Loss of ICP22 in HSV-1 Elicits Immune Infiltration and Maintains Stromal Keratitis Despite Reduced Primary and Latent Virus Infectivity

Herpes simplex keratitis: A brief clinical overview

The aim of our minireview is to provide a brief overview of the diagnosis, clinical aspects, treatment options, management, and current literature available regarding herpes simplex keratitis (HSK). This type of corneal viral infection is caused by the herpes simplex virus (HSV), which can affect several tissues, including the cornea. One significant aspect of HSK is its potential to cause recurrent episodes of inflammation and damage to the cornea. After the initial infection, the HSV can establish a latent infection in the trigeminal ganglion, a nerve cluster near the eye. The virus may remain dormant for extended periods. Periodic reactivation of the virus can occur, leading to recurrent episodes of HSK. Factors triggering reactivation include stress, illness, immunosuppression, or trauma. Recurrent episodes can manifest in different clinical patterns, ranging from mild epithelial involvement to more severe stromal or endothelial disease. The severity and frequency of recurrences vary among individuals. Severe cases of HSK, especially those involving the stroma and leading to scarring, can result in vision impairment or even blindness in extreme cases. The cornea's clarity is crucial for good vision, and scarring can compromise this, potentially leading to visual impairment. The management of HSK involves not only treating acute episodes but also implementing long-term strategies to prevent recurrences and attempt repairs of corneal nerve endings via neurotization. Antiviral medications, such as oral Acyclovir or topical Ganciclovir, may be prescribed for prophylaxis. The immune response to the virus can contribute to corneal damage. Inflammation, caused by the body's attempt to control the infection, may inadvertently harm the corneal tissues. Clinicians should be informed about triggers and advised on measures to minimize the risk of reactivation. In summary, the recurrent nature of HSK underscores the importance of both acute and long-term management strategies to preserve corneal health and maintain optimal visual function.

Absence of CD80 reduces HSV-1 replication in the eye and delays reactivation but not latency levels

Herpes simplex virus-1 (HSV-1) infections are among the most frequent serious viral eye infections in the U.S. and are a major cause of viral-induced blindness. HSV-1 infection is known to induce T cell activation, proliferation, and differentiation that play crucial roles in the development of virus-induced inflammatory lesions, leading to eye disease and causing chronic corneal damage. CD80 is a co-stimulatory molecule and plays a leading role in T cell differentiation. Previous efforts to limit lesion severity by controlling inflammation at the cellular level led us to ask whether mice knocked out for CD80 would show attenuated virus replication following reactivation. By evaluating the effects of CD80 activity on primary and latent infection, we found that in the absence of CD80, virus replication in the eyes and virus reactivation in latent trigeminal ganglia were both significantly reduced. However, latency in latently infected CD80-/- mice did not differ significantly from that in wild-type (WT) control mice. Reduced virus replication in the eyes of CD80-/- mice correlated with significantly expanded CD11c gene expression as compared to WT mice. Taken together, our results indicate that suppression of CD80 could offer significant beneficial therapeutic effects in the treatment of Herpes Stromal Keratitis (HSK).IMPORTANCEOf the many problems associated with recurrent ocular infection, reducing virus reactivation should be a major goal of controlling ocular herpes simplex virus-1 (HSV-1) infection. In this study, we have shown that the absence of CD80 reduces HSV-1 reactivation, which marks the establishment of a previously undescribed mechanism underlying viral immune evasion that could be exploited to better manage HSV infection.

The Archer and the Prey: The Duality of PAF1C in Antiviral Immunity

In the ongoing arms race between virus and host, fine-tuned gene expression plays a critical role in antiviral signaling. However, viruses have evolved to disrupt this process and promote their own replication by targeting host restriction factors. Polymerase-associated factor 1 complex (PAF1C) is a key player in this relationship, recruiting other host factors to regulate transcription and modulate innate immune gene expression. Consequently, PAF1C is consistently targeted by a diverse range of viruses, either to suppress its antiviral functions or co-opt them for their own benefit. In this review, we delve into the current mechanisms through which PAF1C restricts viruses by activating interferon and inflammatory responses at the transcriptional level. We also highlight how the ubiquity of these mechanisms makes PAF1C especially vulnerable to viral hijacking and antagonism. Indeed, as often as PAF1C is revealed to be a restriction factor, viruses are found to have targeted the complex in reply.

