Epstein-Barr Virus Neutralization Research Articles

A novel high throughput assay to quantify Epstein-Barr virus neutralizing antibody activity against B-cell and epithelial cell infections for vaccine and therapeutic developments

Epstein-Barr Virus (EBV) is the causative agent of infectious mononucleosis and has been associated with a variety of malignancies. In vivo, EBV infects B cells and epithelial cells. However, the current EBV neutralization assays, especially those against B cell infection, are low throughput, laborious and lack of sensitivity. In this study, we optimized the EBV-GFP based micro-neutralization assay by selecting the most susceptible cell substrates, Akata 4E3 for B cell and HEK293T for epithelial cell. The newly developed procedure is high throughput. The cell type specific neutralization was confirmed using monoclonal antibodies specific to gp350 and gH/gL/gp42. A panel of human sera was also tested. Natural human EBV seropositive sera could neutralize EBV in both B cell and epithelial cell assays efficiently with a majority of human sera generating near 100% EBV neutralization. The EBV neutralizing antibody titers were highly correlated with antibodies specific to gp350, gH, EBV total proteins, and to a less degree with antibodies against gp42. Collectively, we demonstrated this improved neutralization assay is suitable to evaluating the humoral responses elicited by EBV vaccine candidates in preclinical animal models or in large-scale human trials.

Epstein Barr Virus: Development of Vaccines and Immune Cell Therapy for EBV-Associated Diseases.

Epstein-Barr virus (EBV) is the first human tumor virus discovered and is strongly implicated in the etiology of multiple lymphoid and epithelial cancers. Each year EBV associated cancers account for over 200,000 new cases of cancer and cause 150,000 deaths world-wide. EBV is also the primary cause of infectious mononucleosis, and up to 70% of adolescents and young adults in developed countries suffer from infectious mononucleosis. In addition, EBV has been shown to play a critical role in the pathogenesis of multiple sclerosis. An EBV prophylactic vaccine that induces neutralizing antibodies holds great promise for prevention of EBV associated diseases. EBV envelope proteins including gH/gL, gB and gp350 play key roles in EBV entry and infection of target cells, and neutralizing antibodies elicited by each of these proteins have shown to prevent EBV infection of target cells and markedly decrease EBV titers in the peripheral blood of humanized mice challenged with lethal dose EBV. Recent studies demonstrated that immunization with the combination of gH/gL, gB and/or gp350 induced markedly increased synergistic EBV neutralizing activity compared to immunization with individual proteins. As previous clinical trials focused on gp350 alone were partially successful, the inclusion of gH/gL and gB in a vaccine formulation with gp350 represents a promising approach of EBV prophylactic vaccine development. Therapeutic EBV vaccines have also been tested clinically with encouraging results. Immunization with various vaccine platforms expressing the EBV latent proteins EBNA1, LMP1, and/or LMP2 promoted specific CD4+ and CD8+ cytotoxic responses with anti-tumor activity. The addition of EBV envelope proteins gH/gL, gB and gp350 has the potential to increase the efficacy of a therapeutic EBV vaccine. The immune system plays a critical role in the control of tumors, and immune cell therapy has emerged as a promising treatment of cancers. Adoptive T-cell therapy has been successfully used in the prevention and treatment of post-transplant lymphoproliferative disorder. Chimeric antigen receptor T cell therapy and T cell receptor engineered T cell therapy targeting EBV latent proteins LMP1, LMP2 and/or EBNA1 have been in development, with the goal to increase the specificity and efficacy of treatment of EBV associated cancers.

Immunization with Epstein–Barr Virus Core Fusion Machinery Envelope Proteins Elicit High Titers of Neutralizing Activities and Protect Humanized Mice from Lethal Dose EBV Challenge

