Antibody-based strategy exhibits puzzling racial disparities
The much-anticipated results of the world's first Phase III clinical trial of an AIDS vaccine showed that it was statistically no better than a placebo in preventing HIV infections.
But there was also an unexpected result. According to an analysis of the data, released last week by the vaccine's developer, VaxGen, blacks had 78% fewer HIV infections than those receiving a placebo, and a group of nonwhites that included blacks and Asians had 67% fewer infections. Only a small percentage of blacks and nonwhites were enrolled in the study, however, raising the possibility of a statistical fluke.
Another ongoing Phase III trial of AIDSVAX, conducted on injecting drug users in Thailand, will conclude in June. Results from that study, which will be released later this year, might shed light on the baffling results, researchers say.
The three-year study of AIDSVAX consisted of 5,009 volunteers, two-thirds of whom received injections of a genetically engineered version of the gp120 surface protein on the AIDS virus. It was hoped that the recombinant protein would stimulate production of antibodies that would then bind to gp120 on the virus, incapacitating it.
VaxGen Communications Director Jim Key notes that black and other nonwhite participants produced higher levels of vaccine-induced antibodies, a finding that VaxGen is continuing to analyze. "There's a possible correlation between that and protection," Key says.
As to what might possibly confer immunity on a separate racial group, Tom Coates, director of the University of California, San Francisco's Center for AIDS Prevention Studies, says he's hard-pressed to come up with a biologically plausible mechanism. "At this point, it defies explanation," he says. VaxGen will present a more complete analysis of its data later.
But despite the vaccine's apparent failure, "we now have a vaccine trial where we've got real data on real people, and we can examine those data to see what might have happened," Coates says. "In the main, this advances the field of vaccine research for HIV."-
|TARGETED Researchers hoped antibodies would bind to the HIV surface protein gp120.|
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