Observations on the EB virus envelope and virus-determined membrane antigen (MA) polypeptides

Four Decades of Prophylactic EBV Vaccine Research: A Systematic Review and Historical Perspective

Background

Epstein-Barr virus (EBV) is the causal agent of infectious mononucleosis and has been associated with various cancers and autoimmune diseases. Despite decades of research efforts to combat this major global health burden, there is no approved prophylactic vaccine against EBV. To facilitate the rational design and assessment of an effective vaccine, we systematically reviewed pre-clinical and clinical prophylactic EBV vaccine studies to determine the antigens, delivery platforms, and animal models used in these studies.

Methods

We searched Cochrane Library, ClinicalTrials.gov, Embase, PubMed, Scopus, Web of Science, WHO’s Global Index Medicus, and Google Scholar from inception to June 20, 2020, for EBV prophylactic vaccine studies focused on humoral immunity.

Results

The search yielded 5,614 unique studies. 36 pre-clinical and 4 clinical studies were included in the analysis after screening against the exclusion criteria. In pre-clinical studies, gp350 was the most commonly used immunogen (33 studies), vaccines were most commonly delivered as monomeric proteins (12 studies), and mice were the most used animal model to test immunogenicity (15 studies). According to an adaptation of the CAMARADES checklist, 4 pre-clinical studies were rated as very high, 5 as high, 13 as moderate quality, 11 as poor, and 3 as very poor. In clinical studies, gp350 was the sole vaccine antigen, delivered in a vaccinia platform (1 study) or as a monomeric protein (3 studies). The present study was registered in PROSPERO (CRD42020198440).

Conclusions

Four major obstacles have prevented the development of an effective prophylactic EBV vaccine: undefined correlates of immune protection, lack of knowledge regarding the ideal EBV antigen(s) for vaccination, lack of an appropriate animal model to test vaccine efficacy, and lack of knowledge regarding the ideal vaccine delivery platform. Our analysis supports a multivalent antigenic approach including two or more of the five main glycoproteins involved in viral entry (gp350, gB, gH/gL, gp42) and a multimeric approach to present these antigens. We anticipate that the application of two underused challenge models, rhesus macaques susceptible to rhesus lymphocryptovirus (an EBV homolog) and common marmosets, will permit the establishment of in vivo correlates of immune protection and attainment of more generalizable data.

Systematic Review Registration

https://www.crd.york.ac.uk/prospero/display_record.php?RecordID=198440, identifier PROSPERO I.D. CRD4202019844.

Prophylactic and therapeutic strategies for Epstein-Barr virus-associated diseases: emerging strategies for clinical development

INTRODUCTION

Epstein-Barr virus (EBV) infects more than 95% of the world's population and is associated with infectious mononucleosis as well as a number of cancers in various geographical locations. Despite its significant health burden, no licenced prophylactic or therapeutic vaccines are available. Areas covered: Over the last two decades, our understanding of the role of EBV infection in the pathogenesis and immune regulation of EBV-associated diseases has provided new lines of research to conceptualize various novel prophylactic and therapeutic approaches to control EBV-associated disease. In this review, we evaluate the prophylactic and therapeutic vaccine approaches against EBV and various immunotherapeutic strategies against a number of EBV-associated malignancies. This review also describes the existing and future prospects of improved EBV-targeted therapeutic strategies. Expert opinion: It is anticipated that these emerging strategies will provide answers for the major challenges in EBV vaccine development and help improve the efficacy of novel therapeutic strategies.

Vaccine Development for Epstein-Barr Virus

Epstein-Barr virus (EBV) is the primary cause of infectious mononucleosis and is associated with several malignancies, including nasopharyngeal carcinoma, gastric carcinoma, Hodgkin lymphoma, Burkitt lymphoma, and lymphomas in immunocompromised persons, as well as multiple sclerosis. A vaccine is currently unavailable. While monomeric EBV gp350 was shown in a phase 2 trial to reduce the incidence of infectious mononucleosis, but not the rate of EBV infection, newer formulations of gp350 including multimeric forms, viruslike particles, and nanoparticles may be more effective. A vaccine that also includes additional viral glycoproteins, lytic proteins, or latency proteins might improve the effectiveness of an EBV gp350 vaccine. Clinical trials to determine if an EBV vaccine can reduce the rate of infectious mononucleosis or posttransplant lymphoproliferative disease should be performed. The former is important since infectious mononucleosis can be associated with debilitating fatigue as well as other complications, and EBV infectious mononucleosis is associated with increased rates of Hodgkin lymphoma and multiple sclerosis. A vaccine to reduce EBV posttransplant lymphoproliferative disease would be an important proof of principle to prevent an EBV-associated malignancy. Trials of an EBV vaccine to reduce the incidence of Hodgkin lymphoma, multiple sclerosis, or Burkitt lymphoma would be difficult but feasible.

