Andrew C. Hickey

A neutralizing human monoclonal antibody protects against lethal disease in a new ferret model of acute nipah virus infection.

Nipah virus is a broadly tropic and highly pathogenic zoonotic paramyxovirus in the genus Henipavirus whose natural reservoirs are several species of Pteropus fruit bats. Nipah virus has repeatedly caused outbreaks over the past decade associated with a severe and often fatal disease in humans and animals. Here, a new ferret model of Nipah virus pathogenesis is described where both respiratory and neurological disease are present in infected animals. Severe disease occurs with viral doses as low as 500 TCID50 within 6 to 10 days following infection. The underlying pathology seen in the ferret closely resembles that seen in Nipah virus infected humans, characterized as a widespread multisystemic vasculitis, with virus replicating in highly vascular tissues including lung, spleen and brain, with recoverable virus from a variety of tissues. Using this ferret model a cross-reactive neutralizing human monoclonal antibody, m102.4, targeting the henipavirus G glycoprotein was evaluated in vivo as a potential therapeutic agent. All ferrets that received m102.4 ten hours following a high dose oral-nasal Nipah virus challenge were protected from disease while all controls died. This study is the first successful post-exposure passive antibody therapy for Nipah virus using a human monoclonal antibody.

Antibodies to Nipah or Nipah-like Viruses in Bats, China

To the Editor: Hendra virus (HeV) and Nipah virus (NiV), the only known members of the genus Henipavirus, are 2 emerging paramyxoviruses that are highly pathogenic in a variety of vertebrate animals, including humans (1). Since the initial discovery of the viruses in Australia and Malaysia (2,3), sporadic HeV outbreaks have been reported from 1995 to 2007 in Australia (4), and regular NiV outbreaks have occurred in Bangladesh (5) and India (6). Numerous frugivorous bat species (genus Pteropus), and some insectivous bat species have been found to be reservoir hosts of henipaviruses in Australia and Asian countries (7–9). In this study conducted during 2004–2007, bats were trapped within their natural habitat from 10 provinces in mainland People’s Republic of China. Serum, pharyngeal, and fecal swab samples were collected and stored as described previously (10). An ELISA was developed to detect antibodies to the NiV nucleocapsid (N) and attachment glycoprotein (G) proteins. For confirmation, ELISA-positive samples were tested by using Western blot against a recombinant NiV G fragment (aa 71–193) fused with the maltose-binding protein. Virus neutralization tests were conducted with live NiV and HeV under Biosaftey Level 4 containment in Australia. In addition, a surrogate neutralization test was developed by using recombinant env– HIV-1, pseudotyped with NiV G and F. RNA was extracted by using the QIA amp Viral RNA Mini Kit (QIAGEN, Hilden, Germany). Reverse transcription–PCR (RT-PCR) was performed by using primers against the NiV N gene as described previously (3). In total, 692 bat serum specimens were screened for antibody to NiV N or G protein (or both) by ELISA, and 33 were positive (Appendix Table). These specimens were from 9 of the 23 bat species examined in this study. Of the 33 serum samples reactive in ELISA, 25 with sufficient quantity left were further tested by Western blot, and 17 of 25 serum samples were reactive with MBP-NiV G fusion fragment, but not with the control MBP. None of the samples inhibited entry of NiV F/G-pseudotyped virus or neutralized either HeV or NiV. No NiV-specific RNA was detected by RT-PCR among 479 fecal swab samples and 67 throat swab samples tested; therefore, virus isolation was not attempted. This study systematically investigated NiV presence among bats in China. The detection of henipavirus antibody suggests that several bat species have been exposed to NiV or a closely related virus. The prevalence of antibody was especially prominent among Myotis species from Yunnan Province. Antibody was detected in samples from 3 of 4 Myotis species captured in the same location in 2006 and 2007. A relatively high prevalence of henipavirus antibody was also found among Rousettus leschenaultia samples from Hainan Province in 2007. Notably, Yunnan and Hainan are both located in southern China. Although pteropid bats are not found in China, these data suggest henipaviruses could be introduced into China by other susceptible bat species that overlap their habitat with pteropid bats in neighboring countries. Several possibilities may explain the failure to detect neutralizing antibodies. One might be the unique immune response among those nonpteropid bats, which results in a low level of neutralizing antibodies that are difficult to detect in the current assay systems. Alternatively, and perhaps more likely, >1 Nipah-like viruses could be circulating among the bat populations sampled in this study, producing antibodies that cross-react with, but do not neutralize, the prototype Malaysian NiV virus isolate. This phenomenon has been observed previously by our group for severe acute respiratory syndrome (SARS)–like viruses in horseshoe bats, whose sera cross-reacted with, but did not neutralize, the SARS virus in humans (10). Obtaining serologic evidence of viruses in bat populations is typically more successful as a screening tool than either nucleic acid based assays or virus isolation; this is likely attributable to the often low-level of virus replication, the transient nature of the infection in bats, or both. The inability to amplify NiV sequences may have been attributable to the viral RNA present among these samples being below the threshold of detection in our assay or to the absence of infection in the population at the time of sampling. In addition, the primers used in the PCR may target regions of the NiV N protein that exhibit substantial sequence divergence in a Nipah-like virus. Bat species in the genera Rousettus, Myotis, Miniopterus, and Hipposideros naturally reside in trees, buildings, and caves that can be in close proximity to human residential areas, which increases the potential of transmission of zoonotic pathogens from bats to humans. The increased risk for these zoonotic infections to spread from bats to humans in areas of cohabitation is best illustrated by the repeated spillover events involving NiV in Bangladesh (5). Given the present initial evidence of exposure among bats in mainland China shown here, there is an urgent need to continue and expand surveillance studies for henipaviruses in China and elsewhere on the Asian continent.