Herpes Simplex Type 1 UL43 Multiple Membrane-Spanning Protein Increases Energy Metabolism in Host Cells through Interacting with ARL2

Non-essential proteins for viral replication affect host cell metabolism, while the function of the UL43 protein of herpes simplex virus 1 (HSV-1) is not clear. Herein, we performed a comprehensive microarray analysis of HUVEC cells infected with HSV-1 and its UL43-deficient mutant and found significant variation in genes associated with cellular energy metabolic pathways. The localization of UL43 protein in host cells and how it affects cellular energy metabolism pathways were further investigated. Internalization analysis showed that the UL43 protein could be endocytosis-mediated by YPLF motif (aa144-147) and localized to mitochondria. At the same time, more ATP was produced by coupling with mitochondrial small G protein ARF-like 2 (ARL2) GTPase, which triggered the phosphorylation of ANT1 (SLC25A4) to affect the opening degree of mitochondrial permeability transition pore (mPTP), and significantly promoted the aerobic oxidation and oxidative phosphorylation of glucose. Our study shows that UL43 mediates the improvement of host cell metabolism after HSV-1 infection. Additionally, UL43 protein could be a valuable ATP-stimulating factor for mammalian cells.

Herpes Simplex Virus 1 Glycoproteins Differentially Regulate the Activity of Costimulatory Molecules and T Cells

Over the past 70 years, multiple approaches to develop a prophylactic or therapeutic vaccine to control herpes simplex virus (HSV) infection have failed to protect against primary infection, reactivation, or reinfection. In contrast to many RNA viruses, neither primary HSV infection nor repeated clinical recurrence elicits immune responses capable of completely preventing virus reactivation; yet the 12 known HSV-1 glycoproteins are the major inducers and targets of humoral and cell-mediated immune responses following infection. While costimulatory molecules and CD4/CD8 T cells both contribute significantly to HSV-1-induced immune responses, the specific effects of individual HSV-1 glycoproteins on CD4, CD8, CD80, and CD86 activities are not known. To determine how nine major HSV-1 glycoproteins affect T cells and costimulatory molecule function, we tested the independent effects of gB, gC, gD, gE, gG, gH, gI, gK, and gL on CD4, CD8, CD80, and CD86 promoter activities in vitro. gD, gK, and gL had a suppressive effect on CD4, CD8, CD80, and CD86 promoter activities, while gG and gH specifically suppressed CD4 promoter activity. In contrast, gB, gC, gE, and gI stimulated CD4, CD8, CD80, and CD86 promoter activities. Luminex analysis of splenocytes and bone-marrow-derived dendritic cells (BMDCs) transfected with each glycoprotein showed differing cytokine/chemokine milieus with higher responses in splenocytes than in BMDCs. Our results with the tested major HSV-1 glycoproteins suggest that costimulatory molecules and T cell responses to the nine glycoproteins can be divided into (i) stimulators (i.e., gB, gC, gE, and gI), and (ii) nonstimulators (i.e., gD, gK, and gL). Thus, consistent with our previous studies, a cocktail of select HSV-1 viral genes may induce a wider spectrum of immune responses, and thus protection, than individual genes. IMPORTANCE Currently no effective vaccine is available against herpes simplex virus (HSV) infection. Thus, there is a critical need to develop a safe and effective vaccine to prevent and control HSV infection. The development of such approaches will require an advanced understanding of viral genes. This study provides new evidence supporting an approach to maximize vaccine efficacy by using a combination of HSV genes to control HSV infection.

Optineurin in ocular herpes infection

Herpes Simplex Virus-1 (HSV-1) is a neurotropic virus that can infect humans in the eye and travel to the trigeminal ganglion to establish latency. HSV-1 causes various disease states in both the primary and secondary sites of infection including the eye and the nervous system. This DNA virus exploits various adaptive measures to infect host cells, hijack host cell proteins, evade host immune response and spread from cell-to-cell to avoid immune detection. Recent data suggest that Optineurin (OPTN), a host protein, is a key restriction factor that prevents cell-to-cell spread of HSV-1 and guards against serious damage to the nervous system during infection. In recent years OPTN has gained increased attention because of its involvement in cellular mechanisms that promote homeostasis and prevent neurodegeneration. At the center of it all is the role OPTN plays as a receptor for selective autophagy. This review summarizes our latest understanding of the viral lifecycle, disease pathologies, and OPTN-mediated protective mechanisms during HSV-1 infection of the eye and the nervous system. We specifically highlight recent discoveries that implicate OPTN as crucial in the prevention of ocular and neurodegenerative diseases.

