Development of effective therapies against West Nile virus infection

West Nile virus infections are here! Are we prepared to face another flavivirus epidemic?

Emerging arthropod-borne viruses (arboviruses), such as chikungunya and Zika viruses, are a major threat to public health in countries like Brazil where biodiversity is high and medical care is sometimes precarious. West Nile fever is a disease caused by the West Nile Virus (WNV), an RNA virus belonging to the Flaviviridae family. It is transmitted by infected mosquitoes to numerous animals like birds, reptiles and mammals, including human and non-human primates. In the last decade, the number of reported cases of WNV infection in humans and animals has increased in the Americas. Circulation of WNV in forests and rural areas in Brazil has been detected based on serological surveys and, in 2014, the first case of West Nile fever was confirmed in a patient from Piauí State. In 2018, the virus was isolated for the first time from a horse from a rural area in the state of Espírito Santo presenting with a neurological disorder; this raises the possibility that other cases of WNV encephalitis may have occurred without clinical recognition and without laboratory diagnosis by specific assays. The imminent WNV outbreak poses a challenge for Brazilian clinicians and researchers. In this review, we summarize the basic biological and ecological characteristics of this virus and the clinical presentation and treatment of febrile illnesses caused by WNV. We also discuss the epidemiological aspects, prophylaxis of WNV infections, and monitoring strategies that could be applied in the possibility of a WNV outbreak in Brazil.

An essential role of PI3K in the control of West Nile virus infection

The phosphatidyl-inositol-3 kinases (PI3K) pathway regulates a variety of cellular processes, including cell proliferation, RNA processing, protein translation, autophagy, apoptosis and antiviral immunity. Many viruses depend on PI3K signaling for replication. However, its role in flaviviral infection has not been clearly defined. Here we report that PI3K signaling is critical for the control of West Nile virus (WNV) infection by regulating type I IFN (IFN-I) response. Inhibition of PI3K activity by 3-methyl adenine (3-MA), Wortmannin (WM) and LY294002 (LY) increased viral titers by 3-16 folds in primary mouse macrophages, embryonic fibroblasts and human cell lines. Both 3-MA and LY repressed IFN-I mRNA and protein expression significantly. Surprisingly, WM enhanced the mRNA expression of IFN-I and TNF-α, and TNF-α protein production modestly, while dramatically decreased the secreted IFN-I. Further studies showed that the catalytic subunit p110δ of class I PI3K played a role in induction of antiviral immune responses. Lastly translocation of interferon regulatory factor 7(IRF7) from the cytosol to the nuclei was effectively blocked in the presence of PI3K inhibitors. Our results clearly define an antiviral role of PI3K by modulating immune responses and demonstrate differential mode of action of three PI3K inhibitors on IFN-I.

Risk factors for West Nile virus infection and disease in populations and individuals

West Nile virus (WNV) is a mosquito-borne enveloped positive-strand RNA virus that emerged in North America in 1999 in New York City. Over the past 15 years, WNV has become established throughout the USA and has spread into Canada, Mexico and the Caribbean. CDC reports indicate >41,000 clinical cases, including more than 1700 fatalities. An estimated 3 million people in the USA may have been infected to date. Infection with WNV is dependent on many factors including climate, mosquito habitats and immunologically naïve bird populations. In addition, variations within individuals contribute to the risk of severe disease, in particular, advanced age, hypertension, immunosuppression and critical elements of the immune response. Recent advances in technology now allow detailed analysis of complex immune interactions relevant to disease susceptibility.

Anti-inflammatory activity of intravenous immunoglobulins protects against West Nile virus encephalitis

West Nile virus (WNV), an important global human pathogen, targets neurons to cause lethal encephalitis, primarily in elderly and immunocompromised patients. Currently, there are no approved therapeutic agents or vaccines to treat WNV encephalitis. Recent studies have suggested that inflammation is a major contributor to WNV encephalitis morbidity. In this study we evaluated the use of IVIG (intravenous immunoglobulins - a clinical product comprising pooled human IgG) as an anti-inflammatory treatment in a model of lethal WNV infection. We report here that IVIG and pooled human WNV convalescent sera (WNV-IVIG) inhibited development of lethal WNV encephalitis by suppressing central nervous system (CNS) infiltration by CD45(high) leukocytes. Pathogenic Ly6C(high) CD11b(+) monocytes were the major infiltrating subset in the CNS of infected control mice, whereas IVIG profoundly reduced infiltration of these pathogenic Ly6C(high) monocytes into the CNS of infected mice. Interestingly, WNV-IVIG was more efficacious than IVIG in controlling CNS inflammation when mice were challenged with a high-dose inoculum (10(5) versus 10(4) p.f.u.) of WNV. Importantly, adsorption of WNV E-glycoprotein neutralizing antibodies did not abrogate IVIG protection, consistent with virus neutralization not being essential for IVIG protection. These findings confirmed the potent immunomodulatory activity of generic IVIG, and emphasized its potential as an effective immunotherapeutic drug for encephalitis and other virus induced inflammatory diseases.

