IkL/L cells express functional Ikaros proteins at ~10% of WT levels, and although IkL/L mice die from Notch-dependent T cell leukemias at 4–6 months of age, the animals studied (6–8 weeks of age) showed no signs of transformation (normal CD4/CD8 profiles, T cell receptor chain usage, Notch pathway activation) [19–21]. Here, CD4 is linked to T-cell leukemia.