Immune Response of Chimpanzee to Purified Melanoma 250 Kilodalton Tumor-associated Antigen

Melanoma high molecular weight tumor-associated antigen (TAA), having a molecular weight of 250 kilodaltons (Kd), was purified from a crude cell membrane extract through a combination of lectin affinity, immunoadsorption, and high performance liquid molecular filtration chromatography. Compared to the starting extract, purified TAA was 600-fold higher in TAA activity per microgram of protein. Purified TAA was used to immunize a chimpanzee and the resulting antiTAA immune response was evaluated. Postimmune chimpanzee serum reacted in solid phase radioimmunoassay against purified TAA with a titer in excess of 100,000. In contrast, preimmune serum had a titer of less than 100 in the same assay. By immunoprecipitation analysis, we were able to demonstrate reactivity of the chimpanzee immune serum with a 250 Kd TAA in spent culture medium from melanoma cells metabolically labeled with 35S-methionine and with iodinated purified 250 Kd TAA. Reactivity of the chimpanzee antiserum for the 250 Kd TAA was confirmed in blocking and reciprocal immunodepletion studies using murine monoclonal antibody 9.2.27. These studies suggest that the 250 Kd TAA defined by murine monoclonal antibodies may prove to be immunogenic in man and that manipulation of the immune response to this TAA might be used to the clinical benefit of the patient.