Analysis of human tumor cells for Ia-like antigens with monoclonal antibodies.

Cultured and noncultured human solid tumors were analyzed for expression of Ia-like antigens with the use of two monoclonal antibodies and a rabbit antiserum against human Ia-like antigens. Of 27 tumor cells tested, 3 melanomas bound antibodies [e.g., 21,563 cpm 131I-labeled staphylococcal protein A ([131I]SpA) with monoclonal antibody Q5/6], but 24 others (1 melanoma, 9 neuroblastomas, 1 medulloblastoma, 3 gliomas, 4 sarcomas, 2 colon carcinomas, 2 transitional cell carcinomas of the bladder, 1 teratoma, and 1 squamous cell carcinoma of the lung) did so minimally or not at all (0-427 cpm [131I]SpA with antibody Q5/6. Monoclonal antibody Q5/6 was quantitatively absorbed with homogenates of 32 noncultured tumors to determine if Ia-like antigens were expressed by neoplastic cells in vivo. Ten milligrams (wet wt) each of 5 of 7 noncultured melanomas removed more than 83% (median, 85%) of the antibody. In contrast, 10 mg each of 10 neuroblastomas, 7 carcinomas, 4 sarcomas, and 4 Wilms' tumors removed less than 47% (median, 19%) of the antibody; even 100 mg of these tumors removed less than 68% (median, 44%) of the antibody.