ICP0 antagonizes Stat 1-dependent repression of herpes simplex virus: implications for the regulation of viral latency

HSV-1 selectively packs the transcription factor Oct-1 into EVs to facilitate its infection

HSV-1 hijacks the cellular vesicular secretion system and promotes the secretion of extracellular vesicles (EVs) from infected cells. This is believed to facilitate the maturation, secretion, intracellular transportation and immune evasion of the virus. Intriguingly, previous studies have shown that noninfectious EVs from HSV-1-infected cells exert antiviral effects on HSV-1 and have identified host restrictive factors, such as STING, CD63, and Sp100 packed in these lipid bilayer-enclosed vesicles. Octamer-binding transcription factor-1 (Oct-1) is shown here to be a pro-viral cargo in non-virion-containing EVs during HSV-1 infection and serves to facilitate virus dissemination. Specifically, during HSV-1 infection, the nuclear localized transcription factor Oct-1 displayed punctate cytosolic staining that frequently colocalized with VP16 and was increasingly secreted into the extracellular space. HSV-1 grown in cells bereft of Oct-1 (Oct-1 KO) was significantly less efficient at transcribing viral genes during the next round of infection. In fact, HSV-1 promoted increased exportation of Oct-1 in non-virion-containing EVs, but not the other VP16-induced complex (VIC) component HCF-1, and EV-associated Oct-1 was promptly imported into the nucleus of recipient cells to facilitate the next round of HSV-1 infection. Interestingly, we also found that EVs from HSV-1-infected cells primed cells for infection by another RNA virus, vesicular stomatitis virus. In summary, this investigation reports one of the first pro-viral host proteins packed into EVs during HSV-1 infection and underlines the heterogenetic nature and complexity of these noninfectious double-lipid particles.

Human cytomegalovirus UL138 interaction with USP1 activates STAT1 in infection

Innate immune responses are crucial for limiting virus infection. However, viruses often hijack our best defenses for viral objectives. Human Cytomegalovirus (HCMV) is a beta herpesvirus which establishes a life-long latent infection. Defining the virus-host interactions controlling latency and reactivation is vital to the control of viral disease risk posed by virus reactivation. We defined an interaction between UL138, a pro-latency HCMV gene, and the host deubiquitinating complex, UAF1-USP1. UAF1 is a scaffold protein pivotal for the activity of ubiquitin specific peptidases (USP), including USP1. UAF1-USP1 sustains an innate immune response through the phosphorylation and activation of signal transducer and activator of transcription-1 (pSTAT1), as well as regulates the DNA damage response. After the onset of viral DNA synthesis, pSTAT1 levels are elevated in infection and this depends upon UL138 and USP1. pSTAT1 localizes to viral centers of replication, binds to the viral genome, and influences UL138 expression. Inhibition of USP1 results in a failure to establish latency, marked by increased viral genome replication and production of viral progeny. Inhibition of Jak-STAT signaling also results in increased viral genome synthesis in hematopoietic cells, consistent with a role for USP1-mediated regulation of STAT1 signaling in the establishment of latency. These findings demonstrate the importance of the UL138-UAF1-USP1 virus-host interaction in regulating HCMV latency establishment through the control of innate immune signaling. It will be important going forward to distinguish roles of UAF1-USP1 in regulating pSTAT1 relative to its role in the DNA damage response in HCMV infection.

Role of Innate Interferon Responses at the Ocular Surface in Herpes Simplex Virus-1-Induced Herpetic Stromal Keratitis

Herpes simplex virus type 1 (HSV-1) is a highly successful pathogen that primarily infects epithelial cells of the orofacial mucosa. After initial lytic replication, HSV-1 enters sensory neurons and undergoes lifelong latency in the trigeminal ganglion (TG). Reactivation from latency occurs throughout the host’s life and is more common in people with a compromised immune system. HSV-1 causes various diseases depending on the site of lytic HSV-1 replication. These include herpes labialis, herpetic stromal keratitis (HSK), meningitis, and herpes simplex encephalitis (HSE). HSK is an immunopathological condition and is usually the consequence of HSV-1 reactivation, anterograde transport to the corneal surface, lytic replication in the epithelial cells, and activation of the host’s innate and adaptive immune responses in the cornea. HSV-1 is recognized by cell surface, endosomal, and cytoplasmic pattern recognition receptors (PRRs) and activates innate immune responses that include interferons (IFNs), chemokine and cytokine production, as well as the recruitment of inflammatory cells to the site of replication. In the cornea, HSV-1 replication promotes type I (IFN-α/β) and type III (IFN-λ) IFN production. This review summarizes our current understanding of HSV-1 recognition by PRRs and innate IFN-mediated antiviral immunity during HSV-1 infection of the cornea. We also discuss the immunopathogenesis of HSK, current HSK therapeutics and challenges, proposed experimental approaches, and benefits of promoting local IFN-λ responses.

Human Cytomegalovirus UL138 Interaction with USP1 Activates STAT1 in infection

Innate immune responses are crucial for limiting virus infection. However, viruses often hijack our best defenses for viral objectives. Human Cytomegalovirus (HCMV) is a beta herpesvirus which establishes a life-long latent infection. Defining the virus-host interactions controlling latency and reactivation is vital to the control of viral disease risk posed by virus reactivation. We defined an interaction between UL138, a pro-latency HCMV gene, and the host deubiquintase complex, UAF1-USP1. UAF1 is a scaffold protein pivotal for the activity of ubiquitin specific peptidases (USP), including USP1. UAF1-USP1 sustains an innate immune response through the phosphorylation and activation of signal transducer and activator of transcription-1 (pSTAT1), as well as regulates the DNA damage response. After the onset of viral DNA synthesis, pSTAT1 levels are elevated and this depends upon UL138 and USP1. pSTAT1 localizes to viral centers of replication, binds to the viral genome, and influences UL138 expression. Inhibition of USP1 results in a failure to establish latency, marked by increased viral genome replication and production of viral progeny. Inhibition of Jak-STAT signaling also results in increased viral genome synthesis in hematopoietic cells, consistent with a role for USP1-mediated regulation of STAT1 signaling in the establishment of latency. These findings demonstrate the importance of the UL138-UAF1-USP1 virus-host interaction in regulating HCMV latency establishment through the control of innate immune signaling. It will be important going forward to distinguish roles of UAF1-USP1 in regulating pSTAT1 relative to its role in the DNA damage response in HCMV infection.

Importance

Human cytomegalovirus (HCMV) is one of nine herpesviruses that infect humans. Following a primary infection, HCMV establishes a life-long latent infection that is marked by sporadic, and likely frequent reactivation events. While these reactivation events are asymptomatic in the immune competent host, they pose important disease risks for the immune compromised, including solid organ or stem cell transplant recipients. Its complex interactions with host biology and deep coding capacity make it an excellent model for defining mechanisms important for viral latency and reactivation. Here we define an interaction with host proteins that commandeer typically antiviral innate immune signaling for the establishment of latency.

Blue light irradiation exerts anti-viral and anti-inflammatory properties against herpes simplex virus type 1 infection

The aim of this study was to investigate the antiviral and anti-inflammatory functions of blue light (BL) in cutaneous viral infections. Previously, we examined the photo-biogoverning role of 450 nm BL in SARS-CoV-2-infected cells, which showed that photo-energy could inhibit viral activation depending on the number of photons. However, the communication network between photo-energy irradiation and immune cells involved in viral infections has not been clarified. We verified viral activation, inflammatory responses, and relevant downstream cascades caused by human simplex virus type I (HSV-1) after BL irradiation. To examine the antiviral effect of BL, we further tested whether BL could disturb viral absorption or entry into host cells. The results showed that BL irradiation, but not green light (GL) exposure, specifically decreased plaque-forming activity and viral copy numbers in HSV-1-infected cells. Accumulated BL irradiation inhibited the localization of viral proteins and the RNA expression of characteristic viral genes such as UL19, UL27, and US6, thus exerting to an anti-viral effect. The results also showed that BL exposure during viral absorption interfered with viral entry or destroyed the virus, as assessed by plaque formation and quantitative PCR assays. The levels of the pro-inflammatory mediators interleukin (IL)-18 and IL-1β in M1-polarized macrophages were increased by HSV-1 infection. However, these increases were attenuated by BL irradiation. Importantly, BL irradiation decreased cGAS and STING expression, as well as downstream NF-κB p65, in M1-polarized HSV-1-infected macrophages, demonstrating anti-viral and anti-inflammatory properties. These findings suggest that BL could serve as an anti-viral and anti-inflammatory therapeutic candidate to treat HSV-1 infections.

