HLA-I) transgenic mice have proven to be useful models for studying human MHC-related immune responses over the last two decades. However, differences in the processing and presentation machinery between humans and mice may have profound effects on HLA-I restricted antigen presentation. In this study, we generated a novel human TAP-LMP (hTAP-LMP) gene cluster transgenic mouse model carrying an intact human TAP complex and two human immunoproteasome LMP subunits, PSMB8/PSMB9. By crossing the hTAP-LMP strain with different HLA-I transgenic mice, we found that the expression levels of human HLA-I molecules, especially the A3 supertype members (e.g., A11 and A33), were remarkably enhanced in corresponding HLA-I/hTAP-LMP transgenic mice. Moreover, we found that humanized processing and presentation machinery increased antigen presentation of HLA-A11-restricted epitopes and promoted the rapid reduction of hepatitis B virus (HBV) infection in HLA-A11/hTAP-LMP mice. Together, our study highlights that HLA-I/hTAP-LMP mice are an improved model for studying antigen presentation of HLA-I molecules and their related CTL responses.

Novel melanoma therapy

With the rapid succession of new effective agents for melanoma in the recent years, the paradigm for treatment of metastatic melanoma is changing. The success of combining multiple effective agents compared with outcomes of monotherapy also brings increasing complexity in the treatment algorithm for various subsets of metastatic melanoma patients. We reviewed the recent reports on novel melanoma therapy to shed light on rational decision-making in treating these patients.

Molecular Pathways: Mechanism of Action for Talimogene Laherparepvec, a New Oncolytic Virus Immunotherapy

Oncolytic viruses are native or engineered viruses that preferentially replicate in and lyse cancer cells. Selective tumor cell replication is thought to depend on infection of neoplastic cells, which harbor low levels of protein kinase R (PKR) and dysfunctional type I IFN signaling elements. These changes allow more efficient viral replication, and with selected deletion of specific viral genes, replication in normal cells with activated PKR may not be possible. Direct tumor cell lysis, release of soluble tumor antigens, and danger-associated molecular factors are all thought to help prime and promote tumor-specific immunity. Talimogene laherparepvec (T-VEC) is a genetically modified herpes simplex virus, type I and is the first oncolytic virus to demonstrate a clinical benefit in patients with melanoma. T-VEC has also been evaluated for the treatment of head and neck cancer, pancreatic cancer, and likely other types of cancer will be targeted in the near future. T-VEC has been modified for improved safety, tumor-selective replication, and induction of host immunity by deletion of several viral genes and expression of human granulocyte-macrophage colony stimulating factor. Although the mechanism of action for T-VEC is incompletely understood, the safety profile of T-VEC and ability to promote immune responses suggest future combination studies with other immunotherapy approaches including checkpoint blockade through PD-1, PD-L1, and CTLA-4 to be a high priority for clinical development. Oncolytic viruses also represent unique regulatory and biosafety challenges but offer a potential new class of agents for the treatment of cancer.

Oncolytic viruses: a new class of immunotherapy drugs

Oncolytic viruses represent a new class of therapeutic agents that promote anti-tumour responses through a dual mechanism of action that is dependent on selective tumour cell killing and the induction of systemic anti-tumour immunity. The molecular and cellular mechanisms of action are not fully elucidated but are likely to depend on viral replication within transformed cells, induction of primary cell death, interaction with tumour cell antiviral elements and initiation of innate and adaptive anti-tumour immunity. A variety of native and genetically modified viruses have been developed as oncolytic agents, and the approval of the first oncolytic virus by the US Food and Drug Administration (FDA) is anticipated in the near future. This Review provides a comprehensive overview of the basic biology supporting oncolytic viruses as cancer therapeutic agents, describes oncolytic viruses in advanced clinical trials and discusses the unique challenges in the development of oncolytic viruses as a new class of drugs for the treatment of cancer.