Designing an effective vaccine to prevent Epstein-Barr virus-associated diseases: challenges and opportunities

INTRODUCTION

Epstein-Barr virus (EBV) is a ubiquitous herpesvirus associated with a number of clinical manifestations. Primary EBV infection in young adolescents often manifests as acute infectious mononucleosis and latent infection is associated with multiple lymphoid and epithelial cancers and autoimmune disorders, particularly multiple sclerosis. Areas covered: Over the last decade, our understanding of pathogenesis and immune regulation of EBV-associated diseases has provided an important platform for the development of novel vaccine formulations. In this review, we discuss developmental strategies for prophylactic and therapeutic EBV vaccines which have been assessed in preclinical and clinical settings. Expert commentary: Major roadblocks in EBV vaccine development include no precise understanding of the clinical correlates of protection, uncertainty about adjuvant selection and the unavailability of appropriate animal models. Recent development of new EBV vaccine formulations provides exciting opportunities for the formal clinical assessment of novel formulations.

Kinetics of Epstein-Barr Virus (EBV) Neutralizing and Virus-Specific Antibodies after Primary Infection with EBV

Prospective studies of antibodies to multiple Epstein-Barr virus (EBV) proteins and EBV neutralizing antibodies in the same individuals before, during, and after primary EBV infection have not been reported. We studied antibody responses to EBV in college students who acquired primary EBV infection during prospective surveillance and correlated the kinetics of antibody response with the severity of disease. Neutralizing antibodies and enzyme-linked immunosorbent assay (ELISA) antibodies to gp350, the major target of neutralizing antibody, reached peak levels at medians of 179 and 333 days after the onset of symptoms of infectious mononucleosis, respectively. No clear correlation was found between the severity of the symptoms of infectious mononucleosis and the peak levels of antibody to individual viral proteins or to neutralizing antibody. In summary, we found that titers of neutralizing antibody and antibodies to multiple EBV proteins increase over many months after primary infection with EBV.

Epstein-barr virus vaccines

Epstein–Barr virus (EBV) is the primary cause of infectious mononucleosis (IM) and is associated with epithelial cell malignancies such as nasopharyngeal carcinoma and gastric carcinoma, as well as lymphoid malignancies including Hodgkin lymphoma, Burkitt lymphoma, non-Hodgkin lymphoma and post-transplant lymphoproliferative disorder. EBV vaccines to prevent primary infection or disease, or therapeutic vaccines to treat EBV malignancies have not been licensed. Most efforts to develop prophylactic vaccines have focused on EBV gp350, which is the major target of neutralizing antibody. A single phase 2 trial of an EBV gp350 vaccine has been reported; the vaccine reduced the rate of IM but not virus infection. The observation that infusion of EBV-specific T cells can reduce disease due to Hodgkin lymphoma and nasopharyngeal carcinoma provides a proof of principle that a therapeutic vaccine for these and other EBV-associated malignancies might be effective. Most therapeutic vaccines have targeted EBV LMP2 and EBV nuclear antigen-1. As EBV is associated with nearly 200 000 new malignancies each year worldwide, an EBV vaccine to prevent these diseases is needed.

EBV-Specific Immune Response: Early Research and Personal Reminiscences

Early research on Epstein-Barr virus (EBV) developed from serological observations that were made soon after the discovery of the virus. Indeed, the definition of the humoral response to a variety of EBV proteins dominated the early literature and was instrumental in providing the key evidence for the association of the virus with infectious mononucleosis (IM), Burkitt's lymphoma (BL), and nasopharyngeal carcinoma (NPC). Each of these disease associations involved a distinct pattern of serological reactivity to the EBV membrane antigens (MA), early antigens (EA), and the EBV nuclear antigen (EBNA). When it became generally accepted that the marked lymphocytosis , which is a hallmark of acute IM, was dominated by T cells, considerable effort was directed toward untangling the specificities that might be associated with restricting the proliferation of newly infected B cells. Early evidence was divided between support for both EBV non-specific and/or HLA non-restricted components. However, all results needed to be reassessed in light of the observation that T cells died by apoptosis within hours of separation from fresh blood from acute IM patients. The observation that EBV-infected cultures from immune (but not non-immune) individuals began to die (termed regression) about 10 days post-seeding, provided the first evidence of a specific memory response which was apparently capable of controlling the small pool of latently infected B cells which all immune individuals possess. In this early era, CD8(+) T cells were thought to be the effector population responsible for this phenomenon, but later studies suggested a role for CD4(+) cells. This historical review includes reference to key early observations in regard to both the specific humoral and cellular responses to EBV infection from the time of the discovery of the virus until 1990. As well, we have included personal recollections in regard to the events surrounding the discovery of the memory T cell response since we believe they add a human dimension to a chapter focussed on early history.

Soluble rhesus lymphocryptovirus gp350 protects against infection and reduces viral loads in animals that become infected with virus after challenge

