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

According to wsj.com, 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 cure infected people. But the ever-evolving virus has eluded them.

Now, a team from the Scripps Research Institute and other institutions said it has identified a way to prevent HIV from infecting cells, using an approach that resembles gene therapy or transfer rather than eliciting an immune response.

HIV normally invades cells through two receptors. The new protein blocks the points where the virus binds to both cellular 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 study 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.”

The approach has been tested only on four rhesus monkeys, not humans.

“This innovative research holds promise for moving us toward two important goals: achieving long-term protection from HIV infection, and putting HIV into sustained remission in chronically infected people,” said Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, which funded the work.

Scientists not involved with the work said it shows promise and should move into human testing quickly. An estimated 35 million people are infected with HIV, but only 13.6 million receive drug treatment that controls the amount of virus in their bodies, keeping it from multiplying and allowing them to lead relatively normal lives.