Based on analyses in mature T cells, a transcriptional circuitry is proposed in mature thymocytes, that enables expression of IL-7Rα, CCR7 and Klf12, which itself controls thymic egress by increasing expression of the receptor for sphingosine 1-phophate (S1P1), T cell trafficking and quiescence. Foxo1 activity is inhibited by PI-3 kinase-dependent phosphorylation, that promotes its sequestration in the cytosol, contributing to the self-limiting IL-7Rα expression characteristic of mature T cells176. It may also act as a ‘licensing’ factor in the thymus to prevent the release of self reactive thymocytes due to their persistent TCR signaling.