Amino-terminal epitopes are exposed when full-length open reading frame 2 of hepatitis E virus is expressed in Escherichia coli, but carboxy-terminal epitopes are masked

Prophylactic Hepatitis E Vaccine

The hepatitis E has been increasingly recognized as an underestimated global disease burden in recent years. Subpopulations with more serious infection associated damage or death include pregnant women, patients with basic liver diseases, and elderly persons. Vaccine would be the most effective means for prevention of HEV infection. The lack of an efficient cell culture system for HEV makes the development of classic inactive or attenuated vaccine infeasible. Hence, the recombinant vaccine approaches are explored deeply. The neutralizing sites are located almost exclusively in the capsid protein, pORF2, of the virion. Based on pORF2, many vaccine candidates showed potential of protecting primate animals, two of them were tested in human and evidenced to be well-tolerated in adults and highly efficacious in preventing hepatitis E. The world's first hepatitis E vaccine, Hecolin^® (HEV 239 vaccine), was licensed in China and launched in 2012.

Immunobiology and Host Response to HEV

Hepatitis E virus (HEV) usually causes acute self-limiting hepatitis but sometimes leads to chronic infection in immunocompromised persons. HEV is not directly cytopathic. Immunologically mediated events after HEV infection are believed to play important roles in the pathogenesis and clearance of infection. The anti-HEV antibody responses have been largely clarified since the determination of major antigenic determinant of HEV, which is located in the C-terminal portion of ORF2. This major antigenic determinant also forms the conformational neutralization epitopes. Robust anti-HEV immunoglobulin M (IgM) and IgG responses usually develop 3-4 weeks after infection in experimentally infected nonhuman primates. In humans, potent specific IgM and IgG responses occur in the very early phase of the disease and are critical in eliminating the virus, in concert with the innate and adaptive T-cell immune responses. Testing anti-HEV IgM is valuable in the diagnosis of acute hepatitis E. The long-term persistence and protection of anti-HEV IgG provide the basis for estimating the prevalence of HEV infection and for the development of a hepatitis E vaccine. Although human HEV has four genotypes, all the viral strains are considered to belong to a single serotype. It is becoming increasingly clear that the innate and adaptive T-cell immune responses play critical roles in the clearance of the virus. Potent and multispecific CD4+ and CD8+ T cell responses to the ORF2 protein occur in patients with acute hepatitis E, and weaker HEV-specific CD4+ and CD8+ T cell responses appear to be associated with chronic hepatitis E in immunocompromised individuals.

Antigenic Characterization of ORF2 and ORF3 Proteins of Hepatitis E Virus (HEV)

To evaluate the antigenic properties of Hepatitis E Virus (HEV) Open Reading Frame 2 and 3 (ORF2 and ORF3) codified proteins, we expressed different portions of ORF2 and the entire ORF3 in E. coli, a truncated ORF2, was also expressed in baculovirus. A panel of 37 monoclonal antibodies (MAbs) was raised against ORF2 (1-660 amino acids) and MAbs were mapped and characterized using the ORF2 expressed portions. Selected HEV positive and negative swine sera were used to evaluate ORF2 and ORF3 antigens' immunogenicity. The MAbs were clustered in six groups identifying six antigenic regions along the ORF2. Only MAbs binding to the sixth ORF2 antigenic region (394-608 aa) were found to compete with HEV positive sera and efficiently catch the recombinant antigen expressed in baculovirus. The ORF2 portion from 394-608 aa demonstrated to include most immunogenic epitopes with 85% of HEV positive swine sera reacting against the region from 461-544 aa. Only 5% of the selected HEV sera reacted against the ORF3 antigen.

Immunobiology and Host Response to HEV

Hepatitis E virus (HEV) causes acute self-limiting hepatitis in most cases and chronic infection in rare circumstances. It is believed to be noncytopathic, so immunologically mediated events should play important roles in its pathogenesis and infection outcomes. The anti-HEV antibody response was clarified when the major antigenic determinants on the ORF2 polypeptide were determined, which are located in its C-terminal portion. This subregion also forms the conformational neutralization epitopes. Robust anti-HEV immunoglobulin M (IgM) and IgG responses usually develop 3-4 weeks after infection in experimentally infected nonhuman primates. In humans, potent specific IgM and IgG responses occur in the very early phase of the disease and are critical in eliminating the virus, in concert with the innate and adaptive T-cell immune responses. They are also very valuable in the diagnosis of acute hepatitis E, when patients are tested for both anti-HEV IgM and IgG. The long-term persistence and protection of anti-HEV IgG provide the basis for estimating the prevalence of HEV infection and for the development of a hepatitis E vaccine. Although HEV has four genotypes, all the viral strains are considered to belong to a single serotype. It is becoming increasingly clear that the innate and adaptive T-cell immune responses play critical roles in the clearance of the virus. Potent and multispecific CD4⁺ and CD8⁺ T-cell responses to the ORF2 protein occur in patients with acute hepatitis E, and weaker HEV-specific CD4⁺ and CD8⁺ T-cell responses appear to be associated with chronic hepatitis E in immunocompromised individuals.

Hepatitis E virus: Current epidemiology and vaccine

Hepatitis E virus infections have been continuously reported in Indian subcontinent, Africa, southeast and central Asia, posing great health threats to the public, especially to pregnant women. Hecolin® is the only licensed HEV vaccine developed by Xiamen Innovax Biotech Co., Ltd. Extensive characterizations on antigenicity, physicochemical properties, efficacy in clinical trials, and manufacturing capability have made Hecolin® a promising vaccine for HEV control. However, there are many obstacles in large scale application of Hecolin®. Efforts are needed to further evaluate safety and efficacy in HEV risk populations, and to complement HEV standards for quality control. Passing World Health Organization prequalification and licensing outside China are priorities as these are also hindering Hecolin® promotion. Multilateral cooperation among Chinese vaccine manufacturers, Chinese National Regulatory Authorization (NRA) and WHO will expedite the entrance of Hecolin® into international market, so that Hecolin® could play its due role in global hepatitis E control.

Lessons learned from successful human vaccines: Delineating key epitopes by dissecting the capsid proteins

Recombinant VLP-based vaccines have been successfully used against 3 diseases caused by viral infections: Hepatitis B, cervical cancer and hepatitis E. The VLP approach is attracting increasing attention in vaccine design and development for human and veterinary use. This review summarizes the clinically relevant epitopes on the VLP antigens in successful human vaccines. These virion-like epitopes, which can be delineated with molecular biology, cryo-electron microscopy and x-ray crystallographic methods, are the prerequisites for these efficacious vaccines to elicit functional antibodies. The critical epitopes and key factors influencing these epitopes are discussed for the HEV, HPV and HBV vaccines. A pentamer (for HPV) or a dimer (for HEV and HBV), rather than a monomer, is the basic building block harboring critical epitopes for the assembly of VLP antigen. The processing and formulation of VLP-based vaccines need to be developed to promote the formation and stabilization of these epitopes in the recombinant antigens. Delineating the critical epitopes is essential for antigen design in the early phase of vaccine development and for critical quality attribute analysis in the commercial phase of vaccine manufacturing.

