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.