Published online 23 November 2010 | Nature | doi:10.1038/news.2010.627

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Antiretroviral drugs shown to cut HIV transmission to men at high risk.

Study participants who reported taking retrovirals 90% of the time had a 72.8% reduction in risk of becoming infected with HIV. Frank May/dpa/Corbis

The antiretroviral medicines taken by patients infected with HIV could also protect people not yet infected but at high risk of becoming so, according to the results of a large-scale clinical trial. But questions remain about whether such a strategy would work as an HIV prevention policy.

The US$43.6-million study, published today in the New England Journal of Medicine, included 2,499 subjects from Peru, Ecuador, South Africa, Brazil, Thailand and the United States who were born male (although 1% now identify themselves as women), who had had sex with men, and who showed no HIV antibodies in their blood at the time of enrolling in the study1.

The study "provides the first proof" that pills that control HIV in infected people can also help prevent new infections, says Robert Grant, an HIV researcher at the University of California, San Francisco, and the study's lead author.

In the trial, called the Pre-Exposure Prophylaxis Initiative (iPrEx), one group of patients received a daily dose of a single pill — marketed as Truvada by drug firm Gilead Sciences of Foster City, California — combining emtricitibane and tenofovir, two oral antiretroviral medicines. The other group received a placebo. Of the 100 participants that became infected with HIV during the course of the study, 36 were from the former group and 64 from the latter, translating to a nearly 44% reduction in risk for subjects taking the active pills.

Participants who received the drugs and who reported taking their pills 90% of the time experienced a much higher protection rate of 72.8%. And those who had high levels of the drugs in their blood showed an even greater degree of protection: 92%.

"With a vaccine, it either works or it doesn't work, but here it really depends on the individual who's taking it," says Anthony Fauci, director of the US National Institute of Allergy and Infectious Diseases (NIAID).

Prevention questions

The NIAID provided $27.9 million in funding for the study, with the rest provided by the Bill & Melinda Gates Foundation. The drugs were donated by Gilead Sciences.

Different US agencies such as the Centers for Disease Control and Prevention and the Food and Drug Administration must now begin to look closely at the study's findings to determine how it might fit in with ongoing HIV prevention programmes, Fauci says.

"This is going to be a very active topic of discussion," he says.

He cautions, however, that although men who have sex with men represent one of the highest-risk groups for HIV infection, the study must be validated in other at-risk populations.

The findings are encouraging and could help some people, but the strategy's effectiveness still needs to be determined, says Daniel Halperin, an HIV prevention expert at Harvard School of Public Health in Boston, Massachusetts, who was not involved with the study.

"These kinds of things could be very useful, obviously, but they could backfire," he says, for example by making people feel safe enough to have unprotected sex or engage in other risky behaviours.

Subjects in the study, however, actually decreased their risk-taking behaviour, notes Grant, stressing that the approach will need to be used "with other prevention services that will have to go along with it as a package".

Costs and benefits

A follow-up phase of the study will try to develop better approaches to compliance with the drugs, which can cause nausea. It will also track side effects, as well as whether participants become resistant to the therapy over a longer time scale than possible in the original study.

There are also questions of cost and access, says Halperin — especially in regions such as Africa, where a huge number of individuals are at high risk of contracting the virus. "There, we can't even get retrovirals to the people that need them", much less those who are not yet infected, he says.

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In the developing world, the combination drug used in the trial is available for as little as $0.40 per day, Grant says, but this is no small sum for a daily regimen.

"With HIV we've shown that behavioural changes and things like circumcision really make a difference," Halperin says, adding that prioritizing a biomedical solution over proven behavioural strategies may be impractical.

Some researchers also question whether providing preventative antiretrovirals for high-risk individuals will be able to help slow the spread of the disease in a population, says James Kublin, director of the HIV Vaccine Trials Network and a global health researcher at the University of Washington, both in Seattle. "The best long-term hope to end the epidemic continues to be a safe, durable and effective vaccine," Kublin adds.