Structural basis for the neutralization of hepatitis E virus by a cross-genotype antibody

Hepatitis E virus (HEV), a non-enveloped, positive-sense, single-stranded RNA virus, is a major cause of enteric hepatitis. Classified into the family Hepeviridae, HEV comprises four genotypes (genotypes 1-4), which belong to a single serotype. We describe a monoclonal antibody (mAb), 8G12, which equally recognizes all four genotypes of HEV, with ∼ 2.53-3.45 nM binding affinity. The mAb 8G12 has a protective, neutralizing capacity, which can significantly block virus infection in host cells. Animal studies with genotypes 1, 3 and 4 confirmed the cross-genotype neutralizing capacity of 8G12 and its effective prevention of hepatitis E disease. The complex crystal structures of 8G12 with the HEV E2s domain (the most protruded region of the virus capsid) of the abundant genotypes 1 and 4 were determined at 4.0 and 2.3 Å resolution, respectively. These structures revealed that 8G12 recognizes both genotypes through the epitopes in the E2s dimerization region. Structure-based mutagenesis and cell-model assays with virus-like particles identified several conserved residues (Glu549, Lys554 and Gly591) that are essential for 8G12 neutralization. Moreover, the epitope of 8G12 is identified as a key epitope involved in virus-host interactions. These findings will help develop a common strategy for the prevention of the most abundant form of HEV infection.

Identification of an antigenic domain in the N-terminal region of avian hepatitis E virus (HEV) capsid protein that is not common to swine and human HEVs

The antigenic domains located in the C-terminal 268 amino acid residues of avian hepatitis E virus (HEV) capsid protein have been characterized. This region shares common epitopes with swine and human HEVs. However, epitopes in the N-terminal 338 amino acid residues have never been reported. In this study, an antigenic domain located between amino acids 23 and 85 was identified by indirect ELISA using the truncated recombinant capsid proteins as coating antigens and anti-avian HEV chicken sera as primary antibodies. In addition, this domain did not react with anti-swine and human HEV sera. These results indicated that the N-terminal 338 amino acid residues of avian HEV capsid protein do not share common epitopes with swine and human HEVs. This finding is important for our understanding of the antigenicity of the avian HEV capsid protein. Furthermore, it has important implications in the selection of viral antigens for serological diagnosis.

Use of immuno-dominant epitope derived from genotype 4 as a diagnostic reagent for detecting the antibodies against Hepatitis E Virus

Background

Despite the genotype 4 has become the dominant cause of hepatitis E disease in China, none antigen derived from genotype 4 of hepatitis E virus (HEV) was used in current commercial anti-HEV immunoassay, and the serological reactivity of antigen derive from genotype 4 is not well-charactered.

Methods

We expressed and purified the 4 main immuno-dominant epitopes derived from genotype 1 and 4 including ORF2 (410-621aa) of genotype 4, ORF3 (47-114aa) of genotype 4, ORF2 (396-606aa) of genotype 1 and ORF3 (56-123aa) of genotype 4.

Results

The ORF2 of genotype 4 displayed good diagnostics performance according to ROC analysis using in-house panel, and the immunoassays based the ORF2 of genotype 4 was then developed to detect the anti-HEV IgG antibodies and evaluated further in 530 anti-HEV IgG positive specimens and 380 negative specimens. The sensitivity and the specificity is 98.1% (520/530) and 94.7% (360/380) for immunoassay based on ORF2 of genotype 4, 96.6% (512/530) and 92.6% (352/380) for commercial immunoassay based on genotype 1. It is noted that all of the positive samples will be detected by combing two assays together. The anti-HEV immunoassays based on genotype 4 are in accordance with Chinese anti-HEV national standard,and show an good agreement of 95.8% with commercial assay (kappa=0.913, P=0.014).

Conclusions

The immunoassay based on ORF2G4 displays good performance, and combining assay based on genotype 1 together with genotype 4 will benefit the HEV diagnosis in large scale samples.

Characterization of antigenic domains and epitopes in the ORF3 protein of a Chinese isolate of avian hepatitis E virus

Avian hepatitis E virus (HEV) is an emerging virus associated with the big liver and spleen disease or hepatitis-splenomegaly syndrome in chickens and subclinical infections by the virus are also common. The complete genome of avian HEV contains three open-reading frames (ORFs) in which ORF2 protein is part of virus particles and thus contains primary epitopes. Antigenic epitopes of avian HEV ORF2 protein have been described but those associated with the ORF3 have not. To analyze the antigenic domains and epitopes in the ORF3 protein of a Chinese isolate of avian HEV (CaHEV), we generated a series of antigens comprised of the complete ORF3 and also five truncated overlapping ORF3 peptides. The antibodies used in this study were mouse antisera and monoclonal antibodies against ORF3, positive chicken sera from Specific Pathogen Free chickens experimentally infected with CaHEV and clinical chicken sera. Using these antigens and antibodies, we identified three antigenic domains at amino acids (aa) 1-28, 55-74 and 75-88 in which aa 75-88 was a dominant domain. The dominant domain contained at least two major epitopes since field chickens infected with avian HEV produced antibodies against the domain and epitopes. These results provide useful information for future development of immunoassays for the diagnosis of avian HEV infection.

Point-of-care testing and the control of infectious diseases

Point-of-care tests (POCTs) play an important role in bridging the gap between centralized laboratory diagnostics and peripheral healthcare service providers. Particularly in infectious diseases such as HIV/AIDS and TB where early detection is imperative to improve disease outcome, uptake of an accurate test that is simple, rapid and robust can significantly alter the epidemiology and control of the disease. However, a good POCT can only serve its full potential when adopted in a comprehensive programmatic context linking patients to on-site case management. Immunochromatographic lateral flow devices for detection of antibody or antigen currently dominate available POCTs, and development of such devices has relied on the discovery and optimization of definitive biomarkers suitable for such platforms. In the future, however, there will be an increasing need to develop cost-effective POCTs that address biomarkers that are well established in laboratory settings but are not currently amenable to point-of-care, such as molecular tests for drug resistance in TB and viral load in HIV and viral hepatitis.

Antigenic determinants of hepatitis E virus and vaccine-induced immunogenicity and efficacy

There is emerging evidence for an under-recognized hepatitis E virus (HEV) as a human pathogen. Among different reasons for this neglect are the unsatisfactory performance and under-utilization of commercial HEV diagnostic kits; for instance, the number of anti-HEV IgM kits marketed in China is about one-fifth of that of hepatitis A kits. Over the last two decades, substantial progress has been achieved in furthering our knowledge on the HEV-specific immune responses, antigenic features of HEV virions, and development of serological assays and more recently prophylactic vaccines. This review will focus on presenting the evidence of the importance of HEV infection for certain cohorts such as pregnant women, the key antigenic determinants of the virus, and immunogenicity and clinical efficacy conferred by a newly developed prophylactic vaccine. Robust immunogenicity, greater than 195-fold and approximately 50-fold increase of anti-HEV IgG level in seronegative and seropositive vaccinees, respectively, as well as impressive clinical efficacy of this vaccine was demonstrated. The protection rate against the hepatitis E disease and the virus infection was shown to be 100% (95% CI 75-100) and 78% (95% CI 66-86), respectively.

