Chemically induced murine T lymphomas: continued rearrangement within the T-cell receptor beta-chain gene during serial passage

Myeloid, B and T lymphoid and mixed lineage thymic lymphomas in the irradiated mouse

Thymic lymphoma is a very common spontaneous and/or induced malignancy in both inbred mice and in transgenic mouse models of human cancer. Although a thymic lymphoma is defined as thymus-dependent T-cell malignancy, diagnostic criteria vary between studies and considerable heterogeneity has been reported. To define and classify the thymic lymphomas that arose in our study of X-irradiated (CBA/HxC57BL/6)F1, F1 backcross and F1 intercross mice, 66 thymic lymphomas were immunogenotyped for immunoglobulin heavy chain (IgH) and T-cell receptor beta (TCRbeta) gene rearrangements, and/or analysed for expression of lineage-specific markers and allelic loss on chromosome 4. The data indicate that 33% of the thymic lymphomas are very similar to mouse radiation-induced acute myeloid (AML) and mixed lineage (IgH(R), TCRbeta(G)) pre-B lympho-myeloid (L-MLs) leukaemias, 33% are mixed lineage (IgH(R), TCRbeta(R)) B/T lymphoid and <33% can be described as single lineage (IgH(G), TCRbeta(R)) T-cell malignancies. As the myeloid and L-ML leukaemias are not thymus-dependent this suggests that a malignant myeloid or pre-B lympho-myeloid cell can colonize the spleen to give an AML or L-ML leukaemia, or can colonize the thymus where TCRbeta gene rearrangement(s) may be induced to give the mixed lineage thymic lymphomas. Thus, assuming the single lineage T-cell thymic lymphomas fulfil the criteria of a thymus-dependent T-cell malignancy, thymic lymphomas are comprised of at least three distinct malignancies.

Spontaneous follicular center cell lymphomas of B cell origin in cataract mice

Spontaneous lymphomas from a strain of hereditary cataract (CAC-nct/+) mice were examined by light and electron microscopy and by immunohistochemical reaction for the mouse heavy and light immunoglobulin chains. Lymphomas occurred in 28 out of 45 male cataract mice and in 34 out of 52 females at 25 to 65 weeks of age. All of the lymphoma-bearing mice showed an enlargement of the spleen and mesenteric lymph nodes, and some mice also had hepatomegaly. Morphologically, all tumors were composed of a mixed population of small and large cells. Neoplastic cells had features of follicular center cell lymphomas, such as scant to moderate amounts of cytoplasm and cleaved and/or round nuclei with a large nuclear-to-cytoplasmic ratio. Large cells were often admixed with small cells, and had vesicular nuclei with prominent nucleoli juxtaposed to the nuclear membrane. Intracytoplasmic eosinophilic inclusions were observed in occasional cells, but Golgi apparatus was poorly developed and rough-surfaced endoplasmic reticulum was scant, unlike those in plasma cells. C-particles were seen in all lymphoma-bearing mice by electron microscopy. Intracisternal A-particles were detected in some mice. Immunohistochemically, neoplastic lymphoid cells were positive for the kappa light chain and the surface/cytoplasmic immunoglobulin M. These results indicate that lymphoid cell neoplasms found in hereditary cataract mice originate from follicular center B cells.

Absence of mouse mammary tumor virus proviral amplification in chemically induced lymphomas of RF/J mice

RF/J mice are susceptible to the induction of thymic lymphomas by the carcinogens 3-methylcholanthrene and N-methyl-N-nitrosourea. Given the association of mouse mammary tumor virus (MMTV) with certain thymomas, we examined genomic DNA from chemically induced lymphomas of RF/J mice for new MMTV proviruses. Of 13 tissue culture lines derived from 3-methylcholanthrene-induced tumors, 5 had acquired new proviruses. MMTV amplification coincided with the appearance of viral mRNAs and proteins. However, no primary tumors or animal-passaged tumors contained new proviruses. These observations indicate that MMTV does not have a role in the tumor induction process, although it may become activated and amplified in tissue culture lines derived from tumors.

Lymphotropic papovavirus early region is specifically regulated transgenic mice and efficiently induces neoplasia

Transgenic mice have been generated which carry the early region of lymphotropic papovavirus (LPV). Eight of eleven founder animals died before 3 months of age after developing one or both of two distinct proliferative disorders. Of the three surviving animals, two are known to have rearranged or partial copies of the LPV genes. The majority of the founder animals (six) developed debilitating choroid plexus tumors by 26 to 42 days. Although this is the same tumor type induced by the simian virus 40 T-antigen gene, those induced by LPV appeared at a much younger age. The LPV early region was expressed in the brain tumors of these mice, as well as in the thymus and spleen. Expression in the latter two tissues reflects the cell-type specificity of the LPV enhancer demonstrated in cultured cells (i.e., lymphoid cells). Two founder animals (LP41 and LP50) gave rise to lines of mice that routinely develop lymphoproliferative disorders. LP50 and its LPV-positive offspring developed aggressive lymphomas and choroid plexus tumors. The transgenic offspring of LP41 also developed lymphomas. High levels of LPV RNA were expressed in the lymphomas of these mice as well as in the spleens and thymuses. The origin of the lymphomas from B- and T-cell lineages suggests that the LPV early genes are expressed in and can transform both of these cell types in vivo.