Isolation and characterization of a novel human monoclonal antibody that neutralizes tetanus toxin.

A human monoclonal antibody, designated 53-2-4, has been isolated and characterized in terms of its ability to interact with clostridial neurotoxins. In enzyme-linked immunosorbent assay assays the antibody reacted with native tetanus toxin, tetanus toxoid and the C fragment obtained from the carboxyterminus of the toxin (AA 864-1314). The antibody did not react with the B fragment of tetanus toxin (AA 1-863) or with six serotypes of botulinum neurotoxin (A to F). Both culture supernatant from the clonal line producing the antibody as well as homogeneous protein obtained by affinity purification of the antibody neutralized tetanus toxin. When tested in vivo, the antibody provided complete production against a supralethal injection of toxin; when tested in vitro, the antibody produced at least 99% inactivation of a 1 x 10(-9) M solution of toxin. The exceptional neutralizing activity of the antibody was attributed to its high affinity for the toxin (4.2 x 10(-10) mol/liter). Animal experiments revealed a novel phenomenon that has been labeled delayed intoxication. At the appropriate ratio of antibody to antigen, the toxin was retained in the host in a latent form. After several days the biological activity of the toxin became apparent and there was onset of nervous system poisoning. Isolated tissue experiments showed that each antibody molecule is capable of associating with two antigen molecules. The antibody has greater neutralizing activity when mixed with free toxin than when mixed with toxin already bound to plasma membrane receptors.