Enhancing anti-tumor immunity of natural killer cells through targeting IL-15R signaling.

Interleukin-15 receptor (IL-15R) agonists induce anti-tumor immunity in pre-clinical models. However, dose-limiting toxicity has hampered their clinical development. We performed genome-wide CRISPR screens to reveal the complete IL-15R signaling mechanism in natural killer (NK) cells and discovered that ubiquitin-dependent IL-15R degradation is the dominant mechanism restraining IL-15R signaling. Key hits included the NEDD8 E2-conjugating enzyme UBE2F, the ubiquitin E3-ligase ARIH2, and Cullin-5 RING E3 ligase (CRL5) members. We found that UBE2F was required for neddylation and activation of CUL5, whereas ARIH2 contributed to CRL5-mediated IL-15RB degradation. Ablation of ARIH2 or UBE2F increased IL-15RB surface expression and enhanced signaling, resulting in proinflammatory cytokine production and augmented natural and CAR-mediated cytotoxicity. In mice lacking Arih2, Rnf7, or Ube2f, we observed that the IL-15R hyperresponsive NK cells exhibited superior in vivo anti-tumor immunity against primary and disseminated metastatic tumors. Thus, we have identified the enzymes UBE2F and ARIH2 as tractable immunotherapy drug targets.