IL-2 was approved for the treatment of advanced renal cell carcinoma (RCC)3 and metastatic melanoma,4 whereas IFN-α was approved for the treatment of hairy cell leukaemia,5 follicular non-Hodgkin lymphoma,6 melanoma7 and AIDS-related Kaposi’s sarcoma.8 The clinical use of these cytokines marked a milestone in cancer immunotherapy, as it was the first demonstration that immunotherapy could favourably tilt the balance between cancer and the anti-tumour immune response, leading to durable objective responses. This evidence concerns the gene IL2 and cancer.