CD80 and breast carcinoma: Several mechanisms have been suggested to result in the immune defects seen in breast cancer patients, such as a lower number of blood lymphocytes 1,2 and elevated levels of T-regulatory lymphocytes in breast cancer.3 B7-H3 belongs to the B7 family as a known co-inhibitory ligand.4 The receptor for B7-H3 has not been clearly identified, so the mechanisms underlying the effects of B7-H3 on the immune system remain unclear, particularly in terms of targeting T cells for suppression.