PD-1

Class

Anti-PD-1 checkpoint inhibitor

Notes

original target text: PD-1 | original target text: PD-1 (inhibitor)

Programmed cell death protein 1 (PD-1) is a receptor found on the surface of activated T cells, the white blood cells responsible for recognizing and destroying abnormal or infected cells. When PD-1 binds its ligands, PD-L1 or PD-L2, it delivers an inhibitory signal that dampens T-cell activity. This checkpoint exists physiologically to prevent excessive immune responses and autoimmunity, but many tumors exploit it by expressing PD-L1 to suppress the T cells that would otherwise attack them. Blocking PD-1, typically with monoclonal antibodies that occupy the receptor and prevent ligand binding, releases this brake and allows T cells to resume recognizing and killing cancer cells. This approach, known as checkpoint inhibition, has become a foundational strategy across many solid tumors and some hematologic cancers, often used alone or combined with chemotherapy, radiation, or other immune-modulating agents. Because the mechanism restores a natural immune function rather than introducing a new one, its effects can be durable in patients who respond, though the same removal of an inhibitory checkpoint can also unmask immune activity against normal tissues, producing inflammatory side effects. PD-1 remains one of the most extensively targeted immune checkpoints in oncology, illustrating how modulating regulatory signals in the immune system can be harnessed against disease.