IDO1 and cancer: Strikingly, ACACA expression exhibited significant negative correlations with the immune checkpoint-related genes (PDCD1, LAG3, LAGLS9, IDO1, CD244, CTLA4 and TIGIT), while showing positive associations with other genes (TGFBR1, KDR, IL10RB, CD160 and CD274) across most cancer types (Figure 3D).