Malignant NK/T-cell lymphoma associated with simian Epstein-Barr virus infection in a Japanese macaque (Macaca fuscata)

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.

T-cell/Histiocyte-rich Large B-cell Lymphoma of the Larynx in a Juvenile Japanese Macaque (Macaca fuscata)

An 11-month-old female Japanese macaque (Macaca fuscata), born in captivity in a research institute, suddenly died without clinical signs. Necropsy examination revealed a nodular mass protruding from the left ventral aspect of the larynx, compressing the epiglottis anteriorly. Histopathologically, the laryngeal mass was comprised of medium- to large-sized atypical cells. Immunohistochemically, these were positive for CD20 and partially positive for CD79α. Among the atypical cells were CD3⁺ T cells and CD68⁺ histiocytes. Based on the findings, this case was diagnosed as T-cell/histiocyte-rich large B-cell lymphoma. Epstein-Barr virus (EBV)-encoded small RNAs were frequently detected in the atypical cells by in-situ hybridization, which was consistent with the finding that the macaque was seropositive for EBV antigen. This is the first report showing the potential association of simian lymphocryptovirus, the simian homologue of EBV, with lymphoma in a juvenile non-human primate.

Hepatocellular carcinoma with intracranial metastasis in a Japanese macaque (Macaca fuscata)

BACKGROUND

A 23-year-old male Japanese macaque (Macaca fuscata) showed left ptosis, which progressed to exophthalmos.

METHODS

The macaque underwent a clinical examination, CT and MRI, and was euthanized. Necropsy and histopathological examination were performed after euthanasia.

RESULTS

The CT revealed and MRI confirmed an intracranial mass at the skull base with orbital extension. At necropsy, there were a large hepatic mass and an intracranial mass compressing the left temporal lobe of the brain. Histopathological and immunohistological examinations revealed that the masses were hepatocellular carcinoma (HCC) and a metastatic lesion. In both the primary and metastatic lesions, neoplastic hepatocytes were arranged mainly in a trabecular pattern. Immunohistochemically, the tumor cells were positive for cytokeratin (AE1/AE3 and CAM5.2) and hepatocyte paraffin 1 and negative for cytokeratin 7 and 20 and vimentin.

CONCLUSION

To our knowledge, this is the first case report of HCC with intracranial metastasis in a macaque.

Intravascular T-cell lymphoma in a patas monkey (Erythrocebus patas)

A 9-year-old female captive patas monkey (Erythrocebus patas) presented with poor general condition, inability to stand, petechiae, anaemia, thrombocytopenia, and leukocytosis. Due to poor response to treatment, the animal was euthanized 16 days later. Postmortem examination revealed hemorrhages in several organs and bilateral cerebral infarctions. Histologically, prominent accumulations of large neoplastic lymphocytes in cerebral and meningeal blood vessels were demonstrated within the lesions and in other organs (e.g., bone marrow, ovary, intestine). Immunohistochemically, neoplastic cells expressed CD3 and Ki-67. PCR revealed a lymphocryptovirus (LCV) infection, while Epstein–Barr nuclear antigen 2 (EBNA2) could not be demonstrated within neoplastic cells by means of immunohistochemistry. Based on the pathological findings, an intravascular lymphoma (IVL) of T-cell origin was diagnosed. To the authors' knowledge, this is the first report on this rare entity in a nonhuman primate.

Characterization of spontaneous malignant lymphomas in Japanese macaques (Macaca fuscata)

Lymphomas are common spontaneous tumors in nonhuman primates but remain poorly characterized in Japanese macaques (Macaca fuscata). This study examined 5 cases of spontaneous malignant lymphoma in Japanese macaques, focusing on the immunophenotypes and presence of simian lymphocryptoviruses, which are Epstein-Barr virus-related herpesviruses in nonhuman primates. The macaques with lymphoma were 5 to 28 years old, indicating that lymphomas develop over a wide age range. The common macroscopic findings were splenomegaly and enlargement of lymph nodes. Histologic and immunohistochemical analyses revealed that all cases were non-Hodgkin type and exhibited a T-cell phenotype, positive for CD3 but negative for CD20 and CD79α. The lymphomas exhibited diverse cellular morphologies and were subdivided into 3 types according to the World Health Organization classification. These included 3 cases of peripheral T-cell lymphoma, not otherwise specified; 1 case of T-cell prolymphocytic leukemia; and 1 case of an unclassifiable T-cell lymphoma. Positive signals were detected by in situ hybridization in 2 of the 4 examined cases using probes for the Epstein-Barr virus-encoded small RNA (EBER). Furthermore, the presence of M. fuscata lymphocryptovirus 2, a macaque homolog of Epstein-Barr virus, was demonstrated in EBER-positive cases by polymerase chain reaction amplification followed by direct sequencing. Immunohistochemistry using antibody to the Epstein-Barr virus-encoded nuclear antigen 2 was negative, even in the EBER-positive cases. The present study suggests that T-cell lymphoma is more common than B-cell lymphoma in Japanese macaques and that M. fuscata lymphocryptovirus 2 is present in some cases.

Rhesus lymphocryptovirus type 1-associated B-cell nasal lymphoma in SIV-infected rhesus macaques

Epstein-Barr virus (EBV) is a worldwide endemic gamma herpesvirus of the genus Lymphocryptovirus (LCV) that infects more than 90% of the world's population. EBV has been associated with a variety of malignancies, but it has a demonstrated role in lymphomas, especially in immunosuppressed individuals. Lymphomas of the nasal cavity, paranasal sinuses, and nasopharynx are uncommon and constitute less than 5% of all extranodal lymphomas. Sinonasal non-Hodgkin's lymphomas have been reported in patients infected with human immunodeficiency virus (HIV) at an increased frequency. Rhesus LCV (rhLCV), the rhesus viral homolog of EBV, has been cloned and is associated with B-cell lymphomas in immunosuppressed rhesus macaques. We report two cases of B-cell lymphoma within the nasal cavity from 2 simian immunodeficiency virus-infected rhesus macaques with acquired immunodeficiency syndrome. The B-cell phenotype and rhLCV association were demonstrated by immunohistochemistry and confocal microscopy. The majority of the nuclei of the neoplastic B lymphocytes were EBNA-2 positive. RhLCV type 1 sequences were verified from the neoplasms by polymerase chain reaction. Nasal lymphoma is an unusual presentation of rhLCV-associated B-cell lymphoma in immunosuppressed rhesus macaques. These tumors demonstrate comparable viral pathogenesis with EBV-induced nasal lymphomas in HIV-positive people.