CD40 and neoplasm: However, CK6, another anti-KIT monoclonal antibody developed by Looy et al., failed to inhibit tumor growth in patient-derived xenograft (PDX) model, and had no synergistic antitumor effect with imatinib [244]. CD40, which is mainly expressed on the surface of APCs, is a member of the tumor necrosis factor receptor superfamily (TNFRSF) and also known as TNFRSF5.