Viral inhibition of the transporter associated with antigen processing (TAP): a striking example of functional convergent evolution

Herpesviruses are large DNA viruses that are highly abundant within their host populations. Even in the presence of a healthy immune system, these viruses manage to cause lifelong infections. This persistence is partially mediated by the virus entering latency, a phase of infection characterized by limited viral protein expression. Moreover, herpesviruses have devoted a significant part of their coding capacity to immune evasion strategies. It is believed that the close coexistence of herpesviruses and their hosts has resulted in the evolution of viral proteins that specifically attack multiple arms of the host immune system. Cytotoxic T lymphocytes (CTLs) play an important role in antiviral immunity. CTLs recognize their target through viral peptides presented in the context of MHC molecules at the cell surface. Every herpesvirus studied to date encodes multiple immune evasion molecules that effectively interfere with specific steps of the MHC class I antigen presentation pathway. The transporter associated with antigen processing (TAP) plays a key role in the loading of viral peptides onto MHC class I molecules. This is reflected by the numerous ways herpesviruses have developed to block TAP function. In this review, we describe the characteristics and mechanisms of action of all known virus-encoded TAP inhibitors. Orthologs of these proteins encoded by related viruses are identified, and the conservation of TAP inhibition is discussed. A phylogenetic analysis of members of the family Herpesviridae is included to study the origin of these molecules. In addition, we discuss the characteristics of the first TAP inhibitor identified outside the herpesvirus family, namely, in cowpox virus. The strategies of TAP inhibition employed by viruses are very distinct and are likely to have been acquired independently during evolution. These findings and the recent discovery of a non-herpesvirus TAP inhibitor represent a striking example of functional convergent evolution.

An MHC class I immune evasion gene of Marek׳s disease virus

Marek׳s disease virus (MDV) is a widespread α-herpesvirus of chickens that causes T cell tumors. Acute, but not latent, MDV infection has previously been shown to lead to downregulation of cell-surface MHC class I (Virology 282:198-205 (2001)), but the gene(s) involved have not been identified. Here we demonstrate that an MDV gene, MDV012, is capable of reducing surface expression of MHC class I on chicken cells. Co-expression of an MHC class I-binding peptide targeted to the endoplasmic reticulum (bypassing the requirement for the TAP peptide transporter) partially rescued MHC class I expression in the presence of MDV012, suggesting that MDV012 is a TAP-blocking MHC class I immune evasion protein. This is the first unique non-mammalian MHC class I immune evasion gene identified, and suggests that α-herpesviruses have conserved this function for at least 100 million years.

Animal models of herpes simplex virus immunity and pathogenesis

Herpes simplex viruses are ubiquitous human pathogens represented by two distinct serotypes: herpes simplex virus (HSV) type 1 (HSV-1); and HSV type 2 (HSV-2). In the general population, adult seropositivity rates approach 90% for HSV-1 and 20-25% for HSV-2. These viruses cause significant morbidity, primarily as mucosal membrane lesions in the form of facial cold sores and genital ulcers, with much less common but more severe manifestations causing death from encephalitis. HSV infections in humans are difficult to study in many cases because many primary infections are asymptomatic. Moreover, the neurotropic properties of HSV make it much more difficult to study the immune mechanisms controlling reactivation of latent infection within the corresponding sensory ganglia and crossover into the central nervous system of infected humans. This is because samples from the nervous system can only be routinely obtained at the time of autopsy. Thus, animal models have been developed whose use has led to a better understanding of multiple aspects of HSV biology, molecular biology, pathogenesis, disease, and immunity. The course of HSV infection in a spectrum of animal models depends on important experimental parameters including animal species, age, and genotype; route of infection; and viral serotype, strain, and dose. This review summarizes the animal models most commonly used to study HSV pathogenesis and its establishment, maintenance, and reactivation from latency. It focuses particularly on the immune response to HSV during acute primary infection and the initial invasion of the ganglion with comparisons to the events governing maintenance of viral latency.

MHC class I molecules are incorporated into human herpesvirus-6 viral particles and released into the extracellular environment

Human herpesvirus-6 (HHV-6), which belongs to the betaherpesvirus subfamily, mainly replicates in T lymphocytes. Here, we show that MHC class I molecules are incorporated into HHV-6 viral particles and released into the extracellular environment. In addition, HHV-6A/B-infected T cells showed reduced surface and intracellular expression of MHC class I molecules. The cellular machinery responsible for molecular transport appears to be modified upon HHV-6 infection, causing MHC class I molecules to be transported to virion assembly sites.

