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

Abstract

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 (NCR+ILC3s) 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 NCR+ILC3s 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 NCR+ILC3 differentiation, but conversely suppressed IL-15–dependent cNK cell generation in CD45RA+Flt-3−c-Kitlow, a novel innate lymphocyte-committed HPC subpopulation. In contrast, Notch signaling induced CD45RA−Flt-3+c-Kithigh multipotent HPCs to generate CD34+CD7+CD62Lhigh, the earliest thymic progenitor–like cells, which preserved high cNK/T cell potential, but lost NCR+ILC3 potential. These findings implicate the countervailing functions of Notch signaling in the fate decision between NCR+ILC3 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 NCR+ILC3 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 NCR+ILC3 commitment.

Identification of Novel Human NK Cell Progenitor Subsets

“…In contrast, in vitro culture of identical progenitors in IL-7 + IL-15 and Notch-ligand resulted in the proliferation of both CD7 + and CD7 − progenitors, arguing against IL-15 purely inducing CD7 on responsive progenitors ( Figure 1 A). Consistent with a recent report [ 17 ], Notch signalling and IL-7 appear to impair commitment towards the NK cell lineage as evidenced by reduction in proliferating CD7 + progenitors. We next assessed if CD7 + progenitors derived from cord blood conserved this preferential sensitivity to IL-15.…”

Notch Signaling as a Regulator of the Tumor Immune Response: To Target or Not To Target?

“…Notch1 knockdown completely blocks T cell development and increases the accumulation of ectopic B cells in the thymus ( 12 , 13 ). Moreover, Notch1 [and maybe also Notch 2 ( 14 )] regulates the early phases of T cell differentiation in the thymus (through DLL4), but its expression needs to be decreased before T cells can fully differentiate ( 15 ). Upon migration of immature B cells from bone marrow to spleen, an increased level of Notch2 expression regulates the maturation of a subset of B cells that reside in the marginal zone, MZB cells.…”

“…However, Notch2 does not control other mature B cells including follicular B cells and plasma cells ( 16 ). Moreover, in vitro studies have shown that Notch signaling enhances T- and NK cell differentiation from human hematopoietic progenitor cells (CD34 + ), while inhibiting B cell differentiation ( 14 , 17 ). Notch also has opposing roles in controlling cell fate decisions between two different types of NK cells, i.e., conventional NK cells versus innate lymphoid cell (ILC)-derived natural cytotoxicity receptor (NCR) NKp44 + group (NCR + ILC3)—at different maturational stages of progenitor cells.…”

“…This is dependent on the type of the progenitor cells. Notch can augment the differentiation of one type of these NK cells while suppressing the other types ( 14 ).…”

Interleukin-7 Receptor Alpha in Innate Lymphoid Cells: More Than a Marker

“…Whereas, high IL-7 and medium Notch signaling favors ILC2 and ILC1/NK cell differentiation, low IL-7 and high Notch signaling favors T cell differentiation in mice (76). The results are however different when human hematopoietic progenitor cells are treated in a similar manner, where IL-7, and Notch signaling induce ILC3 differentiation while suppressing IL-15 induced NK cell differentiation (77). These findings reveal contrasting roles for IL-7 in ILC differentiation which can be explained by differences in mouse and human hematopoiesis and progenitor sources.…”