Monoclonal antibodies raised against mid-gut carcinoid tumor cells

Three monoclonal IgG 2a antibodies were produced after immunization of mice with dispersed cells from a human mid-gut carcinoid tumor. Acetone-fixed cryosections of 57 primary and metastatic mid-gut carcinoid tumors as well as 2 hind-gut (rectal) carcinoids showed a conspicuous immunoreaction while a thymic carcinoid was essentially unstained with the antibodies. The 3 antibodies yielded a similar pattern of immunostaining. The immunoreaction comprised more than 95% of the carcinoid tumor cells, and it was more uniform and intense in primary tumors than in mesenteric, hepatic, and ovarian metastases of the mid-gut carcinoid tumors. Immunofluorescence studies on suspended carcinoid tumor cells showed that the antibodies bound to the surface membrane of the cells. The antibodies immunostained enterocytes of the small and large bowel, intestinal metaplasia of the stomach mucosa as well as colorectal adenocarcinomas. Endocrine pancreatic tumors producing vasoactive intestinal polypeptide, gastrin, somatostatin, and/or pancreatic polypeptide as well as the epithelium of pancreatic ducts were also stained with the antibodies, whereas a large number of other normal and abnormal human tissues, including benign and malignant insulinomas, were unreactive. The findings indicate that the antibodies recognize differentiation antigens on the carcinoid tumor cell surface preserved also on endocrine and nonendocrine cells of the normal bowel mucosa. The restricted tissue reactivity of the antibodies suggests that they may constitute useful tools in the histological characterization of carcinoid tumors. Further studies may reveal if they are applicable for immunolocalization and perhaps even immunotherapy of these neoplasms.