ICP22/IE63 Mediated Transcriptional Regulation and Immune Evasion: Two Important Survival Strategies for Alphaherpesviruses

In the process of infecting the host, alphaherpesviruses have derived a series of adaptation and survival strategies, such as latent infection, autophagy and immune evasion, to survive in the host environment. Infected cell protein 22 (ICP22) or its homologue immediate early protein 63 (IE63) is a posttranslationally modified multifunctional viral regulatory protein encoded by all alphaherpesviruses. In addition to playing an important role in the efficient use of host cell RNA polymerase II, it also plays an important role in the defense process of the virus overcoming the host immune system. These two effects of ICP22/IE63 are important survival strategies for alphaherpesviruses. In this review, we summarize the complex mechanism by which the ICP22 protein regulates the transcription of alphaherpesviruses and their host genes and the mechanism by which ICP22/IE63 participates in immune escape. Reviewing these mechanisms will also help us understand the pathogenesis of alphaherpesvirus infections and provide new strategies to combat these viral infections.

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.

HSV-1 ICP22 Is a Selective Viral Repressor of Cellular RNA Polymerase II-Mediated Transcription Elongation

The Herpes Simplex Virus (HSV-1) immediate-early protein ICP22 interacts with cellular proteins to inhibit host cell gene expression and promote viral gene expression. ICP22 inhibits phosphorylation of Ser2 of the RNA polymerase II (pol II) carboxyl-terminal domain (CTD) and productive elongation of pol II. Here we show that ICP22 affects elongation of pol II through both the early-elongation checkpoint and the poly(A)-associated elongation checkpoint of a protein-coding gene model. Coimmunoprecipitation assays using tagged ICP22 expressed in human cells and pulldown assays with recombinant ICP22 in vitro coupled with mass spectrometry identify transcription elongation factors, including P-TEFb, additional CTD kinases and the FACT complex as interacting cellular factors. Using a photoreactive amino acid incorporated into ICP22, we found that L191, Y230 and C225 crosslink to both subunits of the FACT complex in cells. Our findings indicate that ICP22 interacts with critical elongation regulators to inhibit transcription elongation of cellular genes, which may be vital for HSV-1 pathogenesis. We also show that the HSV viral activator, VP16, has a region of structural similarity to the ICP22 region that interacts with elongation factors, suggesting a model where VP16 competes with ICP22 to deliver elongation factors to viral genes.

A Review of the Multipronged Attack of Herpes Simplex Virus 1 on the Host Transcriptional Machinery

During lytic infection, herpes simplex virus (HSV) 1 induces a rapid shutoff of host RNA synthesis while redirecting transcriptional machinery to viral genes. In addition to being a major human pathogen, there is burgeoning clinical interest in HSV as a vector in gene delivery and oncolytic therapies, necessitating research into transcriptional control. This review summarizes the array of impacts that HSV has on RNA Polymerase (Pol) II, which transcribes all mRNA in infected cells. We discuss alterations in Pol II holoenzymes, post-translational modifications, and how viral proteins regulate specific activities such as promoter-proximal pausing, splicing, histone repositioning, and termination with respect to host genes. Recent technological innovations that have reshaped our understanding of previous observations are summarized in detail, along with specific research directions and technical considerations for future studies.

Suppression of CD80 expression by ICP22 affect HSV-1 replication and CD8+IFNγ+ infiltrates in the eye of infected mice but not latency-reactivation

Previously, we reported that herpes simplex virus type 1 (HSV-1) ICP22 binds to the CD80 promoter and suppresses its expression in vitro and in vivo. To better understand the impact of ICP22 binding to CD80 on HSV-1 infectivity and pathogenicity, we mapped the region of ICP22 required to bind the CD80 promoter to a 40-amino-acid (aa) region of ICP22. We constructed a recombinant HSV-1 expressing a truncated form of ICP22 that lacks these 40 aa, which does not bind to the CD80 promoter (KOS-ICP22Δ40) and retains the ability to replicate efficiently in rabbit skin cells, in contrast to ICP22-null virus. The replication of this recombinant virus in vitro and in vivo was higher than that of the ICP22-null virus, but virus replication kinetics were lower than those of the wild-type (WT) control virus. Similar to ICP22-null virus, the KOS-ICP22Δ40 mutant virus increased CD80 expression in dendritic cells (DCs) and interferon gamma (IFN-γ) expression in CD8⁺ T cells but not CD4⁺ T cells in infected mouse corneas. In contrast to the significantly reduced virus replication in the eyes of ocularly infected mice, the levels of latency reactivation were similar between KOS-ICP22Δ40 virus and WT virus. Thus, blocking ICP22 binding to the CD80 promoter using a recombinant virus expressing a truncated ICP22 that lacks CD80 promoter binding appears to reduce virus replication and enhance CD8⁺IFN-γ⁺ infiltrates in corneas of infected mice, with no effect on latency reactivation.