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

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

Animal models for COVID-19: advances, gaps and perspectives

COVID-19, caused by SARS-CoV-2, is the most consequential pandemic of this century. Since the outbreak in late 2019, animal models have been playing crucial roles in aiding the rapid development of vaccines/drugs for prevention and therapy, as well as understanding the pathogenesis of SARS-CoV-2 infection and immune responses of hosts. However, the current animal models have some deficits and there is an urgent need for novel models to evaluate the virulence of variants of concerns (VOC), antibody-dependent enhancement (ADE), and various comorbidities of COVID-19. This review summarizes the clinical features of COVID-19 in different populations, and the characteristics of the major animal models of SARS-CoV-2, including those naturally susceptible animals, such as non-human primates, Syrian hamster, ferret, minks, poultry, livestock, and mouse models sensitized by genetically modified, AAV/adenoviral transduced, mouse-adapted strain of SARS-CoV-2, and by engraftment of human tissues or cells. Since understanding the host receptors and proteases is essential for designing advanced genetically modified animal models, successful studies on receptors and proteases are also reviewed. Several improved alternatives for future mouse models are proposed, including the reselection of alternative receptor genes or multiple gene combinations, the use of transgenic or knock-in method, and different strains for establishing the next generation of genetically modified mice.

STAT1 and Its Crucial Role in the Control of Viral Infections

The signal transducer and activator of transcription (STAT) 1 protein plays a key role in the immune response against viruses and other pathogens by transducing, in the nucleus, the signal from type I, type II and type III IFNs. STAT1 activates the transcription of hundreds of genes, some of which have been well characterized for their antiviral properties. STAT1 gene deletion in mice and complete STAT1 deficiency in humans both cause rapid death from severe infections. STAT1 plays a key role in the immunoglobulin class-switch recombination through the upregulation of T-bet; it also plays a key role in the production of T-bet+ memory B cells that contribute to tissue-resident humoral memory by mounting an IgG response during re-infection. Considering the key role of STAT1 in the antiviral immune response, many viruses, including dangerous viruses such as Ebola and SARS-CoV-2, have developed different mechanisms to inhibit this transcription factor. The search for drugs capable of targeting the viral proteins implicated in both viral replication and IFN/STAT1 inhibition is important for the treatment of the most dangerous viral infections and for future viral pandemics, as shown by the clinical results obtained with Paxlovid in patients infected with SARS-CoV-2.

UV-LED irradiation reduces the infectivity of herpes simplex virus type 1 by targeting different viral components depending on the peak wavelength

Herpes simplex virus type 1 (HSV-1) is an enveloped virus that mainly infects humans. Given its high global prevalence, disinfection is critical for reducing the risk of infection. Ultraviolet-light-emitting diodes (UV-LEDs) are eco-friendly irradiating modules with different peak wavelengths, but the molecules degraded by UV-LED irradiation have not been clarified. To identify the target viral molecules of UV-LEDs, we exposed HSV-1 suspensions to UV-LED irradiation at wavelengths of 260-, 280-, 310-, and 365-nm and measured viral DNA, protein, and lipid damage and infectivity in host cells. All UV-LEDs substantially reduced by inhibiting host cell transcription, but 260- and 280-nm UV-LEDs had significantly stronger virucidal efficiency than 310- and 365-nm UV-LEDs. Meanwhile, 260- and 280-nm UV-LEDs induced the formation of viral DNA photoproducts and the degradation of viral proteins and some phosphoglycerolipid species. Unlike 260- and 280-nm UV-LEDs, 310- and 365-nm UV-LEDs decreased the viral protein levels, but they did not drastically change the levels of viral DNA photoproducts and lipophilic metabolites. These results suggest that UV-LEDs reduce the infectivity of HSV-1 by targeting different viral molecules based on the peak wavelength. These findings could facilitate the optimization of UV-LED irradiation for viral inactivation.

The Durability of Vaccine Efficacy against Ocular HSV-1 Infection Using ICP0 Mutants 0∆NLS and 0∆RING Is Lost over Time

Vaccines to viral pathogens in experimental animal models are often deemed successful if immunization enhances resistance of the host to virus challenge as measured by cumulative survival, reduction in virus replication and spread and/or lessen or eliminate overt tissue pathology. Furthermore, the duration of the protective response against challenge is another important consideration that drives a vaccination regimen. In the current study, we assessed the durability of two related vaccines, 0∆NLS and 0∆RING, against ocular herpes simplex virus type 1 (HSV-1) challenge in mice thirty days (short-term) and one year (long-term) following the vaccine boost. The short-term vaccine efficacy study found the 0∆RING vaccine to be nearly equivalent to the 0∆NLS vaccine in comparison to vehicle-vaccinated mice in terms of controlling virus replication and preserving the visual axis. By comparison, the long-term assessment of the two vaccines found notable differences and less efficacy overall as noted below. Specifically, the results show that in comparison to vehicle-vaccinated mice, the 0∆NLS and 0∆RING vaccinated groups were more resistant in terms of survival and virus shedding following ocular challenge. Moreover, 0∆NLS vaccinated mice also possessed significantly less infectious virus in the peripheral and central nervous systems but not the cornea compared to mice vaccinated with vehicle or 0∆RING which had similar levels. However, all vaccinated groups showed similar levels of blood and lymphatic vessel genesis into the central cornea 30 days post infection. Likewise, corneal opacity was also similar among all groups of vaccinated mice following infection. Functionally, the blink response and visual acuity were 25-50% lower in vaccinated mice 30 days post infection compared to measurements taken prior to infection. The results demonstrate a dichotomy between resistance to infection and functional performance of the visual axis that collectively show an overall loss in vaccine efficacy long-term in comparison to short-term studies in a conventional prime-boost protocol.

Essential role of M1 macrophages in blocking cytokine storm and pathology associated with murine HSV-1 infection

Ocular HSV-1 infection is a major cause of eye disease and innate and adaptive immunity both play a role in protection and pathology associated with ocular infection. Previously we have shown that M1-type macrophages are the major and earliest infiltrates into the cornea of infected mice. We also showed that HSV-1 infectivity in the presence and absence of M2-macrophages was similar to wild-type (WT) control mice. However, it is not clear whether the absence of M1 macrophages plays a role in protection and disease in HSV-1 infected mice. To explore the role of M1 macrophages in HSV-1 infection, we used mice lacking M1 activation (M1^-/- mice). Our results showed that macrophages from M1^-/- mice were more susceptible to HSV-1 infection in vitro than were macrophages from WT mice. M1^-/- mice were highly susceptible to ocular infection with virulent HSV-1 strain McKrae, while WT mice were refractory to infection. In addition, M1^-/- mice had higher virus titers in the eyes than did WT mice. Adoptive transfer of M1 macrophages from WT mice to M1^-/- mice reduced death and rescued virus replication in the eyes of infected mice. Infection of M1^-/- mice with avirulent HSV-1 strain KOS also increased ocular virus replication and eye disease but did not affect latency-reactivation seen in WT control mice. Severity of virus replication and eye disease correlated with significantly higher inflammatory responses leading to a cytokine storm in the eyes of M1^-/- infected mice that was not seen in WT mice. Thus, for the first time, our study illustrates the importance of M1 macrophages specifically in primary HSV-1 infection, eye disease, and survival but not in latency-reactivation.

Macrophages circulating in the blood or present in different tissues constitute an important barrier against infection. We previously showed that the absence of M2 macrophages does not impact HSV-1 infectivity in vivo. However, in this study we demonstrated an essential role of M1 macrophages in protection from primary HSV-1 replication, death, and eye disease but not in latency-reactivation.

Simple and rapid high-throughput assay to identify HSV-1 ICP0 transactivation inhibitors

Herpes simplex virus 1 (HSV-1) is a ubiquitous virus that results in lifelong infections due to its ability to cycle between lytic replication and latency. As an obligate intracellular pathogen, HSV-1 exploits host cellular factors to replicate and aid in its life cycle. HSV-1 expresses infected cell protein 0 (ICP0), an immediate-early regulator, to stimulate the transcription of all classes of viral genes via its E3 ubiquitin ligase activity. Here we report an automated, inexpensive, and rapid high-throughput approach to examine the effects of small molecule compounds on ICP0 transactivator function in cells. Two HSV-1 reporter viruses, KOS6β (wt) and dlx3.1-6β (ICP0-null mutant), were used to monitor ICP0 transactivation activity through the HSV-1 ICP6 promoter:lacz expression cassette. A ≥10-fold difference in β-galactosidase activity was observed in cells infected with KOS6β compared to dlx3.1-6β, demonstrating that ICP0 potently transactivates the ICP6 promoter. We established the robustness and reproducibility with a Z'-factor score of ≥0.69, an important criterium for high-throughput analyses. Approximately 19,000 structurally diverse compounds were screened and 76 potential inhibitors of the HSV-1 transactivator ICP0 were identified. We expect this assay will aid in the discovery of novel inhibitors and tools against HSV-1 ICP0. Using well-annotated compounds could identify potential novel factors and pathways that interact with ICP0 to promote HSV-1 gene expression.

