PD-L2/PDCD1-L2/CD273 [MD420]

Programmed cell death ligand 2 (PD-L2), also known as cluster of differentiation 273 (CD273) or B7-DC, is a transmembrane protein mostly expressed by antigen-presenting cells. It serves as a second ligand for programmed cell death protein 1 (PD-1), complementing PD-L1 in mediating peripheral immune tolerance and maintaining immune homeostasis during infection. Highest expression was detected in heart, placenta, liver, pancreas, spleen, and lymph node. Lower amounts of expression were observed in lung, smooth muscle, and thymus. Elevated PD-L2 expression has also been observed in various malignancies, including lung, colorectal, as well as breast cancers, and is often associated with poor prognosis. On previously activated T cells, PD-L2 interaction with PD-1 inhibits TCR-mediated proliferation and cytokine production, suggesting an inhibitory role in regulating immune responses. In contrast, a co‑stimulatory function for the PD-L2 on resting T cells activated with sub-optimal TCR signals has also been reported.