A plasmid construct encoding murine interferon beta antagonizes the replication of herpes simplex virus type I in vitro and in vivo

Corneal gene therapy: Structural and mechanistic understanding

Cornea, a dome-shaped and transparent front part of the eye, affords 2/3rd refraction and barrier functions. Globally, corneal diseases are the leading cause of vision impairment. Loss of corneal function including opacification involve the complex crosstalk and perturbation between a variety of cytokines, chemokines and growth factors generated by corneal keratocytes, epithelial cells, lacrimal tissues, nerves, and immune cells. Conventional small-molecule drugs can treat mild-to-moderate traumatic corneal pathology but requires frequent application and often fails to treat severe pathologies. The corneal transplant surgery is a standard of care to restore vision in patients. However, declining availability and rising demand of donor corneas are major concerns to maintain ophthalmic care. Thus, the development of efficient and safe nonsurgical methods to cure corneal disorders and restore vision in vivo is highly desired. Gene-based therapy has huge potential to cure corneal blindness. To achieve a nonimmunogenic, safe and sustained therapeutic response, the selection of a relevant genes, gene editing methods and suitable delivery vectors are vital. This article describes corneal structural and functional features, mechanistic understanding of gene therapy vectors, gene editing methods, gene delivery tools, and status of gene therapy for treating corneal disorders, diseases, and genetic dystrophies.

Gene therapy in the anterior eye segment

This review provides comprehensive information about the advances in gene therapy in the anterior segment of the eye including cornea, conjunctiva, lacrimal gland, and trabecular meshwork. We discuss gene delivery systems including viral and non-viral vectors as well as gene editing techniques, mainly CRISPR-Cas9, and epigenetic treatments including antisense and siRNA therapeutics. We also provide a detailed analysis of various anterior segment diseases where gene therapy has been tested with corresponding outcomes. Disease conditions include corneal and conjunctival fibrosis and scarring, corneal epithelial wound healing, corneal graft survival, corneal neovascularization, genetic corneal dystrophies, herpetic keratitis, glaucoma, dry eye disease, and other ocular surface diseases. Although most of the analyzed results on the use and validity of gene therapy at the ocular surface have been obtained in vitro or using animal models, we also discuss the available human studies. Gene therapy approaches are currently considered very promising as emerging future treatments of various diseases, and this field is rapidly expanding.

Study of interferon-β antiviral activity against Herpes simplex virus type 1 in neuron-enriched trigeminal ganglia cultures

Herpes simplex virus type 1 (HSV-1) causes a lytic infection in epithelial cells before being captured and moved via retrograde axonal transport to the nuclei of the sensory neurons of the trigeminal ganglion or dorsal root, where it establishes a latent infection. HSV-1 infection induces an antiviral response through the production of Beta Interferon (IFN-β) in infected trigeminal ganglia. The aim of this work was to characterize the response induced by IFN-β in neuron-enriched trigeminal ganglia primary cultures infected with HSV-1. An antiviral effect of IFN-β in these cultures was observed, including reduced viral production and increased cell survival. In contrast, viral infection significantly decreased both double stranded RNA dependent protein kinase (Pkr) transcription and Jak-1 and Stat-1 phosphorylation, suggesting a possible HSV-1 immune evasion mechanism in trigeminal cells. Additionally, HSV-1 infection upregulated Suppressor of Cytokine Signaling-3 (Socs3) mRNA; upregulation of socs3 was inhibited in IFN-β treated cultures. HSV-1 infection increased the number of Socs3 positive cells and modified the intracellular distribution of Socs3 protein, in infected cells. This neuron-enriched trigeminal ganglia culture model could be used to elucidate the HSV-1 viral cycle in sensory neurons and to study cellular antiviral responses and possible viral evasion mechanisms that underlie the choice between viral replication and latency.

Targeting herpetic keratitis by gene therapy

Ocular gene therapy is rapidly becoming a reality. By November 2012, approximately 28 clinical trials were approved to assess novel gene therapy agents. Viral infections such as herpetic keratitis caused by herpes simplex virus 1 (HSV-1) can cause serious complications that may lead to blindness. Recurrence of the disease is likely and cornea transplantation, therefore, might not be the ideal therapeutic solution. This paper will focus on the current situation of ocular gene therapy research against herpetic keratitis, including the use of viral and nonviral vectors, routes of delivery of therapeutic genes, new techniques, and key research strategies. Whereas the correction of inherited diseases was the initial goal of the field of gene therapy, here we discuss transgene expression, gene replacement, silencing, or clipping. Gene therapy of herpetic keratitis previously reported in the literature is screened emphasizing candidate gene therapy targets. Commonly adopted strategies are discussed to assess the relative advantages of the protective therapy using antiviral drugs and the common gene therapy against long-term HSV-1 ocular infections signs, inflammation and neovascularization. Successful gene therapy can provide innovative physiological and pharmaceutical solutions against herpetic keratitis.

