September 4 2009
The search for an HIV vaccine has taken a major step forward with the discovery of two new immune system fighters, as well as a vulnerable spot on the virus that causes AIDS.
Researchers have announced they've found two new antibodies that attack the AIDS virus, opening the door to a way to create a vaccine against the incurable illness.
Researchers led by Dennis Burton of The Scripps Research Institute in La Jolla, California, made the discovery after sifting through the blood of 1,800 people infected with AIDS.
They identified two antibodies that seem to neutralize the virus, dubbing the immune system fighters PG9 and PG16. They are the first new HIV antibodies to have been identified in more than 10 years of AIDS research and appear to be 10 times more effective at disarming the virus than already-discovered antibodies.
At the same time, the researchers found a new weak spot on the virus that the antibodies attack, they report in the journal Science. The researchers found the antibodies target a part of the "spike" that viruses use to infect cells.
"So now we may have a better chance of designing a vaccine that will elicit such broadly neutralizing antibodies, which we think are key to successful vaccine development," said Burton.
Wayne Koff of the International AIDS Vaccine Initiative, or IAVI, which sponsored the study, said the findings are an exciting advance toward the goal of an effective AIDS vaccine "because now we've got a new, potentially better target on HIV to focus our efforts for vaccine design," he said.
IAVI director Dr. Seth Berkley said the findings will not lead directly to a vaccine. But he says they offer a new way to design one.
While treatments to slow down AIDS infections have been developed in recent years, there is still no cure. Researchers trying to design a vaccine have come up empty-handed, hamstrung by the fact that the virus infects the very immune cells that are supposed to protect the body.
Most frustrating, the virus is constantly mutating, so that any one patient can be infected with millions of different versions, each one appearing different to the immune system.
But Burton's team says the newly discovered antibodies are effective against a broad array of HIV strains. He says they don't appear to attack every strain but in the lab experiments, they did attack about 80 per cent of strains tested, which he says is exceptional considering how variable HIV viruses are.
Vaccines work by training the immune system to generate antibodies against foreign pathogens, such as bacteria and viruses. Antibodies bind or latch on to specific portions of a virus and then prevent that virus from infecting healthy cells.
Eventually, the antibody also calls in other immune cells, known as T cells, to destroy the invading virus.
The discoveries may also make it possible to use antibodies to treat AIDS, by creating an immunoglobulin or gamma globulin, such as the one often used to treat early hepatitis. But the eventual goal is a vaccine that could stop the virus from infecting a person in the first place, Berkley said.
According to the International AIDS Vaccine Initiative, more than 20 million people have died so far in the AIDS pandemic and about 33 million are living with HIV.