CD274 and breast cancer: Chatterjee et al. (2020) reported that breast cancer cells secrete exosomes carrying PD-L1 and are highly immunosuppressive. Additionally, exosome PD-L1 is stimulated by TGF-β, which blocks the phosphorylation of src family proteins and promotes CD8 T cell dysfunction. Therefore, exosome PD-L1 has considerable potential for the diagnosis and treatment of breast cancer patients (Martinez et al., 2017).