The Race between Host Antiviral Innate Immunity and the Immune Evasion Strategies of Herpes Simplex Virus 1

Herpes simplex virus 1 (HSV-1) is very successful in establishing acute and latent infections in humans by counteracting host antiviral innate immune responses. HSV-1 has evolved various strategies to evade host antiviral innate immunity and some cellular survival-associated pathways. Since there is still no vaccine available for HSV-1, a continuous update of information regarding the interaction between HSV-1 infection and the host antiviral innate immunity will provide novel insights to develop new therapeutic strategies for HSV-1 infection and its associated diseases. Here, we update recent studies about how HSV-1 evades the host antiviral innate immunity, specifically how HSV-1 proteins directly or indirectly target the adaptors in the antiviral innate immunity signaling pathways to downregulate the signal transduction. Additionally, some classical intracellular stress responses, which also play important roles in defense of viral invasion, will be discussed here. With a comprehensive review of evasion mechanisms of antiviral innate immunity by HSV-1, we will be able to develop potential new targets for therapies and a possible vaccine against HSV-1 infections.

Herpes Simplex Viruses Whose Replication Can Be Deliberately Controlled as Candidate Vaccines

Over the last few years, we have been evaluating a novel paradigm for immunization using viruses or virus-based vectors. Safety is provided not by attenuation or inactivation of vaccine viruses, but by the introduction into the viral genomes of genetic mechanisms that allow for stringent, deliberate spatial and temporal control of virus replication. The resulting replication-competent controlled viruses (RCCVs) can be activated to undergo one or, if desired, several rounds of efficient replication at the inoculation site, but are nonreplicating in the absence of activation. Extrapolating from observations that attenuated replicating viruses are better immunogens than replication-defective or inactivated viruses, it was hypothesized that RCCVs that replicate with wild-type-like efficiency when activated will be even better immunogens. The vigorous replication of the RCCVs should also render heterologous antigens expressed from them highly immunogenic. RCCVs for administration to skin sites or mucosal membranes were constructed using a virulent wild-type HSV-1 strain as the backbone. The recombinants are activated by a localized heat treatment to the inoculation site in the presence of a small-molecule regulator (SMR). Derivatives expressing influenza virus antigens were also prepared. Immunization/challenge experiments in mouse models revealed that the activated RCCVs induced far better protective immune responses against themselves as well as against the heterologous antigens they express than unactivated RCCVs or a replication-defective HSV-1 strain. Neutralizing antibody and proliferation responses mirrored these findings. We believe that the data obtained so far warrant further research to explore the possibility of developing effective RCCV-based vaccines directed to herpetic diseases and/or diseases caused by other pathogens.

The Latency-Associated Transcript Inhibits Apoptosis via Downregulation of Components of the Type I Interferon Pathway during Latent Herpes Simplex Virus 1 Ocular Infection

The herpes simplex virus (HSV-1) latency-associated transcript (LAT) has been shown to inhibit apoptosis via inhibiting activation of proapoptotic caspases. However, the mechanism of LAT control of apoptosis is unclear, because LAT is not known to encode a functional protein, and the LAT transcript is found largely in the nucleus. We hypothesized that LAT inhibits apoptosis by regulating expression of genes that control apoptosis. Consequently, we sought to establish the molecular mechanism of antiapoptosis functions of LAT at a transcriptional level during latent HSV-1 ocular infection in mice. Our results suggest the following. (i) LAT likely inhibits apoptosis via upregulation of several components of the type I interferon (IFN) pathway. (ii) LAT does not inhibit apoptosis via the caspase cascade at a transcriptional level or via downregulating Toll-like receptors (TLRs). (iii) The mechanism of LAT antiapoptotic effect is distinct from that of the baculovirus inhibitor of apoptosis (cpIAP) because replacement of LAT with the cpIAP gene resulted in a different gene expression pattern than in either LAT+ or LAT- viruses. (iv) Replacement of LAT with the cpIAP gene does not cause upregulation of CD8 or markers of T cell exhaustion despite their having similar levels of latency, further supporting that LAT and cpIAP function via distinct mechanisms.IMPORTANCE The HSV-1 latency reactivation cycle is the cause of significant human pathology. The HSV-1 latency-associated transcript (LAT) functions by regulating latency and reactivation, in part by inhibiting apoptosis. However, the mechanism of this process is unknown. Here we show that LAT likely controls apoptosis via downregulation of several components in the JAK-STAT pathway. Furthermore, we provide evidence that immune exhaustion is not caused by the antiapoptotic activity of the LAT.

Immunization by Replication-Competent Controlled Herpesvirus Vectors

We hypothesized that vigorous replication of a pathogen may be critical for eliciting the most potent and balanced immune response against it. Hence, attenuation/inactivation (as in conventional vaccines) should be avoided. Instead, the necessary safety should be provided by placing replication of the pathogen under stringent control and by activating time-limited replication of the pathogen strictly in an administration region in which pathology cannot develop. Immunization will then occur in the context of highly efficient pathogen replication and uncompromised safety. We found that localized activation in mice of efficient but limited replication of a replication-competent controlled herpesvirus vector resulted in a greatly enhanced immune response to the virus or an expressed heterologous antigen. This finding supports the above-mentioned hypothesis and suggests that the vectors may be promising novel agents worth exploring for the prevention/mitigation of infectious diseases for which efficient vaccination is lacking, in particular in immunocompromised patients.

Replication-competent controlled virus vectors were derived from the virulent herpes simplex virus 1 (HSV-1) wild-type strain 17syn+ by placing one or two replication-essential genes under the stringent control of a gene switch that is coactivated by heat and an antiprogestin. Upon activation of the gene switch, the vectors replicate in infected cells with an efficacy that approaches that of the wild-type virus from which they were derived. Essentially no replication occurs in the absence of activation. When administered to mice, localized application of a transient heat treatment in the presence of systemic antiprogestin results in efficient but limited virus replication at the site of administration. The immunogenicity of these viral vectors was tested in a mouse footpad lethal challenge model. Unactivated viral vectors—which may be regarded as equivalents of inactivated vaccines—induced detectable protection against lethality caused by wild-type virus challenge. Single activation of the viral vectors at the site of administration (rear footpads) greatly enhanced protective immune responses, and a second immunization resulted in complete protection. Once activated, vectors also induced far better neutralizing antibody and HSV-1-specific cellular immune responses than unactivated vectors. To find out whether the immunogenicity of a heterologous antigen was also enhanced in the context of efficient transient vector replication, a virus vector constitutively expressing an equine influenza virus hemagglutinin was constructed. Immunization of mice with this recombinant induced detectable antibody-mediated neutralization of equine influenza virus, as well as a hemagglutinin-specific cellular immune response. Single activation of viral replication resulted in a severalfold enhancement of these immune responses.

IMPORTANCE We hypothesized that vigorous replication of a pathogen may be critical for eliciting the most potent and balanced immune response against it. Hence, attenuation/inactivation (as in conventional vaccines) should be avoided. Instead, the necessary safety should be provided by placing replication of the pathogen under stringent control and by activating time-limited replication of the pathogen strictly in an administration region in which pathology cannot develop. Immunization will then occur in the context of highly efficient pathogen replication and uncompromised safety. We found that localized activation in mice of efficient but limited replication of a replication-competent controlled herpesvirus vector resulted in a greatly enhanced immune response to the virus or an expressed heterologous antigen. This finding supports the above-mentioned hypothesis and suggests that the vectors may be promising novel agents worth exploring for the prevention/mitigation of infectious diseases for which efficient vaccination is lacking, in particular in immunocompromised patients.

