Tolerance and antiviral effect of ribavirin in patients with Argentine hemorrhagic fever

Treatment of highly virulent mammarenavirus infections-status quo and future directions

INTRODUCTION

Mammarenaviruses are negative-sense bisegmented enveloped RNA viruses that are endemic in Africa, the Americas, and Europe. Several are highly virulent, causing acute human diseases associated with high case fatality rates, and are considered to be significant with respect to public health impact or bioterrorism threat.

AREAS COVERED

This review summarizes the status quo of treatment development, starting with drugs that are in advanced stages of evaluation in early clinical trials, followed by promising candidate medical countermeasures emerging from bench analyses and investigational animal research.

EXPERT OPINION

Specific therapeutic treatments for diseases caused by mammarenaviruses remain limited to the off-label use of ribavirin and transfusion of convalescent sera. Progress in identifying novel candidate medical countermeasures against mammarenavirus infection has been slow in part because of the biosafety and biosecurity requirements. However, novel methodologies and tools have enabled increasingly efficient high-throughput molecular screens of regulatory-agency-approved small-molecule drugs and led to the identification of several compounds that could be repurposed for the treatment of infection with several mammarenaviruses. Unfortunately, most of them have not yet been evaluated in vivo. The most promising treatment under development is a monoclonal antibody cocktail that is protective against multiple lineages of the Lassa virus in nonhuman primate disease models.

Single dose rVSVΔG-JUNVGP vaccine protects guinea pigs against lethal Junin virus challenge

Junin virus (JUNV) is a pathogen of biodefense importance due to its potential for aerosol transmission and mortality rates reaching 30%. Currently, there are no JUNV vaccines licensed by the United States Food and Drug Administration (FDA) for at-risk individuals. A vaccine based on recombinant vesicular stomatitis virus (rVSV) has been effectively used to prevent Ebola virus disease in humans. Here, we evaluated the protective efficacy of a rVSV expressing the JUNV glycoprotein (rVSVΔG-JUNVGP) in a guinea pig model of lethal JUNV disease. Two groups of guinea pigs, one prime and one prime-boost, were vaccinated with rVSVΔG-JUNVGP; six control animals remained unvaccinated. Survival for prime and prime-boost vaccinated animals was 100% while the challenge virus was uniformly lethal in all control animals. Animals in both vaccine groups developed robust, high avidity IgG antibody titers post-vaccination as well as detectable neutralizing antibodies while control animals failed to develop detectable antibody responses. This study demonstrates for the first time that rVSV expressing the JUNV GP fully protects guinea pigs from lethal JUNV challenge with a single injection vaccine.

Therapy for Argentine hemorrhagic fever in nonhuman primates with a humanized monoclonal antibody

Despite the relatively high disease burden of arenaviruses in South America and Africa, there are currently no Food and Drug Administration-approved drugs for use in preventing or treating any arenavirus infection. Currently, the sole clinically validated treatment option for Argentine hemorrhagic fever (AHF), caused by Junin virus (JUNV), is administration of immune plasma. While the relative success associated with this treatment supports passive immunotherapy interventions, the recent expansion of mAbs used in a clinical setting for infectious diseases offer a highly specific, consistently potent, and generally safe alternative to immune plasma. Here we show that a humanized mAb is highly efficacious in guinea pig and nonhuman primate models of AHF.

The COVID-19 pandemic has reemphasized the need to identify safe and scalable therapeutics to slow or reverse symptoms of disease caused by newly emerging and reemerging viral pathogens. Recent clinical successes of monoclonal antibodies (mAbs) in therapy for viral infections demonstrate that mAbs offer a solution for these emerging biothreats. We have explored this with respect to Junin virus (JUNV), an arenavirus classified as a category A high-priority agent and the causative agent of Argentine hemorrhagic fever (AHF). There are currently no Food and Drug Administration-approved drugs available for preventing or treating AHF, although immune plasma from convalescent patients is used routinely to treat active infections. However, immune plasma is severely limited in quantity, highly variable in quality, and poses significant safety risks including the transmission of transfusion-borne diseases. mAbs offer a highly specific and consistently potent alternative to immune plasma that can be manufactured at large scale. We previously described a chimeric mAb, cJ199, that provided protection in a guinea pig model of AHF. To adapt this mAb to a format more suitable for clinical use, we humanized the mAb (hu199) and evaluated it in a cynomolgus monkey model of AHF with two JUNV isolates, Romero and Espindola. While untreated control animals experienced 100% lethality, all animals treated with hu199 at 6 d postinoculation (dpi) survived, and 50% of animals treated at 8 dpi survived. mAbs like hu199 may offer a safer, scalable, and more reproducible alternative to immune plasma for rare viral diseases that have epidemic potential.

[Use of ribavirin in viruses other than hepatitis C. A review of the evidence]

Ribavirin is a molecule with antiviral activity against different viruses. In clinical practice, it has made its niche almost exclusively for the treatment of the hepatitis C virus. However, there are other diseases in which it could be of benefit and it has the advantage of being suitable for oral, intravenous and inhaled administration. We conducted a review of the indications of the main drug agencies (Spanish, European and American) and other possible indications, mainly haemorrhagic fevers and coronavirus.

Apoptosis during arenavirus infection: mechanisms and evasion strategies

In recent years there has been a greatly increased interest in the interactions of arenaviruses with the apoptotic machinery, and particularly the extent to which these interactions may be an important contributor to pathogenesis. Here we summarize the current state of our knowledge on this subject and address the potential for interplay with other immunological mechanisms known to be regulated by these viruses. We also compare and contrast what is known for arenavirus-induced apoptosis with observations from other segmented hemorrhagic fever viruses.

Genomic profiling of host responses to Lassa virus: therapeutic potential from primate to man

Lassa virus infection elicits distinctive changes in host gene expression and metabolism. We focus on changes in host gene expression that may be biomarkers that discriminate individual pathogens or may help to provide a prognosis for disease. In addition to assessing mRNA changes, functional studies are also needed to discriminate causes of disease from mechanisms of host resistance. Host responses that drive pathogenesis are likely to be targets for prevention or therapy. Host responses to Lassa or its related arenaviruses have been monitored in cell culture, in animal models of hemorrhagic fever, in Lassa-infected nonhuman primates and, to a limited extent, in infected human beings. Here, we describe results from those studies and discuss potential targets for reducing virus replication and mitigating disease.

