Studies of a melanoma tumor-associated antigen detected in the spent culture medium of a human melanoma cell line by allogeneic antibody. II. Immunobiologic characterization.

A tumor-associated antigen (TAA) was isolated from spent culture medium of human melanoma cell line UCLA-SO-M14 (M14). After radioiodination and further purification, it was used in a radioimmunoassay (RIA). When tested in RIA for anti-TAA activity, 56% (111/200) of sera from melanoma patients, 21% (21/100) of sera from sarcoma patients, and 19% (19/100) of sera from carcinoma patients, as well as 12% (6/50) sera from pregnant women and 10% (10/100) apparently normal sera, were positive. The variations (0.25-3.8 micrograms/mg total protein) in specific TAA activity in 20 different batches of spent media collected for 18 months exhibited patterns of gradual increases and decreases, suggesting a cell growth cycle-related phenomenon. Binding between the allogeneic antibody and 125I-labeled TAA was inhibited by 70% (32/47) of melanoma spent media and cells (from culture or biopsy). Conversely, only 7% (3/33) spent medium or membrane extracts of other tumor cells and 0% (1/69) of human normal, fetal, or placental cells were positive in competitive RIA. The TAA was immunologically different from normal tissue antigens, blood-group antigens, human leukocyte antigens, and microbial antigens. These immunobiologic properties of the TAA isolated from M14 spent culture medium and used in the RIA suggested that such TAA was melanoma associated.