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

Animal Models for Gammaherpesvirus Infections: Recent Development in the Analysis of Virus-Induced Pathogenesis

Epstein–Barr virus (EBV) is involved in the pathogenesis of various lymphomas and carcinomas, whereas Kaposi’s sarcoma-associated herpesvirus (KSHV) participates in the pathogenesis of endothelial sarcoma and lymphomas. EBV and KSHV are responsible for 120,000 and 44,000 annual new cases of cancer, respectively. Despite this clinical importance, no chemotherapies or vaccines have been developed for virus-specific treatment and prevention of these viruses. Humans are the only natural host for both EBV and KSHV, and only a limited species of laboratory animals are susceptible to their experimental infection; this strict host tropism has hampered the development of their animal models and thereby impeded the study of therapeutic and prophylactic strategies. To overcome this difficulty, three main approaches have been used to develop animal models for human gammaherpesvirus infections. The first is experimental infection of laboratory animals with EBV or KSHV. New-world non-human primates (NHPs) and rabbits have been mainly used in this approach. The second is experimental infection of laboratory animals with their own inherent gammaherpesviruses. NHPs and mice have been mainly used here. The third, a recent trend, employs experimental infection of EBV or KSHV or both to immunodeficient mice reconstituted with human immune system components (humanized mice). This review will discuss how these three approaches have been used to reproduce human clinical conditions associated with gammaherpesviruses and to analyze the mechanisms of their pathogenesis.

Gammaherpesvirus infection and malignant disease in rhesus macaques experimentally infected with SIV or SHIV

Human gammaherpesviruses are associated with malignancies in HIV infected individuals; in macaques used in non-human primate models of HIV infection, gammaherpesvirus infections also occur. Limited data on prevalence and tumorigenicity of macaque gammaherpesviruses, mostly cross-sectional analyses of small series, are available. We comprehensively examine all three-rhesus macaque gammaherpesviruses -Rhesus rhadinovirus (RRV), Rhesus Lymphocryptovirus (RLCV) and Retroperitoneal Fibromatosis Herpesvirus (RFHV) in macaques experimentally infected with Simian Immunodeficiency Virus or Simian Human Immunodeficiency Virus (SIV/SHIV) in studies spanning 15 years at the AIDS and Cancer Virus Program of the Frederick National Laboratory for Cancer Research. We evaluated 18 animals with malignancies (16 lymphomas, one fibrosarcoma and one carcinoma) and 32 controls. We developed real time quantitative PCR assays for each gammaherpesvirus DNA viral load (VL) in malignant and non-tumor tissues; we also characterized the tumors using immunohistochemistry and in situ hybridization. Furthermore, we retrospectively quantified gammaherpesvirus DNA VL and SIV/SHIV RNA VL in longitudinally-collected PBMCs and plasma, respectively. One or more gammaherpesviruses were detected in 17 tumors; generally, one was predominant, and the relevant DNA VL in the tumor was very high compared to surrounding tissues. RLCV was predominant in tumors resembling diffuse large B cell lymphomas; in a Burkitt-like lymphoma, RRV was predominant; and in the fibrosarcoma, RFHV was predominant. Median RRV and RLCV PBMC DNA VL were significantly higher in cases than controls; SIV/SHIV VL and RLCV VL were independently associated with cancer. Local regressions showed that longitudinal VL patterns in cases and controls, from SIV infection to necropsy, differed for each gammaherpesvirus: while RFHV VL increased only slightly in all animals, RLCV and RRV VL increased significantly and continued to increase steeply in cases; in controls, VL flattened. In conclusion, the data suggest that gammaherpesviruses may play a significant role in tumorogenesis in macaques infected with immunodeficiency viruses.

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.

Lymphocryptovirus phylogeny and the origins of Epstein-Barr virus

Specimens from wild and captive primates were collected and novel members of the genus Lymphocryptovirus (subfamily Gammaherpesvirinae) were searched for utilizing PCR for the DNA polymerase gene. Twenty-one novel viruses were detected. Together with previous findings, more than 50 distinct lymphocryptoviruses (LCVs) are now known, with hosts from six primate families (Hominidae, Hylobatidae, Cercopithecidae, Atelidae, Cebidae and Pitheciidae). Further work extended genomic sequences for 25 LCVs to 3.4-7.4 kbp. Phylogenetic trees were constructed, based on alignments of protein sequences inferred from the LCV genomic data. The LCVs fell into three major clades: Clade A, comprising New World viruses; Clade B, containing both Old World monkey viruses and hominoid viruses including Epstein-Barr virus (EBV); and Clade C, containing other hominoid viruses. By comparison with the primate tree, it was proposed that major elements of the LCV tree represented synchronous evolution with host lineages, with the earliest node in both trees being the separation of Old and New World lines, but that some virus lineages originated by interspecies transfer. From comparisons of branch lengths, it was inferred that evolutionary substitution in Clade B has proceeded more slowly than elsewhere in the LCV tree. It was estimated that in Clade B a subclade containing EBV, a gorilla virus and two chimpanzee viruses derived from an Old World monkey LCV line approximately 12 million years ago, and another subclade containing an orang-utan virus and a gibbon virus derived from a macaque LCV line approximately 1.2 million years ago.

