PD-1-PD-L1 binding leads to peripheral CD8+ T cell "exhaustion" phenotype
PD-1-PD-L1 binding leads to peripheral CD8+ T cell "exhaustion" phenotype
In a state of chronic antigen presentation, such as malignancy, the chronic presence of antigen or pro-inflammatory cytokines (IL-12, IFNgamma, etc) can upregulate PD-1 expression on the T cell; tumor clones can also select for PD-L1 expression. With PD-1-PD-L1 binding, even in the presence of the costimulatory molecule, "peripheral exhaustion" can occur.