Baculovirus expression of chimeric hepatitis B virus core particles with hepatitis E virus epitopes and their use in a hepatitis E immunoassay

The position of Spy Tag/Catcher system in hepatitis B core protein particles affects the immunogenicity and stability of the synthetic vaccine

Presenting exogenous antigens on virus-like particles (VLPs) through "plug-and-display" decoration strategies based on SpyTag/SpyCatcher isopeptide bonding have emerged as attractive technology for vaccine synthesis. However, whether the position of ligation site in VLPs will impose effects on immunogenicity and physiochemical properties of the synthetic vaccine remains rarely investigated. Here in the present work, the well-established hepatitis B core (HBc) protein was used as chassis to construct dual-antigen influenza nanovaccines, with the conserved epitope peptides derived from extracellular domain of matrix protein M2 (M2e) and hemagglutinin (HA) as target antigens. The M2e antigen was genetically fused to the HBc in the MIR region, together with the SpyTag peptide, which was fused either in the MIR region or at the N-terminal of the protein, so that a recombinant HA antigen (rHA) linked to SpyCatcher can be displayed on it, at two different localizations. Both synthetic nanovaccines showed ability in inducing strong M2e and rHA-specific antibodies and cellular immunogenicity; nevertheless, the one in which rHA was conjugated by N-terminal Tag ligation, was superior to another one synthesized by linking the rHA to MIR region SpyTagged-HBc in all aspects, including higher antigen-specific immunogenicity responses, lower anti-HBc carrier antibody, as well as better dispersion stability. Surface charge and hydrophobicity properties of the two synthetic nanovaccines were analyzed, results revealed that linking the rHA to MIR region SpyTagged-HBc lead to more significant and disadvantageous alteration in physiochemical properties of the HBc chassis. This study will expand our knowledge on "plug-and-display" decoration strategies and provide helpful guidance for the rational design of HBc-VLPs based modular vaccines by using SpyTag/Catcher synthesis.

BK virus and cancer in Uganda

As part of an epidemiological study of cancer in Uganda, we investigated the titre of antibodies against BK virus among 821 people with different cancer types and benign tumours. Among study participants, 790 were considered seropositive for anti-BK virus antibodies and all analyses were conducted on transformed data. The mean optical density (a measure of antibody titre) for all patients combined (including the 31 who were considered seronegative) was 1.03 (standard error 0.01), but was 5% higher in women than in men (P=0.05), and 8% higher among HIV seropositive than seronegative people (P=0.002). Otherwise, there were few consistent associations between anti-BK virus antibodies and any social and lifestyle factor investigated. Differences in the mean optical density for each cancer type were estimated using multivariate analysis of variance with adjustment for sex, age group and HIV serostatus, using all other patients as controls. The mean optical density was about 17% lower among those with oral cancer (optical density 0.86, standard error 0.06; P=0.01, based on 30 patients) and about 20% higher among those with prostate cancer (optical density 1.22, standard error 0.09; P=0.01, based on 11 cases) than among all other patients combined. The number of cases of each cancer was too small to exclude the possibility of these findings arising by chance. No other cancer site or type was significantly associated with low, or with high anti-BK virus antibody titres.

Heat treatment of unclarified Escherichia coli homogenate improved the recovery efficiency of recombinant hepatitis B core antigen

Heat precipitation procedure has been regularly incorporated as a selective purification step in various thermostable proteins expressed in different hosts. This method is efficient in precipitation of most of the host proteins and also deactivates various host proteases that can be harmful to the desired gene products. In this study, introduction of heat treatment procedure in the purification of hepatitis B core antigen (HBcAg) produced in Escherichia coli has been investigated. Thermal treatment of the cell homogenate at 60 degrees C for 30 min prior to subsequent clarification steps has resulted in 1.4 times and 18% higher in purity and recovery yield, respectively, compared to the non-heat-treated cell homogenate. In direct capture of HBcAg by using anion-exchangers from unclarified feedstock, pre-conditioning the feedstock by heat treatment at 60 degrees C for 45 min has increased the recovery yield of HBcAg by 2.9-fold and 42% in purity compared to that treated for 10 min. Enzyme-linked immunosorbent assay (ELISA) analysis showed that the antigenicity of the core particles was not affected by the heat treatment process.

Antibody levels against BK virus and prostate, kidney and bladder cancers in the EPIC-Oxford cohort

In a case–control study nested within the EPIC-Oxford cohort, there were no statistically significant differences in the prevalence or titre of antibodies against BK virus measured in plasma taken prior to diagnosis between cases with cancer of the prostate (n=31), kidney (n=5) or bladder (n=9) and controls (n=45).