IMPORTANCE Direct binding of HSV-1 ICP22 to the CD80 promoter downregulates the expression of the costimulatory molecule CD80 but not CD86. In this study, we fine mapped the region of ICP22 required for binding to the CD80 promoter and constructed a recombinant virus containing a deletion in ICP22 that failed to bind to the CD80 promoter. This recombinant virus replicated less efficiently in vitro and in vivo than did the WT control virus, although CD80-expressing CD11c⁺ cells and IFN-γ-expressing CD8⁺ T cells were increased. Interestingly, the levels of latency and reactivation in the two viruses were similar despite lower virus replication in the eyes of infected mice. Therefore, blocking the interaction of ICP22 with the CD80 promoter could be used to temper the immune response.

Absence of CD28-CTLA4-PD-L1 Costimulatory Molecules Reduces Herpes Simplex Virus 1 Reactivation

We previously reported that herpes simplex virus 1 (HSV-1) ICP22 binds to CD80 and suppresses CD80 expression in vitro and in vivo. Similar to ICP22, the cellular costimulatory molecules CD28, CTLA4, and PD-L1 also bind to CD80. In this study, we asked whether, similar to ICP22-null virus, the absence of these costimulatory molecules will reduce HSV-1 infectivity. To test our hypothesis, CD28^−/−, CD28^−/− CTLA4^−/−, PD-L1^−/−, and wild-type control BALB/c mice were ocularly infected with HSV-1 strain KOS. Levels of virus replication in the eye, corneal scarring (CS), latency, and reactivation in infected mice were determined. Expression of different genes in the trigeminal ganglia (TG) of latently infected mice was also determined by NanoString and quantitative reverse transcription-PCR (qRT-PCR). In the absence of costimulatory molecules, latency levels were higher than those in wild-type control mice, but despite higher latency, a significant number of TG from infected knockout mice did not reactivate. Reduced reactivation correlated with downregulation of 26 similar cellular genes that are associated with inflammatory signaling and innate immune responses. These results suggest that lower reactivation directly correlates with lower expression of interferon signaling. Thus, despite having different modes of actions, we identified a similar function for CD28, CTLA4, and PD-L1 in HSV-1 reactivation that is dependent on their interactions with CD80. Therefore, blocking these interactions could be a therapeutic target for HSV-1-induced reactivation.

Multifaceted Roles of ICP22/ORF63 Proteins in the Life Cycle of Human Herpesviruses

Herpesviruses are extremely successful parasites that have evolved over millions of years to develop a variety of mechanisms to coexist with their hosts and to maintain host-to-host transmission and lifelong infection by regulating their life cycles. The life cycle of herpesviruses consists of two phases: lytic infection and latent infection. During lytic infection, active replication and the production of numerous progeny virions occur. Subsequent suppression of the host immune response leads to a lifetime latent infection of the host. During latent infection, the viral genome remains in an inactive state in the host cell to avoid host immune surveillance, but the virus can be reactivated and reenter the lytic cycle. The balance between these two phases of the herpesvirus life cycle is controlled by broad interactions among numerous viral and cellular factors. ICP22/ORF63 proteins are among these factors and are involved in transcription, nuclear budding, latency establishment, and reactivation. In this review, we summarized the various roles and complex mechanisms by which ICP22/ORF63 proteins regulate the life cycle of human herpesviruses and the complex relationships among host and viral factors. Elucidating the role and mechanism of ICP22/ORF63 in virus-host interactions will deepen our understanding of the viral life cycle. In addition, it will also help us to understand the pathogenesis of herpesvirus infections and provide new strategies for combating these infections.

