IDO1 and gastric cancer: Based on microarray screening and further validation, Jiang et al. [95] found that inducible T cell co-stimulatory factor (EV-ICOS) and indoleamine 2,3-dioxygenase 1 (EV-IDO1) can effectively predict and monitor irAE in ICI- treated GC and serve as biomarkers of irAE.