Mechanistic and functional validation in human AML lines, primary blasts, and two syngeneic mouse models (MLL-AF9, AML1-ETO9a) shows that exogenous leptin markedly blunts Ara-C cytotoxicity, whereas the high-affinity LEPR antagonist Allo-aca restores chemosensitivity without altering baseline leukemia growth. The gene discussed is KMT2A; the disease is acute myeloid leukemia.