CXCL12 and breast cancer: 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.