Indoleamine 2,3-dioxygenase (IDO) is an enzyme of interest in immuno-oncology. It has immunosuppressive effects that result from its role in tryptophan catabolism. IDO1 catalyzes the initial rate-limiting step in the degradation of the essential amino acid tryptophan along the kynurenine pathway. IDO inhibits a tryptophan sufficiency signal that stimulates...