IDO1 and melanoma: Notably, TIGIT expression was positively correlated with the expression of programmed cell death 1 (PDCD1), programmed cell death 1 ligand 2 (PDCD1LG2), cytotoxic T-lymphocyte associated protein 4 (CTLA4), lymphocyte activating 3 (LAG3), indoleamine 2,3-dioxygenase 1 (IDO1), interleukin 10 (IL-10), and transforming growth factor beta 1 (TGFB1), especially in gastroesophageal tumors and melanoma (Figure 11).