Hepatitis E virus enters liver cells through receptor-dependent clathrin-mediated endocytosis

We investigated the virus-host interaction for hepatitis E virus (HEV) by performing competitive binding assays using in vitro assembled virus-like particles (VLPs). We used Escherichia coli expressed native capsid protein (pORF2) and its mutants with an attached Gly((5))-Ala (linker) reporter [enhanced green fluorescent protein (EGFP)/firefly luciferase (Fluc)]. Transmission electron microscopy and nanoparticle tracking showed near uniform particles of approximately 30-35 nm in diameter for pORF2 VLPs and 60-100 nm for reporter-linked VLPs. Binding of reporter-linked full-length (1-660aa) and N-terminal truncated (Δ1-112aa) pORF2 VLPs to Huh7 cell surfaces was found to be specific with 1.92 ± 0.065 × 10(5) sites per cell. Saturation binding indicated an equilibrium dissociation constant (K(d)) of 121.1 ± 23.83 and 123.8 ± 16.15 nm for pORF2-linker-EGFP and pORF2-linker-Fluc VLPs respectively. A similar binding pattern was observed for Δ1-112aa pORF2-linker-EGFP and Δ1-112aa pORF2-linker-Fluc VLPs with K(d) values of 123.6 ± 10.60 and 135.6 ± 16.19 nm respectively. The affinity (log K(i)) of pORF2 binding on Huh7 cells in the presence of EGFP-tagged and Fluc-tagged pORF2 VLPs was found to be approximately 2.0. However, no VLP formation or binding was observed with refolded C-terminal truncated (Δ458-660aa) pORF2. We investigated HEV internalization using fluorescent VLPs (EGFP-VLPs), which showed vesicle-mediated uptake starting at 5 min post-incubation. The uptake of VLPs could be stopped by inhibitors for clathrin-dependent endocytosis, but not by caveosome inhibitors. No binding and uptake of EGFP-VLPs were observed on non-hepatic cell lines (HeLa and SiHa). These findings suggest that HEV attaches to the host cell via a specific high affinity receptor and enters the cytoplasm by clathrin-mediated endocytosis.

Serological diagnostics of hepatitis E virus infection

Development of accurate diagnostic assays for the detection of serological markers of hepatitis E virus (HEV) infection remains challenging. In the course of nearly 20 years after the discovery of HEV, significant progress has been made in characterizing the antigenic structure of HEV proteins, engineering highly immunoreactive diagnostic antigens, and devising efficient serological assays. However, many outstanding issues related to sensitivity and specificity of these assays in clinical and epidemiological settings remain to be resolved. Complexity of antigenic composition, viral genetic heterogeneity and varying epidemiological patterns of hepatitis E in different parts of the world present challenges to the refinement of HEV serological diagnostic assays. Development of antigens specially designed for the identification of serological markers specific to acute infection and of IgG anti-HEV specific to the convalescent phase of infection would greatly facilitate accurate identification of active, recent and past HEV infections.

Efficient cell culture systems for hepatitis E virus strains in feces and circulating blood

Attempts have been made to propagate hepatitis E virus (HEV) in primary hepatocyte culture and various other cultured cells. However, the replication ability of HEV recovered from culture media remains extremely low. Recently, efficient culture systems have been established in PLC/PRF/5 (hepatocellular carcinoma) and A549 (lung cancer) cell lines for HEV strains of genotypes 3 and 4 in our laboratory. They originated in fecal extracts from patients containing HEV RNA in extremely high-titers (10(7)  copies/ml), and named the JE03-1760F (genotype 3) and HE-JF5/15F (genotype 4) strains, respectively. HEV RNA in culture supernatants reached 10(8)  copies/ml in titer, and were transmitted successively through many passages. An infectious HEV cDNA clone (pJE03-1760F/wt) was constructed that has replication activity comparable to that of the wild-type JE03-1760F in feces. The ORF3 protein is indispensable for shedding HEV particles from cells in the reverse genetics system. HEV recovered from culture media, as well as circulating HEV, possess ORF3 proteins on the surface and are covered with cellular membranes, and therefore, ORF2 epitopes are buried in these particles. In contrast, HEV excreted into feces are naked nucleocapsids without a lipid layer or surface expression of the ORF3 protein. HEV in sera of patients with acute hepatitis E can infect and replicate in PLC/PRF/5 and A549 cells, with efficiency comparable to the circulating HEV RNA levels. High-efficiency cell culture systems for infectious viruses, thus developed, are expected to open up a new era and resolve many mysteries in the epidemiology, molecular biology, and treatment of HEV.

Toward the development of a hepatitis E vaccine

Hepatitis E virus (HEV) causes large epidemics of enterically transmitted acute hepatitis and accounts for a majority of sporadic acute hepatitis in endemic countries. Due to a very high mortality rate among infected pregnant women and substantial morbidity, disability and costs associated with hepatitis E, concerted efforts are being made to develop an efficacious vaccine. Experimental vaccines, based on recombinant proteins derived from the capsid gene of HEV, have been shown efficacious in pre-clinical trials in macaques conferring cross-protection against various genotypes. Two vaccine candidates, the rHEV vaccine expressed in baculovirus and the HEV 239 vaccine, expressed in Escherichia coli, were successfully evaluated in Phase II/III trials. However, at this time no approved vaccine against hepatitis E is commercially available.

The nucleotides on the stem-loop RNA structure in the junction region of the hepatitis E virus genome are critical for virus replication

The roles of conserved nucleotides on the stem-loop (SL) structure in the intergenic region of the hepatitis E virus (HEV) genome in virus replication were determined by using Huh7 cells transfected with HEV SL mutant replicons containing reporter genes. One or two nucleotide mutations of the AGA motif on the loop significantly reduced HEV replication, and three or more nucleotide mutations on the loop abolished HEV replication. Mutations on the stem and of the subgenome start sequence also significantly inhibited HEV replication. The results indicated that both the sequence and the SL structure in the junction region play important roles in HEV replication.

Screening of specific diagnostic peptides of swine hepatitis E virus

Background

Swine hepatitis E virus (swHEV) is a zoonotic disease that is considered a major problem in pig production and presents a threat to human health. Elucidation of the major antigenic epitopes of swHEV is essential for the effective control of swHEV epidemics.

Results

By bioinformatic analysis, we identified and then synthesized 12 peptides from open reading frames (ORFs) ORF1, ORF2 and ORF3, including swHEV-1 - swHEV-12. Using the results from ELISA, we selected swHEV-11 as the best candidate antigen and used it as a coating antigen for the development of peptide-based swine anti-HEV ELISA kits. The coefficient of variation (CV) the coefficient of variation (CV) varied between 4.3-7.2% in the same batch, and between 8.2-17.7% in six different batches. When comparing our swine peptide-based kit with the commercial recombinant-based kit, the humane anti-HEV IgG test had a 73.4% correspondence rate for them.

Conclusion

This is the first systemic study to screen the diagnostic peptides of swHEV and our findings strongly suggest that peptide swHEV-11 is a potent diagnostic reagent of swHEV that could be used in the development of highly efficient diagnostic assays for the specific and highly sensitive detection of anti-HEV activity in swine serum samples.

