Fate Decision Between Group 3 Innate Lymphoid and Conventional NK Cell Lineages by Notch Signaling in Human Circulating Hematopoietic Progenitors.

The role of Notch signaling in human innate lymphoid cell (ILC) differentiation is unclear, although IL-7 and IL-15 promote differentiation of natural cytotoxicity receptor (NCR) NKp44 group 3 ILCs (NCRILC3s) and conventional NK (cNK) cells from CD34 hematopoietic progenitor cells (HPCs) ex vivo. In this study, we analyzed the functions of Notch in the differentiation of NCRILC3s and cNK cells from human HPC subpopulations circulating in peripheral blood by limiting dilution and clonal assays using high-throughput flow cytometry. We demonstrated that Notch signaling in combination with IL-7 induced NCRILC3 differentiation, but conversely suppressed IL-15-dependent cNK cell generation in CD45RAFlt-3c-Kit, a novel innate lymphocyte-committed HPC subpopulation. In contrast, Notch signaling induced CD45RAFlt-3c-Kit multipotent HPCs to generate CD34CD7CD62L, the earliest thymic progenitor-like cells, which preserved high cNK/T cell potential, but lost NCRILC3 potential. These findings implicate the countervailing functions of Notch signaling in the fate decision between NCRILC3 and cNK cell lineages at different maturational stages of human HPCs. Inhibition of Notch functions by Abs specific for either the Notch1 or Notch2 negative regulatory region suggested that both Notch1 and Notch2 signals were involved in the fate decision of innate lymphocyte-committed HPCs and in the generation of earliest thymic progenitor-like cells from multipotent HPCs. Furthermore, the synergistic interaction between Notch and IL-7 in NCRILC3 commitment was primarily explicable by the induction of IL-7 receptor expression in the innate lymphocyte-committed HPCs by Notch stimulation, suggesting the pivotal role of Notch in the transcriptional control required for human NCRILC3 commitment.