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LONDON (Reuters) - Treating tumours with salmonella bacteria can induce an immune response that kills cancer cells, scientists have found - a discovery that may help them create tumour-killing immune cells to inject into patients.Researchers from Italy and the United States who worked with mouse and human cancer cells in laboratories said their work might help in developing a new drug in a class of cancer treatments called immunotherapies or therapeutic vaccines, which harness the body's immune system to fight disease."We did experiments first in mice and then in cancer cells and immune cells from human patients, and found that the salmonella was doing exactly the same job," Maria Rescigno of European Institute of Oncology in Milan, who worked on the study, said in a telephone interview. "Now we are ready to go into (testing on) humans, but we are waiting for authorisation."The scientists said they thought the salmonella bacteria, which they used in a safe form that did not cause illness itself, helped to flag up cancer cells to the body's immune system, which was then able to find and kill them.In the very earliest stages of cancer, patrolling immune cells often recognise cancer cells as abnormal and destroy them, they explained in their study, which was published in the journal Science Translational Medicine on Wednesday.PROTEINThis process relies on connexin 43, a protein that forms tiny communication channels between different types of cells. Fragments of tumour proteins called peptides escape through these channels, enter immune cells and act as "red flags" triggering a specific immune response against the disease.But as cancer cells grow and proliferate, they can become invisible to immune cells because not enough connexin 43 is made to keep the "red flag" process going.In this study, the scientists looked mainly at cells from melanoma - the deadliest form of skin cancer and one which has no cure and few effective treatments.Rescigno and colleagues found that injecting salmonella into cancerous mice and melanoma cells from humans increased the amount of connexin 43 in the tumour cells. As a result, new communication channels formed, and immune cells were activated and went on to kill the tumour cells.The technique also protected mice from cancer spreading to other parts of the body, Rescigno said, suggesting a potential "vaccination-style" preventative strategy.Immunotherapy drugs - medicines that enlist the help of the body's immune system to fight disease - are a relatively new form of cancer treatment.In April, the U.S. Food and Drug Administration medicines regulators approved Dendreon Corp's Provenge, a therapeutic vaccine designed to stimulate the immune system to attack prostate cancer, as the first vaccine to treat tumours.An experimental immunotherapy drug called ipilimumab being developed by Bristol-Myers Squibb showed promise in fighting melanoma in trial data released in June.Rescigno said the team used melanoma cells in the study because it was one of the deadliest forms of the disease, but the same technique could also be trialled in other types of cancer.