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Bacterial cancer vaccines show glimpses of activity

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Therapeutic vaccines could prove to be a good way to tackle cancer. A few shots and--it is hoped--only a few side effects, rather than long treatments with traditional chemotherapy drugs that make people feel terrible. Dendreon's ($DNDN) Provenge was the first cancer vaccine on the market, and there are a number of others in development. Results from early clinical trials of two of these, this time from Aduro BioTech, have shown glimpses of activity in patients with advanced and untreatable cancer.

The paper, published in Clinical Cancer Research, combined the results of clinical trials of two of Aduro BioTech's vaccines, both based on Listeria monocytogenes, a bacterium that usually causes food poisoning, but can stimulate a strong immune response.

The first vaccine, ANZ-100, is a live-attenuated vaccine (a live bacterium that has been weakened). In mouse studies, this vaccine traveled to the liver and set off an immune response there, increasing the lifespan of mice with cancer that had metastasized to their livers. In the clinical trial, the vaccine was given to 9 people with advanced cancer and liver metastases who were no longer responding to treatment, and they seemed to handle the vaccine well.

In the second vaccine, CRS-207, the same weakened bacterium had this time been genetically modified so it produced human mesothelin, a marker expressed by a number of different tumors. The CRS-207 trial involved 17 people with mesothelioma, lung, pancreatic or ovarian cancers. All are mesothelin-expressing cancers, and all advanced and untreatable. There were no unexpected side effects of the vaccine, and the patient's immune systems reacted to the mesothelin produced by the vaccine. Even though these patients were only expected to live for three to 6 months, 37% of the people receiving the vaccine lived for 15 months or more.

Although Phase I trials are only designed to give researchers evidence about the vaccine's safety, sometimes, as in this case, they can give the first clues to their efficacy. A lot more work will be needed, however. The CRS-207 vaccine is in a larger, longer Phase II clinical trial in patients with metastatic pancreatic cancer, in which it will be compared with another form of treatment.

- read the press release
- check out the abstract

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