B7-H3, assigned as CD276, is a type I transmembrane protein and shares 20-27% amino acid identity with other B7 family members. Human B7-H3 has a single extracellular variable-type immunoglobulin (IgV)-IgC domain, a signature intracellular domain, and an additional isoform, known as 4Ig-B7-H3, containing nearly exact tandem duplication of the IgV-IgC domain and most likely caused by exon duplication. B7-H3 mRNA is broadly expressed in normal tissues whereas its protein expression is relatively rare. The expression of B7-H3 is induced on T cells, natural killer (NK) cells, and antigen-presenting cells (APCs), including dendritic cells (DCs) and macrophages. It can be upregulated during the maturation from monocytes to DCs, or during the interaction between DCs and regulatory T cells. B7-H3 has been shown to be a co-stimulatory molecule that inhibits T-cell responses. B7-H3 has also been identified to bind TLT-2 involved in the intracellular signaling pathway.