CD276, also known as B7-H3, is a member of the B7 superfamily with signature IgV and IgG regions in extracellular domains. It is a type I transmembrane protein and shares 20–27% amino acid identity with other B7 family members. B7-H3 is involved in the activation of T lymphocytes, and regulates murine bone formation. It is also reported that B7-H3 may play an important role in muscle-immune interactions, providing further evidence of the active role of muscle cells in local immunoregulatory processes. B7-H3 is expressed on T-cells, natural killer cells, and antigen presenting cells, as well as some non-immune cells, such as osteoblasts, fibroblasts, fibroblast-like synoviocytes and epithelial cells. High expression of B7-H3 in tumor vasculature also correlates with poor survival in patients, suggesting that it may play a role in tumor cell migration.