Pathological findings of TCF8 mutant mice. (A) Gross autopsy of TCF8 mutant mice with thymic tumors. A large thymic tumor () was observed at the mediastinum of the dissected mouse. (B) Hematoxylin and eosin staining of tumor sections from the mouse as indicated. The normal thymic cellular architecture in the TCF8 mutant mice is replaced with monotonous fields of large, highly mitotic lymphoblasts with small Hassall bodies (◀). The scale bar indicates 20 μm. Original magnification ×400. (C) The tumor cells invaded the lung, vascular tissues, and heart in the mouse. The scale bar indicates 500 μm. Original magnification ×25. (D) The tumor cells invaded the muscular tissues of the chest wall. The scale bar indicates 50 μm. Original magnification ×200. (E) Hematoxylin and eosin staining of peripheral lymph nodes. Tumor cells showed a diffuse proliferation of monomorphic lymphoma cells, focally mixed with tingible body macrophages (“starry-sky appearance”) (◀). The scale bar indicates 100 μm. Original magnification ×100. (F) Hematoxylin and eosin staining of peripheral lymph nodes. The scale bar indicates 20 μm. Original magnification ×400. (G) Tumor cells from the thymic tumor were analyzed by staining with a combination of monoclonal antibodies, either Thy1.2-PE with B220-FITC (left) or CD4-PE with CD8-FITC (right) and FACS. (H) The tumor cells of the CD3⁺B220⁻ population did not express Vβ6.1 TCR (left), but showed weak expression of Vβ8.1-8.2 TCR (right). (I) Tumor cells from the liver (left) or spleen (right) were analyzed by staining with a combination of monoclonal antibodies, CD4-PE and CD8-FITC.