Scientists may yet be able to overcome their biggest hurdle in the development of an effective HIV vaccine by using gene transfer technology.
The researchers used gene transfer technology, which produces molecules that block infection, to successfully protect monkeys from infection by a virus closely related to HIV-the simian immunodeficiency virus, or SIV-that causes AIDS in rhesus monkeys.
"We used a leapfrog strategy, bypassing the natural immune system response that was the target of all previous HIV and SIV vaccine candidates," Nature magazine quoted study leader Dr. Philip R. Johnson, chief scientific officer at The Children's Hospital of Philadelphia, as saying.
Johnson developed the novel approach over a ten-year period, but warned that many hurdles still remain before the technique could be translated into an HIV vaccine for humans.
Most attempts at developing an HIV vaccine have used substances aimed at stimulating the body's immune system to produce antibodies or killer cells that would eliminate the virus before or after it infected cells in the body. But, the approach has not been proved fruitful until now.
However, the approach used in the current study was divided into two phases-in the first phase, researchers created antibody-like proteins (called immunoadhesins) that were specifically designed to bind to SIV and block it from infecting cells.
After it was proven to work against SIV in the laboratory, DNA representing SIV-specific immunoadhesins was engineered into a carrier virus designed to deliver the DNA to monkeys.
The researchers chose adeno-associated virus (AAV) as the carrier virus because it is a very effective way to insert DNA into the cells of a monkey or human.
In the second part of the study, the team injected AAV carriers into the muscles of monkeys, where the imported DNA produced immunoadhesins that entered the blood circulation.
After a month of administrating the AAV carriers, the immunized monkeys were injected with live, AIDS-causing SIV.
It was found that the majority of the immunized monkeys were completely protected from SIV infection, and all were protected from AIDS, unlike a group of unimmunized monkeys, who were infected by SIV, and two-thirds died of AIDS complications.
"To ultimately succeed, more and better molecules that work against HIV, including human monoclonal antibodies, will be needed," said Johnson and his co-authors.
The study has appeared in the online version of Nature Medicine.