Biologic and antigenic characteristics of Epstein-Barr virus-related Herpesviruses of chimpanzees and baboons

Treatment Options for Epstein-Barr Virus-Related Disorders of the Central Nervous System

Epstein-Barr virus (EBV), a causative agent for several types of lymphomas and mucosal cancers, is a human lymphotropic herpesvirus with the capacity to establish lifelong latent infection. More than 90% of the human population worldwide is infected. The primary infection is usually asymptomatic in childhood, whereas infectious mononucleosis (IM) is common when the infection occurs in adolescence. Primary EBV infection, with or without IM, or reactivation of latent infection in immunocompromised individuals have been associated with a wide range of neurologic conditions, such as encephalitis, meningitis, acute disseminated encephalomyelitis, and cerebellitis. EBV is also involved in malignant lymphomas in the brain. An increasing number of reports on EBV-related disorders of the central nervous system (CNS) including the convincing association with multiple sclerosis (MS) have put in focus EBV-related conditions beyond its established link to malignancies. In this review, we present the clinical manifestations of EBV-related CNS-disorders, put them in the context of known EBV biology and focus on available treatment options and future therapeutic approaches.

Non-human Primate Lymphocryptoviruses: Past, Present, and Future

Epstein-Barr virus (EBV) orthologues from non-human primates (NHPs) have been studied for nearly as long as EBV itself. Cross-reactive sera and DNA hybridization studies provided the first glimpses of the closely related herpesviruses that belonged to the same gamma-1 herpesvirus, or lymphocryptovirus, genus, as EBV. Over the years, detailed molecular and sequence analyses of LCVs that infect humans and other NHPs revealed similar colinear genome structures and homologous viral proteins expressed during latent and lytic infection. Despite these similarities, experimental infection of NHPs with EBV did not result in acute symptoms or persistent infection as observed in humans, suggesting some degree of host species restriction. Genome sequencing and a molecular clone of an LCV isolate from naturally infected rhesus macaques combined with domestic colonies of LCV-naïve rhesus macaques have opened the door to a unique experimental animal model that accurately reproduces the normal transmission, acute viremia, lifelong persistence, and immune responses found in EBV-infected humans. This chapter will summarize the advances made over the last 50 years in our understanding of LCVs that naturally infect both Old and New World NHPs, the recent, groundbreaking developments in the use of rhesus macaques as an animal model for EBV infection, and how NHP LCVs and the rhLCV animal model can advance future EBV research and the development of an EBV vaccine.

Host Range Restriction of Epstein-Barr Virus and Related Lymphocryptoviruses

Epstein-Barr-related herpesviruses, or lymphocryptoviruses (LCV), naturally infect humans and nonhuman primates (NHP), but their host range is not well characterized. Using LCV and B cells from multiple species of Hominidae and Cercopithecidae, we show that LCV can immortalize B cells from some nonnative species but that growth transformation is restricted to B cells from their own family of hominoids or Old World NHP, suggesting a high degree of LCV adaptation to their natural primate host.

An examination of chimpanzee use in human cancer research

Advocates of chimpanzee research claim the genetic similarity of humans and chimpanzees make them an indispensable research tool to combat human diseases. Given that cancer is a leading cause of human death worldwide, one might expect that if chimpanzees were needed for, or were productive in, cancer research, then they would have been widely used. This comprehensive literature analysis reveals that chimpanzees have scarcely been used in any form of cancer research, and that chimpanzee tumours are extremely rare and biologically different from human cancers. Often, chimpanzee citations described peripheral use of chimpanzee cells and genetic material in predominantly human genomic studies. Papers describing potential new cancer therapies noted significant concerns regarding the chimpanzee model. Other studies described interventions that have not been pursued clinically. Finally, available evidence indicates that chimpanzees are not essential in the development of therapeutic monoclonal antibodies. It would therefore be unscientific to claim that chimpanzees are vital to cancer research. On the contrary, it is reasonable to conclude that cancer research would not suffer, if the use of chimpanzees for this purpose were prohibited in the US. Genetic differences between humans and chimpanzees, make them an unsuitable model for cancer, as well as other human diseases.

Genetic diversity and molecular evolution of human and non-human primate Gammaherpesvirinae

The Gammaherpesvirinae sub-family is divided into two genera: Lymphocryptovirus and Rhadinovirus. Until the middle of the 1990s, the Rhadinovirus genus was only represented by Herpesvirus saimiri and Herpesvirus ateles, which infect New World monkey species. Until the year 2000, Epstein-Barr virus (EBV), the human prototype of the Lymphocryptovirus, and simian homologues had only been detected in humans and Old World non-human primates. It was thought, therefore, that the separation of the continents had resulted in drastic changes in Gammaherpesvirinae evolution. The discovery of Kaposi's sarcoma-associated herpesvirus in humans, belonging to the Rhadinovirus, followed by the identification of CalHV3 (Callitrichine herpesvirus 3), a lymphocryptovirus of the marmoset, challenged this paradigm. The description of numerous viruses belonging to this sub-family from various Old and New World primate species enabled a cospeciation hypothesis for these viruses and their hosts to be developed. This review focuses on the current knowledge of primate Gammaherpesvirinae genetic diversity and molecular evolution. We discuss the various theories based on current genetic data regarding evolutionary relationships between lymphocryptoviruses of Old World primates, the use of these data as a tool to study evolutionary relationships between New World monkey species, and the possible existence of a ninth human herpesvirus belonging to the Rhadinovirus genus.

Prevalence and molecular characterization of the polymerase gene of gibbon lymphocryptovirus

BACKGROUND

Lymphocryptovirus (LCV) is found in various non-human primates. As a herpesvirus naturally infecting gibbons it is closely related to human Epstein-Barr virus (EBV) with which it shares considerable genetic, biological and epidemiologic features.

METHODS

We collected blood samples from 70 gibbons (51 Hylobates lar, 18 Hylobates pileatus and 1 Hylobates agilis) for further separation into serum and peripheral blood mononuclear cells (PBMC).

RESULTS

Only 13 of 70 (18.6%) sera were serologically positive for human EBV IgG but 64 of 70 (91.4%) PBMCs yielded the partial LCV DNA polymerase gene by semi-nested PCR, which we subjected to direct sequencing. All sequences showed 84% nucleic acid and 91% amino acid identity to human EBV. Phylogenetic tree analysis demonstrated gibbon LCVs clustered separately from other gammaherpesvirinae but closely related to LCV of other species.

