STAT5A/5B-deficient HSCs possess inferior competitive repopulating capacity.

Peripheral blood, thymus, and bone marrow were harvested from irradiated recipients 10 weeks after receiving either 2 × 10⁵ competitor cells only (“No Tester,” n = 2), 2 × 10⁵ competitor cells plus STAT5A/5B^+/+ tester cells (“STAT5A/5B^+/+Tester,” n = 3), or 2 × 10⁵ competitor cells plus STAT5A/5B^−/− tester cells (“STAT5A/5B^−/−Tester,” n = 6). FACS analysis was performed by using lineage markers and CD45.1 and CD45.2, and the results for the indicated lineage-specific subsets are displayed. (A) Peripheral blood cells positive for Gr-1⁺ (P < .001), B220⁺ (P < .001), or CD3⁺(P = .002). (B) Cells from hematolymphoid organs, including bone marrow cells expressing for Gr-1 (P < .001), B220 (P = .001), Ter-119 (P = .001), or CD41 (P < .001) and thymocytes expressing CD3 (P < .001). (C) Bone marrow cells from the lin⁺ (P < .001), lin^dimSca-1^neg/lo (P < .001), and lin^dimSca-1⁺ (P < .001) subsets; in this case CD45.2⁺ cells were scored according to CD45.1⁻ phenotype.