Flow cytometric analysis and immunoglobulin gene rearrangement studies of tumor cells from transgenic animals. (A) Flow cytometric analysis of involved tissues from from affected mice. I-line mice and N-line mice with lymphoma phenotype (I-836) show a large population of early B cells (B220⁺, CD3⁻, CD43⁺, BP-1⁺, CD117⁺, IgM⁻) in lymph node tumors (shown), as well as in bone marrow, spleen, and peripheral blood (data not shown). N-line animals with leukemic phenotype (N-2051) do not have adenopathy, but show a similar immunophenotype in the spleen (shown), marrow and blood (not shown). Normal cells can also be seen in these samples. Cells from an N-line animal with mediastinal tumor phenotype (N-2288) show tumor cells that are CD3⁺, B220⁻, CD2⁺, aβTCR⁺, and both CD4⁺/CD8⁺, as well as CD4⁺/CD8⁻ and CD4⁻/CD8⁺. (B-D) Immunoglobulin and T-cell receptor gene rearrangements in tumors from transgenic animals. (B)EcoRI digests, μVJ probe; faint low–molecular-weight bands in transgenic samples are due to nonspecific probe binding. (C)EcoRI + BamHI digests, kC probe; (D) HindIII digests, βTCR probe. Southern blot analyses of genomic DNA from tumor samples show clonal rearrangements of the immunoglobulin heavy-chain locus in I-line mice. The N-line founder shows a clonal rearrangement of the βTCR locus. Conversely, tumors from I-line mice do not show rearrangements of the kappa light-chain locus or βTCR locus. Genomic tail DNA from an unaffected littermate is used as a control and the germline bands are indicated by an arrow.