PD-L1 (CD274)

PD-L1 (programmed death-ligand 1) is the cell-surface ligand that engages PD-1 on T cells and transmits the “stand down” signal tumors use to disable immune attack.

Function

PD-L1 is expressed on antigen-presenting cells and on cells in immune-privileged sites, where its engagement of PD-1 limits T-cell activity. Its expression is inducible by inflammatory signals (interferon-γ) and by oncogenic pathways (PI3K, MYC), and in tumors it appears both on tumor cells themselves and on myeloid cells in the microenvironment. The ligand’s cytoplasmic tail has reported signaling roles of its own, so the PD-L1 interaction is bidirectional rather than a one-way brake.

In cancer

PD-L1 expression is