CONCLUSIONS

Based on LCV DNA detection, we discovered a high prevalence of LCV infection among gibbons. Further characterization of non-human primate LCV might thus provide new insight into both evolution and pathogenicity of gammaherpesvirinae.

Orangutan herpesvirus

A male orangutan suffered from ulcers at the buccal mucosa. We obtained swab fluid from the base of both vesicles and ulcers and collected blood for further separation into serum, plasma and peripheral blood mononuclear cells (PBMC) for detection of antibody to herpesvirus by serology and herpesvirus DNA by polymerase chain reaction (PCR) using consensus degenerate primers. Serology was positive for human EBV IgG but negative for Epstein-Barr virus (EBV) immunoglobulin (IgM), as well as for both human cytomegalovirus and herpes simplex virus IgG and IgM. Upon PCR, we obtained a 232-bp product of virus DNA from PBMC, but not from lesions, serum or plasma. We confirmed the positive result by direct sequencing and compared the nucleotide sequence with other nucleotide sequences applying the BLAST program from GenBank. The sequence was similar to lymphocryptovirus of macaque (93%), marmoset (93%), gorilla (90%) and human EBV (90%). We aligned this sequence with other sequences in GenBank and performed phylogenetic analysis, showing that it probably belongs to the gammaherpesvirus group.

Species-specific transformation of T cells by HV(MNE)

HV(MNE) is an Epstein-Barr virus (EBV)-like lymphocryptovirus (LCV) originally isolated from a Macaca nemestrina with CD8(+) T cell mycosis fungoides/cutaneous T cell lymphoma (Blood 98 (2001), 2193). HV(MNE) transforms rabbit T cells in vitro and causes T cell lymphoma in New Zealand white rabbits. Here we demonstrate that HV(MNE) also immortalizes T cells from mustached tamarins but not those from owl monkeys, common marmosets, squirrel monkeys, black-capped capuchins, and humans. Cytogenetic and FACS analysis revealed the true origin and T cell lineage of the transformed tamarin T cell lines. Tamarin T cells contained HV(MNE) DNA sequence and displayed a decreased requirement for the IL-2 cytokine for growth. Thus, this EBV-like virus from M. nemestrina differs from the other EBV-like viruses found in nonhuman primates inasmuch as it appears to preferentially transform T cells.

Transcriptional regulatory properties of Epstein-Barr virus nuclear antigen 3C are conserved in simian lymphocryptoviruses

Epstein-Barr virus (EBV) nuclear antigen 3C (EBNA-3C) is a large transcriptional regulator essential for EBV-mediated immortalization of B lymphocytes. We previously identified interactions between EBNA-3C and two cellular transcription factors, J kappa and Spi proteins, through which EBNA-3C regulates transcription. To better understand the contribution of these interactions to EBNA-3C function and EBV latency, we examined whether they are conserved in the homologous proteins of nonhuman primate lymphocryptoviruses (LCVs), which bear a strong genetic and biological similarity to EBV. The homologue of EBNA-3C encoded by the LCV that infects baboons (BaLCV) was found to be only 35% identical in sequence to its EBV counterpart. Of particular significance, this homology localized predominantly to the N-terminal half of the molecule, which encompasses the domains in EBNA-3C that interact with J kappa and Spi proteins. Like EBNA-3C, both BaLCV and rhesus macaque LCV (RhLCV) 3C proteins bound to J kappa and repressed transcription mediated by EBNA-2 through its interaction with J kappa. Both nonhuman primate 3C proteins were also able to activate transcription mediated by the Spi proteins in the presence of EBNA-2. Like EBNA-3C, a domain encompassing the putative basic leucine zipper motif of the BaLCV-3C protein directly interacted with both Spi-1 and Spi-B. Surprisingly, a recently identified motif in EBNA-3C that mediates repression was not identifiable in the BaLCV-3C protein. Finally, although the C terminus of BaLCV-3C bears minimal homology to EBNA-3C, it nonetheless contains a C-terminal domain rich in glutamine and proline that was able to function as a potent transcriptional activation domain, as does the C terminus of EBNA-3C. The conservation of these functional motifs despite poor overall homology among the LCV 3C proteins strongly suggests that the interactions of EBNA-3C with J kappa and Spi do indeed play significant roles in the life cycle of EBV.

Characterization of the Cyno-EBV LMP1 homologue and comparison with LMP1s of EBV and other EBV-like viruses

EBV latent membrane protein 1 (LMP1) is essential for EBV-mediated transformation and has been associated with several cases of malignancies. EBV-like viruses in Cynomolgus monkeys (Macaca fascicularis) have been associated with high lymphoma rates in immunosuppressed monkeys. In the study, the entire coding region of the Cyno-EBV LMP1 gene was cloned, sequenced and expressed in human embryonic kidney (HEK) cells 293. The Cyno-EBV LMP1 homologue sequence predicted a 588 amino acid (a.a.) protein with a short 19 a.a. N-terminus, six transmembrane domains and a long carboxy tail of 404 a.a. The protein contained a series of seven 9 a.a.-tandem repeats and two 20 a.a.-repeats, which harbored two potential TRAF binding motifs, PxQxT/S. These repeats shared no homology with the repeats in any other LMP1. However, the proline-rich sequence GPxxPx(6) found within the 11 a.a.-repeats of EBV LMP1 was conserved in Cyno-EBV carboxy tail and contained two consensus JAK/STAT sequences PxxPxP. A cluster of eight histidine residues was found in proximity to the last transmembrane domain of Cyno-EBV LMP1 and was exploited as a natural protein tag in expression studies. Western blot analysis revealed a major polypeptide of 110 kDa. Comparative functional studies showed that Cyno-EBV LMP1 expressed in HEK 293 cells shares the same ability as EBV LMP1 to induce NFkappaB driven CAT activity.