West nile virus and equine encephalitis viruses: new perspectives

Mosquito-borne diseases affect horses worldwide. Mosquito-borne diseases generally cause encephalomyelitis in the horse and can be difficult to diagnose antemortem. In addition to general disease, and diagnostic and treatment aspects, this review article summarizes the latest information on these diseases, covering approximately the past 5 years, with a focus on new equine disease encroachments, diagnostic and vaccination aspects, and possible therapeutics on the horizon.

Mapping and analysis of West Nile virus-specific monoclonal antibodies: prospects for vaccine development

Seasonal epidemics of West Nile virus (WNV) infection now occur throughout North America, causing clinical symptoms ranging from fever to encephalitis. There are no specific treatment options or licensed vaccines. Several classically developed vaccine candidates are being evaluated in clinical trials. However, questions of safety and/or immunogenicity may limit their usefulness. Mapping of human and murine antibody repertoires against the WNV envelope protein after WNV infection have revealed important insights into the protective immune response against the virus. This review will give an overview of vaccines under development and summarize current data on E-protein antigenicity that could aid in the design of next generation WNV vaccines.

West Nile Virus: biology, transmission, and human infection

West Nile Virus was introduced into the Western Hemisphere during the late summer of 1999 and has been causing significant and sometimes severe human diseases since that time. This article briefly touches upon the biology of the virus and provides a comprehensive review regarding recent discoveries about virus transmission, virus acquisition, and human infection and disease.

Cross protection against lethal West Nile virus challenge in mice immunized with recombinant E protein domain III of Japanese encephalitis virus

Japanese encephalitis virus (JEV) and West Nile virus (WNV) are closely related mosquito-borne flaviviruses that cause severe encephalitic diseases with global impact. Cross protection among JEV and WNV has been previously described, and most cross reactive epitopes were identified within the domain II of E protein (EDII). In this study, the E protein domain III (EDIII) of JEV was successfully expressed in Escherichia coli, purified by a Ni-NTA column and characterized by Western blotting assay. Competitive inhibition assay showed that this recombinant JEV EDIII blocks the entry of JEV into BHK-21 cells. Mice immunized with the recombinant JEV EDIII developed high IgG and neutralizing antibodies titers against JEV. Most importantly, antibodies induced by JEV EDIII could neutralize WNV in vitro and partially protected mice against lethal WNV challenge. These results demonstrate that immunization with JEV EDIII induces cross-protective immunity against WNV infection, indicating a possible role of EDIII for the cross-protection among flavivirus.

Chimeric vaccine composed of viral peptide and mammalian heat-shock protein 60 peptide protects against West Nile virus challenge

The protective efficacy and immunogenicity of a chimeric peptide against West Nile virus (WNV) was evaluated. This virus is the aetiological agent of West Nile fever, which has recently emerged in the western hemisphere. The rapid spread of WNV throughout North America, as well as the constantly changing epidemiology and transmission of the virus by blood transfusion and transplantation, have raised major public-health concerns. Currently, there are no effective treatments for WNV or vaccine for human use. We previously identified a novel, continuous B-cell epitope from domain III of the WNV envelope protein, termed Ep15. To test whether this epitope can protect against WNV infection, we synthesized a linear chimeric peptide composed of Ep15 and the heat-shock protein 60 peptide, p458. The p458 peptide is an effective carrier peptide for subunit vaccines against other infectious agents. We now report that mice immunized with the chimeric peptide, p458-Ep15, were resistant to lethal challenges with three different WNV strains. Moreover, their brains were free of viral genome and infectious virus. Mice immunized with Ep15 alone or with p431-Ep15, a control conjugate, were not protected. The chimeric p458-Ep15 peptide induced WNV-specific immunoglobulin G antibodies that neutralized the virus and induced the secretion of interferon-gammain vitro. Challenge of chimeric peptide-immunized mice considerably enhanced WNV-specific neutralizing antibodies. We conclude that this chimeric peptide can be used for formulation of a human vaccine against WNV.

