Karyotypic variation of cells from murine thymic lymphomas during short-term culture

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.

Characterization of cell markers in type B retroviral-induced thymic lymphomas--II. Surface antigen phenotype, karyotype and proviral integration pattern in cultured lymphoma cells and cloned lines

This study examined the surface antigen phenotype, karyotype and proviral integration patterns of cultured cells from murine thymic lymphomas induced by injecting neonatal mice with the type B leukemogenic retrovirus (DMBA-LV). Cells from the primary thymic lymphomas were established in mass culture and from these, clonal tumor cell lines were derived. During in vitro culture of lymphoma cells, Lyt 1-2+ cells predominated with an apparent selection against cells of the Lyt 1+2- and Lyt 1+2+ phenotypes. Of 21 cloned lines established, five had a diploid chromosome complement and expressed the Lyt 1-2+ phenotype. The other 16 clones lines were characterized by trisomy of chromosome 15 and expressed the Lyt 1+2+ or Lyt 1-2+ phenotype. Cells characterized by either a diploid or trisomy chromosome complement were capable of growth in vivo. Southern blot analyses showed that during growth in culture, cells from the mass cultures and cloned lines continued to acquire low numbers of new integrated DMBA-LV proviral copies while maintaining the basic proviral integration pattern present in the DNA from cells of the primary lymphomas. These findings support the notion that the acquisition of new genetic information in cells from DMBA-LV-induced thymic lymphomas may contribute to the continual generation of tumor heterogeneity.