Antigen-induced acquisition of effector CD8⁺ T-cell phenotype is promoted by IL-2 and IL-15 but suppressed by IL-21. Naive pmel-1 Thy1.1 CD8⁺ T cells were primed with cognate antigen and the indicated cytokine for 3 days. (A-C) Flow cytometric determination of granzyme B, CD44, and IL-2Rα expression by Thy1.1 lymphocytes. (D) Real-time RT-PCR determination of Eomes expression 3 days after priming in 10 ng/mL of the indicated cytokine. Error bars indicate the standard error of the mean. (E) CFSE dilution 4 days after antigen priming of naive pmel-1 Thy1.1 CD8⁺ T cells with the indicated cytokine. Histograms are gated on Thy1.1 cells. The open histogram overlay indicates CFSE labeling prior to stimulation.