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FARAI CHIDEYA, host:

Now, we're joined by Susan Buchbinder. She co-chaired the team conducting the AIDS vaccine test with Merck. Welcome, Susan.

Dr. SUSAN BUCHBINDER (Co-chair, STEP Study): Thank you.

CHIDEYA: So, your team worked with Merck to do the test. How did that work?

Dr. BUCHBINDER: Well, we're part of a global network of investigators that's sponsored by the National Institutes of Health. It's the HIV Vaccine Trials Network. And the HVTN or this trial network joined together with Merck to test this HIV vaccine, to see if we could prevent HIV infection or hopefully control the infection if someone were later exposed to HIV.

CHIDEYA: Now, you worked on the test affecting people in the Americas. Tell me a little bit about how long that went on in duration and who you targeted.

Dr. BUCHBINDER: Sure. So, we first started enrolling study volunteers in December of 2004 and had completed enrollment this - earlier this year. We've enrolled 3,000 individuals in North and South America, and the Caribbean and Australia for this particular trial. And then earlier this year, we started a sister study in South Africa that was also slated to enroll 3,000 volunteers.

CHIDEYA: The sister study in South Africa has gotten a lot of notice for the concept that people may be discouraged by this withdrawal of this vaccine. Do you think that this could have a psychological effect on people, either viewing medicine as - particularly clinical trials - as safe, or for their own self-protection to prevention?

Dr. BUCHBINDER: So, what I think is very important is that we need all of the prevention tools we have available and we need to develop new tools to try to prevent new infections. There are about 11,000 new infections each and every day in the world, and we desperately need new prevention strategies for those populations who are most at risk.

What we were really pleased about was that this was - this has been a global effort to try to find an effective HIV vaccine. And this specific study got us an answer, and a very important answer, to the question about whether this most promising vaccine might actually provide some protection. We were very disappointed that it didn't provide protection, but I think that people should be heartened by the fact that we had built in a number of safety measures in the trials, so that the data were being looked at quite regularly.

And at our first look at the data to see whether or not protection was being provided, we found that the - there was no protection being provided, and so we stopped the vaccinations here in the United States and throughout the America, this part of the STEP study, but also in the sister trial Phambili that was taking place in South Africa.

CHIDEYA: It wasn't just though that it wasn't affected, the infection rates were actually slightly higher among people who had gotten the vaccine. Were you surprised by that, and how do you react as a scientist to that?

Dr. BUCHBINDER: Well, I think we were all surprised to see that the number of infections was somewhat higher in the vaccine group compared to the placebo group. And I first want to reiterate that the vaccine itself does not cause HIV infection. But what we're looking very closely at is whether or not this vaccine might be generating an immune response that makes people more susceptible to infection if they're later exposed. And we don't know the answer to that question yet. Again, we build in many safety measures within these studies to be monitoring number of infections in both groups. And we caught this trend at the earliest possible time that it could've been caught, and again, stopped additional vaccinations at that time, and are now exploring the three possible explanations for this increase in numbers.

And the three possible explanations are that it may be due to the vaccine, it may be due to other differences between the vaccine and placebo groups that are completely unrelated to the vaccine, or it could be a chance event, because that the number of infections that we saw on either group was still relatively small and the follow-up is relatively short.

CHIDEYA: So you say that the vaccine may, in one scenario, have increased susceptibility, but it doesn't cause AIDS. Explain the science behind that, why this vaccine could not cause AIDS?

Dr. BUCHBINDER: Sure. So we don't use any whole or killed HIV in making the vaccine. The vaccine is actually using a carrier protein - it's a weakened cold virus. And in that - into that weakened cold virus, there is some information about HIV, but it's synthetic. It's not the whole virus. It's not pieces of the virus. There's no way that it can recombine to actually cause infection. And what we again saw was that there was somewhat increased number of infections in the vaccine group compared to the placebo group, but these were all in individuals who had had exposures to HIV through other practices, through sexual contact or drug use.

CHIDEYA: Susan, when you think about this case, there is scientific reality and then there is historical reality - emotional reality. African-Americans have not always been on the kinder side of medicine - you have things like the Tuskegee syphilis experiments. And there is a perception that the medical establishment is not always going to look out for the interest of African-Americans or for people, in general, who were not privileged. Will this, regardless of what you've just told us, undermine your ability to get people for clinical trials?

Dr. BUCHBINDER: Well, I think it's really important to acknowledge that medical science has not treated a number of vulnerable populations well previously. And that that's really been a travesty and really can't be allowed to happen again.

I think we've been really encouraged by the support that we've gotten from communities that are most totally impacted by this epidemic in contributing in many ways to the design and conduct of the study and are relying on, again, very diverse input as we pour over the data and try to understand what this trial is telling us and how to move forward. So I would agree with you that I think that there has been - there've been real concerns about trust in the medical establishment.

We've worked very closely with communities in designing, building and implementing these trials, and we will continue to work very closely with diverse communities because it's really critical that communities that are most heavily impacted by this epidemic be a fundamental core part of all of the trials that we design to try to build new prevention strategies because those are the communities that are going to be in great need of additional prevention strategies.

CHIDEYA: Well, Susan, thank you so much.

Dr. BUCHBINDER: Thank you very much.

CHIDEYA: Susan Buchbinder is protocol co-chair for the Step study, the AIDS vaccine trial that is testing the Merck AIDS vaccine in the Americas. The sister study in South Africa is called Phambili.

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