Molecular cloning of a human monoclonal antibody reactive to ganglioside GM3 antigen on human cancers.

In this study we report the characterization of a human monoclonal antibody (HuMab), L612, that reacts with ganglioside GM3 and has therapeutic application for the treatment of human neoplasms, particularly melanoma. A permanent IgM-secreting Epstein-Barr virus-transformed B-cell line L612 was established. L612 HuMab bound specifically to neoplastic cell lines in culture and in tissue biopsy specimens such as melanoma, colon, breast, and lung cancer. The antibody did not bind to normal cells or biopsy tissue. HuMab L612 showed the highest reactivity to melanoma cells, particularly to those with high concentrations of GM3. Immunostaining on high-performance thin-layer chromatography plates demonstrated that L612 HuMab bound to GM3 purified from melanoma cells. Removal of the sialic acid from GM3 abolished antibody binding. HuMab L612 also reacted to GM4 purified from egg yolk, indicating that it recognizes an NeuAc alpha 2-3 galactose antigen determinant. HuMab L612 heavy and light chains were sequenced and determined to belong to the mu heavy chain variable subgroup III and kappa chain variable subgroup IV families, respectively. The studies indicate that the L612 HuMab has significant therapeutic potential for a wide variety of human cancers.