These data reveal that with the progression of AML, leukemic ST2+ Treg cells are increasingly enriched in the T cell pool of the leukemic niche (BM, spleen, or liver), which correlates with depletion of total leukemic CD8 as well as increased exhaustion resulting in a diminished type 1 phenotype. The gene discussed is IL1RL1; the disease is acute myeloid leukemia.