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Semen Boosts AIDS Virus, Study Finds

Men's semen appears to give the AIDS virus an extra boost, researchers reported Wednesday in a finding they say may explain why it’s so hard to develop creams or gels to prevent infection.

But there’s one class of drugs that can get around this problem, and might offer a way forward for the field of microbicides — products that women, like men, could use to protect against infection.

"We think this may be one of the factors explaining why so many drugs that efficiently blocked HIV infection in laboratory experiments did not work in a real world setting," said Nadia Roan of the University of California, San Francisco and the Gladstone Institutes.

Semen, the fluid that carries sperm, also contains bundles of protein called amyloid fibrils. The human immunodeficiency virus (HIV) attaches to them in clusters that help them invade cells. The clusters also appear to be able to repel the drugs used in microbicides.

When Roan and colleagues tested different microbicides on HIV samples, they found that including semen in the mix made in 10 times easier for the virus to infect cells, and made the microbicides as much as 20 times less effective, they reported in the journal Science Translational Medicine.

"Microbicides were originally developed as a way to empower and protect women in sub-Saharan Africa who often don't have a way to negotiate safe sex or condom use,” said Dr. Warner Greene director of the Gladstone Institute of Virology and Immunology.

“However, the first generation of microbicides were largely ineffective or worse, some even leading to increased transmission of the virus." One HIV drug called maraviroc gets around this and might offer a good way forward, the researchers said.

Why Isn't There an AIDS Vaccine Yet? 0:42

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-- Maggie Fox