Figure 1. Mechanism by which tumor cells resist adaptive immune responses. Activated CD8⁺ T cells expressing the PD-1 receptor are recruited to the tumor and become activated to secrete interferon γ (IFNγ). The local production of IFNγ induces the expression of PD-L1 on the surface of tumor cells, resulting in the delivery of a PD-1-transduced, immunosuppressive signal to CD8⁺ T cells that drives anergy.