Immune Escape via a Transient Gene Expression Program Enables Productive Replication of a Latent Pathogen

How type I and II interferons prevent periodic reemergence of latent pathogens in tissues of diverse cell types remains unknown. Using homogeneous neuron cultures latently infected with herpes simplex virus 1, we show that extrinsic type I or II interferon acts directly on neurons to induce unique gene expression signatures and inhibit the reactivation-specific burst of viral genome-wide transcription called phase I. Surprisingly, interferons suppressed reactivation only during a limited period early in phase I preceding productive virus growth. Sensitivity to type II interferon was selectively lost if viral ICP0, which normally accumulates later in phase I, was expressed before reactivation. Thus, interferons suppress reactivation by preventing initial expression of latent genomes but are ineffective once phase I viral proteins accumulate, limiting interferon action. This demonstrates that inducible reactivation from latency is only transiently sensitive to interferon. Moreover, it illustrates how latent pathogens escape host immune control to periodically replicate by rapidly deploying an interferon-resistant state.

Herpesvirus-Associated Lymphadenitis Distorts Fibroblastic Reticular Cell Microarchitecture and Attenuates CD8 T Cell Responses to Neurotropic Infection in Mice Lacking the STING-IFNα/β Defense Pathways

Type I IFN (IFN-α/β)-driven immune responses to acute viral infection are critical to counter replication and prevent dissemination. However, the mechanisms underlying host resistance to HSV type 1 (HSV-1) are incompletely understood. In this study, we show that mice with deficiencies in IFN-α/β signaling or stimulator of IFN genes (STING) exhibit exacerbated neurovirulence and atypical lymphotropic dissemination of HSV-1 following ocular infection. Synergy between IFN-α/β signaling and efficacy of early adaptive immune responses to HSV-1 were dissected using bone marrow chimeras and adoptive cell transfer approaches to profile clonal expansion, effector function, and recruitment of HSV-specific CD8(+) T cells. Lymphotropic viral dissemination was commensurate with abrogated CD8(+) T cell responses and pathological alterations of fibroblastic reticular cell networks in the draining lymph nodes. Our results show that resistance to HSV-1 in the trigeminal ganglia during acute infection is conferred in part by STING and IFN-α/β signaling in both bone marrow-derived and -resident cells, which coalesce to support a robust HSV-1-specific CD8(+) T cell response.

Resident T Cells Are Unable To Control Herpes Simplex Virus-1 Activity in the Brain Ependymal Region during Latency

HSV type 1 (HSV-1) is one of the leading etiologies of sporadic viral encephalitis. Early antiviral intervention is crucial to the survival of herpes simplex encephalitis patients; however, many survivors suffer from long-term neurologic deficits. It is currently understood that HSV-1 establishes a latent infection within sensory peripheral neurons throughout the life of the host. However, the tissue residence of latent virus, other than in sensory neurons, and the potential pathogenic consequences of latency remain enigmatic. In the current study, we characterized the lytic and latent infection of HSV-1 in the CNS in comparison with the peripheral nervous system following ocular infection in mice. We used RT-PCR to detect latency-associated transcripts and HSV-1 lytic cycle genes within the brain stem, the ependyma (EP), containing the limbic and cortical areas, which also harbor neural progenitor cells, in comparison with the trigeminal ganglia. Unexpectedly, HSV-1 lytic genes, usually identified during acute infection, are uniquely expressed in the EP 60 d postinfection when animals are no longer suffering from encephalitis. An inflammatory response was also mounted in the EP by the maintenance of resident memory T cells. However, EP T cells were incapable of controlling HSV-1 infection ex vivo and secreted less IFN-γ, which correlated with expression of a variety of exhaustion-related inhibitory markers. Collectively, our data suggest that the persistent viral lytic gene expression during latency is the cause of the chronic inflammatory response leading to the exhaustion of the resident T cells in the EP.

Changes in Corneal Innervation after HSV-1 Latency Established with Different Reactivation Phenotypes

PURPOSE OF THE STUDY

We used a rabbit model infected with high phenotypic reactivators (HPRs) as well as recombinant HSV-1 (herpes simplex virus 1) with deletions to study their effect on corneal innervations after latency was established.

MATERIALS AND METHODS

Corneas from noninfected New Zealand white rabbits were used to obtain the entire map of corneal innervation. Others were inoculated with the HSV-1 strains McKrae, 17Syn+, or recombinant mutants with glycoprotein K (gK) deletion, or with infected early protein 0 (ICP0) deletion. The animals were euthanized at 124 to 125 days postinfection and the corneas were immunostained with a mouse monoclonal anti-βIII tubulin antibody. Images were acquired with a fluorescence microscope and corneal sub-basal nerve density was calculated on the basis of the whole mount images. Differences between the HSV-infected eyes, and comparison with normal control, were analyzed.

RESULTS

In the noninfected rabbit, the stroma was densely innervated in the central area and as a consequence the sub-basal epithelial nerve bundles were shorter, and no vortex was found. The HSV-infected corneas showed nerve damage in both epithelial and stromal nerves. Corneas infected with ICP0 and gK deletion mutants showed mild to moderate damage, while those infected with 17Syn+ and McKrae strains were seriously damaged. In the eyes infected with ICP0 and gK deletion, there were reduced numbers of sub-basal nerve bundles, but most of the corneas retained a normal stromal network. Corneas infected with 17 Syn+ and McKrae displayed destroyed nerve structures and formation of a scar tissue in the central cornea, in which only a few nerve fibers could be detected.

CONCLUSION

HSV-1 primary corneal infection seriously damages the corneal nerves, persisting for more than 4 months. Reduction of axonal transport (by gK deletion) or virus replication (by ICP0 deletion) significantly attenuated the nerve damage induced by the virus.

Promyelocytic leukemia protein isoform II inhibits infection by human adenovirus type 5 through effects on HSP70 and the interferon response

Promyelocytic leukemia (PML) proteins have been implicated in antiviral responses but PML and associated proteins are also suggested to support virus replication. One isoform, PML-II, is required for efficient transcription of interferon and interferon-responsive genes. We therefore investigated the PML-II contribution to human adenovirus 5 (Ad5) infection, using shRNA-mediated knockdown. HelaΔII cells showed a 2-3-fold elevation in Ad5 yield, reflecting an increase in late gene expression. This increase was found to be due in part to the reduced innate immune response consequent upon PML-II depletion. However, the effect was minor because the viral E4 Orf3 protein targets and inactivates this PML-II function. The major benefit to Ad5 in HelaΔII cells was exerted via an increase in HSP70; depletion of HSP70 completely reversed this replicative advantage. Increased Ad5 late gene expression was not due either to the previously described inhibition of inflammatory responses by HSP70 or to effects of HSP70 on major late promoter or L4 promoter activity, but might be linked to an observed increase in E1B 55K, as this protein is known to be required for efficient late gene expression. The induction of HSP70 by PML-II removal was specific for the HSPA1B gene among the HSP70 gene family and thus was not the consequence of a general stress response. Taken together, these data show that PML-II, through its various actions, has an overall negative effect on the Ad5 lifecycle.

A Highly Efficacious Herpes Simplex Virus 1 Vaccine Blocks Viral Pathogenesis and Prevents Corneal Immunopathology via Humoral Immunity

Correlates of immunologic protection requisite for an efficacious herpes simplex virus 1 (HSV-1) vaccine remain unclear with respect to viral pathogenesis and clinical disease. In the present study, mice were vaccinated with a novel avirulent, live attenuated virus (0ΔNLS) or an adjuvanted glycoprotein D subunit (gD-2) similar to that used in several human clinical trials. Mice vaccinated with 0ΔNLS showed superior protection against early viral replication, neuroinvasion, latency, and mortality compared to that of gD-2-vaccinated or naive mice following ocular challenge with a neurovirulent clinical isolate of HSV-1. Moreover, 0ΔNLS-vaccinated mice exhibited protection against ocular immunopathology and maintained corneal mechanosensory function. Vaccinated mice also showed suppressed T cell activation in the draining lymph nodes following challenge. Vaccine efficacy correlated with serum neutralizing antibody titers. Humoral immunity was identified as the correlate of protection against corneal neovascularization, HSV-1 shedding, and latency through passive immunization. Overall, 0ΔNLS affords remarkable protection against HSV-1-associated ocular sequelae by impeding viral replication, dissemination, and establishment of latency.

IMPORTANCE

HSV-1 manifests in a variety of clinical presentations ranging from a rather benign "cold sore" to more severe forms of infection, including necrotizing stromal keratitis and herpes simplex encephalitis. The present study was undertaken to evaluate a novel vaccine to ocular HSV-1 infection not only for resistance to viral replication and spread but also for maintenance of the visual axis. The results underscore the necessity to reconsider strategies that utilize attenuated live virus as opposed to subunit vaccines against ocular HSV-1 infection.

