PD-L1，also known as CD274 or B7H1，stands for programmed cell death ligand 1. It is a type I transmembrane protein that is thought to repress immune responses by binding to its receptor (PD1)，thus inhibiting T-cell activation，proliferation，and cytokine production. It contains V-like and C-like immunoglobulin domains. PD-L1 expression is regulated by various cytokines，such as TNF-α or LPS (ISSN: 1848-7718). Increased expression of this protein in certain types of cancers，e.g.，renal cell carcinoma or colon cancer，correlates with poor prognosis.