A Functional Type I Interferon Pathway Drives Resistance to Cornea Herpes Simplex Virus Type 1 Infection by Recruitment of Leukocytes

Type I interferons are critical antiviral cytokines produced following herpes simplex virus type-1 (HSV-1) infection that act to inhibit viral spread. In the present study, we identify HSV-infected and adjacent uninfected corneal epithelial cells as the source of interferon-α. We also report mice deficient in the A1 chain of the type I IFN receptor (CD118(-/-)) are extremely sensitive to ocular infection with low doses (100 PFU) of HSV-1 as seen by significantly elevated viral titers in the cornea compared to wild type (WT) controls. The enhanced susceptibility correlated with a loss of CD4(+) and CD8(+) T cell recruitment and aberrant chemokine production in the cornea despite mounting an adaptive immune response in the draining mandibular lymph node of CD118(-/-) mice. Taken together, these results highlight the importance of IFN production in both the innate immune response as well as eliciting chemokine production required to facilitate adaptive immune cell trafficking.

Corneal gene therapy

Gene therapy to the cornea can potentially correct inherited and acquired diseases of the cornea. Factors that facilitate corneal gene delivery are the accessibility and transparency of the cornea, its stability ex vivo and the immune privilege of the eye. Initial corneal gene delivery studies characterized the relationship between intraocular modes of administration and location of reporter gene expression. The challenge of achieving effective topical gene transfer, presumably due to tear flow, blinking and low penetration of the vector through epithlelial tight junctions left no alternative but invasive administration to the anterior chamber and corneal stroma. DNA vaccination, RNA interference and gene transfer of cytokines, growth factors and enzymes modulated the corneal microenvironment. Positive results were obtained in preclinical studies for prevention and treatment of corneal graft rejection, neovascularization, haze and herpetic stromal keratitis. These studies, corneal gene delivery systems and modes of administration, and considerations regarding the choice of animal species used are the focus of this review. Opportunities in the field of corneal gene therapy lie in expanding the array of corneal diseases investigated and in the implementation of recent designs of safer vectors with reduced immunogenicity and longer duration of gene expression.

Blocking Mouse MMP-9 Production in Tumor Cells and Mouse Cornea by Short Hairpin (sh) RNA Encoding Plasmids

In this study, we assessed the efficacy of the specific knockdown of matrix metalloprotein-9 (MMP-9) in vitro and in vivo using short hairpin RNA (shRNA) against MMP-9. Two plasmids were generated encoding shRNA (pshRNA) targeted against two distinct MMP-9 gene sequences. Transfection of these pshMMP-9s could be shown to specifically inhibit MMP-9 expression both in vivo and in vitro. The effect occurred in vitro both in cells that endogenously produce MMP-9 and in cells exogenously transfected with an MMP-9-encoding plasmid. Using an in vivo transfection approach, the pshMMP- 9 was also effective at inhibiting MMP-9 protein expression in the mouse cornea. pshMMP-9s were also tested against herpes simplex virus (HSV) in the cornea. Delivery of the pshMMP-9 stopped angiogenesis and decreased the severity of herpetic keratitis. However, interferon-alpha (IFN-alpha) and IFN- beta induced by pshRNA might also contribute to inhibition of herpetic simplex keratitis (HSK) in the cornea.