Inhibition of HSV-1 Replication by Gene Editing Strategy

HSV-1 induced illness affects greater than 85% of adults worldwide with no permanent curative therapy. We used RNA-guided CRISPR/Cas9 gene editing to specifically target for deletion of DNA sequences of the HSV-1 genome that span the region directing expression of ICP0, a key viral protein that stimulates HSV-1 gene expression and replication. We found that CRISPR/Cas9 introduced InDel mutations into exon 2 of the ICP0 gene profoundly reduced HSV-1 infectivity in permissive human cell culture models and protected permissive cells against HSV-1 infection. CRISPR/Cas9 mediated targeting ICP0 prevented HSV-1-induced disintegration of promonocytic leukemia (PML) nuclear bodies, an intracellular event critical to productive HSV-1 infection that is initiated by interaction of the ICP0 N-terminus with PML. Combined treatment of cells with CRISPR targeting ICP0 plus the immediate early viral proteins, ICP4 or ICP27, completely abrogated HSV-1 infection. We conclude that RNA-guided CRISPR/Cas9 can be used to develop a novel, specific and efficacious therapeutic and prophylactic platform for targeted viral genomic ablation to treat HSV-1 diseases.

Antibodies Are Required for Complete Vaccine-Induced Protection against Herpes Simplex Virus 2

Herpes simplex virus 2 (HSV-2) 0ΔNLS is a live HSV-2 ICP0- mutant vaccine strain that is profoundly attenuated in vivo due to its interferon-hypersensitivity. Recipients of the HSV-2 0ΔNLS vaccine are resistant to high-dose HSV-2 challenge as evidenced by profound reductions in challenge virus spread, shedding, disease and mortality. In the current study, we investigated the requirements for HSV-2 0ΔNLS vaccine-induced protection. Studies using (UV)-inactivated HSV-2 0ΔNLS revealed that self-limited replication of the attenuated virus was required for effective protection from vaginal or ocular HSV-2 challenge. Diminished antibody responses in recipients of the UV-killed HSV-2 vaccine suggested that antibodies might be playing a critical role in early protection. This hypothesis was investigated in B-cell-deficient μMT mice. Vaccination with live HSV-2 0ΔNLS induced equivalent CD8+ T cell responses in wild-type and μMT mice. Vaccinated μMT mice shed ~40-fold more infectious HSV-2 at 24 hours post-challenge relative to vaccinated wild-type (B-cell+) mice, and most vaccinated μMT mice eventually succumbed to a slowly progressing HSV-2 challenge. Importantly, passive transfer of HSV-2 antiserum restored full protection to HSV-2 0ΔNLS-vaccinated μMT mice. The results demonstrate that B cells are required for complete vaccine-induced protection against HSV-2, and indicate that virus-specific antibodies are the dominant mediators of early vaccine-induced protection against HSV-2.

Replication-Competent Controlled Herpes Simplex Virus

We present the development and characterization of a replication-competent controlled herpes simplex virus 1 (HSV-1). Replication-essential ICP4 and ICP8 genes of HSV-1 wild-type strain 17syn+ were brought under the control of a dually responsive gene switch. The gene switch comprises (i) a transactivator that is activated by a narrow class of antiprogestins, including mifepristone and ulipristal, and whose expression is mediated by a promoter cassette that comprises an HSP70B promoter and a transactivator-responsive promoter and (ii) transactivator-responsive promoters that drive the ICP4 and ICP8 genes. Single-step growth experiments in different cell lines demonstrated that replication of the recombinant virus, HSV-GS3, is strictly dependent on an activating treatment consisting of administration of a supraphysiological heat dose in the presence of an antiprogestin. The replication-competent controlled virus replicates with an efficiency approaching that of the wild-type virus from which it was derived. Essentially no replication occurs in the absence of activating treatment or if HSV-GS3-infected cells are exposed only to heat or antiprogestin. These findings were corroborated by measurements of amounts of viral DNA and transcripts of the regulated ICP4 gene and the glycoprotein C (gC) late gene, which was not regulated. Similar findings were made in experiments with a mouse footpad infection model.

IMPORTANCE

The alphaherpesviruses have long been considered vectors for recombinant vaccines and oncolytic therapies. The traditional approach uses vector backbones containing attenuating mutations that restrict replication to ensure safety. The shortcoming of this approach is that the attenuating mutations tend to limit both the immune presentation and oncolytic properties of these vectors. HSV-GS3 represents a novel type of vector that, when activated, replicates with the efficiency of a nonattenuated virus and whose safety is derived from deliberate, stringent regulation of multiple replication-essential genes. By directing activating heat to the region of virus administration, replication is strictly confined to infected cells within this region. The requirement for antiprogestin provides an additional level of safety, ensuring that virus replication cannot be triggered inadvertently. Replication-competent controlled vectors such as HSV-GS3 may have the potential to be superior to conventional attenuated HSV vaccine and oncolytic vectors without sacrificing safety.

Cellular Protein WDR11 Interacts with Specific Herpes Simplex Virus Proteins at the trans-Golgi Network To Promote Virus Replication

It has recently been proposed that the herpes simplex virus (HSV) protein ICP0 has cytoplasmic roles in blocking antiviral signaling and in promoting viral replication in addition to its well-known proteasome-dependent functions in the nucleus. However, the mechanisms through which it produces these effects remain unclear. While investigating this further, we identified a novel cytoplasmic interaction between ICP0 and the poorly characterized cellular protein WDR11. During an HSV infection, WDR11 undergoes a dramatic change in localization at late times in the viral replication cycle, moving from defined perinuclear structures to a dispersed cytoplasmic distribution. While this relocation was not observed during infection with viruses other than HSV-1 and correlated with efficient HSV-1 replication, the redistribution was found to occur independently of ICP0 expression, instead requiring viral late gene expression. We demonstrate for the first time that WDR11 is localized to the trans-Golgi network (TGN), where it interacts specifically with some, but not all, HSV virion components, in addition to ICP0. Knockdown of WDR11 in cultured human cells resulted in a modest but consistent decrease in yields of both wild-type and ICP0-null viruses, in the supernatant and cell-associated fractions, without affecting viral gene expression. Although further study is required, we propose that WDR11 participates in viral assembly and/or secondary envelopment.

IMPORTANCE

While the TGN has been proposed to be the major site of HSV-1 secondary envelopment, this process is incompletely understood, and in particular, the role of cellular TGN components in this pathway is unknown. Additionally, little is known about the cellular functions of WDR11, although the disruption of this protein has been implicated in multiple human diseases. Therefore, our finding that WDR11 is a TGN-resident protein that interacts with specific viral proteins to enhance viral yields improves both our understanding of basic cellular biology as well as how this protein is co-opted by HSV.

A novel approach for addressing diseases not yielding to effective vaccination? Immunization by replication-competent controlled virus

Vaccination involves inoculation of a subject with a disabled disease-causing microbe or parts thereof. While vaccination has been highly successful, we still lack sufficiently effective vaccines for important infectious diseases. We propose that a more complete immune response than that elicited from a vaccine may be obtained from immunization with a disease-causing virus modified to subject replication-essential genes to the control of a gene switch activated by non-lethal heat in the presence of a drug-like compound. Upon inoculation, strictly localized replication of the virus would be triggered by a heat dose administered to the inoculation site. Activated virus would transiently replicate with an efficiency approaching that of the disease-causing virus and express all viral antigens. It may also vector heterologous antigens or control co-infecting microbes.

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

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

The Current State of Vaccine Development for Ocular HSV-1 Infection

HSV-1 continues to be the leading cause of infectious corneal blindness. Clinical trials for vaccines against genital HSV infection have been ongoing for more than three decades. Despite this, no approved vaccine exists, and no formal clinical trials have evaluated the impact of HSV vaccines on eye health. We review here the current state of development for an efficacious HSV-1 vaccine and call for involvement of ophthalmologists and vision researchers.