Crosstalk Between Epithelial Cells, Neurons and Immune Mediators in HSV-1 Skin Infection

Herpes simplex virus type 1 (HSV-1) infection is highly prevalent in humans, with approximately two-thirds of the world population living with this virus. However, only a fraction of those carrying HSV-1, which elicits lifelong infections, are symptomatic. HSV-1 mainly causes lesions in the skin and mucosae but reaches the termini of sensory neurons innervating these tissues and travels in a retrograde manner to the neuron cell body where it establishes persistent infection and remains in a latent state until reactivated by different stimuli. When productive reactivations occur, the virus travels back along axons to the primary infection site, where new rounds of replication are initiated in the skin, in recurrent or secondary infections. During this process, new neuron infections occur. Noteworthy, the mechanisms underlying viral reactivations and the exit of latency are somewhat poorly understood and may be regulated by a crosstalk between the infected neurons and components of the immune system. Here, we review and discuss the immune responses that occur at the skin during primary and recurrent infections by HSV-1, as well as at the interphase of latently-infected neurons. Moreover, we discuss the implications of neuronal signals over the priming and migration of immune cells in the context of HSV-1 infection.

"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.

Role of TH17 Responses in Increasing Herpetic Keratitis in the Eyes of Mice Infected with HSV-1

Purpose

T_H17 cells play an important role in host defense and autoimmunity yet very little is known about the role of IL17 in herpes simplex virus (HSV)-1 infectivity. To better understand the relationship between IL17 and HSV-1 infection, we assessed the relative impact of IL17A-deficiency and deficiency of its receptors on HSV-1 responses in vivo.

Methods

We generated IL17RA^−/− and IL17RA^−/−RC^−/− mice in-house and infected them along with IL17A^−/− and IL17RC^−/− mice in the eyes with 2 × 10⁵ PFU/eye of wild type (WT) HSV-1 strain McKrae. WT C57BL/6 mice were used as control. Virus replication in the eye, survival, corneal scarring (CS), angiogenesis, levels of latency-reactivation, and levels of CD8 and exhaustion markers (PD1, TIM3, LAG3, CTLA4, CD244, and CD39) in the trigeminal ganglia (TG) of infected mice were determined on day 28 postinfection.

Results

No significant differences in virus replication in the eye, survival, latency, reactivation, and exhaustion markers were detected among IL17A^−/−, IL17RA^−/−, IL17RC^−/−, IL17RA^−/−RC^−/−, and WT mice. However, mice lacking IL17 had significantly less CS and angiogenesis than WT mice. In addition, angiogenesis levels in the absence of IL17RC and irrespective of the absence of IL17RA were significantly less than in IL17A- or IL17RA-deficient mice.

Conclusions

Our results suggest that the absence of IL17 protects against HSV-1-induced eye disease, but has no role in protecting against virus replication, latency, or reactivation. In addition, our data provide rationale for blocking IL17RC function rather than IL17A or IL17RA function as a key driver of HSV-1-induced eye disease.

An Economic Evaluation of Voretigene Neparvovec for the Treatment of Biallelic RPE65-Mediated Inherited Retinal Dystrophies in the UK

INTRODUCTION

Voretigene neparvovec (VN) is a gene therapy and the first approved pharmacological treatment for biallelic RPE65-mediated inherited retinal dystrophies (IRD), a rare condition that starts in early life and causes vision to progressively deteriorate towards complete blindness. In a phase III trial, treatment with VN significantly improved functional vision and visual function, and in October 2019 the National Institute for Health and Care Excellence (NICE) Highly Specialised Technologies (HST) process recommended VN for patients in England and Wales. We assessed the cost-effectiveness of VN compared with best supportive care (BSC) in individuals with biallelic RPE65-mediated IRD in the UK.

METHODS

A Markov model was developed to estimate the incremental cost per quality-adjusted life-year (QALY) gained for VN compared with BSC, from the perspective of the UK National Health Service and Personal Social Services. Phase III trial data were used to inform transition probabilities up to year 1, after which the treatment effect was assumed to be maintained for 40 years, followed by a decline in vision. A bespoke elicitation exercise involving clinical experts, patients and carers was conducted to estimate utility values for each model health state.

RESULTS

At list price, VN is associated with incremental costs of £612,404 and incremental QALYs of 6.4, resulting in an incremental cost-effectiveness ratio (ICER) of £95,072 per QALY gained. Voretigene neparvovec is associated with a significant undiscounted QALY gain (20.5) and is therefore eligible for additional QALY weighting under the NICE HST process; an ICER of up to £205,000 per QALY gained could be considered cost-effective under this framework.