Epstein–Barr virus (EBV) is the primary cause of infectious mononucleosis and is strongly implicated in the etiology of multiple lymphoid and epithelial cancers. EBV core fusion machinery envelope proteins gH/gL and gB coordinately mediate EBV fusion and entry into its target cells, B lymphocytes and epithelial cells, suggesting these proteins could induce antibodies that prevent EBV infection. We previously reported that the immunization of rabbits with recombinant EBV gH/gL or trimeric gB each induced markedly higher serum EBV-neutralizing titers for B lymphocytes than that of the leading EBV vaccine candidate gp350. In this study, we demonstrated that immunization of rabbits with EBV core fusion machinery proteins induced high titer EBV neutralizing antibodies for both B lymphocytes and epithelial cells, and EBV gH/gL in combination with EBV trimeric gB elicited strong synergistic EBV neutralizing activities. Furthermore, the immune sera from rabbits immunized with EBV gH/gL or trimeric gB demonstrated strong passive immune protection of humanized mice from lethal dose EBV challenge, partially or completely prevented death respectively, and markedly decreased the EBV load in peripheral blood of humanized mice. These data strongly suggest the combination of EBV core fusion machinery envelope proteins gH/gL and trimeric gB is a promising EBV prophylactic vaccine.

Development of a robust, higher throughput green fluorescent protein (GFP)-based Epstein-Barr Virus (EBV) micro-neutralization assay

The goal of most prophylactic vaccines is to elicit robust and effective neutralizing antibodies against the human pathogen target. The titer of neutralizing antibodies to Epstein-Barr Virus (EBV) is a useful biomarker for evaluating EBV vaccines. Here, the development and optimization of a 96-well micro-neutralization fluorescent imaging assay (FIA) using an EBV virus-encoding green fluorescent protein (GFP) to infect adherent EBV recipient cells is reported. The conditions were optimized for generating reproducible EBV-GFP virus, for maintaining viral infectivity for months, and for efficient viral infection of recipient cell culture. The utility of the EBV-GFP FIA neutralization assay was demonstrated in a mouse study of an investigational adjuvanted EBV gp350 subunit vaccine. This assay confirmed the generation of high titers of anti-EBV-neutralizing antibodies which correlated well with the established Raji cell-based flow cytometry-based EBV neutralization assay, as well as with anti-gp350 IgG titers. In naturally infected EBV+ human serum samples, a good correlation between anti-gp350 IgG ELISA titer and EBV-GFP FIA neutralization antibody titer was also observed. Taken together, these results demonstrate the establishment of a scalable high throughput EBV-GFP FIA micro-neutralization assay suitable to measure humoral EBV vaccine response in a large-scale human trial.

A novel tetrameric gp3501–470 as a potential Epstein–Barr virus vaccine

Infectious mononucleosis and B-cell transformation in response to infection with Epstein–Barr virus (EBV) is dependent upon binding of the EBV envelope glycoprotein gp350 to CD21 on B-cells. Gp350-specific antibody comprises most of the EBV neutralizing activity in the serum of infected patients, making this protein a promising target antigen for a prophylactic EBV vaccine. We describe a novel, tetrameric gp350-based vaccine that exhibits markedly enhanced immunogenicity relative to its monomeric counterpart. Plasmid DNA was constructed for synthesis, within transfected CHO cells, of a tetrameric, truncated (a.a. 1–470) gp350 protein (gp3501–470). Tetrameric gp3501–470 induced ∼20-fold higher serum titers of gp3501–470-specific IgG and >19-fold enhancements in neutralizing titers at the highest dose, and was >25-fold more immunogenic on a per-weight basis than monomeric gp3501–470. Further, epidermal immunization with plasmid DNA encoding gp3501–470 tetramer induced 8-fold higher serum titers of gp3501–470-specific IgG relative to monomer. Tetrameric gp3501–470 binding to human CD21 was >24-fold more efficient on a per-weight basis than monomer, but neither tetramer nor monomer mediated polyclonal human B-cell activation. Finally, the introduction of strong, universal tetanus toxoid (TT)-specific CD4+ T-cell epitopes into the tetrameric gp3501–470 had no effect on the gp3501–470-specific IgG response in naïve mice, and resulted in suppressed gp3501–470-specific IgG responses in TT-primed mice. Collectively, these data suggest that tetrameric gp3501–470 is a potentially promising candidate for testing as a prophylactic EBV vaccine, and that protein multimerization, using the approach described herein, is likely to be clinically relevant for enhancing the immunogenicity of other proteins of vaccine interest.