Development of an Acute and Highly Pathogenic Nonhuman Primate Model of Nipah Virus Infection

Nipah virus (NiV) is an enigmatic emerging pathogen that causes severe and often fatal neurologic and/or respiratory disease in both animals and humans. Amongst people, case fatality rates range between 40 and 75 percent and there are no vaccines or treatments approved for human use. Guinea pigs, hamsters, cats, ferrets, pigs and most recently squirrel monkeys (New World monkey) have been evaluated as animal models of human NiV infection, and with the exception of the ferret, no model recapitulates all aspects of NiV-mediated disease seen in humans. To identify a more viable nonhuman primate (NHP) model, we examined the pathogenesis of NiV in African green monkeys (AGM). Exposure of eight monkeys to NiV produced a severe systemic infection in all eight animals with seven of the animals succumbing to infection. Viral RNA was detected in the plasma of challenged animals and occurred in two of three subjects as a peak between days 7 and 21, providing the first clear demonstration of plasma-associated viremia in NiV experimentally infected animals and suggested a progressive infection that seeded multiple organs simultaneously from the initial site of virus replication. Unlike the cat, hamster and squirrel monkey models of NiV infection, severe respiratory pathology, neurological disease and generalized vasculitis all manifested in NiV-infected AGMs, providing an accurate reflection of what is observed in NiV-infected humans. Our findings demonstrate the first consistent and highly pathogenic NHP model of NiV infection, providing a new and critical platform in the evaluation and licensure of either passive and active immunization or therapeutic strategies for human use.

A Neutralizing Human Monoclonal Antibody Protects African Green Monkeys from Hendra Virus Challenge