HV(MNE), a novel lymphocryptovirus related to Epstein-Barr virus, induces lymphoma in New Zealand White rabbits

HV(MNE) is a novel Epstein-Barr (EBV)-like virus isolated from a Macaca nemestrina with CD8(+) T-cell mycosis fungoides-cutaneous T-cell lymphoma. Here it is demonstrated that intravenous inoculation of irradiated HV(MNE)-infected T cells or cell-free virus from the J94356(PBMC) cell line in New Zealand White rabbits results in seroconversion to the viral capsid antigen (VCA) of EBV; all animals that seroconverted to VCA developed malignant lymphoma within months of inoculation. In contrast, control rabbits, inoculated with heat-inactivated culture supernatants from the same cell line, failed to seroconvert to VCA and did not develop disease. Disseminated lymphoma cells of mixed origin were detected in most vital organs, including the spleen, liver, lungs, kidneys, and heart of the affected rabbits. Neoplastic infiltrates were also observed in lymph nodes, thymus, skin, and subcutaneous tissues. HV(MNE) DNA and EBV-like RNA expression was demonstrated in the lymphomatous organs and in 2 transformed T-cell lines, one established from the lymph node and the other from the blood of the 2 lymphomatous animals. Analysis of one of these T-cell lines demonstrated the persistence of HV(MNE) DNA, expression of an LMP1-like protein, and acquisition of interleukin-2 independence, and constitutive activation of the Jak/STAT pathway. Thus, HV(MNE) in rabbits provides a valuable animal model for human T-cell lymphoma whereby genetic determinants for T-cell transformation by this EBV-like animal virus can be studied.

Simian homologues of Epstein-Barr virus

Gamma-herpesviruses closely related to the Epstein-Barr virus (EBV) are known to naturally infect Old World non-human primates and are classified in the same lymphocryptovirus (LCV) genera. LCV infecting humans and Old World primates share similar biology, and recent studies have demonstrated that these viruses share a similar repertoire of viral genes. Surprisingly, the latent infection genes associated with cell growth transformation demonstrate the most striking sequence divergence, but the functional mechanisms for these genes are generally well conserved. The recent discovery of LCVs naturally infecting New World primates has rewritten the old paradigm of LCV host range restriction to humans and Old World non-human primates, so that these viruses are more widespread than previously believed. However, the New World LCV genome has significant and interesting differences from EBV and other Old World LCVs despite similar biological properties. Thus, the simian homologues of EBV can provide an important animal model for studying LCV pathogenesis, and the similarities and differences that have evolved among these related viruses can provide a unique perspective towards a better understanding of EBV.

Amino acids of Epstein-Barr virus nuclear antigen 3A essential for repression of Jkappa-mediated transcription and their evolutionary conservation

Epstein-Barr virus (EBV) nuclear antigen 3A (EBNA-3A) is essential for virus-mediated immortalization of B lymphocytes in vitro and is believed to regulate transcription of cellular and/or viral genes. One known mechanism of regulation is through its interaction with the cellular transcription factor Jkappa. This interaction downregulates transcription mediated by EBNA-2 and Jkappa. To identify the amino acids that play a role in this interaction, we have generated mutant EBNA-3A proteins. A mutant EBNA-3A protein in which alanine residues were substituted for amino acids 199, 200, and 202 no longer downregulated transcription. Surprisingly, this mutant protein remained able to coimmunoprecipitate with Jkappa. Using a reporter gene assay based on the recruitment of Jkappa by various regions spanning EBNA-3A, we have shown that this mutation abolished binding of Jkappa to the N-proximal region (amino acids 125 to 222) and that no other region of EBNA-3A alone was sufficient to mediate an association with Jkappa. To determine the biological significance of the interaction of EBNA-3A with Jkappa, we have studied its conservation in the simian lymphocryptovirus herpesvirus papio (HVP) by cloning HVP-3A, the homolog of EBNA-3A encoded by this virus. This 903-amino-acid protein exhibited 37% identity with its EBV counterpart, mainly within the amino-terminal half. HVP-3A also interacted with Jkappa through a region located between amino acids 127 and 223 and also repressed transcription mediated through EBNA-2 and Jkappa. The evolutionary conservation of this function, in proteins that have otherwise significantly diverged, argues strongly for an important biological role in virus-mediated immortalization of B lymphocytes.

Structural, functional, and genetic comparisons of Epstein-Barr virus nuclear antigen 3A, 3B, and 3C homologues encoded by the rhesus lymphocryptovirus

EBNA-3A, -3B, and -3C are three latent infection nuclear proteins important for Epstein-Barr virus (EBV)-induced B-cell immortalization and the immune response to EBV infection. All three are hypothesized to function as transcriptional transactivators, but little is known about their precise mechanism of action or their role in EBV pathogenesis. We have cloned and studied the three EBNA-3 homologues from a closely related lymphocryptovirus (LCV) which naturally infects rhesus monkeys. The rhesus LCV EBNA-3A, -3B, and -3C homologues have 37, 40, and 36% amino acid identity with the EBV genes, respectively. Function, as measured by in vitro assays, also appears to be conserved with the EBV genes, since the rhesus LCV EBNA-3s can interact with the transcription factor RBP-Jkappa and the rhesus LCV EBNA-3C encodes a Q/P-rich domain with transcriptional activation properties. In order to better understand the relationship between these EBV and rhesus LCV latent infection genes, we asked if the rhesus LCV EBNA-3 locus could be recombined into the EBV genome and if it could substitute for the EBV EBNA-3s when assayed for human B-cell immortalization. Recombination between the EBV genome and rhesus LCV DNA was reasonably efficient. However, these studies suggest that the rhesus LCV EBNA-3 locus was not completely interchangeable with the EBV EBNA-3 locus for B-cell immortalization and that at least one determinant of the species restriction for LCV-induced B-cell immortalization maps to the EBNA-3 locus. The overall conservation of EBNA-3 structure and function between EBV and rhesus LCV indicates that rhesus LCV infection of rhesus monkeys can provide an important animal model for studying the role of the EBNA-3 genes in LCV pathogenesis.

Strong selective pressure for evolution of an Epstein-Barr virus LMP2B homologue in the rhesus lymphocryptovirus

Latent membrane protein 2B (LMP2B) is expressed during latent Epstein-Barr virus (EBV) infection, but little is known about its role. The goal of this study was to determine whether an LMP2B homologue is conserved in the rhesus monkey lymphocryptovirus (LCV). Both rhesus LCV LMP2A and LMP2B genes were cloned and sequenced. The rhesus LCV LMP2B gene is positionally conserved, and the EBNA-2 responsiveness and the bidirectional nature of the LMP1-LMP2B promoter have also been functionally conserved. However, this region of the genome encoding the LMP1, LMP1-LMP2B promoter, and LMP2B first exon demonstrates the most dramatic nucleotide sequence divergence between human and nonhuman LCV observed to date. Evolution of the rhesus LCV LMP2B promoter and transcript despite the dynamic nature of this genomic region reflects strong selective pressure for a yet-to-be-identified LMP2B function.

