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

Demonstration in vitro of cell mediated immunity to Epstein-Barr virus in cotton-top tamarins.

In the course of developing an effective Epstein-Barr (EB) virus vaccine, the immune responses in cotton-top tamarins to a tumourigenic dose of EB virus were studied. Cell mediated responses were measured using a tissue culture 'growth inhibition' assay where peripheral blood lymphocytes were tested for their ability to inhibit the outgrowth of autologous EB virus transformed lymphoblastoid cells. This system has previously been recognized as a very sensitive assay for detecting cell-mediated responses to EB virus in man. Using this assay no cell-mediated immunity was detected up to the time of death in two tamarins following injection with a tumourigenic dose of EB virus. However, two other animals which had recovered from tumours induced by a first dose of EB virus 18 months previously when subsequently re-stimulated with a second tumourigenic dose did exhibit cell-mediated responses. These latter animals remained healthy following the re-challenge and did not show evidence of EB virus-induced disease