PD-L1

Class

anti-PD-L1 monoclonal antibody (tagitanlimab)

Pathway

PD-1/PD-L1 immune checkpoint blockade

PD-L1 (programmed death-ligand 1) is a cell-surface protein expressed on tumor cells and on various normal and immune cells. It binds the receptor PD-1 on activated T lymphocytes, delivering an inhibitory signal that dampens T-cell activity. This interaction is part of a normal feedback system that limits immune responses and protects healthy tissue from collateral damage during inflammation. Many tumors exploit this pathway by upregulating PD-L1, effectively disguising themselves from immune attack by engaging PD-1 on tumor-infiltrating T cells. Agents that block PD-L1 (or its partner PD-1) interrupt this inhibitory signal, releasing a brake on T-cell function and allowing the immune system to recognize and attack cancer cells more effectively. This general strategy, known as immune checkpoint blockade, has broad relevance across many solid tumor types where immune evasion via this axis contributes to disease progression. Because the pathway is a normal regulator of immune tolerance, blocking it can also unleash immune activity against healthy tissue, producing inflammatory side effects. PD-L1-directed antibodies are one of two principal ways to interrupt this axis, the other being direct blockade of the PD-1 receptor itself, and various modalities including antibody-drug conjugates have been explored to combine checkpoint blockade with direct tumor cell targeting.