Epstein–Barr virus (EBV) is the first identified human oncogenic virus that can establish asymptomatic life-long persistence. EBV is an oncogenic herpesvirus associated with various neoplastic diseases, such as lymphoproliferative diseases in immunocompromised patients, various lymphomas and epithelial cancers. An EBV prophylactic vaccine holds great promise for prevention of EBV associated cancers such as Burkitt’s lymphoma (BL), Hodgkin lymphoma (HL), Post-transplant lymphoproliferative disorder (PTLD), Nasopharyngeal cancer (NPC), and Gastric cancer (GC), and would also be the most cost-effective approach for the management of infectious mononucleosis (IM) as well as EBV associated autoimmune disease such as Multiple sclerosis (MS).
Fig. 1 Schematic presentation of Epstein-Barr virus.
(Houen G, Trier NH. Front Immunol. 2021)
Epstein–Barr virus (or human herpesvirus 4 (HHV-4)), is a member of the γ-herpesviruses family. EBV has a linear, double-stranded DNA genome that is approximately 170 kilobase pairs in length, which encodes more than 80 proteins and 46 functional small untranslated RNAs.
EBV has an outer lipid envelope, derived from the producing host cell, wherein several viral proteins are embedded in addition to host cell-derived membrane proteins. Many of the viral envelope membrane proteins are glycoproteins (gPs). Currently, 13 gPs have been identified, 12 of which are expressed only during the productive, lytic replication cycle and one of which (BARF1, a decoy viral colony-stimulating factor 1 receptor (vCSF1R)) may be expressed during latency as well. Inside the envelope is the viral tegument, in which the capsid is embedded with its enclosed genome and associated proteins.
Fig 2. EBV entry and infection of target cells.
(Cui X, Snapper CM. Front Immunol. 2021)
The life cycle of EBV is composed of primary infection, latency, and lytic reactivation phases. In addition, EBV has an ability to infect several cell types. The target cells of EBV are B lymphocytes and epithelial cells. EBV envelope glycoproteins gH/gL, gB and gp350 play key roles in EBV infection of target cells, where gH/gL and gB constitute the "core fusion machinery" mediating fusion with the cell membrane. The native conformation of gB is a trimer, and gH and gL naturally form a heterodimer. Envelope proteins gH/gL and gB are essential for EBV infection of both B cells and epithelial cells, whereas gp350 is important for efficient infection of B cells.
EBV has evolved a multitude of immune evasion mechanisms, including wrapping itself in host cell-derived membranes (envelopment) and the ability to switch between latent and lytic life stages. Most of the immune evasion proteins of EBV are expressed during the lytic cycle. Many EBV proteins serve two or more functions.
Firstly, glycoproteins, present on the surface of viruses and virus-infected cells, have typically been primary candidates for development of vaccines to prevent infection and/or disease. gp350 is a type I membrane protein and is important for efficient infection of B cells in vitro. gH/gL and gB are essential for herpesvirus infection of cells and gp42 is required for EBV entry into B cells. Secondly, more recent studies show that multiple lytic proteins including BMLF1 (a post-transcriptional regulatory protein), BMRF1 (polymerase-associated processivity factor), BNRF1 (the major tegument protein), BORF1 (DNA packaging protein), BcLF1 (major capsid protein), and BXLF1 (thymidine kinase) are targets of CD4 cells. Lastly, several epitopes within EBNA2 induce immunodominant CD8 T cell responses, and that EBNA-2 CD8 T cells recognize EBV infected B cells within one day after virus infection of B cells before CD8 T cells that recognize other latent proteins. EBNA-2 and EBNA-LP are also targets of CD4 T cells.
A prophylactic EBV vaccine uses the strategies to induce antibody response mainly neutralizing antibodies to block EBV infection of its target cells, whereas non-neutralizing antibodies as well as cell mediated immune response further improve prophylactic efficacy. Therapeutic EBV vaccines aim at boosting the existing or inducing novel antiviral adaptive immune responses in patients with EBV-associated cancers.
