CD276 (B7-H3) is a member of the B7/CD28 superfamily of costimulatory molecules serving as an accessory modulator of T cell response. B7 family molecules, which are expressed on antigen-presenting cells and display extracellular regions containing immunoglobulin (Ig) variable (V)- and constant (C)-like domains, are known to modulate T cell receptor (TCR)-mediated T cell activation by providing co-signals that are either stimulatory or inhibitory. B7-H3 provides a stimulatory signal to T cells. However, recent studies suggest a negative regulatory role for B7-H3 in T cell responses. B7-H3 inhibited T cell proliferation mediated by antibody to T cell receptor or allogeneic antigen-presenting cells. B7-H3 is a negative regulator that preferentially affects T(H)1 responses. 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. Recently, B7-H3 expression has also been found in a variety of different human cancers, including prostate cancer, clear cell renal cell carcinoma (ccRCC), non-small-cell lung cancer (NSCLC), pancreatic cancer, gastric cancer, ovarian cancer, colorectal cancer (CRC) and urothelial cell carcinoma. B7-H3 was expressed in some human cancers and correlated with poor outcome of cancer patients.