As a mark of death, the modified proteins called monoclonal antibodies are expected to stick to cancer cells and flag down immune fighters to destroy a tumor. But such a strategy, for whatever reason, have generally failed. Now scientists may have found a way to turn monoclonal antibodies into killing machines, after all: by linking them together. The results, reported in the current issue of Proceedings of the National Academy of Sciences , suggest that antibody dimers could be a promising new approach to the development of treatments against cancer.
These rare monoclonal antibodies are capable of killing cultured tumor cells seem to make it through an unexpected mechanism: instead attract other immune cells, antibodies trigger the tumor cell to stop dividing or undergo apoptosis, or programmed cell death. A team led by Ellen Vitetta of the University of Texas Southwestern Medical Center at Dallas has undertaken to examine this phenomenon in cells of Burkitt lymphoma, a disease in which a type of white blood cell called B cells divide uncontrollably, resulting tumors anywhere in the body. Monoclonal antibodies for latching to several different receptors on lymphoma cells were almost powerless. In large quantities, however, an antibody against a CD19 receptor showed poor ability to inhibit cell growth. Some of these antibodies, the researchers found, had formed pairs; when separated and tested alone, these dimers packed a powerful punch.
Researchers then tested dimers of monoclonal antibodies against other receptors lymphoma. All were better to stop the growth of tumor cells or promoting cell death. The researchers also tested the anti-CD19 antibody in mice with human Burkitt lymphoma tumors. Mice receiving the dimers, they found, lived up to 80% longer than the mice given the monomers. "It is an interesting observation," says immunologist Martin Glennie of Southampton University, U.K., "but the mechanism remains unclear." Vitetta The team will try to understand that in other tests in mice.
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