A Novel Epstein-Barr Virus-Like Virus, HVMNE, in aMacaca Nemestrina With Mycosis Fungoides

Epstein-Barr virus (EBV) infection of humans has been associated with the development of lymphoid malignancies mainly of B-cell lineage, although occasionally T-cell lymphomas have been reported. We describe here the characterization of a novel EBV-like virus (HVMNE) isolated from a simian T-cell lymphotropic virus type I/II (STLV-I/II) seronegative pigtailed macaque (Macaca nemestrina) with a cutaneous T-cell lymphoma. Immunohistochemistry studies on the skin lesions demonstrated that the infiltrating cells were of the CD3+/CD8+ phenotype. Two primary transformed CD8+ T-cell lines were obtained from cultures of peripheral blood mononuclear cells (PBMC) and skin, and, with time, both cell lines became interleukin-2–independent and acquired the constitutive activation of STAT proteins. Polymerase chain reaction analysis of the DNA from the cell lines and tissues from the lymphomatous animal demonstrated the presence of a 536-bp DNA fragment that was 90% identical to EBV polymerase gene sequences, whereas the same DNA was consistently negative for STLV-I/II sequences. Electron microscopy performed on both cell lines, after sodium butyrate treatment, showed the presence of a herpes-like virus that was designated HVMNE according to the existing nomenclature. In situ hybridization studies using EBV Epstein-Barr viral-encoded RNA probes showed viral RNA expression in both CD8+ T-cell lines as well as in the infiltrating CD8+ T cells of skin-tissue biopsies. Phylogenetic analysis of a 465-bp fragment from the polymerase gene of HVMNE placed this virus within theLymphocryptovirus genus and demonstrated that HVMNEis a distinct virus, clearly related to human EBV and other EBV-like herpesviruses found in nonhuman primates.

A Novel Epstein-Barr Virus-Like Virus, HVMNE, in aMacaca Nemestrina With Mycosis Fungoides

Epstein-Barr virus (EBV) infection of humans has been associated with the development of lymphoid malignancies mainly of B-cell lineage, although occasionally T-cell lymphomas have been reported. We describe here the characterization of a novel EBV-like virus (HVMNE) isolated from a simian T-cell lymphotropic virus type I/II (STLV-I/II) seronegative pigtailed macaque (Macaca nemestrina) with a cutaneous T-cell lymphoma. Immunohistochemistry studies on the skin lesions demonstrated that the infiltrating cells were of the CD3+/CD8+ phenotype. Two primary transformed CD8+ T-cell lines were obtained from cultures of peripheral blood mononuclear cells (PBMC) and skin, and, with time, both cell lines became interleukin-2–independent and acquired the constitutive activation of STAT proteins. Polymerase chain reaction analysis of the DNA from the cell lines and tissues from the lymphomatous animal demonstrated the presence of a 536-bp DNA fragment that was 90% identical to EBV polymerase gene sequences, whereas the same DNA was consistently negative for STLV-I/II sequences. Electron microscopy performed on both cell lines, after sodium butyrate treatment, showed the presence of a herpes-like virus that was designated HVMNE according to the existing nomenclature. In situ hybridization studies using EBV Epstein-Barr viral-encoded RNA probes showed viral RNA expression in both CD8+ T-cell lines as well as in the infiltrating CD8+ T cells of skin-tissue biopsies. Phylogenetic analysis of a 465-bp fragment from the polymerase gene of HVMNE placed this virus within theLymphocryptovirus genus and demonstrated that HVMNEis a distinct virus, clearly related to human EBV and other EBV-like herpesviruses found in nonhuman primates.

Vaccine strategies against Epstein-Barr virus-associated diseases: lessons from studies on cytotoxic T-cell-mediated immune regulation

Development of a vaccine against Epstein-Barr virus (EBV) is constrained by the latency phenotypes adopted by different EBV-associated diseases. Over the last few years an immense body of information on the pattern of viral gene expression in EBV-associated diseases and the role of cytotoxic T cells in the control of these diseases has accumulated. It would seem reasonable to suggest that emerging technologies are at a level where vaccine trials aimed at controlling infectious mononucleosis, post-transplant lymphoproliferative disease, nasopharyngeal carcinoma and Hodgkin's disease are justified. On the other hand, a more cautious approach may be required for the development of vaccines or immunotherapeutic strategies against Burkitt's lymphoma.

Mechanisms that regulate Epstein-Barr virus EBNA-1 gene transcription during restricted latency are conserved among lymphocryptoviruses of Old World primates

Epstein-Barr virus (EBV), the only known human lymphocryptovirus (LCV), displays a remarkable degree of genetic and biologic identity to LCVs that infect Old World primates. Within their natural hosts, infection by these viruses recapitulates many key aspects of EBV infection, including the establishment of long-term latency within B lymphocytes, and is therefore a potentially valuable animal model of EBV infection. However, it is unclear whether these LCVs have adopted or maintained the same mechanisms used by EBV to express essential viral proteins, such as EBNA-1, in the face of cell-mediated repression of EBV gene expression that occurs upon establishment of the asymptomatic carrier state. To address this issue, we determined whether the endogenous LCVs of baboon (Cercopithecine herpesvirus 12) and rhesus macaque (Cercopithecine herpesvirus 15) have the functional equivalent of the EBV promoter Qp, which mediates exclusive expression of EBNA-1 during the restricted programs of EBV latency associated with the carrier state. Our results indicate that (i) both the baboon and rhesus macaque LCVs have a genomic locus that is highly homologous to the EBV Qp region, (ii) key cis-regulatory elements of Qp are conserved in these LCV genomes and compose promoters that are functionally indistinguishable from EBV Qp, and (iii) EBNA-1 transcripts identical in structure to EBV Qp-specific EBNA-1 mRNAs are present in nonhuman LCV-infected cells, demonstrating that these Qp homologs are indeed utilized as alternative EBNA-1 promoters. These observations indicate that the molecular mechanisms which regulate EBV gene expression during restricted latency have been conserved among the LCVs. The contribution of these mechanisms to viral persistence in vivo can now be experimentally tested in nonhuman primate models of LCV infection.

