High levels of lactic acid in tumors interfered with autophagy of naive T cells and impaired anti‐tumor response in mouse models.[1a] Autophagy is critical to the integrity of mitochondria, which determine the differentiation of effector T cells through metabolic reprogramming.[100] High level of arginase 2 (ARG2) expression in tumor‐infiltrating Tregs can maintain high level of autophagy. Here, ARG2 is linked to neoplasm.