CD274 and cancer: Recent studies have revealed that both cell-surface PD-L1 and ExoPD-L1 play crucial roles in immunosuppression, tumor progression, and response to cancer immunotherapy (Zou et al., 2016; Chen G. et al., 2018; Theodoraki et al., 2018b; Fan et al., 2019; Kim et al., 2019; Xie F. et al., 2019; Cordonnier et al., 2020; Huang et al., 2020; Tang et al., 2020).