Figure 2. Mechanisms of PD pathway–induced immunosuppression in the tumor microenvironment.
Tumor cells and other cells in tumor microenvironment can express high levels of PD-L1, which results in suppressed immunity upon interaction with PD-1. PD-L1–expressing cells use multiple mechanisms to suppress tumor immunity. PD-L1+ tumor cells and antigen-presenting cells (APCs) can induce T cell apoptosis, anergy, functional exhaustion, and IL-10 production. They can also mediate DC suppression and induce the differentiation of Tregs. PD-L1 can also act as a molecular shield on tumor cells and protect tumor cells from lysis by cytotoxic T lymphocytes (CTLs). iTreg, induced Treg.