HIV Digest	HIV Digest Archive

In a collaborative effort, Merck & Co., the HIV Vaccine Trials Network, and National Institutes of Allergy and Infectious Diseases are beginning phase II clinical trials of Merck's AIDS vaccine candidate MRKAd5 in the United States, Canada, Australia, Latin America, and the Caribbean.

An HIV vaccine would ideally both block initial infection and fight any remaining virus. However, Merck's MRKAd5 does not contain the external HIV virus coat component that is needed to activate neutralizing antibodies that could prohibit initial infection. Instead, MRKAd5 contains three man-made copies of genes from HIV's core. Researchers hope these will trigger cytotoxic T-cells to destroy HIV-infected human cells, thus preventing or delaying the onset of the disease.

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The prototype vaccine prevented or delayed the onset of AIDS-like disease in animal testing, said Robert Belshe, professor of medicine at Saint Louis University, one of the testing sites. "This is a step forward. It's clearly not the final vaccine. We still need antibodies. This is half the equation," he said.

The company and the researchers said they believe the vaccine is safe, based on phase I testing involving 250 people. In the phase II trial, which is expected to last at least 4.5 years, volunteers will receive either three vaccine injections or three placebo injections over six months. All participants will be instructed in safe sex and other preventive behaviors. Researchers will examine the rate of infection and the severity of disease in the two groups.

"It's an exciting trial conceptually," said Lawrence Corey, lead researcher of HVTN. The candidate has "given the best immune response," he said, adding that he receives no stock or personal funding from Merck.

Editor's Note: from the Wall Street Journal