Normal human sera of healthy adults contain natural IgM antibodies which are cytotoxic for human neuroblastoma cells. In this study, we evaluated the anti-neuroblastoma activity of these natural IgM antibodies in nude rats bearing solid human neuroblastoma tumours. A single intravenous (i.v.) injection of purified cytotoxic IgM led to uptake of IgM in the tumours with massive perivascular complement activation and accumulation of neutrophil granulocytes after 24 h. Five consecutive i.v. injections of purified cytotoxic IgM into neuroblastoma-bearing animals resulted in complete growth arrest of even large established solid tumours which lasted for several weeks after discontinuation of the injections, whereas tumours of control animals continued to grow exponentially during the observation period. These studies suggest that natural anti-neuroblastoma IgM may have a potential as a novel therapeutic modality in the treatment of human neuroblastoma.