CONCLUSION

The results of the model show VN to be a cost-effective use of healthcare resources in the UK at list price. The availability of a commercial discount in the UK (as considered in the NICE appraisal) means that in reality the ICER will be even lower. Plain language summary available for this article.

Expression of Murine CD80 by Herpes Simplex Virus 1 in Place of Latency-Associated Transcript (LAT) Can Compensate for Latency Reactivation and Anti-apoptotic Functions of LAT

High rates of wild-type (WT) herpes simplex virus 1 (HSV-1) latency reactivation depend on the anti-apoptotic activities of latency-associated transcript (LAT). Replacing LAT with the baculovirus inhibitor of apoptosis protein (cpIAP) or cellular FLIP (FLICE-like inhibitory protein) gene restored the WT latency reactivation phenotype to that of a LAT-minus [LAT(-)] virus, while similar recombinant viruses expressing interleukin-4 (IL-4) or interferon gamma (IFN-γ) did not. However, HSV-1 recombinant virus expressing cpIAP did not restore all LAT functions. Recently, we reported that a similar recombinant virus expressing CD80 in place of LAT had higher latency reactivation than a LAT-null virus. The present study was designed to determine if this CD80-expressing recombinant virus can restore all LAT functions as observed with WT virus. Our results suggest that overexpression of CD80 fully rescues LAT function in latency reactivation, apoptosis, and immune exhaustion, suggesting that LAT and CD80 have multiple overlapping functions.IMPORTANCE Recurring ocular infections caused by HSV-1 can cause corneal scarring and blindness. A major function of the HSV-1 latency-associated transcript (LAT) is to establish high levels of latency and reactivation, thus contributing to the development of eye disease. Here, we show that the host CD80 T cell costimulatory molecule functions similarly to LAT and can restore the ability of LAT to establish latency, reactivation, and immune exhaustion as well as induce the expression of caspase 3, caspase 8, caspase 9, and Bcl2. Our results suggest that, in contrast to several other previously tested genes, CD80-expressing virus can completely compensate for all known and tested LAT functions.

CD80 Plays a Critical Role in Increased Inflammatory Responses in Herpes Simplex Virus 1-Infected Mouse Corneas

We recently reported that herpes simplex virus 1 (HSV-1) infection suppresses CD80 but not CD86 expression in vitro and in vivo This suppression required the HSV-1 ICP22 gene. We also reported that overexpression of CD80 by HSV-1 exacerbated corneal scarring in BALB/c mice. We now show that this recombinant virus (HSV-CD80) expressed high levels of CD80 both in vitro in cultured rabbit skin cells and in vivo in infected mouse corneas. CD80 protein was detected on the surface of infected cells. The virulence of the recombinant HSV-CD80 virus was similar to that of the parental strain, and the replication of HSV-CD80 was similar to that of control virus in vitro and in vivo Transcriptome analysis detected 75 known HSV-1 genes in the corneas of mice infected with HSV-CD80 or parental virus on day 4 postinfection. Except for significantly higher CD80 expression in HSV-CD80-infected mice, levels of HSV-1 gene expression were similar in corneas from HSV-CD80-infected and parental virus-infected mice. The number of CD8+ T cells was higher, and the number of CD4+ T cells was lower, in the corneas of HSV-CD80-infected mice than in mice infected with parental virus. HSV-CD80-infected mice displayed a transient increase in dendritic cells. Transcriptome analysis revealed mild differences in dendritic cell maturation and interleukin-1 signaling pathways and increased expression of interferon-induced protein with tetratricopeptide repeats 2 (Ifit2). Together, these results suggest that increased CD80 levels promote increased CD8+ T cells, leading to exacerbated eye disease in HSV-1-infected mice.IMPORTANCE HSV-1 ocular infections are the leading cause of corneal blindness. Eye disease is the result of a prolonged immune response to the replicating virus. HSV-1, on the other hand, has evolved several mechanisms to evade clearance by the host immune system. We describe a novel mechanism of HSV-1 immune evasion via ICP22-dependent downregulation of the host T cell costimulatory molecule CD80. However, the exact role of CD80 in HSV-1 immune pathology is not clear. In this study, we show that eye disease is independent of the level of HSV-1 replication and that viral expression of CD80 has a detrimental role in corneal scarring, likely by increasing CD8+ T cell recruitment and activation.