The key to defeating HIV, researchers speculate, is by removing a chemical 'invisibility cloak' that makes HIV-infected cells look healthy.
Human cells defend themselves against immune attack by displaying proteins on their surface that mark them as "self".
When the immune system detects these proteins, it holds back. One way HIV evades immune attack is by hijacking one of these proteins - CD59 - and using it to disguise itself and the cells it infects as healthy, human cells.
This cloak doesn't kick in directly following HIV infection. First, antigens on HIV's surface prompt the immune system to pump out vast quantities of anti-HIV antibodies, which bind to the antigen and even trigger the destruction of some HIV.
But once the infection is established, the CD59 cloak prevents further immune attack on the viral particles and infected cells, which also display the antigen.
"HIV patients have a very strong antibody response, but unfortunately it doesn't work," New Scientist quoted Qigui Yu of the Indiana University School of Medicine in Indianapolis, as saying.
To kick-start this immune attack, the researchers wanted to find a way to remove this cloak. They knew that a bacterium found in the human throat secretes a toxin called intermedilysin that binds to CD59. By isolating the toxin's binding site they made a small molecule called rILYd4.
When they added this molecule to blood from people with HIV, it enabled the antibodies already in the blood to destroy viral particles. Red blood cells and uninfected immune cells were unscathed, probably because there were no antibodies specific to these cells present.
Yu has preliminary results suggesting rILYd4 fights infected cells too.
The study has been published in The Journal of Immunology.