Sur-TCR-Tg mice develop lethal leukemia. (A) Leukemia developed in progeny of all 3 founders beginning at 4 to 6 months, with equivalent latency and penetrance in Sur-TCR-Rag^+/− and Sur-TCR-Rag^−/− mice. (B) T-ALL mice (right) had enlarged spleens (top) and thymi (bottom) at necropsy compared with WT mice (left). (C) Hematoxylin and eosin (H&E) staining of thymus (top), and anti-TdT immunohistochemistry of spleen (bottom) in preleukemic 6-week-old Sur-TCR-Tg mice (left) and T-ALL 6-month-old Sur-TCR-Tg mice (right) (×50 magnification). T-ALL mice show complete effacement of the affected organs. (B-C) Examples from 1 representative mouse, and similar results were observed in >6 animals of each type.