The dream of an HIV vaccine has been thwarted again and again because the virus evolves so rapidly that the immune system can't keep up. But the results from a new trial in monkeys suggest that certain antibodies have a powerful enough therapeutic effect that they may warrant clinical trials.

Many researchers had given up on antibodies, which are used by the immune system to identify the signature proteins on the outside of invading cells, targeting them for destruction. The HIV virus changes so rapidly that any antibodies that target the virus only work for a little while—the virus stays one step ahead while the immune system struggles to play catch-up.

But researchers discovered antibodies that target the converse part of the virus's structure—the features that are critical to its function and don't change much over time. These antibodies were discovered in HIV-infected people whose immune systems seemed to keep most strains of HIV in check.

In a paper published this week in Nature, a research team led by Harvard Medical School scientists worked with monkeys infected with a monkey-human-hybrid version of HIV known as SHIV. Injection of these monkeys with just one type of these antibodies drastically reduced the levels of the virus—to the point where it was undetectable. The effect lasted several months, and in a couple of test subjects, the virus never returned.

Unlike the conventional antiretroviral therapy available for HIV infections, the antibodies clear the virus particles that are circulating in the system and kill the infected cells that produce more of the virus. Antiretroviral therapy drugs only stop the virus from spreading, but they don't kill the infected cells. So if patients stop their regimen of pills, the virus is poised and ready to rebound.

Combining the two treatment strategies could "revolutionize efforts to cure HIV," according to the authors of a viewpoint paper Nature published along with the research. The same issue also included a paper describing an NIH study that had similar results using these "neutralizing" antibodies to help the immune system fight the virus down to very low levels.

The scientists are careful to caution that although their new antibody shows therapeutic promise in rhesus monkeys, a lot of work will be needed to determine if it would be effective in humans. Also, because HIV is so variable, the antibodies may not work as well on every strain of HIV.

Currently, the antibodies are given by injection, which is undoubtedly less convenient that the antiretroviral pills. But the research is a big step in understanding how the immune system can attack and knock back HIV. Perhaps this will open the door to vaccines and other methods for the body to develop its own antibody protection that will fight the virus more effectively.

Nature, 2013. DOI: 10.1038/nature12744 (About DOIs).