Early efforts in EBV vaccine development were focused on gp350, but gp350-induced antibodies do not protect epithelial cells from EBV infection. Recombinant EBV gH/gL and gB proteins induced markedly higher EBV neutralizing antibodies compared to gp350, where a trimeric form of gH/gL and a tetrameric form of gp350 elicited significantly higher EBV neutralizing activities compared to their monomeric counterparts. The combination of EBV gH/gL, gB and gp350 could be an ideal EBV prophylactic vaccine that can elicit markedly high synergistic EBV neutralizing activity with the potential to induce sterilizing immunity. EBV gp350, gH, gL, and gB can also induce CD4+ and CD8+ T cell immune responses, and have demonstrated to inhibit proliferation of EBV-infected primary B cells.
The first successful EBV VLPs were created by the deletion of the EBV terminal repeats, and potential oncogenes namely EBNA2, 3A, 3B and 3C, LMP1 and BZLF1. Later, the viral packaging and nuclear egress proteins BFLF1/BFRF1A were further deleted to improve safety. More immunogenic EBV VLPs were made by fusing latent antigens EBNA1 and EBNA3C to the major tegument protein BNRF1 of EBV. The EBV VLPs produced were able to stimulate potent CD4+ T cell responses against structural as well as latent EBV protein epitopes, and reduced EBV loads in the peripheral blood of humanized mice after immunization.
The rapid and successful development of synthesized mRNA vaccines against SARS-CoV2 has encouraged the development of synthesized mRNA EBV vaccines. After demonstrating its mRNA vaccine candidate encoding gp350, gB, gH/gL and gp42 induced significantly higher EBV neutralizing titers in mice compared to human sera, Moderna has initiated phase I clinical trial of its mRNA EBV vaccine.
The viral vector vaccine platform has mainly been used for the development of therapeutic EBV vaccines. The targets of EBV therapeutic vaccines are focused on EBNA1, LMP2 and/or LMP1. One of the approaches used a recombinant adenoviral vector to deliver LMP2 antigen, and demonstrated a dose dependent increase in the proportion of LMP2-specific CD3+ CD4+ cells in the peripheral blood of immunized NPC patients in a clinical trial. A modified vaccinia ankara (MVA) expressing the carboxyl terminus of EBNA1 and full-length LMP2 as a fusion protein (MVA-EL) was shown to efficiently expand the EBNA1- and LMP2-specific CD4+ and CD8+ T cells from the peripheral blood lymphocytes of seropositive healthy donors. Recombinant viral vector vaccines can deliver a wide range of epitopes, but the anti-viral vector immune responses elicited after repeated immunizations are a big obstacle, which could markedly decrease the efficacy of viral vector vaccines.
References
| Cat. No | Product Name | Expression System | Application | |
| DAG3084 | Native EBV VCA gp 125 | Human B cells | WB, ELISA | Inquiry |
| DAGA-3074 | Recombinant EBV p18 (BFRF3) Protein [His] | E. coli | WB, ELISA | Inquiry |
| DAG1584 | Recombinant EBV p23 (BLRF2) Protein [His] | E. coli | WB, ELISA | Inquiry |
| DAG-T2771 | Recombinant EBV p54 [His] | E. coli | WB, ELISA | Inquiry |
| DAG-T2772 | Recombinant EBV p138 [His] | E. coli | WB, ELISA | Inquiry |
| DAG1578 | Recombinant EBV p72 (EBNA1) [His] | E. coli | WB, ELISA | Inquiry |
| DAGA-3072 | Recombinant EBV gp350/220 [His] | HEK293 cells | WB, ELISA | Inquiry |
| DAG2018 | Recombinant EBV gH (Ectodomain) [His] | HEK293 cells | WB, ELISA | Inquiry |
| DAG2019 | Recombinant EBV gH, gp42 (Ectodomain) [His] | HEK293 cells | WB, ELISA | Inquiry |
