rhBST-2, CF (50 UG)

Background: BST-2/Tetherin

BST-2, also known as tetherin or CD317, is a type II transmembrane protein that is constitutively expressed in several cell types including T cells, B cells, monocytes and macrophages, as well as on several cancer cell lines including the B cell lineage in multiple myeloma (1, 2). Originally named bone marrow stromal cell antigen 2, BST-2 was identified to inhibit viral replication due to its unusual topology (3-5). The extracellular C-terminus of the protein is modified with GPI (glycosylphosphatidylinositol) membrane anchor, which enables BST-2 to interact at each of its ends with the cell or the viral membrane. The ectodomain of the protein also contains three cysteine residues that can form intermolecular disulfide bonds to form parallel dimers (2). Human BST-2 consists of a 20 amino acid (aa) cytoplasmic domain, a 28 aa transmembrane segment, and a 113 aa extracellular domain (ECD). Within the ECD, human BST-2 shares 41% and 35% aa sequence identity with mouse and rat BST-2, respectively. BST-2 was identified as a major mediator of the innate immune defense against enveloped viruses. BST-2 was shown to interact with formed viral particles tethering them to surface of infected cells, thereby reducing viral release (6). BST-2 inhibits the release of diverse group of enveloped viruses including members of the retrovirus, togavirus, filovirus, arenavirus, flavivirus, rhabdovirus, orthohepadnavirus, orthomyxovirus, poxvirus, paramyxovirus, and herpesvirus families (7-9). The mechanism BST-2 inhibition of viral budding was suggested to be through directly bridging the host and viral membranes through simultaneous embedding of its two opposing membrane anchors (9). To counteract BST-2 functions, many viruses have evolved to develop strategies to antagonize BST-2 function (9, 10). In addition to inhibiting viral release, BST-2 can act as an innate immune sensor of viral infections by acting as a pattern recognition receptor that activates NF-kappa B to induce inflammatory responses through interactions with the immunoglobulin-like transcript 7 (ILT7/LILRA4) (10, 11).