Bay Area Reporter - September 20, 2007
Matthew S. Bajko, m.bajko@ebar.com

The trial, called STEP, was testing the efficacy of Merck & Company's experimental HIV vaccine known as V520. But after reviewing the trial data, the independent Data Safety Monitoring Board for STEP recommended that the vaccination be discontinued because the information showed the vaccine failed to work.

The vaccine's failure came as a huge surprise, and dealt a blow to hopes of finding a preventative tool to stop the spread of AIDS. But those involved in the trial sounded a hopeful note that the data gleamed from the studies would still provide useful insight.

"We share in the disappointment of the research and HIV communities today. Sadly, developing an effective AIDS vaccine remains one of the most challenging tasks facing modern medicine," said Peter S. Kim, Ph.D., president, Merck Research Laboratories, in a statement. "Merck's 20-year HIV research program has led to improved scientific understanding of HIV and to true breakthrough medicines. We are committed to studying the data closely and sharing it with the scientific community to inform the on-going search for an effective HIV vaccine."

The clinical trial, begun in 2004, enrolled 3,000 HIV-negative volunteers who were at high risk for HIV infection in the multi-site, double blind, placebo-controlled study. Researchers followed the volunteers for 13 months.

In San Francisco, 137 gay and bisexual men had been enrolled in the phase II trial. Staffers in the city's HIV research section of the health department began contacting the participants Friday to alert them of the study's cancellation.

"I was surprised. No one anticipated this response. This vaccine had shown a good immune response in prior trials," said Gavin Morrow-Hall, a community educator with the research section who helped recruit participants for the trial. "The vaccinations will not continue, but we still hope to see our study participants because there is still a lot of information we can learn about the vaccine."

It is the third HIV vaccine trial to end in failure. Steve Oxendine, an HIV programming consultant, served on the local community advisory board for the trial. While disappointed that the vaccine did not work, he said that he remains optimistic that researchers some day will be able to develop a successful vaccine.

"The thing that is difficult about this disease, specifically different from other vaccines, this virus attacks the very system you need to immunize someone," said Oxendine. "I have trouble with the word failure, just simply because if you look at the way any other vaccine was developed it went through the same process.

"The other two took five years to figure out it failed. This one we got fairly early in the process," he added.

In addition to shutting down the STEP trial, enrollment and vaccination in another trial being conducted by the HIV Vaccine Trials Network in South Africa, called Phambili, and two additional phase I trials have been discontinued.

"This is a huge disappointment for all of us who have been involved in the search for an HIV vaccine," said Dr. Glenda Gray, principal investigator of the HVTN-sponsored Phambili trial. "HIV is ravaging our communities, and all the scientists, participants and communities involved in HIV vaccine studies have been affected by this epidemic. The scientific community must continue the race to find a vaccine to help secure an HIV free generation for the future."

Merck's vaccine was a mixture of three components; each made with a weakened version of the common cold virus as a carrier, along with three synthetically produced HIV genes. Participants could not contract HIV from the vaccine.

Along with testing to see if the vaccine prevented new infections, researchers were also looking to see if it reduced the amount of virus in those who developed infections. It failed on both counts.

According to Merck, among the volunteers who received at least one dose of the three-dose vaccine series, 24 people out 741 who received the vaccine tested positive for HIV. Of the 762 participants who received the placebo, 21 became HIV-positive.

In the subgroup of those who had received at least two vaccinations and who were HIV-negative for at least the first 12 weeks of the trial, 19 people out of 672 given the vaccine and 11 people out of the 691 given the placebo tested positive for HIV.

In addition, the vaccine did not reduce the amount of virus in the bloodstream of those who became infected; HIV RNA levels approximately 8 to 12 weeks after diagnosis of infection were similar in the vaccine and the placebo arms.

"This trial was the first test of concept trial that provided us information on this vaccine more quickly and efficiently than with a traditional Phase III design," said Dr. Larry Corey, principal investigator of the HVTN. "While we are very disappointed that this vaccine candidate did not demonstrate protection, the data from this trial will provide critical insights into this disease and future vaccine development."

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