Key role of T cell defects in age-related vulnerability to West Nile virus

West Nile virus (WNV) infection causes a life-threatening meningoencephalitis that becomes increasingly more prevalent over the age of 50 and is 40–50× more prevalent in people over the age of 70, compared with adults under the age of 40. In a mouse model of age-related vulnerability to WNV, we demonstrate that death correlates with increased viral titers in the brain and that this loss of virus control with age was the result of defects in the CD4 and CD8 T cell response against WNV. Specific age-related defects in T cell responses against dominant WNV epitopes were detected at the level of cytokine and lytic granule production, each of which are essential for resistance against WNV, and in the ability to generate multifunctional anti-WNV effector T cells, which are believed to be critical for robust antiviral immunity. In contrast, at the peak of the response, old and adult T cells exhibited superimposable peptide sensitivity. Most importantly, although the adult CD4 or CD8 T cells readily protected immunodeficient mice upon adoptive transfer, old T cells of either subset were unable to provide WNV-specific protection. Consistent with a profound qualitative and quantitative defect in T cell immunity, old brains contained at least 12× fewer total effector CD8 T cells compared with adult mice at the peak of brain infection. These findings identify potential targets for immunomodulation and treatment to combat lethal WNV infection in the elderly.

Using high titer West Nile intravenous immunoglobulin from selected Israeli donors for treatment of West Nile virus infection

BACKGROUND

West Nile Virus (WNV) is endemic in Israel and a significant level of antibodies is present in the population due to natural exposure. Anecdotal cases suggested that the presence of anti-WNV antibodies in intravenous immunoglobulin (IVIG) from Israeli donors (IVIG-IL) assisted the recovery of patients with severe WNV infection.

METHODS

To enhance the therapeutic efficacy of IVIG-IL against WNV infection, OMRIX Biopharmaceuticals, Israel, have developed a strategy for selection of plasma units from a 10% fraction of Israeli blood donors with anti-WNV antibodies. Positive units were processed into pharmaceutical grade WNV IVIG (WNIG). Following inoculation with WNV, mice received i.p. injections of different doses (0.01-8 mg/mouse) of IVIG-IL or WNIG, according to the specific experimental protocol.

RESULTS

WNIG was about 10 times more potent (per gr of IgG) than was regular IVIG-IL when tested by ELISA and neutralization assays. In a mouse lethal WNV infection model, prophylactic treatment with WNIG was at least 5-10-fold more potent as compared to treatment with IVIG-IL. Treatment with WNIG during active encephalitis, three or four days following WNV infection, had a significant protective effect. WNIG was also very effective in protecting immunosuppressed mice. Indeed, treatment of dexamethasone-immunosuppressed mice with 0.2 or 1.0 mg WNIG 4 h after virus infection, led to 100% survival.

CONCLUSION

IVIG produced from selected plasma donated in WNV endemic regions can be used to produce WNV IVIG with superior activity for therapeutic and prophylactic measures.

Tumor necrosis factor alpha protects against lethal West Nile virus infection by promoting trafficking of mononuclear leukocytes into the central nervous system

West Nile virus (WNV) is a neurotropic flavivirus that has emerged globally as a significant cause of viral encephalitis in humans, especially in immunocompromised individuals. Previous studies have shown essential protective roles for antiviral cytokines (e.g., alpha interferon [IFN-alpha] and IFN-gamma) against WNV in mice. However, studies using cell culture offer conflicting answers regarding whether tumor necrosis factor alpha (TNF-alpha) has an anti-WNV function. To test the biological significance of TNF-alpha against WNV in vivo, experiments were performed with TNF receptor-1 (TNF-R1)-deficient and TNF-alpha-depleted C57BL/6 mice. TNF-R1(-/-) mice had enhanced mortality and decreased survival time after WNV infection compared to congenic wild-type mice. Consistent with this, administration of a neutralizing anti-TNF-alpha monoclonal antibody also decreased survival after WNV infection. Relatively small differences in viral burdens in peripheral tissues of TNF-R1(-/-) mice were observed, and this occurrence correlated with a modest antiviral effect of TNF-alpha on primary macrophages but not dendritic cells. In contrast, the viral titers detected in the central nervous systems of TNF-R1(-/-) mice were significantly increased compared to those of wild-type mice, although TNF-alpha did not have a direct antiviral effect in primary neuron cultures. Whereas no defect in priming of adaptive B- and T-cell responses in TNF-R1(-/-) mice was observed, there were significant reductions in accumulations of CD8+ T cells and macrophages in the brain. Our data are most consistent with a model in which interaction of TNF-alpha with TNF-R1 protects against WNV infection by regulating migration of protective inflammatory cells into the brain during acute infection.

