Immunization strategies against henipaviruses

A single dose investigational subunit vaccine for human use against Nipah virus and Hendra virus

Nipah and Hendra viruses are highly pathogenic bat-borne paramyxoviruses recently included in the WHO Blueprint priority diseases list. A fully registered horse anti-Hendra virus subunit vaccine has been in use in Australia since 2012. Based on the same immunogen, the Hendra virus attachment glycoprotein ectodomain, a subunit vaccine formulation for use in people is now in a Phase I clinical trial. We report that a single dose vaccination regimen of this human vaccine formulation protects against otherwise lethal challenges of either Hendra or Nipah virus in a nonhuman primate model. The protection against the Nipah Bangladesh strain begins as soon as 7 days post immunization with low dose of 0.1 mg protein subunit. Our data suggest this human vaccine could be utilized as efficient emergency vaccine to disrupt potential spreading of Nipah disease in an outbreak setting.

A Cross-Reactive Humanized Monoclonal Antibody Targeting Fusion Glycoprotein Function Protects Ferrets Against Lethal Nipah Virus and Hendra Virus Infection

BACKGROUND

Nipah virus (NiV) and Hendra virus (HeV) are zoonotic paramyxoviruses that cause severe disease in both animals and humans. There are no approved vaccines or treatments for use in humans; however, therapeutic treatment of both NiV and HeV infection in ferrets and non-human primates with a cross-reactive, neutralizing human monoclonal antibody (mAb), m102.4, targeting the G glycoprotein has been demonstrated. In a previous study, we isolated, characterized, and humanized a cross-reactive, neutralizing anti-F mAb (h5B3.1). The mAb h5B3.1 blocks the required F conformational change needed to facilitate membrane fusion and virus infection, and the epitope recognized by h5B3.1 has been structurally defined; however, the efficacy of h5B3.1 in vivo is unknown.

METHODS

The post-infection antiviral activity of h5B3.1 was evaluated in vivo by administration in ferrets after NiV and HeV virus challenge.

RESULTS

All subjects that received h5B3.1 from 1 to several days after infection with a high-dose, oral-nasal virus challenge were protected from disease, whereas all controls died.

CONCLUSIONS

This is the first successful post-exposure antibody therapy for NiV and HeV using a humanized cross-reactive mAb targeting the F glycoprotein, and the findings suggest that a combination therapy targeting both F and G should be evaluated as a therapy for NiV/HeV infection.

Post-exposure prophylactic vaccine candidates for the treatment of human Risk Group 4 pathogen infections

Introduction: The development of therapeutics and vaccines to combat Risk Group 4 pathogens, which are associated with high case-fatality rates, is a high priority. Postexposure prophylactic vaccines have the potential to bridge classical therapeutic and vaccine applications, but little progress has been reported to date.Areas covered: This review provides an overview of postexposure prophylactic vaccine candidates against Risk Group 4 pathogens.Expert opinion: A few candidate postexposure prophylactic vaccines protect experimental animals infected with a few Risk Group 4 pathogens, such as filoviruses or hantaviruses, but the efficacy of candidate vaccines has not been similarly reported for most other high-consequence pathogens. A major drawback for the further development of existing candidates is the lack of understanding of their mechanisms of action, knowledge of which could help to identify focused paths forward in vaccine development and licensure. These drawbacks to further development ultimately slow progress toward postexposure prophylactic vaccine licensure.

Nipah virus: epidemiology, pathology, immunobiology and advances in diagnosis, vaccine designing and control strategies - a comprehensive review

Nipah (Nee-pa) viral disease is a zoonotic infection caused by Nipah virus (NiV), a paramyxovirus belonging to the genus Henipavirus of the family Paramyxoviridae. It is a biosafety level-4 pathogen, which is transmitted by specific types of fruit bats, mainly Pteropus spp. which are natural reservoir host. The disease was reported for the first time from the Kampung Sungai Nipah village of Malaysia in 1998. Human-to-human transmission also occurs. Outbreaks have been reported also from other countries in South and Southeast Asia. Phylogenetic analysis affirmed the circulation of two major clades of NiV as based on currently available complete N and G gene sequences. NiV isolates from Malaysia and Cambodia clustered together in NiV-MY clade, whereas isolates from Bangladesh and India clusterered within NiV-BD clade. NiV isolates from Thailand harboured mixed population of sequences. In humans, the virus is responsible for causing rapidly progressing severe illness which might be characterized by severe respiratory illness and/or deadly encephalitis. In pigs below six months of age, respiratory illness along with nervous symptoms may develop. Different types of enzyme-linked immunosorbent assays along with molecular methods based on polymerase chain reaction have been developed for diagnostic purposes. Due to the expensive nature of the antibody drugs, identification of broad-spectrum antivirals is essential along with focusing on small interfering RNAs (siRNAs). High pathogenicity of NiV in humans, and lack of vaccines or therapeutics to counter this disease have attracted attention of researchers worldwide for developing effective NiV vaccine and treatment regimens.

