MOLECULAR-CLONING OF A HUMAN MONOCLONAL-ANTIBODY REACTIVE TO GANGLIOSIDE-G(M3) ANTIGEN ON HUMAN CANCERS

In this study we report the characterization of a human monoclonal ant ibody (HuMab), L612, that reacts with ganglioside G(M3) and has therap eutic application for the treatment of human neoplasms, particularly m elanoma. A permanent IgM-secreting Epstein-Barr virus-transformed B-ce ll line L612 was established. L612 HuMab bound specifically to neoplas tic cell lines in culture and in tissue biopsy specimens such as melan oma, colon, breast, and lung cancer. The antibody did not bind to norm al cells or biopsy tissue. HuMab L612 showed the highest reactivity to melanoma cells, particularly to those with high concentrations of G(M 3). Immunostaining on high-performance thin-layer chromatography plate s demonstrated that L612 HuMab bound to G(M3) purified from melanoma c ells. Removal of the sialic acid from G(M3) abolished antibody binding . HuMab L612 also reacted to G(M4) purified from egg yolk, indicating that it recognizes an NeuAcalpha2-3 galactose antigen determinant. HuM ab 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 hum an cancers.