Cell dose response for engraftment of C57BL/6 background BM cells following injection into nonirradiated W/W^v hosts. (A) To determine the dose-response relationship for C57BL/6 wild-type mouse engraftment, BM cells were injected at doses of 5 × 10⁴, 1 × 10⁵, and 5 × 10⁵ cells into W/W^v hosts. (B) The same doses were also injected for C57BL/6 STAT5ab^–/– donor BM cells. For both C57BL/6 wild-type and STAT5ab^–/– BM injections, engraftment was determined 16 weeks later by hemoglobin electrophoresis. Shown on the right of each panel are the Hb_s and Hb_d controls.