My-bi HSCs give rise to progeny with a blunted response to IL-7. BMCs were cultured with (▪) or without (□) 10 ng IL-7 for 6 days. (A) The number of viable cells retrieved after culture is expressed as a percentage of the number of cells seeded. Data are representative of 7 independent experiments with control BM and 3 experiments with independent My-bi HSCs. The My-bi HSCs analyzed here had been injected into IL-7R knockout hosts. Thus, host-type cells could not contribute to the response. Cell numbers recovered from IL-7–supplemented cultures derived from a host repopulated by a My-bi clone are not different from those recovered from control BM cultured without IL-7 (P = .55). The number of cells recovered after IL-7 stimulation from control BMCs and previously transplanted (multiclonal) BMCs (B) or BMCs from a host that had received a balanced HSC clone (C) are not significantly different (P = .43 and P = .7644, respectively). The differences for both groups between cultures with (▪) and without (□) IL-7 are significantly different (P ≥ .03). All data are means ± SD of duplicate cultures. (D) Immunofluorescence analysis of the BMC cells from panel A after culture. The percentage of B220+ (▦) and Gr1+ plus Mac-1+ cells (▨) in the donor-type population after culture is shown. All cultures contained at least 70% donor-type cells.