PDCD1 and neoplasm: Moreover, ExoPD-L1 can function as efficiently as PD-L1 on the tumor cell surface through direct ligation to PD-1 on the surface of lymphocytes in tumor foci (Chen G. et al., 2018; Lubin et al., 2018; Ricklefs et al., 2018; Theodoraki et al., 2018b; Yang et al., 2018; Fan et al., 2019; Kim et al., 2019; Poggio et al., 2019; Cordonnier et al., 2020; Huang et al., 2020).