Yan-Ru Feng

Receptor Binding, Fusion Inhibition, and Induction of Cross-Reactive Neutralizing Antibodies by a Soluble G Glycoprotein of Hendra Virus

ABSTRACT Hendra virus (HeV) and Nipah virus (NiV) are closely related emerging viruses comprising the Henipavirus genus of the Paramyxovirinae, which are distinguished by their ability to cause fatal disease in both animal and human hosts. These viruses infect cells by a pH-independent membrane fusion event mediated by their attachment (G) and fusion (F) glycoproteins. Previously, we reported on HeV- and NiV-mediated fusion activities and detailed their host-cell tropism characteristics. These studies also suggested that a common cell surface receptor, which could be destroyed by protease, was utilized by both viruses. To further characterize the G glycoprotein and its unknown receptor, soluble forms of HeV G (sG) were constructed by replacing its cytoplasmic tail and transmembrane domains with an immunoglobulin κ leader sequence coupled to either an S-peptide tag (sGS-tag) or myc-epitope tag (sGmyc-tag) to facilitate purification and detection. Expression of sG was verified in cell lysates and culture supernatants by specific affinity precipitation. Analysis of sG by size exclusion chromatography and sucrose gradient centrifugation demonstrated tetrameric, dimeric, and monomeric species, with the majority of the sG released as a disulfide-linked dimer. Immunofluorescence staining revealed that sG specifically bound to HeV and NiV infection-permissive cells but not to a nonpermissive HeLa cell line clone, suggesting that it binds to virus receptor on host cells. Preincubation of host cells with sG resulted in dose-dependent inhibition of both HeV and NiV cell fusion as well as infection by live virus. Taken together, these data indicate that sG retains important native structural features, and we further demonstrate that administration of sG to rabbits can elicit a potent cross-reactive neutralizing antibody response against infectious HeV and NiV. This HeV sG glycoprotein will be exceedingly useful for structural studies, receptor identification strategies, and vaccine development goals for these important emerging viral agents.

Potent Neutralization of Hendra and Nipah Viruses by Human Monoclonal Antibodies

ABSTRACT Hendra virus (HeV) and Nipah virus (NiV) are closely related emerging viruses comprising the Henipavirus genus of the Paramyxovirinae. Each has a broad species tropism and can cause disease with high mortality in both animal and human hosts. These viruses infect cells by a pH-independent membrane fusion event mediated by their attachment (G) and fusion (F) envelope glycoproteins (Envs). Seven Fabs, m101 to -7, were selected for their significant binding to a soluble form of Hendra G (sG) which was used as the antigen for panning of a large naïve human antibody library. The selected Fabs inhibited, to various degrees, cell fusion mediated by the HeV or NiV Envs and virus infection. The conversion of the most potent neutralizer of infectious HeV, Fab m101, to immunoglobulin G1 (IgG1) significantly increased its cell fusion inhibitory activity: the 50% inhibitory concentration was decreased more than 10-fold to approximately 1 μg/ml. The IgG1 m101 was also exceptionally potent in neutralizing infectious HeV; complete (100%) neutralization was achieved with 12.5 μg/ml, and 98% neutralization required only 1.6 μg/ml. The inhibition of fusion and infection correlated with binding of the Fabs to full-length G as measured by immunoprecipitation and less with binding to sG as measured by enzyme-linked immunosorbent assay and Biacore. m101 and m102 competed with the ephrin-B2, which we recently identified as a functional receptor for both HeV and NiV, indicating a possible mechanism of neutralization by these antibodies. The m101, m102, and m103 antibodies competed with each other, suggesting that they bind to overlapping epitopes which are distinct from the epitopes of m106 and m107. In an initial attempt to localize the epitopes of m101 and m102, we measured their binding to a panel of 11 G alanine-scanning mutants and identified two mutants, P185A and Q191 K192A, which significantly decreased binding to m101 and one, G183, which decreased binding of m102 to G. These results suggest that m101 to -7 are specific for HeV or NiV or both and exhibit various neutralizing activities; they are the first human monoclonal antibodies identified against these viruses and could be used for treatment, prophylaxis, and diagnosis and as research reagents and could aid in the development of vaccines.