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

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

Novel roles of cytoplasmic ICP0: proteasome-independent functions of the RING finger are required to block interferon-stimulated gene production but not to promote viral replication

The immediate-early protein ICP0 from herpes simplex virus 1 (HSV-1) plays pleiotropic roles in promoting viral lytic replication and reactivation from latency. Most of the known actions of ICP0 occur in the nucleus and are thought to involve the E3 ubiquitin ligase activity of its RING finger domain, which targets proteins for degradation via the proteasome. Although ICP0 translocates to the cytoplasm as the infection progresses, little is known about its activities in this location. Here, we show that cytoplasmic ICP0 has two distinct functions. In primary cell cultures and in an intravaginal mouse model, cytoplasmic ICP0 promotes viral replication in the absence of an intact RING finger domain. Additionally, ICP0 blocks the activation of interferon regulatory factor 3 (IRF3), a key transcription factor of the innate antiviral response, in a mechanism that requires the RING finger domain but not the proteasome. To our knowledge, this is the first observation of a proteasome-independent function of the RING finger domain of ICP0. Collectively, these results underscore the importance of cytoplasm-localized ICP0 and the diverse nature of its activities. Importance: Despite ICP0 being a well-studied viral protein, the significance of its cytoplasmic localization has been largely overlooked. This is, in part, because common experimental manipulations result in the restriction of ICP0 to the nucleus. By overcoming this constraint, we both further characterize the ability of cytoplasmic ICP0 to inhibit antiviral signaling and show that ICP0 at this site has unexpected activities in promoting viral replication. This demonstrates the importance of considering location when analyzing protein function and adds a new perspective to our understanding of this multifaceted protein.

A forward phenotypically driven unbiased genetic analysis of host genes that moderate herpes simplex virus virulence and stromal keratitis in mice

Both viral and host genetics affect the outcome of herpes simplex virus type 1 (HSV-1) infection in humans and experimental models. Little is known about specific host gene variants and molecular networks that influence herpetic disease progression, severity, and episodic reactivation. To identify such host gene variants we have initiated a forward genetic analysis using the expanded family of BXD strains, all derived from crosses between C57BL/6J and DBA/2J strains of mice. One parent is highly resistant and one highly susceptible to HSV-1. Both strains have also been fully sequenced, greatly facilitating the search for genetic modifiers that contribute to differences in HSV-1 infection. We monitored diverse disease phenotypes following infection with HSV-1 strain 17syn+ including percent mortality (herpes simplex encephalitis, HSE), body weight loss, severity of herpetic stromal keratitis (HSK), spleen weight, serum neutralizing antibody titers, and viral titers in tear films in BXD strains. A significant quantitative trait locus (QTL) on chromosome (Chr) 16 was found to associate with both percent mortality and HSK severity. Importantly, this QTL maps close to a human QTL and the gene proposed to be associated with the frequency of recurrent herpetic labialis (cold sores). This suggests that a single host locus may influence these seemingly diverse HSV-1 pathogenic phenotypes by as yet unknown mechanisms. Additional suggestive QTLs for percent mortality were identified—one on Chr X that is epistatically associated with that on Chr 16. As would be anticipated the Chr 16 QTL also modulated weight loss, reaching significance in females. A second significant QTL for maximum weight loss in male and female mice was mapped to Chr 12. To our knowledge this is the first report of a host genetic locus that modulates the severity of both herpetic disease in the nervous system and herpetic stromal keratitis.

The differential interferon responses of two strains of Stat1-deficient mice do not alter susceptibility to HSV-1 and VSV in vivo

Stat1 is a pivotal transcription factor for generation of the interferon (IFN)-dependent antiviral response. Two Stat1 knockout mouse lines have been previously generated, one deleted the N-terminal domain (ΔNTD) and one in the DNA-binding domain (ΔDBD). These widely-used strains are assumed interchangeable, and both are highly susceptible to various pathogens. In this study, primary cells derived from ΔNTD mice were shown to be significantly more responsive to IFN, and established an antiviral state with greater efficiency than cells derived from ΔDBD mice, following infection with vesicular stomatitis virus and herpes simplex virus type-1. Also, while mice from both strains succumbed rapidly and equally to virus infection, ΔDBD mice supported significantly higher replication in brains and livers than ΔNTD mice. Endpoint-type experimental comparisons of these mouse strains are therefore misleading in failing to indicate important differences in virus replication and innate response.

Herpes simplex virus type 1 virion-derived US11 inhibits type 1 interferon-induced protein kinase R phosphorylation

The herpes simplex virus type 1 (HSV-1) VRTK(-) strain that was previously isolated in our laboratory as an acyclovir-resistant thymidine kinase (TK)-deficient mutant, is more sensitive to type 1 interferon than is the parent strain VR3. The properties of this mutant were investigated to clarify the mechanism for its hyper-sensitivity to interferon (IFN). It was found that: (i) IFN-pretreated cells, but not those treated with IFN after adsorption, are hyper-sensitive to IFN; (ii) the mutant cannot inhibit protein kinase R phosphorylation efficiently during the early stage of replication (2 hrs post-infection); (iii) expression of US11 in infected cells and its incorporation into the virion is reduced in the mutant compared to the wild type, despite the fact that a similar degree of DNA synthesis occurs during replication of both strains and; (iv) over-expression of wild-type viral TK has no effect on the phenotype of the VRTK(-) strain, indicating that the phenotype is induced by a mutation(s) that does not involve the TK gene. These results suggested that the presence of US11 in the virion, but not that expressed after infection, plays an important role in the escape function of HSV-1 from the antiviral activity of type 1 IFN.

Promyelocytic leukemia protein modulates establishment and maintenance of latent gammaherpesvirus infection in peritoneal cells

Promyelocytic leukemia protein (PML) is an essential organizer of PML nuclear bodies (NBs), which carry out a variety of activities, including antiviral functions. Herpesviruses from all subfamilies encode proteins that counteract PML NB-mediated antiviral defenses by multiple mechanisms. However, because of the species specificity of herpesviruses, only a limited number of in vivo studies have been undertaken to investigate the effect of PML or PML NBs on herpesvirus infection. To address this central issue in herpesvirus biology, we studied the course of infection in wild-type and PML⁻/⁻ mice using murine gammaherpesvirus 68 (MHV68), which encodes a tegument protein that induces PML degradation. While acute infection in PML⁻/⁻ mice progressed similarly to that in wild-type mice, the lytic reactivation frequency was higher in peritoneal exudate cells, due to both an increase of MHV68 genome-positive cells and greater reactivation efficiency. We also detected a higher frequency of persistent infection in PML⁻/⁻ peritoneal cells. These findings suggest that the PML protein can repress the establishment or maintenance of gammaherpesvirus latency in vivo. Further use of the PML⁻/⁻ mouse model should aid in dissecting the molecular mechanisms that underlie the role of PML in gammaherpesvirus latency and may yield clues for how PML modulates herpesvirus latency in general.

hTERT extends the life of human fibroblasts without compromising type I interferon signaling

Primary cells are often used to study viral replication and host-virus interactions as their antiviral pathways have not been altered or inactivated; however, their use is restricted by their short lifespan. Conventional methods to extend the life of primary cultures typically utilize viral oncogenes. Many of these oncogenes, however, perturb or inactivate cellular antiviral pathways, including the interferon (IFN) response. It has been previously shown that expression of the telomerase reverse transcriptase (TERT) gene extends the life of certain cell types. The effect that TERT expression has on the innate antiviral response to RNA- and DNA-containing viruses has not been examined. In the current study, we introduced the human TERT (hTERT) gene into a primary human embryonic lung (HEL-299) cell strain, which is known to respond to the type I IFN, IFN-β. We show that the resulting HEL-TERT cell line is capable of replicating beyond 100 population doublings without exhibiting signs of senescence. Treatment with IFN-β resulted in the upregulation of four model IFN stimulated genes (ISGs) in HEL-299 and HEL-TERT cells. Both cell lines supported the replication of herpes simplex virus type 1 (HSV-1) and vesicular stomatitis virus (VSV) and impaired the replication of both viruses upon IFN-β pretreatment. Introduction of the viral oncoprotein, simian virus 40 (SV40) large T-antigen, which is frequently used to immortalize cells, largely negated this effect. Taken together, our data indicate that expression of hTERT does not alter type 1 IFN signaling and/or the growth of two viruses, making this cell line a useful reagent for studying viral replication and virus-cell interactions.

Viral interactions with microtubules: orchestrators of host cell biology?

Viral interaction with the microtubule (MT) cytoskeleton is critical to infection by many viruses. Most data regarding virus–MT interaction indicate key roles in the subcellular transport of virions/viral genomic material to sites of replication, assembly and egress. However, the MT cytoskeleton orchestrates diverse processes in addition to subcellular cargo transport, including regulation of signaling pathways, cell survival and mitosis, suggesting that viruses, expert manipulators of the host cell, may use the virus–MT interface to control multiple aspects of cell biology. Several lines of evidence support this idea, indicating that specific viral proteins can modify MT dynamics and/or structure and regulate processes such as apoptosis and innate immune signaling through MT-dependent mechanisms. Here, the authors review general aspects of virus–MT interactions, with emphasis on viral mechanisms that modify MT dynamics and functions to affect processes beyond virion transport. The emerging importance of discrete viral protein–MT interactions in pathogenic processes indicates that these interfaces may represent new targets for future therapeutics and vaccine development.

