CHICAGO (Reuters) - An experimental vaccine helped protect monkeys from an especially deadly form of the AIDS virus, raising new hope for an effective vaccine in people, U.S. researchers said on Wednesday.
The vaccine reduced the risk of infection by 80 percent among monkeys exposed to a primate version of the virus, while monkeys that became infected had lower amounts of the virus in their blood, the team reported in the journal Nature.
"It is an important advance in knowledge," Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, said in a telephone interview.
Scientists are especially excited because the study helped identify a key part of the immune system that is needed to offer protection from the human immunodeficiency virus, or HIV, that causes AIDS.
"It is nailing down in a more precise way what kind of an immune response a vaccine needs to induce to protect against the acquisition of infection as well as suppression of virus if someone happens to get infected," Fauci said.
The result is promising enough that the researchers are planning to test the vaccine in humans next year.
Efforts so far to make an AIDS vaccine have not been successful but a 2009 study in Thailand involving 16,000 people showed for the first time that a vaccine could safely prevent HIV infection in a small number of volunteers.
The researchers used weakened versions of two viruses commonly used in vaccine development -- a common cold virus called an adenovirus and a smallpox virus -- to deliver the primate version of the HIV antigen into the body and trigger an immune response.
"The vaccines we tested have had very extensive experience in the clinic, which means the transition from the animal work to the human work will be very easy," said Colonel Nelson Michael, director of the U.S. Military HIV Research Program at the Walter Reed Army Institute of Research, who worked on both the study in Thailand and the latest effort.
After vaccinating the monkeys, the team exposed the animals to an aggressive version of simian immunodeficiency virus, or SIV.
"This was really a high bar to get over," Michael said in a telephone interview. "We were excited to see these vaccine types protected these animals."
After repeated exposure to SIV, eventually most of the animals did become infected but even then, the vaccine appeared to offer added protection.
"We saw two things that were really important. A protection against infection, but even in animals that became infected, we saw reduced levels of virus," Michael said.
Next, the team did a series of tests to see what parts of the monkeys' immune system became active. They found that a key portion of a gene called an envelope, which the virus uses to get inside cells, was critical to protecting the animals.
"This is going to be the anchor for a next generation of vaccines that will propel us past Thailand," Michael said.
He cautioned that the studies so far are in monkeys and the real test will be human trials, which he expects to start in January 2013.
The group is working closely with vaccine maker Crucell, a unit of Johnson & Johnson.
There is no cure for AIDS but cocktails of drugs can keep the disease at bay for many years. New research shows they can also prevent the virus from spreading to sexual partners to some degree.
But because HIV is spread in so many ways -- during sex, on needles shared by drug users, in breast milk and in blood -- there is no single easy way to prevent infection and a vaccine is still considered the best hope for conquering the virus.
Some 34 million people globally are infected with HIV and more than 25 million people have died of AIDS, according to the United Nations agency UNAIDS.