Antigen-specific primary immune response of human B-lymphocytes after in vitro immunization with GM3 ganglioside

In vitro immunization of human B-lymphocytes was performed with liposomes containing the monosialoganglioside GM3, with or without either complete tetanus toxoid or a synthetic T helper epitope derived from tetanus toxin (determinant 830–843). The immunized B-cells were Epstein–Barr virus transformed and the human anti-ganglioside antibody response was evaluated using an indirect ELISA against different mono- and disialogangliosides. Clones producing antigen-specific human antibodies of the IgM isotype against the ganglioside GM3 used as the immunogen were selected and one clone, IM-11, was further characterized. In addition, a method of positive selection using GM3-coated magnetic beads has been developed which allowed us to rescue unstable clones. The binding of the human antibody M-11 to a large panel of glycosphingolipids separated on thin-layer plates was studied. The human MAb IM-11 was found to bind strongly to NeuAcGM3, IV³NeuAcnLc₄ and sulfate containing glycosphingolipids and weakly to NeuGcGM3. Immunohistological staining of melanoma and breast cancer biopsy sections showed a selective reactivity of IM-11 with tumor cells which varied among different tumors.