Detection of infectious agents in brain of patients with acute hemorrhagic leukoencephalitis

Acute hemorrhagic leukoencephalitis (AHL) is a rare and usually fatal disorder characterized clinically by an acute onset of neurologic abnormalities. It may occur in association with a viral illness or vaccination. Radiology and brain biopsy are essential for the diagnosis. The etiology of AHL is unclear. We postulated that viral/bacterial infection might be responsible, directly or through an immune-mediated mechanism, for this acute inflammatory myelinopathy. Fifteen cases of AHL were studied. Infectious agents, including varicella zoster virus (VZV), herpes simplex virus (HSV), human herpes virus-6 (HHV-6), cytomegalovirus, Epstein-Barr virus, and Mycoplasma, were investigated in brain specimens using the polymerase chain reaction (PCR), reverse transcriptase (RT)-PCR, and immunohistochemistry. Using PCR, HSV DNA was found in four cases, VZV DNA in two, and HHV-6 DNA in one. Among the control cases, two were HSV DNA positive. Further investigation to detect HSV RNA and antigens in HSV DNA-positive cases revealed that two cases with AHL were both HSV RNA and antigen positive. AHL is a hyperacute disease, which is considered the most acute form of acute disseminated encephalomyelitis (ADEM). Our findings suggests that a viral infection may be implicated in its pathogenesis, most likely through an indirect mechanism; however, as only a few cases of this rare disease were examined, statistical significance was not achieved. As a number of patients with disorders of the ADEM group may progress to develop multiple sclerosis (MS), we argue that an organism that has produced the former may remain in the brain tissue and be subsequently involved in the production of a self-sustained disorder such as MS.

Absence of PKR attenuates the anti-HSV-1 activity of an adenoviral vector expressing murine IFN-beta

A study was undertaken to evaluate the efficacy of an adenoviral vector containing the murine interferon-beta (IFN-beta) transgene (Ad:IFN-beta) against herpes simplex virus type 1 (HSV-1) infection in two transduced cell lines. The transduction of the adenoviral vector efficiency, ranging from 2% to 100%, was dependent on the multiplicity of infection (moi) (0.4-50 plaque-forming units [pfu]/cell). Supernatants from cells transduced with the Ad:IFN-beta but not the adenoviral null vector (Ad:Null) contained biologically active IFN-beta (6.6-106 U/ml depending on the moi). Cells transduced with the Ad:IFN-beta displayed up to 25-fold reduction in viral titers compared with cells transduced with the Ad:Null or nontransduced cell controls. The suppression in viral titer correlated with a reduction in viral gene (alpha, beta, and gamma) and protein expression. The expression of IFN beta-responsive genes, including protein kinase R (PKR) and 2',5'-oligoadenylate synthetase (OAS), were significantly elevated in the Ad:IFN-beta-transduced cells by 12-fold and 25-fold, respectively. However, after infection with HSV-1, a transient but significant drop in PKR but not OAS gene expression was observed 10 h postinfection. The absence of PKR but not RNase L significantly attenuated the antiviral efficacy of the transgene. Collectively, these results illustrate the feasibility of employing a viral vector to deliver a potent antiviral gene to targeted cells without any obvious detriment to the vector itself and support an important role for PKR as a mediator of the anti-HSV-1 activity of type I IFN.

Topical application of the cornea post-infection with plasmid DNA encoding interferon-alpha1 but not recombinant interferon-alphaA reduces herpes simplex virus type 1-induced mortality in mice

A study was undertaken to compare the efficacy of recombinant interferon (rIFN)-alphaA to plasmid DNA encoding IFN-alpha1 against ocular herpes simplex virus type 1 (HSV-1) infection. The topical application of rIFN-alphaA (100-300 units/eye) onto the cornea of mice subsequently infected 24 h later with HSV-1 antagonized viral-induced mortality. The enhancement in cumulative survival in the rIFN-alphaA-treated mice correlated with a reduction of viral titers recovered in the eye and trigeminal ganglion (TG) at 3 and 6 days post-infection. The protective effect was site-specific such that when rIFN-alphaA was administered orally or intranasally, no efficacy against HSV-1 was observed. However, the protective effect was time-dependent. Specifically, when the rIFN-alphaA (100-1000 units/eye) was administered at 24 h post-infection, no protective effect was observed against HSV-1 compared to the vehicle-treated group. In contrast, plasmid DNA (100 microg/eye) containing the IFN-alpha1 transgene showed significant protection when topically applied 24 h post-infection. Although the transgene was found to traffic distal from the site of application (eye), including the trigeminal ganglion and the spleen where CD11b(+) and CD11c(+) cells express the transgene, the migration of the transgene did not correlate with efficacy. Collectively, the results suggest that naked DNA encoding type I IFN applied post-infection provides a greater degree of protection against ocular HSV-1 infection in comparison with recombinant protein effectively antagonizing viral replication and spread.

