We and others have previously shown that accumulation of CD4+CD8+ DP cells in spleen (SPL), lymph nodes and peripheral blood (PB) represents a pathognomonic feature of T-cell leukemias sustained by enforced expression of NIC in pre-T-cells or in bone marrow of mice.5, 7 As shown in Figure 3c, upper panels, and Supplementary Figure 3a, DP cells appeared in the SPL of 6-week-old double mutant N3IC-tg/Pin1−/− mice in a similarly increased percentage with respect to N3IC-tg littermates, when compared with wt (Pin1+/+) mice. This evidence concerns the gene PIN1 and T-cell leukemia.