An antibody against the F glycoprotein inhibits Nipah and Hendra virus infections

Nipah virus (NiV) and Hendra virus (HeV) are zoonotic henipaviruses (HNVs) responsible for outbreaks of encephalitis and respiratory illness with fatality rates of 50–100%. No vaccines or licensed therapeutics currently exist to protect humans against NiV or HeV. HNVs enter host cells by fusing the viral and cellular membranes via the concerted action of the attachment (G) and fusion (F) glycoproteins, the main targets of the humoral immune response. Here, we describe the isolation and humanization of a potent monoclonal antibody cross-neutralizing NiV and HeV. Cryo-electron microscopy, triggering and fusion studies show the antibody binds to a prefusion-specific quaternary epitope, conserved in NiV F and HeV F glycoproteins, and prevents membrane fusion and viral entry. This work supports the importance of the HNV prefusion F conformation for eliciting a robust immune response and paves the way for using this antibody for prophylaxis and post-exposure therapy with NiV- and HeV-infected individuals.

An antibody that recognizes the F glycoproteins from Nipah and Hendra viruses can neutralize both viruses and recognizes a quaternary epitope in the prefusion F trimer, preventing conformational changes required for fusion.

Nipah virus: epidemiology, pathology, immunobiology and advances in diagnosis, vaccine designing and control strategies - a comprehensive review

Nipah (Nee-pa) viral disease is a zoonotic infection caused by Nipah virus (NiV), a paramyxovirus belonging to the genus Henipavirus of the family Paramyxoviridae. It is a biosafety level-4 pathogen, which is transmitted by specific types of fruit bats, mainly Pteropus spp. which are natural reservoir host. The disease was reported for the first time from the Kampung Sungai Nipah village of Malaysia in 1998. Human-to-human transmission also occurs. Outbreaks have been reported also from other countries in South and Southeast Asia. Phylogenetic analysis affirmed the circulation of two major clades of NiV as based on currently available complete N and G gene sequences. NiV isolates from Malaysia and Cambodia clustered together in NiV-MY clade, whereas isolates from Bangladesh and India clusterered within NiV-BD clade. NiV isolates from Thailand harboured mixed population of sequences. In humans, the virus is responsible for causing rapidly progressing severe illness which might be characterized by severe respiratory illness and/or deadly encephalitis. In pigs below six months of age, respiratory illness along with nervous symptoms may develop. Different types of enzyme-linked immunosorbent assays along with molecular methods based on polymerase chain reaction have been developed for diagnostic purposes. Due to the expensive nature of the antibody drugs, identification of broad-spectrum antivirals is essential along with focusing on small interfering RNAs (siRNAs). High pathogenicity of NiV in humans, and lack of vaccines or therapeutics to counter this disease have attracted attention of researchers worldwide for developing effective NiV vaccine and treatment regimens.

Therapeutic potential of targeting the Eph/ephrin signaling complex

The Eph-ephrin signaling pathway mediates developmental processes and the proper functioning of the adult human body. This distinctive bidirectional signaling pathway includes a canonical downstream signal cascade inside the Eph-bearing cells, as well as a reverse signaling in the ephrin-bearing cells. The signaling is terminated by ADAM metalloproteinase cleavage, internalization, and degradation of the Eph/ephrin complexes. Consequently, the Eph-ephrin-ADAM signaling cascade has emerged as a key target with immense therapeutic potential particularly in the context of cancer. An interesting twist was brought forth by the emergence of ephrins as the entry receptors for the pathological Henipaviruses, which has spurred new studies to target the viral entry. The availability of high-resolution structures of the multi-modular Eph receptors in complexes with ephrins and other binding partners, such as peptides, small molecule inhibitors and antibodies, offers a wealth of information for the structure-guided development of therapeutic intervention. Furthermore, genomic data mining of Eph mutants involved in cancer provides information for targeted drug development. In this review we summarize the distinct avenues for targeting the Eph-ephrin signaling pathway, including its termination by ADAM proteinases. We highlight the latest developments in Eph-related pharmacology in the context of Eph-ephrin-ADAM-based antibodies and small molecules. Finally, the future prospects of genomics- and proteomics-based medicine are discussed.

Rescue and characterization of recombinant cedar virus, a non-pathogenic Henipavirus species

BACKGROUND

Hendra virus and Nipah virus are zoonotic viruses that have caused severe to fatal disease in livestock and human populations. The isolation of Cedar virus, a non-pathogenic virus species in the genus Henipavirus, closely-related to the highly pathogenic Hendra virus and Nipah virus offers an opportunity to investigate differences in pathogenesis and receptor tropism among these viruses.