Epstein-Barr virus (EBV) is a human lymphocryptovirus that is associated with several malignancies. Elevated EBV DNA in the blood is observed in transplant recipients prior to, and at the time of post-transplant lymphoproliferative disease; thus, a vaccine that either prevents EBV infection or lowers the viral load might reduce certain EBV malignancies. Two major approaches have been suggested for an EBV vaccine- immunization with either EBV glycoprotein 350 (gp350) or EBV latency proteins (e.g. EBV nuclear antigens [EBNAs]). No comparative trials, however, have been performed. Rhesus lymphocryptovirus (LCV) encodes a homolog for each gene in EBV and infection of monkeys reproduces the clinical, immunologic, and virologic features of both acute and latent EBV infection. We vaccinated rhesus monkeys at 0, 4 and 12 weeks with (a) soluble rhesus LCV gp350, (b) virus-like replicon particles (VRPs) expressing rhesus LCV gp350, (c) VRPs expressing rhesus LCV gp350, EBNA-3A, and EBNA-3B, or (d) PBS. Animals vaccinated with soluble gp350 produced higher levels of antibody to the glycoprotein than those vaccinated with VRPs expressing gp350. Animals vaccinated with VRPs expressing EBNA-3A and EBNA-3B developed LCV-specific CD4 and CD8 T cell immunity to these proteins, while VRPs expressing gp350 did not induce detectable T cell immunity to gp350. After challenge with rhesus LCV, animals vaccinated with soluble rhesus LCV gp350 had the best level of protection against infection based on seroconversion, viral DNA, and viral RNA in the blood after challenge. Surprisingly, animals vaccinated with gp350 that became infected had the lowest LCV DNA loads in the blood at 23 months after challenge. These studies indicate that gp350 is critical for both protection against infection with rhesus LCV and for reducing the viral load in animals that become infected after challenge. Our results suggest that additional trials with soluble EBV gp350 alone, or in combination with other EBV proteins, should be considered to reduce EBV infection or virus-associated malignancies in humans.

Epstein-Barr virus (EBV) is the primary cause of infectious mononucleosis and is associated with several cancers. Presently there is no licensed vaccine to prevent EBV diseases. Two types of candidate vaccines are under development; one involves immunization with the major glycoprotein (gp350) on the outside of the virus, while the other involves vaccination with EBV proteins expressed during latency. We compared these two types of candidate vaccines in a rhesus monkey model of EBV and found that the gp350 vaccine induced better protection from infection. In addition, animals that received the rhesus EBV glycoprotein and became infected had a lower level of rhesus EBV DNA in the blood at 23 months after challenge than animals that received the rhesus EBV latency protein vaccine that subsequently were infected. Since levels of EBV DNA in the blood have been predictive for EBV lymphomas in transplant patients, the ability of rhesus EBV gp350 to reduce levels of rhesus EBV in the blood after infection suggests the EBV gp350 could have a role in reducing certain EBV-associated cancers. This is the first test of candidate vaccines in the rhesus monkey model of EBV and shows that this model should be useful in further evaluation of EBV vaccines.

Antibodies to lytic infection proteins in lymphocryptovirus-infected rhesus macaques: a model for humoral immune responses to epstein-barr virus infection

Humoral immune responses to rhesus lymphocryptovirus (rhLCV) lytic infection proteins were evaluated in the rhesus macaque animal model for Epstein-Barr virus (EBV) infection. We found a hierarchy of humoral responses to 14 rhLCV lytic infection proteins in naturally infected rhesus macaques, with (i) widespread and robust responses to four glycoproteins expressed as late proteins, (ii) frequent but less robust responses to a subset of early proteins, and (iii) low-level responses to immediate-early proteins. This hierarchy of humoral responses was similar to that reported for EBV-infected humans, with the notable exception of the response to rhBARF1. Serum antibodies to rhBARF1 were frequently detected in healthy rhLCV-infected macaques, but in humans, anti-BARF1 antibodies have been reported primarily in patients with EBV-positive nasopharyngeal carcinoma (NPC). The macaque data accurately predicted that serum antibodies against BARF1 are a normal response to EBV infection when human serum samples are analyzed. The rhesus macaque animal provides a unique perspective on humoral responses to EBV infection in humans and can be a valuable model for EBV vaccine development.

Indirect measurement of Epstein-Barr virus neutralising antibodies by ELISA

A rapid and effective ELISA for measuring Epstein-Barr virus (EBV)-neutralizing antibodies in human sera was devised to replace the existing cumbersome method involving the inhibition of fetal cord blood B-cell transformation by the virus. The new method will be invaluable for assessing antibody responses in human subjects participating in EBV gp340 vaccine trials. The ELISA developed uses the human serum antibody to be tested to inhibit standardised binding of an EBV-neutralizing monoclonal antibody (mAb) to gp340 itself or its recombinant derivatives. A serum which has high EBV-neutralizing antibody titres inhibits the binding of neutralizing mAb to gp340 more than a serum with low levels. EBV neutralisation antibody titres obtained by the new inhibition ELISA correlate well with values obtained using the lengthy conventional assay where inhibition of B-cell transformation is assessed. The new assay can be carried out in a few hours compared to 4-5 weeks for the conventional test and could be automated for processing very large sample numbers in vaccine trials.

Immunisation of common marmosets with vaccinia virus expressing Epstein-Barr virus (EBV) gp340 and challenge with EBV

Epstein-Barr virus (EBV) is the cause of infectious mononucleosis and is associated with a variety of life-threatening diseases in humans. Therefore the development of an effective vaccine is an important objective. Many of the initial studies of vaccine efficacy analyse the ability of vaccine preparations to prevent the induction of lymphomas in cottontop tamarins by the B95-8 strain of EBV. We used a vaccinia virus recombinant expressing gp340, vMA1, tested previously in the cotton-top tamarin, to evaluate a common marmoset model in which the challenge virus, M81, resembles more closely the wild-type strains of EBV in the general population than does the standard B95-8 strain. We characterised the M81 strain of EBV with respect to the sequence of its gp340/220 gene and in regard to the presence of a region deleted in B95-8. Replication of the challenge virus in the group vaccinated with vMA1 was decreased when compared to control groups.

