A new study presented Monday at the annual Conference on Retroviruses and Opportunistic Infections (CROI) in Boston suggested the potential of an anti-HIV gel in protecting rectal tissue cells from infection with the virus that causes AIDS.
The gel made by Gilead Sciences Inc. contains the antiretroviral drug tenofovir, which, when applied in the vagina in previous trials, reduced HIV infection by 34% compared with placebo. Researchers have wanted to know whether the gel could protect against anal transmission of the virus, since the risk of infection from unprotected anal sex may be more than 20 times that of unprotected vaginal sex. In part, that’s because the rectal wall is one-cell thick, compared with the multiple layers of vaginal walls. (More on Time.com: Senior Class Project: HIV Tests for All)
For the new study, researchers from the Microbicide Trials Network, University of Pittsburgh and Magee-Womens Research Institute recruited 18 sexually abstinent HIV-negative men and women to participate. The volunteers were first asked either to apply the anti-HIV gel to the rectum once or to take an oral tenofovir pill once. Then, the patients followed up by applying either tenofovir gel or placebo gel every day for six days at home; a final, seventh dose was applied in the lab.
Researchers biopsied rectal tissue after the initial dose and again after the week of gel or placebo applications, allowing them to compare several different experimental conditions. In the lab, HIV was introduced to the biopsied cells. Researchers found that the tissue cultures from patients who used the tenofovir gel daily for a week withstood HIV infection significantly better than those from patients who used placebo or the anti-HIV gel only once. The single tenofovir pill had no impact on HIV prevention.
Although the gel was generally safe, only 25% of participants said they liked it. Two volunteers suffered gastrointestinal side effects like diarrhea and cramps. Still, 75% of the study group said they would consider using it in the future. Researchers are currently reformulating the vaginal microbicide with less glycerin, a common additive in many gels, which they hope will make it more tolerable for use in the delicate rectal area. (More on Time.com: HIV Drugs May Prevent Infection in Healthy Individuals)
In another study presented at CROI, researchers reported the results of a trial involving 144 women in the U.S., Uganda and South Africa, who took a daily oral dose of tenofovir for six weeks, followed by a vaginally applied tenofovir gel every day for six weeks, and then both in conjunction for an additional six weeks.
The researchers did not monitor HIV infection rates, but they did measure the levels of the antiretroviral drug present in the women’s blood and tissue. When taking the daily pill alone, women had 20 times the concentration of the drug in the bloodstream than when they used the gel. When using the gel, they had 100 times the concentration of the drug in vaginal tissue, compared with taking the oral dose. It is not clear, however, whether blood concentration or tissue cell concentration will prove more important in preventing HIV infection.
In this study, American women reported preferring the oral dose, while African participants like the gel better, with many reporting that it increased sexual pleasure. (More on Time.com: Researchers Crack the Mystery of AIDS Immunity)
Historically, gels have not shown enough promise as HIV prevention for health experts to recommend using them. But other recent data have suggested that combination antiretroviral drugs, which are normally used for HIV treatment, may hold significant potential for prevention. As Alice Park reported on Healthland last November, the first large-scale study of a combination antiretroviral pill (tenofovir/emtricitabine), found that it was effective in preventing infection in a group of healthy, high-risk people:
In a trial involving nearly 2,500 HIV-negative gay men who were at high risk of contracting HIV, in six countries, scientists found that those who took the currently prescribed treatment dose of a combination anti-HIV medication known as Truvada had a 44% lower rate of HIV infection than those taking a placebo during the study’s longest follow up of nearly three years. Among those who took their medications more faithfully on a daily basis, the benefit was even greater; their risk of acquiring HIV dropped to 73% compared to placebo.
In January, the Centers for Disease Control and Prevention issued its first “interim guidelines” on using Truvada for HIV prevention, a practice familiarly known as PrEP (for pre-exposure prophylaxis), in high-risk men.