Monoclonal Antibodies to 125 kd and 95 kd Proteins on Human Melanoma Cells: Comparison with Other MonoclonalDefined Melanoma Antigens

Abstract

Two monoclonal antibodies produced by hybridomas were identified by an indirect ¹²⁵I-protein A binding assay that define cell surface antigens expressed on cultured human melanoma cells but not on autologous lymphoblastoid cells. The first antibody, 705F6 (an IgG_2b immunoglobulin), bound to 14/14 melanoma lines, 6/9 carcinomas and sarcomas, 7/7 gliomas and neuroblastomas, 2/2 fetal cell lines, 0/8 lymphoblastoid cell lines, and weakly to 2/4 leukemia lines. The second monoclonal antibody, 436G10 (IgG₁), reacted with 10/14 melanomas, 5/13 carcinomas and sarcomas, 2/7 gliomas and neuroblastomas, and weakly with the fetal cells, but not with the leukemic or lymphoblastoid cell lines. Comparison of 705F6 and 436G10 with 28 other monoclonal antibodies from different laboratories identified several with similar binding patterns to a panel of tumor and nontumor cell lines. Crossblocking of ¹²⁵I-labeled 436G10 was not observed by R23, I12 or L10 antibodies. However, 705F6 was completely blocked by monoclonal 376.96S, showing that these two antibodies bind to the same antigenic determinant. The 705F6 antibody immunoprecipitated a 95 kd (kilodalton) membrane protein and the 436G10 antibody bound a 125 kd protein from ¹²⁵I-labeled melanoma cells. The broad distribution of these two proteins on melanomas and other solid tumors suggests that they define common oncodevelopmental antigens expressed on proliferating cells.