Characterization of a 90‐100 kDa tumor‐associated antigen in the sera of melanoma patients

Using allogeneic antibody, we previously described a highmolecular‐weight glycoprotein in the urine of 68% of melanoma patients. This glycoprotein has been termed urinarytumor‐associated antigen (U‐TAA). A murine monoclonal antibody (MAb) specific for U‐TAA (AD1‐40F4) has been developed. By the use of AD1‐40F4, U‐TAA was detected in serum samples from 63% (33/52) of stage II and stage III melanoma patients, but from only 5% (1/20) of normal controls. This report describes the physical and immunochemical properties of U‐TAA in the serum. The antigen elutes from a DEAE‐Sephacel column in association with IgG in the void volume and as free antigen in a second peak. The molecular mass of the free antigen is 590–620 kDa and it sediments in the region of 28–29% sucrose by density gradient ultracentrifugation. Free antigen has an isoelectric point of 6.1. This high molecular weight antigen is composed of smaller subunits linked by reducible bonds. The AD1‐40F4 reactive epitope resides on a 90–100 kDa subunit. These results provide evidence that U‐TAA which is produced by melanoma cells in vitro is present in the circulation of melanoma patients.