A recombinant Hendra virus G glycoprotein-based subunit vaccine protects ferrets from lethal Hendra virus challenge

The henipaviruses, Hendra virus (HeV) and Nipah virus (NiV), are two deadly zoonotic viruses for which no vaccines or therapeutics have yet been approved for human or livestock use. In 14 outbreaks since 1994 HeV has been responsible for multiple fatalities in horses and humans, with all known human infections resulting from close contact with infected horses. A vaccine that prevents virus shedding in infected horses could interrupt the chain of transmission to humans and therefore prevent HeV disease in both. Here we characterise HeV infection in a ferret model and show that it closely mirrors the disease seen in humans and horses with induction of systemic vasculitis, including involvement of the pulmonary and central nervous systems. This model of HeV infection in the ferret was used to assess the immunogenicity and protective efficacy of a subunit vaccine based on a recombinant soluble version of the HeV attachment glycoprotein G (HeVsG), adjuvanted with CpG. We report that ferrets vaccinated with a 100 μg, 20 μg or 4 μg dose of HeVsG remained free of clinical signs of HeV infection following a challenge with 5000 TCID₅₀ of HeV. In addition, and of considerable importance, no evidence of virus or viral genome was detected in any tissues or body fluids in any ferret in the 100 and 20 μg groups, while genome was detected in the nasal washes only of one animal in the 4 μg group. Together, our findings indicate that 100 μg or 20 μg doses of HeVsG vaccine can completely prevent a productive HeV infection in the ferret, suggesting that vaccination to prevent the infection and shedding of HeV is possible.

Extensively cross-reactive anti-HIV-1 neutralizing antibodies induced by gp140 immunization

An immunization regimen was evaluated in rabbits consisting of the soluble, oligomeric form of envelope glycoprotein of HIV-1, strain R2 (gp140R2), or the surface component of the same envelope (Env), gp120R2, in the adjuvant AS02A. The gp140R2 was selected based on its unusual CD4-independent phenotype and the exceptionally broad neutralizing response in the infected donor. The gp140R2 immunogen induced antibodies that achieved 50% neutralization of 48/48, and 80% neutralization of 43/46 primary strains of diverse HIV-1 subtypes tested. The strains tested included members of standard panels of subtype B and C strains, and other diverse strains known to be neutralization resistant. The gp120R2 induced antibodies that neutralized 9/48 of the same strains. Neutralization was IgG-mediated and HIV-1-specific. These results demonstrate that induction of truly broad spectrum neutralizing antibodies is an achievable goal in HIV-1 vaccine development.

A recombinant subunit vaccine formulation protects against lethal Nipah virus challenge in cats.

Abstract Nipah virus (NiV) and Hendra virus (HeV) are closely related deadly zoonotic paramyxoviruses that have emerged and re-emerged over the last 10 years. In this study, a subunit vaccine formulation containing only recombinant, soluble, attachment glycoprotein from HeV (sGHeV) and CpG adjuvant was evaluated as a potential NiV vaccine in the cat model. Different amounts of sGHeV were employed and sG-induced immunity was examined. Vaccinated animals demonstrated varying levels of NiV-specific Ig systemically and importantly, all vaccinated cats possessed antigen-specific IgA on the mucosa. Upon oronasal challenge with NiV (50,000TCID50), all vaccinated animals were protected from disease although virus was detected on day 21 post-challenge in one animal. The ability to elicit protective systemic and mucosal immunity in this animal model provides significant progress towards the development of a human subunit vaccine against henipaviruses.

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.

Site occupancy and glycan compositional analysis of two soluble recombinant forms of the attachment glycoprotein of Hendra virus

Hendra virus (HeV) continues to cause morbidity and mortality in both humans and horses with a number of sporadic outbreaks. HeV has two structural membrane glycoproteins that mediate the infection of host cells: the attachment (G) and the fusion (F) glycoproteins that are essential for receptor binding and virion-host cell membrane fusion, respectively. N-linked glycosylation of viral envelope proteins are critical post-translation modifications that have been implicated in roles of structural integrity, virus replication and evasion of the host immune response. Deciphering the glycan composition and structure on these glycoproteins may assist in the development of glycan-targeted therapeutic intervention strategies. We examined the site occupancy and glycan composition of recombinant soluble G (sG) glycoproteins expressed in two different mammalian cell systems, transient human embryonic kidney 293 (HEK293) cells and vaccinia virus (VV)-HeLa cells, using a suite of biochemical and biophysical tools: electrophoresis, lectin binding and tandem mass spectrometry. The N-linked glycans of both VV and HEK293-derived sG glycoproteins carried predominantly mono- and disialylated complex-type N-glycans and a smaller population of high mannose-type glycans. All seven consensus sequences for N-linked glycosylation were definitively found to be occupied in the VV-derived protein, whereas only four sites were found and characterized in the HEK293-derived protein. We also report, for the first time, the existence of O-linked glycosylation sites in both proteins. The striking characteristic of both proteins was glycan heterogeneity in both N- and O-linked sites. The structural features of G protein glycosylation were also determined by X-ray crystallography and interactions with the ephrin-B2 receptor are discussed.

