Researchers from the U.S. National Institute of Allergy and Infectious Diseases (NIAID) found that each of four HIV antibodies helped protect macaque monkeys from repeated exposure to a modified version of HIV, although some of the antibodies protected the animals longer than others.
Experts said the findings, published April 27 in the journal Nature, represent progress in a new approach to eventually creating an HIV vaccine.
Scientists have worked for decades toward the goal of having an HIV vaccine, with little success.
In 2009, a clinical study known as the "Thai trial" produced the first vaccine to offer some protection against HIV, the virus that causes AIDS, but it only lessened transmission by a modest degree. Scientists are still studying a range of vaccine candidates they hope will be more effective.
With any traditional vaccine, the idea is to get the immune system to generate antibodies that will recognize and attack a specific foreign invader, explained Rowena Johnston, vice president of research for amfAR, a nonprofit that supports HIV/AIDS research.
But scientists have also wondered whether it could be possible to directly inject HIV-targeting antibodies into the body, said Johnston, who was not involved in the latest study.
In recent years, researchers have isolated a number of powerful antibodies that certain people with HIV produce against the virus.
One, called VRC01, was isolated from an HIV-infected man and later found to neutralize almost all known HIV strains in the world, according to NIAID.
That antibody has already moved into early human clinical trials, said Dr. David Hardy, a spokesperson for the HIV Medicine Association.
"The real value of this new study is that it shows there are at least three good [antibody] candidates to move into trials," said Hardy, who was not involved in the research.
For the study, the NIAID scientists started with three HIV-fighting antibodies -- VRC01 and two others. They created a fourth by genetically tweaking VRC01.
The researchers found that all four antibodies temporarily protected macaque monkeys from infection with SHIV -- a combination of HIV and the simian form of HIV that naturally infects many primates.
A single infusion of one of the antibodies -- dubbed 10-1074 -- kept the infection at bay for up to 23 weeks.
The researchers also found that the genetically altered version of VRC01 offered nearly double the protective window of the original version.
According to Johnston, that's an interesting finding because it suggests that with more genetic tinkering, the antibodies could be altered so protection lasts longer.
Many questions remain, however. Research with animals often doesn't produce the same effect in humans. And even if one or more antibodies can safely stave off HIV infection in humans, there are practical barriers to using them in the real world, both Johnston and Hardy said.
Creating antibodies in the lab is very expensive, so there is the cost issue, Johnston pointed out.
And because the body eventually degrades the infused antibodies, Hardy said, the treatment would have to be repeated.
An NIAID-run clinical trial is starting in sub-Saharan Africa, looking at whether VRC01 infusions can prevent HIV infection in women at high risk. The infusions will be given every two months.
But it's not yet clear, according to Hardy, whether antibody infusions could be realistically adopted in the low-income countries where most HIV infections occur.
Johnston added, "This is not something that's going to be available tomorrow, but this is a great step in the right direction."
Antibody infusions would be more feasible in higher-income countries like the United States. Right now, Hardy said, the HIV drug Truvada is approved for preventing infection in people at high risk. A periodic infusion of antibodies could potentially be easier than taking that daily -- and expensive -- pill, he said.
But Hardy also pointed to the bigger picture: Now that researchers are learning which antibodies neutralize HIV, they may be able to "work backwards" to develop vaccines that spur the immune system to produce those antibodies.
That won't be "easy," he stressed, but it's a different approach to finding the elusive HIV vaccine.
In the United States, where antiretroviral drugs have turned AIDS into a manageable condition, people may forget it remains one of the top causes of death worldwide, Hardy pointed out.
"This epidemic is not, by any means, over," he said.
NIAID has more on HIV vaccine research.
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