Epstein–Barr virus neutralizing antibody levels and risk of multiple sclerosis

Previous infection with Epstein–Barr virus (EBV) and infectious mononucleosis are established multiple sclerosis (MS) risk factors, and elevated serum titers of anti-EBV nuclear antigen (anti-EBNA) antibodies in healthy adults are strongly correlated with future MS risk. In this prospective study, we investigated the association between EBV neutralizing antibodies and MS risk. MS risk tended to be higher in individuals with high titers of neutralizing antibodies compared to those with low titers (relative risk [RR] = 2.2, 95% confidence interval [CI] 0.97–5.1). This association was attenuated after adjustment for anti-EBNA1 IgG Ab titers (RR = 1.4, 95% CI 0.5–3.5). This preliminary finding warrants further study in a larger population.

Epstein–Barr virus neutralizing and early antigen antibodies in multiple sclerosis

Our objective was to determine whether antibodies against the Epstein-Barr virus (EBV) nuclear antigen-1 (EBNA-1), early antigen (EA), and EBV neutralizing antibodies (NeutAb) are altered in multiple sclerosis (MS). We measured EBNA-1 IgG, EA IgG, and EA IgA using quantitative ELISA. We measured NeutAb using a quantitative competitive ELISA. We studied 80 patients with MS, 80 matched controls, and 19 patients with MS with samples collected both whilst stable and in relapse. Epstein-Barr virus nuclear antigen-1 IgG and EA IgA were increased in MS compared to controls. The EBNA-1 index value was 23.3 ± 18.3 in the patients with MS (mean ± SD) and 16.3 ± 17.4 in the controls (P = 0.007, paired t-test). EA IgA had a median value of 1.964 in the patients with MS and 1.248 in the controls (P = 0.029, Wilcoxon signed rank test). EA IgG and NeutAb were not significantly different. None of the antibody levels were altered in relapse. The correlation between concentrations of different antibodies was minimal. IgG antibodies to EBNA-1 are significantly increased in MS. IgA antibodies against EBV EA are also increased. The EBV neutralizing antibody response is similar in MS and controls.

Human antibody titers to Epstein–Barr Virus (EBV) gp350 correlate with neutralization of infectivity better than antibody titers to EBV gp42 using a rapid flow cytometry-based EBV neutralization assay

Measurement of neutralizing antibodies to Epstein-Barr virus (EBV) is important for evaluation of candidate vaccines. The current neutralization assay is based on antibody inhibition of EBV transformation of B cells and requires 6 weeks to perform. We developed a rapid, quantitative flow cytometry assay and show that neutralizing antibody titers measured by the new assay strongly correlate with antibody titers in the standard transformation-based assay. Antibodies to EBV gp350 and gp42 have been shown to block infection of B cells by EBV. Using new assays to quantify antibodies to these glycoproteins, we show for the first time that human plasma contains high titers of antibody to gp42; these titers correlate with neutralization of EBV infectivity or transformation. Furthermore, we show that antibody titers to EBV gp350 correlate more strongly with neutralization than antibody titers to gp42. These assays should be useful in accessing antibody responses to candidate EBV vaccines.

Human antibody titers to Epstein-Barr Virus (EBV) gp350 correlate with neutralization of infectivity better than antibody titers to EBV gp42 using a rapid flow cytometry-based EBV neutralization assay

Human antibody titers to Epstein-Barr Virus (EBV) gp350 correlate with neutralization of infectivity better than antibody titers to EBV gp42 using a rapid flow cytometry-based EBV neutralization assay

Epstein-Barr Virus gp350-Specific Antibody Titers And Antibody-Dependent Cellular Cytotoxic Effector Function In Different Groups Of Patients: A Study Using Cloned gp350-Expressing Transfected Human T Cell Targets

An NK cell activity-resistant human lymphoid T cell line (CEM-NKr) expressing the transfected Epstein-Barr virus (EBV) gp350 gene was used in membrane immunofluorescence (MIF) and antibody-dependent cellular cytotoxicity (ADCC) assays to analyze the gp350-specific humoral and ADCC responses in groups of EBV-seropositive persons. Results show that there is no correlation between gp350-specific ADCC-mediating antibody titers and MIF or EBV neutralizing antibody titers. For example, sera from patients in the acute phase of infectious mononucleosis, while positive by MIF assay or EBV neutralization test, were not reactive in the ADCC assay. Results also show that nasopharyngeal carcinoma (NPC) patients on MIF present high IgG titers against gp350 compared with healthy persons. Anti-gp350 IgA antibodies were detected in all groups tested; however, titers were highest in the NPC group.