Vaccination of ferrets with a recombinant G glycoprotein subunit vaccine provides protection against Nipah virus disease for over 12 months.

BackgroundNipah virus (NiV) is a zoonotic virus belonging to the henipavirus genus in the family Paramyxoviridae. Since NiV was first identified in 1999, outbreaks have continued to occur in humans in Bangladesh and India on an almost annual basis with case fatality rates reported between 40% and 100%.MethodsFerrets were vaccinated with 4, 20 or 100 μg HeVsG formulated with the human use approved adjuvant, CpG, in a prime-boost regime. One half of the ferrets were exposed to NiV at 20 days post boost vaccination and the other at 434 days post vaccination. The presence of virus or viral genome was assessed in ferret fluids and tissues using real-time PCR, virus isolation, histopathology, and immunohistochemistry; serology was also carried out. Non-immunised ferrets were also exposed to virus to confirm the pathogenicity of the inoculum.ResultsFerrets exposed to Nipah virus 20 days post vaccination remained clinically healthy. Virus or viral genome was not detected in any tissues or fluids of the vaccinated ferrets; lesions and antigen were not identified on immunohistological examination of tissues; and there was no increase in antibody titre during the observation period, consistent with failure of virus replication. Of the ferrets challenged 434 days post vaccination, all five remained well throughout the study period; viral genome – but not virus - was recovered from nasal secretions of one ferret given 20 μg HeVsG and bronchial lymph nodes of the other. There was no increase in antibody titre during the observation period, consistent with lack of stimulation of a humoral memory response.ConclusionsWe have previously shown that ferrets vaccinated with 4, 20 or 100 μg HeVsG formulated with CpG adjuvant, which is currently in several human clinical trials, were protected from HeV disease. Here we show, under similar conditions of use, that the vaccine also provides protection against NiV-induced disease. Such protection persists for at least 12 months post-vaccination, with data supporting only localised and self-limiting virus replication in 2 of 5 animals. These results augur well for acceptability of the vaccine to industry.

Long-Term Telomere Dynamics: Modest Increase of Cell Turnover in HIV-Infected Individuals Followed for up to 14 Years

To quantify the long-term dynamics of telomere lengths and the effect of HIV infection on lymphocyte turnover rates, we measured in a blinded study longitudinal samples from 6 individuals using a highly accurate method based on two-dimensional calibration of DNA sizes. For two uninfected controls followed 8 and 10 years the average telomeric terminal restriction fragment (TRF) shortening rate in peripheral blood mononuclear cells (PBMCs) was 50 and 60 bp/year, respectively, in agreement with previous measurements of cross-sectional samples. The TRF lengths of PBMCs from two slow progressors followed for 14 years declined by a rate of 120 ±10 bp/year, i.e. 2-fold higher than the rate of TRF shortening for uninfected individuals. The rate of TRF shortening was higher in CD8 (140 ±10 bp/year) than in CD4 (100 ±10 bp/year) cells. The CD8 cell TRFs of the two fast progressors shortened faster (240 ±10 bp/year) and the rate of CD4 cell TRF shortening in one of the fast progressors was 160 bp/year. These data suggest that HIV infection causes only a modest increase in the lymphocyte turnover which we speculate could be due to chronic activation of the immune system, and may not result in the exhaustion of its regenerative capacity and immunopathogenesis.

Telomere dynamics in HIV-1 infected and uninfected chimpanzees measured by an improved method based on high-resolution two-dimensional calibration of DNA sizes.

We developed an improved method for accurately measuring telomere lengths based on two‐dimensional calibration of DNA sizes combined with pulsed field electrophoresis and quantitative analysis of high‐resolution gel images. This method was used to quantify the length of telomeres in longitudinal samples of peripheral blood mononuclear cells (PBMCs) from five chimpanzees infected with human immunodeficiency virus type 1 (HIV‐1) and three uninfected animals, 14 to 27 years of age. The average length of the telomere restriction fragments (TRF) of infected and uninfected chimpanzees were 11.7 ± 0.25 kbp, and 11.6 ± 0.61 kbp, respectively, and were about 1 kbp and 3 kbp longer than those of human infants and 30 year old adults, respectively. There was a trend of a slight decrease (30–60 bp per year) in the TRF of two HIV infected chimpanzees over 30–35 months, while the TRF of one naive chimpanzee slightly increased over 20 months. Although the number of chimpanzees in this study is small and no statistically significant linear dependencies on time were observed, it appears that in chimpanzees, rates of shortening of the TRF are comparable or smaller than in adult humans and are not significantly affected by HIV‐1 infection, which may be related to the inability of HIV‐1 to cause disease in these animals.