Establishment of stable mouse/human-human hybrid cell lines producing large amounts of anti-tetanus human monoclonal antibodies with high neutralizing activity.

To establish stable hybrid cell lines producing human anti-tetanus antibody with high toxin-neutralizing activity, peripheral lymphocytes from humans hyperimmunized with tetanus toxoid were, after in vitro antigen stimulation, fused with a mouse/human heteromyeloma or human lymphoblastoid cell line and cloned. Unlike the IgM secretors (six clones), the IgG secretors we obtained (six clones) produced anti-tetanus human monoclonal antibodies with high neutralizing activity (the highest one, cell line G2, 4.3 IU/100 micrograms IgG). Appropriate combinations of three or four kinds of monoclonal antibodies of the IgG type resulted in markedly increased neutralizing activity comparable with that of anti-tetanus human polyclonal immunoglobulin preparations currently used clinically on the basis of toxin-specific IgG content. Five of these cell lines produced 10-20 micrograms of antibody per ml for more than 3 months. The cell line G2 produced 6 mg of antibody per day in serum-free medium in a 500-ml bioreactor in perfusion culture and 13-104 mg in a nude mouse. These cell lines satisfied, for the first time, the minimal requirements for applying human monoclonal antibodies to clinical use.