Important note: Information in this article was accurate in 2007. The state of the art may have changed since the publication date.
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Washington Blade - November 22, 2007
Dyana Bagby
Study investigators, researchers and activists gathered in Seattle Nov. 7 for the first public and detailed discussion of data coming from the STEP trial and its sister trial, the Phambili study in South Africa.
According to analyses presented, those volunteers with pre-existing immunity to the cold virus used as a carrier - or "vector" - for synthetic HIV genes in the vaccine were more likely to contract HIV than those who received the placebo. Keith Gottesdiener, vice president of Vaccine & Infectious Disease Clinical Research for Merck Research Laboratories, presented the information during a teleconference Nov. 7 from Seattle.
Circumcised vaccine participants also seemed to have a lower risk of contracting HIV according to early data research, Gottesdiener added, but noted this was "significant" in overall analysis.
Researchers also stated that all those infected with HIV who received the actual vaccine and placebo were men, except for one woman, despite women being 35 to 40 percent of participants, Gottesdiener said.
The data that halted both trials came from the STEP trial, which consisted of mostly gay men in the U.S., the Caribbean, Australia and South America.
Both the STEP and Phambili trials were halted when researchers determined the vaccine did not stave off HIV infection or reduce viral loads of those who became HIV positive. The data also indicated a higher susceptibility to HIV among those who received the actual vaccine and not the placebo.
Globally, 3,000 volunteers participated in the HIV vaccine trial. All volunteers were HIV negative when they began participation.
Further analyses are being conducted and trial partners will share the data as it becomes available with the broader scientific community at future meetings and in publications over the next several months, according to Merck. A presentation is scheduled at the Conference on Retroviruses & Opportunistic Infections in Boston in February.
Dr. Mark Mulligan, executive director of the Hope Clinic in Atlanta, has stressed the vaccine itself cannot cause HIV.
Researchers explained Nov. 7 the vaccine was created using a mixture of three components, each made with a defective version (one that cannot replicate) of one of the common cold viruses, adenovirus type 5 (Ad5), which served as a delivery vector for three synthetically produced HIV genes.
Preliminary data showed 24 cases of HIV infection among the 741 volunteers who received at least one dose of the vaccine, while 21 cases of HIV infection were seen in the 762 participants who received at least one dose of the placebo.
Gottesdiener explained the numbers become more significant when broken down by the amount of ad5 participants already had in their systems.
"As we progress to the higher Ad5 levels, the split begins," he said. "The trends are more pronounced in the high Ad5 group."
Among the 778 male volunteers who had high levels of pre-existing immunity to Ad5 (greater than 200 units), 21 volunteers who received the vaccine became HIV positive and nine cases of HIV infection were observed in the volunteers who had received placebo.
Those with an Ad5 ratio between 200 and 1,000, the numbers show 14 vaccine recipients contracting HIV while seven who received the placebo contracted HIV.
"Why the vaccine caused higher rates, particularly in those with a higher Ad5, could be unrelated with the vaccine or could be due to the vaccine," Gottesdiener said. If not due to the vaccine, the higher rates in the different groups could be caused by several factors, he added. "There could be a difference in risk-taking behavior over time, and this analysis is just beginning. And there is always the possibility of just chance," he said.
But it remains possible that the vaccine is responsible, and researchers are looking into the immune response of participants, he said.
Researchers acknowledged being "surprised" by the vaccine trial data, but stressed again that the best way to study how the vaccine failed and how to design one that potentially works is to study blinded results.
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