Since MLL-AF9 and DNMT3A/FLT3ITD-driven leukemia may display the formation of extramedullary tumors, including in the spleen and liver32, we measured KLRG1+ST2+ Treg cells from other leukemic sites such as the spleen and liver and found similar phenotype as what was observed in the BM niche (Fig. 2A). This evidence concerns the gene MLLT3 and leukemia.