Transcriptional activation signals found in the Epstein-Barr virus (EBV) latency C promoter are conserved in the latency C promoter sequences from baboon and Rhesus monkey EBV-like lymphocryptoviruses (cercopithicine herpesviruses 12 and 15)

The Epstein-Barr virus (EBV) EBNA2 protein is a transcriptional activator that controls viral latent gene expression and is essential for EBV-driven B-cell immortalization. EBNA2 is expressed from the viral C promoter (Cp) and regulates its own expression by activating Cp through interaction with the cellular DNA binding protein CBF1. Through regulation of Cp and EBNA2 expression, EBV controls the pattern of latent protein expression and the type of latency established. To gain further insight into the important regulatory elements that modulate Cp usage, we isolated and sequenced the Cp regions corresponding to nucleotides 10251 to 11479 of the EBV genome (-1079 to +144 relative to the transcription initiation site) from the EBV-like lymphocryptoviruses found in baboons (herpesvirus papio; HVP) and Rhesus macaques (RhEBV). Sequence comparison of the approximately 1,230-bp Cp regions from these primate viruses revealed that EBV and HVP Cp sequences are 64% conserved, EBV and RhEBV Cp sequences are 66% conserved, and HVP and RhEBV Cp sequences are 65% conserved relative to each other. Approximately 50% of the residues are conserved among all three sequences, yet all three viruses have retained response elements for glucocorticoids, two positionally conserved CCAAT boxes, and positionally conserved TATA boxes. The putative EBNA2 100-bp enhancers within these promoters contain 54 conserved residues, and the binding sites for CBF1 and CBF2 are well conserved. Cp usage in the HVP- and RhEBV-transformed cell lines was detected by S1 nuclease protection analysis. Transient-transfection analysis showed that promoters of both HVP and RhEBV are responsive to EBNA2 and that they bind CBF1 and CBF2 in gel mobility shift assays. These results suggest that similar mechanisms for regulation of latent gene expression are conserved among the EBV-related lymphocryptoviruses found in nonhuman primates.

Infection of human B lymphocytes with lymphocryptoviruses related to Epstein-Barr virus

Lymphocryptoviruses (LCVs) naturally infecting Old World nonhuman primates are closely related to the human LCV, Epstein-Barr virus (EBV), and share similar genome organization and sequences, biologic properties, epidemiology, and pathogenesis. LCVs can efficiently immortalize B lymphocytes from the autologous species, but the ability of a given LCV to immortalize B cells from other Old World primate species is variable. We found that LCV from rhesus monkeys did not immortalize human B cells, and EBV did not immortalize rhesus monkey B cells. In this study, baboon LCV could not immortalize human peripheral blood B cells but could readily immortalize rhesus monkey B cells. Thus, efficient LCV-induced B-cell immortalization across distant Old World primate species appears to be restricted by a species-specific block. To further characterize this species restriction, we first cloned the rhesus monkey LCV major membrane glycoprotein and discovered that the binding epitope for the EBV receptor, CD21, was highly conserved. Stable infections of human B cells with recombinant amplicons packaged in rhesus monkey or baboon LCV envelopes were also consistent with a species-restricted block occurring after virus binding and penetration. Transient infections of human B cells with simian LCV resulted in latent LCV EBNA-2 gene expression and activation of cell CD23 gene expression. EBV-immortalized human B cells could be coinfected with baboon LCV, and the simian virus persisted and replicated in human B cells. Thus, several lines of evidence indicate that the species restriction for efficient LCV-induced B-cell immortalization occurs beyond virus binding and penetration. This has important implications for the study of LCV infection in Old World primate models and for human xenotransplantation where simian LCVs may be inadvertently introduced into humans.

An animal model for acute and persistent Epstein-Barr virus infection

Epstein-Barr virus (EBV) is a human lymphocryptovirus that causes infectious mononucleosis, persists asymptomatically for life in nearly all adults, and is associated with the development of B cell lymphomas and nasopharyngeal carcinomas. A highly similar rhesus lymphocryptovirus naturally endemic in rhesus monkeys was used to orally infect naïve animals from a pathogen-free colony. This animal model reproduced key aspects of human EBV infection, including oral transmission, atypical lymphocytosis, lymphadenopathy, activation of CD23(+) peripheral blood B cells, sustained serologic responses to lytic and latent EBV antigens, latent infection in the peripheral blood, and virus persistence in oropharyngeal secretions. This system may be useful for studying the pathogenesis, prevention, and treatment of EBV infection and associated oncogenesis.

Comparative analysis identifies conserved tumor necrosis factor receptor-associated factor 3 binding sites in the human and simian Epstein-Barr virus oncogene LMP1

Nonhuman primates are naturally infected with a B-lymphotropic herpesvirus closely related to Epstein-Barr virus (EBV). These simian EBV share considerable genetic, biologic, and epidemiologic features with human EBV, including virus-induced tumorigenesis. However, latent, transformation-associated viral genes demonstrate marked sequence divergence among species despite the conserved functions. We have cloned the latent membrane protein 1 (LMP1) homologs from the simian EBV naturally infecting baboons (cercopithicine herpesvirus 12, herpesvirus papio) and rhesus monkeys (cercopithicine herpesvirus 15) for a comparative study with the human EBV oncogene. The transmembrane domains are well conserved, but there is striking sequence divergence of the carboxy-terminal cytoplasmic domain essential for B-cell immortalization and interaction with the tumor necrosis factor receptor signaling pathway. Nevertheless, the simian EBV LMP1s retain most functions in common with EBV LMP1, including the ability to induce NF-(kappa)B activity in human cells, to bind the tumor necrosis factor-associated factor 3 (TRAF3) in vitro, and to induce expression of tumor necrosis factor-responsive genes, such as ICAM1, in human B lymphocytes. Multiple TRAF3 binding sites containing a PXQXT/S core sequence can be identified in the simian EBV LMP1s by an in vitro binding assay. A PXQXT/S-containing sequence is also present in the cytoplasmic domain of the Hodgkin's disease marker, CD30, and binds TRAF3 in vitro. The last 13 amino acids containing a PXQXT/S sequence are highly conserved in human and simian EBV LMP1 but do not bind TRAF3, suggesting a distinct role for this conserved region of LMP1. The conserved TRAF3 binding sites in LMP1 and the CD30 Hodgkin's disease marker provides further evidence that a TRAF3-mediated signal transduction pathway may be important in malignant transformation.