METHODS

We constructed full-length cDNA clones of Cedar virus from synthetic oligonucleotides and rescued two replication-competent, recombinant Cedar virus variants: a recombinant wild-type Cedar virus and a recombinant Cedar virus that expresses a green fluorescent protein from an open reading frame inserted between the phosphoprotein and matrix genes. Replication kinetics of both viruses and stimulation of the interferon pathway were characterized in vitro. Cellular tropism for ephrin-B type ligands was qualitatively investigated by microscopy and quantitatively by a split-luciferase fusion assay.

RESULTS

Successful rescue of recombinant Cedar virus expressing a green fluorescent protein did not significantly affect virus replication compared to the recombinant wild-type Cedar virus. We demonstrated that recombinant Cedar virus stimulated the interferon pathway and utilized the established Hendra virus and Nipah virus receptor, ephrin-B2, but not ephrin-B3 to mediate virus entry. We further characterized virus-mediated membrane fusion kinetics of Cedar virus with the known henipavirus receptors ephrin-B2 and ephrin-B3.

CONCLUSIONS

The recombinant Cedar virus platform may be utilized to characterize the determinants of pathogenesis across the henipaviruses, investigate their receptor tropisms, and identify novel pan-henipavirus antivirals. Moreover, these experiments can be conducted safely under BSL-2 conditions.

Hendra virus and Nipah virus animal vaccines

Hendra virus (HeV) and Nipah virus (NiV) are zoonotic viruses that emerged in the mid to late 1990s causing disease outbreaks in livestock and people. HeV appeared in Queensland, Australia in 1994 causing a severe respiratory disease in horses along with a human case fatality. NiV emerged a few years later in Malaysia and Singapore in 1998-1999 causing a large outbreak of encephalitis with high mortality in people and also respiratory disease in pigs which served as amplifying hosts. The key pathological elements of HeV and NiV infection in several species of mammals, and also in people, are a severe systemic and often fatal neurologic and/or respiratory disease. In people, both HeV and NiV are also capable of causing relapsed encephalitis following recovery from an acute infection. The known reservoir hosts of HeV and NiV are several species of pteropid fruit bats. Spillovers of HeV into horses continue to occur in Australia and NiV has caused outbreaks in people in Bangladesh and India nearly annually since 2001, making HeV and NiV important transboundary biological threats. NiV in particular possesses several features that underscore its potential as a pandemic threat, including its ability to infect humans directly from natural reservoirs or indirectly from other susceptible animals, along with a capacity of limited human-to-human transmission. Several HeV and NiV animal challenge models have been developed which have facilitated an understanding of pathogenesis and allowed for the successful development of both active and passive immunization countermeasures.

Henipaviruses

The first henipaviruses, Hendra virus (HeV), and Nipah virus (NiV) were pathogenic zoonoses that emerged in the mid to late 1990s causing serious disease outbreaks in livestock and humans. HeV was recognized in Australia 1994 in horses exhibiting respiratory disease along with a human case fatality, and then NiV was identified during a large outbreak of human cases of encephalitis with high mortality in Malaysia and Singapore in 1998–1999 along with respiratory disease in pigs which served as amplifying hosts. The recently identified third henipavirus isolate, Cedar virus (CedPV), is not pathogenic in animals susceptible to HeV and NiV disease. Molecular detection of additional henipavirus species has been reported but no additional isolates of virus have been reported. Central pathological features of both HeV and NiV infection in humans and several susceptible animal species is a severe systemic and often fatal neurologic and/or respiratory disease. In people, both viruses can also manifest relapsed encephalitis following recovery from an acute infection, particularly NiV. The recognized natural reservoir hosts of HeV, NiV, and CedPV are pteropid bats, which do not show clinical illness when infected. With spillovers of HeV continuing to occur in Australia and NiV in Bangladesh and India, these henipaviruses continue to be important transboundary biological threats. NiV in particular possesses several features that highlight a pandemic potential, such as its ability to infect humans directly from natural reservoirs or indirectly from other susceptible animals along with a capacity of limited human-to-human transmission. Several henipavirus animal challenge models have been developed which has aided in understanding HeV and NiV pathogenesis as well as how they invade the central nervous system, and successful active and passive immunization strategies against HeV and NiV have been reported which target the viral envelope glycoproteins.