Immunogenicity and efficacy of a bacterially expressed HEV ORF3 peptide, assessed by experimental infection of primates

A 12.4-kDa peptide, corresponding to the entire ORF3 protein of hepatitis E virus (HEV), derived from human HEV genotype 4 and expressed in Escherichia coli as a fusion protein with a 17.5-kDa fragment of interleukin (IL)-1beta at the N-terminus, was recognized by HEV-reactive sera. Eight monkeys were immunized with the purified peptide, and seven were used as non-immunized controls. All 15 monkeys were challenged with HEV genotype 1 or 4. All control animals developed infection and hepatitis, and all but one vaccinated monkey became infected. Nevertheless, the vaccine was effective in reducing the virus titer and shortening the duration of viremia and fecal shedding. Furthermore, the vaccine provided some protection against hepatitis (1 of 2 monkeys in the two-dose regimen and 4 of 6 in the three-dose regimen did not develop severe hepatitis) compared to the controls. These results suggest that immunization with the bacterially expressed peptide may partially prevent experimental hepatitis, and even infection, in primates, following intravenous challenge with high doses of two HEV genotypes.

Hepatitis E vaccine: current status and future prospects

HEV, a positive ssRNA and nonenveloped virus, is endemic in many developing countries and one of the most frequent causes of acute hepatitis after fecal–oral transmission. Pregnant women are at particular risk for a fatal course of disease, including maternal and fetal mortality. Recent reports indicate that HEV genotype 3, possibly related to zoonotic transmission, may cause chronic hepatitis in some immunosuppressed organ transplant patients. Various approaches have been conducted to develop HEV vaccines, but only one candidate, a recombinant HEV (rHEV) vaccine generated from Spodoptera frugiperda-9 cells by baculoviruses expressing the HEV capsid antigen, has reached clinical Phase I and II trials so far. These trials suggest that the rHEV vaccine is safe and can prevent clinically overt acute hepatitis E in high-risk populations. We herein review the different approaches in HEV-vaccine development and critically discuss the current status and future directions of the rHEV vaccine used in clinical trials.

A new artificial antigen of the hepatitis E virus

An artificial antigen composed of 12 small antigenic regions derived from the ORF2 and ORF3 HEV proteins was designed. The gene encoding for this artificial antigen was assembled from synthetic oligonucleotides by a new method called Restriction Enzyme-Assisted Ligation (REAL). The diagnostic relevance of this second generation HEV mosaic protein (HEV MA-II) was demonstrated by testing this antigen against a panel of 142 well defined anti-HEV positive and anti-HEV negative serum samples. The data obtained in this study support the substantial diagnostic potential of this HEV mosaic antigen.

Challenge studies in Rhesus monkeys immunized with candidate hepatitis E vaccines: DNA, DNA-prime-protein-boost and DNA-protein encapsulated in liposomes

Complete ORF2 gene (1983bp) of hepatitis E virus (HEV) and the 450bp region within ORF2 containing neutralizing epitope (NE) cloned in pVAX1 and corresponding proteins expressed in baculovirus and prokaryotic systems respectively were evaluated as vaccine candidates. Two doses of liposome encapsulated DNA plus corresponding protein with both ORF2 and NE regions (Lipo-ORF2-DP and Lipo-NE-DP) showed 100% seroconversion and comparable anti-HEV titres in Swiss albino mice. These vaccine candidates were further evaluated as DNA, DNA-prime-protein-boost (DPPB) and liposome formulations in Rhesus monkeys. Monkeys receiving ORF2/NE DNA seroconverted after fourth dose while those immunized employing ORF2-DPPB format seroconverted at 7 weeks post third dose. In view of the delayed weak antibody response, these monkeys were not challenged. Though Lipo-ORF2-DP was immunogenic, 2 of the 4 monkeys developed HEV infection following homologous virus challenge of 100 Monkey Infectious Dose(50). Both monkeys immunized with Lipo-NE-DP and 1 of the 2 monkeys immunized with NE-DPPB showed complete protection, the second monkey being protected from hepatitis with limited viral replication. Irrespective of the type of immunogen, all challenged monkeys were protected from hepatitis. The results document Lipo-NE-DP to be a promising vaccine candidate needing further evaluation.

Double-antigen enzyme-linked immunosorbent assay for detection of hepatitis E virus-specific antibodies in human or swine sera

A new double-antigen sandwich-based enzyme-linked immunosorbent assay (ELISA) for the detection of total antibodies (immunoglobulin G [IgG] and IgM) specific for hepatitis E virus (HEV) was developed by utilizing well-characterized recombinant protein ET2.1 and its peroxidase-labeled counterpart. Our study showed that the ELISA detected all the positive patient samples (n = 265) regardless of whether they contained IgM or IgG antibodies, or both, while it maintained an excellent specificity of 98.8% with samples from various patient or healthy control groups (total number of samples, 424). The test had a detection limit for anti-HEV IgG antibodies that was equivalent to 62 mIU/ml of the international reference. Compared with the serological status of the specimens determined on the basis of tests performed at the individual collection sites, the testing outcome generated by the new ELISA had a good agreement of 99.3%, with a kappa value of 0.985. The positive predictive value and the negative predictive value for the new test reached 98.1% and 100%, respectively. This ELISA had a positive delta value of 4.836 and a negative delta value of 3.314 (where delta is a measure of the number of standard deviations by which the cutoff is separated from the mean of the sample groups) (N. Crofts, W. Maskill, and I. D. Gust, J. Virol. Methods 22:51-59, 1988), indicating that it had an excellent ability to differentiate the infected and noninfected cohorts. Furthermore, the new design enables the detection of antibodies not only in human samples but also in pig samples. Our preliminary data showed that the ELISA could detect seroconversion in samples from pigs at as early as 14 days postinoculation. The potential utility of detecting specific antibodies in pigs will be an added advantage for managing the disease, with suggested zoonotic implications.

Hepatitis E vaccine

Hepatitis E is an emerging disease in resource-poor regions of the world. It is estimated that about 2 billion people live in areas endemic for this disease. The inability to reproducibly culture hepatitis E virus makes it impossible to develop traditional live or inactivated vaccines. However, significant progress has been made in developing and testing recombinant subunit vaccines based on the viral capsid protein. This review summarizes these efforts.

Comparison of a new immunochromatographic test to enzyme-linked immunosorbent assay for rapid detection of immunoglobulin m antibodies to hepatitis e virus in human sera

An immunochromatographic test for rapid detection of IgM antibodies in patients with acute hepatitis E infection was developed utilizing the well-characterized recombinant protein EP2.1 and monoclonal antibody 4B2. The new rapid test based on a novel reverse-flow technology was able to generate a positive result within 2 to 3 min. Our study showed that this test was able to detect anti-HEV IgM antibodies in 96.7% of the patient samples tested (n = 151) while maintaining an excellent specificity of 98.6% with samples from various patient or healthy control groups (total n = 208). Furthermore, this rapid test gave a good specificity of 90.9% when tested with rheumatoid factor (RF)-positive sera (RF value of < or =850 IU/ml; n = 11) although a higher concentration of RF in samples might cause cross-reactivity. The new test has a good agreement of 97.2% with a kappa value of 0.943 when compared with a reference enzyme-linked immunosorbent assay. The positive predictive value and the negative predictive value for the rapid test thus reached 98.0 and 97.6%, respectively. This is the first rapid, point-of-care test for hepatitis E and will be especially useful for the diagnosis of acute hepatitis E virus infection in field and emergency settings and in resource-poor countries.

