Fate determination of the cells from tumour-bearing mice that had produced IL-17A (ex-Th17 cells) shows that a considerable proportion of eYFP+ cells begin expressing Foxp3 and the percentages of ex-Th17 Foxp3+ CD4+ T cells gradually increases (Fig. 1b and Supplementary Fig. 1c), while the percentage of eYFP+Foxp3neg cells (that is, ‘true' Th17 cells) declines at the later time points (Supplementary Fig. 1d). The gene discussed is FOXP3; the disease is neoplasm.