Prompted by the observation that NKp46-expressing NK cells infiltrate hypoxic tumours (Fig. 1a), and in order to test the role of HIF-1α in NK cells, we created an in vivo, targeted deletion of HIF-1α in NK cells, via crosses of the loxP-flanked HIF-1α allele14 to the Ncr1 (NKp46) promoter-driven Cre recombinase15,16, specific to NKp46-expressing innate lymphoid cells17, including NK cells (HIF-1αfl+/fl+/Ncr1cre + mice, termed HIF-1α KO). Here, HIF1A is linked to neoplasm.