Researchers have developed a vaccine that protects Rhesus monkeys against SIV, the simian version of the human immunodeficiency virus that causes AIDS in humans. Scientists say the experiment could lead to improved treatments for AIDS, and speed development of an effective HIV vaccine.
Building on the results of a large experimental AIDS-vaccine trial in Thailand reported in 2009, researchers developed a two-stage vaccine made up of proteins from the simian immunodeficiency virus, or SIV, that protects a significant percentage of Rhesus macaques against the disease. SIV is a model for HIV because the human virus cannot infect monkeys.
Colonel Nelson Michael is a molecular virologist with the U.S Military HIV Research Program at the Walter Reed Army Institute, and senior author of the research.
“We have now very good evidence, with new generation vaccines that we are seeing, the kinds of promising results in animals that would propel us to spend significant resources to test these vaccines in humans, which is what we are planning to do,” said Michael.
Investigators first gave their laboratory monkeys a genetically modified “primary” vaccine containing SIV proteins, followed six months later by a “boost” vaccine containing the same proteins. The vaccines were genetically modified to use different, harmless viruses to deliver the SIV proteins.
They also contained something left out of previous experimental vaccines that researchers believe makes the SIV more effective - portions of the virus’ outer envelope or shell.
Each week after the Rhesus monkeys received the vaccines, researchers tried to infect the monkeys with an aggressive strain of SIV.
The vaccines reduced the animals' chances of becoming infected by 80 percent. Eventually, after repeated exposures, all of the animals became infected, but, according to Michael, they had far less virus in their blood than unvaccinated monkeys.
"If it is true in the human condition, that means individuals would have less circulating virus, they would be less sick, they would not need to go on therapy for a longer period of time but, probably most important, they would not transmit virus as easily to uninfected partners,” said Michael.
Anthony Fauci, director of the U.S. National Institute of Allergy and Infectious Diseases, cautions that drugs developed through animal studies often can have different results in humans. But Fauci believes the study is an important step toward a human AIDS vaccine.
“The results were good and they gave us some significant insight into the kinds of responses you might want to elicit or induce in humans with a comparable vaccine,” said Fauci.
In fact, trials of a human version of the two-stage monkey vaccine are underway to test its safety and effectiveness. If all goes well, larger human trials of an HIV vaccine are planned in healthy adults in the US, eastern Africa, South Africa and Thailand, probably sometime next year.
An article by Michael and colleagues on the SIV vaccine is published in the journal Nature.