Carbohydrates as antigenic determinants of tumor‐associated antigens recognized by monoclonal anti‐tumor antibodies produced in a syngeneic system

Abstract

Two monoclonal antibodies (KH‐1 and KH‐2) against a transplanted fibrosarcoma (KMT‐17) in WKA rats were produced by fusing a mouse myeloma (P₃‐X63‐Ag8.653) with spleen cells from syngeneic rats hyperimmunized with KMT‐17. Both antibodies showed complement‐dependent cytotoxicity against KMT‐17. By absorption of cytotoxicity, KH‐1 reacted with homologous tumor, other syngeneic fibrosarcomas (KMT‐80 and KMT‐75), and lung and kidney from normal rats. However, KH‐2 reacted with many kinds of tumors and various normal tissues. Antigen specificity was tested by complement fixation and/or solidphase radioimmunoassay using glycolipids isolated from KMT‐17 cells and authentic glycolipids. KH‐1 reacted with globotriglycosyl ceramide which was not detected on KMT‐17 cells and in cross‐reacted weakly with IV³‐α‐galactosyl‐lactoneotetraglycosyl ceramide, one of the major glycolipids of KMT‐17. The immune reaction was inhibited by α‐methyl‐galactose. KH‐2 reacted with lactosyl ceramide and lactoneotetraglycosyl ceramide. The reaction was more potently inhibited by lactose than by β‐methyl‐galactose. Antibodies with similar specificity to either KH‐1 or KH‐2 were elevated in syngeneic rat sera after serial immunization with viable KMT‐17 cells.