Prevalence of antibodies to hepatitis E virus in residents of a district in Havana, Cuba

A seroepidemiological study of hepatitis E virus (HEV) infection was conducted in a district of Havana, where hepatitis A virus (HAV) is considered endemic. The levels of anti-HEV antibodies were evaluated by enzyme-linked immunosorbent assay (ELISA) based on the recombinant protein GST-ORF2.1. Anti-HEV antibodies were detected in 11 of 209 (5.3%) of serum samples, compared to 71.3% for anti-HAV antibodies. No risk factors reported previously for HEV infection showed a significant association with the presence of anti-HEV antibodies, whereas anti-HAV antibodies were strongly associated with increasing age. HEV may be considered endemic in this area and is likely to have a significant clinical impact.

Acidic pH enhances structure and structural stability of the capsid protein of hepatitis E virus

Hepatitis E virus (HEV) is enterically transmitted and endemic to tropical areas of the world. The major capsid protein of HEV is pORF2 ( approximately 74 kDa), encoded by open reading frame 2 (ORF2). When expressed in insect cells, it is processed into a approximately 55 kDa form (n-pORF2). We also generated a mutant, m-pORF2, lacking a C-terminal hydrophobic region shown earlier to be required for its homo-oligomerization. Circular dichroism was used to measure the secondary structure and stability of these proteins as a function of pH and temperature. With decreasing pH both proteins acquired increasing alpha-helicity and thermal stability in terms of midpoint of denaturation and the Gibbs energy change.

Evaluation of antibody-based and nucleic acid-based assays for diagnosis of hepatitis E virus infection in a rhesus monkey model

We have evaluated four hepatitis E virus (HEV) specific antibody assays, using sequential samples taken from 86 rhesus monkeys at intervals for up to 86 weeks after they had been infected with different doses of HEV. The animals are a common experimental model of hepatitis E. The large collection of sequential samples used avoids uncertainties encountered in previous studies regarding the precise infection status of study subjects and minimizes bias due to the individuality of response to infection. One assay (YES IgG) was produced with synthetic peptides; the others (E2 IgM, E2 IgG, and GL IgG) were produced with recombinant antigens. The results were compared with the viral RNA contents of the serum and stool samples and the occurrence of these virological and immunological markers in the course of the infection was temporally related to the development of hepatitis. Diagnostic utility of the markers was assessed according to their response rates and prevalence at different times in the course of infection. All the animals produced E2 IgG and developed viremia and all but one also produced E2 IgM and excreted the virus in stool, whereas response rates for the other antibodies were lower and decreased with virus dose. Hepatitis occurred over a period of 4 weeks between 3 and 7 weeks after infection. Virological activity occurred mainly during the incubation period and the prevalence of viral markers declined rapidly after the onset of hepatitis. Production of the E2 antibodies immediately preceded the onset of hepatitis, and this was followed about one week later by production of the other antibodies. Seroprevalence E2 IgM reached a peak value 3 weeks after the onset of hepatitis, whereas seroprevalence of GL IgG and YES IgG peaked after the disease had subsided. E2 IgG persisted in all animals for the entire duration of the experiment of up to 86 weeks and possibly beyond and, thus, can serve as a useful epidemiological marker of HEV infection.

A new enzyme immunoassay for the detection of antibody to hepatitis E virus

BACKGROUND AND AIM

The purpose of the present study was to develop enzyme immunoassay (EIA) for the detection of IgG anti-hepatitis E virus (HEV) activity using two new recombinant proteins as antigenic targets, and to evaluate these EIA with the aid of statistical methods.

METHODS

Two proteins, a mosaic protein and pB166 containing region 452-617 aa of the ORF2 of the HEV Burma strain, were used to develop the new HEV EIA. This EIA was evaluated using several panels of serum specimens obtained from: (i) acutely HEV-infected patients; (ii) patients with non-A, non-C hepatitis; (iii) normal blood donors (NBD) from non-endemic countries; and (iv) experimentally infected chimpanzees.

RESULTS

A new HEV EIA was developed using two new recombinant proteins. This assay was able to detect anti-HEV activity in all specimens from acutely HEV-infected patients. When NBD were tested, more than 15% of specimens were found to be IgG anti-HEV positive. All NBD anti-HEV-positive specimens were tested with overlapping synthetic peptides spanning the entire HEV ORF2-encoded protein. More than 90% of the anti-HEV-positive NBD specimens immunoreacted with an average of 15 synthetic peptides derived from different regions of the HEV ORF2 protein. These data suggest that the HEV EIA is at least 90% specific in detecting remote HEV infections.

CONCLUSION

The new HEV EIA developed in the present study is a highly specific diagnostic assay for the detection of anti-HEV activity in serum specimens obtained from different epidemiologic settings.

The putative capsid protein of the newly identified avian hepatitis E virus shares antigenic epitopes with that of swine and human hepatitis E viruses and chicken big liver and spleen disease virus

We recently identified a novel virus, designated avian hepatitis E virus (avian HEV), from chickens with hepatitis-splenomegaly (HS) syndrome in the USA. We showed that avian HEV is genetically related to swine and human HEVs. Here we report the antigenic cross-reactivity of the putative open reading frame 2 (ORF2) capsid protein of avian HEV with those of swine and human HEVs and the Australian chicken big liver and spleen disease virus (BLSV). The region encoding the C-terminal 268 amino acid residues of avian HEV ORF2 was cloned into expression vector pRSET-C. The truncated ORF2 protein was expressed in E. coli as a fusion protein and purified by affinity chromatography. Western blot analysis revealed that the avian HEV ORF2 protein reacted with antisera against the Sar-55 strain of human HEV and with convalescent antisera against swine HEV and the US2 strain of human HEV, as well as with antiserum against BLSV. Convalescent sera from specific-pathogen-free chickens experimentally infected with avian HEV also reacted with the recombinant capsid proteins of swine HEV and Sar-55 human HEV. Antisera against the US2 human HEV also reacted with recombinant ORF2 proteins of both swine HEV and Sar-55 human HEV. The antigenic cross-reactivity of the avian HEV putative capsid protein with those of swine and human HEVs was further confirmed, for the most part, by ELISA assays. The data indicate that avian HEV shares certain antigenic epitopes in its putative capsid protein with swine and human HEVs, as well as with BLSV. The results have implications for HEV diagnosis and taxonomy.

