FIG. 3.

53BP1^−/− mice are tumor prone. (A) CD4 and CD8 cell surface expression of cells from two different thymic lymphomas was assessed by flow cytometry. (B) Massive thymic lymphoma (T) in a 4-month-old 53BP1^−/− mouse. (C) Hematoxylin-and-eosin-stained sections from the thymus, spleen, and kidney of a 53BP1^−/− animal with thymic lymphoma. Monomorphic lymphoblastic tumor cells are dominant in all three tissues. The arrows indicate mitotic figures. G, glomerulus; PT, proximal tubulus. (D) Overall survival of 53BP1^+/+ (n = 54), 53BP1^+/− (n = 97), and 53BP1^−/− (n = 101) mice over a period of 10 months.