Development of human natural killer cells and other innate lymphoid cells

• NK cells and other ILC share a ID2+ precursor.
• Developmental relationships exist among different innate lymphoid cells.
• NK cells and ILC3 subsets share NCR expression.
• Immature NK cells and ILC2 share CD161, IL-13, and IL-5 expression.
• Possible role of different ILC in HSCT.

Innate lymphoid cells (ILC) have recently gained much attention in immunology. They represent a novel developmentally related family. Three distinct subsets have been identified on the basis of phenotypic and functional criteria and termed ILC1, ILC2, and ILC3. The available data suggest that ILC play an important role in innate defenses against different pathogens, in lymphoid organogenesis, and in tissue remodeling. All these aspects are relevant in hematopoietic stem cell transplantation (HSCT), particularly in the haplo-HSCT setting, in which donor NK cells are known to play a major therapeutic role, while the involvement of other ILC is still undefined. In this context, it has been postulated that all ILC share a common precursor expressing the ID2 transcription factor. While the differentiation of human NK cells (belonging to ILC1) is now well characterized both in vitro and in vivo, limited information is available on the development of human ILC2 and ILC3 and of their relationships with NK cells. In this review, we will summarize the present knowledge on the developmental relationship among different ILC, with particular focus on early stages of NK cell differentiation, and their features shared with ILC2 and ILC3.