Cytotoxic T lymphocyte-associated antigen-4 (CTLA-4), a surface cell receptor that has a natural ligand CD80, is expressed in human OSA tumors.18,19 When ligand CD80 comes into contact with a CTLA-4 receptor, an immune response induces apoptosis within OSA cells. This evidence concerns the gene CD80 and obstructive sleep apnea syndrome.