A neutralizing human monoclonal antibody can fully protect nonhuman primates from disease after a lethal Hendra virus challenge. Outfoxing an Emerging Infectious Disease A bat loses its home; a farm animal can’t breathe; a deadly pandemic infection is born. Beautiful and courageous scientists rush frantically to find a vaccine to stem the tide of the infection. Of such heady material, blockbusters like the current thriller Contagion are made. Yet parts of this scenario are rooted in reality. Hendra viruses naturally infect pteropid fruit bats (flying foxes) but cause lethal respiratory disease in horses, which may become infected after exposure to bat urine or birthing fluids. This infection can spread to humans in contact with the horses, leading to respiratory failure and encephalitis. Indeed, since their discovery in Australia in 1994, Hendra viruses have been the star of an increasing number of spillover events, with at least 17 registered in 2011—more than all the previous years combined. Yet, unlike in the movies, Bossart et al. are ahead of the curve: They have developed a human therapeutic monoclonal antibody that can protect African green monkeys from disease. When treated up to 3 days after infection, the monkeys began to recover by day 16, and all treated monkeys survived the infection. In contrast, control monkeys succumbed to the disease by day 8 after infection. Although the authors’ therapeutic human antibody must undergo further dose and safety studies in both their animal model and humans, these studies provide a therapeutic option to treat emerging Hendra virus infections in people. Hendra virus (HeV) is a recently emerged zoonotic paramyxovirus that can cause a severe and often fatal disease in horses and humans. HeV is categorized as a biosafety level 4 agent, which has made the development of animal models and testing of potential therapeutics and vaccines challenging. Infection of African green monkeys (AGMs) with HeV was recently demonstrated, and disease mirrored fatal HeV infection in humans, manifesting as a multisystemic vasculitis with widespread virus replication in vascular tissues and severe pathologic manifestations in the lung, spleen, and brain. Here, we demonstrate that m102.4, a potent HeV-neutralizing human monoclonal antibody (hmAb), can protect AGMs from disease after infection with HeV. Fourteen AGMs were challenged intratracheally with a lethal dose of HeV, and 12 subjects were infused twice with a 100-mg dose of m102.4 beginning at either 10, 24, or 72 hours after infection and again about 48 hours later. The presence of viral RNA, infectious virus, and HeV-specific immune responses demonstrated that all subjects were infected after challenge. All 12 AGMs that received m102.4 survived infection, whereas the untreated control subjects succumbed to disease on day 8 after infection. Animals in the 72-hour treatment group exhibited neurological signs of disease, but all animals started to recover by day 16 after infection. These results represent successful postexposure in vivo efficacy by an investigational drug against HeV and highlight the potential impact a hmAb can have on human disease.

Identification of Hendra Virus G Glycoprotein Residues That Are Critical for Receptor Binding

ABSTRACT Hendra virus (HeV) is an emerging paramyxovirus capable of infecting and causing disease in a variety of mammalian species, including humans. The virus infects its host cells through the coordinated functions of its fusion (F) and attachment (G) glycoproteins, the latter of which is responsible for binding the virus receptors ephrinB2 and ephrinB3. In order to identify the receptor binding site, a panel of G glycoprotein constructs containing mutations was generated using an alanine-scanning mutagenesis strategy. Based on a predicted G structure, charged amino acids residing in regions that could be homologous to those in the measles virus H attachment glycoprotein known to be involved in its protein receptor interaction were targeted. Using a coprecipitation-based assay, seven single-amino-acid substitutions in HeV G were identified as having significantly impaired binding to both the ephrinB2 and ephrinB3 viral receptors: D257A, D260A, G439A, K443A, G449A, K465A, and D468A. The impairment of receptor interaction conferred a concomitant diminution in their abilities to promote membrane fusion when coexpressed with F. The G glycoprotein mutants were also recognized by three or more conformation-dependent monoclonal antibodies of a panel of five, were expressed on the cell surface, and retained their abilities to bind and coprecipitate F. Interestingly, some of these mutant G glycoproteins coprecipitated with F more efficiently than wild-type G. Taken together, these data provide strong biochemical and functional evidence that some of these residues could be part of a conformation-dependent, discontinuous, and overlapping ephrinB2 and -B3 binding domain within the HeV G glycoprotein.

