However, on the other hand, PBK was strongly positively correlated with CCL20, CMC2 and HILPDA, and CCL20 was reported to upregulate indoleamine 2,3-dioxygenase (IDO) expression through the IFN-γ signaling pathway, causing IDO to suppress CD8+ T cell responses and induce tumor immune evasion, and previous studies observed that immunosuppressive factors IDO and PD-L1 in the organism high expression levels in metastatic melanoma CD8+ T cells appeared over47. This evidence concerns the gene IDO2 and metastatic melanoma.