Positively charged synthetic peptides from structural proteins of papillomaviruses abrogate human papillomavirus infectivity

Human papillomavirus (HPV) virus-like particles (VLP) and synthetic peptides corresponding to positively-charged sequences of the major and minor capsid proteins were tested for their efficacy in inhibiting the infectivity of HPV 31 pseudovirions by blocking virus entry into cells. A greater than 80% reduction of transfection was observed with one HPV-31 peptide at a concentration of 10 microg/ml. Moreover, the blocking was not type-specific since similar reduction in transfection was observed with peptides from other HPV types at a concentration of 60 microg/ml. This concentration was non-toxic for the cells. These findings indicate that some of the positively-charged sequences of the L1 and L2 HPV capsid proteins of papillomavirus are compounds that might be locally active against sexually transmitted papillomavirus. The findings provide further evidence that cellular glycosamino-glycans (GAGs) are functional receptors for HPVs.

Assembly of human severe acute respiratory syndrome coronavirus-like particles

Viral particles of human severe acute respiratory syndrome coronavirus (SARS CoV) consist of three virion structural proteins, including spike protein, membrane protein, and envelope protein. In this report, virus-like particles were assembled in insect cells by the co-infection with recombinant baculoviruses, which separately express one of these three virion proteins. We found that the membrane and envelope proteins are sufficient for the efficient formation of virus-like particles and could be visualized by electron microscopy. Sucrose gradient purification followed by Western blot analysis and immunogold labeling showed that the spike protein could be incorporated into the virus like particle also. The construction of engineered virus-like particles bearing resemblance to the authentic one is an important step towards the development of an effective vaccine against infection of SARS CoV.

Clinical and epidemiological relevance of quantitating hepatitis E virus-specific immunoglobulin M

Diagnosis of acute hepatitis E by detection of hepatitis E virus (HEV)-specific immunoglobulin M (IgM) is an established procedure. We investigated whether quantitation of HEV IgM and its ratio to HEV total Ig furnished more information than conventional IgM tests that are interpreted as positive or negative. A previously described indirect immunoassay for total Ig against a baculovirus-expressed HEV capsid protein was modified to quantitate HEV-specific IgM in Walter Reed (WR) antibody units by using a reference antiserum and the four-parameter logistic model. A receiver-operating characteristics curve derived from 197 true-positive specimens and 449 true-negative specimens identified 30 WR units/ml as an optimum cut point. The median HEV IgM level in 36 patients with acute hepatitis E fell from 3,000 to 100 WR units/ml over 6 months, suggesting that 100 WR units/ml would be a more appropriate cut point for distinguishing recent from remote IgM responses. Among three hepatitis E case series, determination of the HEV IgM-to-total-Ig ratio in acute-phase serum revealed that most patients had high ratios consistent with primary infections whereas a few had low ratios, suggesting that they had sustained reinfections that elicited anamnestic antibody responses. The diagnostic utility of the new IgM test was similar to that of a commercially available test that uses different HEV antigens. In conclusion, we found that HEV IgM can be detected specifically in >95% of acute hepatitis E cases defined by detection of the virus genome in serum and that quantitation of HEV IgM and its ratio to total Ig provides insight into infection timing and prior immunity.

Quantitation of immunoglobulin to hepatitis E virus by enzyme immunoassay

We developed a quantitative enzyme immunoassay (EIA) for antibody to hepatitis E virus (HEV) by using truncated HEV capsid protein expressed in the baculovirus system to improve seroepidemiology, to contribute to hepatitis E diagnosis, and to enable vaccine evaluations. Five antigen lots were characterized; we used a reference antiserum to standardize antigen potency. We defined Walter Reed antibody units (WR U) with a reference antiserum by using the four-parameter logistic model, established other reference pools as assay standards, and determined the conversion factor: 1 WR U/ml = 0.125 World Health Organization unit (WHO U) per ml. The EIA performed consistently; median intra- and inter-test coefficients of variation were 9 and 12%, respectively. The accurate minimum detection limit with serum diluted 1:1,000 was 5.6 WR U/ml; the test could detect reliably a fourfold antibody change. In six people followed from health to onset of hepatitis E, the geometric mean antibody level rose from 7.1 WR U/ml to 1,924.6 WR U/ml. We used the presence of 56- and 180-kDa bands by Western blotting as a confirmatory test and to define true-negative and -positive serum specimens. A receiver-operating characteristics plot identified 30 WR U/ml as an optimum cut-point (sensitivity, 86%; specificity, 89%). The EIA detected antibody more sensitively than a commercially available test. The EIA was transferred to another laboratory, where four operators matched reference laboratory results for a panel of unknowns. Quantitation of antibody to HEV and confirmation of its specificity by Western blotting make HEV serology more meaningful.