HSV-2 specifically down regulates HLA-C expression to render HSV-2-infected DCs susceptible to NK cell killing

Both NK cells and CTLs kill virus-infected and tumor cells. However, the ways by which these killer cells recognize the infected or the tumorigenic cells are different, in fact almost opposite. CTLs are activated through the interaction of the TCR with MHC class I proteins. In contrast, NK cells are inhibited by MHC class I molecules. The inhibitory NK receptors recognize mainly MHC class I proteins and in this regard practically all of the HLA-C proteins are recognized by inhibitory NK cell receptors, while only certain HLA-A and HLA-B proteins interact with these receptors. Sophisticated viruses developed mechanisms to avoid the attack of both NK cells and CTLs through, for example, down regulation of HLA-A and HLA-B molecules to avoid CTL recognition, leaving HLA-C proteins on the cell surface to inhibit NK cell response. Here we provide the first example of a virus that through specific down regulation of HLA-C, harness the NK cells for its own benefit. We initially demonstrated that none of the tested HSV-2 derived microRNAs affect NK cell activity. Then we show that surprisingly upon HSV-2 infection, HLA-C proteins are specifically down regulated, rendering the infected cells susceptible to NK cell attack. We identified a motif in the tail of HLA-C that is responsible for the HSV-2-meduiated HLA-C down regulation and we show that the HLA-C down regulation is mediated by the viral protein ICP47. Finally we show that HLA-C proteins are down regulated from the surface of HSV-2 infected dendritic cells (DCs) and that this leads to the killing of DC by NK cells. Thus, we propose that HSV-2 had developed this unique and surprising NK cell-mediated killing strategy of infected DC to prevent the activation of the adaptive immunity.

Approximately 20% of all humans are latently and asymptomatically infected with HSV-2. This suggests that the virus developed mechanisms to avoid immune cell detection; many of which are still unknown. Infected cells are killed mainly by two lymphocyte populations; NK cells and CTLs that belong to the innate and the adaptive immunity, respectively. While the killing machinery of these two cell types is similar, almost identical, the ways by which they discriminate between infected and uninfected cells is different. CTLs are activated, primarily by DCs, to become effector cells. They then recognize virus-derived peptides in the groove of MHC class I molecules and eliminate the virally infected cells. In contrast, NK cells recognize infected cells through several NK cell activating receptors, while the recognition of MHC class I proteins by NK cells leads to inhibition of NK cell killing. Viruses, such as HIV, developed mechanisms to interfere with the function of both NK cells and CTLs via targeting of specific MHC class I proteins. Here we show that HSV-2 developed a MHC class I-dependent mechanism in which the virus, through specific targeting of HLA-C by the viral protein ICP47, harness the NK cells for its own benefit, probably to avoid the activation of adaptive immune response.

Oncolytic viruses in the treatment of bladder cancer

Bladder carcinoma is the second most common malignancy of the urinary tract. Up to 85% of patients with bladder cancer are diagnosed with a tumor that is limited to the bladder mucosa (Ta, T1, and CIS). These stages are commonly termed as non-muscle-invasive bladder cancer (NMIBC). Although the treatment of NMIBC has greatly improved in recent years, there is a need for additional therapies when patients fail bacillus Calmette-Guérin (BCG) and chemotherapeutic agents. We propose that bladder cancer may be an ideal target for oncolytic viruses engineered to selectively replicate in and lyse tumor cells leaving normal cells unharmed. In support of this hypothesis, here we review current treatment strategies for bladder cancer and their shortcomings, as well as recent advancements in oncolytic viral therapy demonstrating encouraging safety profiles and antitumor activity.

