IDO1 and neoplasm: IDO1 has emerged as a key player in suppressing anti-tumor responses and fostering tumor immune evasion [11].The immunosuppressive effect of IDO1 is driven by the depletion of Trp and the accumulation of Kyn, that affects immune cells such as NK cells [12, 13], effector T cells [14], Tregs [15], tolerant dendritic cells (DCs) [16], and MDSCs [17], leading to tumor immune evasion [18].