New Lines of Attack in H.I.V. Prevention
By DONALD G. McNEIL Jr.
Published: November 8, 2010
The hottest news in AIDS in the last year was the partial success in a South African clinical trial of a microbicide — a gel women can put in their vaginas to kill the virus before it can infect them.
John Hersey
The whole field of protection before sex is “red-hot cool right now,” said Sharon L. Hillier, a gynecology professor at the University of Pittsburgh’s medical school and principal investigator of theMicrobicide Trials Network. “People are really energized.”
Although the gel offered only about 40 percent protection against the virus, it was the first form of protection that women could use without men knowing, which is crucial because so many men around the world absolutely refuse — sometimes violently — to wear condoms when having sex with their wives or girlfriends.
Other clinical trials will report their results in 2011 and 2012 and, if all goes well, researchers hope to have a product or two ready to enter the market by 2013.
The first may not be a gel, however.
In the next few months, said Mitchell Warren, executive director of AVAC, an advocacy group for AIDS prevention, “we’re going to see a cascade of results” from trials of what is called “oral pre-exposure prophylaxis,” or “oral prep” for short. In them, men and women who are not infected with the AIDS virus but who regularly engage in high-risk sex, like anal sex without condoms or sex for money with strangers, take a daily dose of one or two of the antiretroviral drugs normally taken by infected people. If many fewer of those subjects become infected than subjects taking a placebo, a second breakthrough will have been achieved.
Should that happen, regulatory authorities may approve pills faster than a gel, because they have already been found safe and effective for treatment.
But that doesn’t mean a gel isn’t still worth pursuing, said Dr. Salim Abdool Karim, a professor of epidemiology at the University of KwaZulu-Natal in South Africa and a leader of the microbicide trial for which results were released in July.
Gels have advantages. The drug in them stays in the vaginal tissue, so it is unlikely that anyone who gets infected anyway would develop a drug-resistant form of the virus. And unlike pills, gels also protect against herpes.
Also, as several experts pointed out, women like having choices in birth control: some prefer a daily pill, some prefer condoms, or IUDs, or shots that last three months, or skin implants that last three years. Presumably, they will also want choices in AIDS prevention.
“The simple truth is: one size does not fit all,” Dr. Karim said.
Because 95 percent of gay American men and 40 percent of heterosexual American women have had anal sex at least once during their lifetimes, according to surveys, rectal versions of the gel are being developed. Tests of new, less viscous formulations that are less likely to draw water into the rectum, making use unpleasant, will begin soon, said Dr. Ian McGowan, another leader of microbicide trials at the University of Pittsburgh’s medical school.
Gay and bisexual black and Hispanic men, who are now the highest AIDS risk groups in the United States, will be recruited soon in Boston, Pittsburgh and Puerto Rico to see if they find the gels acceptable, he said.
But first it is crucial to make sure gels don’t inflame the rectal lining, which is more fragile than the vagina’s. Since H.I.V. zeros in on activated immune cells, inflammation increases infection risk. Brief tests of irritation and acceptability will be done on people advised to remain celibate during the tests, he added. Larger trials, in which thousands of men and women regularly practicing anal sex are given gel or placebo will not begin for two to three more years.
“The rectal microbicide field is about 10 years behind the vaginal one,” Dr. McGowan said.
That is partly due to misconceptions.
“When you mention rectal microbicides, a lot of people say ‘Oh, come on,’ because they think you have to protect the whole colon, and it’s meters long,” Dr. McGowan said. In fact, researchers believe protecting only the last six to eight inches will suffice.
A 2008 British study showed that rectal tenofovir gel was very protective in monkeys that were then given anal doses of the virus that causes simian AIDS.
Farther over the horizon, another method is being tested for possible deployment by 2015 or so. Next year, a trial will begin of a vaginal ring containing a new antiretroviral drug, dapivirine. Dapivirine was never approved as a pill because the body doesn’t absorb it well, but it can build up in vaginal tissue. Also, it is so concentrated that a month’s worth fits in a ring that allows a tiny amount to trickle out each day.
| 08.11.10 | 16h09 • Mis à jour le 08.11.10 | 16h09