Human herpesviridae methods of natural killer cell evasion

Human herpesviruses cause diseases of considerable morbidity and mortality, ranging from encephalitis to hematologic malignancies. As evidence emerges about the role of innate immunity and natural killer (NK) cells in the control of herpesvirus infection, evidence of viral methods of innate immune evasion grows as well. These methods include interference with the ligands on infected cell surfaces that bind NK cell activating or inhibitory receptors. This paper summarizes the most extensively studied NK cell receptor/ligand pairs and then describes the methods of NK cell evasion used by all eight herpesviruses through these receptors and ligands. Although great strides have been made in elucidating their mechanisms, there is still a disparity between viruses in the amount of knowledge regarding innate immune evasion. Further research of herpesvirus innate immune evasion can provide insight for circumventing viral mechanisms in future therapies.

Herpes virus fusion and entry: a story with many characters

Herpesviridae comprise a large family of enveloped DNA viruses all of whom employ orthologs of the same three glycoproteins, gB, gH and gL. Additionally, herpesviruses often employ accessory proteins to bind receptors and/or bind the heterodimer gH/gL or even to determine cell tropism. Sorting out how these proteins function has been resolved to a large extent by structural biology coupled with supporting biochemical and biologic evidence. Together with the G protein of vesicular stomatitis virus, gB is a charter member of the Class III fusion proteins. Unlike VSV G, gB only functions when partnered with gH/gL. However, gH/gL does not resemble any known viral fusion protein and there is evidence that its function is to upregulate the fusogenic activity of gB. In the case of herpes simplex virus, gH/gL itself is upregulated into an active state by the conformational change that occurs when gD, the receptor binding protein, binds one of its receptors. In this review we focus primarily on prototypes of the three subfamilies of herpesviruses. We will present our model for how herpes simplex virus (HSV) regulates fusion in series of highly regulated steps. Our model highlights what is known and also provides a framework to address mechanistic questions about fusion by HSV and herpesviruses in general.

The herpes simplex virus type 1 latency-associated transcript inhibits phenotypic and functional maturation of dendritic cells

We recently found that the herpes simplex virus-1 (HSV-1) latency-associated transcript (LAT) results in exhaustion of virus-specific CD8⁺ T cells in latently-infected trigeminal ganglia (TG). In this study we sought to determine if this impairment may involve LAT directly and/or indirectly interfering with DC maturation. We found that a small number of HSV-1 antigen-positive DCs are present in the TG of latently-infected CD11c/eYFP mice; however, this does not imply that these DCs are acutely or latently infected. Some CD8⁺ T cells are adjacent to DCs, suggesting possible interactions. It has previously been shown that wild-type HSV-1 interferes with DC maturation. Here we show for the first time that this is associated with LAT expression, since compared to LAT⁻ virus: (1) LAT⁺ virus interfered with expression of MHC class I and the co-stimulatory molecules CD80 and CD86 on the surface of DCs; (2) LAT⁺ virus impaired DC production of the proinflammatory cytokines IL-6, IL-12, and TNF-α; and (3) DCs infected in vitro with LAT⁺ virus had significantly reduced the ability to stimulate HSV-specific CD8⁺ T cells. While a similar number of DCs was found in LAT⁺ and LAT⁻ latently-infected TG of CD11c/eYFP transgenic mice, more HSV-1 Ag-positive DCs and more exhausted CD8 T cells were seen with LAT⁺ virus. Consistent with these findings, HSV-specific cytotoxic CD8⁺ T cells in the TG of mice latently-infected with LAT⁺ virus produced less IFN-γ and TNF-α than those from TG of LAT⁻-infected mice. Together, these results suggest a novel immune-evasion mechanism whereby the HSV-1 LAT increases the number of HSV-1 Ag-positive DCs in latently-infected TG, and interferes with DC phenotypic and functional maturation. The effect of LAT on TG-resident DCs may contribute to the reduced function of HSV-specific CD8⁺ T cells in the TG of mice latently infected with LAT⁺ virus.

