IDO1 and hepatocellular carcinoma: In another study, CCL15 can recruit suppressive CCR1+CD14+ monocytes into HCC tissues and promote immune escape by upregulating the expression of PD-L1, B7-H3, and IDO and activating STAT1/3, AKT, ERK, and other signaling pathways in an autocrine manner to promote HCC progression 35.