Improved engraftment of STAT5ab^+/null recipients on either the BoyJ (CD45.1) or F1 (CD45.1/CD45.2) background. (A,B) Wild-type or STAT5ab^+/null mice on the CD45.1 background were injected with 5 × 10⁶ CD45.2 BM cells. The numbers of mice injected from 3 separate injection dates were wild type (n = 8) and STAT5ab^+/null (n = 8). The percentage of donor chimerism (% CD45.2⁺ cells) in each recipient mouse was determined 4, 8, and 18 weeks after transplantation. Multilineage analysis in Gr-1, B220, and CD4 cells was determined 18 weeks after transplantation on 4 of the wild-type and all of the mutant recipients. (C) A representative dot plot from the secondary transplantation is shown (one donor into 5 recipients). Data are from a pool of 3 wild-type or 3 STAT5ab^+/null engrafted mice used as donors. (D,E) Recipient mice on the F1 background were transplanted with 5 × 10⁶ CD45.1 BM cells on a single injection date. The percentage of donor chimerism (% CD45.1⁺CD45.2⁻ cells) in each recipient mouse was determined 7, 19, and 25 weeks after transplantation for wild-type (n = 8) and STAT5ab^+/null (n = 7) mice. One mouse died between 19 and 25 weeks. For multilineage analysis, the percentage of CD45.1⁺CD45.2⁻ cells was determined for Gr-1, B220, or CD4 cells in each recipient mouse 25 weeks after transplantation. (F) Representative dot plot (gated first on Gr-1, B220, Ter119, or CD4) after secondary transplantation with a pool of 3 wild-type and 3 STAT5ab^+/null engrafted mice (one donor into 5 recipients). Above each plot in panels C and F are mean plus or minus SD values of the percentage of donor chimerism from 5 recipients.