Lin28b-transgenic mice develop T-cell tumors. (A) Survival of Lin28b mice from C3 (n = 17) and D4 (n = 19) founders compared with WT littermate controls (n = 27). Median survival was 14.5 and 16 months for the D4 and C3 lines, respectively, P < .0001 compared with WT controls by log-rank test. (B) Eosinophil counts from PTCL mice with a mean age of 12 months compared with WT mice, also mean age 12 months. *P < .05. (C-D) CD3 staining of tumor cells (C; dashed line, isotype control; solid line, CD3) and CD4 positivity of tumor cells from mouse 6180 (D). (E) Immunohistochemistry of tissues from mouse 6180. Scale bars for the spleen indicate 500 μm (low magnification) and 50 μm (high magnification inset). Scale bars for the liver and lung indicate 500 μm (low magnification) and 200 μm (high magnification inset). Black square indicates area enlarged for inset. (F) Southern blot for Tcrb gene rearrangements. SstI-restricted genomic DNA, hybridized to a TCRb probe *Germline band; white arrows, nongermline-rearranged bands. (G) Immunoblot for Lin28b expression. Lanes 1-7, Lin28b tumor no. 6266, 6222, 6226, 6297, 6316, 6358, and 6549 with WT spleen as the negative control. (H) Immunoblot for Syk expression. Lanes 1 through 7, Lin28b tumors 6266, 6222, 6226, 6297, 6316, 6358, and 6569; lane 8, WT spleen (positive control); lane 9, WT brain (negative control). (I) LIN28A and LIN28B expression in patients with PTCL³⁴  compared with mean values of activated CD4⁺ (aCD4) T cells (n = 4). Solid blue (LIN28B) and solid red (LIN28A) lines represent means for activated CD4⁺ T cells; dashed lines represents 1 SD from these means. Each bar represents 1 PTCL patient; data are presented on a logarithmic scale.