Monoclonal antibodies that detect different antigenic determinants of the same human osteosarcoma-associated antigen

Monoclonal antibodies (MoAbs) against human osteosarcoma cells were obtained by the fusion of NS/1 mouse myeloma cells with spleen cells from the human osteosarcoma cell line-immunized BALB/c mice. Two hybrid clones were established and designated as 2H10 and 2D3. Both MoAbs reacted strongly with all osteosarcoma tissues but not with other bone and soft tissue tumors such as chondrosarcoma, malignant fibrous histiocytoma, liposarcoma, leiomyosarcoma, and rhabdomyosarcoma. In addition, neither MoAb reacted with tumor cell lines and tissues obtained from other cancers. Immunohistochemical analysis demonstrated that 2H10 and 2D3 reacted with endothelial cells in sarcoma tissues, but not with those of other tumors and normal tissues. 2H10 also reacted with cells on the basal layer of epidermis of the skin. 2H10- and 2D3-defined antigen has an approximate molecular weight of 75,000 under nonreducing and reducing conditions, indicating that the antigen has a single chain structure and there is no intramolecular disulfide bond. 2H10- and 2D3-defined antigen has a pI value between 5.5 and 6.2. Sequential immunoprecipitation analysis clearly demonstrated that 2H10 and 2D3 recognized the same antigen molecule. However, further analysis suggested the possibility that 2H10 and 2D3 MoAbs recognized the different antigenic determinants on the same antigen molecule.