IDO-IN-9 is primarily used in research settings as a potent inhibitor of indoleamine 2,3-dioxygenase 1 (IDO1). This enzyme plays a critical role in immune suppression by catalyzing the breakdown of tryptophan, an essential amino acid, into kynurenine. By inhibiting IDO1, IDO-IN-9 helps to restore immune function, making it a valuable tool in studying cancer immunotherapy. Researchers utilize it to explore how blocking IDO1 can enhance the body’s ability to fight tumors, particularly in combination with other immunotherapies. Additionally, it is employed in preclinical studies to investigate its potential in treating autoimmune diseases and chronic infections where immune suppression is a concern. Its application extends to understanding the role of IDO1 in inflammatory processes and immune tolerance.