EBNA-2 of herpesvirus papio diverges significantly from the type A and type B EBNA-2 proteins of Epstein-Barr virus but retains an efficient transactivation domain with a conserved hydrophobic motif

EBNA-2 contributes to the establishment of Epstein-Barr virus (EBV) latency in B cells and to the resultant alterations in B-cell growth pattern by up-regulating expression from specific viral and cellular promoters. We have taken a comparative approach toward characterizing functional domains within EBNA-2. To this end, we have cloned and sequenced the EBNA-2 gene from the closely related baboon virus herpesvirus papio (HVP). All human EBV isolates have either a type A or type B EBNA-2 gene. However, the HVP EBNA-2 gene falls into neither the type A category nor the type B category, suggesting that the separation into these two subtypes may have been a recent evolutionary event. Comparison of the predicted amino acid sequences indicates 37% amino acid identity with EBV type A EBNA-2 and 35% amino acid identity with type B EBNA-2. To define the domains of EBNA-2 required for transcriptional activation, the DNA binding domain of the GAL4 protein was fused to overlapping segments of EBV EBNA-2. This approach identified a 40-amino-acid (40-aa) EBNA-2 activation domain located between aa 437 and 477. Transactivation ability was completely lost when the amino-terminal boundary of this domain was moved to aa 441, indicating that the motif at aa 437 to 440, Pro-Ile-Leu-Phe, contains residues critical for function. The aa 437 boundary identified in these experiments coincides precisely with a block of conserved sequences in HVP EBNA-2, and the comparable carboxy-terminal region of HVP EBNA-2 also functioned as a strong transcriptional activation domain when fused to the Gal4(1-147) protein. The EBV and HVP EBNA-2 activation domains share a mixed proline-rich, negatively charged character with a striking conservation of positionally equivalent hydrophobic residues. The importance of the individual amino acids making up the Pro-Ile-Leu-Phe motif was examined by mutagenesis. Any alteration of these residues was found to reduce transactivation efficiency, with changes at the Pro-437 and Phe-440 positions producing the most deleterious effects. Activation of the EBV latency C promoter by EBNA-2 was shown to be dependent on the presence of the carboxy-terminal activation domain. However, this requirement was generic, rather than specific, since the EBNA-2 activation domain could be replaced with those from the herpes simplex virus (HSV) VP16 protein or the EBV Rta protein. Potential karyophilic signals within EBNA-2 were examined by introducing oligonucleotides encoding positively charged amino acid groupings that might serve in this capacity into a cytoplasmic test protein, HSV delta IE175, and by examining the intracellular localization of the resulting proteins. This assay identified a strong nuclear localization signal between EBV amino acids (aa) 478 to 485, which was conserved in HVP, and a weaker noncanonical signal between EBV aa 341 to 355, which was not conserved in HVP.

Generation of macaque B lymphoblastoid cell lines with simian Epstein-Barr-like viruses: transformation procedure, characterization of the cell lines and occurrence of simian foamy virus

Two simian Epstein-Barr-like viruses, a rhesus Epstein-Barr virus and Herpesvirus papio, were used to transform B cells from rhesus or cynomolgus macaques. The resulting cell lines exhibited predominantly a B lymphocyte phenotype and expressed Epstein-Barr virus antigens. The majority of B lymphoblastoid cell lines from macaques, which were seropositive for simian foamy virus, developed giant cells in culture. The cytopathic agent was identified as a foamy virus and was transmissible to human embryonal fibroblasts. Treatment of cell cultures with AZT abolished giant cell formation.

Natural killer cells in rhesus monkeys: properties of effector cells which lyse Raji targets

Spontaneously occurring natural killer cell activity of rhesus monkey peripheral blood mononuclear cells was assayed against five human cell lines, three of which were Epstein-Barr virus (EBV) positive, including the human B cell line Raji. The lytic activity to Raji cells was high, significantly higher than to any other cell line tested. Raji cells are normally insensitive to spontaneous lysis by human NK cells, and the contrasting vigor of the rhesus monkey cytolytic activity to Raji prompted us to investigate the properties of this effector cell. We found the effector cell-mediating lysis of Raji to be nonadherent and phagocytic with lytic activity slightly enhanced in the E-rosette-forming cell (ERFC+) fraction and decreased in the ERFC- fraction. Further isolation of FcIgG receptor-positive and FcIgG receptor-negative subsets by rosetting resulted in significant enrichment of NK activity to Raji in the positive fraction and a loss of activity in the negative fraction. Depletion studies with various monoclonal antibodies (mAb's) confirmed that nearly all lytic activity was contained in the CD16+ (Leu 11b+) population, while subsets of effector cells expressed CD2 (9.6) and CD8 (OKT8). Depletion of CD4 (OKT4)-, HLADR (OKIa)-, or LFA1 (MAC-1)-positive populations failed to reduce NK activity. We compared the phenotypic properties of alloimmune effector cells exhibiting specificity for allogeneic donor targets with those exhibiting lysis of Raji targets. Results indicated that allospecific cytotoxic T lymphocytes expressed a CD16-, CD2+ phenotype, a pattern distinct from that of the effector cell population recognizing Raji targets. The presence of CD2 mAb's in the culture had no effect on NK lytic activity. In contrast, mAbs CD8 and Leu 11b were inhibitory. This would suggest a functional role for CD8 and FcIgG molecules in the lysis of Raji cells by rhesus effectors. In summary, these studies describe a distinct population of effector cells in the blood of rhesus monkeys which exhibit spontaneous lytic activity to Raji cells and exhibit the properties of NK cells.

