IDO1 and breast cancer: Notably, high expression of IDO1 was paralleled by a relevant increase of immune checkpoints (PDCD1 (PD-1), CD274 (PD-L1), PDCD1LG2 (PD-L2), LAG3 and CTLA4) level in our cohort of non-responder BC patients compared to responders (Fig. S3A).