More than 25 years into the AIDS epidemic, many drugs are used to treat HIV, but an alarming number of patients are becoming resistant to therapy, driving research into new ways to combat the virus.

Data from clinical trials of several promising new products will be unveiled at a conference of leading HIV researchers in Los Angeles next week.

"There is a confluence of new drugs in the pipeline that people are pretty excited about," said Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases.

These include next-generation versions of longstanding HIV fighters as well as drugs that combat the virus through innovative mechanisms, including blocking it from entering immune system cells.

The human immunodeficiency virus that causes AIDS infects more than 1 million people in the United States and nearly 40 million worldwide. An estimated 40,000 Americans become infected each year.

About half of U.S. patients treated for infections with HIV have stopped responding to at least one drug, said Dr. John Mellors, chief of infectious diseases at the University of Pittsburgh.

Resistance is becoming a problem because the virus can mutate, particularly if patients fail to rigorously follow complicated drug regimens.

On Tuesday, Merck & Co. will release results of a trial of MK-0518, which is likely to be the first in a new class of drugs, known as integrase inhibitors, designed to block genetic information needed for HIV to reproduce. Merck plans to seek U.S. approval for the drug in the second quarter.

"It looks like a very exciting result," said Mellors. He said clinicians are starting to see response rates in patients previously heavily treated for HIV that are similar to effectiveness seen among first-time patients.

On Wednesday, Gilead Sciences Inc., maker of top-selling HIV pill Truvada, will present data from a mid-stage trial of its experimental integrase inhibitor,

GS-9137.

Norbert Bischofberger, head of research for Gilead, said comparisons with Merck's data would be problematic because patients in the Gilead study were not allowed to use other therapies until the company obtained information on potential drug interactions.

About four months into the six-month Gilead study, patients were allowed to use protease inhibitors, a commonly used family of HIV drugs, he said.

Another promising new class of medicines works by blocking HIV from entering and taking up residence in T cells, a type of white blood cell vital to the immune system.

The drugs work by jamming receptors -- or docking stations -- that dot the surface of the T cells and act as doorways into the cells. If HIV is barred entry, the virus cannot replicate.

Because the receptors are made of a protein called CCR5, the crop of drugs are called CCR5 inhibitors.

On Tuesday, Pfizer Inc. will present data from a late-stage trial of its CCR5 inhibitor, maraviroc, now awaiting U.S. and European approval. Patients in the trial had fared poorly on previous HIV treatments.

"If maraviroc is approved, it would change the landscape of treatment and be the first new oral class of HIV treatments in a decade, since the approval of protease inhibitors," said Howard Mayer, a Pfizer executive in charge of maraviroc's development.

Because CCR5 inhibitors do not attack the virus itself, as all four existing classes of HIV treatments do, Mayer said HIV might be less able to come up with ways of resisting their effects.

On Wednesday, Johnson & Johnson, which last year launched its first AIDS drug, Prezista, will announce results from a mid-stage trial of its next-generation non-nucleoside reverse transcriptase inhibitor, known as TMC278, which works by blocking an enzyme the HIV virus needs to replicate.

The 14th Conference on Retroviruses and Opportunistic Infections will be held at the Los Angeles Convention Center.

Treating genital herpes may slow the progression of the AIDS virus in those infected with both viruses, researchers reported on Wednesday.

The test involving 140 women in the West African country of Burkina Faso found that when herpes was being treated with 500 milligrams of the drug valacyclovir twice daily for three months, the women were less likely to shed, or spread, the AIDS virus.

In addition, the treatment reduced the levels of AIDS virus in the blood, the research group led by Dr. Nicolas Nagot of the London School of Hygiene and Tropical Medicine found.

The drug's effect increased steadily over time, so "a longer duration of treatment might have led to an even greater reduction" in the amount of HIV detected, the researchers conclude in the New England Journal of Medicine.

Valacyclovir, made and sold by GlaxoSmithKline under the brand name Valtrex, is one of several drugs that can treat herpes.

Among people already infected with HIV, up to 70 percent in Europe and 90 percent in Africa also carry the virus for genital herpes, HSV-2.

Until now, doctors have placed less emphasis on genital herpes because it is not as dangerous as HIV.

