Human NKp44+IL-22+ cells and LTi-like cells constitute a stable RORC+ lineage distinct from conventional natural killer cells.

Lymphoid tissue inducer (LTi) cells are required for lymph node formation during fetal development, and recent evidence implies a role in mucosal immunity in the adult. LTi cells share some phenotypic features of conventional natural killer (NK; cNK) cells; however, little is known to date about the relationship between these two cell types. We show that lineage(-) (Lin(-)) CD127(+)RORC(+) LTi-like cells in human tonsil are precursors to CD56(+)CD127(+)RORC(+)NKp46(+) cells, which together comprise a stable RORC(+) lineage. We find that LTi-like cells and their CD56(+) progeny can be expanded and cloned ex vivo without loss of function and without conversion into cNK cells. Clonal analysis reveals heterogeneity of cytokine production within the CD127(+) LTi-like population. Furthermore, we identify within the tonsil a cNK precursor population that is characterized as Lin(-)CD117(+)CD161(+)CD127(-) cells. Overall, we propose that CD127(+)RORC(+) cells, although they share some characteristics with cNK cells, represent a functionally and developmentally distinct lineage.