August 4, 2011
The world's largest ongoing HIV vaccine study is changing the scope of its primary goals to include an investigation of whether the experimental vaccine regimen prevents HIV infection. Previously, the study's main goal was to determine whether the vaccine regimen decreases the amount of virus in the blood of vaccine recipients who later become infected with HIV, and preventing HIV acquisition was one of the study's secondary goals. However, promising data from other recent studies suggest that this vaccine regimen developed at the National Institutes of Health (NIH) might be more protective than originally anticipated. Called HVTN 505, the study began in 12 U.S. cities in June 2009 with sponsorship and funding from the National Institute of Allergy and Infectious Diseases (NIAID), part of NIH. The NIAID-funded HIV Vaccine Trials Network (HVTN) is conducting the study.
HVTN 505 is testing the safety and efficacy of a two-part HIV vaccine regimen consisting of one vaccine designed to prime the immune system followed by another vaccine designed to boost the immune response. This regimen was developed by NIAID's Vaccine Research Center. The participants in the Phase IIb placebo-controlled clinical trial are 18- to 50-year-old HIV-negative circumcised men and transgender women who have sex with men. At the time of enrollment, study participants must be free of antibodies to the adenovirus type 5 common cold virus. The booster vaccine contains a weakened version of this virus.
NIAID is expanding HVTN 505 by increasing enrollment from 1,350 participants to 2,200. Having a larger study population will enable scientists to detect whether the experimental vaccine regimen is at least 50 percent effective at preventing HIV acquisition during the 18 months following immunization.
The decision to expand the trial's primary objectives and size was motivated by scientific findings that came to light after HVTN 505 began. First, the September 2009 results of a major HIV vaccine trial in Thailand showed for the first time that a vaccine can generate modest protection against HIV infection in humans. Consequently, NIAID decided to take a closer look at the immune responses elicited by its other HIV vaccine candidates in clinical trials, including HVTN 505.
Second, a series of studies in nonhuman primates demonstrated that the monkey version of the HVTN 505 vaccine regimen prevented infection by the monkey equivalent of HIV (called SIV) 50 percent of the time in two-thirds of the monkeys tested. This protection occurred in the presence of robust cellular responses and low levels of SIV-neutralizing antibodies. These results suggested that the experimental HVTN 505 vaccine regimen may have the capacity to prevent HIV acquisition in people.
The HVTN is conducting the study under the leadership of Scott M. Hammer, M.D., the chief of the Division of Infectious Diseases and the Harold C. Neu professor of medicine in the College of Physicians and Surgeons at Columbia University.
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