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A targeted immune system molecule can help control the AIDS virus, offering a new tool for people infected with the deadly virus.

Researchers have tested the so-called monoclonal antibody in patients and found one infusion could control the virus for a month – potentially freeing patients of having to take daily cocktails of pills.

It’s still experimental, but it’s the first therapy of this kind to show it’s safe for people infected with the human immunodeficiency (HIV) virus.

“The goal is a once-a-year shot for prevention and a combination approach for cure,” says Michel Nussenzweig of Rockefeller University in New York, who led the study.

“The goal is a once-a-year shot for prevention and a combination approach for cure."

This particular antibody is one of a handful found in the blood of people who are infected with HIV but who don’t get sick. Their immune systems naturally control the virus. It attaches to the cells that HIV likes to infect – immune cells called CD4 T-cells – and stops the virus from getting in.

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Nussenzweig and colleagues tested the antibody, called 3BNC117, in 17 people with HIV and 12 uninfected people.

The higher the dose, the better the protection, the researchers reported in the journal Nature. And it seemed to be safe, even in uninfected people.

In some, the levels of the virus in their blood plummeted. In six who got the lowest doses, there was little effect at all.

“We conclude that, as a single agent, 3BNC117 is safe and effective in reducing HIV-1 viraemia, and that immunotherapy should be explored as a new modality for HIV-1 prevention, therapy and cure,” Nussenzweig's team wrote.

It could be good news for HIV patients, who often have trouble taking medication daily. But infused antibodies are usually more expensive than pills, although it’s far from clear how much this one might cost if it ever made it to market.

"A combination of antibodies will probably become the best approach to immune control.”

There are more, similar, antibodies that can be tested.

“This one is the first to be tested for safety in people and the results look promising and it results in a moderate reduction in the amount of virus in the bloodstream,” said Robin Weiss, a virus expert at University College London who was not involved in the study.

“However, we know that HIV is clever at evolving resistance to antibodies just as it does to antiretroviral drugs. Therefore, a combination of antibodies will probably become the best approach to immune control.”

Researchers are still looking for better ways to treat HIV, which infects 1.2 million people in the United States alone. There’s no cure and no good vaccine. AIDS has killed nearly 40 million people globally.