Epstein-Barr virus-related herpesvirus from a rhesus monkey (Macaca mulatta) with malignant lymphoma

A herpesvirus (RhEBV) was isolated from a lymphoblastoid cell line (LCL) that became established from a malignant lymphoma in a rhesus monkey. The predominant cell marker in the LCL was that of B lymphocytes. RhEBV-induced viral capsid (VCA) and nuclear antigens (NA) in the LCL were serologically related to similar antigens known to be induced by human Epstein-Barr virus (EBV). RhEBV was of nonhuman primate origin and was clearly differentiated from EBV in the anti-complement immunofluorescence reaction using human and non-human primate sera with antibodies to the NA induced by the respective viruses. While human sera reacted with NA induced by both EBV and RhEBV, monkey sera failed to recognize the NA induced by EBV. RhEBV-induced NA was present in nearly all the cells of a suspension prepared from the tumor tissue mass, but not in the monolayer fibroblasts derived from the tumor tissue or in the blood and lymph-node lymphocytes of clinically healthy animals. RhEBV induced in vitro transformation and establishment of LCLs from peripheral blood lymphocytes of normal rhesus and cynomolgus monkeys but not from those of 6 other non-human primate species tested. The LCLs, with predominant B-lymphocyte markers, established after treatment with RhEBV, all had evidence of the virus infection since nearly all cells in the culture expressed the virus-induced NA.

Seroepizootiology of the herpesvirus Papio (HVP) infection in healthy baboons (Papio hamadryas) of high- and low-lymphoma risk populations

Seroepizootiology of Herpesvirus Papio (HVP) infection was studied in three groups of healthy hamadryas baboons (Papio hamadryas): the main Sukhumi (high-lymphoma) stock, forest Sukhumi (lymphoma-free) stock and newly imported wild animals. The prevalence to HVP infection, as judged by anti-VCA-HVP positivity, was approximately the same in both Sukhumi stocks (86% and 90% respectively) and it was significantly lower in the pooled group of newly imported baboons. It is interesting that prevalence of HVP infection in the different independent groups varied markedly (35-79%). Geometric mean titers of positives in all groups were approximately the same. The prevalence of HVP infection was age-dependent. It increased during the first years of life reaching the maximum (about 100%) at the age of 5 years being stable up to the age of 18 years and "decreased" at very old ages (over 18 years). The prevalence of HVP infection in newly imported baboons increased with age up to 71% in a group of the "oldest" monkeys and did not plateau. No significant sex differences in anti-HVP titers were found. Anti-EA-HVP-positive (with one exception) and anti-HUPNA-positive animals were found only in the main Sukhumi stock. Thus, "serologic activity" against HVP infection was the highest in the ligh-lymphoma stock.

One of two Epstein-Barr virus nuclear antigens contains a glycine-alanine copolymer domain

A gene fusion between an Epstein-Barr virus (EBV) triplet nucleotide repeat array (IR3), which has homology to host DNA, and lacZ was used to demonstrate that this EBV sequence encodes part of the Epstein-Barr nuclear antigen (EBNA). The IR3 sequence is translated into a glycine-alanine copolymer that reacts with anti-EBNA human sera. Some EBV-immune human antisera recognize a second intranuclear protein that is also specific for latently infected cells and is designated EBNA2. EBNA2 is not related to EBNA1 because the molecular mass of EBNA2 is 82 kilodaltons, whereas that of EBNA1 varies from 68 to 85 kilodaltons among cells transformed by different EBV isolates; also EBNA2 does not contain the copolymer domain of EBNA1.

Simple repeat sequence in Epstein-Barr virus DNA is transcribed in latent and productive infections

The BamHI K region of Epstein-Barr virus DNA is transcribed in latently infected cells from Burkitt tumors and in growth-transformed B-lymphocytes latently infected with Epstein-Barr virus. We determined the nucleotide sequence of a 1,153-base pair HinfI fragment in BamHI fragment K from the B95-8 Epstein-Barr virus isolate. The fragment contains a remarkable 708-base pair simple sequence repeat array, designated IR3, which is composed of only three nucleotide triplet elements: GGG, GCA, and GGA. The triplets are organized into three repeat units: GCAGGA, GCAGGAGGA, and GGGGCAGGA. Immediately 3' of IR3 are tandem nearly perfect direct repeats of two different 24-base pair sequences. IR3 is conserved at a colinear position in the DNAs of other Epstein-Barr virus isolates, and a homologous sequence maps at the same location in the genome of a genetically related baboon herpesvirus, herpesvirus papio. IR3 is transcribed from left to right in latently infected, growth-transformed IB4 cells. It encodes part of a 2.0-kilobase exon of the 3.7-kilobase cytoplasmic polyadenylated RNA previously detected in IB4 cells (van Santen et al., Proc. Natl. Acad. Sci. U.S.A. 78:1930-1934, 1981). IR3 also encodes parts of 2.4- and 1.0-kilobase RNAs in productively infected B95-8 cells.

DNA of herpesvirus pan, a third member of the Epstein-Barr virus-Herpesvirus papio group

The DNA of herpesvirus pan, a primate B-lymphotropic herpesvirus, shares about 40% well-conserved sequence relatedness with Epstein-Barr virus (EBV) and herpesvirus papio DNAs. Labeled cloned fragments from the EBV recombinant DNA library were cross hybridized to blots of EcoRI, XbaI, and BamHI restriction endonuclease fragments of herpesvirus pan DNA to identify and map homologous sequences in the herpesvirus pan genome. Regions of colinear homology were demonstrated between 6 x 10(6) daltons and 108 x 10(6) daltons in the DNAs. The structural organization of herpesvirus pan DNA was similar to the format of Epstein-Barr virus and herpesvirus papio DNAs. The DNA consists of two domains of largely unique sequence complexity, a segment US of 9 x 10(6) daltons and a segment UL of 88 x 10(6) daltons. US and UL are separated by a variable number of tandem repetitions of a sequence IR (2 x 10(6) daltons). There was homology between DNA which mapped at 26 to 28 x 10(6) daltons and 93 to 95 x 10(6) daltons in UL. The terminal reiteration component, TR, of herpesvirus pan DNA and sequences which mapped to the left of 6 x 10(6) daltons and to the right of 108 x 10(6) daltons had no detectable homology with the corresponding regions of Epstein-Barr virus DNA.

Colinearity between the DNAs of Epstein-Barr virus and herpesvirus papio

Epstein Barr virus (EBV) and herpesvirus papio (HVPapio) DNAs share a common format and 40% homology. Labeled cloned fragments of EBV DNA were hybridized to blots of XbaI, EcoRI, HindIII, and SalI fragments of HVPapio DNA. EBV fragments which mapped from 2 x 10(6) to 54 x 10(6) and from 59 x 10(6) to 106 x 10(6) daltons hybridized to fragments at identical map positions in HVPapio DNA. Regions of nonhomology were demonstrated at 0 x 10(6) to 2 x 10(6), 54 x 10(6) to 59 10(6), and 106 x 10(6) to 115 x 10(6) daltons.

