Merck to Double Enrollment in AIDS Vaccine Trial After Promising Results

Researchers conducting clinical trials of an AIDS vaccine made by pharmaceutical company Merck said they plan to double enrollment in the trials to 3,000 participants because results have exceeded their expectations, the Wall Street Journal reports. The trials are aimed at determining whether volunteers' immune responses can prevent or control HIV. The vaccine, called MRKAd5, contains an adenovirus -- a common cold virus -- that carries manmade copies of three HIV genes that are designed to stimulate the body's CD4+ T cells, which are immune system cells that destroy cells infected with the virus. Researchers have found that the vaccine has boosted participants' T cells 50 to 100 times their baseline number, a response comparable to the immune reaction to vaccines for diseases such as smallpox and measles. However, the vaccine does not prompt the body to generate antibodies, which are essential to immune protection. The trial was launched in January and is a collaborative effort of Merck, the HIV Vaccine Trials Network and NIH's National Institute of Allergy and Infectious Diseases. Final results are not expected before 2008 (Chase, Wall Street Journal, 9/23).

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