Reactivity of monoclonal antibody (mAb) GD9 with a cytoplasmic antigen preserved in formalin-fixed, paraffin-embedded gastrointestinal tumors.

In order to develop monoclonal antibodies to tumor associated antigens which are preserved in formalin-fixed, paraffin-embedded tissues, BALB/c mice were immunized with a formalin-fixed paraffin-embedded melanoma lesion. One of the resulting monoclonal antibodies, monoclonal antibody (mAb) GD9, stained formalin-fixed, paraffin-embedded melanoma lesions. When tested with a large panel of normal tissues from adults and from two fetuses of 4 and 16 week gestation and of benign and malignant tumors of different embryological origin, the mAb GD9 stained normal small bowel mucosa, areas of gastric intestinal metaplasia, the 6 pancreatic carcinoid tumors tested and a high percentage of gastrointestinal tumors. In the latter group, the reactivity with well differentiated tumors was higher than with poorly differentiated ones. Furthermore, the percentage of malignant cells stained by mAb GD9 in differentiated tumors was higher than in poorly differentiated ones. In the latter, the staining was diffuse and granular, while in the former, the staining was located in the cytoplasm close to the glandular lumen. The reactivity of mAb GD9 with colon carcinomas did not correlate with the Duke's staging and with the clinical course of the disease. The results of the immunohistochemical staining of normal tissues and benign and malignant lesions suggest that the specificity of mAb GD9 is different from that of previously described monoclonal antibodies which recognize tumor associated antigens expressed by tumors of the gastrointestinal tract.