Washington - Researchers have discovered antibodies that can protect against a wide range of Aids viruses and said they may be able to use them to design a vaccine against the fatal and incurable virus.
The bodies of some people make these immune system proteins after they are infected with the Aids virus, when it is too late for them to do much good. But a properly designed vaccine might help the body make them much sooner, the researchers reported in Friday's issue of the journal Science.
"I am more optimistic about an Aids vaccine at this point in time than I have been probably in the last 10 years," Dr Gary Nabel of the National Institute of Allergy and Infectious Diseases, who led the study, said in a telephone interview. Two of the antibodies can attach to and neutralize 90% of the various mutations of the human immunodeficiency virus that causes Aids, Nabel said.
"This is an antibody that evolved after the fact. That is part of the problem we have in dealing with HIV - once a person becomes infected, the virus always gets ahead of the immune system," Nabel said.
"What we are trying to do with a vaccine is get ahead of the virus."
Aids infects about 33 million people globally, according to the United Nations Aids agency Unaids. It has killed 25 million people since the pandemic began in the early 1980s and there is no vaccine or cure, although drugs can help control it.
The virus is difficult to fight in part because it attacks immune system cells and in part because it mutates constantly, making it a moving target for drugs or the immune system.
It has been almost impossible to make a vaccine that will affect the virus. Last September, researchers reported their biggest success yet with a vaccine that appeared to slow the rate of infection by about 30% in Thai volunteers but the trial raised many questions.
Moving targets
Researchers have been looking for parts of the virus that do not mutate so they can design vaccines that will protect against these constantly changing versions.
Nabel's team found two of the antibodies in the blood of a patient infected with HIV who had not become ill despite the infection. Such people are called non-progressors and researchers study their immune systems to find out why they control the virus better than most patients.
They then found the immune system cells called B-cells that made these particular antibodies, using a new molecular device that they invented.
In yet another experiment, they managed to freeze one of the antibodies in the process of attaching to and neutralising the virus, getting an atomic-level image in a process called x-ray crystallography.
Being able to "see" what the structure looks like could enable researchers to design a vaccine using a process called rational vaccine design, akin to an established technique for making drugs called rational drug design, Nabel said.
It may also be possible to design gene therapy to help patients make these antibodies themselves, or use an older technique that transfuses the antibodies directly.
One of the antibodies, called VRC01, partially mimics the way an immune cell called a CD4 T-cell attaches to a piece of the Aids virus called gp120, the researchers said.
"The antibodies attach to a virtually unchanging part of the virus, and this explains why they can neutralize such an extraordinary range of HIV strains," Dr John Mascola, who worked on the study, said in a statement.
"The discovery of these exceptionally broadly neutralizing antibodies to HIV and the structural analysis that explains how they work are exciting advances that will accelerate our efforts to find a preventive HIV vaccine for global use," NIAID director Dr Anthony Fauci added in a statement.
"In addition, the technique the teams used to find the new antibodies represents a novel strategy that could be applied to vaccine design for many other infectious diseases."
