Interleukin-35 impairs human NK cell effector functions and induces their ILC1-like conversion with tissue residency features

While Natural Killer (NK) cells are key players in immune defenses against pathogens and cancers, by directly killing dangerous cells and supporting antitumor functions of other immune cells, they progressively get dysfunctional in chronic inflammatory diseases through mechanisms that remain insufficiently understood. NK cell development, survival, activation, and functions are highly regulated by cytokines. Among them, Interleukin 35 (IL-35), a new member of the IL-12 family released during chronic inflammations, plays a role in immune suppression. However, the direct effect of IL-35 on NK cells is still unknown. In this study, we observed that IL-35-exposed human primary NK cells display dampened proliferation and effector functions associated with differential expressions of activating and inhibitory NK receptors. Brief exposure to IL-35 inhibited NK cell activation and ability to secrete pro-inflammatory cytokines and chemokines, while promoting their production of pro-angiogenic factors and TGF-β. Furthermore, prolonged exposure to IL-35 placed NK cells in a functionally hyporesponsive state associated with a TGF-β-dependent conversion into CD9+ CD103+ CD49a+ ILC1-like cells. Single cell RNAseq further confirmed these observations and revealed an ILC1-like heterogeneity associated to the initial NK subpopulation undergoing the conversion. Thus, our findings identify a new role of IL-35 as a driver of NK cell plasticity leading to the acquisition of tissue residency features and weakened effector functions that might play a role in physiopathological contexts and represent an attractive target for future immunotherapies.