Hepatitis E virus infection in haemodialysis patients: a case-control study in Saudi Arabia

To determine the prevalence of antibody to hepatitis E virus (IgM anti-HEV) among haemodialysis patients and evaluate whether there was an increased risk of infection and exposure to HEV in an area of endemic viral hepatitis, serum samples obtained from 83 Saudi patients on chronic haemodialysis (group 1), 400 sex- and age-matched healthy subjects (group 2) and hospital patients (group 3) were tested for the IgM anti-HEV and IgG anti-HEV. The prevalence of anti-HEV among the patients (group 1) and the healthy controls were 4.8% and 0.3%, respectively. The difference (4.5%) was statistically significant, with a calculated odds ratio (OR) of 20.2 (95% CI = 2.1-481.0; P = 0.0002). In contrast, there was no significant difference in the prevalence rates of IgG anti-HEV (7.2% vs 10.8%) in both groups. In nonhaemodialysis patients with various diseases, 1.6% (1 of 64) of outpatients (group 3) and none (0 of 113) of the ward patients (group 4) was positive for IgM anti-HEV. Thus, the prevalence (4 of 83) of IgM anti-HEV in the haemodialysis patients was significantly higher than the rate (1 of 177) in the combined groups of nonhaemodialysis hospital patients. The calculated OR was 8.9 (95% CI = 0.92, 212.8; P = 0.037). IgM antibody to hepatitis A virus (IgM anti-HAV) was not detected in any subjects, and the prevalence rates of IgG anti-HAV were similar in the patients and controls (72.3% and 74.3% in groups 1 and 2, respectively, and 75.7% combined groups 3 and 4). The study indicated a significantly higher risk of acute HEV infection among patients on chronic haemodialysis. It is possible that these were nosocomial infections acquired by person-to-person transmission in the haemodialysis unit. However, it is more probable that the infections were community acquired, a conclusion supported albeit indirectly by the lack of a significant difference between the prevalence in haemodialysis patients (4.8%) and outpatients (1.6%). In areas of endemic HEV, appropriate strategies should be adopted to prevent the risk of HEV among haemodialysis patients.

Chimeric recombinant hepatitis E virus-like particles as an oral vaccine vehicle presenting foreign epitopes

Many viral and bacterial pathogens establish infections through mucosal surfaces in their initial stage. However, only a few nonreplicating molecules successfully induce strong mucosal immune reaction without the addition of adjuvants by oral administration. To overcome this difficulty, we investigated whether hepatitis E virus-like particles (HEV-VLPs) could be utilized as a carrier molecule for foreign antigenic epitopes and to stimulate mucosal immunity without the need for adjuvants. To accomplish this goal, we incorporated a B cell epitope tag, consisting of 11 amino acids at the C-terminal of HEV-VLP. The chimeric VLP showed morphology similar to that of the mature HEV virion and VLP. The inserted epitope was reactive with a specific monoclonal antibody in the VLP form, suggesting that it was exposed on the surface of the VLP. After oral administration without adjuvant, this chimeric HEV induced significant levels of specific IgG and IgA to both the inserted epitope and HEV-VLP in intestinal secretions. These humoral immune responses were observed as early as 2 weeks after the first immunization. These results suggest the potential of HEV-VLP as a mucosal vaccine carrier vehicle for the presentation of antigenic epitopes through oral administration.

Detection of sporadic cases of hepatitis E virus (HEV) infection in China using immunoassays based on recombinant open reading frame 2 and 3 polypeptides from HEV genotype 4

We reported previously on the complete sequence of hepatitis E virus (HEV) genotype 4, isolated from patients with sporadic cases of acute HEV infection in China. At least eight HEV genotypes have now been described worldwide, and further isolates await classification. Current immunoassays for the detection of anti-HEV antibodies are based on polypeptides from genotypes 1 and 2 only and may be inadequate for the reliable detection of other genotypes. Because genotypes 1 and 4 predominate in China, we wished to investigate the antigenic reactivities of HEV genotype 4 proteins. Four overlapping regions of open reading frame 2 (ORF2) (FB5, amino acids [aa] 1 to 130; E4, aa 67 to 308; F2-2, aa 288 to 461; E5, aa 414 to 672) and the entire ORF3 product were expressed in Escherichia coli as fusion proteins. Enzyme immunoassays based on each of the five purified polypeptides were evaluated with sera from patients with sporadic cases of acute HEV infection. Individual immunoassays derived from HEV genotype 4 detected more cases of acute hepatitis E than a commercial assay. Some serum samples, which were positive for anti-HEV immunoglobulin G only by assays based on HEV genotype 4, were positive for HEV RNA by reverse transcription-PCR. Polypeptide FB5, from the N terminus of ORF2, had the greatest immunoreactivity with sera from patients with acute hepatitis E. These data indicate that the N terminus of ORF2 may provide epitopes which are highly reactive with acute-phase sera and that assays based on genotypes 1 and 2 alone may be inadequate for the detection of HEV infection in China, where sporadic cases of HEV infection are caused predominantly by HEV genotypes 4 and 1.

Recombinant vaccines for hepatitis E

Hepatitis E virus causes epidemics of acute hepatitis in many developing countries. It infrequently causes disease in developed countries, but avirulent strains might circulate. Some evidence suggests that hepatitis E might be a zoonosis. There is probably only a single serotype. A candidate vaccine consisting of baculovirus-expressed recombinant capsid protein protected macaques from hepatitis E--it passed phase I clinical trials and is currently scheduled for phase II/III clinical trials.

Identification and characterization of the neutralization epitope(s) of the hepatitis E virus

The neutralization epitope(s) of the hepatitis E virus (HEV) was studied by an in vitro neutralization assay using antibodies obtained by immunization of mice with 51 overlapping 30-mer synthetic peptides spanning the region 221-660 amino acids (aa) of the HEV open reading frame 2 encoded protein (pORF2) and 31 overlapping recombinant proteins of different sizes derived from the entire pORF2 of the HEV Burma strain. Antibodies against synthetic peptides and short recombinant proteins of approximately 100 aa did not neutralize HEV, suggesting the HEV neutralization epitope(s) is conformation-dependent. However, one recombinant protein of approximately 400 aa in length comprising the pORF2 sequence at position 274-660 aa as well as all truncated derivatives of this protein containing region 452-617 aa elicited antibodies, demonstrating HEV neutralizing activity. These findings establish for the first time that the minimal size fragment, designated pB166, that can efficiently model the neutralization epitope(s) is 166 aa in length and is located at position 452-617 aa of the HEV pORF2. Additionally, antibodies against pB166 were found to cross-neutralize three different HEV genotypes, suggesting that a common neutralization epitope(s) may exist within the different HEV genotypes. Thus, recombinant proteins constructed in this study may be considered as potential candidates for the development of an HEV subunit vaccine as well as for the development of highly sensitive and specific diagnostic tests.

Conformational antigenic determinants generated by interactions between a bacterially expressed recombinant peptide of the hepatitis E virus structural protein

A 23 kDa peptide locating to amino acid residues 394 to 604 of the major Hepatitis E Virus (HEV) structural protein was expressed in E. coli. This peptide was found to interact naturally with one another to form homodimers and it was recognized strongly and commonly in its dimeric form by HEV reactive human sera. The antigenic activity associated with the dimeric form was abrogated when the dimer was dissociated into monomer and the activity was reconstituted after the monomer was re-associated into dimer again. The dimeric form of the peptide elicited a vigorous antibody response in experimental animals and the resulting antisera were found to cross-react against HEV, effecting an efficient immune capture of the virus. These results attributed the antigenic activity associated with the dimeric form of the peptide to conformational antigenic determinants generated as a result of interaction between the peptide molecules. It is suggested that some of these antigenic determinants may be expressed by the HEV capsid and raised the possibility of this bacterially expressed peptide as an HEV vaccine candidate.

