The application relates to specific binding members that bind OX40. The specific binding members comprise an OX40 antigen-binding site located in a constant domain of the specific binding member and find application in the treatment of cancer and infectious diseases, for example.本申請案係關於結合OX40之特異性結合成員。該等特異性結合成員包含定位於特異性結合成員之恆定域中的OX40抗原結合位點,且應用於例如癌症及感染性疾病之治療。