Engraftment of C57BL/6 background STAT5ab^–/– BM cells following injection into nonirradiated W/W^v hosts. To determine whether STAT5ab^–/– BM cells could engraft into W/W^v mice, we injected in 3 separate transplants donor STAT5ab^–/– (n = 4) or wild-type (n = 3) BM cells into nonirradiated W/W^v recipients. The mice were analyzed 20 weeks after injection by hemoglobin electrophoresis for the relative level of donor cell engraftment (top panel). Shown on the right are Hb_s, Hb_d, and W/W^v controls. The engraftment level was also confirmed at the DNA level in BM and spleen (SP) tissues from 5 primary recipients of STAT5ab^–/– BM and 3 primary recipients of wild-type BM derived from 2 different donors. Donor number below each set indicates which of the primary recipients were from the same donor mouse. The percentage of Hb_s is also shown below each lane to indicate the level of donor C57BL/6 contribution. Analysis was done by Southern blot for the donor hemoglobin type (bottom panel). An Hb_s control is shown on this blot. Although the loading of lanes was not equal, this did not preclude densitometry analysis of individual lanes for the percentage contribution of Hb_s and Hb_d.