In mouse breast cancer bone metastases, using the CXCR4 antagonist AMD3465 combined with the indoleamine 2, 3-dioxygenase 1 (IDO1) inhibitor D-1-methyltryptophan to block the CXCL12/CXCR4 axis reduces the number of Tregs within the tumor and weakens immune suppression, thus inhibiting the progression of breast cancer bone metastasis and prolonging mouse survival62. Here, CXCR4 is linked to breast cancer.