Stat5b-mediated CD8⁺ thymic T-cell expansion and lymphoma on the TCRα^−/− background. (A) Thymic CD4/CD8 profiles of 4-week-old TCRα^−/− mice with and without the Stat5b transgene. Numbers indicate the percentage of cells in each quadrant, and total cellularity is indicated above each dot plot. Note the increase in the percentage of CD8⁺ SP cells (with comparable total cellularity) in Stat5b TG/TCRα^−/− mice. (B) CD4/CD8 profiles of 12-week-old TCRα^−/− mice with and without the Stat5b transgene. The Stat5b TG/TCRα^−/− mice had grossly enlarged thymi and spleens consistent with T-cell lymphoblastic lymphoma. (C) CD3 and HSA surface expression on CD8⁺ SP thymocytes in TCRα^−/− mice. Numbers indicate the MFI for the CD8⁺ SP population as well as the percentage of mature cells (gated on CD3^hi/HSA^lo). Representative data are shown from 1 of 4 similar experiments involving a total of 12 Stat5b TG/TCRα^−/− and 10 TCRα^−/− mice.