The first AIDS vaccine to go into large-scale trials in the U.S. did not protect against infection in people who were at high risk of exposure. However, limited data suggests that non-Caucasians may respond more favorably and generate some protection. AIDSVAX is being developed by VaxGen, a California company.
The vaccine is made of gp120, a protein on the surface of HIV. The hope was to train the immune system to recognize this protein and build up a response so that it could mobilize when exposed to real HIV. Some 4,521 people completed the trial, with two-thirds receiving at least three shots of the vaccines spaced six months apart, and a third receiving a placebo or dummy shot.
'Overall what we see is the trial failed,' said VaxGen president Donald Francis in a telephone news conference on February 24. 'There was no evidence of enhanced protection,' both vaccinated and unvaccinated groups became infected with HIV at the same rate over the course of the trial.
But one group stood out statisticallyBlack volunteers who received the vaccine were 78% more likely to not become infected than were those in the placebo arm. This group included a large number of sex workers, some 8.1% ( 9 people ) of whom in the placebo arm became infected with HIV during the trial, while 2.0% ( 4 people ) of those who received the vaccine became infected.
The small number of patients involved made it difficult to read too much into the percentages. As an industry analyst noted, 'We are talking about two patients in the Black group who could have changed the statistical significance of this study.'
VaxGen VP Phillip Berman readily acknowledged that the numbers were small. He took comfort in 'supporting data of the antibody response' that suggests there really is something different going on with the immune system of these patients, it is not just a fluke.
'The antibody response, both Black and white, of the people who were protected was higher,' he explained. 'It looks like the vaccinated ones got infected with a different virus'; there was a stronger CD4 response which resulted in a lower viral set point when the immune system asserted some effective control over the infection; and that correlates with slower disease progression.
'Each of those things makes me feel increasingly comfortable with the small numbers,' said Berman. 'Is it an answer? No, but we're on the right track.' They are continuing to analyze the data and blood samples gathered during the trial.
Berman raised the possibility that genetic influences may account for these differences. Some genetic variations already have been identified that make it more difficult for people to become infected with HIV, while others believe them more likely to have a bad reaction to specific drugs.
Seth Berkley, MD, head of the International AIDS Vaccine Initiative ( IAVI ) , called the news 'disappointing,' but not unsurprising. He said that detailed analysis of the data might offer clues to developing better vaccine candidates.
'It's disappointing, but this trial should not be characterized as a failure,' said Chris Collins, executive director of the AIDS Vaccine Advocacy Coalition ( AVAC ) . 'It is one important step in what likely will be a long term effort.'