Herpes simplex virus 1 tropism for human sensory ganglion neurons in the severe combined immunodeficiency mouse model of neuropathogenesis

The tropism of herpes simplex virus (HSV-1) for human sensory neurons infected in vivo was examined using dorsal root ganglion (DRG) xenografts maintained in mice with severe combined immunodeficiency (SCID). In contrast to the HSV-1 lytic infectious cycle in vitro, replication of the HSV-1 F strain was restricted in human DRG neurons despite the absence of adaptive immune responses in SCID mice, allowing the establishment of neuronal latency. At 12 days after DRG inoculation, 26.2% of human neurons expressed HSV-1 protein and 13.1% expressed latency-associated transcripts (LAT). Some infected neurons showed cytopathic changes, but HSV-1, unlike varicella-zoster virus (VZV), only rarely infected satellite cells and did not induce fusion of neuronal and satellite cell plasma membranes. Cell-free enveloped HSV-1 virions were observed, indicating productive infection. A recombinant HSV-1-expressing luciferase exhibited less virulence than HSV-1 F in the SCID mouse host, enabling analysis of infection in human DRG xenografts for a 61-day interval. At 12 days after inoculation, 4.2% of neurons expressed HSV-1 proteins; frequencies increased to 32.1% at 33 days but declined to 20.8% by 61 days. Frequencies of LAT-positive neurons were 1.2% at 12 days and increased to 40.2% at 33 days. LAT expression remained at 37% at 61 days, in contrast to the decline in neurons expressing viral proteins. These observations show that the progression of HSV-1 infection is highly restricted in human DRG, and HSV-1 genome silencing occurs in human neurons infected in vivo as a consequence of virus-host cell interactions and does not require adaptive immune control.

Ex vivo organotypic corneal model of acute epithelial herpes simplex virus type I infection

Herpes keratitis is one of the most severe pathologies associated with the herpes simplex virus-type 1 (HSV-1). Herpes keratitis is currently the leading cause of both cornea-derived and infection-associated blindness in the developed world. Typical presentation of herpes keratitis includes infection of the corneal epithelium and sometimes the deeper corneal stroma and endothelium, leading to such permanent corneal pathologies as scarring, thinning, and opacity. Corneal HSV-1 infection is traditionally studied in two types of experimental models. The in vitro model, in which cultured monolayers of corneal epithelial cells are infected in a Petri dish, offers simplicity, high level of replicability, fast experiments, and relatively low costs. On the other hand, the in vivo model, in which animals such as rabbits or mice are inoculated directly in the cornea, offers a highly sophisticated physiological system, but has higher costs, longer experiments, necessary animal care, and a greater degree of variability. In this video article, we provide a detailed demonstration of a new ex vivo model of corneal epithelial HSV-1 infection, which combines the strengths of both the in vitro and the in vivo models. The ex vivo model utilizes intact corneas organotypically maintained in culture and infected with HSV-1. The use of the ex vivo model allows for highly physiologically-based conclusions, yet it is rather inexpensive and requires time commitment comparable to that of the in vitro model.

Rabbit and mouse models of HSV-1 latency, reactivation, and recurrent eye diseases

The exact mechanisms of HSV-1 establishment, maintenance, latency, reactivation, and also the courses of recurrent ocular infections remain a mystery. Comprehensive understanding of the HSV-1 disease process could lead to prevention of HSV-1 acute infection, reactivation, and more effective treatments of recurrent ocular disease. Animal models have been used for over sixty years to investigate our concepts and hypotheses of HSV-1 diseases. In this paper we present descriptions and examples of rabbit and mouse eye models of HSV-1 latency, reactivation, and recurrent diseases. We summarize studies in animal models of spontaneous and induced HSV-1 reactivation and recurrent disease. Numerous stimuli that induce reactivation in mice and rabbits are described, as well as factors that inhibit viral reactivation from latency. The key features, advantages, and disadvantages of the mouse and rabbit models in relation to the study of ocular HSV-1 are discussed. This paper is pertinent but not intended to be all inclusive. We will give examples of key papers that have reported novel discoveries related to the review topics.

Inhibition of Indoleamine-2,3-dioxygenase (IDO) in Glioblastoma Cells by Oncolytic Herpes Simplex Virus

Successful oncolytic virus treatment of malignant glioblastoma multiforme depends on widespread tumor-specific lytic virus replication and escape from mitigating innate immune responses to infection. Here we characterize a new HSV vector, JD0G, that is deleted for ICP0 and the joint sequences separating the unique long and short elements of the viral genome. We observed that JD0G replication was enhanced in certain glioblastoma cell lines compared to HEL cells, suggesting that a vector backbone deleted for ICP0 may be useful for treatment of glioblastoma. The innate immune response to virus infection can potentially impede oncolytic vector replication in human tumors. Indoleamine-2,3-dioxygenase (IDO) is expressed in response to interferon γ (IFNγ) and has been linked to both antiviral functions and to the immune escape of tumor cells. We observed that IFNγ treatment of human glioblastoma cells induced the expression of IDO and that this expression was quelled by infection with both wild-type and JD0G viruses. The role of IDO in inhibiting virus replication and the connection of this protein to the escape of tumor cells from immune surveillance suggest that IDO downregulation by HSV infection may enhance the oncolytic activity of vectors such as JD0G.

Future of an "Asymptomatic" T-cell Epitope-Based Therapeutic Herpes Simplex Vaccine

Considering the limited success of the recent herpes clinical vaccine trial [1], new vaccine strategies are needed. Infections with herpes simplex virus type 1 and type 2 (HSV-1 & HSV-2) in the majority of men and women are usually asymptomatic and results in lifelong viral latency in neurons of sensory ganglia (SG). However, in a minority of men and women HSV spontaneous reactivation can cause recurrent disease (i.e., symptomatic individuals). Our recent findings show that T cells from symptomatic and asymptomatic men and women (i.e. those with and without recurrences, respectively) recognize different herpes epitopes. This finding breaks new ground and opens new doors to assess a new vaccine strategy: mucosal immunization with HSV-1 & HSV-2 epitopes that induce strong in vitro CD4 and CD8 T cell responses from PBMC derived from asymptomatic men and women (designated here as "asymptomatic" protective epitopes") could boost local and systemic "natural" protective immunity, induced by wild-type infection. Here we highlight the rationale and the future of our emerging "asymptomatic" T cell epitope-based mucosal vaccine strategy to decrease recurrent herpetic disease.

Histone modifications in herpesvirus infections

In eukaryotic cells, gene expression is not only regulated by transcription factors but also by several epigenetic mechanisms including post-translational modifications of histone proteins. There are numerous histone modifications described to date and methylation, acetylation, ubiquitination and phosphorylation are amongst the best studied. In parallel, certain viruses interact with the very same regulatory mechanisms, hereby manipulating the normal epigenetic landscape of the host cell, to fit their own replication needs. This review concentrates on herpesviruses specifically and how they interfere with the histone-modifying enzymes to regulate their replication cycles. Herpesviruses vary greatly with respect to the cell types they infect and the clinical diseases they cause, yet they share various common features including their capacity to encode viral proteins which affect and interfere with the normal functions of histone-modifying enzymes. Studying the epigenetic manipulation/dysregulation of herpesvirus-host interactions not only generates novel insights into the pathogenesis of these viruses but may also have important therapeutic implications.

Control of HSV-1 latency in human trigeminal ganglia--current overview

Although recurrent Herpes simplex virus type 1 (HSV-1) infections are quite common in humans, little is known about the exact molecular mechanisms involved in latency and reactivation of the virus from its stronghold, the trigeminal ganglion. After primary infection, HSV-1 establishes latency in sensory neurons, a state that lasts for the life of the host. Reactivation of the virus leads to recurrent disease, ranging from relatively harmless cold sores to ocular herpes. If herpes encephalitis-often a devastating disease-is also caused by reactivation or a new infection, is still a matter of debate. It is widely accepted that CD8(+) T cells as well as host cellular factors play a crucial role in maintaining latency. At least in the animal model, IFNγ and Granzyme B secretion of T cells were shown to be important for control of viral latency. Furthermore, the virus itself expresses factors that regulate its own latency-reactivation cycle. In this regard, the latency associated transcript, immediate-early proteins, and viral miRNAs seem to be the key players that control latency and reactivation on the viral side. This review focuses on HSV-1 latency in humans in the light of mechanisms learned from animal models.

