In some clinical phase I/II models, epacadostat (INCB024360), one of IDO1 inhibitors, plus an ICI generally was well tolerated and produced relatively higher objective response rates (ORRs) in multiple advanced solid tumors (Hamid et al., 2017; Lara et al., 2017; Perez et al., 2017; Smith et al., 2017), primarily through the reactivation of tumor-infiltrating T cells and/or the decrease of tumor-resident immunosuppressive regulatory T cells (Spranger et al., 2014). The gene discussed is IDO1; the disease is neoplasm.