Immunophenotype of Spontaneous Hematolymphoid Tumors Occurring in Young and Aging Female CD-1 Mice. [Corrected]

Spontaneous B-cell lymphoma in the cranial mediastinal lymph node of an aged male C57BL/6J mouse

B-cell lymphoma is generally observed in the spleen, mesenteric lymph nodes, and Peyer's patches in aged mice and rarely appears in other organs. Herein, we report a case of spontaneous B-cell lymphoma originating from the cranial mediastinal lymph node in a male 75-week-old C57BL/6J mouse. Macroscopically, a white mass was found at the base of the heart with no connection to the thymus. Microscopic examination revealed a solid proliferation of tumor cells with large nuclei at the center of the mass. Some macrophages, normal-sized lymphocytes, and lymphatic sinuses were found in both central and peripheral areas. Immunohistochemical analysis showed positive staining for cluster of differentiation 19, paired box protein 5, immunoglobulin M, and Ki-67 but not for cytokeratin AE1/AE3. These findings were not completely consistent with the established mouse lymphoma classification, leading to a diagnosis of B-cell lymphoma originating from the cranial mediastinal lymph node. This case report is the first to document a B-cell lymphoma in the cranial mediastinal lymph nodes in an aged C57BL/6J mouse.

Utility of CD138/syndecan-1 immunohistochemistry for localization of plasmacytes is tissue-dependent in B6 mice

Objective

Inflammation is present in many diseases and identification of immune cell infiltration is a common assessment. CD138 (syndecan-1) is a recommended immunohistochemical marker for human plasmacytes although it is also expressed in various epithelia and tumors. Similarly, CD138 is a marker for murine plasmacytes, but its tissue immunostaining is not well-defined. Endogenous CD138 expression is an important confounding factor when evaluating plasmacyte infiltration. We studied two plasmacyte markers (CD138 and Kappa light chains) for endogenous immunostaining in five organs and one tumor from B6 mice.

Results

Plasmacytes in Peyer’s patches were positive for CD138 and Kappa markers without endogenous immunostaining. Endogenous CD138 immunostaining was widespread in liver, kidney, lung and a malignant peripheral nerve sheath tumor (MPNST) versus regionalized immunostaining in skin and small intestine wall. Endogenous Kappa immunostaining was absent in all tissues except for plasmacytes. Tissues with widespread endogenous CD138 immunostaining were contrasted by absence of endogenous Kappa immunostaining. Here, plasmacytes would not be distinguished by CD138, but would be obvious by Kappa immunostaining. Our study suggests that utility of immunostaining for plasmacytes by CD138 is tissue dependent in mice. Additionally, Kappa immunostaining may be a useful alternative in mouse tissues with confounding endogenous CD138 immunostaining.

Immunohistochemical Characterization of Proliferative Lesions in the Thymus of Aging CD-1 Mice From Two Studies on the RITA Database, With Special Reference to the Perivascular Space

Thymic lymphoid hyperplasia is a common age-related finding, which occurs particularly in female CD-1 mice. The main differential diagnoses are malignant lymphoma and thymoma. A systematic investigation of control groups from two carcinogenicity studies was performed including measurements of thymic size, and the immunohistochemistry (IHC) markers pan-Cytokeratin (pan-CK) for thymic epithelial cells; CD3 and CD45R/B220 for T and B lymphocytes, respectively; CD31 for endothelial cells; and F4/80 for macrophages. Thymoma can be differentiated by increased numbers of proliferating epithelial cells demonstrated by pan-CK IHC staining. Differentiation between lymphoid hyperplasia and lymphoma is more challenging as a mixture of B and T lymphocytes can be present in both findings. The present investigation showed that the thymic perivascular space is the compartment where the increased numbers of lymphocytes in hyperplasia are localized and not the medulla, as previously thought. The lymphoepithelial compartment is atrophic to the same extent in thymi diagnosed with age-related involution or lymphoid hyperplasia. Both diagnoses are thus related to variations in lymphoid cellularity of the nonepithelial perivascular space, which is continuous with the perithymic tissue. Likewise, lymphomas have a predilection to colonize the perivascular space and to spare the lymphoepithelial compartment.

