Mice coexpressing Bcl-X_L and c-Myc develop clonal B- and plasma cell tumors. (A) (Left) Spleens from a double transgenic (top) and littermate control (bottom) mousee. (Right) H&E-stained spleen section of a double transgenic mouse. Cells are pleomorphic with an elevated mitotic index. (B) H&E-stained section of a lung of a double transgenic mouse. Aggregates of lymphocytes line the alveolar walls. (C) Radiography (top) demonstrates areas of bone lysis, and the H&E-stained section of the femur of a double transgenic mouse (bottom) shows replacement of bone marrow by sheets of plasma cells. (D) Southern analysis of samples collected from double transgenic mice (DP indicates double positive). Original magnifications: × 10 (C, top panel); × 40 (B; C, bottom panel); and × 100 (A, right panel).