IDO1 and neoplasm: In this review, we present the proliferative role of 15 immune checkpoints, including PD1, PD-L1, FGL1, CD155, CD47, SIRPα, CD276, IDO1, SIGLEC-15, TIM3, Galectin-9, CD70, CD27, 4-1BBL, and HVEM, in tumor progression.