Reduced IL-15–dependent proliferation of CD44^high CD8 T cells and NK cells in vitro. (A) Histograms show expression of cytokine receptor chains on CD44^high CD62L^high CD8 T cells from wt (empty histograms) and c-myc⁺/– mice (filled histograms). (B) Sorted CD44^low and CD44^high CD8 T cells from wt and c-myc⁺/– mice were CFSE labeled and cultured in the presence of various concentrations of IL-15 for 4 days. (C) NK-enriched splenocytes from wt and c-myc⁺/– mice were CFSE labeled and cultured in the presence of various concentrations of IL-15 for 5 days. Graphs in panels B and C show the percentage of cells that have undergone more than 1 division.