Research-Relevant Conditions and Pathology of Laboratory Mice, Rats, Gerbils, Guinea Pigs, Hamsters, Naked Mole Rats, and Rabbits

Animals are valuable resources in biomedical research in investigations of biological processes, disease pathogenesis, therapeutic interventions, safety, toxicity, and carcinogenicity. Interpretation of data from animals requires knowledge not only of the processes or diseases (pathophysiology) under study but also recognition of spontaneous conditions and background lesions (pathology) that can influence or confound the study results. Species, strain/stock, sex, age, anatomy, physiology, spontaneous diseases (noninfectious and infectious), and neoplasia impact experimental results and interpretation as well as animal welfare. This review and the references selected aim to provide a pathology resource for researchers, pathologists, and veterinary personnel who strive to achieve research rigor and validity and must understand the spectrum of "normal" and expected conditions to accurately identify research-relevant experimental phenotypes as well as unusual illness, pathology, or other conditions that can compromise studies involving laboratory mice, rats, gerbils, guinea pigs, hamsters, naked mole rats, and rabbits.

Novel spontaneous myelodysplastic syndrome mouse model

Background

Myelodysplastic syndrome (MDS) is a group of disorders involving hemopoietic dysfunction leading to leukemia. Although recently progress has been made in identifying underlying genetic mutations, many questions still remain. Animal models of MDS have been produced by introduction of specific mutations. However, there is no spontaneous mouse model of MDS, and an animal model to simulate natural MDS pathogenesis is urgently needed.

Methods

In characterizing the genetically diverse mouse strains of the Collaborative Cross (CC) we observed that one, designated JUN, had abnormal hematological traits. This strain was thus further analyzed for phenotypic and pathological identification, comparing the changes in each cell population in peripheral blood and in bone marrow.

Results

In a specific-pathogen free environment, mice of the JUN strain are relatively thin, with healthy appearance. However, in a conventional environment, they become lethargic, develop wrinkled yellow hair, have loose and light stools, and are prone to infections. We found that the mice were cytopenic, which was due to abnormal differentiation of multipotent bone marrow progenitor cells. These are common characteristics of MDS.

Conclusions

A mouse strain, JUN, was found displaying spontaneous myelodysplastic syndrome. This strain has the advantage over existing models in that it develops MDS spontaneously and is more similar to human MDS than genetically modified mouse models. JUN mice will be an important tool for pathogenesis research of MDS and for evaluation of new drugs and treatments.

Conditioning Regimens in Long-Term Pre-Clinical Studies to Support Development of Ex Vivo Gene Therapy: Review of Nonproliferative and Proliferative Changes

Hematopoietic stem cell gene therapy has become a successful therapeutic strategy for some inherited genetic disorders. Pre-clinical toxicity studies performed to support the human clinical trials using viral-mediated gene transfer and autologous hematopoietic stem and progenitor cell (HSPC) transplantation are complex and the use of mouse models of human diseases makes interpretation of the results challenging. In addition, they rely on the use of conditioning agents that must induce enough myeloablation to allow engraftment of transduced and transplanted HSPC. Busulfan and total body irradiation (TBI) are the most commonly used conditioning regimens in the mouse. Lenticular degeneration and atrophy of reproductive organs are expected histopathological changes. Proliferative and nonproliferative lesions can be observed with different incidence and distribution across strains and mouse models of diseases. The occurrence of these lesions can interfere with the interpretation of pre-clinical toxicity and tumorigenicity studies performed to support the human clinical studies. As such, it is important to be aware of the background incidence of lesions induced by different conditioning regimens. We review the histopathology results from seven long-term studies, five using TBI and two using busulfan.

Identification of aspartame-induced haematopoietic and lymphoid tumours in rats after lifetime treatment

Lymphomas and leukaemias involving the lung have in some cases been hard to distinguish from respiratory tract infection in Sprague-Dawley (SD) rats from long-term bioassays. In order to differentiate between tumours and immune cell infiltrates, updated pathological criteria and nomenclature were used and immunohistochemistry (IHC) was applied to haematopoietic and lymphoid tissue tumours (HLTs) in the original prenatal long-term Aspartame (APM) study performed by the Ramazzini Institute (RI). All 78 cases of HLTs from treated and control groups were re-examined based on light microscopic morphological characteristics and subjected to a panel of IHC markers including Ki67, CD3, PAX5, CD20, CD68, TdT, CD45, CD14 and CD33. The analysis confirmed the diagnoses of HLTs in 72 cases, identified 3 cases of preneoplastic lesions (lymphoid hyperplasia), and categorized 3 cases as inflammatory lesions. A statistically significant increase in total HLTs (p = 0.006), total lymphomas (p = 0.032) and total leukaemias (p = 0.031) in treated female rats was confirmed (high dose vs control), and a statistically significant linear trend for each HLT type was also observed. After the HLT cases re-evaluation, the results obtained are consistent with those reported in the previous RI publication and reinforce the hypothesis that APM has a leukaemogenic and lymphomatogenic effect.