RIG-I enhanced interferon independent apoptosis upon Junin virus infection

Junin virus (JUNV) is the etiological agent of Argentine hemorrhagic fever (AHF), a human disease with a high case-fatality rate. It is widely accepted that arenaviral infections, including JUNV infections, are generally non-cytopathic. In contrast, here we demonstrated apoptosis induction in human lung epithelial carcinoma (A549), human hepatocarcinoma and Vero cells upon infection with the attenuated Candid#1 strain of, JUNV as determined by phosphatidylserine (PS) translocation, Caspase 3 (CASP3) activation, Poly (ADP-ribose) polymerase (PARP) cleavage and/or chromosomal DNA fragmentation. Moreover, as determined by DNA fragmentation, we found that the pathogenic Romero strain of JUNV was less cytopathic than Candid#1 in human hepatocarcinoma and Vero, but more apoptotic in A549 and Vero E6 cells. Additionally, we found that JUNV-induced apoptosis was enhanced by RIG-I signaling. Consistent with the previously reported role of RIG-I like helicase (RLH) signaling in initiating programmed cell death, we showed that cell death or DNA fragmentation of Candid#1-infected A549 cells was decreased upon siRNA or shRNA silencing of components of RIG-I pathway in spite of increased virus production. Similarly, we observed decreased DNA fragmentation in JUNV-infected human hepatocarcinoma cells deficient for RIG-I when compared with that of RIG-I-competent cells. In addition, DNA fragmentation detected upon Candid#1 infection of type I interferon (IFN)-deficient Vero cells suggested a type I IFN-independent mechanism of apoptosis induction in response to JUNV. Our work demonstrated for the first time apoptosis induction in various cells of mammalian origin in response to JUNV infection and partial mechanism of this cell death.

Toll-like receptor 2-mediated innate immune responses against Junín virus in mice lead to antiviral adaptive immune responses during systemic infection and do not affect viral replication in the brain

Successful adaptive immunity to virus infection often depends on the initial innate response. Previously, we demonstrated that Junín virus, the etiological agent responsible for Argentine hemorrhagic fever (AHF), activates an early innate immune response via an interaction between the viral glycoprotein and Toll-like receptor 2 (TLR2). Here we show that TLR2/6 but not TLR1/2 heterodimers sense Junín virus glycoprotein and induce a cytokine response, which in turn upregulates the expression of the RNA helicases RIG-I and MDA5. NF-κB and Erk1/2 were important in the cytokine response, since both proteins were phosphorylated as a result of the interaction of virus with TLR2, and treatment with an Erk1/2-specific inhibitor blocked cytokine production. We show that the Junín virus glycoprotein activates cytokine production in a human macrophage cell line as well. Moreover, we show that TLR2-mediated immune response plays a role in viral clearance because wild-type mice cleared Candid 1 (JUNV C1), the vaccine strain of Junín virus, more rapidly than did TLR2 knockout mice. This clearance correlated with the generation of Junín virus-specific CD8(+) T cells. However, infected wild-type and TLR2 knockout mice developed TLR2-independent blocking antibody responses with similar kinetics. We also show that microglia and astrocytes but not neurons are susceptible to infection with JUNV C1. Although JUNV C1 infection of the brain also triggered a TLR2-dependent cytokine response, virus levels were equivalent in wild-type and TLR2 knockout mice. Importance: Junín virus is transmitted by rodents native to Argentina and is associated with both systemic disease and, in some patients, neurological symptoms. Humans become infected when they inhale aerosolized Junín virus. AHF has a 15 to 30% mortality rate, and patients who clear the infection develop a strong antibody response to Junín virus. Here we investigated what factors determine the immune response to Junín virus. We show that a strong initial innate immune response to JUNV C1 determines how quickly mice can clear systemic infection and that this depended on the cellular immune response. In contrast, induction of an innate immune response in the brain had no effect on virus infection levels. These findings may explain how the initial immune response to Junín virus infection could determine different outcomes in humans.

Comparative analysis of disease pathogenesis and molecular mechanisms of New World and Old World arenavirus infections

Arenaviruses can cause fatal human haemorrhagic fever (HF) diseases for which vaccines and therapies are extremely limited. Both the New World (NW) and Old World (OW) groups of arenaviruses contain HF-causing pathogens. Although these two groups share many similarities, important differences with regard to pathogenicity and molecular mechanisms of virus infection exist. These closely related pathogens share many characteristics, including genome structure, viral assembly, natural host selection and the ability to interfere with innate immune signalling. However, members of the NW and OW viruses appear to use different receptors for cellular entry, as well as different mechanisms of virus internalization. General differences in disease signs and symptoms and pathological lesions in patients infected with either NW or OW arenaviruses are also noted and discussed herein. Whilst both the OW Lassa virus (LASV) and the NW Junin virus (JUNV) can cause disruption of the vascular endothelium, which is an important pathological feature of HF, the immune responses to these related pathogens seem to be quite distinct. Whereas LASV infection results in an overall generalized immune suppression, patients infected with JUNV seem to develop a cytokine storm. Additionally, the type of immune response required for recovery and clearance of the virus is different between NW and OW infections. These differences may be important to allow the viruses to evade host immune detection. Understanding these differences will aid the development of new vaccines and treatment strategies against deadly HF viral infections.

Favipiravir (T-705) inhibits Junín virus infection and reduces mortality in a guinea pig model of Argentine hemorrhagic fever

Background

Junín virus (JUNV), the etiologic agent of Argentine hemorrhagic fever (AHF), is classified by the NIAID and CDC as a Category A priority pathogen. Presently, antiviral therapy for AHF is limited to immune plasma, which is readily available only in the endemic regions of Argentina. T-705 (favipiravir) is a broadly active small molecule RNA-dependent RNA polymerase inhibitor presently in clinical evaluation for the treatment of influenza. We have previously reported on the in vitro activity of favipiravir against several strains of JUNV and other pathogenic New World arenaviruses.

Methodology/Principal Findings

To evaluate the efficacy of favipiravir in vivo, guinea pigs were challenged with the pathogenic Romero strain of JUNV, and then treated twice daily for two weeks with oral or intraperitoneal (i.p.) favipiravir (300 mg/kg/day) starting 1–2 days post-infection. Although only 20% of animals treated orally with favipiravir survived the lethal challenge dose, those that succumbed survived considerably longer than guinea pigs treated with placebo. Consistent with pharmacokinetic analysis that showed greater plasma levels of favipiravir in animals dosed by i.p. injection, i.p. treatment resulted in a substantially higher level of protection (78% survival). Survival in guinea pigs treated with ribavirin was in the range of 33–40%. Favipiravir treatment resulted in undetectable levels of serum and tissue viral titers and prevented the prominent thrombocytopenia and leucopenia observed in placebo-treated animals during the acute phase of infection.