Henipavirus Encephalitis: Recent Developments and Advances

The genus Henipavirus within the family Paramyxoviridae includes the Hendra virus (HeV) and Nipah virus (NiV) which were discovered in the 1990s in Australia and Malaysia, respectively, after emerging to cause severe and often fatal outbreaks in humans and animals. While HeV is confined to Australia, more recent NiV outbreaks have been reported in Bangladesh, India and the Philippines. The clinical manifestations of both henipaviruses in humans appear similar, with a predominance of an acute encephalitic syndrome. Likewise, the pathological features are similar and characterized by disseminated, multi-organ vasculopathy comprising endothelial infection/ulceration, vasculitis, vasculitis-induced thrombosis/occlusion, parenchymal ischemia/microinfarction, and parenchymal cell infection in the central nervous system (CNS), lung, kidney and other major organs. This unique dual pathogenetic mechanism of vasculitis-induced microinfarction and neuronal infection causes severe tissue damage in the CNS. Both viruses can also cause relapsing encephalitis months and years after the acute infection. Many animal models studied to date have largely confirmed the pathology of henipavirus infection, and provided the means to test new therapeutic agents and vaccines. As the bat is the natural host of henipaviruses and has worldwide distribution, spillover events into human populations are expected to occur in the future.

Detailed morphological characterisation of Hendra virus infection of different cell types using super-resolution and conventional imaging

BACKGROUND

Hendra virus (HeV) is a pleomorphic virus belonging to the Paramyxovirus family. Our long-term aim is to understand the process of assembly of HeV virions. As a first step, we sought to determine the most appropriate cell culture system with which to study this process, and then to use this model to define the morphology of the virus and identify the site of assembly by imaging key virus encoded proteins in infected cells.

METHODS

A range of primary cells and immortalised cell lines were infected with HeV, fixed at various time points post-infection, labelled for HeV proteins and imaged by confocal, super-resolution and transmission electron microscopy.

RESULTS

Significant differences were noted in viral protein distribution depending on the infected cell type. At 8 hpi HeV G protein was detected in the endoplasmic reticulum and M protein was seen predominantly in the nucleus in all cells tested. At 18 hpi, HeV-infected Vero cells showed M and G proteins throughout the cell and in transmission electron microscope (TEM) sections, in pleomorphic virus-like structures. In HeV infected MDBK, A549 and HeLa cells, HeV M protein was seen predominantly in the nucleus with G protein at the membrane. In HeV-infected primary bovine and porcine aortic endothelial cells and two bat-derived cell lines, HeV M protein was not seen at such high levels in the nucleus at any time point tested (8,12, 18, 24, 48 hpi) but was observed predominantly at the cell surface in a punctate pattern co-localised with G protein. These HeV M and G positive structures were confirmed as round HeV virions by TEM and super-resolution (SR) microscopy. SR imaging demonstrated for the first time sub-virion imaging of paramyxovirus proteins and the respective localisation of HeV G, M and N proteins within virions.

CONCLUSION

These findings provide novel insights into the structure of HeV and show that for HeV imaging studies the choice of tissue culture cells may affect the experimental results. The results also indicate that HeV should be considered a predominantly round virus with a mean diameter of approximately 280 nm by TEM and 310 nm by SR imaging.

Hendra virus vaccine, a one health approach to protecting horse, human, and environmental health

In recent years, the emergence of several highly pathogenic zoonotic diseases in humans has led to a renewed emphasis on the interconnectedness of human, animal, and environmental health, otherwise known as One Health. For example, Hendra virus (HeV), a zoonotic paramyxovirus, was discovered in 1994, and since then, infections have occurred in 7 humans, each of whom had a strong epidemiologic link to similarly affected horses. As a consequence of these outbreaks, eradication of bat populations was discussed, despite their crucial environmental roles in pollination and reduction of the insect population. We describe the development and evaluation of a vaccine for horses with the potential for breaking the chain of HeV transmission from bats to horses to humans, thereby protecting horse, human, and environmental health. The HeV vaccine for horses is a key example of a One Health approach to the control of human disease.

A treatment for and vaccine against the deadly Hendra and Nipah viruses

Hendra virus and Nipah virus are bat-borne paramyxoviruses that are the prototypic members of the genus Henipavirus. The henipaviruses emerged in the 1990s, spilling over from their natural bat hosts and causing serious disease outbreaks in humans and livestock. Hendra virus emerged in Australia and since 1994 there have been 7 human infections with 4 case fatalities. Nipah virus first appeared in Malaysia and subsequent outbreaks have occurred in Bangladesh and India. In total, there have been an estimated 582 human cases of Nipah virus and of these, 54% were fatal. Their broad species tropism and ability to cause fatal respiratory and/or neurologic disease in humans and animals make them important transboundary biological threats. Recent experimental findings in animals have demonstrated that a human monoclonal antibody targeting the viral G glycoprotein is an effective post-exposure treatment against Hendra and Nipah virus infection. In addition, a subunit vaccine based on the G glycoprotein of Hendra virus affords protection against Hendra and Nipah virus challenge. The vaccine has been developed for use in horses in Australia and is the first vaccine against a Biosafety Level-4 (BSL-4) agent to be licensed and commercially deployed. Together, these advances offer viable approaches to address Hendra and Nipah virus infection of livestock and people.

A Hendra virus G glycoprotein subunit vaccine protects African green monkeys from Nipah virus challenge

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.