Hypoxia-inducible factor 2-alpha promotes fitness of cytokine-activated human natural killer cells
Natural Killer (NK) cells are innate effector cells with potent antiviral, antitumor, and immunoregulatory functions that are relevant for the treatment of human diseases. There is a pressing need to better understand the mechanisms governing cellular fitness and functional persistence of NK cells to generate therapeutics regimens of sufficient durability to achieve meaningful clinical benefit. Given the central role of interleukin-2 (IL-2) and IL-15 in the survival and proliferation of NK cells, we sought to identify transcription factors induced by these cytokines that are essential for maintaining the fitness of human NK cells from healthy human blood donors. Culture in IL-2 or IL-15 increased protein expression of hypoxia inducible factor 2 alpha (HIF-2, encoded by EPAS1) but not HIF-1 in NK cells. Unexpectedly, induction of HIF-2 was not dependent on limited oxygen availability. CRISPR targeting of EPAS1 or pharmacological inhibition of HIF-2 protein expression markedly compromised the survival of cytokine-activated human NK cells. In contrast, inhibition of canonical HIF-2 transcription factor activity via blocking HIF-2/HIF-1{beta} heterodimer formation had no apparent effects on NK cell viability, function, or metabolism. These results suggest that cytokines, rather than hypoxia, activate an unconventional HIF-1{beta} independent, HIF-2 pathway that helps to maintain NK cells during cellular activation, revealing the potential promise of manipulating HIF-2 to improve the efficacy of adoptive NK cell therapies.