PD-L1 Recombinant Rabbit mAb (S-3933-78)

PD-L1 (Programmed Death-Ligand 1, CD274, B7-H1) is a ~33 kDa type I trans-membrane glycoprotein that belongs to the B7 family of immune co-signaling molecules; it is expressed constitutively at low levels on resting T, B, and myeloid-lineage cells and is strongly up-regulated by pro-inflammatory cytokines such as IFN-γ, TNF-α, IL-4, GM-CSF and by oncogenic signaling pathways (EGFR, ALK, KRAS, PI3K-AKT, STAT3, HIF-1α, NF-κB) in a wide spectrum of epithelial, hematopoietic, and mesenchymal tumors. Upon engagement with its cognate inhibitory receptor PD-1 (CD279) expressed on activated T, B, and NK cells, PD-L1 delivers a negative signal that recruits SHP-1/2 phosphatases to the immunological synapse, thereby blocking PI3K-AKT and ZAP70 signaling, suppressing T-cell proliferation, cytokine production (IL-2, IFN-γ, TNF-α, granzyme B), and survival while promoting the induction and maintenance of peripheral tolerance, tissue-resident T-cell exhaustion, and Treg expansion. Clinically, PD-L1 protein expression—detected by FDA-approved 22C3, 28-8, SP142, or SP263 IHC assays—is a predictive biomarker for anti-PD-1/PD-L1 checkpoint inhibitors used across more than 20 cancer types, with high membranous tumor and/or immune cell staining (≥1–50 % cutoff depending on tumor type) correlating with improved objective response rates and progression-free survival; conversely, PD-L1 overexpression is itself an independent adverse prognostic factor in untreated solid tumors, reflecting immune evasion and aggressive biology.