With the deepening of research, IDO has been found to play an important role in maternal‐foetal immune tolerance, tumour immune escape and regulation of transplant immune tolerance.17, 18 Current research on IDO‐mediated immunoregulatory mechanisms involves the following processes: Overexpression of IDO can lead to a decrease in local tryptophan content, an increase in kynurenine and other metabolites. Here, IDO1 is linked to neoplasm.