NLG919 is an orally available potent inhibitor of the indoleamine-2,3- dioxygenase (IDO1) pathway, a crucial pathway involved in allergic inflammation that mediates immunosuppressive effects through metabolization of tryptophan to kynurenine. NLG919 affects differentiation and proliferation of T cells by inducing downstream signaling via GCN2, mTOR and AHR, with values of Ki = 7 nM and EC50 = 75 nM. NLG919 is being investigated for the treatment of immunosuppression associated with cancer.