Conclusions/Significance

The remarkable protection afforded by i.p. favipiravir intervention beginning 2 days after challenge is the highest ever reported for a small molecule antiviral in the difficult to treat guinea pig JUNV challenge model. These findings support the continued development of favipiravir as a promising antiviral against JUNV and other related arenaviruses.

Argentine hemorrhagic fever (AHF) is a severe and often-fatal disease caused by infection with Junín virus (JUNV). Presently, there is an unmet need to develop new therapeutics to address current medical, public health and national security concerns, as JUNV is considered a potential bioterror agent amenable to aerosolization and intentional release. In the present study, favirpiravir, a promising anti-JUNV drug in clinical development for the treatment of influenza, was evaluated in an experimental small animal model of AHF. Guinea pigs challenged with JUNV were treated with favipiravir twice daily for two weeks starting 1–2 days after infection. Consistent with pharmacokinetic analysis that showed greater plasma levels of favipiravir in animals dosed by intraperitoneal injection, administration by this route resulted in a dramatic protective effect as 78% animals survived the infection compared to 11% in the placebo-treated group. Favipiravir treatment inhibited JUNV replication and prevented the development of disease observed in animals receiving placebo during the acute stage of infection. The high level efficacy observed following post-exposure prophylaxis with favipiravir is the highest ever reported for a small molecule antiviral in the guinea pig JUNV challenge model and thus supports its continued development as a promising antiviral therapy for the treatment of AHF.

Drug discovery technologies and strategies for Machupo virus and other New World arenaviruses

INTRODUCTION

Seven arenaviruses cause viral hemorrhagic fever in humans: the Old World arenaviruses Lassa and Lujo, and the New World Clade B arenaviruses Machupo (MACV), Junín (JUNV), Guanarito (GTOV), Sabiá (SABV), and Chapare (CHPV). All of these viruses are Risk Group 4 biosafety pathogens. MACV causes human disease outbreak with high case-fatality rates. To date, at least 1,200 cases with ≈200 fatalities have been recorded.

AREAS COVERED

This review summarizes available systems and technologies for the identification of antivirals against MACV. Furthermore, the article summarizes animal models that have been used for the in vivo evaluation of novel inhibitors. The article highlights present treatments for arenaviral diseases and provides an overview of efficacious small molecules and other therapeutics reported to date. Finally, the article summarizes strategies to identify novel inhibitors for anti-arenaviral therapy.

EXPERT OPINION

New high-throughput approaches to quantitate infection rates of arenaviruses, as well as viruses modified to carry reporter genes, will accelerate compound screens and drug discovery efforts. RNAi, gene expression profiling and proteomics studies will identify host targets for therapeutic intervention. New discoveries in the cell entry mechanism of MACV and other arenaviruses as well as extensive structural studies of arenaviral L and NP could facilitate the rational design of antivirals effective against all pathogenic New World arenaviruses.

Progress in the experimental therapy of severe arenaviral infections

A number of viruses in the family Arenaviridae cause severe illness in humans. Lassa virus in West Africa and a number of agents in South America produce hemorrhagic fever in persons exposed to aerosolized excretions of the pathogens' rodent hosts. Because arenaviruses are not transmitted by arthropods, and person-to-person spread is rare, human infections occur singly and sporadically, and are usually not diagnosed until the patient is severely ill. Because the arenaviruses are naturally transmitted by the airborne route, they also pose a potential threat as aerosolized bioterror weapons. The broad-spectrum antiviral drug ribavirin was shown to reduce mortality from Lassa fever, and has been tested against Argentine hemorrhagic fever, but it is not an approved treatment for either disease. Human immune convalescent plasma was proven to be effective for Argentine hemorrhagic fever in a controlled trial. New treatments are needed to block viral replication without causing toxicity and to prevent the increased vascular permeability that is responsible for hypotension and shock. In this paper, we review current developments in the experimental therapy of severe arenaviral infections, focusing on drugs that have been tested in animal models, and provide a perspective on future research.

An antibody recognizing the apical domain of human transferrin receptor 1 efficiently inhibits the entry of all new world hemorrhagic Fever arenaviruses

Five New World (NW) arenaviruses cause human hemorrhagic fevers. Four of these arenaviruses are known to enter cells by binding human transferrin receptor 1 (hTfR1). Here we show that the fifth arenavirus, Chapare virus, similarly uses hTfR1. We also identify an anti-hTfR1 antibody, ch128.1, which efficiently inhibits entry mediated by the glycoproteins of all five viruses, as well as replication of infectious Junín virus. Our data indicate that all NW hemorrhagic fever arenaviruses utilize a common hTfR1 apical-domain epitope and suggest that therapeutic agents targeting this epitope, including ch128.1 itself, can be broadly effective in treating South American hemorrhagic fevers.

Inhibition of Junin virus RNA synthesis by an antiviral acridone derivative

There are no specific approved drugs for the treatment of agents of viral hemorrhagic fevers (HF) and antiviral therapies against these viruses are urgently needed. The present study characterizes the potent and selective antiviral activity against the HF causing arenavirus Junin virus (JUNV) of the compound 10-allyl-6-chloro-4-methoxy-9(10H)-acridone, designated 3f. The effectiveness of 3f to inhibit JUNV multiplication was not importantly affected by the initial multiplicity of infection, with similar effective concentration 50% (EC(50)) values in virus yield inhibition assays performed in Vero cells in the range of 0.2-40 plaque forming units (PFU)/cell. Mechanistic studies demonstrated that 3f did not affect the initial steps of adsorption and internalization. The subsequent process of viral RNA synthesis was strongly inhibited, as quantified by real time RT-PCR in compound-treated cells relative to non-treated cells. The addition of exogenous guanosine rescued the infectivity and RNA synthesis of JUNV in 3f-treated cells in a dose-dependent manner, but the reversal was partial, suggesting that the reduction of the GTP pool contributed to the antiviral activity of 3f, but it was not the main operative mechanism. The comparison of 3f with two other viral RNA inhibitors, ribavirin and mycophenolic acid, showed that ribavirin did not act against JUNV through the cellular enzyme inosine monophosphate dehydrogenase (IMPDH) inhibition whereas the anti-JUNV activity of mycophenolic acid was mainly targeted at this enzyme.

