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New Approach to Blocking H.I.V. Raises Talk of an AIDS Vaccine

A new compound has blocked H.I.V. infection so well in monkeys that it may be able to function as a vaccine against AIDS, the scientists who designed it reported Wednesday.

H.I.V. has defied more than 30 years of conventional efforts to fashion a vaccine. The new method stimulates muscle cells to produce proteins that somewhat resemble normal antibodies, which have Y-shaped heads. These proteins have both a head and a tail, and they use them to simultaneously block two sites on each “spike” that the virus uses to attach itself to a cell.

If both sites can be blocked on every spike, the virus becomes helpless and drifts off unattached into eventual oblivion by the immune system.

“It’s a twofer,” said Dr. Anthony S. Fauci, director of the National Institute of Allergy and Infectious Diseases, which supported the work. “It’s very impressive, and the method is quite promising. But it’s still just in an animal model, so we’ll need to see evidence of whether it works in humans.”

But the protein produced by Dr. Farzan, bent into its claw shape, blocks both the CD4-binding site and the CCR5-binding site. It does so in a very tight “match” difficult for the virus to block by means of “escape mutations” — changes in shape that partially prevent engineered antibodies from attaching.

“It fools the virus into thinking its interacting with a cell,” Dr. Farzan said.

The virus is so successfully tricked that it begins to undergo the shape changes needed to attack a real cell — but there is nothing behind the protein to attack.