(1) Lactylation enhances MDSC‐mediated immunosuppression: Lactylation promotes Arg1 and IDO1 expression, increasing MDSC suppression of T cells. (2) Regulates metabolic adaptation: Lactylation enhances MDSC utilization of lactate, promoting their persistence in the tumor microenvironment. (3) Inhibits T cell function: Lactylation increases reactive oxygen species (ROS) production, impairing T cell activity. The gene discussed is IDO1; the disease is neoplasm.