T-cell-mediated apoptosis and elimination of IFN-γ-expanded KSL cells. (A) Activated CD8 T cells were sorted from the BM of B6 mice pretreated with sublethal TBI and FVB LN cell infusion (induced BM failure) and then mixed with KSL cells from IFN-γ-treated (10 μg per mouse) or control B6 mice at a CD8:KSL cell ratio of 10:1. Cells were cultured at 37°C for 60 minutes. IFN-γ-treated KSL cells (n = 4) had significantly higher proportion of annexin V⁺ cells compared with untreated KSL cells (n = 2). (B) In another experiment, KSL cells from IFN-γ-injected (n = 2) or untreated control (n = 3) B6 mice were mixed with activated CD4 and CD8 T cells at a KSL:CD4:CD8 ratio of 1:5:10 and cultured at 37°C for 60 minutes. Activated CD4 and CD8 T cells caused an increase in annexin V⁺ cells in IFN-γ-expanded KSL cells. (C) FVB mice were treated with IFN-γ (10 μg per mouse) on day 0 (IFN-γ; n = 4), IFN-γ (10 μg per mouse) on day 0 plus 6 × 10⁴ activated CD8 T cells per mouse on day 1 (IFN-γ+CD8; n = 3), 6 × 10⁴ activated CD8 T cells only per mouse on day 1 (CD8; n = 4), or nothing (control; n = 4) and were euthanized on day 2 to harvest BM cells for flow cytometry analyses. Total number of KSL cells recovered was significantly reduced in the IFN-γ+CD8 treatment group compared with the IFN-γ group. SSC-A, side scatter-area. *P < .05; **P < .01.