The multifaceted roles of USP7: new therapeutic opportunities

The deubiquitylating enzyme USP7 (HAUSP) sits at a critical node regulating the activities of numerous proteins broadly characterized as tumor suppressors, DNA repair proteins, immune responders, viral proteins, and epigenetic modulators. Aberrant USP7 activity may promote oncogenesis and viral disease making it a compelling target for therapeutic intervention. Disclosed drug discovery programs have identified inhibitors of USP7 such as P005091 with cellular proof of concept and anti-proliferative activity in cancer models. Taken together, USP7 inhibitors hold promise as a new strategy for the treatment of disease.

Functional genomics reveals an essential and specific role for Stat1 in protection of the central nervous system following herpes simplex virus corneal infection

Innate immune deficiencies result in a spectrum of severe clinical outcomes following infection. In particular, there is a strong association between loss of the signal transducer and activator of transcription (Stat) pathway, breach of the blood-brain barrier (BBB), and virus-induced neuropathology. The gene signatures that characterize resistance, disease, and mortality in the virus-infected nervous system have not been defined. Herpes simplex virus type 1 (HSV-1) is commonly associated with encephalitis in humans, and humans and mice lacking Stat1 display increased susceptibility to HSV central nervous system (CNS) infections. In this study, two HSV-1 strains were used, KOS (wild type [WT]), and Δvhs, an avirulent recombinant lacking the virion host shutoff (vhs) function. In addition, two mouse strains were used: strain 129 (control) and a Stat1-deficient (Stat1(-/-)) strain. Using combinations of these virus and mouse strains, we established a model of infection resulting in three different outcomes: viral clearance without neurological disease (Δvhs infection of control mice), neurological disease followed by viral clearance (Δvhs infection of Stat1(-/-) mice and WT infection of control mice), or neurological disease followed by death (WT infection of Stat1(-/-) mice). Through the use of functional genomics on the infected brain stems, we determined gene signatures that were representative of the three infection outcomes. We demonstrated a pathological signature in the brain stem of Stat1-deficient mice characterized by upregulation of transcripts encoding chemokine receptors, inflammatory markers, neutrophil chemoattractants, leukocyte adhesion proteins, and matrix metalloproteases. Additionally, there was a greater than 100-fold increase in the inflammatory markers interleukin 1β (IL-1β) and IL-6. Consistent with this gene signature, we demonstrated profound CNS inflammation with a concomitant lethal breach of the BBB. Taken together, our results indicated an essential role for normal Stat1-dependent signaling in mediating a nonpathological immune response to viral CNS infection.

Herpes simplex virus 1 ICP0 phosphorylation site mutants are attenuated for viral replication and impaired for explant-induced reactivation

In cell culture experiments, phosphorylation appears to be a critical regulator of the herpes simplex virus 1 (HSV-1) immediate-early (IE) protein, ICP0, which is an E3 ubiquitin ligase that transactivates viral gene expression. Three major regions of phosphorylation in ICP0 (amino acids 224 to 232, 365 to 371, and 508 to 518) have been identified, and mutant viruses that block phosphorylation sites within each region (termed Phos 1, 2, and 3, respectively) have been constructed. Previous studies indicated that replication of Phos 1 is significantly reduced compared to that of wild-type virus in cell culture (C. Boutell, et al., J. Virol. 82:10647-10656, 2008). To determine the effects these phosphorylation site mutations have on the viral life cycle in vivo, mice were ocularly infected with wild-type HSV-1, the Phos mutants, or their marker rescue counterparts. Subsequently, viral replication, establishment of latency, and viral explant-induced reactivation of these viruses were examined. Relative to wild-type virus, Phos 1 eye titers were reduced as much as 7- and 18-fold on days 1 and 5 postinfection, respectively. Phos 2 eye titers showed a decrease of 6-fold on day 1 postinfection. Titers of Phos 1 and 2 trigeminal ganglia were reduced as much as 16- and 20-fold, respectively, on day 5 postinfection. Additionally, the reactivation efficiencies of Phos 1 and 2 were impaired relative to wild-type HSV-1, although both viruses established wild-type levels of latency in vivo. The acute replication, latency, and reactivation phenotypes of Phos 3 were similar to those of wild-type HSV-1. We conclude from these studies that phosphorylation is likely a key modulator of ICP0's biological activities in a mouse ocular model of HSV-1 infection.

Bioluminescent imaging reveals divergent viral pathogenesis in two strains of Stat1-deficient mice, and in αßγ interferon receptor-deficient mice

Pivotal components of the IFN response to virus infection include the IFN receptors (IFNR), and the downstream factor signal transducer and activator of transcription 1 (Stat1). Mice deficient for Stat1 and IFNR (Stat1(-/-) and IFNαßγR(-/-) mice) lack responsiveness to IFN and exhibit high sensitivity to various pathogens. Here we examined herpes simplex virus type 1 (HSV-1) pathogenesis in Stat1(-/-) mice and in IFNαßγR(-/-) mice following corneal infection and bioluminescent imaging. Two divergent and paradoxical patterns of infection were observed. Mice with an N-terminal deletion in Stat1 (129Stat1(-/-) (N-term)) had transient infection of the liver and spleen, but succumbed to encephalitis by day 10 post-infection. In stark contrast, infection of IFNαßγR(-/-) mice was rapidly fatal, with associated viremia and fulminant infection of the liver and spleen, with infected infiltrating cells being primarily of the monocyte/macrophage lineage. To resolve the surprising difference between Stat1(-/-) and IFNαßγR(-/-) mice, we infected an additional Stat1(-/-) strain deleted in the DNA-binding domain (129Stat1(-/-) (DBD)). These 129Stat1(-/-) (DBD) mice recapitulated the lethal pattern of liver and spleen infection seen following infection of IFNαßγR(-/-) mice. This lethal pattern was also observed when 129Stat1(-/-) (N-term) mice were infected and treated with a Type I IFN-blocking antibody, and immune cells derived from 129Stat1(-/-) (N-term) mice were shown to be responsive to Type I IFN. These data therefore show significant differences in viral pathogenesis between two commonly-used Stat1(-/-) mouse strains. The data are consistent with the hypothesis that Stat1(-/-) (N-term) mice have residual Type I IFN receptor-dependent IFN responses. Complete loss of IFN signaling pathways allows viremia and rapid viral spread with a fatal infection of the liver. This study underscores the importance of careful comparisons between knockout mouse strains in viral pathogenesis, and may also be relevant to the causation of HSV hepatitis in humans, a rare but frequently fatal infection.

Herpes simplex virus immediate-early protein ICP0 is targeted by SIAH-1 for proteasomal degradation

Herpes simplex virus (HSV) immediate-early protein ICP0 is a transcriptional activator with E3 ubiquitin ligase activity that induces the degradation of ND10 proteins, including the promyelocytic leukemia protein (PML) and Sp100. Moreover, ICP0 has a role in the derepression of viral genomes and in the modulation of the host interferon response to virus infection. Here, we report that ICP0 interacts with SIAH-1, a cellular E3 ubiquitin ligase that is involved in multiple cellular pathways and is itself capable of mediating PML degradation. This novel virus-host interaction profoundly stabilized SIAH-1 and recruited this cellular E3 ligase into ICP0-containing nuclear bodies. Moreover, SIAH-1 mediated the polyubiquitination of HSV ICP0 in vitro and in vivo. After infection of SIAH-1 knockdown cells with HSV, higher levels of ICP0 were produced, ICP0 was less ubiquitinated, and the half-life of this multifunctional viral regulatory protein was increased. These results indicate an inhibitory role of SIAH-1 during lytic infection by targeting ICP0 for proteasomal degradation.

HSV-1 ICP0: paving the way for viral replication

Herpes simplex virus type 1 (HSV-1) has two distinct phases of its viral life cycle: lytic and latent. One viral immediate-early protein that is responsible for determining the balance between productive lytic replication and reactivation from latency is infected cell protein 0 (ICP0). ICP0 is a 775-amino acid really interesting new gene (RING)-finger-containing protein that possesses E3 ubiquitin ligase activity, which is required for ICP0 to activate HSV-1 gene expression, disrupt nuclear domain (ND) 10 structures, mediate the degradation of cellular proteins, and evade the host cell's intrinsic and innate antiviral defenses. This article examines our current understanding of ICP0's transactivating, E3 ubiquitin ligase, and antihost defense activities and their inter-relationships to one another. Lastly, we will discuss how these properties of ICP0 may be utilized as possible targets for HSV-1 antiviral therapies.