Cross-presentation and genome-wide screening reveal candidate T cells antigens for a herpes simplex virus type 1 vaccine

Herpes simplex virus type 1 (HSV-1) not only causes painful recurrent oral-labial infections, it can also cause permanent brain damage and blindness. There is currently no HSV-1 vaccine. An effective vaccine must stimulate coordinated T cell responses, but the large size of the genome and the low frequency of HSV-1-specific T cells have hampered the search for the most effective T cell antigens for inclusion in a candidate vaccine. We have now developed what we believe to be novel methods to efficiently generate a genome-wide map of the responsiveness of HSV-1-specific T cells, and demonstrate the applicability of these methods to a second complex microbe, vaccinia virus. We used cross-presentation and CD137 activation-based FACS to enrich for polyclonal CD8+ T effector T cells. The HSV-1 proteome was prepared in a flexible format for analyzing both CD8+ and CD4+ T cells from study participants. Scans with participant-specific panels of artificial APCs identified an oligospecific response in each individual. Parallel CD137-based CD4+ T cell research showed discrete oligospecific recognition of HSV-1 antigens. Unexpectedly, the two HSV-1 proteins not previously considered as vaccine candidates elicited both CD8+ and CD4+ T cell responses in most HSV-1-infected individuals. In this era of microbial genomics, our methods - also demonstrated in principle for vaccinia virus for both CD8+ and CD4+ T cells - should be broadly applicable to the selection of T cell antigens for inclusion in candidate vaccines for many pathogens.

The capacity of UL49.5 proteins to inhibit TAP is widely distributed among members of the genus Varicellovirus

The lifelong infection by varicelloviruses is characterized by a fine balance between the host immune response and immune evasion strategies used by these viruses. Virus-derived peptides are presented to cytotoxic T lymphocytes by major histocompatibility complex (MHC) class I molecules. The transporter associated with antigen processing (TAP) transports the peptides from the cytosol into the endoplasmic reticulum, where the loading of MHC-I molecules occurs. The varicelloviruses bovine herpesvirus 1 (BoHV-1), pseudorabies virus, and equid herpesviruses 1 and 4 have been found to encode a UL49.5 protein that inhibits TAP-mediated peptide transport. To investigate to what extent UL49.5-mediated TAP inhibition is conserved within the family of Alphaherpesvirinae, the homologs of another five varicelloviruses, one mardivirus, and one iltovirus were studied. The UL49.5 proteins of BoHV-5, bubaline herpesvirus 1, cervid herpesvirus 1, and felid herpesvirus 1 were identified as potent TAP inhibitors. The varicella-zoster virus and simian varicellovirus UL49.5 proteins fail to block TAP; this is not due to the absence of viral cofactors that might assist in this process, since cells infected with these viruses did not show reduced TAP function either. The UL49.5 homologs of the mardivirus Marek's disease virus 1 and the iltovirus infectious laryngotracheitis virus did not block TAP, suggesting that the capacity to inhibit TAP via UL49.5 has been acquired by varicelloviruses only. A phylogenetic analysis of viruses that inhibit TAP through their UL49.5 proteins reveals an interesting hereditary pattern, pointing toward the presence of this capacity in defined clades within the genus Varicellovirus.

Diversity in CD8(+) T cell function and epitope breadth among persons with genital herpes

CD8(+) T cells are known to be important in clearing herpes simplex virus (HSV) infections. However, investigating the specific antiviral mechanisms employed by HSV-2-specific T cell populations is limited by a lack of reagents such as CD8(+) T cell epitopes and specific tetramers. Using a combination of intracellular cytokine staining flow cytometry and ELISpot methods, we functionally characterized peripheral HSV-2-specific CD8(+) T cells from peripheral blood mononuclear cell (PBMC) that recognize 14 selected HSV-2 open-reading frames (ORFs) from 55 HSV-2 seropositive persons; within these ORFs, we subsequently identified more than 20 unique CD8(+) T cell epitopes. CD8(+) T cells to HSV-2 exhibited significant heterogeneity in their functional characteristics, proliferation, production of inflammatory cytokines, and potential to degranulate ex vivo. The diversity in T cell response in these ex vivo assessments offers the potential of defining immune correlates of HSV-2 reactivation in humans.