Effective oral favipiravir (T-705) therapy initiated after the onset of clinical disease in a model of arenavirus hemorrhagic Fever

Background

Lassa and Junín viruses are the most prominent members of the Arenaviridae family of viruses that cause viral hemorrhagic fever syndromes Lassa fever and Argentine hemorrhagic fever, respectively. At present, ribavirin is the only antiviral drug indicated for use in treatment of these diseases, but because of its limited efficacy in advanced cases of disease and its toxicity, safer and more effective antivirals are needed.

Methodology/Principal Findings

Here, we used a model of acute arenaviral infection in outbred guinea pigs based on challenge with an adapted strain of Pichindé virus (PICV) to further preclinical development of T-705 (Favipiravir), a promising broad-spectrum inhibitor of RNA virus infections. The guinea pig-adapted passage 19 PICV was uniformly lethal with an LD₅₀ of ∼5 plaque-forming units and disease was associated with fever, weight loss, thrombocytopenia, coagulation defects, increases in serum aspartate aminotransferase (AST) concentrations, and pantropic viral infection. Favipiravir (300 mg/kg/day, twice daily orally for 14 days) was highly effective, as all animals recovered fully from PICV-induced disease even when therapy was initiated one week after virus challenge when animals were already significantly ill with marked fevers and thrombocytopenia. Antiviral activity and reduced disease severity was evidenced by dramatic reductions in peak serum virus titers and AST concentrations in favipiravir-treated animals. Moreover, a sharp decrease in body temperature was observed shortly after the start of treatment. Oral ribavirin was also evaluated, and although effective, the slower rate of recovery may be a sign of the drug's known toxicity.

Conclusions/Significance

Our findings support further development of favipiravir for the treatment of severe arenaviral infections. The optimization of the experimental favipiravir treatment regimen in the PICV guinea pig model will inform critical future studies in the same species based on challenge with highly pathogenic arenaviruses such as Lassa and Junín.

Several viruses in the Arenaviridae family cause severe life-threatening hemorrhagic fever syndromes, which are considered neglected tropical diseases in endemic areas of Africa and South America. Ribavirin, the only licensed antiviral indicated for use has limited efficacy when treating advanced cases of disease and is associated with toxicity. In the present study, we use a model of acute arenaviral disease in guinea pigs based on infection with an adapted strain of the Pichindé arenavirus (PICV) to further preclinical development of a promising broad-spectrum antiviral drug candidate, favipiravir. Oral favipiravir was highly effective in the treatment of sick animals with marked fevers, as all recovered fully from lethal PICV infection even when therapy was initiated one week after virus challenge. Antiviral activity and reduced disease severity was evidenced by dramatic reductions in serum virus loads and serum aspartate aminotransferase, an enzyme released into the bloodstream following tissue damage and a marker for severe arenaviral infections. Moreover, a sharp decrease in fever was observed shortly after the onset of treatment. Our findings support further development of favipiravir for the treatment of severe arenaviral infections, for which there are presently no safe and effective therapies for treating advanced cases of disease.

Human CD8⁺ and CD4⁺ T cell memory to lymphocytic choriomeningitis virus infection

Although cellular immunity to acute lymphocytic choriomeningitis virus (LCMV) infection has been well characterized in experimental studies in mice, the T cell response to this virus in humans is incompletely understood. Thus, we analyzed the breadths, magnitudes, and differentiation phenotypes of memory LCMV-specific CD8(+) and CD4(+) T cells in three human donors displaying a variety of disease outcomes after accidental needle stick injury or exposure to LCMV. Although only a small cohort of donors was analyzed at a single time point postinfection, several interesting observations were made. First, we were able to detect LCMV-specific CD8(+) and CD4(+) T cell responses directly ex vivo at 4 to 8 years after exposure, demonstrating the longevity of T cell memory in humans. Second, unlike in murine models of LCMV infection, we found that the breadths of memory CD8(+) and CD4(+) T cell responses were not significantly different from one another. Third, it seemed that the overall CD8(+) T cell response was augmented with increasing severity of disease, while the LCMV-specific CD4(+) T cell response magnitude was highly variable between the three different donors. Next, we found that LCMV-specific CD8(+) T cells in the three donors analyzed seemed to undergo an effector memory differentiation program distinct from that of CD4(+) T cells. Finally, the levels of expression of memory, costimulatory, and inhibitory receptors on CD8(+) and CD4(+) T cell subsets, in some instances, correlated with disease outcome. These data demonstrate for the first time LCMV-specific CD8(+) and CD4(+) T cells in infected humans and begin to provide new insights into memory T cell responses following an acute virus infection.

Development of a new tacaribe arenavirus infection model and its use to explore antiviral activity of a novel aristeromycin analog

Background

A growing number of arenaviruses can cause a devastating viral hemorrhagic fever (VHF) syndrome. They pose a public health threat as emerging viruses and because of their potential use as bioterror agents. All of the highly pathogenic New World arenaviruses (NWA) phylogenetically segregate into clade B and require maximum biosafety containment facilities for their study. Tacaribe virus (TCRV) is a nonpathogenic member of clade B that is closely related to the VHF arenaviruses at the amino acid level. Despite this relatedness, TCRV lacks the ability to antagonize the host interferon (IFN) response, which likely contributes to its inability to cause disease in animals other than newborn mice.

Methodology/Principal Findings

Here we describe a new mouse model based on TCRV challenge of AG129 IFN-α/β and -γ receptor-deficient mice. Titration of the virus by intraperitoneal (i.p.) challenge of AG129 mice resulted in an LD₅₀ of ∼100 fifty percent cell culture infectious doses. Virus replication was evident in the serum, liver, lung, spleen, and brain 4–8 days after inoculation. MY-24, an aristeromycin derivative active against TCRV in cell culture at 0.9 µM, administered i.p. once daily for 7 days, offered highly significant (P<0.001) protection against mortality in the AG129 mouse TCRV infection model, without appreciably reducing viral burden. In contrast, in a hamster model of arenaviral hemorrhagic fever based on challenge with clade A Pichinde arenavirus, MY-24 did not offer significant protection against mortality.

