Merck Begins Enrolling Participants Worldwide for Potential HIV/AIDS Vaccine’s Phase II Trials
Pharmaceutical company Merck and the HIV Vaccine Trials Network on Monday announced that they have begun enrolling participants worldwide in a Phase II study -- a collaboration of Merck, HVTN and the National Institute for Allergy and Infectious Diseases -- of a potential HIV/AIDS vaccine, the AP/Las Vegas Sun reports. The vaccine candidate -- called MRKAd5 HIV-1 gag/pol/nef, or trivalent -- aims to "persuade" CD4+ T cells to "attack" HIV when it enters the cell, according to the AP/Sun. In order to transfer three synthetically produced HIV genes to the cells, the trivalent vaccine uses a strain of the common cold that has been modified so that it is unable to reproduce or cause people to contract a cold (Gold, AP/Las Vegas Sun, 1/24). There is no risk that participants will contract HIV from the study itself, Dow Jones Newswires reports (Corbett Dooren, Dow Jones Newswires, 1/24).
The Phase II trial, called the Step Study, last month began enrolling 1,500 participants at high risk for sexual transmission of HIV (King, Seattle Times, 1/24). Participants will include male and female volunteers ages 18 to 45 of diverse racial groups, who also will receive counseling on how to reduce their risk of HIV infection, according to Reuters AlertNet (Pierson, Reuters AlertNet, 1/24). The double-blind study will be conducted in 13 U.S. cities and Puerto Rico, as well as Santo Domingo, Dominican Republic; Port-au-Prince, Haiti; Iquitos, Peru; Lima, Peru; Toronto; and Sydney, Australia. The participants -- half of whom will be given a placebo and half the trivalent vaccine -- will receive three injections over six months. The study is expected to last four years, during which volunteers also will be tested for HIV every six months. Although participants will receive counseling, researchers still expect some volunteers to contract HIV during the duration of the trial, according to the Times. These participants will be monitored to determine if the vaccine can lower their viral load (Seattle Times, 1/24). Results from the trial are not expected until 2010, after which additional studies might be required before the vaccine is approved for public use (Dow Jones Newswires, 1/24).
"It's an exciting trial conceptually," Lawrence Corey, HVTN principal investigator, said, adding that compared with other vaccines aimed at triggering CD4+ T cells, the trivalent vaccine has "given the best immune response" (Chase, Wall Street Journal, 1/25). According to Sarah Alexander, HVTN associate director, while the Merck vaccine is the "most promising candidate we've seen so far ... something better could come along tomorrow" (AP/Las Vegas Sun, 1/24). Robert Belshe, professor of medicine at Saint Louis University -- one of the vaccine testing sites -- said that he is "optimistic" about the vaccine candidate because it prevented or delayed AIDS-related diseases in animals, according to the Journal. "This is a step forward," Belshe said, adding, "It's clearly not the final vaccine. We still need antibodies. This is half the equation" (Wall Street Journal, 1/25). According to the International AIDS Vaccine Initiative, there currently are approximately 50 preventive and combination vaccine candidates in human clinical trials (Bowe, Financial Times, 1/25).