A review of hepatitis E virus

Hepatitis E virus (HEV) is a major cause of outbreaks and sporadic cases of viral hepatitis in tropical and subtropical countries but is infrequent in industrialized countries. The virus is transmitted by the fecal-oral route with fecally contaminated drinking water being the usual vehicle. Hepatitis resulting from HEV infection is a moderately severe jaundice that is self-limiting in most patients. Young adults, 15 to 30 years of age, are the main targets of infection, and the overall death rate is 0.5 to 3.0%. However, the death rate during pregnancy approaches 15 to 25%. Death of the mother and fetus, abortion, premature delivery, or death of a live-born baby soon after birth are common complications of hepatitis E infection during pregnancy. Hepatitis E virus is found in both wild and domestic animals; thus, HEV is a zoonotic virus. The viruses isolated from swine in the United States or Taiwan are closely related to human HEV found in those areas. The close genetic relationship of the swine and human virus suggests that swine may be a reservoir of HEV. In areas where swine are raised, swine manure could be a source of HEV contamination of irrigation water or coastal waters with concomitant contamination of produce or shellfish. Increasing globalization of food markets by industrialized countries has the potential of introducing HEV into new areas of the world. The purpose of this review is to cover certain aspects of hepatitis E including the causative agent, the disease, diagnosis, viral detection, viral transmission, epidemiology, populations targeted by HEV, and the role of animals as potential vectors of the virus.

A C-Terminal Hydrophobic Region is Required for Homo-Oligomerization of the Hepatitis E Virus Capsid (ORF2) Protein

Hepatitis E virus (HEV) is the causative agent of hepatitis E, an acute form of viral hepatitis. The open reading frame 2 (ORF2) of HEV encodes the viral capsid protein, which can self-oligomerize into virus-like particles. To understand the domains within this protein important for capsid biogenesis, we have carried out in vitro analyses of association and folding patterns of wild type and mutant ORF2 proteins. When expressed in vitro or in transfected cells, the ORF2 protein assembled as dimers, trimers and higher order forms.While N-terminal deletions upto 111 amino acids had no effect, the deletion of amino acids 585-610 led to reduced homo-oligomerization. This deletion also resulted in aberrant folding of the protein, as determined by its sensitivity to trypsin. This study suggests that a C-terminal hydrophobic region encompassing amino acids 585-610 of the ORF2 protein might be critical for capsid biogenesis.

Identification of immunodominant and conformational epitopes in the capsid protein of hepatitis E virus by using monoclonal antibodies

Antibody to the capsid (PORF2) protein of hepatitis E virus (HEV) is sufficient to confer immunity, but knowledge of B-cell epitopes in the intact capsid is limited. A panel of murine monoclonal antibodies (MAbs) was generated following immunization with recombinant ORF2.1 protein, representing the C-terminal 267 amino acids (aa) of the 660-aa capsid protein. Two MAbs reacted exclusively with the conformational ORF2.1 epitope (F. Li, J. Torresi, S. A. Locarnini, H. Zhuang, W. Zhu, X. Guo, and D. A. Anderson, J. Med. Virol. 52:289-300, 1997), while the remaining five demonstrated reactivity with epitopes in the regions aa 394 to 414, 414 to 434, and 434 to 457. The antigenic structures of both the ORF2.1 protein expressed in Escherichia coli and the virus-like particles (VLPs) expressed using the baculovirus system were examined by competitive enzyme-linked immunosorbent assays (ELISAs) using five of these MAbs and HEV patient sera. Despite the wide separation of epitopes within the primary sequence, all the MAbs demonstrated some degree of cross-inhibition with each other in ORF2. 1 and/or VLP ELISAs, suggesting a complex antigenic structure. MAbs specific for the conformational ORF2.1 epitope and a linear epitope within aa 434 to 457 blocked convalescent patient antibody reactivity against VLPs by approximately 60 and 35%, respectively, while MAbs against epitopes within aa 394 to 414 and 414 to 434 were unable to block patient serum reactivity. These results suggest that sequences spanning aa 394 to 457 of the capsid protein participate in the formation of strongly immunodominant epitopes on the surface of HEV particles which may be important in immunity to HEV infection.

Recombinant subunit ORF2.1 antigen and induction of antibody against immunodominant epitopes in the hepatitis E virus capsid protein

A recombinant subunit antigen (ORF2.1), representing the carboxy-terminal 267 amino acids of the 660-amino-acid hepatitis E virus (HEV) capsid protein, was expressed in Escherichia coli and used for the immunisation of rats. Purified antigen formulated with either Aluminium Hydroxide Gel Adjuvant (Alum) or Titermax gave high and equivalent levels of antibody after three doses. Responses to two doses of 15, 75, or 150 microg antigen, formulated with Alum and given at 0 and 4 weeks, were also equivalent by 17 weeks after immunisation. Rats initially developed antibody to a wide range of linear epitopes in the ORF2.1 region, but by 27 weeks the predominant response detected by Western immunoblotting was restricted to the conformational epitope unique to ORF2.1 [Li et al. (1997) Journal of Medical Virology 52:289-300], a pattern that was also observed when comparing acute-phase patient serum samples with serum samples from convalescing patients. Antibody from immunised rats blocked the majority of patients' serum reactivity in enzyme-linked immunosorbent assay against both ORF2.1 (57-92% inhibition) and virus-like particles of HEV produced using the baculovirus system (74-97% inhibition). Together, these results suggest that the ORF2.1 subunit vaccine induces an antibody response against immunodominant, conformational epitopes in the viral capsid, which largely mimics that seen in convalescent patients, who are presumed to be immune to HEV infection.

Recombinant hepatitis E capsid protein self-assembles into a dual-domain T = 1 particle presenting native virus epitopes

The three-dimensional structure of a self-assembled, recombinant hepatitis E virus particle has been solved to 22-A resolution by cryo-electron microscopy and three-dimensional image reconstruction. The single subunit of 50 kDa is derived from a truncated version of the open reading frame-2 gene of the virus expressed in a baculovirus system. This is the first structure of a T = 1 particle with protruding dimers at the icosahedral two-fold axes solved by cryo-electron microscopy. The protein shell of these hollow particles extends from a radius of 50 A outward to a radius of 135 A. In the reconstruction, the capsid is dominated by dimers that define the 30 morphological units. The outer domain of the homodimer forms a protrusion, which corresponds to the spike-like density seen in the cryo-electron micrograph. This particle retains native virus epitopes, suggesting its potential value as a vaccine.

