WASHINGTON (AP) - Researchers studying specimens from 3,000 people have confirmed a second gene mutation that inhibits the disease progression of HIV, the virus that causes that AIDS.
In a study being published Friday in the journal Science, scientists at the National Cancer Institute said the altered gene, along with one discovered earlier, account for about 30 percent of the long-term survivors of HIV infection. This suggests that still other gene mutations exist that protect against HIV, the researchers said.
The mutation, in a gene called CCR2, tends to protect people infected with the HIV virus from rapid deterioration into AIDS, an advanced stage of the HIV disease. An earlier study identified a protective mutation in a gene called CCR5.
"These gene alterations tell us that nature already has devised a therapy that works without significant side effects," said Stephen O'Brien, a doctoral researcher at the cancer institute and senior author of the study. "If we can pinpoint how these altered genes contain HIV, it may be possible to use this knowledge to develop treatments that help people delay the onset of AIDS."
Both CCR2 and CCR5 are genes that produce chemokine receptors, a group of proteins found on the surface of immune system blood cells. Studies last year showed that people lacking both normal copies of the CCR5 gene do not become infected with HIV despite repeated exposure. Those with one missing copy of the CCR5 gene can become infected but take years longer to progress into AIDS.
Earlier laboratory studies suggested that a CCR2 mutation also retarded HIV infection, but the new study is the first to confirm this in actual clinical studies. The study shows that patients with the CCR2 mutation develop AIDS up to four years later than patients who have the normal CCR2 gene.
The researchers said the CCR2 mutation apparently is present in 20 percent to 25 percent of Americans, in about the same proportion in all races.
Scientists said they are still searching for other mutations to hobble the HIV infection.
"There's bound to be other gene alterations present in the human gene pool that influence HIV's ability to infect immune cells and cause AIDS," said Michael Smith, also a researcher at NCI and the study's lead author. "We just have to find them."