Notch signaling is required for induction of an innate T cell development program in human thymus

CD4 CD8 double positive (DP) thymocytes progressively shut down Notch signaling after β-selection allowing progression of the DP program and positive selection of conventional CD4 and CD8 single positive T cells. In contrast, innate CD8+ T cells are selected from DP precursors shortly after β-selection. Here, we investigated whether notch signaling is required for the initiation of the innate T cell developmental program upon TCR engagement. We show that, after β-selection, Notch activation limits progression to late DP cells and favors the development of TCRαβ/CD3 expressing CD8dim early DP progenitors. TCR engagement in these Notch dependent TCRαβ+ early DP precursors does not induce prominent apoptosis, but rather induces T-bet expression by an mTOR-dependent mechanism. Our findings indicate that Notch signaling drives the launch of an innate effector program in response to TCR agonist selection in the thymus. Three samples are analyzed. The first sample comes from native thymus tissue. CD34+ postnatal thymocytes were transduced to express either TCRalpha (second sample) or TCRbeta (third sample). Subsequently, the transduced thymocytes were cultured on OP9-DL1 cells. When the cells were double positive, the cells were harvested sorted for immature CD3+ DP cells transgenic for the TCR.