A human monoclonal antibody recognizing a surface antigen on stomach cancer cells

Lymph-node lymphocytes of a patient with stomach cancer were fused with the mouse-human heterohybridoma, HM-5. A clone (2F9) was isolated that showed stable production of an IgM antibody reactive with NUGC-4 stomach cancer cell line. This antibody reacted predominantly with a cell surface antigen on cell lines originating from gastro-intestinal cancer and adenocarcinoma of lung, whereas it was not generally reactive with other types of cancers, or with normal kidney cells or fibroblasts. Biotin-labeled 2F9 antibody clearly stained cell smears and the nude mouse tumor of NUGC-4, but it did not show a positive reaction with stomach cancer tissues obtained from more than 10 patients, indicating that the antigen detected is very weakly expressed on tumor cells or on a limited number of stomach cancers. The antigen shed from NUGC-4 cell line was detected in the culture supernatant. 2F9 antibody precipitated a glycoprotein with a molecular weight of over 200 kilodaltons as well as a possible glycolipid, from NUGC-4 cells labeled with [3H]glucosamine or [35S]-H2SO4. Periodic acid treatment of the tissue section decreased reactivity with 2F9 antibody, but heat, neuraminidase or protease treatment did not. These results suggested that the epitope is present on a carbohydrate moiety not containing sialic acid, and that a part of the antigen molecule is sulfated.