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New Hope In HIV Prevention Research: International Microbicide Conference Focuses On What Works And Next Steps

April 16, 2012

Researchers, activists and funders are meeting this week in Sydney to discuss the state of HIV prevention research. The biennial International Microbicides Conference, which was opened on Sunday evening by the Honorable Tanya Plibersek MP, Australian Minster of Health, is taking place amid renewed optimism about development and delivery of new HIV prevention options with the potential for ending the AIDS epidemic, including anti-retroviral based microbicides and pre-exposure prophylaxis (PrEP).

For more than a decade, microbicide researchers and advocates have been meeting to assess the state of the field. Welcoming delegates, Professor John Kaldor of the Kirby Institute at the University of New South Wales, co-chair of the conference, noted, “This is the first microbicide conference to take place in the context of knowing a microbicide works and knowing PrEP works.”

In the keynote address, Professor Salim Abdool Karim, Pro Vice-Chancellor (Research), University of KwaZulu-Natal and Director of CAPRISA from South Africa, spoke about the implications and lessons learned two years on of the results of the landmark CAPRISA 004 trial, which provided proof of concept for ARV-based vaginal microbicides.

“We have learned several lessons from CAPRISA 004 about conducting large HIV prevention trials, about women’s risk factors for HIV infection and the correlates of HIV protection, said Abdool Karim.

“Our experiences with CAPRISA 004 and results of other HIV prevention trials over the past two years have shown the need for dogged persistence, the need to develop diverse approaches and to be prepared for surprising results. The good news is, despite some setbacks, we’re in a better place now than we’ve ever been in the fight to find new ways to prevent HIV among young women. And we know that we can change the trajectory of the epidemic if we can change the HIV incidence rates in young women,” Abdool Karim added.

Much of the research presented at the conference on Monday focused on the promise of PrEP, which involves HIV-negative people at risk for HIV using antiretroviral medications (ARVs) to reduce the risk of HIV infection.

In the opening plenary session, Dr. Connie Celum of the University of Washington in the U.S., and principal investigator of the Partners PrEP Study, laid out the state of evidence from PrEP efficacy trials and what the results from these trials mean for addressing prevention needs of different groups of men and women at risk of HIV infection. A range of PrEP trials in different populations have shown efficacy from none to moderate (39% to 42%) to high (75%).

“We should celebrate the pivotal discoveries of the past few years that demonstrate that antiretroviral drugs work for HIV prevention,” said Dr. Celum. “The oral and topical tenofovir-based PrEP trials have demonstrated that this strategy works in diverse populations, and the degree of efficacy is correlated with adherence.”

“There are aspects of PrEP that we still need to learn more about, including adherence, risk perception, and how to deliver these tenofovir-based PrEP options to populations who are at greatest risk of HIV infection. Ultimately we need to find longer-acting products that are less adherence dependent,” she added.

Dr. Kenneth H. Mayer of The Fenway Institute in Boston in the U.S. and Dean Murphy of the National Centre in HIV Social Research, the University of New South Wales led a symposium, “What is needed to make PrEP an effective prevention technology for gay men and other MSM?” The session looked at lessons learned from PrEP clinical trials to date and how PrEP might be rolled out for men who have sex with men (MSM).

Dr. Mayer provided an overview of the iPrEx PrEP study, which provided proof of concept for PrEP in late 2010.

“The iPrEx study provided clues that point to what we need to do to move PrEP from clinical trials to real world use for gay men and other men who have sex with men. Our challenge now is to translate what we’ve learned from iPrEx and what we are learning from follow-up studies of iPrEx and other studies into effective programs that will make PrEP available to gay men who need it in the U.S., Australia and around the world.”

“There is much work to be done to ensure that gay men and their healthcare providers understand both the promises and the limitations of PrEP. But we know that PrEP has the potential to be a powerful prevention option.” Mayer added.

Other research presented at the conference on Monday looked at the biology of mucosal transmission of HIV and rectal microbicides. In a plenary session, Betsy C. Herold of the Albert Einstein College of Medicine in the Bronx in the U.S. noted that there are still gaps in our knowledge of the biological factors of HIV transmission that may have played a part in the differing ARV-based prevention results.

“As we move to design new microbicide and PrEP trials we need to understand much more about the biology of sexual transmission of HIV and more about how the drugs in microbicides or PrEP may be impacted by the use of hormonal contraception, biological changes in adolescence, sexually transmitted infections or other factors that may increase HIV risk,” said Herold.

A rectal-specific formulation of tenofovir gel was effective against HIV in laboratory tests of human rectal tissue, according to researchers from the University of Pittsburgh and University of North Carolina in the U.S. Because the risk of acquiring HIV through unprotected anal sex is so high —at least 20 times greater than through vaginal sex — there is interest in developing a rectal microbicide that can help prevent against infection. Tenofovir gel was originally developed for use in the vagina. Recently, researchers reformulated the vaginal gel with less glycerin to make it more amenable for rectal use, and this reformulated version of the vaginal gel will soon be tested in a Phase II clinical trial. Still, there will likely be the need for a gel that’s specifically designed for use in the rectum, which differs from the vagina in two important ways: the rectum’s lining is much thinner — only one cell thick — and with a pH of 7, the rectum is neutral, whereas the vagina is more acidic, explained Charlene Dezzutti, Ph.D., of the University of Pittsburgh. An early phase clinical trial of the rectal-specific formulation of tenofovir gel is being planned, she added.

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