NOS2 and breast cancer: Our results also showed that BCC‐Ex significantly reduced the expressions of CXCR4 and CX3CR1 and elevated the mRNA levels of Arg‐1, IL‐6, IL‐10 and iNOS, which was related to MDSCs immunosuppression (Figure 3B‐G), suggesting that the exosomes released from breast cancer cells down‐regulated the expression of chemokine receptors in bone marrow cells, up‐regulated the expression of genes related to MDSCs immunosuppression, and differentiated bone marrow cells into MDSCs.