Defining the levels of secreted non-structural protein NS1 after West Nile virus infection in cell culture and mice

Infection with West Nile virus (WNV) causes a febrile illness that can progress to meningitis or encephalitis, primarily in humans that are immunocompromised or elderly. For successful treatment of WNV infection, accurate and timely diagnosis is essential. Previous studies have suggested that the flavivirus non-structural protein NS1, a highly conserved and secreted glycoprotein, is a candidate protein for rapid diagnosis. Herein, we developed a capture enzyme-linked immunosorbent assay (ELISA) to detect WNV NS1 using two anti-NS1 monoclonal antibodies (mAbs) that map to distinct sites on the protein. The capture ELISA efficiently detected as little as 0.5 ng/ml of soluble NS1 and exhibited no cross-reactivity for yellow fever, Dengue, and St. Louis encephalitis virus NS1. The capture ELISA reliably detected NS1 in plasma at day 3 after WNV infection, prior to the development of clinical signs of disease. As the time course of infection continued, the levels of detectable NS1 diminished, presumably because of interference by newly generated anti-NS1 antibodies. Indeed, treatment of plasma with a solution that dissociated NS1 immune complexes extended the window of detection. Overall, the NS1-based capture ELISA is a sensitive readout of infection and could be an important tool for diagnosis or screening small molecule inhibitors of WNV infection.

The relative contribution of antibody and CD8+ T cells to vaccine immunity against West Nile encephalitis virus

West Nile virus (WNV) is a mosquito borne, neurotropic flavivirus that causes a severe central nervous system (CNS) infection in humans and animals. Although commercial vaccines are available for horses, none is currently approved for human use. In this study, we evaluated the efficacy and mechanism of immune protection of two candidate WNV vaccines in mice. A formalin-inactivated WNV vaccine induced higher levels of specific and neutralizing antibodies compared to a DNA plasmid vaccine that produces virus-like particles. Accordingly, partial and almost complete protection against a highly stringent lethal intracranial WNV challenge were observed in mice 60 days after single dose immunization with the DNA plasmid and inactivated virus vaccines, respectively. In mice immunized with a single dose of DNA plasmid or inactivated vaccine, antigen-specific CD8(+) T cells were induced and contributed to protective immunity as acquired or genetic deficiencies of CD8(+) T cells lowered the survival rates. In contrast, in boosted animals, WNV-specific antibody titers were higher, survival rates after challenge were greater, and an absence of CD8(+) T cells did not appreciably affect mortality. Overall, our experiments suggest that in mice, both inactivated WNV and DNA plasmid vaccines are protective after two doses, and the specific contribution of antibody and CD8(+) T cells to vaccine immunity against WNV is modulated by the prime-boost strategy.

Gamma interferon plays a crucial early antiviral role in protection against West Nile virus infection

West Nile virus (WNV) causes a severe central nervous system (CNS) infection in humans, primarily in the elderly and immunocompromised. Prior studies have established an essential protective role of several innate immune response elements, including alpha/beta interferon (IFN-alpha/beta), immunoglobulin M, gammadelta T cells, and complement against WNV infection. In this study, we demonstrate that a lack of IFN-gamma production or signaling results in increased vulnerability to lethal WNV infection by a subcutaneous route in mice, with a rise in mortality from 30% (wild-type mice) to 90% (IFN-gamma(-/-) or IFN-gammaR(-/-) mice) and a decrease in the average survival time. This survival pattern in IFN-gamma(-/-) and IFN-gammaR(-/-) mice correlated with higher viremia and greater viral replication in lymphoid tissues. The increase in peripheral infection led to early CNS seeding since infectious WNV was detected several days earlier in the brains and spinal cords of IFN-gamma(-/-) or IFN-gammaR(-/-) mice. Bone marrow reconstitution experiments showed that gammadelta T cells require IFN-gamma to limit dissemination by WNV. Moreover, treatment of primary dendritic cells with IFN-gamma reduced WNV production by 130-fold. Collectively, our experiments suggest that the dominant protective role of IFN-gamma against WNV is antiviral in nature, occurs in peripheral lymphoid tissues, and prevents viral dissemination to the CNS.