Phenotype of thymic lymphomas in the mouse

A new immunobiological view of radiation-promoted lymphomagenesis

Whole-body irradiation produces T-cell leukaemias/ lymphomas (TCL) in some strains of inbred mice in an X-ray dose-related manner. Radiation biologists have related the rapid "initiation' and early appearance of preleukaemic cells in these mice to unrepaired DNA damage inflicted by radiation. Following initiation, radiation-altered thymic differentiation fosters multi-step transformation changes in proto-oncogenes and suppressor gene expression in individual clones of non-invasive preleukaemia cells as they progress to malignancy. The malignant clones arising from small numbers of initiated preleukaemia thymocytes become fully transformed only after several more months to a year after irradiation in those strains of mice which develop T-cell lymphomas. When the RFM mouse was subjected to sublethal whole-body X-ray, only 50% of the mice developed TCL by 6 months, yet nearly all developed preleukaemia thymocytes. The T-cell-mediated immune response of the irradiated host has never been substantiated to contribute to malignant TCL development. Until recently, X-ray-induced TCL were not known to carry common tumour rejection antigens TATA. However, several studies have revealed that both preleukaemia cells and fully malignant TCL express an immunogenic, common oncofoetal glycoprotein, termed 44kD OFA. OFA-activated memory CD4 Tm and CD8 Ten. T-effector cells in irradiated mice expressing OFA. As most irradiated RFM mice exhibit preleukaemia thymocytes yet only half develop tumours, this finding implicates active host T-cell effector responses in X-ray-initiated tumorigenesis. Further, the recent discovery of OFA-specific CD8 Ts clones in irradiated mice, which inhibited cytotoxicity of CD8 clones to OFA or TSTA, may explain which mice develop T-cell lymphomas.

A RadLV-induced gamma delta T cell lymphoma displaying an antitumoral cytotoxicity

We described previously the induction by RadLV infection of a lymphoma (NS8) expressing a cytolytic activity against an MCA-induced fibrosarcoma. We report here that the cytolytic activity of these immortalized CD3+, CD8+ T cells is non-MHC-restricted. We then determined the structure and expression of the TCR chains expressed by these cells. Only partial rearrangement of the beta chain associated to an abnormally short transcript was detected in NS8 cells, whereas the gamma chain is rearranged and normally transcribed. On the opposite, rearrangement and expression of these genes were found in the other RadLV-induced lymphomas analysed. Moreover, gamma delta TCR proteins were detected on the cell surface of NS8 cells only, whereas the alpha beta complex, presents on the other T cell lines, was not expressed by NS8 cells. The ability of NS8 cells or of cells obtained from activated lymph nodes (harvested from mice grafted with the T2 sarcoma used to induce the NS8 line) to lyse the T2 sarcoma cell line was analysed. With both types of lymphocytes, the cytotoxicity was partially inhibited by a preincubation of the effector cells with anti-gamma delta antibodies. These results demonstrate that gamma delta lymphocytes can mediate anti-tumour cytotoxicity and NS8 lymphoma line may be representative of the TCR gamma delta CD8+ T cell subpopulation expressing non MHC-restricted cytotoxicity and displaying antitumoral activity.

Oligoclonality of Moloney leukemias

Induction of leukemia by non-transforming retroviruses results in the appearance of various hematopoietic tumors. It is believed that these tumors are monoclonal. In this work, the clonal nature of Moloney leukemia virus (MoLV)-induced tumors was studied. Two genetic parameters were used in order to identify leukemic clones: the pattern of the proviral integration sites and the rearrangement of the T-cell receptor complex (TCR). In more than 60% of the mice, different leukemic clones populated tumors developed in different organs of the same animal. Genotypic analysis of cell lines derived from a leukemic organ revealed that the tumor is composed of more than one clone. Phenotypic analysis of subclones which were derived from a monoclonal cell line showed variability in the expression of the Thy 1.2 and MHC antigens. The results indicate that MoLV-induced tumors are of oligoclonal nature. Each leukemic organ contains a mixture of leukemic clones, of which one is dominant.

Cellular events in radiation-induced lymphomagenesis

Fractionated whole-body irradiation induces thymic lymphomas in most of treated C57Bl/Ka mice. The cellular events occurring during the latency period consist of the emergence of preleukaemic cells and of marked alterations to the T-cell lineage and the microenvironment within the thymus. The proportions of the various thymocyte subsets are modified, suggesting a blockage in the normal differentiation process. Thymic epithelial cells are functionally modified, leading to decreased interactions with immature thymocytes. Interestingly, bone marrow grafting early after irradiation, which inhibits the development of lymphomas, induces the disappearance of preleukaemic cells from the thymus, whereas thymocyte subpopulations and thymic epithelium are restored. Interferon gamma and tumor necrosis factor alpha also prevent the onset of lymphomas. Studies on the effect of bone marrow transplantation and cytokine inoculation in split-dose irradiated mice should allow characterization of the factors that modulate the progression of preleukaemic cells towards the neoplastic state.

Characterization of cell markers in type B retroviral-induced thymic lymphomas--I. Surface antigen phenotype and karyotype in developing and primary lymphomas

CFW/D mice injected neonatally with a type B retrovirus, (DMBA-LV), rapidly develop thymic lymphomas. The present study examined simultaneously the karyotype and the expression of surface antigens on thymocytes from DMBA-LV treated mice at 28, 35 and 42 days of age during the development of lymphomas, and of cells from primary lymphomas. DMBA-LV treatment resulted in disturbances in the proportions of thymic Lyt 1+2-, Lyt 1-2+ and Lyt 1+2+ subpopulations. As a group, virus-treated mice showed a significant decrease in the size of the Lyt 1+2- subpopulation in thymuses during tumor development. However, developing tumors and primary tumors showed individual patterns of alteration in the proportions of thymocyte subpopulations rather than consistent trends for any one thymocyte subpopulation to increase or decrease. Cells with the abnormal chromosome complement, trisomy 15, were present early in the development of tumors and became the predominant karyotype in fully developed tumors. A correlation between the appearance of trisomy 15 and a particular thymocyte surface antigen phenotype was not detected. The results suggest that retrovirus infection disrupts, but does not eliminate the ability of developing thymocytes to form phenotypically distinct subpopulations.

N-methyl-N-nitrosourea-induced and spontaneous AKR/J thymic lymphomas express distinct differentiation antigen phenotypes

Spontaneous and N-methyl-N-nitrosourea (MNU)-induced AKR/J thymic lymphomas were characterized for expression of several lymphocyte differentiation antigens. The majority (53%) of spontaneous lymphomas expressed both Lyt-2 and L3T4 antigens, similar to the predominant normal thymocyte subset. In contrast, 63% of the thymic lymphomas induced by the chemical carcinogen MNU, expressed an Lyt-2+ L3T4- antigenic profile. Although this profile suggested that MNU-induced lymphomas are phenotypically similar to a mature thymocyte subset, the presence of ThB antigen on Lyt-2+ L3T4- lymphomas did not support this notion. Diagonal gel electrophoresis of 125I-labeled membrane extracts and immunoprecipitates revealed that 17 of 29 Lyt-2+ L3T4-MNU-induced lymphomas expressed cell surface T-cell receptor heterodimer components. Northern blot analyses confirmed that the T-cell receptor material was composed of alpha and beta polypeptide chains. The results from this study indicate a distinct origin or differentiation potential of the target cells involved in viral and chemical induced lymphomagenesis of AKR/J mice.