Definition

A bispecific antibody directed against the tumor-associated antigen (TAA) and immunoregulatory protein B7-homologue 3 (B7-H3, CD276) and the co-stimulatory T-cell surface glycoprotein CD28, with potential immunostimulating and antineoplastic activities. Upon administration of anti-B7-H3/CD28 bispecific antibody XmAb808, this bispecific antibody binds to both B7-H3 on certain tumor cells and CD28 on cytotoxic T-lymphocytes (CTLs). This activates and redirects CTLs to B7-H3-expressing tumor cells, which may result in the CTL-mediated cell death of B7-H3-expressing tumor cells. B7-H3, a type I transmembrane protein and a member of the B7 co-stimulatory protein superfamily, is overexpressed on certain tumor cell types and on various immune cells. It is a negative regulator of the T-cell activation and its overexpression plays a key role in tumor cell invasion and metastasis.