IDO1 and breast cancer: Similarly, combining two different drugs together and then delivering them in vivo by nanotechnology is also a good option using a pre-drug NP (DOX/IND@NPs) based on a mouse model of BC, which delivered adriamycin (DOX) and indolimod (IND) to block the IDO pathway, further suppressing Treg levels and generating antitumor immunity [267].