AEGiS-ATDN: Merck Vaccine Studies for HIV+

Important note: Information in this article was accurate in 2001. The state of the art may have changed since the publication date.

Merck Vaccine Studies for HIV+

Information Bulletin #13 May June 2001

To be eligible for this study you must be on a potent anti-retroviral drug regimen and have had an undetectable RNA viral load level (less than 500) for at least 12 consecutive months. You must have at least 500 CD4 cells and not have had less than 200 in the last 12 months. Participants must be negative for Hepatitis B surface antigen, and negative for Hepatitis C antibodies. Women cannot be pregnant, breastfeeding, or planning to conceive during the study period. People interested in obtaining information about where the study is available should call the Merck National Service Center at (800) 672-6372. In New York City, Cornell, New York University, and Mount Sinai are expected to conduct this study.

Different strategies have been used to develop vaccines to prevent HIV infection. Although none of the vaccines being studied has yet been shown to prevent someone from becoming HIV-positive, researchers have learned a lot about how the immune system reacts to vaccines. They believe that a very strong, very specific response by the immune system is required. Using a deactivated virus that can cause a cold-like illness (the adenovirus), along with bits and pieces of the HIV virus, Merck has begun testing a vaccine that could provoke a strong, anti-HIV response. This might prevent HIV-infection, as well as treat someone who is already HIV-positive.

Merck studied their vaccine in a group of monkeys. One group of monkeys was given the vaccine, and then challenged with a very large dose of an especially strong, HIV-like virus. Another group of monkeys - the control group - was only given a very large dose of the same virus. Most of the monkeys who just got the virus quickly developed AIDS and died. The group of monkeys that got the vaccine first, then were challenged with the virus, however, became infected but had low viral load, did not lose CD4 cells, and remain healthy at this time. Researchers don't know how long the vaccinated monkeys will stay healthy, but the results were promising enough that Merck began testing the vaccine in HIV-negative people.

Merck's vaccine is the first of its kind to move into studies in HIV-positive people. The studies are testing a technique called prime/boost. The prime introduces fake pieces of HIV's genes (called naked DNA) into the body. Naked DNA, by itself, may not produce a strong enough response from the immune system, so a boost is used. The boost is a modified form of adenovirus (a cold virus) with some HIV genes incorporated into it. The adenovirus base is a vector used to carry the HIV genes directly to the immune system. There are other vaccines in development using a prime/boost strategy, but with different vectors. The idea is to target untrained CD4 cells to recognize the pieces of HIV as a threat. These CD4 cells will then begin to reproduce, creating millions of cells all of which are targeted to kill HIV.

Because no one really knows if the vaccine is safe, or even what dose to study in people, Phase I studies are being conducted of different variations of the Merck vaccine. A Phase I study helps to determine if a product is safe, how it is absorbed into the body, and what the proper dosing range is for that particular product. In Merck's study, different combinations of adenovirus, HIV proteins including gag, pol and nef, and genetic material (DNA) from the HIV virus will be tested to determine the best mix of ingredients, and the best prime/boost strategy to use for their vaccine.
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