Conclusions/Significance

MY-24 is believed to act as an inhibitor of S-adenosyl-L-homocysteine hydrolase, but our findings suggest that it may ameliorate disease by blunting the effects of the host response that play a role in disease pathogenesis. The new AG129 mouse TCRV infection model provides a safe and cost-effective means to conduct early-stage pre-clinical evaluations of candidate antiviral therapies that target clade B arenaviruses.

Coverage of related pathogenic species by multivalent and cross-protective vaccine design: arenaviruses as a model system

The arenaviruses are a family of negative-sense RNA viruses that cause severe human disease ranging from aseptic meningitis to hemorrhagic fever syndromes. There are currently no FDA-approved vaccines for the prevention of arenavirus disease, and therapeutic treatment is limited to the use of ribavirin and/or immune plasma for a subset of the pathogenic arenaviruses. The considerable genetic variability observed among the seven arenaviruses that are pathogenic for humans illustrates one of the major challenges for vaccine development today, namely, to overcome pathogen heterogeneity. Over the past 5 years, our group has tested several strategies to overcome pathogen heterogeneity, utilizing the pathogenic arenaviruses as a model system. Because T cells play a prominent role in protective immunity following arenavirus infection, we specifically focused on the development of human vaccines that would induce multivalent and cross-protective cell-mediated immune responses. To facilitate our vaccine development and testing, we conducted large-scale major histocompatibility complex (MHC) class I and class II epitope discovery on murine, nonhuman primate, and human backgrounds for each of the pathogenic arenaviruses, including the identification of protective HLA-restricted epitopes. Finally, using the murine model of lymphocytic choriomeningitis virus infection, we studied the phenotypic characteristics associated with immunodominant and protective T cell epitopes. This review summarizes the findings from our studies and discusses their application to future vaccine design.

Polyfunctional CD4+ T cell responses to a set of pathogenic arenaviruses provide broad population coverage

Background

Several arenaviruses cause severe hemorrhagic fever and aseptic meningitis in humans for which no licensed vaccines are available. A major obstacle for vaccine development is pathogen heterogeneity within the Arenaviridae family. Evidence in animal models and humans indicate that T cell and antibody-mediated immunity play important roles in controlling arenavirus infection and replication. Because CD4⁺ T cells are needed for optimal CD8⁺ T cell responses and to provide cognate help for B cells, knowledge of epitopes recognized by CD4⁺ T cells is critical to the development of an effective vaccine strategy against arenaviruses. Thus, the goal of the present study was to define and characterize CD4⁺ T cell responses from a broad repertoire of pathogenic arenaviruses (including lymphocytic choriomeningitis, Lassa, Guanarito, Junin, Machupo, Sabia, and Whitewater Arroyo viruses) and to provide determinants with the potential to be incorporated into a multivalent vaccine strategy.

Results

By inoculating HLA-DRB1*0101 transgenic mice with a panel of recombinant vaccinia viruses, each expressing a single arenavirus antigen, we identified 37 human HLA-DRB1*0101-restricted CD4⁺ T cell epitopes from the 7 antigenically distinct arenaviruses. We showed that the arenavirus-specific CD4⁺ T cell epitopes are capable of eliciting T cells with a propensity to provide help and protection through CD40L and polyfunctional cytokine expression. Importantly, we demonstrated that the set of identified CD4⁺ T cell epitopes provides broad, non-ethnically biased population coverage of all 7 arenavirus species targeted by our studies.

Conclusions

The identification of CD4⁺ T cell epitopes, with promiscuous binding properties, derived from 7 different arenavirus species will aid in the development of a T cell-based vaccine strategy with the potential to target a broad range of ethnicities within the general population and to protect against both Old and New World arenavirus infection.

TC83 replicon vectored vaccine provides protection against Junin virus in guinea pigs

Junin virus (JUNV) is the etiological agent of the potentially lethal, reemerging human disease, Argentine hemorrhagic fever (AHF). The mechanism of the disease development is not well understood and no antiviral therapy is available. Candid 1, a live-attenuated vaccine, has been developed by the US Army and is being used in the endemic area to prevent AHF. This vaccine is only approved for use in Argentina. In this study we have used the alphavirus-based approach to engineer a replicon system based on a human (United States Food and Drug Administration Investigational New Drug status) vaccine TC83 that express heterologous viral antigens, such as glycoproteins (GPC) of Junin virus (JUNV). Preclinical studies testing the immunogenicity and efficacy of TC83/GPC were performed in guinea pigs. A single dose of the live-attenuated alphavirus based vaccine expressing only GPC was immunogenic and provided partial protection, while a double dose of the same vaccine provided a complete protection against JUNV. This is the first scientific report to our knowledge that the immune response against GPC alone is sufficient to prevent lethal disease against JUNV in an animal model.

Inhibition of Lassa virus glycoprotein cleavage and multicycle replication by site 1 protease-adapted alpha(1)-antitrypsin variants

Background

Proteolytic processing of the Lassa virus envelope glycoprotein precursor GP-C by the host proprotein convertase site 1 protease (S1P) is a prerequisite for the incorporation of the subunits GP-1 and GP-2 into viral particles and, hence, essential for infectivity and virus spread. Therefore, we tested in this study the concept of using S1P as a target to block efficient virus replication.

Methodology/Principal Finding

We demonstrate that stable cell lines inducibly expressing S1P-adapted α₁-antitrypsin variants inhibit the proteolytic maturation of GP-C. Introduction of the S1P recognition motifs RRIL and RRLL into the reactive center loop of α₁-antitrypsin resulted in abrogation of GP-C processing by endogenous S1P to a similar level observed in S1P-deficient cells. Moreover, S1P-specific α₁-antitrypsins significantly inhibited replication and spread of a replication-competent recombinant vesicular stomatitis virus expressing the Lassa virus glycoprotein GP as well as authentic Lassa virus. Inhibition of viral replication correlated with the ability of the different α₁-antitrypsin variants to inhibit the processing of the Lassa virus glycoprotein precursor.

Conclusions/Significance

Our data suggest that glycoprotein cleavage by S1P is a promising target for the development of novel anti-arenaviral strategies.

