Adaptive from Innate: Human IFN-γ(+)CD4(+) T Cells Can Arise Directly from CXCL8-Producing Recent Thymic Emigrants in Babies and Adults

We recently demonstrated that the major effector function of neonatal CD4(+) T cells is to produce CXCL8, a prototypic cytokine of innate immune cells. In this article, we show that CXCL8 expression, prior to proliferation, is common in newly arising T cells (so-called “recent thymic emigrants”) in adults, as well as in babies. This effector potential is acquired in the human thymus, prior to TCR signaling, but rather than describing end-stage differentiation, such cells, whether isolated from neonates or adults, can further differentiate into IFN-γ–producing CD4(+) T cells. Thus, the temporal transition of host defense from innate to adaptive immunity is unexpectedly mirrored at the cellular level by the capacity of human innate-like CXCL8-producing CD4(+) T cells to transition directly into Th1 cells.