Purification and characterization of Epstein-Barr virus gp340/220 produced by a bovine papillomavirus virus expression vector system

Our initial results with a bovine papilloma virus (BPV) vector expression system indicated that we could produce significant amounts of Epstein-Barr virus (EBV) gp340/220 in the supernatant of a mouse fibroblast cell line. We have now extended these findings to show that the truncated version of gp340/220, where the membrane anchor sequence is deleted, is produced even after extended passage of the cells, at a level of approximately 1 mg/4 x 10(8) cells. A simple purification protocol using Sephacryl S300HR and gelatin agarose gives a product which is greater than 90% pure. This product is recognized by anti-gp340 monoclonal antibodies from five different epitope groups and induces antibody that recognizes the authentic gp340/220 and neutralizes EBV in vitro. The purified gp340/220 can be used in ELISA and stimulates the proliferation of T-cell clones specific for gp340/220. These characteristics, together with the fact that BPV-transformed lines have been utilized for the production of pharmaceuticals for use in humans, suggest that this gp340/220 is suitable as a source of antigen for vaccination to prevent EBV infection and related diseases.

Epstein-Barr virus gene expression in malignant lymphomas induced by experimental virus infection of cottontop tamarins

Inoculation of cottontop tamarins with a large dose of Epstein-Barr virus (EBV) leads to the induction of multiple EBV genome-positive lymphomas. These tumors have been characterized as oligoclonal or monoclonal large-cell malignant lymphomas that closely resemble the EBV genome-positive B-cell lymphomas that arise in human allograft recipients. The expression of latent and lytic EBV-encoded proteins was investigated in these virus-induced tamarin lymphomas and in derived cell lines. The tamarin tumors were found to express EBV nuclear antigen 1 (EBNA 1), EBNA 2, EBNA leader protein, and the latent membrane protein (LMP) as determined both by immunohistochemical staining and by immunoblotting. However, within the limits of the immunoblotting assays, no expression of the EBNA 3a protein family could be detected. Assays for lytic-cycle proteins by using both polyclonal human sera and monoclonal antibodies against viral capsid antigen, early antigen, and membrane antigen (gp340/220) showed minimal, if any, expression of these antigens in the lymphoma biopsies. In contrast, the cell lines derived from these lymphomas, even in early passage, expressed abundant levels of the lytic-cycle antigens and also expressed the EBNA 3a protein as well as EBNA 1, EBNA 2, EBNA leader protein, and LMP. This finding suggests that the virus-lymphoma cell interaction, in particular the switch to lytic cycle, is subject to some form of host control in vivo. The expression of EBNA 2 and LMP in these tamarin lymphomas strengthens their resemblance to posttransplant lymphomas in humans, since these human tumors are also EBNA 2 and LMP positive (L. S. Young, C. Alfieri, K. Hennessy, H. Evans, C. O'Hara, K. Anderson, A. Rickinson, E. Kieff, and J. I. Cohen, submitted for publication). Since both proteins are known to be important effector molecules of virus-induced B-cell growth transformation in vitro, their expression in these lymphomas constitutes the best evidence for a direct oncogenic role for EBV in vivo.

Inhibition of Epstein-Barr virus (EBV) release from P3HR-1 and B95-8 cell lines by monoclonal antibodies to EBV membrane antigen gp350/220

Antibody-mediated inhibition of Epstein-Barr virus (EBV) release from the EBV-productive cell lines P3HR-1 and B95-8 was probed with two monoclonal antibodies (MAbs), 72A1 and 2L10, which immunoprecipitated the same EBV membrane antigen (MA) gp350/220 found with the 1B6 MAb with which inhibition of EBV release from P3HR-1 cells was first described. These three MAbs were not equivalent in either MA reactivities or functional effects, reflecting the variable expression of different epitopes of gp350/220. 1B6 recognized MA on P3HR-1 cells, which expressed predominately the gp220 form of MA. 1B6 did not recognize (or barely recognized) a determinant on B95-8 cells. MAbs 2L10 and 72A1 reacted as well with B95-8 cells as they did with P3HR-1 cells. MAbs 1B6 and 2L10 neutralized neither P3HR-1 nor B95-8 virus, but 72A1 neutralized both viruses. MAbs 1B6 and 72A1 inhibited P3HR-1 virus release, as measured by the assay for infectious virus and by DNA hybridization analysis of released virus, but 2L10 had no such activity. 72A1 (but not 1B6) inhibited release of EBV from B95-8 cells. These experiments pointed to the presence of three different epitopes on gp350/220, identified with the respective MAbs and having varying involvement in virus neutralization and virus release inhibition.