The virus family Arenaviridae includes several hemorrhagic fever causing agents such as Lassa, Guanarito, Junin, Machupo, and Sabia virus that pose a major public health concern to the human population in West African and South American countries. Current treatment options to control fatal outcome of disease are limited to the ribonucleoside analogue ribavirin, although its use has some significant limitations. The lack of effective treatment alternatives emphasizes the need for novel antiviral therapeutics to counteract these life-threatening infections. Maturation cleavage of the viral envelope glycoprotein by the host cell proprotein convertase site 1 protease (S1P) is critical for infectious virion production of several pathogenic arenaviruses. This finding makes this protease an attractive target for the development of novel anti-arenaviral therapeutics. We demonstrate here that highly selective S1P-adapted α₁-antitrypsins have the potential to efficiently inhibit glycoprotein processing, which resulted in reduced Lassa virus replication. Our findings suggest that S1P should be considered as an antiviral target and that further optimization of modified α₁-antitrypsins could lead to potent and specific S1P inhibitors with the potential for treatment of certain viral hemorrhagic fevers.

Treatment of Argentine hemorrhagic fever

Argentine hemorrhagic fever (AHF) is a rodent-borne illness caused by the arenavirus Junin that is endemic to the humid pampas of Argentina. AHF has had significant morbidity since its emergence in the 1950s, with a case-fatality rate of the illness without treatment between 15% and 30%. The use of a live attenuated vaccine has markedly reduced the incidence of AHF. Present specific therapy involves the transfusion of immune plasma in defined doses of neutralizing antibodies during the prodromal phase of illness. However, alternative forms of treatment are called for due to current difficulties in early detection of AHF, related to its decrease in incidence, troubles in maintaining adequate stocks of immune plasma, and the absence of effective therapies for severely ill patients that progress to a neurologic–hemorrhagic phase. Ribavirin might be a substitute for immune plasma, provided that the supply is guaranteed. Immune immunoglobulin or monoclonal antibodies should also be considered. New therapeutic options such as those being developed for systemic inflammatory syndromes should also be valuated in severe forms of AHF.

Viral hemorrhagic fevers

A taxonomically diverse set of single-stranded ribonucleic acid(ssRNA) viruses from four diverse viral families Arenaviridae,Bunyaviridae, Filoviridae, and Flaviviridae cause an acute systemic febrile syndrome called viral hemorrhagic fever (VHF). The syndrome produces combinations of prostration, malaise, increased vascular permeability, and coagulation maladies. In severe illness,VHF may include generalized bleeding but the bleeding does not typically constitute a life-threatening loss of blood volume. To a certain extent, it is a sign of damage to the vascular endothelium and is an indicator of disease severity in specific target organs. Although the viruses that cause hemorrhagic fever (HF) can productively replicate in endothelial cells, much of the disease pathology including impairment to the vascular system is thought to result primarily from the release of a variety of mediators from virus-infected cells, such as monocytes and macrophages that subsequently alter vascular function and trigger the coagulation disorders that epitomize these infections. While significant progress has been made over the last several years in dissecting out the molecular biology and pathogenesis of the HF viruses, there are currently no vaccines or drugs licensed available for most of the VHFs.

Arenaviruses other than Lassa virus

The family Arenaviridae includes 23 viral species, of which 5 can cause viral hemorrhagic fevers with a case fatality rate of about 20%. These five viruses are Junin, Machupo, Guanarito, Sabia and Lassa virus, the manipulation of which requires biosafety level 4 facilities. They are included in the Category A Pathogen List established by the Center for Disease Control and Prevention that groups agents with the greatest potential for adverse public health impact and mass casualties whether a situation characterized by a ill-intentioned abuse of natural or engineered arenavirus would be encountered. The aims of this article are to (i) summarize the current situation; (ii) provide information to help anticipating the effects to be expected in such a situation; and to (iii) emphasize the need for fundamental research to allow the development of diagnostic, prevention and therapeutic tools as countermeasures to weaponized arenaviruses.

Ribavirin--current status of a broad spectrum antiviral agent

Ribavirin is a very broad-spectrum virustatic antiviral agent, first synthesised in 1972. It is characterised by low toxicity apart from reversible anaemia, usually mild. Its multiple mechanisms of action mean that viral resistance rarely develops. It can be administered orally, intravenously, or via a nebuliser. It has shown varying degrees of clinical efficacy in a variety of human diseases including respiratory tract infections due to respiratory syncytial virus and influenza, measles, herpesvirus infections, HIV infection, Lassa fever, haemorrhagic fever with renal syndrome, and (in combination with IFN-alpha) chronic hepatitis C infection. It may well prove of value against other emerging exotic infections (e.g., West Nile virus, Nipah virus).

Passive transfer of antibodies protects immunocompetent and imunodeficient mice against lethal Ebola virus infection without complete inhibition of viral replication

Ebola hemorrhagic fever is a severe, usually fatal illness caused by Ebola virus, a member of the filovirus family. The use of nonhomologous immune serum in animal studies and blood from survivors in two anecdotal reports of Ebola hemorrhagic fever in humans has shown promise, but the efficacy of these treatments has not been demonstrated definitively. We have evaluated the protective efficacy of polyclonal immune serum in a mouse model of Ebola virus infection. Our results demonstrate that mice infected subcutaneously with live Ebola virus survive infection and generate high levels of anti-Ebola virus immunoglobulin G (IgG). Passive transfer of immune serum from these mice before challenge protected upto 100% of naive mice against lethal Ebola virus infection. Protection correlated with the level of anti-Ebola virus IgG titers, and passive treatment with high-titer antiserum was associated with a delay in the peak of viral replication. Transfer of immune serum to SCID mice resulted in 100% survival after lethal challenge with Ebola virus, indicating that antibodies alone can protect from lethal disease. Thus antibodies suppress or delay viral growth, provide protection against lethal Ebola virus infection, and may not require participation of other immune components for protection.

Additive effect of neutralizing antibody and antiviral drug treatment in preventing virus escape and persistence

Poorly cytopathic or noncytopathic viruses can escape immune surveillance and establish a chronic infection. Here we exploited the strategy of combining antiviral drug treatment with the induction of a neutralizing antibody response to avoid the appearance of neutralization-resistant virus variants. Despite the fact that H25 immunoglobulin transgenic mice infected with lymphocytic choriomeningitis virus mounted an early neutralizing antibody response, the virus escaped from neutralization and persisted. After ribavirin treatment of H25 transgenic mice, the appearance of neutralization-resistant virus was prevented and virus was cleared. Thus, the combination of virus-neutralizing antibodies and chemotherapy efficiently controlled the infection, whereas each defense line alone did not. Similar additive effects may be unexpectedly efficient and beneficial in humans after infections with persistent viruses such as hepatitis C virus and hepatitis B virus and possibly human immunodeficiency virus.

