In vitro differentiation of postselection thymocytes by γc cytokine signaling. IL-7 is uniquely potent in driving CD8 cell differentiation. IL-21 signaling induces expansion of postselection thymocytes without CD8 lineage commitment, while IL-4 promotes differentiation of eomesodermin (EOMES) positive innate CD8 T cells. The non-γc cytokine IL-13, which uses the IL-4Rα, weakly induces CD8 cell differentiation. All other tested γc cytokines had no effect on postselection thymocytes. Professional illustration by Debra T. Dartez.