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‐S. A clonc (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, hut 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 [(3)H]glucosamine or [(35)S]‐H(2)SO(4). 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.