Impaired CD8⁺ and γδ T-cell development in Stat5a/b^null/null survivor mice. (A) Picture of a Stat5a/b^null/null survivor mouse (left) compared with a Stat5a/b^+/+ littermate at the age of 4 weeks. Representative body weight values and numbers of Stat5a/b^null/null mice and littermates surviving up to day 8, weaning (day 21), or day 42 are depicted. (B) Numbers of CD4^–/CD8^–/γδTCR⁺ T lymphocytes in thymi of Stat5a/b^null/null, Stat5a/b^ΔN/ΔN, and respective littermate controls. (C) Flow cytometric analysis of CD4⁺, CD8⁺, and CD4⁺/CD8⁺ cells in thymi and lymph nodes of 5 Stat5a/b^null/null survivors and 2 individual Stat5a/b^null/+ and 2 Stat5a/b^+/+ littermate controls. Data are summarized in bar graphs. Due to the small size of thymi and lymph nodes, cells were pooled and did therefore not allow generation of error bars (B-C).