Vaccine may treat cancer

In a major breakthrough in cancer research, a team of scientists led by University Microbiology Professor Yvonne Paterson has discovered a vaccine with the potential to prevent the growth of malignant tumors and shrink existing tumors. Although the vaccine has only been tested on animals, it may be just a few years before the vaccine becomes a standard therapy in the treatment of several human cancers, including cervical cancer -- the leading cause of cancer deaths among women worldwide -- and skin cancer. Cancer tumors form when t-cells -- the killer cells sometimes referred to as "the hallmark of immunity" -- do not recognize tumor cells as hostile and therefore do not attack the tumor and check its growth. The vaccine operates using the unique properties of the bacteria Listeria monocytogenes, which is found in unpasturized milk. This bacteria can live inside of tumor cells, where it elicits an immune response that the tumors themselves do not provoke. To test the vaccine, scientists immunized mice with the bacteria, which is genetically engineered to produce a viral protein called NP, which acts as an antigen and induces a response from the immune system. They then injected the mice with tumor-stimulating cells that produced the same antigen. The researchers found that 16 of 20 mice failed to develop tumors, while all of the mice in a control group had tumors. In another experiment in which the bacteria was injected into mice that already had the tumors, nine-tenths produced t-cells that killed both the bacteria and the tumors. These experiments tested the ability of the vaccine to prevent the growth of tumors and also to treat established tumors. "If you immunize animals with this bacterium, they will produce t-cells that will kill them," Paterson said. "That's very exciting. No one has ever showed that by inducing a good immune response you can make a palpable, visible tumor go away." The vaccine works for virally derived tumors, which account for 10 to 20 percent of all cancers, including cervical cancer and skin cancer. A benefit of this vaccine is its universal application -- it does not have to be tailor-made for each individual patient. "Once we know what the tumor specific antigen is, we can target specific tumors for a whole population of people that have the same tumor," Paterson said. In a year or two, the vaccine will be tested for safety and toxicity. It will then go through second and third phase clinical trials and be tested for ethicacy. The study, conducted by researchers at the University and Johns Hopkins University, is published in the latest edition of the journal Nature Medicine.

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