Expression of the Epstein-Barr virus gp350/220 gene in rodent and primate cells

The gene encoding the Epstein-Barr virus envelope glycoproteins gp350 and gp220 was inserted downstream of the cytomegalovirus immediate-early, Moloney murine leukemia virus, mouse mammary tumor virus, or varicella-zoster virus gpI promoters in vectors containing selectable markers. Host cell and recombinant vector systems were defined which enabled the isolation of rodent or primate cell clones which expressed gp350/220 in substantial quantities. Continued expression of gp350/220 required maintenance of cells under positive selection for linked markers and periodic cloning. gp350/220 expressed in various host cells varied slightly in electrophoretic mobility, probably reflecting differences in glycosylation. Insertion of a stop codon into the gp350/220 open reading frame, upstream of the putative membrane anchor sequence, resulted in efficient secretion of truncated gp350 and gp220 from rat pituitary (GH3) cells. gp350/220 expressed in mammalian cells is highly immunogenic and elicits virus-neutralizing antibodies when administered to mice.

Epstein-Barr virus-associated malignancies

The infectious aspects of cancer in humans were epidemiologically pioneered by Dr. David Burkitt through his observations of lymphomatous tumors seen in children in equatorial Africa. Years, later, the Epstein-Barr virus (EBV) was shown to be intimately associated with such tumors and is now recognized as a component of some B-cell lymphomas and nasopharyngeal carcinoma. Still the questions of an active, passive, or accessory role persist. The ability of this virus to cause immunosuppressive hemopoietic disturbances in individuals infected with EBV but not developing cancer raise questions about host susceptibility, host immune response, and possible coconspiring, infectious, oncogenic agents. Recent associations of EBV antibody found in diseases, such as squamous cell carcinoma of the head and neck and acquired immunodeficiency syndromes, point to its possible accessory role as an immunosuppressive agent. The ability of EBV to spread by extracellular and intracellular mechanisms demonstrates its variable infectious potential. Numerous EBV-transformed human cell lines attest to its ability to confer "immortality" with uncontrolled growth patterns. This review critically examines the association of EBV with various malignancies, the type of evidence which links it there, and the implications for further investigations and therapy.

Inhibition of Epstein-Barr virus (EBV) release from the P3HR-1 Burkitt's lymphoma cell line by a monoclonal antibody against a 200,000 dalton EBV membrane antigen

In raising murine hybridoma antibodies against Epstein-Barr virus (EBV)-induced membrane antigens (MA), we found one antibody that blocked the release of infectious EBV from cultured P3HR-1 cells. This monoclonal antibody (mAb) recognized a 200 kD, phosphonoacetic acid-sensitive (late) MA, and did not directly neutralize virus without complement. When this mAb was added to 33 degrees C-cultured, spontaneously EBV-producing P3HR-1 cells, the intracellular expression of viral capsid antigen and infectious virus was not inhibited, but the appearance of infectious virus in the culture medium was significantly reduced. The duration of this suppression was dependent upon the concentration of the mAb, an effect being observed to a 1:4 X 10(5) titer of the ascites mAb preparation. A more acute effect of suppression of EBV release was observed in a second model of 12-o-tetradecanoyl phorbol-13-acetate and n-butyrate induction of EBV in 37 degrees C-cultured P3HR-1 cells. Again, intracellular infectious virus production was not inhibited, but the level of infectious virus in the culture medium was significantly reduced as early as 1 and 2 d of culture with antibody. This effect was reversed within 31 h after replacement of mAb-containing medium with fresh medium. This description of antibody-mediated inhibition of EBV release might lead to the characterization of another form of immune defense for the control of EBV infections.

Large-scale purification of Epstein-Barr virus membrane antigen gp340 with a monoclonal antibody immunoabsorbent

A purification method has been elaborated to isolate Epstein-Barr (EB) virus membrane antigen, gp340, in milligram amounts. The gp340 was prepared from detergent extracts of B95-8 cells by affinity chromatography with a monoclonal antibody immunoabsorbent. Bound material was eluted and the eluate, consisting of 50% gp340, was then fractionated by gel filtration. The final gp340 product was antigenically active and 95% pure. The purification method was found to be rapid and reproducible with no loss of the ability of the immunoabsorbent to retain gp340 after repeated elution. The procedure provides suitable material to permit the detailed structural analysis of gp340 necessary for both vaccine design and for the investigation of the role of gp340 in immunity to EB virus infection.

The Leeuwenhoek lecture, 1983. A prototype vaccine to prevent Epstein-Barr virus-associated tumours

EB virus is a herpesvirus that infects all human communities. The infection is life-long and usually asymptomatic. Excessive reaction to primary infection leads to infectious mononucleosis while immunological failures give fatal lymphoproliferative diseases. The virus is associated with endemic Burkitt's lymphoma and undifferentiated nasopharyngeal carcinoma. In world cancer terms Burkitt's lymphoma is insignificant, but nasopharyngeal carcinoma has a high incidence in certain important populations. By analogy with herpesvirus-induced animal cancers, prevention of infection should greatly reduce subsequent development of tumours. A prototype vaccine has therefore been produced based on the virus-determined antigen (MA gp340) that elicits virus-neutralizing antibodies. A sensitive assay has permitted the elaboration of an efficient antigen preparation method and the product has been rendered highly immunogenic, as tested in mice and rabbits, by incorporation in liposomes. The only animal suitable for experimental EB virus infection is the little-known cottontop tamarin; a breeding colony has been successfully established and protection against virus challenge assessed in immunized tamarins. The overall structure of the antigen has been determined in preparation for future production by synthesis or rDNA technology.

