The 29E.2A3 monoclonal antibody specifically recognizes Programmed cell death 1 ligand 1 (PDCD1 ligand 1, PDCD1L1, PDCD1LG1) which is also known as Programmed death ligand 1 (PD-L1 or PDL1) as well as CD274, or B7 homolog 1 (B7-H1, B7H1). PD-L1 (CD274) and PD-L2 (CD273) are type I transmembrane glycoproteins that belong to the B7 family within the Ig gene superfamily and serve as ligands for CD279 (Program Death 1/PD-1). PD-L1 (CD274) is expressed on antigen-presenting cells including activated monocytes, macrophages, and dendritic cells (DCs) as well as activated T cells, B cells, NK cells, and keratinocytes. PD-L1 (CD274) is also variably expressed on placental trophoblasts, myocardial endothelium, cortical thymic epithelial cells, and tumor cells. PD-L1-mediated signaling through PD-1 regulates T cell responses important for providing protective immunity while maintaining peripheral tolerance. This immune signaling checkpoint may also suppress antitumor immune responses and prevent tumor rejection. The 29E.2A3 antibody reportedly blocks PD-L1 (CD274) binding to CD279 (PD-1) and can enhance the proliferation and cytokine production of activated T cells.