A Novel Human Monoclonal Antibody Directed to a Tumor‐associated Antigen

Twelve human monoclonal antibodies (HuMAb) were established by the fusion of (mouse × human) heteromyeloma cells with B‐lymphoblastoid cells derived from the regional lymph nodes of three patients with squamous cell carcinoma of the lung. They were tested for reactivity to two kinds of proteins (purified protein derivatives and bovine serum albumin) by ELISA, Sq‐19 (squamous cell carcinoma) culture cells by indirect membrane immunofluorescence tests, and Sq‐19 tumor xenograft by immunohistological study. Among them, one HuMAb 904F (IgM, λ) was selected. In indirect membrane immunofluorescence tests, this 904F antibody reacted with various kinds of cell lines, e.g. lung cancer, esophageal cancer, endometrial cancer, and stomach cancer. It did not react with malignant hematopoietic and diploid fibroblast cell lines. Immunohistologically, it stained the tumor nests of squamous cell carcinoma, adenocarcinoma, and large cell carcinoma of the lung. It also stained those of esophagus and colon, but not those of small cell carcinoma of lung, or stomach. On frozen‐section specimens of normal tissues from various organs, it showed only limited areas of positive staining. Limited positive findings were observed at a reticular zone of the adrenal gland, at the esophagus as weak staining, and at islets of the pancreas as very weak staining. Western blotting analysis demonstrated that it recognized a 54 kDa trypsin‐sensitive molecule which is expressed on the surface of tumor cells. These results suggest the 904F monoclonal antibody detects a novel tumor‐associated antigen which is recognized by the human immune system.