B7 homolog 3 (B7-H3), a member of the immunoglobulin superfamily, is also known CD276, which contains two Ig-like C2-type (immunoglobulin-like) domains and two Ig-like V-type (immunoglobulin-like) domains. B7-H3 may participate in the regulation of T-cell-mediated immune response. B7-H3 also plays a protective role in tumor cells by inhibiting natural-killer mediated cell lysis as well as a role of marker for detection of neuroblastoma cells. Furthermore, B7-H3 is involved in the development of acute and chronic transplant rejection and in the regulation of lymphocytic activity at mucosal surfaces. It could also play a key role in providing the placenta and fetus with a suitable immunological environment throughout pregnancy.