Gels to protect women from infection with the AIDS virus have shown hints that they may work, researchers said on Monday.

But two studies show that men who take powerful HIV cocktails can still pass the virus on in their semen, even if it cannot be found in the blood.

The studies presented at a meeting of AIDS in Canada show slow progress in finding ways to slow the pandemic of deadly human immunodeficiency virus, which infects 33 million people globally and which has killed 25 million.

Dr. Salim Abdool Karim of the Center for the AIDS Program of Research in South Africa and colleagues tested a gel made by Massachusetts-based Indevus Pharmaceuticals called PRO 2000 in women.

They are trying to find a microbicide — a gel or cream that women and perhaps men can use to protect against the AIDS virus when their partners cannot or will not use a condom.

PRO 2000 reduced the rate of HIV infection by a third, they told the meeting. "This is the first study that now shows that we have a promising candidate," Karim told a news conference.

"We do not regard it as a definitive conclusion that PRO 2000 is a microbicide but we certainly view it as very promising."

The researchers tested another microbicide called BufferGel made by ReProtect Inc, but were unable to find any significant indication that it helped. The study was only designed to show the gels were safe, an especially important issue because other studies have shown would-be microbicides actually raised the risk of infection.

DRUGS AS PROTECTION

Two studies in monkeys showed combinations of Gilead Sciences Inc.'s HIV drug Viread, or tenofovir, combined with its newer drug emtricitabine, marketed under the brand name Truvada, could protect monkeys from infection with a monkey virus similar to HIV both as a gel or in pills.

Dr. Gerardo Garcia-Lerma and colleagues at the U.S. Centers for Disease Control and Prevention gave Viread and Truvada pills to monkeys in an approach called pre-exposure prophylaxis and found the monkeys were completely protected.

CDC's Drs. Charles Dobard and Walid Heneine treated monkeys with one of two gels, one containing Viread alone and one with both drugs. Either gel worked equally well in protecting the monkeys, they told the meeting.

But two studies showed that men who take drug cocktails known as highly active antiretroviral therapy or HAART can still pass the virus in their semen.

Prameet Sheth of the University of Toronto in Canada, and Anne-Genevieve Marcelin of the Pitie-Salpetriere in Paris, both found that men whose blood seemed clear of HIV nonetheless had some in their semen.

"I would argue that it is infectious although we don't know what level of virus is required," Sheth told the news conference.

The drug cocktails do not cure AIDS, but they do drive down levels of the virus to so-called undetectable levels in blood. This helps stop the virus from destroying the immune system and keeps patients healthy.

The hope had been they would reduce the spread of AIDS, and on a population level that may still be true, the researchers told the meeting.

But both teams found when they tested individual men, they often had virus in their semen, which means they could infect someone else if they had unprotected sex. It was not clear why the virus could be found in semen but not in blood but experts know it is impossible to completely suppress the virus.