Stat5b-mediated thymocyte and splenic expansion in pre-TCRα^−/− mice. (A) Thymic CD4/CD8 profiles of 10-week-old pre-TCRα^−/− mice with and without the Stat5b transgene, with pre-TCRα^+/− serving as controls. Numbers indicate the percentage of cells in each quadrant, and total cellularity is indicated above each dot plot. (B) HSA surface expression on CD8⁺ SP thymocytes in pre-TCRα^−/− mice. Numbers indicate the MFI for the CD8⁺ SP population as well as the percentage within the gated region. (C) Splenic CD4/CD8 profiles from the same mice. Numbers indicate the percentage of cells in each quadrant, and total cellularity is indicated above each dot plot. (D) HSA staining on CD8⁺ splenocytes. Numbers indicate the MFI for the CD8⁺ SP population as well as the percentage within the gated region. (E) CD44/IL-2Rβ profile gated on CD8⁺ T cells. The CD44^hiIL-2Rβ^hi memory population are expanded in Stat5b TG/pre-TCRα^−/− mice. Numbers indicate percentage of CD44^hiIL-2Rβ^hi memory phenotype CD8⁺ cells within the gated region, and numbers in parentheses indicate percentage of total splenocytes within gated region. Representative data are shown from 1 of 4 similar experiments involving a total of 8 Stat5b TG/pre-TCRα^−/− and 8 pre-TCRα^−/− mice.