Competitive long-term repopulating ability of wild-type, c-Mpl^-/-, and STAT5ab^-/- BM cells in vivo. (A) BM cells from Ly-5.2 background wild-type, c-Mpl^-/-, or STAT5ab^-/- mice were collected from 1 donor mouse (experiment 1) or 2 donor mice (experiment 2) and mixed 5:1 with wild-type BM cells from congenic Ly-5.1 mice and injected into lethally irradiated hosts (Ly-5.1). Seventeen weeks later recipient mice were analyzed by FACS for Ly-5.2⁺ cells in multiple peripheral blood hematopoietic lineages (Gr-1, myeloid; B220, B-lymphocyte; CD4, T-lymphocyte; and Ter119, erythroid progenitor) from 3 recipients (experiment 1) and 3 recipients (experiment 2). The results of experiment 1 and experiment 2 (n = 6) were averaged. Shown is the percentage of Ly-5.2⁺ cells in multiple lineages of primary recipients, representing 3 donor mice from 2 separate experiments. The results of total Ly-5.2⁺ cells in all 10 primary recipients were similar to the multilineage analysis (data not shown). At 26 weeks (experiment 1) and 17 weeks (experiment 2), these mice were killed, and the BM cells were injected into secondary Ly-5.1 recipients, and after 12 to 16 additional weeks the engraftment in the total peripheral blood mononuclear fraction was determined by FACS (described in “Results”). (B) At 17 weeks after transplantation, a portion of the BM from the second of the 2 competitive repopulation experiments was harvested from the primary mice that received transplants and used for analysis of the relative engraftment in BM populations enriched for c-Kit expression. Ly-5.1–negative control and Ly-5.2–positive controls that did not receive transplants are shown on the left for both peripheral blood and BM analyses. Error bars indicate standard deviation.