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.

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.

Viruses and Hodgkin disease: no evidence of novel herpesviruses in non-EBV-associated lesions

The Epstein-Barr virus (EBV) is associated with a proportion of cases of Hodgkin disease (HD) and this association is believed to be causal. Epidemiological studies suggest that an infectious agent is involved in the aetiology of young adult HD, however, cases in this age group are less likely to have EBV-associated disease than cases diagnosed in early childhood or older adult years. Molecular studies have failed to find a consistent association between HD and other candidate viruses, and the aetiology of non-EBV-associated cases remains obscure. We looked for evidence of herpesvirus infection in samples of non-EBV-associated HD using a highly sensitive, degenerate PCR assay. Despite exhaustive sequence analysis of PCR products, no novel herpesviruses were identified. These results suggest that it is extremely unlikely that a novel herpesvirus is involved in the pathogenesis of non-EBV-associated HD.

Characterization of an Epstein-Barr virus-related gammaherpesvirus from common marmoset (Callithrix jacchus)

A gammaherpesvirus related to Epstein-Barr virus (EBV; Human herpesvirus 4) infects otherwise healthy common marmosets (Callithrix jacchus). Long-term culture of common marmoset peripheral blood lymphocytes resulted in outgrowth of spontaneously immortalized lymphoblastoid cell lines, primarily of B cell lineage. Electron microscopy of cells and supernatants showed herpesvirus particles. There were high rates of serological cross-reactivity to other herpesviruses (68-86%), but with very low geometric mean antibody titres [1:12 to human herpesvirus 6 and 1:14 to Herpesvirus papio (Cercopithecine herpesvirus 12)]. Sequence analysis of the conserved herpesvirus DNA polymerase gene showed that the virus is a member of the lymphocryptovirus subgroup and is most closely related to a lymphocryptovirus from rhesus macaques and is closely related to EBV and Herpesvirus papio. High seroprevalence (79%, with geometric mean antibody titre of 1:110) among 28 common marmosets from two geographically distinct colonies indicated that the virus is likely present in many common marmosets in captivity. A New World primate harbouring a lymphocryptovirus suggests that this subgroup arose much earlier than previously thought.

Posttransplant lymphoproliferative disorder associated with primate gamma-herpesvirus in cynomolgus monkeys used in pig-to-primate renal xenotransplantation and primate renal allotransplantation

BACKGROUND

A series of immunosuppressed cynomolgus monkeys were used in porcine-to-primate and primate-to-primate renal transplantation. In a number of animals nodal and extranodal lymphomas as well as areas of lymphoid hyperplasia in multiple organs (posttransplant lymphoproliferative disorder, PTLD) were recorded.

METHODS

PTLD was characterized with respect to manifestation sites, histopathology, immunophenotype, and association with primate Epstein Barr-like Virus by in situ hybridization and quantitative polymerase chain reaction.

RESULTS

PTLD was observed in 10 of 245 xenotransplanted and 9 of 231 allotransplanted monkeys; its detection in xenotransplanted animals was significantly earlier after transplantation than that in allo-transplanted animals (median, 40 and 104 days, respectively; P<0.001). In the xenotransplanted animals, four cases showed a B-cell lymphoma and six cases were nonneoplastic (lymphoid hyperplasia). All nine PTLD cases from allotransplanted animals were diagnosed as lymphoma. There was no clear relationship between the use of a particular drug or drug combination in maintenance immunosuppression and the occurrence of PTLD. Fourteen of 19 animals (six of the cases from xenotransplants, eight from the allotransplant series) were positive by in situ hybridization with oligonucleotide probes detecting primate gamma-herpesvirus.

CONCLUSION

These data indicate that PTLD in the xeno- and allotransplanted cynomolgus monkeys are associated with primate gamma-herpesvirus-induced B-cell proliferation.

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.