In normal conditions Tregs help to downregulate the immune system to reduce the risk of autoimmunity but in cancer when their number increases in the tumour microenvironment, they downregulate the functions of effector CD8+ CTLs and CD4+ CD25− T-cells by secretion of inhibitory compounds TGF-β and IL10 and thus help in tumour growth. This evidence concerns the gene TGFB1 and neoplasm.