Human herpesvirus 7 u21 downregulates classical and nonclassical class I major histocompatibility complex molecules from the cell surface

Herpesviruses have evolved numerous strategies to evade detection by the immune system. Notably, most of the herpesviruses interfere with viral antigen presentation to cytotoxic T lymphocytes (CTLs) by removing class I major histocompatibility complex (MHC) molecules from the infected cell surface. Clearly, since the herpesviruses have evolved an extensive array of mechanisms to remove class I MHC molecules from the cell surface, this strategy serves them well. However, class I MHC molecules often serve as inhibitory ligands for NK cells, so viral downregulation of all class I MHC molecules should leave the infected cell open to NK cell attack. Some viruses solve this problem by selectively downregulating certain class I MHC products, leaving other class I products at the cell surface to serve as inhibitory NK cell ligands. Here, we show that human herpesvirus 7 (HHV-7) U21 binds to and downregulates all of the human class I MHC gene products, as well as the murine class I molecule H-2K(b). HHV-7-infected cells must therefore possess other means of escaping NK cell detection.

Innate and adaptive immune responses to herpes simplex virus

Immune responses against HSV-1 and HSV-2 are complex and involve a delicate interplay between innate signaling pathways and adaptive immune responses. The innate response to HSV involves the induction of type I IFN, whose role in protection against disease is well characterized in vitro and in vivo. Cell types such as NK cells and pDCs contribute to innate anti-HSV responses in vivo. Finally, the adaptive response includes both humoral and cellular components that play important roles in antiviral control and latency. This review summarizes the innate and adaptive effectors that contribute to susceptibility, immune control and pathogenesis of HSV, and highlights the delicate interplay between these two important arms of immunity.

Chronic cortical and subcortical pathology with associated neurological deficits ensuing experimental herpes encephalitis

Long-term neurological sequela is common among herpes simplex encephalitis (HSE) survivors. Animal models for HSE are used to investigate mechanisms of acute disease, but little has been done to model chronic manifestations of HSE. The current study presents a detailed, systematic analysis of chronic neuropathology, including characterization of topography and sequential progression of degenerative lesions and inflammation. Subsequent to intranasal HSV-1 infection, inflammatory responses that were temporally and spatially distinct persisted in infected cortical and brain stem regions. Neutrophils were present exclusively within the olfactory bulb and brain stem regions during the acute phase of infection, while the chronic inflammation was marked by plasma cells, lymphocytes and activated microglia. The chronic lymphocytic infiltrate, cytokine production, and activated microglia were associated with the loss of cortical neuropile in the entorhinal cortex and hippocampus. Animals surviving the acute infection showed a spectrum of chronic lesions from decreased brain volume, neuronal loss, activated astrocytes, and glial scar formation to severe atrophy and cavitations of the cortex. These lesions were also associated with severe spatial memory deficits in surviving animals. Taken together, this model can be utilized to further investigate the mechanisms of neurological defects that follow in the wake of HSE.

Immune control of mammalian gamma-herpesviruses: lessons from murid herpesvirus-4

Many acute viral infections can be controlled by vaccination; however, vaccinating against persistent infections remains problematic. Herpesviruses are a classic example. Here, we discuss their immune control, particularly that of gamma-herpesviruses, relating the animal model provided by murid herpesvirus-4 (MuHV-4) to human infections. The following points emerge: (i) CD8(+) T-cell evasion by herpesviruses confers a prominent role in host defence on CD4(+) T cells. CD4(+) T cells inhibit MuHV-4 lytic gene expression via gamma-interferon (IFN-gamma). By reducing the lytic secretion of immune evasion proteins, they may also help CD8(+) T cells to control virus-driven lymphoproliferation in mixed lytic/latent lesions. Similarly, CD4(+) T cells specific for Epstein-Barr virus lytic antigens could improve the impact of adoptively transferred, latent antigen-specific CD8(+) T cells. (ii) In general, viral immune evasion necessitates multiple host effectors for optimal control. Thus, subunit vaccines, which tend to prime single effectors, have proved less successful than attenuated virus mutants, which prime multiple effectors. Latency-deficient mutants could make safe and effective gamma-herpesvirus vaccines. (iii) The antibody response to MuHV-4 infection helps to prevent disease but is suboptimal for neutralization. Vaccinating virus carriers with virion fusion complex components improves their neutralization titres. Reducing the infectivity of herpesvirus carriers in this way could be a useful adjunct to vaccinating naive individuals with attenuated mutants.