Antiviral effect of brassinosteroids against herpes virus and arenaviruses

A natural brassinosteroid and a series of synthetic derivatives were found to be good inhibitors of herpes simplex virus type 1 (HSV-1) and arenavirus replication in cell culture. The synthetic compounds tested were analogues of the 24(S) ethylbrassinone. Compounds (22 R,23 R,24S)-2alpha, 3alpha,5alpha,22,23-pentahydroxy-stigmastan-6-one and (22R,23R,24S)-3beta-bromo-5alpha,22,23-trihydroxy stigmastan-6-one were cytotoxic at concentrations of 20-40 microM. (22S,23S,24S)-2alpha,3alpha,22,23-tetrahydroxy-5alpha, stigmastan-6-one, (22R,23R,24S)-3beta-acetoxy-22,23-dihydroxy-5alpha-choles tan-6-one, (22S,23S,24S)-3beta-bromo-22,23-dihydroxy-5alpha-cholestan-6 -one and (22S,23S,24S)-3beta-bromo-5alpha,22,23-trihydroxy-stigmastan -6-one were the most active of the series against HSV-1, with selectivity index (SI) values (CC50/EC50) ranging from 10.6 to 16.5. The majority of the compounds were potent inhibitors of arenaviruses, (22S,23S,24S)-3beta-bromo-5alpha,22,23-trihydroxy-stigmastan -6-one being the most active, with SI values of 307.8 and 692.5 for Tacaribe and Junin viruses, respectively. The antiviral activity of brassinosteroid derivatives was not because of direct inactivation; time-of-addition experiments suggested that a late step in HSV-1 multiplication was affected, whereas arenaviruses remained susceptible to the compounds throughout the replicative cycle.

Antiviral agents for non-human immunodeficiency virus infections

Several new agents for treating viral infections have been developed in recent years. All available agents are virustatic, inhibiting specific steps in the process of viral replication. No agent is active against nonreplicating or latent viruses. Acyclovir is useful in the treatment of genital herpes, herpes simplex encephalitis, mucocutaneous herpetic infection, varicella infection in the immunosuppressed host, and herpes zoster infection in the normal and the immunosuppressed host. It can also be used for prevention of herpesvirus infection in immunocompromised patients. Ganciclovir is indicated for the treatment of cytomegalovirus retinitis in patients with the acquired immunodeficiency syndrome and is effective in the treatment and prevention of cytomegalovirus infection in other immunocompromised patients. Famciclovir and valacyclovir are effective in the management of herpes simplex and varicella-zoster infection. Amantadine and rimantadine are useful therapeutically and prophylactically in the management of influenza A virus infection. Chronic hepatitis B infection can respond to lamivudine therapy, and the optimal treatment of hepatitis C is the combination of interferon alfa and ribavirin. Despite pronounced toxic effects, foscarnet and cidofovir are effective antiviral agents in specific settings.

Myristic acid analogs are inhibitors of Junin virus replication

The effects of two myristic acid analogs on Junin virus (JV) replication were investigated. The compounds chosen for the study were DL-2-hydroxymyristic acid (2OHM), an inhibitor of N-myristoyltransferase (NMT), which binds the enzyme and blocks protein myristoylation, and 13-oxamyristic acid (13OM), a competitive inhibitor of NMT which incorporates into the protein instead of myristic acid. Both types of analogs achieved dose-dependent inhibition of viral multiplication at concentrations not affecting cell viability. The 50% inhibitory concentration values determined by a virus-yield inhibition assay for different strains of JV, including a human pathogenic strain, and for the related arenavirus, Tacaribe, were in the range 1.6 to 20.1 microM, with 13OM as the most active compound. From time of addition and removal experiments, it can be concluded that both analogs inhibit a late stage in the JV replicative cycle, and their effect was partially reversible. The cytoplasmic and surface expression of JV glycoproteins was not affected in the presence of the compounds, as revealed by immunofluorescence staining, suggesting that JV glycoprotein myristoylation would not be essential for the intracellular transport of the envelope proteins, but it may have an important role in their interaction with the plasma membrane during virus budding.

Inhibition of arenavirus multiplication in vitro by phenotiazines

Trifluoperazine (TFP) and chlorpromazine (CPZ), two pharmacologically active phenotiazine derivatives, were evaluated for their inhibitory activity on the replication of the arenaviruses Junin (JV), the etiological agent of Argentine hemorrhagic fever, Tacaribe virus and Pichinde virus. Both compounds achieved a concentration-dependent inhibition of viral multiplication at concentrations not affecting cell viability. The 50% inhibitory concentration (IC50) values determined by a virus yield inhibition assay for several strains of JV, including a human pathogenic strain, were in the range of 7.7-23.0 microM and the 90% inhibitory concentration (IC90) fluctuated between 16.6 and 35.2 microM. From time of addition and removal experiments, it can be concluded that CPZ inhibited an early stage in the replicative cycle of JV, probably viral entry. TFP also affected JV penetration when present soon after virus adsorption, and also interfered with a later step of viral maturation when added after 7 h of infection. The expression of viral antigens in the cytoplasm of infected cells was highly reduced in the presence of the compounds, as revealed by immunofluorescence staining, whereas no JV proteins were detected at the cell membrane. The distribution pattern of viral proteins was altered in the few cells exhibiting positive fluorescence after treatment with the phenotiazines. The TFP-induced inhibitory effect on JV multiplication was significantly reversed in the presence of 5 microM calmodulin. These data indicate that TFP and CPZ inhibit JV replication in vitro. Our findings suggest that the integrity of the actin microfilaments may be required for optimal arenavirus multiplication.

Antiviral treatment of Argentine hemorrhagic fever

Argentine hemorrhagic fever is a systemic viral disease caused by Junin virus, with a mortality of 15-30% in untreated individuals. Current specific therapy is highly effective in reducing mortality, and consists of the early administration of immune plasma in defined doses of specific neutralizing antibodies per kg of body weight. However, several reasons suggest the need to investigate alternative therapies. Ribavirin, a broad spectrum antiviral agent, is effective in the treatment of other viral hemorrhagic fevers, and the studies done with Junin virus infections to date indicate that this drug may also have a beneficial effect in Argentine hemorrhagic fever.

