CD8A and breast cancer: Interestingly, in addition to the role played by breast cancer cell-originating Exo-PD-L1 in tumorigenesis and tumor development, Sun et al. suggested that the Exo-PD-L1 derived from bone marrow significantly increased the lung metastasis of cells from the murine breast cancer line 4T1 by damaging the antitumor CD8+ T cell responses at metastatic sites [130].In addition, as the most malignant type of breast cancer, the triple-negative breast cancer cell derived microparticles can also load PD-L1, especially in patients receiving chemoradiotherapy.