IDO1 and neoplasm: In support of this approach, a recent study showed that AHR inhibition elicited anti-tumour activity alone and further increased efficacy when combined with gemcitabine or PD-L1 blockade in diverse syngeneic mouse tumour models.197 Furthermore, by inhibiting the expression of IDO1, IDO2 and TDO2,33,34,75,157 AHR antagonism might even prevent effects of these enzymes that are independent of downstream AHR activation.