Reduced levels of c-Myc strongly impair IL-15 responsiveness of CD44^high CD8 T cells in vivo. (A) Total splenocytes from wt (Thy1.1⁺) and c-myc^+/– (Thy1.1⁺Thy1.2⁺) mice were CFSE labeled and adoptively cotransferred into sublethally irradiated IL-15^–/– mice and wt controls (Thy1.2⁺). Histograms show CFSE profiles from donor wt and c-myc⁺/– CD8 T cells 7 days after adoptive transfer. (B-C) Bar graphs show the mean percentages ± SD of CD44^low and CD44^high CD8 T cells (B) and NK cells (C) in the spleen from the progeny of c-myc⁺/– IL-15⁺/– crossed with IL-15⁺/– mice. Bar 1 shows wt; bar 2, c-myc⁺/–; bar 3, IL-15⁺/–; bar 4, c-myc⁺/–IL-15⁺/–; bar 5, IL15^–/–; and bar 6, c-myc⁺/–IL15^–/–.*P < .05 group 3 versus 4; **P < .01 group 1 versus 2.