Detection of neutralizing antibodies against human papillomaviruses (HPV) by inhibition of gene transfer mediated by HPV pseudovirions

The goal of this study was to develop a human papillomavirus (HPV) neutralization assay using HPV pseudovirions generated in vitro. For this purpose, gene transfer efficiency of HPV virus-like particles (VLPs) was improved by using direct interaction between a reporter plasmid and the VLPs. Electron microscopic observation of the interaction between DNA molecules and VLPs revealed that VLPs always interact with a single DNA molecule and that VLPs bind to the end of linearized DNA molecules. An 100-fold improvement in the gene transfer was obtained by simple interaction between a linearized DNA molecule and VLPs. Moreover, direct interaction methods offer the possibility of transferring plasmids a size higher than that of the papillomavirus genome. The approach that we developed to generate HPV-16 and HPV-31 pseudovirions proved to be suitable for testing neutralizing antibodies in human sera both after immunization and after natural infection.

Gene transfer using human papillomavirus pseudovirions varies according to virus genotype and requires cell surface heparan sulfate

Artificial viruses consisting of DNA plasmid packaged in vitro into virus-like particles (VLPs) are new vehicles for gene transfer. We therefore investigated the ability of nine human papillomavirus (HPV) VLPs to interact with heterologous DNA and transfer genes. HPV 16, 18, 31, 33, 39, 45, 58, 59, and 68 VLPs were able to bind heterologous DNA and to transfer genes into Cos-7 cells. Inhibition of gene transfer by preincubation of the pseudovirions with heparin confirmed that heparan sulfate on the cell surface plays a role as cell receptor for HPVs. As HPV neutralizing antibodies are mainly type-specific, gene transfer with different HPV pseudovirions offers the possibility of their sequential use in vivo for a greater efficacy.

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.

Identification of a novel hepatitis E virus in Nigeria

Sporadic cases of acute hepatitis E among ten native Nigerian adults were reported in Port-Harcourt (Nigeria). Hepatitis E virus (HEV) was detected in serum and/or faecal samples of seven patients by RT-PCR of the open reading frame (ORF)-1 polymerase region and the 3'-end of ORF2. Restriction analysis widely used to distinguish genotypes I and III showed that all Nigerian strains have a pattern similar to the Mexican strain (NotI, nt 286; SmaI, nt 397; no KpnI restriction site) but displayed a BsmI restriction site at nt 213 as do most African HEV strains sequenced so far. Sequence analysis performed from internal ORF1 and ORF2 PCR products displayed strong homogeneity between the HEV isolates, determining a regional cluster. Phylogenetic analysis of nucleotide sequences revealed that these strains were more related to the Mexican prototype genotype III (87% homology in ORF1, 80% homology in ORF2) than to either the African strain genotype I (74% homology in ORF1, 77% homology in ORF2) or the USA strain genotype II (75% homology in ORF1, 77% homology in ORF2). Genetic divergence up to 15% in ORF2 with the Mexican genotype clearly defined a new subgenotype within genotype III. At the amino acid level, Nigerian strains showed more homology with genotype III (96%) than with genotype I (92%). This study clearly determined the co-existence of genotypes I and III in Africa. These Nigerian HEV strains belonging to genotype III, but sharing some properties with genotype I, could be one of the missing links between African and Latin American HEV and could help us to determine the phylogenetic evolution of HEV from the ancestral virus.

DNA-containing and empty hepatitis B virus core particles bind similarly to envelope protein domains

DNA synthesis within the hepatitis B virus (HBV) nucleocapsid appears to be coupled to nucleocapsid envelopment. The nature of the envelopment signal is unknown, but is thought to involve a conformational change at the surface of the capsid that facilitates interaction with HBV envelope proteins. In binding assays in vitro, it was found that empty HBV core particles bound synthetic peptides corresponding to HBV envelope protein domains with the same affinity as did HBV DNA-containing core particles. This suggests that the selection of replication-competent nucleocapsids for envelopment is not related to the capacity of DNA-containing core particles to bind specifically to HBV envelope proteins, and that there must be an alternative mechanism.

Nasal immunization of mice with human papillomavirus type 16 (HPV-16) virus-like particles or with the HPV-16 L1 gene elicits specific cytotoxic T lymphocytes in vaginal draining lymph nodes

Human papillomavirus type 16 (HPV-16) infects the genital tract and is closely associated with the development of cervical cancer. HPV-16 initiates infection at the genital mucosal surface; thus, mucosal immune responses are likely to contribute to defense against HPV-16 infection. However, little information is available regarding the induction of immune responses in the genital tract mucosa. In this study, we evaluated the potential of intranasally administered papillomavirus vaccines to elicit both systemic and vaginal immune responses. HPV-16 virus-like particles (VLPs) produced by self-assembly of L1 protein and the HPV-16 L1 gene cloned into a mammalian expression vector were used as vaccines. Intranasally administered VLPs induced serum immunoglobulin G (IgG) and vaginal IgA secretory antibodies. Very weak serum IgG and vaginal IgA responses were found after DNA immunization. Both splenic and vaginal lymphocytes could be activated by intranasal immunization with VLPs and the HPV-16 L1 gene. Activated CD4(+) Th1-like T cells were shown to synthesize gamma interferon, and activated CD8(+) T cells were demonstrated to be cytotoxic.