Seroprevalence of antibodies to hepatitis E virus in the normal blood donor population and two aboriginal communities in Malaysia

The prevalence of antibodies to hepatitis E virus (HEV) has been examined in many countries, but such studies have generally been limited to majority populations such as those represented in healthy blood donors or cross sections of urban populations. Due to its major route of enteric transmission, large differences in HEV prevalence might be expected between populations in the same country but with different living conditions. Using an ELISA based on GST-ORF2.1 antigen, the prevalence of IgG-class antibodies to HEV was examined in three distinct populations in Malaysia: the normal (urban) blood donor population and two aboriginal communities located at Betau, Pahang and Parit Tanjung, Perak. IgG anti-HEV was detected in 45 (44%) of 102 samples from Betau and 15 (50%) of 30 samples from Parit Tanjung, compared to only 2 (2%) of 100 normal blood donors. The distribution of sample ELISA reactivities was also consistent with ongoing sporadic infection in the aboriginal communities, while there was no significant relationship between HEV exposure and age, sex, or malaria infection. The high prevalence of antibodies to HEV in the two aboriginal communities indicates that this group of people are at high risk of exposure to HEV compared to the general blood donors, and the results suggest that studies of HEV seroprevalence within countries must take into account the possibility of widely varying infection rates between populations with marked differences in living conditions.

Antigenic domains of the open reading frame 2-encoded protein of hepatitis E virus

The antigenic composition of the hepatitis E virus (HEV) protein encoded by open reading frame 2 (ORF2) was determined by using synthetic peptides. Three sets of overlapping 18-, 25-, and 30-mer peptides, with each set spanning the entire ORF2 protein of the HEV Burma strain, were synthesized. All synthetic peptides were tested by enzyme immunoassay against a panel of 32 anti-HEV-positive serum specimens obtained from acutely HEV-infected persons. Six antigenic domains within the ORF2 protein were identified. Domains 1 and 6 located at the N and C termini of the ORF2 protein, respectively, contain strong immunoglobulin G (IgG) and IgM antigenic epitopes that can be efficiently modeled with peptides of different sizes. In contrast, antigenic epitopes identified within the two central domains (3 and 4) were modeled more efficiently with 30-mer peptides than with either 18- or 25-mers. Domain 2 located at amino acids (aa) 143 to 222 was modeled best with 25-mer peptides. A few 30-mer synthetic peptides derived from domain 5 identified at aa 490 to 579 demonstrated strong IgM antigenic reactivity. Several 30-mer synthetic peptides derived from domains 1, 4, and 6 immunoreacted with IgG or IgM with more than 70% of anti-HEV-positive serum specimens. Thus, the results of this study demonstrate the existence of six diagnostically relevant antigenic domains within the HEV ORF2 protein.

Serological evidence for swine hepatitis E virus infection in Australian pig herds

Hepatitis E virus (HEV) is an enterically transmitted human pathogen, with some similarities to caliciviruses. A variant of HEV was recently identified in pigs in the USA, infecting almost 100% of animals in commercial herds. Phylogenetic analysis suggests that this is a true 'swine HEV' distinct from the human virus, but the swine virus may also infect man. Using an in-house ELISA based on a highly conserved, recombinant HEV protein, we have examined collections of sera from Australian pigs for evidence of HEV infection in local pig herds. Sera from one research herd (n = 32) were uniformly non-reactive, and this was used to establish an assay cut-off (= mean + 3 SD of reference pig serum reactivities). Screening of sera from other herds demonstrates that swine HEV is present in Australia, with reactivity observed in 30% (12/40) of random samples from two piggeries, 92-95% of pigs by the age of 16 weeks in two other piggeries (n = 45), and 17% (15/59) of wild-caught pigs. Further studies are required to examine whether HEV causes disease in pigs and to determine the risk of swine HEV transmission to man.

ELISA for IgG-class antibody to hepatitis E virus based on a highly conserved, conformational epitope expressed in Escherichia coli

In assays based on most recombinant hepatitis E virus (HEV) antigens, the IgG antibody responses to HEV are observed commonly to wane or disappear after the acute phase of infection. Such IgG assays have therefore been used for the diagnosis of acute HEV infection, but they have limited usefulness in seroepidemiological studies. Using western immunoblotting, it was shown previously that the open reading frame (ORF) 2.1 antigen, representing the carboxy-terminal 267 amino acids (aa) of the capsid protein, exposes a conformational epitope which allows optimal detection of convalescent antibody compared to other proteins expressed in Escherichia coli. This conformational epitope is shown to be highly conserved between divergent human HEV isolates, and the development of a sensitive and highly specific enzyme immunoassay (ELISA) based on this recombinant antigen is described. The ORF2.1 ELISA allows the detection and quantitation of both acute- and convalescent phase HEV-specific IgG, and will help to define better the antibody responses to the virus and the prevalence of HEV infection worldwide.

Neutralization of different geographic strains of the hepatitis E virus with anti-hepatitis E virus-positive serum samples obtained from different sources

A recently developed polymerase chain reaction (PCR)-based cell culture neutralization assay was used to investigate cross-neutralization of known hepatitis E virus (HEV) strains obtained from various HEV-endemic regions of the world with different anti-HEV-positive serum samples. Serum specimens obtained from cynomolgus macaques experimentally infected with strains from Burma, Mexico, or Pakistan cross-neutralized the infectivity of each strain as well as an isolate from Morocco. Serum samples obtained either from infected patients who reside in HEV-endemic regions of the world or from U.S. residents who became infected while traveling to such regions also neutralized all four strains. In contrast, antibodies obtained from rabbits immunized with full-length Burma strain ORF2 protein neutralized only the Burma and Pakistan strains, not the Mexico or Morocco strains. In addition, antibodies obtained from guinea pigs immunized with an N-terminal truncated Burma strain ORF2 protein neutralized each strain except the Morocco strain. These data strongly suggest that antibodies elicited during an HEV infection demonstrate broad HEV neutralizing activity, whereas antibodies elicited after immunization with recombinant Burma ORF2 protein demonstrate a more limited ability to neutralize various HEV strains obtained from different regions of the world endemic for the disease.

High level expression of the capsid protein of hepatitis E virus in diverse eukaryotic cells using the Semliki Forest virus replicon

The capsid protein of hepatitis E virus (HEV) is encoded by open reading frame 2 (ORF 2) and exhibits variable processing when expressed in insect and COS cells, but nothing is known of its processing in cells relevant to its replication. The full-length ORF 2 protein was expressed at high levels in mammalian cells by insertion of ORF 2 in the Semliki Forest virus (SFV) replicon to generate rSFV/HEV ORF 2K. Expression of the capsid protein was detected readily by metabolic labelling and indirect immunofluorescence in BHK-21 cells transfected with RNA transcripts derived from rSFV/HEV ORF 2K. ORF 2 protein was also expressed at high levels in cells of diverse origin, including liver-derived cell lines Huh7 and HepG2, following infection with recombinant virus derived from cotransfection of BHK-21 cells with the rSFV/HEV ORF 2K and helper SFV replicon RNAs. The addition of hypertonic KCl during metabolic labelling reduced the level of host cell protein synthesis and enhanced the detection of intermediates in ORF 2 protein processing. The wide host range and high level expression directed by SFV replicon particles has particular utility in the analysis of cell-specific factors in the protein processing and assembly of non-cultivable viruses such as HEV.