Among the three cancer immunotherapeutic approaches––PD-L1 blockade, CAR T, and IDO1 inhibition, combinations of two have been attempted: PD-L1 blockade enhances CAR T cell activity [30, 31], and the most recent trials testing an IDO1 inhibitor in combination with anti-PD-1 antibodies demonstrate promising syngeneic activity in multiple types of solid tumors [32]. The gene discussed is IDO1; the disease is cancer.