Scientists have engineered a new molecule they say can block infection with the virus that causes AIDS, a discovery that could lead potentially to a new therapy for patients as well as an alternative to a vaccine. 

Researchers have been trying for three decades to develop an effective vaccine against the human immunodeficiency virus, which causes AIDS. They are also searching for a way to flush HIV out of the bodies of the infected, to cure them. But the ever-evolving virus has eluded them thus far.

Now, a team from the Scripps Research Institute and other institutions says it has identified a new way to prevent HIV from infecting cells, using an approach that resembles gene therapy or transfer.

HIV normally invades the body through two cellular receptors. The new protein the scientists created blocks the points where the virus binds to both receptors, leaving no point of entry.

Because it attaches to both receptors rather than just one, the protein, called eCD4-IG, blocks more HIV strains than any of several powerful antibodies that have been shown to disable the virus, the researchers said. The research was published online Wednesday by the journal Nature.

“It is absolutely 100% effective,” said Michael Farzan, a professor of infectious diseases at the Scripps Research Institute in Jupiter, Fla. and lead author of the study. “There is no question that it is by far the broadest entry inhibitor out there.”

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