TGFB1 and leukemia: ST2+ Treg cells in the leukemic niche secrete large amounts of key regulatory cytokines such as TGFβ and IL-10 compared to ST2+ Treg cells in mice without tumor (Fig. 2B, MLL-AF9 leukemia and Fig. 2C, DNMT3A/FLT3ITD leukemia).