The new study may change that, said Dr. Philip Keiser, who runs the AIDS clinic at the University of Texas Southwestern Medical Center in Dallas, who was not connected with the research.

With existing HIV treatments, "the best we can do right now is to get 70 to 80 percent of patients to the point where we totally suppress the virus. That means that 20 to 30 percent, right off the bat, will not do well," he said in a telephone interview.

He said he would change the way he treats patients who have both HIV and herpes.

"I'll be more aggressive in treating their herpes and keep them on the valacyclovir for a long time," Keiser said. "This may be one of those small refinements that add something to that (success rate) and help our patients do better over the long haul."

Researchers already knew that treating sexually transmitted diseases such as herpes, gonorrhea and syphilis could help make people less likely to become infected with HIV, which is passed most commonly through sex.

Homosexual men in Britain are requesting treatment with Merck & Co Inc's new HPV vaccine Gardasil, with dozens immunized in recent weeks, a London clinic said on Friday.

Gardasil was licensed for use last year against human papillomavirus (HPV) -- a leading cause of cervical cancer in women -- but the sexually transmitted virus can also trigger anal and penile cancers.

"We started offering vaccination to gay men in January and recently we've been giving about 10 a week," said Dr Sean Cummings of the Freedomhealth clinic in London's Harley Street.

Since many sexually active people are already contaminated with HPV, patients are swabbed before vaccination to determine which, if any, sub-types of HPV they may be carrying.

"If you've got a full house (of HPV sub-types) then there is no point in immunizing," Cummings said.

"The situation in gay men is analogous to the early stages of cervical cancer screening and the rates of anal cancer in men who have anal sex are akin to those prior to the cervical cancer screening program, at around 35 per 100,000."

However, some experts said the benefits of vaccinating men were not yet clear.

The Terrence Higgins Trust, Britain's leading HIV and AIDS charity, said the case for mass vaccination in men would depend on the outcome of further clinical trials.

Gardasil costs 450 pounds ($880) for a three-dose course at the Fredomhealth clinic, which has a reputation as a specialist in gay men's health.

In an "extraordinary development" in the fight against AIDS, a medical journal article published Friday says that conclusive data shows there is no question circumcision reduces men's chances of catching HIV by up to 60 percent.

The question now is how to put that fact to work to combat AIDS across Africa.

The findings were first announced in December, when initial results from two major trials — in Kenya and Uganda — showed promising links between circumcision and HIV transmission. However, those trials were deemed so definitive that the tests were halted early.

The full data from the trials, carried out by the U.S. National Institutes of Health, were published Friday in The Lancet.

"This is an extraordinary development," said Dr. Kevin de Cock, director of the World Health Organization's AIDS department. "Circumcision is the most potent intervention in HIV prevention that has been described."

Circumcision has long been suspected of reducing men's susceptibility to HIV infection because the cells in the foreskin of the penis are especially vulnerable to the virus.

A modeling study last year projected that in the next decade, male circumcision could prevent 2 million AIDS infections and 300,000 deaths. Last year, 2.8 million people in sub-Saharan Africa became infected with HIV, and 2.1 million people died.

Experts say the breakthrough's significance is on par with the identification of the virus and the use of lifesaving combination drug therapy.

The two U.S. studies confirm similar results from an earlier trial in South Africa.

But experts warn that solid evidence is not justification for mass circumcisions, noting that African health systems are already overburdened, and circumcision requires more planning than, for example, an immunization campaign.

"It's a tricky one, but it's something we're going to have to move on," said Dr. Catherine Hankins, a scientific adviser at UNAIDS. "Male circumcision is such a sensitive religious and cultural issue that we need to be careful."

Several African countries have met with U.N. agencies to explore strategies for increasing circumcision.

Together with the United Nations AIDS agency, WHO is convening a meeting in Switzerland in March to evaluate the data and decide the next steps in slowing the AIDS pandemic.

In the Kenyan study, 1,391 circumcised men were compared to 1,393 who were not. And in Uganda, 2,474 circumcised men were compared to 2,522 men who were not. Scientists tracked the men for two years and found that those who were circumcised were 51-60 percent less likely to contract HIV.