A Novel Model of Lethal Hendra Virus Infection in African Green Monkeys and the Effectiveness of Ribavirin Treatment

ABSTRACT The henipaviruses, Hendra virus (HeV) and Nipah virus (NiV), are emerging zoonotic paramyxoviruses that can cause severe and often lethal neurologic and/or respiratory disease in a wide variety of mammalian hosts, including humans. There are presently no licensed vaccines or treatment options approved for human or veterinarian use. Guinea pigs, hamsters, cats, and ferrets, have been evaluated as animal models of human HeV infection, but studies in nonhuman primates (NHP) have not been reported, and the development and approval of any vaccine or antiviral for human use will likely require efficacy studies in an NHP model. Here, we examined the pathogenesis of HeV in the African green monkey (AGM) following intratracheal inoculation. Exposure of AGMs to HeV produced a uniformly lethal infection, and the observed clinical signs and pathology were highly consistent with HeV-mediated disease seen in humans. Ribavirin has been used to treat patients infected with either HeV or NiV; however, its utility in improving outcome remains, at best, uncertain. We examined the antiviral effect of ribavirin in a cohort of nine AGMs before or after exposure to HeV. Ribavirin treatment delayed disease onset by 1 to 2 days, with no significant benefit for disease progression and outcome. Together our findings introduce a new disease model of acute HeV infection suitable for testing antiviral strategies and also demonstrate that, while ribavirin may have some antiviral activity against the henipaviruses, its use as an effective standalone therapy for HeV infection is questionable.

A Hendra Virus G Glycoprotein Subunit Vaccine Protects African Green Monkeys from Nipah Virus Challenge

The Hendra virus attachment G glycoprotein fully protects nonhuman primates from lethal Nipah virus challenge. The Ecology of Disease As people expanded their settlements further and further into the flying fox territory, no one could have suspected that the furry fruit-loving bats carried deadly viruses that can cause human epidemics with mortality rates approaching 100%. The recently discovered (and closely related) Nipah and Hendra viruses can infect humans and a wide range of other species, including domestic animals such as horses, pigs, and dogs; and Nipah is known for person-to-person transmission. Since their discovery in the 1990s, outbreaks have been reported nearly every year, particularly in Bangladesh, India, and Australia, and no effective treatment or prevention method currently exists. Now, Bossart et al. show that a vaccine targeting both viruses shows full protection against Nipah virus in a nonhuman primate model. Nipah virus infection in African green monkeys results in symptoms similar to human disease, with severe involvement of the lungs and brain, and multiple other organ systems, leading to a universally lethal outcome. Here, a recombinant vaccine made from the attachment envelope glycoprotein of Hendra virus is used to prevent infection in the monkeys. The animals are vaccinated with this glycoprotein at a range of doses, but the authors find that even the lowest dose they use provides full protection from Nipah virus challenge. In contrast, the control monkey quickly develops diffuse organ involvement and lethal disease, consistent with historic data. These results demonstrate the feasibility of using immunization to prevent infection with Nipah virus and advance the vaccine one step closer to clinical trials in human subjects. In the 1990s, Hendra virus and Nipah virus (NiV), two closely related and previously unrecognized paramyxoviruses that cause severe disease and death in humans and a variety of animals, were discovered in Australia and Malaysia, respectively. Outbreaks of disease have occurred nearly every year since NiV was first discovered, with case fatality ranging from 10 to 100%. In the African green monkey (AGM), NiV causes a severe lethal respiratory and/or neurological disease that essentially mirrors fatal human disease. Thus, the AGM represents a reliable disease model for vaccine and therapeutic efficacy testing. We show that vaccination of AGMs with a recombinant subunit vaccine based on the henipavirus attachment G glycoprotein affords complete protection against subsequent NiV infection with no evidence of clinical disease, virus replication, or pathology observed in any challenged subjects. Success of the recombinant subunit vaccine in nonhuman primates provides crucial data in supporting its further preclinical development for potential human use.