Expression of human and macaque type I IFN transgenes interferes with HSV-1 replication at the transcriptional and translational levels: IFN-beta is more potent than IFN-alpha 2

A study was undertaken to compare the efficacy of plasmid constructs encoding human IFN-alpha 2 and IFN-beta and macaque IFN-beta against herpes simplex virus type 1 in transfected cells. All type I IFN transgenes significantly reduced viral titers in transfected cells by 3 logs. Human IFN-alpha 2-transfected cells produced significantly more IFN (2274 pg/ml) in comparison to IFN-beta-transfected cells (134-165 pg/ml). Viral lytic gene transcript and viral protein levels were lower in IFN-beta- versus IFN-alpha 2-transfected cells, which coincided with elevated PKR and OAS transcript levels and increased total STAT1 and phosphorylated STAT1 (Y701) protein levels in the IFN-beta-transfected cells. Although comparable viral titers were recovered in IFN-alpha 2 and IFN-beta plasmid-transfected cells, IFN-alpha 2 plasmid-transfected cells exhibited significantly more cytopathic effect compared to the IFN-beta transgene-transfected cells. In addition, IFN-alpha 2 transgene-transfected, infected cells displayed a cell cycle profile similar to that of vector-transfected, infected cells, whereas IFN-beta plasmid-transfected cells displayed a profile similar to uninfected control. Collectively, the results indicate that human IFN-beta is superior to IFN-alpha 2 in antagonizing herpes simplex virus type 1 infection.

The immune response to ocular herpes simplex virus type 1 infection

Herpes simplex virus type 1 (HSV-1) is a prevalent microbial pathogen infecting 60% to 90% of the adult world population. The co-evolution of the virus with humans is due, in part, to adaptations that the virus has evolved to aid it in escaping immune surveillance, including the establishment of a latent infection in its human host. A latent infection allows the virus to remain in the host without inducing tissue pathology or eliciting an immune response. During the acute infection or reactivation of latent virus, the immune response is significant, which can ultimately result in corneal blindness or fatal sporadic encephalitis. In fact, HSV-1 is one of the leading causes of infectious corneal blindness in the world as a result of chronic episodes of viral reactivation leading to stromal keratitis and scarring. Significant inroads have been made in identifying key immune mediators that control ocular HSV-1 infection and potentially viral reactivation. Likewise, viral mechanisms associated with immune evasion have also been identified and will be discussed. Lastly, novel therapeutic strategies that are currently under development show promise and will be included in this review. Most investigators have taken full advantage of the murine host as a viable working in vivo model of HSV-1 due to the sensitivity and susceptibility to viral infection, ease of manipulation, and a multitude of developed probes to study changes at the cellular and molecular levels. Therefore, comments in this review will primarily be restricted to those observations pertaining to the mouse model and the assumption (however great) that similar events occur in the human condition.

Plasmid DNA encoding IFN-alpha 1 antagonizes herpes simplex virus type 1 ocular infection through CD4+ and CD8+ T lymphocytes

The present study was undertaken to further characterize the anti-viral efficacy of a plasmid DNA encoding IFN-alpha1 against ocular herpes simplex virus type 1 (HSV-1) infection. In mice ocularly treated with plasmid DNA encoding IFN-alpha 1, the efficacy of the transgene was inversely proportional to the amount of virus used to infect the mice. Ocular treatment of mice with the IFN-alpha 1 transgene was the only mucosal route tested that showed efficacy against ocular HSV-1 infection compared with vaginal or intranasal delivery. Mice treated with the plasmid DNA encoding IFN-alpha 1 showed a significant reduction in viral Ag expression in the eyes and trigeminal ganglion that correlated with a reduction in immune cell infiltration into the cornea and iris on days 3 and 6 postinfection, as evidenced by immunohistochemical staining. Depleting mice of either CD4+ or CD8+ T lymphocytes completely blocked the resistance to herpes simplex virus type 1-induced mortality in mice treated with the IFN-alpha 1 transgene. In the absence of infection, the application of naked DNA encoding IFN-alpha 1 significantly increased the levels of IL-6- and IFN-gamma-inducible protein 10 transcript expression in the corneas 24 h post-treatment. Expression of the plasmid construct following topical application in the eye included the rectus muscles proximal to the cornea as well as the spleen. Collectively, the protective efficacy of the IFN-alpha 1 transgene against ocular HSV-1 infection is dependent upon the local or distal participation of CD4+ and CD8+ T lymphocytes early in the course of the infection, suggesting an indirect effect of the transgene against HSV-1-induced mortality.