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Cold virus may have caused 2007 AIDS vaccine trial failure

One of the biggest disappointments in AIDS research was the failure of Merck & Co.'s STEP trial of an experimental AIDS vaccine, which was terminated prematurely in 2007 when it became apparent that the vaccine seemed to increase the number of people who contracted HIV. Now, British scientists believe they have an explanation for why the vaccine failed, and it has little to do with HIV itself and more to do with the adenovirus that was used to produce the vaccine. The findings may have implications for other experimental vaccines, such as those against malaria and tuberculosis, that also used the adenovirus, as well as for gene therapy.

The adenovirus is what is known as a vector. It is used to carry genes from, in this case, the AIDS virus into cells in the body, where they can produce proteins that stimulate immunity to HIV. Merck used a vector called adenovirus serotype 5 (Ad5), from which they removed genes that could cause disease. Ad5 is very similar to adenoviruses that cause colds, and there's the rub, according to Dr. Steven Patterson of Imperial College London, who led the new study, appearing this week in the Proceedings of the National Academy of Sciences. Many of the patients in the study had previously been exposed to closely related adenoviruses and had built up immunity to the virus.

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