Production of monoclonal antibody to a late intracellular Epstein-Barr virus-induced antigen

A monoclonal antibody designated L2 was produced against a late intracellular protein induced by Epstein-Barr virus (EBV). This protein was expressed in cells producing virus but not in EBV genome-positive nonproducer cell lines, EBV genome-negative cell lines, or producer cultures cultivated in the presence of phosphonoacetic acid as determined by immunofluorescence. In addition, the antibody did not react with the membranes of infected cells indicating that it was not directed against an EBV-induced membrane antigen component. The monoclonal antibody was shown to recognize a glycoprotein with a molecular weight of approximately 125K by SDS-polyacrylamide gel electrophoresis. This glycoprotein was consistently found to be slightly larger when isolated from the P3HR-1 cell line as opposed to the B-95-8 cell line. A similar difference was also noted by comparison of peptide maps of this protein isolated by immunoaffinity chromatography from the two cell lines. Serological studies indicated that this 125K glycoprotein was a major component of the viral capsid-antigen (VCA) complex as defined by immunofluorescence.

Comparative immunogenicity studies on Epstein-Barr virus membrane antigen (MA) gp340 with novel adjuvants in mice, rabbits, and cotton-top tamarins

The effectiveness of immunisation of mice, rabbits, and cotton-top tamarins with small amounts of EB virus MA glycoprotein gp340 , incorporated into artificial liposomes, has been compared using various routes of injection with or without additional adjuvants. Liposomes containing gp340 gave specific high titre antibodies after i.p. or i.v. administration, and the addition of lipid A to the liposomes resulted in a significant enhancement of the response. Antibodies generated by the above procedure were virus neutralising and bound gp340 specifically. These findings indicate an advantageous approach for use with a prototype vaccine for the prevention of EB virus infection.

Synthesis and processing of the three major envelope glycoproteins of Epstein-Barr virus

In pulse-chase experiments, the three major Epstein-Barr virus envelope glycoproteins, gp350/300, gp250/200, and gp85, were shown to be synthesized from separate precursors of 190,000, 160,000, and 83,000 daltons, respectively. These three pulse-labeled species were chased into the mature forms of the glycoproteins between 1 and 3 h after transfer to nonradioactive medium. Digestion of precursor forms with endo-beta-N-acetylglucosaminidase H (endo H) yielded polypeptides of 160,000, 120,000, and 75,000 daltons. Comparison of these results with those from experiments with tunicamycin, which specifically blocks N-linked glycosylation, indicated that some other post-translational modification(s), probably O-linked glycosylation, contributes about 100,000 and 60,000 daltons of apparent molecular mass to gp350/300 and gp250/200, respectively. Experiments with endo H showed that mature gp350/300 and gp250/200 contain complex-type (endo H-resistant) N-linked glycosyl chains, whereas gp85 contains both high-mannose (endo H-sensitive)- and complex-type oligosaccharides. In contrast to the results obtained with the three envelope glycoproteins, no precursor forms of the two unglycosylated protein, p160 (the major Epstein-Barr virus capsid antigen) and p140 (an envelope protein), were detected. The partial proteolytic maps of gp350/300 and gp250/200 were quite similar, suggesting that polypeptide sequence homology could account for at least part of the observed serological cross-reactivity of the two proteins. Taken together, these results demonstrate that the polypeptide portions of gp350/300 and gp250/200 are closely related but not derived from a common precursor. Furthermore, the polypeptide portions comprise half or less of the apparent molecular weight of the mature glycoproteins on sodium dodecyl sulfate-polyacrylamide gel electrophoresis.

Purified Epstein-Barr virus Mr 340,000 glycoprotein induces potent virus-neutralizing antibodies when incorporated in liposomes

The purified Mr 340,000 glycoprotein component of Epstein-Barr (EB) virus-induced membrane antigen complex incorporated into liposomes was shown to be a potent immunogen in mice. High-titer antisera were induced that (i) are specific for membrane antigen components without absorption, (ii) bind the antigens induced by three different EB virus isolates, and (iii) neutralize the ability of the virus to transform fetal cord blood lymphocytes in vitro. The development of this immunogenic form of purified antigen provides an important step towards a potential subunit vaccine against Epstein-Barr virus infection.

Neutralization of lymphocyte immortalization by different strains of Epstein-Barr virus with a murine monoclonal antibody

A murine monoclonal antibody was raised against the B95-8 strain of Epstein-Barr virus (EBV), which was isolated from a case of mononucleosis after blood transfusion (Hoffman et al. Proc. Natl. Acad. Sci. U.S.A. 77:2979, 1980). We provide evidence that neutralization of immortalization by this monoclonal antibody is virus specific, since its potency was inversely related to the dose of challenge virus. Furthermore, the monoclonal antibody recognized antigens on viruses grown in human as well as in marmoset cells. We show that this monoclonal antibody neutralized three other transforming strains of EBV originating, respectively, from American patients with mononucleosis and fatal polyclonal lymphoma and from an African child with Burkitt lymphoma. However the antibody did not neutralize or detect antigens by immunofluorescence in the W91 strain of EBV. The hybridoma antibody did neutralize other EBV strains derived from the same Burkitt lymphoma cell line (Nyevu), as was the case with the W91 strain. This monoclonal antibody provides clear evidence of antigenic differences on the surface of EBVs and will ultimately prove useful in defining the antigenic site on EBV which elicits neutralizing antibody.

