Solid tumors meet their demands for nascent blood vessels and increased glycolysis, to combat hypoxia, by activating multiple genes involved in angiogenesis and glucose metabolism. Hypoxia inducible factor-1 (HIF-1) is a constitutively expressed basic helix-loop-helix transcription factor, formed by the assembly of HIF-1alpha and HIF-1beta (Arnt), that is stablized in response to hypoxia, and rapidly degraded under normoxic conditions. It activates the transcription of genes important for maintaining oxygen homeostasis. Here, we demonstrate that engineered down-regulation of HIF-1alpha by intratumoral gene transfer of an antisense HIF-1alpha plasmid leads to the down-regulation of VEGF, and decreased tumor microvessel density. Antisense HIF-1alpha monotherapy resulted in the complete and permanent rejection of small (0.1 cm in diameter) EL-4 tumors, which is unusual for an anti-angiogenic agent where transient suppression of tumor growth is the norm. It induced NK cell-dependent rejection of tumors, but failed to stimulate systemic T cell-mediated anti-tumor immunity, and synergized with B7-1-mediated immunotherapy to cause the NK cell and CD8 T cell-dependent rejection of larger EL-4 tumors (0.4 cm in diameter) that were refractory to monotherapies. Mice cured of their tumors by combination therapy resisted a rechallenge with parental tumor cells, indicating systemic antitumor immunity had been achieved. In summary, whilst intensive investigations are in progress to target the many HIF-1 effectors, the results herein indicate that blocking hypoxia-inducible pathways and enhancing NK-mediated antitumor immunity by targeting HIF-1 itself may be advantageous, especially when combined with cancer immunotherapy.