We then stained tumor sections for the IDO1 protein and found that the highest IDO1 protein expression was detected in the vehicle group, while the lowest IDO1 protein level was in the l-1MTrp+CPA group (figure 2G and online supplemental figure 3A), indicating an obvious decrease in tumor IDO1 expression after effective IDO1 blockade-containing combinatorial therapy. Here, IDO1 is linked to neoplasm.