Quantification of an Epstein-Barr virus-associated membrane antigen component

A method is described for the preparation of a 125I-labelled membrane antigen (MA) component (gp340) from B95-8 cell membranes using sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE). Good yields of antigenic material were obtained when renaturation of the [125I]gp340 was carried out by removal of SDS in the presence of urea and subsequent removal of the urea. The availability of purified, radiolabelled gp340 has provided the essential basis for the development of a radioimmunoassay which, for the first time, permits quantification of this antigen. The assay has been used to demonstrate that cell membrane MA is a better source of gp340 for large-scale work than is the Epstein-Barr virus envelope and to measure the increase in expression of gp340 following treatment of cells with 12-O-tetradecanoyl-phorbol-13-acetate (TPA).

Identification and isolation of the main component (gp350-gp220) of Epstein-Barr virus responsible for generating neutralizing antibodies in vivo

The majority of hybridomas we have characterized against Epstein-Barr virions react with the major glycoproteins gp350 and gp220 (gp350/220). One of these antibodies, ID4C-1, neutralizes virus infection in vitro. The presence of gp350/220 on the viral envelope could be confirmed directly by immunoelectron microscopy. We used lectin affinity (ricin) and immunoaffinity (ID4C-1) to purify gp350/220 and show that this material is able to induce potent virus-neutralizing antibodies. Absorption of four human and one rabbit anti-Epstein-Barr virus sera with purified gp350/220 suggests that this is the primary component responsible for generating neutralizing antibodies in vivo.

Epstein-Barr virus induced proteins V: comparison of EBV-specific polypeptides from different virus strains

EBV-associated polypeptides induced in different Epstein-Barr Virus (EBV)-producing cell lines by the tumor promotor TPA, and from purified EBV particles derived from the same lines were radioactivity labeled and analyzed by immunoprecipitation with human VCA+MA+ sera. In virus-producing cells no significant differences in the molecular weight of 35S-methionine-labeled EBV-associated polypeptide patterns could be observed. The analysis 125I-labeled polypeptides from purified virus particles of four different strains revealed that, in addition to common polypeptides, individual EBV strains contain strain-specific high molecular weight glycopolypeptides. These polypeptides, constituting part of the membrane antigen complex, are present in varying amounts. While P3HR-1 virus particles contain a major component of 250 000 and small amounts of 340 000 molecular weight polypeptides, Q IMR-WIL virus particles have more 340 00 than 240 000 molecular weight polypeptides. Furthermore, in B95-8 particles and in particles from an EBV strain isolated from an African green monkey (AGM-EBV) respectively, large amounts of 360 000 and 250 000 polypeptides could be observed. Since these glycopolypeptides carry strain-, subgroup- and group-specific antigenic determinants, also found in virus strains produced in human and marmoset cells, it should be further investigated whether these differences in molecular weight are virus-strain- or cell-specific.

Monoclonal antibodies to Epstein-Barr virus-induced, transformation-associated cell surface antigens: binding patterns and effect upon virus-specific T-cell cytotoxicity

Spleen cells from mice immunized with Epstein-Barr virus-transformed lymphoblastoid cells (EB-LCL) were used to generate monoclonal antibodies to cell surface antigens associated with the EB virus-transformed state. Radioimmune and immunofluorescence binding assays identified two antibodies, MHM6 and AC2, which reacted consistently with all EB-LCL tested, with a subpopulation of cells in some but not all EB virus genome-positive Burkitt lymphoma lines, but with none of a range of EB virus genome-negative cell lines of lymphoma or leukaemia origin. While MHM6 appeared to bind an EB virus-related antigen, AC2 bound some other cell surface antigen which was also found on a small subpopulation of cells in lymphocyte cultures stimulated with phytohaemagglutinin or with pokeweed mitogen. MHM6 and AC2 recognized single polypeptides with apparent molecular weights of 45 kd and 80 kd respectively as shown by sodium dodecylsulphate polyacrylamide gel electrophoresis (SDS-PAGE) analysis of 125I-labeled cell surface polypeptides immunoprecipitated with these antibodies. These polypeptides were induced on experimentally-infected B cells within 24 h of the expression of the EB virus nuclear antigen, EBNA, at a time known to coincide with the appearance of the lymphocyte-detected membrane antigen, LYDMA. However, saturating concentration of MHM6 and AC2 were unable to protect EB-LCL target cells from lysis by LYDMA-specific cytotoxic T cells in a chromium-release assay.

Membrane antigen on Epstein--Barr virus-infected human B cells recognized by a monoclonal antibody

This paper describes a monoclonal antibody (B532) that detects a membrane antigen present on greater than or equal to 95% of the B cells from lines carrying the Epstein-Barr virus (EBV) genome. Evidence suggesting that B532 is EBV-related was originally obtained by using a cell-binding radioassay with different cell line substrates. Immunofluorescence and cell-sorter analysis confirmed that the antigen was present in high density on all EBV-infected lymphoblastoid B-cell lines, but not on EBV-negative B-, T-, myeloid, or null cell lines. Isolated normal peripheral blood B and T lymphocytes and monocytes failed to bind B532. The monoclonal antibody did not inhibit in vitro EVB infection nor did it block the killing of EBV-infected targets by cytotoxic T lymphocytes. The cell surface antigen recognized by B532 was shown by immunoprecipitation to have a molecular weight of approximately 45,000.