Herpesvirus papio DNA is similar in organization to Epstein-Barr virus DNA

EcoRI, HindII, SalI, nd XbaI restriction endonuclease maps of herpesvirus papio (HVPapio) DNA were derived by determining the fragment sizes and the linkage relationships between fragments generated by the different enzymes. The data indicate that HVPapio DNA has a single molecular arrangement which is similar to that of Epstein-Barr virus DNA. The size of the DNA was 110 X 10(6) to 114 X 10(6) daltons. Restriction fragments from both ends varied in the number of repeats of a 4 X 10(5)-dalton sequence, TR, and hybridized to each other. This suggests that there is an identical repeating unit, TR, at both ends of the DNA. There were usually six tandem repetitions (range, 1 to 11) of a 2 X 10(6)-dalton sequence, IR, within the DNA. IR separated the DNA into two domains of largely unique sequence complexity, a 9 X 10(6)-dalton segment, Us, and an 88 X 10(6)-dalton segment, UL. There was homology between DNA fragments which mapped at 25 X 10(6) to 29 X 10(6) to 91 X 10(6) to 95 X 10(6) daltons in UL.

Isolation of lymphotropic baboon herpesvirus (HVP) from oral swabs of hamadryas baboons of the Sukhumi monkey colony

Ways of lymphotropic baboon herpesvirus (HVP) secretion and its excretion into the environment were investigated. Oral swabs and feces from the Sukhumi main stock hamadryas baboons characterized by a high risk for malignant lymphoma and the baboon stock living in isolation in the forest were used as materials for the investigations. Macaque groups of the Sukhumi stock were used as controls. It could be shown that the HVP was resistent in the oral cavity of the main stock baboons and was isolated from oral swabs of these animals both from those with malignant lymphoma and clinically healthy individuals. No virus was isolated from feces of these animals. The virus could not be isolated from oral swabs of the isolated baboon stock and macaques.

Herpesvirus papio: state and properties of intracellular viral DNA in baboon lymphoblastoid cell lines

Herpesvirus papio (HVP) is an indigenous B-lymphotropic virus of baboons (Papio sp.) present in latent form in baboon lymphoblastoid cell lines. It shares cross-reacting viral capsid and early antigens with the Epstein-Barr virus (EBV), and HVP DNA and EBV DNA show partial sequence homology. EBV-specific complementary RNA was employed here as a probe to investigate the physical state of the HVP DNA component in baboon lymphoblastoid cells after fractionation of cellular DNA by density gradient centrifugation. Five virus-producing cultures contained both free and integrated HVP DNA sequences while one non-producing cell line had two or three viral genome equivalents per cell in an apparently integrated form. Further analysis of one virus-producing line showed that the free HVP DNA fraction was composed of both linear and circular viral DNA. Contour length measurements of HVP circular DNA molecules by electron microscopy revealed that they were similar in length to the EBV circular DNA present in human lymphoblastoid cells.

Evidence for antigenic distinctness of the Epstein--Barr virus-determined nuclear antigen and the Herpesvirus papio-determined nuclear antigen

Previous serological evidence indicated that Epstein--Barr virus-determined nuclear antigen (EBNA) has cross reactive components with the herpesvirus papio-determined nuclear antigen (HUPNA) and, in addition, it has distinct components of its own, not present in HUPNA. In the present study, this hypothesis was studied by absorption experiments. Absorption of anti-EBNA positive human sera with EBNA abolished both anti-EBNA and anti-HUPNA reactivity. Absorption with HUPNA removed all anti-HUPNA reactivity but did not reduce anti-EBNA to any detectable degree, thus confirming the hypothesis.

Antibody responses to Herpesvirus papio antigens in baboons with lymphoma

An Epstein-Barr virus-related herpesvirus, termed Herpesvirus papio (HVP), was isolated from baboons (Papio hamadryas) at the Institute of Experimental Pathology and Therapy, Sukhumi, USSR, where there is a continuing outbreak of lymphoma. In the present study sera from diseased baboons and from age- and sex-matched control animals were examined for antibodies to HVP antigens. Results showed that animals with lymphoid disease had antibodies to HVP virus capsid, early, soluble, and nuclear antigens at higher frequencies and at higher titers than did control animals. Antibody titers were not age- or sex-related. No concordancy was detected for antibodies to soluble and nuclear antigens. The sera were also examined for antibodies to two other widely distributed viruses of hamadryas baboons, cytomegalovirus and foamy virus. The results of these studies did not indicate a disease-related role for either of these viruses.

Further characterization of a herpesvirus-positive orang-utan cell line and comparative aspects of in vitro transformation with lymphotropic old world primate herpesviruses

An orang-utan (Pongo pygmaeus) suspension line, CP81, was shown to lack myeloid markers of lysozyme activity an d phagocytosis but to be positive for lymphocytic N-alkaline phosphatase activity, and to release a B-cell-tropic herpesvirus. This herpesvirus, termed Herpesvirus pongo, had 30--40% DNA homology with EBV and was present at 2-3 genome copies per CP-81 cell. Gibbon lymphocytes transformed by H. pongo, Epstein-Barr virus (EBV), and H. papio (of baboon, Papio hamadryas, origin) were found to be virus antigen-positive B cells. Gibbon lymphocytes transformed by H. pongo and EBV and transplanted to nude mice by the intracranial (IC) route (had a 75% and a 45% success rate, respectively), while transplants of similar cells transformed by H. papio were only 10% successful. None of these lines transplanted subcutaneously (SC) nor manifested a high degree of colony formation in 0.33% agarose (less than or equal to 0.5%), Gibbon lymphocytes transformed by H. pongo were hypodiploid while those transformed by EBV or H. papio were diploid. CP-81 cells themselves could be transplanted both IC (100%) and SC (70%) and showed a relatively high degree of colony formation in agarose (6.4-7.6%). B95-8 cells (marmoset, Saguinus oedipus-EBV) could be transplanted IC (66%) but not SC and had a low but significant ability to grow in agarose (1.6%). 594S (baboon, P. hamadryas-H. papio) cells could be transplanted IC (25%) but not SC, and grew to very low levels in agarose (0.1%).