An early decrease in Notch activation is required for human TCR-αβ lineage differentiation at the expense of TCR-γδ T cells

Although well characterized in the mouse, the role of Notch signaling in the human T-cell receptor alpha beta (TCR-alpha beta) versus TCR-gamma delta lineage decision is still unclear. Although it is clear in the mouse that TCR-gamma delta development is less Notch dependent compared with TCR-alpha beta differentiation, retroviral overexpression studies in human have suggested an opposing role for Notch during human T-cell development. Using the OP9-coculture system, we demonstrate that changes in Notch activation are differentially required during human T-cell development. High Notch activation promotes the generation of T-lineage precursors and gamma delta T cells but inhibits differentiation toward the alpha beta lineage. Reducing the amount of Notch activation rescues alpha beta-lineage differentiation, also at the single-cell level. Gene expression analysis suggests that this is mediated by differential sensitivities of Notch target genes in response to changes in Notch activation. High Notch activity in-creases DTX1, NRARP, and RUNX3 expression, genes that are down-regulated during alpha beta-lineage differentiation. Furthermore, increased interleukin-7 levels cannot compensate for the Notch dependent TCR-gamma delta development. Our results reveal stage-dependent molecular changes in Notch signaling that are critical for normal human T-cell development and reveal fundamental molecular differences between mouse and human. (Blood. 2009; 113: 2988-2998)