By providing the detailed gene network analysis of NK cells cultured in 20% pO2 for 18 days vs. 1.5% pO2 exposed for 9 days following 9 days with IL-2 plus feeder cell pre-activation, we present the detailed molecular mechanisms underlying this specific hypoxia-induced synergy in NK cell expansion and tumor cytotoxicity. The gene discussed is IL2; the disease is neoplasm.