Programmed Death 1 (PD-1) is a member of the
CD28/CTLA-4 family of T-cell regulators, expressed as a
co-receptor on the surface of activated T-cells, B-cells, and
macrophages. New studies have suggested that the
PD-1/PD-L1 signaling pathway may be linked to anti-tumor
immunity, as PD-L1 has been shown to induce apoptosis of
activated T-cells or inhibit activity of cytotoxic T-cells. In
comparison to CD10 and bcl-6, PD-1 is expressed by fewer Bcells
and has therefore been considered a more specic and
useful diagnostic marker for angioimmunoblastic T-cell
lymphoma. Therapies targeted toward the PD-1 receptor
have shown remarkable clinical responses in patients with
various types of cancer, including non–small cell lung cancer,
melanoma, and renal-cell cancer.