Distribution of epitopes within the amino acid sequence of the Epstein-Barr virus major envelope glycoprotein, gp340, recognized by hyperimmune rabbit sera.

Epstein-Barr virus (EBV) is a major human pathogen for which the development of an effective vaccine remains an important goal. Rabbits were immunized with one of a set of 10 fusion proteins representing protein fragments from the EBV receptor-binding ligand and candidate subunit vaccine gp340. Sera from recipients of fragments from the amino-terminal half of the polypeptide chain bound gp340 in Western blot assays and ELISA but were not virus-neutralizing. The fine epitope specificity of these sera, and of EBV-neutralizing rabbit sera raised against whole EBV and gp340-containing immune-stimulating complexes, were assessed in a peptide ELISA. All but two of these sera bound peptides located between positions 236 and 327 in the 907 amino acids of the gp340 polypeptide chain. Among these it was possible to identify regions containing candidate virus-neutralizing B cell epitopes. The use of a gp340 fusion protein affinity column to isolate antibodies from EBV-neutralizing rabbit sera specific for this region suggests the presence of both continuous and discontinuous B cell epitopes with potential roles in EBV neutralization.

Mapping of B-cell epitopes on the polypeptide chain of the Epstein-Barr virus major envelope glycoprotein and candidate vaccine molecule gp340.

The Epstein-Barr virus (EBV) major envelope glycoprotein gp340 is the subject of current efforts to develop an EBV subunit vaccine. The importance of gp340-specific humoral immunity has been highlighted by studies of natural infection in humans and gp340 immunization of experimental animals. The former studies have demonstrated the presence of gp340-specific serum antibodies which mediate EBV neutralization, complement fixation, and antibody-dependent cellular cytotoxicity. The latter studies have often shown a correlation between the induction of gp340-specific EBV-neutralizing antibodies and protection from virus challenge. We have used a series of bacterial beta-galactosidase-gp340 fusion proteins and overlapping synthetic peptides from the gp340 open reading frame to map the positions of B-cell epitopes within the gp340 primary amino acid sequence. The data reported here indicate the presence of B-cell epitopes within the carboxy-terminal third of the gp340 polypeptide chain. These epitopes could not be detected with a peptide enzyme-linked immunosorbent assay, thereby suggesting that they are discontinuous. Affinity purification of antibodies with a gp340 fusion protein from the carboxy terminus of the gp340 polypeptide chain has been used to show that these antibodies are not EBV neutralizing in vitro. The consequences of these findings for future EBV vaccine development are considered.

Effect of Monoclonal Antibodies to Epstein-Barr Virus Envelope Glycoproteins on Epstein-Barr Virus Neutralization and Binding to Target Cell Receptors

Viral envelope glycoproteins are important in antiviral immunity; however, their precise role in both generating virus-neutralizing antibodies as well as in viral binding to target cell receptors remains largely unexplored. We studied nine monoclonal antibodies (MoAbs) to Epstein-Barr virus (EBV) envelope glycoproteins in order to define the role(s) of their respective epitopes in both EBV neutralization and binding to cellular receptors. Only four MoAbs neutralized EBV infectivity, one requiring complement, and only 1 of these 4 did inhibit EBV binding to target cell receptors. Our results suggest that (1) the epitopes recognized by a majority of these MoAbs play no role in viral neutralization and (2) that the majority of epitopes recognized by the neutralizing antibodies play no role in EBV binding to target cell receptors. This and previous studies would also suggest that only one epitope is involved in EBV binding to its receptor or that, until now, we were able to identify only one EBV-neutralizing MoAb (i.e., 72A1) which is specific for the receptor-binding viral epitope. It is probable that the epitope recognized by 72A1 MoAb is the only glycoprotein domain with a dual role, i.e., in EBV neutralization and binding to target cell receptors.