Production and characterization of monoclonal antibodies against the Epstein-Barr virus membrane antigen

Five murine hybridoma lines that produce monoclonal antibodies against Epstein-Barr virus membrane antigen (MA) were established. Immunoprecipitation experiments demonstrated that three of the antibodies precipitated both the 236,000 (236K) MA and the 212K MA. The other two antibodies precipitated the 86K MA. Antibodies against the 236K-212K MA and the 86K MA mediated complement-dependent cytolysis of Epstein-Barr-virus-infected cells. The antibodies against the 86K MA neutralized both the B95-8 and P3HR-1 viruses.

Identification of Epstein-Barr virus strain differences with monoclonal antibody to a membrane glycoprotein

Two monoclonal antibodies directed against Epstein--Barr virus (EBV)-induced membrane antigens (MA) were isolated in this study. On of the monoclonal antibodies, designated 2F5.6, was an IgG2 which, as detected by membrane and fixed cell immunofluorescence, reacted with MA-positive lymphoblastoid cell lines that produced transforming EBV but not with the MA-positive P3HR-1 cell line that produced the lytic, nontransforming strain of this virus. This antibody precipitated the Mr 320,000/350,000 glycoprotein from B-95 virus infected cultures and the Mr 300,000 and 220,000/250,000 glycoproteins from Raji cells superinfected with P3HR-1 virus but did not precipitate any of these EBV-specific glycoproteins from the P3HR-1 cell line. In contrast, the second monoclonal antibody, IgM designated B10.3, reacted with all virus-producing cell lines including the P3HR-1 cell line. The identity of the glycoprotein that serves as the target for this antibody is still unknown. Neither antibody had neutralizing activity against the B-95 or P3HR-1 strain of EBV. These results indicated that the 2F5.6 monoclonal antibody was directed against an antigenic determinant on the major membrane glycoprotein which is common to transforming strains of EBV but absent from the lytic P3HR-1 stain whereas the B10.3 monoclonal antibody was directed against a group-specific EBV-induced membrane determinant.

Identification of an Epstein-Barr virus nuclear antigen by fluoroimmunoelectrophoresis and radioimmunoelectrophoresis

A 65,000-dalton (65K) antigen found in Raji cells by fluoroimmunoelectrophoresis and radioimmunoelectrophoresis has been identified as an Epstein-Barr virus nuclear antigen (EBNA). This identification is based on the following evidence. The 65K antigen is detected in Raji cells but not in three Epstein-Barr virus (-) human B cell lines. It is not detected with EBNA (-) sera. The 65K antigen is found predominantly in the nucleus and co-elutes with EBNA during partial purification by DNA-Sepharose and Blue Dextran-Sepharose chromatography. Finally, the partially purified 65K antigen is an effective absorbant of EBNA antibody as measured in an anticomplement immunofluorescence assay. Antigens with molecular weights of 72, 70, and 73K have been detected in B95-8, P3HR-1, and Namalwa cells, respectively. These antigens are the likely homologues of the 65K Raji EBNA. In addition, an Epstein-Barr virus-associated, 81K DNA-binding antigen has been detected in both B95-8 and Raji cells.

Reactivation of Epstein-Barr virus-specific cytotoxic T cells by in vitro stimulation with the autologous lymphoblastoid cell line

Unfractionated mononuclear (UM) cells and T cells freshly prepared from the blood of adult donors were co-cultivated in microtest plate wells with progressively lower numbers of cells from the autologous EB-virus-transformed B-cell line. The fresh cells present in co-cultures from EB virus antibody-negative (seronegative) donors regularly facilitated autologous cell line outgrowth, monitored after 4 weeks, whereas outgrowth was markedly inhibited in the corresponding co-cultures from seropositive donors. Larger-scale co-cultures, set up at a ratio of 80-100 fresh UM cells to one autologous virus-transformed B cell, were harvested after 8 to 12 days and the T-cell subpopulation was examined for cytotoxicity both by growth inhibition and by chromium release assays. Cytotoxic T cells were generated exclusively in seropositive donor co-cultures and were strongly active against the autologous virus-transformed cell line without affecting either autologous uninfected B cells or any of a range of EB virus genome-negative target cell lines chosen as sensitive indicators of non-specific cytotoxicity. Recognition of allogeneic EB-virus-transformed cells was restricted to those whose HLA-A and/or B and/or B and/or C antigen expression matched that of the effector cells themselves;; moreover target cell lysis was specifically inhibited in the presence of monoclonal antibodies binding to these HLA antigens. The results indicate that EB-virus-specific HLA-restricted memory T cells, present in the blood of previously-infected individuals, can be reactivated in vitro using the established autologous virus-transformed cell line as a stimulus. THe reactivated cytotoxic cells appear to recognize a virus-induced lymphocyte-detected membrane antigen, LYD-MA, analogous to that first invoked to explain the cytotoxic response to primary EB virus infection observed during infectious monoucleosis.