Residues in the Stalk Domain of the Hendra Virus G Glycoprotein Modulate Conformational Changes Associated with Receptor Binding

ABSTRACT Hendra virus (HeV) is a member of the broadly tropic and highly pathogenic paramyxovirus genus Henipavirus. HeV is enveloped and infects cells by using membrane-anchored attachment (G) and fusion (F) glycoproteins. G possesses an N-terminal cytoplasmic tail, an external membrane-proximal stalk domain, and a C-terminal globular head that binds the recently identified receptors ephrinB2 and ephrinB3. Receptor binding is presumed to induce conformational changes in G that subsequently trigger F-mediated fusion. The stalk domains of other attachment glycoproteins appear important for oligomerization and F interaction and specificity. However, this region of G has not been functionally characterized. Here we performed a mutagenesis analysis of the HeV G stalk, targeting a series of isoleucine residues within a hydrophobic α-helical domain that is well conserved across several attachment glycoproteins. Nine of 12 individual HeV G alanine substitution mutants possessed a complete defect in fusion-promotion activity yet were cell surface expressed and recognized by a panel of conformation-dependent monoclonal antibodies (MAbs) and maintained their oligomeric structure. Interestingly, these G mutations also resulted in the appearance of an additional electrophoretic species corresponding to a slightly altered glycosylated form. Analysis revealed that these G mutants appeared to adopt a receptor-bound conformation in the absence of receptor, as measured with a panel of MAbs that preferentially recognize G in a receptor-bound state. Further, this phenotype also correlated with an inability to associate with F and in triggering fusion even after receptor engagement. Together, these data suggest the stalk domain of G plays an important role in the conformational stability and receptor binding-triggered changes leading to productive fusion, such as the dissociation of G and F.

Human Metapneumovirus Reinfection among Children in Thailand Determined by ELISA Using Purified Soluble Fusion Protein

BACKGROUND Human metapneumovirus (hMPV) is a newly discovered paramyxovirus that causes acute respiratory illness. Despite apparent near-universal exposure during early childhood, immunity is transient. METHODS An indirect screening enzyme-linked immunosorbent assay using a recombinant soluble fusion (F) glycoprotein derived from hMPV was used to test for anti-F IgG in 1,380 pairs of acute- and convalescent-stage serum samples collected from children in Kamphaeng Phet, Thailand. RESULTS Of the 1,380 serum sample pairs tested, 1,376 (99.7%) showed evidence of prior infection with hMPV. Sixty-six paired specimens demonstrated a >or=4-fold rise in titer, for an overall reinfection rate of 4.9%. Two children demonstrated evidence of an initial infection. Forty-eight of the 68 new infections or reinfections occurred in 2000, accounting for 13.2% of all nonflaviviral febrile illnesses in the study population in that year. Of 68 positive cases, 85.3% complained of cough and 66.2% complained of rhinorrhea, compared with 61.4% and 49.0% of negative cases, respectively (P < .01). All positive samples were also tested for an increase in titer of antibodies to respiratory syncytial virus F, and 27% exhibited a >or=4-fold rise. CONCLUSION These results demonstrate that hMPV reinfections cause illness at a rate equal to that seen for initial infections. hMPV may have a more significant impact in older children than previously realized and may be the cause of significant outbreaks in this population.

Serotype-Specific Host Responses in Rhesus Macaques after Primary Dengue Challenge

Dengue virus (DENV) is considered to be the most important arthropod-borne viral disease and causes more than 100 million human infections annually. To further characterize primary DENV infection in vivo, rhesus macaques were infected with DENV-1, DENV-2, DENV-3, or DENV-4 and clinical parameters, as well as specificity and longevity of serologic responses, were assessed. Overt clinical symptoms were not present after infection. However, abnormalities in blood biochemical parameters consistent with heart, kidney, and liver damage were observed, and changes in plasma fibrinogen, D-dimers, and protein C indicated systemic activation of the blood coagulation pathway. Significant homotypic and heterotypic serum immunoglobulins were present in all animals, and IgG persisted for at least 390 days. Serum neutralizing antibody responses were highly serotype specific by day 120. However, some heterotypic neutralizing activity was noted in infected animals. Identification of serotype-specific host responses may help elucidate mechanisms that mediate severe DENV disease after reinfection.