Identification of a tumor-associated target antigen, ATM-1, for a human T-cell clone with activated killer activity and its existence in sera of cancer patients

Abstract

Three human T-cell clones with activated killer activity (5B5, 5C1, and 7B5) which could lyse various tumor cell lines were established. The cytotoxic activity of these clones was decreased by incubation with anti-CD3 monoclonal antibody, suggesting that they recognized tumor cells by T-cell antigen receptor. A monoclonal antibody which blocked the cytotoxic activity of clone 5B5 was obtained. This antibody (N1977) blocked the binding and cytotoxic activity of clone 5B5 at the target cell level, suggesting that the antigen defined by N1977 antibody, designated as ATM-1, was a target molecule recognized by 5B5 cells. ATM-1 in the conditioned medium of a cancer cell line (NBT-2) and serum from a patient with lung cancer was characterized by following its immunoreactivity. On gel filtration, both the conditioned medium and the serum gave three peaks of ATM-1 immunoreactivity, corresponding to approximate molecular weights of 1,200,000, 700,000, and 120,000, respectively. They were chromatofocused at pH 4.0, 4.8, and 6.5, respectively. The high molecular weight forms were shown to be molecules with the disulfide-linked elementary glycoprotein with ATM-1 immunoreactivity and approximate molecular weight of 120,000. Most of the molecules with ATM-1 immunoreactivity bound to both concanavalin A and wheat germ agglutinin, and their binding activity to the antibodies was lost by treatment at 60 degrees C for 30 min. An assay of ATM-1 level in sera was performed by a sandwich enzyme immunoassay. The following positive percentages were obtained from preliminary clinical studies: breast cancer, 67% (8 of 12 cases); hepatocellular carcinoma, 83% (10 of 12 cases); gastric cancer, 58% (7 of 12 cases); lung cancer, 41% (5 of 12 cases); hematological malignancies, 0% (0 of 9 cases); systemic lupus erythematosus, 0% (0 of 8 cases); rheumatoid arthritis, 0% (0 of 8 cases).