Molecular approaches for the treatment of hemorrhagic fever virus infections

Viruses causing hemorrhagic fevers in man belong to the following virus groups: togavirus (Chikungunya), flavivirus (dengue, yellow fever, Kyasanur Forest disease, Omsk hemorrhagic fever), arenavirus (Argentinian hemorrhagic fever, Bolivian hemorrhagic fever, Lassa fever), filovirus (Ebola, Marburg), phlebovirus (Rift Valley fever), nairovirus (Crimian-Congo hemorrhagic fever) and hantavirus (hemorrhagic fever with renal syndrome, nephropathic epidemia). Hemorrhagic fever virus infections can be approached by different therapeutic strategies: (i) vaccination; (ii) administration of high-titered antibodies; and (iii) treatment with antiviral drugs. Depending on the molecular target of their interaction, antiviral agents could be classified as follows: IMP dehydrogenase inhibitors (i.e., ribavirin and its derivatives); OMP decarboxylase inhibitors (i.e., pyrazofurin); CTP synthetase inhibitors (i.e., cyclopentylcytosine and cyclopentenylcytosine); SAH hydrolase inhibitors (i.e., neplanocin A); polyanionic substances (i.e., sulfated polymers); interferon and immunomodulators.

Unexpected adverse reactions during a clinical trial in rural west Africa

Ribavirin has been used widely in various clinical trials, without significant adverse effects beyond reversible, mild anemia. Since 1978 intravenous ribavirin has been used to treat Lassa fever in a remote area of Eastern Sierra Leone, West Africa. In March 1991, brief episodes of rigors in patients receiving ribavirin were reported. An immediate investigation found that 27/93 patients (29%) had records in 1990/91 of at least one episode, the strongest association being with survival of Lassa fever (P = 0.0001). The occurrence or number of rigors in an individual patient was unassociated with sex, age, weight, volume of loading dose, cumulative dose, administration of other drugs, use of intravenous lines or heparin traps. In a review of 12 years of ribavirin administration, 74/2117 injections sampled (3.5%) were associated with a record of rigors. Most occurred before 08.00 h (P less than 0.0001), between 0 and 30 min after injection, lasted 2-45 min, and clustered towards the end of the treatment course (P less than 0.0001). There was no association with drug lot or individual vials. Drug was being given as a bolus (less than 1 min). Since slowing the infusion rate, no further episodes have been reported. Epidemiologic techniques are important tools in rapid assessment of unexpected events particularly when conducting trials in remote locations.

Antiviral agents

In recent years, the antiviral armamentarium has expanded considerably. Currently available agents are virustatic, inhibiting specific steps in the process of viral replication. No agent is active against nonreplicating or latent viruses. Acyclovir is useful in the treatment of genital herpes, herpes simplex encephalitis, mucocutaneous herpetic infection, varicella infection in the immunosuppressed host, and herpes zoster infection in the normal and the immunosuppressed host. It can also be used for prevention of herpesvirus infection in immunocompromised patients. Ganciclovir is indicated for the treatment of cytomegalovirus retinitis in patients with acquired immunodeficiency syndrome (AIDS) and is effective in the management of organ-specific cytomegalovirus infection in other immunocompromised patients. Chronic hepatitis C and condyloma acuminatum due to human papillomavirus respond to therapy with interferon alfa-2b. Patients with human immunodeficiency virus infection and CD4 lymphocyte counts of less than 500 cells/mm3 should be treated with zidovudine. Amantadine is useful in a therapeutic and prophylactic role in the management of influenza A virus infection. With the expanded use of and indications for antiviral therapy, clinically significant resistance to these agents has been encountered with increasing frequency.

Inhibitory effect of selected antiviral compounds on arenavirus replication in vitro

Several compounds, belonging to different classes of nucleoside analogues and sulfated polysaccharides, were evaluated for their inhibitory effects on the replication of the arenaviruses Junin and Tacaribe in VERO cells. S-Adenosylhomocysteine (AdoHcy) hydrolase inhibitors [i.e. adenosine dialdehyde, carbocyclic 3-deazaadenosine (C-c3 Ado), neplanocin A, 3-deazaneplanocin A, 9-(2,3-dihydroxypropyl)adenine [(S)-DHPA], (RS)-3-adenin-9-yl-hydroxypropanoic acid isobutyl ester [(RS)-AHPA], the 2',3'-dihydroxycyclopentenyl derivatives of adenine (DHCA) and 3-deazaadenine (DHCDA)] inhibited arenavirus replication within the concentration range of 1-10 micrograms/ml, while not being toxic for cell morphology or cellular DNA synthesis at a concentration of 100-400 micrograms/ml. Based on the ratio of the concentrations required to inhibit cell proliferation and virus replication, only (S)-DHPA, DHCA, C-c3 Ado and adenosine dialdehyde could be considered as truly selective inhibitors. Tubercidin, cyclopentenyl cytosine, pyrazofurin and ribavirin also inhibited viral cytopathogenicity at concentrations that were well below the cytotoxic threshold. Carbodine (cyclopentyl cytosine) also proved to be a potent inhibitor of arenavirus replication, but it was not as selective as cyclopentenyl cytosine. Very potent and selective inhibitors were the sulfated polysaccharides dextran sulfate, lambda-carrageenan, fucoidan, heparin and pentosan polysulfate: they inhibited virus replication at a concentration of 0.1-2.8 micrograms/ml, whereas the compounds were not inhibitory to cell growth even at a concentration of 200 micrograms/ml.

Prophylactic ribavirin treatment of dengue type 1 infection in rhesus monkeys

The prophylactic efficacy of the broad-spectrum antiviral nucleoside analog ribavirin against flavivirus infection in non-human primates was investigated in a blinded, placebo-controlled study of rhesus monkeys infected with dengue virus. Both placebo- and ribavirin-treated monkeys developed viremia, as measured by direct plaque assay on Aedes albopictus C6/36 cells. Peak viremia occurred between days 3 and 9 after infection. No significant differences in time of onset, duration, or level of viremia were observed between placebo- and ribavirin-treated monkeys. Ribavirin induced predictable and reversible anemia and thrombocytosis. Serum ribavirin reached maximum levels of 30 microM by day 4, which approximates the in vitro minimum inhibitory concentration for dengue virus. Ribavirin appeared ineffective as a prophylactic drug for dengue type 1 viral infection, as evaluated by the magnitude of viremia in this monkey model.