A humanized IgG4 monoclonal antibody against the semaphorin 4D (SEMA4D; CD100) with potential immunomodulating and antineoplastic activities. Upon administration, anti-SEMA4D monoclonal antibody VX15/2503 binds to and neutralizes SEMA4D, thereby preventing binding of SEMA4D to its receptor plexin-B1 (PLXNB1). By blocking the interaction of SEMA4D and PLXNB1, VX15/2503 may cause an inhibition of endothelial cell activation and migration, eventually leading to an inhibition of angiogenesis and tumor cell proliferation. Semaphorin 4D, a large cell surface antigen found on the resting T-cell and overexpressed in a variety of tumor cell types, plays an important role in vascular growth, tumor progression, invasion and immune cell regulation. Check for active clinical trialsusing this agent.