The virological synapse facilitates herpes simplex virus entry into T cells

The virological synapse (VS) is a specialized molecular structure that facilitates the transfer of certain lymphotropic viruses into uninfected T cells. However, the role of the VS in the transfer of nonlymphotropic viruses into T cells is unknown. Herpes simplex virus (HSV) has been shown in vitro to infect T cells and modulate T-cell receptor function, thereby suppressing T-cell antiviral function. However, whether such infection of T cells occurs in vivo is unknown. Here, we examined whether T-cell infection could be observed in human HSV disease and investigated the mechanism of HSV entry into T cells. We found that HSV-infected T cells were readily detectable during human disease, suggesting that infection and modulation of T-cell function plays a role in human immunopathology. HSV infection of both CD4(+) and CD8(+) T cells occurred much more efficiently via direct cell-to-cell spread from infected fibroblasts than by cell-free virus. Activation of T cells increased their permissivity to HSV infection. Cell-to-cell spread to T cells did not require HSV glycoproteins E and I (gE and gI), which are critical for cell-to-cell spread between epithelial cells. Transfer of HSV to T cells required gD, and the four known entry receptors appear to be contributing to viral entry, with a dominant role for the herpesvirus entry mediator and nectin-1. VS-like structures enriched in activated lymphocyte function-associated antigen 1 (LFA-1) were observed at the point of contact between HSV-infected fibroblasts and T cells. Consistent with spread occurring via the VS, transfer of HSV was increased by activation of LFA-1, and cell-to-cell spread could be inhibited by antibodies to LFA-1 or gD. Taken together, these results constitute the first demonstration of VS-dependent cell-to-cell spread for a predominantly nonlymphotropic virus. Furthermore, they support an important role for infection and immunomodulation of T cells in clinical human disease. Targeting of the VS might allow selective immunopotentiation during infections with HSV or other nonlymphotropic viruses.

CD8 T cell control of HSV reactivation from latency is abrogated by viral inhibition of MHC class I

In humans, herpes simplex virus (HSV) establishes latency in sensory nerve ganglia from where it periodically reactivates, whereas in murine models, the virus efficiently establishes latency but rarely reactivates. HSV inhibits MHC class I antigen presentation to CD8 T cells efficiently in humans but poorly in mice, and whether this is a crucial determinant of HSV's ability to reactivate in humans remains uncertain. To test this, we generated a panel of recombinant HSVs that inhibit presentation by murine MHC class I mimicking the effect in humans. Antigen-specific CD8 T cells prevent the in vivo reactivation of wild-type HSV. Despite their presence in the ganglia of latently infected mice, CD8 T cells do not prevent the reactivation of recombinant HSVs that inhibit murine MHC class I in mice. These findings suggest that efficient inhibition of MHC class I by HSV is a key factor in its ability to reactivate in humans.

Genomics and Marek's disease virus

Marek's disease virus (MDV), a lymphotrophic alphaherpesvirus of chickens, causes a disease that is characterized by tumor formation, immunosuppression and neurological disorders. Recent developments in chicken genomics have been applied to studies of MDV and have advanced our understanding of both the virus and the disease it causes. We have constructed and used microarrays to identify host genes that are up-regulated in chicken embryo fibroblasts infected with MDV as a first step to catalog the host response to infection. An additional level of gene regulation lies at the level of microRNAs (miRNAs). miRNAs are a class of small (approximately 22 nt) regulatory molecules encoded by a wide variety of organisms, including some viruses, that block translation or induce degradation of specific mRNAs. Herpesviruses, which replicate in the nuclei of infected cells, are a particularly important class of viruses that express miRNAs. miRNAs from two of the oncogenic herpesviruses; namely, Kaposi's sarcoma herpesvirus (KSHV) and Epstein-Barr virus (EBV) have been cataloged. We recently identified MDV-encoded miRNAs. One cluster of miRNAs flanks the meq oncogene, and a second cluster maps to the latency associated transcript (LAT) region of the genome. The LATs are encoded anti-sense to the ICP4 immediate early gene, and the meq gene, which is unique to pathogenic serotypes of MDV, is the most likely oncoprotein or co-oncoprotein encoded by MDV. The conservation of these sequences is suggestive of an important role in pathogenesis.