LAUSR

Solid tumors remain a major challenge for immunotherapy of cancer due to their immunosuppressive microenvironment. Hypoxia is a common feature of solid tumors and might affect immune cell activation within the tumor tissue. Upon hypoxia the transcription factor Hypoxia inducible factor 1a (HIF-1α) that affects many cellular processes including cell proliferation, survival and effector function becomes induced. Its impact on innate immune cells such as Natural Killer (NK) cells, however, is still incompletely understood. Natural Killer (NK) cells are considered as highly potent effector cells against tumors. Within the tumor tissue, however, NK effector function is often impaired. Our microarray analyses of tumor-infiltrated NK cells revealed upregulated levels of Hif1a. To determine the role of the HIF-1α in NK cell function, we generated the mouse strain Hif1a Δ/Δ Ncr1-iCre Tg in which HIF-1α is deficient in the NKp46 + lineage. Hif1a deficient NK cells showed greatly enhanced anti-tumor activity compared to wild-type NK cells, leading to a pronounced reduction of tumor growth. Tumor-infiltrated Hif1a deficient NK cells expressed lower levels of checkpoint molecules and show enhanced responses to tumor cells indicating a less exhausted phenotype. Hif1a deficient NK cells preferentially utilize oxidative phosphorylation (OXPHOS) than glycolysis to fuel their energy resulting in enhanced IFN-γ production in the hypoxic environment. In addition, using HIF-1α inhibitors we were able to greatly enhance human NK cell anti-tumor activity. Accordingly, our data reveal HIF-1α as a negative metabolic checkpoint for NK cells. Moreover, inhibition of HIF-1α holds high promise to refuel NK cell activation in cancer with a high potential for improving current strategies of NK cell-based cancer immunotherapy. Citation Format: Jing Ni, Lea Buhler, Ana Stojanovic, Annette Arnold, Veronika Sexl, Adelheid Cerwenka. Inhibition of the Hif1a -mediated checkpoint refuels NK activation in cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4743.