Anti-4-1BB/4-1BBL

H4-1BB, the human homologue of 4-1BB, is a 256 amino acid, 27 kDa transmembrane receptor glycoprotein first identified in screens for receptors on mouse concanavalin A-activated helper and cytotoxic T-cell lines (Vinay and Kwon 2006). It was then isolated from PMA plus ionomycin-treated human peripheral T-cell cDNA libraries (Zhou et al. 1995). In humans, 4-1BB maps to chromosome 19p13.3 (Alderson et al. 1994). It is also commonly referred to as CD137, induced by lymphocyte activation (ILA), and tumor necrosis factor receptor superfamily member 9 (TNFRSF9). The receptor, 4-1BB, and its ligand, 4-1BBL, are members of the tumor necrosis factor and tumor necrosis factor receptor superfamilies, respectively (Vinay and Kwon 2012). However, unlike other members of the tumor necrosis factor superfamily, the ecto-domain of 4-1BB forms a homotrimer with an extended, three-bladed propeller structure (Won et al. 2010). 4-1BB also has a cysteine-rich extracellular domain, a transmembrane region, and a cytoplasmic domain that contains a tyrosine kinase p56lck binding site (Vinay and Kwon 2006).