Fig. 1

Exosomal PD-L1 contributes to the resistance to immune checkpoint therapy. ①Tumor-derived exosomes up-regulate the expression of PD-L1 and the production of cytokines by myeloid cells to inhibit the function of T cells. ② PD-L1 expressed on the tumor surface directly binds to PD-1 on T cells, inducing an immune checkpoint response. The checkpoint response can suppress the activation of T cells and make T cells dysfunctional to inhibit anti-tumor immunity. ③ Immune checkpoint therapy can free the T cells limited by checkpoint blockades to rejuvenate immune responses. ④ Exosomal PD-L1 has the same membrane topology as PD-L1 on the cell surface and could suppress the function of T cells and cause the failure of immune checkpoint therapy