Cytomegalovirus is the leading infectious cause of birth defects which can result in deafness and mental retardation in neonates, and can cause severe viral pneumonia and colitis in transplant recipients and sight-threatening retinitis in patients with AIDS. Epstein-Barr virus (EBV) causes infectious mononucleosis and is associated with a number of cancers including Burkitt lymphoma, nasopharyngeal carcinoma, Hodgkin lymphoma, and post-transplant lymphoproliferative disease. Human CMV and EBV naturally infect humans, but not small animals or nonhuman primates. The best models currently available for CMV and EBV are rhesus monkey CMV and EBV. The goal of this study is to develop an effective vaccine for these rhesus viruses and to use these as a model for vaccines for their human counterparts. We are using various approaches including soluble recombinant proteins, recombinant virus vectors expressing viral proteins, and replication defective viruses as vaccines. We have been using an animal model, rhesus monkey EBV in rhesus macaques, to compare various candidate EBV vaccines. Rhesus EBV causes a similar disease in monkeys as EBV does in humans and the viruses have the same number of virus genes that have virtually the same activities. Last year we reported the results of a vaccine trial using a candidate rhesus EBV vaccine in rhesus macaques. We compared the ability of soluble rhesus EBV glycoprotein gp350 with virus-like replicon particles that express rhesus EBV gp350, rhesus EBV EBNA-3A, and rhesus EBV EBNA-3B. The soluble glycoprotein induced high levels of antibody to the virus, while the EBNA-3 proteins induced potent T cell responses. After challenge of the animals with wild-type rhesus EBV, animals vaccinated with soluble rhesus EBV gp350 showed the best level of protection followed by animals that received VRPs expressing rhesus EBV gp350, EBNA-3A, and EBNA-3B as assessed by seroconversion or levels of rhesus EBV DNA or RNA in the blood shortly after challenge. At 2 years after challenge, animals that received gp350 that became infected had lower levels of rhesus EBV DNA in the blood compared with those receiving the other vaccines. Since the level of EBV DNA in the blood is predictive for EBV lymphomas in transplant patients, the ability of gp350 to reduce the level of EBV in the blood of rhesus macaques after infection suggests that this vaccine might have a role in reducing certain EBV-associated cancers. Thus, the initial response to virus challenge may be predictive of the viral load years after vaccination. We are currently studying vaccines to other rhesus EBV glycoproteins and will be immunizing animals with these vaccines and comparing them to the soluble rhesus EBV gp350 vaccine. We have also developed a candidate vaccine virus for rhesus CMV in which we deleted a protein from the virus that is essential for virus growth. The resulting replication-defective virus lacks one viral protein, glycoprotein L (gL), and replicates only in cells expressing rhesus CMV gL. In addition, noncomplementing cells infected with the replication-defective rhesus CMV produced glycoprotein B, the major target of neutralizing antibodies, at levels similar to those observed in cells infected with wild-type virus. We are testing this candidate vaccine in rhesus monkeys. A better understanding of the immune response is required to prevent and control virus infections and should help in the design of vaccines against herpesviruses. We studied a woman with a history of disseminated cytomegalovirus and a very severe herpes simplex virus 2 of the perineum which was not responsive to multiple antiviral medications. She was found to have a mutation in GATA2, a transcription factor which is critical for myeloid cell development and which is associated with low levels of monocytes, B cells, and natural killer cells. We found that our patient had impaired NK cell function in the presence or absence of IL-2. We treated the patient with interferon-alpha which resulted in an increase in the number of NK cells and partially restored the ability of the NK cells to kill target cells. However, interferon-alpha did not correct the low number of NK-bright cells (the less differentiated form of NK cells). The patient's severe herpes simplex virus infection persisted, despite interferon-alpha therapy. Thus, while interferon-alpha increased the number of NK cells and partially improved their function, interferon-alpha did not correct the defect in NK cell development.
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