Nonproliferative and Proliferative Lesions of the Rat and Mouse Hematolymphoid System

The INHAND Project (International Harmonization of Nomenclature and Diagnostic Criteria for Lesions in Rats and Mice) is a joint initiative of the Societies of Toxicologic Pathology from Europe (ESTP), Great Britain (BSTP), Japan (JSTP), and North America (STP) to develop an internationally accepted nomenclature for proliferative and nonproliferative changes in rats and mice. The purpose of this publication is to provide a standardized nomenclature for classifying changes observed in the hematolymphoid organs, including the bone marrow, thymus, spleen, lymph nodes, mucosa-associated lymphoid tissues, and other lymphoid tissues (serosa-associated lymphoid clusters and tertiary lymphoid structures) with color photomicrographs illustrating examples of the lesions. Sources of material included histopathology databases from government, academia, and industrial laboratories throughout the world. Content includes spontaneous lesions as well as lesions induced by exposure to test materials. The nomenclature for these organs is divided into 3 terminologies: descriptive, conventional, and enhanced. Three terms are listed for each diagnosis. The rationale for this approach and guidance for its application to toxicologic pathology are described in detail below.

Morphologic and Immunohistochemical Characterization of Spontaneous Lymphoma/Leukemia in NSG Mice

The NOD.Cg-Prkdc^scid Il2rg^tm1Wjl/SzJ strain (NOD scid gamma, NSG) is a severely immunodeficient inbred laboratory mouse used for preclinical studies because it is amenable to engraftment with human cells. Combining scid and Il2rg^null mutations results in severe immunodeficiency by impairing the maturation, survival, and functionality of interleukin 2-dependent immune cells, including T, B, and natural killer lymphocytes. While NSG mice are reportedly resistant to developing spontaneous lymphomas/leukemias, there are reports of hematopoietic cancers developing. In this study, we characterized the immunophenotype of spontaneous lymphoma/leukemia in 12 NSG mice (20 to 38 weeks old). The mice had a combination of grossly enlarged thymus, spleen, or lymph nodes and variable histologic involvement of the bone marrow and other tissues. All 12 lymphomas were diffusely CD3, TDT, and CD4 positive, and 11 of 12 were also positive for CD8, which together was consistent with precursor T-cell lymphoblastic lymphoma/leukemia (pre-T-LBL). A subset of NSG tissues from all mice and neoplastic lymphocytes from 8 of 12 cases had strong immunoreactivity for retroviral p30 core protein, suggesting an association with a viral infection. These data highlight that NSG mice may develop T-cell lymphoma at low frequency, necessitating the recognition of this spontaneously arising disease when interpreting studies.

Spontaneously occurring lymphohematopoietic tumors in three young Sprague Dawley rats

To assess the toxicological and pharmacological effects of chemicals, it is important to know what kinds of neoplasms naturally occur in the early life of laboratory animals. In the present study, we identified three spontaneous hematopoietic tumors in three of 52 young female Sprague-Dawley rats used in a pharmacological study. These cases included two rats (Case 1 and 2) from a sesame oil-treated group and one rat (Case 3) from a chemical-treated group in the same single gavage study. Case 1 rapidly lost body weight at 13 weeks of age without any clinical signs and died. Round lymphoid tumor cells were found in the spleen, liver, bone marrow, and pancreas. The tumor cells were immunohistochemically positive for CD3 and PCNA, which is suggestive of malignant T-cell lymphoma. Cases 2 and 3 had rapid body weight loss at 14 and 16 weeks of age, respectively, exhibited severe anemia, hypolocomotion, and decreased body temperature, and were euthanized due to a poor prognosis based on severe clinical signs. Pleomorphic large tumor cells were found in the spleen, liver, bone marrow, lymph nodes, heart, kidneys, lung, pancreas, adrenal glands, pituitary gland, ovaries, Harderian gland, and/or eyes. The tumor cells were immunoreactive for CD34, lysozyme, and PCNA, which is suggestive of myeloid leukemia. These cases might provide useful historical control information for rat toxicity studies.

Finding mouse models of human lymphomas and leukemia's using the Jackson laboratory mouse tumor biology database

Many mouse models have been created to study hematopoietic cancer types. There are over thirty hematopoietic tumor types and subtypes, both human and mouse, with various origins, characteristics and clinical prognoses. Determining the specific type of hematopoietic lesion produced in a mouse model and identifying mouse models that correspond to the human subtypes of these lesions has been a continuing challenge for the scientific community. The Mouse Tumor Biology Database (MTB; http://tumor.informatics.jax.org) is designed to facilitate use of mouse models of human cancer by providing detailed histopathologic and molecular information on lymphoma subtypes, including expertly annotated, on line, whole slide scans, and providing a repository for storing information on and querying these data for specific lymphoma models.